CREDO Project Theory

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Cosmic-Ray Extremely Distributed Observatory

I.Popular description of the project

What is this project all about? Dark Matter and Dark Energy compose 95% of the Universe. What could it be that we can’t see it? How about supermassive particles born in the early Universe? Let’s call them X. Theorists say X particles would be good Dark Matter candidates. Moreover, although we can’t see them directly, they could manifest themselves in a way accessible to terrestrial detectors. Even very simple ones – smartphones. X is very old, but not eternal. It might decay presently. We want to look for products of this decay, photons of extremely high energies, 1020 eV or more. This is the energy a well served tennis ball has. Or Mike Tyson’s hit in his good days. But remember, we are speaking about a single photon. What happens to such a photon on its way to Earth? We don’t know. And the terrestrial accelerators will never let us know. One of the options is that such super-energetic photons have no chance to reach Earth unaffected. Due to some fundamental interactions they could initiate cascades of particles, mainly photons – of lower energies. We would chase these cascades which we call super-preshowers. Super-preshowers could be very much spread in space and time. So much that the current observatories can’t see them. That’s why we, scientists, are begging for your help. We need your smpartphone, and we need many of you. You can be a part of a worldwide Dark Messenger detector. You will download an app, which will tell you once you encounter a cosmic particle. Then you need to take it seriously – this might be a member of a Dark Messenger Group. We verify it together: 50% of your enthusiasm for science and 50% of our scientific expertise – a perfect  prescription for a fundamental scientific discovery.

What will be the research? We’ve already opened an international network of cosmic-ray devices, it just needs to grow as much as possible. The network is called CREDO after Cosmic-Ray Extremely Distributed Observatory. „Cosmic-ray” means that we have the data for free and everywhere, no investment in accelerator infrastructure is needed. „Extremely Distributed” means that only the globe (and surroundings) can limit us – wherever the human technology can go, there we can also measure cosmic rays contributing to our Dark Matter strategy. „Observatory” means we are not doing an experiment: we just take what the Universe gives us and try to understand it. And finally CREDO in latin means „I believe” – all we have to believe that doing science, and in particular a very ambitious and fundamental science, which means asking fundamental questions and honestly looking for answers, is an obligation of the humankind: and in a sense it concerns all of us, not only scientists.

            The CREDO network already yields the first data: images easily classifiable by non-scientists. We develop an interface between the world of scientists and the world of non-professional science enthusiasts: Dark Universe Welcome is the name of the internet application in the citizen science platform. Find us, watch us, and join us! You can contribute by downloading an application on your smartphone (find DECO or CRAYFIS) and by classifying images on Dark Universe Welcome. The more of you will employ your smartphone in science, the larger the network will grow and the more images will be sent for classification. And the more of you will classify images, the larger will be the chance to find a Dark Matter signature: a Dark Messenger Group. You might think we only need your smartphone and the pattern classification is only a nice phrase to collect more devices – everybody knows the machines do very well in pattern recognition. If you think so, please do not forget one simple truth about machine pattern recognition: machines need training sets to learn what pattern they are expected to identify. But we are looking for UNEXPECTED PATTERNS, no way to include them in the training sets if we have no idea how they should look like. That is why the human factor is critically important in our project. We, scientists, will simply not make it without your help.

Why do we do this? We don’t know how you feel about our scientific ignorance, but for us, scientsts, it is a very uncomfortable situtation to have no idea what is the nature of the 95% of our surroundings. We simply can not live with this feeling. We understand that maybe not everybody cares and that there are other problems in this world. But what can we do other than doing our job as good as we can – asking questions and looking for answers? What we can do, we can do our job sparingly. That is why we do not ask you for a few billions of dollars for our wonderful project. Instead we just ask you: hey, wait a second – why don’t we try doing together a fundamental scientific test with the infrastructure we already have at hand or around us? This is the esence of the CREDO startegy and the main goal of this proposal. We will just „press the button”, open a completely new window to the Universe and see what is coming to us. Would be good if you are tuned when we realize we see the Unexpected.

II.Project summary

Research project objectives/ Research hypothesis What is the nature of Dark Matter? How to explain the existence of particles of energies greater than 1020 eV? There can be just one explanation of these two mysteries: Super Heavy Dark Matter decay or annihilation. It is assumed that a production of supermassive (i.e. mass ≥ 1023 eV) particles could occur in the early Universe, during the inflation phase. Such particles could annihilate or decay presently, leading to production of jets containing mainly photons, including those of extremely high energies, even 1020 eV, or larger. Such photons could reach Earth unaffected or they might initiate electromagnetic cascades well above the Earth atmosphere. The latter option is presently a scientific terra incognita. Given the fundamental uncertainties about the physics in the considered energy range, one can not be sure about the properties of cascades intiated by extremely energetic photons or by other particles. Such cascades, we call them super-preshowers, are considered here in a general way: without any assumptions about their properties, like e.g. spatial and temporal spread, energy spectrum of particles or the front shape. The practical question we ask is: what types of super-preshowers can be observed on Earth with the presently available infrastructure?

Research project methodology
A pioneer configuration of the existing cosmic-ray infrastructure and a novel data analysis on a global scale is proposed to detect super-preshowers. The main goal is to look for time coincidences of low energy cosmic-rays. It can be achieved both with the already operating large instruments like the Pierre Auger Observatory and with a larger meta-structure, connecting all the existing devices spread over the globe and capable of detecting the secondary cosmic-ray particles. The idea to use all available instruments in operation is based on a novel trigger algorithm: in parallel to a looking for the neighbor surface detectors receiving the signal simulatneously, one should also look for the spatialy isolated stations clustered in a small time window. While the former way is designed to give a trigger on a large single extensive air shower, it will obviously not work with a collection of showers of low energies arriving simultaneously at the detector array. The other method, looking for isolated detector stations clustered in time, would be sensitive to an extended front of low energy showers – a potential signature of super-preshowers. This kind of a novel trigger, if implemented, will give uniqe scientific results and open a new observation channel of the Universe: the super-preshower channel. It is going to be done within the proposed project.

            The above strategy to detect super-preshowers can be extended to extremely wide objects, spread over an area exceeding the dimensions of the observatories that are currently in operation. The idea is very simple: extremely large super-preshower could be observed by extremely distributed observatory: a global network of cosmic-ray detectors. Such a network would include the professional instruments like the Pierre Auger Observatory, Baikal-GVD and ATLAS, the educational arrays like HiSPARC or Showers of Knowledge, and, last but not least, the networks of smartphones equipped with an application allowing detection of particles: CRAYFIS  and DECO. The global analysis would require a script communicating with all the stations, scannning the data and identifying the event candidates and, possibly, discoveries (i.e. clearly non-random arrival time patterns). The event candidates can be further analysed, discussed and classified and a relevant alerting procedure could be introduced if needed.

            The global strategy for the detection of super-preshowers is already being implemented by the international collaboration CREDO (Cosmic-Ray Extremely Distributed Observatory) intiated by the author of this proposal. The proof of concept, i.e. the first classifiable time arrival pattern composed of the signal received by very distant stations, has been presented and ceremonially classified during the CREDO Inauguration Meeting held at the end of August 2016 in Krakow. This demonstration proved not only the scientific concept of the project, it also showed the potential and necessity of involving non-scientists, not only for their pocket cosmic-ray devices but also for active participation in the data classification. If non-profesional science ethusiasts can become involved in the project on a large scale, it will significantly increase the chance for a success of the project: the scale is the key factor in a global strategy, and this scale must also be handled with an adequate manpower.

Expected impact of the research project on the development of science, civilization and society The global cosmic-ray infrastructure proposed here will have a clear impact on the development of astrophysics and, possibly, also on fundamental understanding of physics laws. The results provided by CREDO will be unique in any scenario, both with and without obervation of super-preshowers. Implementing the idea proposed here will open a new information window on physics at extremely large energies – the window to the Unknown. Apart from fundamental scientific objectives a number of additional strategies will be enabled, once the global cosmic-ray infrastructure is active: spaceweather (solar activity) studies, geophysics tests (e.g. earthquake predictions potential through the inverse magnetostrictive effect), education (e.g. economic and understandable access to fundamental science with internet connection only), or a new opening in the perception of science in the society („the world is yours to explore”, „we do fundamental research together”).

III. Detailed description

1.Research Project Objectives

With this proposal two fundamental problems of the contmeporary astrophysics are addressed: 1) What is the nature of Dark Matter? and 2) How to explain the existence of cosmic rays with energies greater than 1020 eV (hereafter referred to as ultra-high energy cosmic rays  – UHECR)? The hypothesis to be tested in the proposed projeect is that these two mysteries of science can be explained with just one scenario. This is in agreement with the Ockham rule which favors the least possible set of solutions to a collection of seemingly independent problems. The scenario we are going to propose and verify is known in the literature as Super Heavy Dark Matter (SHDM) decay or annihilation (see e.g.[1]). It assumes a production of supermassive (ie. E ≥ 1023 eV) particles in the early Universe, during the inflation phase. Such particles could annihilate or decay presently leading to the production of jets containing mainly photons. The energies of these photons could easily be of the order of  1020 eV, the value that seems to be out of reach in the acceleration processes in the potential sources. The key prediction of the scenarios in the SHDM group is that the UHECR flux observed at the Earth should be dominated by photons (see e.g. [2]). On the other hand, the highest energy events observed by the leading collaborations: Pierre Auger and Telescope Array, are not considered photon candidates if the present state-of-art  air shower reconstruction procedures are applied. In fact there are no photon candidates also in the data below 1020 eV collected by these and other observatories, leading to the very stringent upper limits ([3],[4]). The key question we ask with this proposal is about the assumptions under which these upper limits can be interpreted as constraints to SHDM or other exotic scenarios – as it is commonly concluded. As it is argued in the following paragraphs, there are two main doubts about such conclusions: a) the present state of the art analysis does not take into account mechanisms that could lead to a good mimicing of hadronic air showers with the showers induced by photons, and b)  the present state of the art analysis does not take into account mechanisms that could lead to the efficient screening/cascading of the ultra-high energy (UHE) photons on their way to the Earth, so that the products of such screening/cascading are out of reach of the presently operating observatories, which is interpreted as non-observation of UHE photons. If the doubt a) is founded in reality, we do have photons in the data but we do not identify them properly. If the doubt b) adresses  the real properties of cosmic rays then we have no chance to see most of the photons that travel towards us. Both doubts obviously question the conclusion about constraining the SHDM scenarios by the presently accepted upper limits to photon flux. Such a conclusion can be only accepted with the assumption that both doubt a) and b) are irrelevant. The key point of this proposal is that such an assumption can be experimentaly tested using available infrastructure, technique and analysis methods in a novel way.  Given the feasibility of the proposed project explained in the following paragraphs and the fundamental character of the addressed scientific issues one might consider the implementation of the proposal a scientific obligation.

2. Significance of the project

State of the art and proposed novel aproaches

Dark Matter

The mystery of Dark Matter does not have to be explained in detail. The dynamics of the visible Universe cannot be understood without postulating its additional components: Dark Matter and Dark Energy, constituting in total around 95% of the Cosmos. It is highly unsatisfactory to a human being, with the intrinsic capability of asking and looking for answers, to realize that he/she has no idea what is the nature of the most of his/her surrounding. That is why so many scientific efforts are currently undertaken to get a clue on the mysterious 95%. The current status of the understanding of Dark Matter is well illustrated by the bare fact of organizing the conference on non-standard Dark Matter models with encouragement to thinking beyong the paradigm of weakly interacting massive particles (WIMPs). „Warsaw Workshop on Non-Standard Dark Matter: multicomponent scenarios and beyond”, was held on 2-5 June 2016 and the purpose of the meeting was explicitly stated in the meting anouncement by the chair of the Organizing Committee, Prof. Bohdan Grządkowski: „the purpose of the meeting is a discussion of Dark Matter theories going beyong the the standard pardigm of WIMPs”. The meeting was very frankly summarized by Prof. Hai-Bo Yu, who expressed the present consternation about the nature of Dark Matter by encouraging the simplest and naive ideas and questions [5]. The motivation and strategy presented and proposed within this application fully complies with the expectations of Prof. Yu. Attending the Warsaw meeting, talking to the colleagues from the Dark Matter community, and listening to the final take home message by Prof. Hai-Bo Yu inspired the reasearch to be undertaken within the proposed project.

Here we propose an idirect search for one of the non-standard Dark Matter candidates: super heavy particles with masses equal or exceeding 1023 eV. Such particles could be produced in the early Universe during the inflation phase and decay or annihilate presently leading to observable products, mainly photons and neutrinos, in the UHE range [6]. As mentioned above, non-observation of these products is reported, which is interpreted as constraints to SHDM scenarios. It is argued below that this interpretation can be questioned, leading to a novel and feasible research strategy using the cosmic-ray data and detctors.

UHECR – photons

As mentioned above, SHDM scenarios might be directly connected to the other unsolved astrophysical problem: existence of UHECR. The puzzle is not only the pure existence of particles with energies exceeding 1020 eV. We also do not understand why the recorded arrival directions of UHECR do not point back to astrophysical sources [8], why there is a tension between the key experiments about both the UHECR composition and spectrum cutoff ([9], [10]), and why there are general difficulties with explaining the multi-channel data [11]. The complexity of the UHECR puzzle indirectly supports an alternative scenario that could be capable of generating UHE particles without an absolute need for correlation with the sources. While gravitational properties of SHDM particles are rather unquestioned, the distribution of SHDM particles seems to be disputable, e.g. not every galaxy can be an SHDM source. It is for instance not clear in the case of our Galaxy [12]. If SHDM distribution is not too far from uniform on a scale of super galaxy cluster, or if the propagation horizon of UHE photons is more limited than we extrapolate, we might not see SHDM sources. At the same time, taking into account potential interactions of UHE photons on their way to Earth leading to electromagnetic cascading, one expects dependences of the SPS-generated air showers both on arrival directions and on the geographical location of the observatory [13]. Potential of UHECR, and in particular UHE photons, in explaining the nature of Dark Matter seems to be unnoticed by the Dark Matter community. This is illustrated in Fig. 1 showing a slide from the review talk given during the above mentioned warkshop in Warsaw by C. Weniger [7].

Fig. 1 The slide from the review talk by C. Weniger given at the Workshop on Non-Standard Dark Matter in Warsaw,
2-5 June 2016 [7]. The note in red by P. Homola.

The talk concerned the applicability of the cosmic-ray data, mainly photons, to the Dark Matter related studies. It can be seen that the energy range of photons applicable in the Dark Matter search strategies ends, as seen from the perspetive of the author of the talk, at the gammma ray energies (presently this is less then PeV). Such a perspective is understandable if the paradigmatic non-observation of photons among high energy cosmic rays is kept in mind. This pardigmatic perspective is well settled within the astroparticle physics community, to mention the top journal publications inferring the constraints to the deviations from the fundamental physics laws (Lorentz Invarinace) from the upper limits to the UHE photon flux (e.g. [14]). It is therefore of great importance to understand properly the photon upper limit evidence and to be aware of the assumptions leading to the conclusions about fundamental physics. This deeper understanding is very simple: non-observation of UHE photons on Earth concerns UHE photons. Conclusions about the constraints on the sources or processes leading to the production of UHE photons require a number of fundamental assumptions concerning: the electrodynamics at GUT energies [15], hadronic properties of an UHE photon [16], or spacetime structure [17]. Also modeling the propagation of UHE photons through the intergalactic, interstellar and even interplanetary medium require assumptions difficult to verify – to mention only the potential interactions with the fields associated with the charged relativistic particles trapped within  Van Allen belts.

We are unsure about the physics processes at GUT energies, moreover, we expect deviations from Standard Models in cosmology and particle physics because of the apparent disagreement between our most beautiful theories: General Relativity and Quantum Field Theory. Therefore any conclusions where the GUT uncertainties are involved, in particular the conclusions based on the upper limits to UHE photons, are disputable.

Super-preshowers: the missing link?

As explained above, a deeper understadning of the upper limits to UHE photons require an awareness of the assumptions underlying this result. It is also important to understand that constraints on dark matter models or fundamental physics laws can be inferred from the upper limits to UHE photons only assuming no unexpected propagation effects occurning to the UHE photons on the way from the production site to the Earth.  A novel approach to Dark Matter search and to the UHECR mystery to be explored if this proposal is successful is based on a critial revision of this assumption. To put the main idea in the simplest way one

Fig. 2: A basic observational classification of super-preshowers. Different classes refer to different widths of spatial and temporal distributions of super-preshower particles. The question marks represent the uncertainties about the fundamental physisc processes at E=1020 eV or larger. [18].

considers a hypothetic mechanism leading to a cascading of most of the UHE photons before they reach Earth, leading to the efficient shrinking of their astrophysical horizon. If such a mechanism or process occurs in reality, UHE photons have little chance to reach the Earth, and what can be observed on Earth is the result of the mentioned underlying hypothetic mechanism, most likely large electromagnetic cascades. One example of such a cascading process is the preshower effect ([19], [20], [21]) describing an interaction of an UHE photon and secondary electrons with the geomagnetic field. The word „preshower” is used to decribe the result of the initial interaction: shower = many particles instead of one primary UHE photon; and emphasize the location of the interaction vertex: pre = above the atmosphere, i.e. before the extensive air showers (EAS) are intiated by the preshower prarticles. To generalize the notion „prehsower”, the „super-preshower” term was introduced very recently [22]. Super-preshower (SPS) is a cascade of electromagnetic particles originated above the Earth atmosphere, no matter the initiating process, and distance from the Earth. Super-preshowers can be classified with respect to their principal observable properties: spread in space and time. A proposal of such a classification is shown in Fig. 2 [18].

Within the presented classification a cascade inititated due to the preshower effect in the geomagnetic field would be classified as SPS of type A, with Δx of the order of centimeters and completely negligible Δt [21]. If the preshower effect would occur in the vicinity of the Sun one would expect similarly negligible Δt, but Δx should be much larger that in case of an SPS type A, maybe even close to the size of the Earth, i.e. to class C. This „maybe” is one of the unknowns to be quantified within the proposed project, the few calculations done so far can only serve as qualitative approximations ([23], [24]). For instance in Ref. [23] the SPS front is calculated with a private code and assumed to be composed only of photons of energies larger than E=1017 eV, while from the more detailed calculation done in Ref. [24] done with an open source public code PRESHOWER [21] one learns that the SPS spectrum might be extended over a wide range, down to TeV and lower. One of the experimental questions to be addressed within this project is: „what fraction of an SPS front can be detected by devices located on the Earth surface?” It is the question about the SPS particle density on the top of the atmosphere and the particle density, or any other information like Cherenkov light, of the resultant air showers. While we cannot be sure about the processes leading to the development of SPS we can ask which SPS structure (in space and time) can be observed with a specific configuration of the available infrastructure. This is a part of the strategy to be pursued within this proposal, more details are given in the following sections. Here it is important to stress that types of an SPS signal accessible on Earth inlcude the Cherenkov light. This note makes a particular difference for SPS photons of TeV energies. We do not expect an air shower induced by a TeV photon to reach the Earth surface but we do expect the cone of Cherenkov light instead – something that is recorded by gamma ray astronomers.

Once we consider electromagnetic cascading initiated nearby the Sun it is only one more logical step to remove any limits on the distance of the first SPS interaction vertex from the Earth. Let us then take in to account all the electromagnetic cascades initiated somewhere in the Cosmos and discuss their potential to be observed on Earth with the currently available infrastructure or with the instruments easily affordable. For instance, an interaction of an UHE photon with the cosmic microwave background photons should lead to a production of super-preshower, let us call it astrophysical SPS. It is commonly assumed that we do not have any chance to detect an astrophysical SPS on Earth. Consequently, the mentioned interaction is considered a process leading to the extinction of UHE photons, hence limiting their mean free path. Assuming such an extinction is a state-of-art way of dealing with the propagation of UHE photons in the most popular Monte Carlo codes [25]. However, given the fundamental uncertainties concerning the physics at the GUT energies, it is very difficult to exclude a priori that astrophysical SPS can reach Earth with photon densities in reach of terrestrial detecting infrastructure. One might consider an example here: if the primary photon interacts with the background photons to produce an electron pair, then these electrons should emit secondary high energy photons for the same reason – due to the interactions with the background photons. One can say that in consequence a super-preshower is initiated but its detailed spatial and temporal structure is highly uncertain – due to the limitations and uncertainties in the interaction models we have. Continuing the logics, if we only find a way to detect astrophysical SPS, we have the right to expect an increased flux of events comparing to the limits on the UHE photon flux placed by the presently operating observatories. As these observatories migh be sensitive only to „unaffected” photons or to SPS class A, the event horizon is obviously narrower than in the case when also some astrophysical SPS can be seen. In the following sections an idea to organize a cosmic-ray infrastructure sensitive to SPS of all classes is presented.

To summarize this section one can conclude that there must be a „detection limit” somewhere between an obviously detectable super-preshower type A and obviously undetectable astrophysical SPS composed of particles so much spread in space at the Earth that on average no more than one „representing” particle can enter our atmosphere. An attempt to determine this limit will be undertaken if this proposal is successful.

Extensive Air Showers

SPS with narrow lateral distribution of particles, ie. classes A and B, can be detected by the presently operating air shower observatories. In fact one cannot exclude that the data set collected by the key instruments contains
SPS-induced events, but we just do not identify them properly. To illustrate this hypothesis for the case of SPS class A one easily compares the longitudinal develoment of SPS-induced air

Fig. 3: Longitudidal development of air showers induced by protons, iron nuclei and super-preshowers of primary energies E=1019.6 eV,
arriving at the Pierre Auger 
Observatory from geographical South, at zenith angles of 60o. [26].

showers with those initiated by protons or heavy nuclei. Such a comparison is presented in Fig. 3 [26].

Here the popular CONEX [27] program was used. To simulate SPS with CONEX one uses the PRESHOWER option [21] and fixes manually the altitude of first interaction at 10000 km a.s.l. or

Fig. 4: Variation of depth of air shower maximum with the primary energy: data collection and model predictions for different primaries. The average Xmax of 100 super-preshowers initiated by photons of energies E=1019.6 eV is shown as a blue dot. See the text for the other simulation details.[22]

above. The example shown concerns primaries of energies E=1019.6 eV, arriving at the Pierre Auger Observatory from geographical South, at zenith angles of 60o. It is striking that the depths of shower maximum development, Xmax, of SPS-induced showers are very similar to those of EAS initiated by protons.

Fig. 5: Muon production profiles of SPS-induced air showers compared to EAS initiated by protons and iron nuclei. Primary parameters are the same as in Figs. 3 and 4. [26]

Without the „trick”’ with manually increased first interaction altitude, the SPS Xmax distribution would be very well separable from the distributions typical for hadron primaries [see e.g. [28]. In the case of the preshower-type primaries it is then the altitude of the preshower intitiation which makes a critical difference for the key observable sensitive to the primary type – Xmax. It would be well understood if the first interaction is electron pair production: the earlier super-preshower begins, the more photons are radiated by electrons and the lower energy per particle at the top of the atmosphere. Xmax  should then decrease with the increasing number of SPS particles, and the number of SPS particles can increase due to the increased altitude of pair production. In the simulations shown in Fig. 3 the emission from electrons is induced only by the geomagnetic field, that is why increasing the first pair production altitude above 10000 km a.s.l does not cause a further decrease Xmax: at higher altitudes the value of the local geomagnetic field vector is too low to induce the emission of magnetic bremsstrahlung and no additional photons are emitted. An even more striking presentation of super-preshower simulations is shown in Fig. 4 [22]. The blue dot, representing the average Xmax of 100 super-preshowers with primary parameters as in Fig. 3, fits perfectly a Monte Carlo prediction for medium mass primary nucleus, being very close to the available data.The similarity in Xmax of SPS-induced EAS to air showers initiated by nuclei shown in Fig. [4] motivates a consideration of some other observables known to be sensitive to the primary mass and independent of the depth of shower maximum. Here we will discuss the muon number, Nμ, on ground and muon longitudinal profile, dNμ/dX. First of all it is important to recall a basic expectation for the muon content in air showers: photon-induced EAS should contain much less muons than those initiated by nuclei, unless we are mistaken about the present extrapolations of the photonuclear cross-section [28]. That is why Nμ can be used as a good discriminator between photon and hadron primaries. Indeed, as shown in Fig. 5 [26], dNμ/dX and, correspondingly Nμ in SPS-induced showers is factor 5-8 smaller than in the EAS initiated by nuclei, if standard interaction models are used.

Keeping in mind the shown difference in the muon content in photonic and hadronic showers one should not forget about the uncertainties in the interaction models we use. In particular, the uncertainty about the hadronic properties of a photon leads to a significant uncertainty in the photonuclear cross section. This is illustrated in Fig. 6 [29]. The photonuclear interaction cross section increased within the range of the available models might compensate factor 5-8 mentioned above. In consequence one cannot exclude that SPS-induced air showers can mimic also the muon content and longitudinal profile of EAS induced by nuclei. One therefore should be careful about the definite conclusions concerning the photon component in the observed cosmic ray flux without a deeper study including SPS simulations. For the same reason one can get motivated to identify other observables that could potentially allow a distinction between SPS and hadronic primaries. One of the possible directions would point to the lateral distribution function (LDF) of air shower particles near the shower axis. While it is a challenge to extract a valuable information on LDF near the shower axis from a ground array of particle counters (eg. the Surface Detector of the Pierre Auger Observator) due to the signal saturation, it might be possible to do much better with the radio technique. One can also hope for more new SPS-sensitive observables inaccessible with current configuations of the key observatories but feasible to implement. For instance, a significant electromagnetic component of an air shower initiated by a super-preshower emerges, by definition of SPS, already at the top of the atmosphere, while in the case a hadronic primaries it happens much later, typically at around 20-30 km a.s.l. One can therefore expect, that electromagnetic air shower observables like distribution of Cherenkov radiation or polarization of the Cherenkov photons might be sensitive to super-preshowers. A better understanding and measurements of such observables is possible and this is one of the goals of this project.

Fig. 6: Uncertainty in modelling photonuclear intereactions (red labeling by P.Homola).[29]

Given the fundamental uncertainty about the photonucleear cross-section and no perspective to reduce it with manmade accelerators, it has been pointed out altready in 2006 by M. Risse et al. ([29]) that one could invert the logics of air shower experiments to get a refreshing perspective and reach new scientific value: instead of interpreting air shower properties using the extrapolations of cross sections one could infer the cross sections from the properties of air showers. Thanks to the constantly increasing data statistics this strategy is presently more available than when it was proposed. As explained above, a parameter sensitive to photonuclear interaction should be Nμ, provided we can identify the primary as a photon or super-preshower. The recent results from the Pierre Auger Observatory seem to reveal the unexpected excess in Nμ: there seems to be more muons in the observed air showers than predicted by the available models of hadronic interactions, even assuming heavy primaries (iron) [30]. The muon excess is hard to explain with the avialable models and it has already triggered an effort to tuning them [31]. On the other hand it has not been checked in detail how the presently accepted alternative extrapolations, with the photonuclear cross-sections even up to the order of magnitude larger than the „official” ([32]) values, would influence the properties of air showers. In particular, it has not been checked whether the alternative photonuclear cross-section could give Nμ larger in SPS-induced showers than in EAS initiated by nuclei. It is important to note that such a study is not trivial. Given the complexity of the available air shower simulation codes and necessity of a consistent treatment of all the interactions (eg. one needs to replace the photonuclear cross-section not only for primary photons but also for virtual gammas) a check in this direction requires a dedicated study [33]. Performing this study is planned the proposed project.  Only having at hand the study on uncertainties about the muon content in SPS-induced showers one can discuss with larger confidence the hypothetic contribution of the SPS component in the already available data collected by the cosmic-ray observatories.


As explained above, cosmic-ray observatories designed to trigger on ultra-high energy events can be sensitive to super-preshowers type A and B but they might not see SPS type C or D. If an observatory is exposed only to SPS particles of energies below the operating trigger, there will be no observation. On the other hand one can imagine an alternative detection method of SPS-C and SPS-D with already existing infrastructure. If educational cosmic-ray detectors, university particle counters and private electronic devices equipped with photosensors and appropriate applications could be organized in a worldwide network, it can be used as a powerful observatory dedicated to search for ensambles of cosmic particles arriving at the Earth in extremely extended fronts.

The idea of a worldwide network has very recently took the shape of an international collaboration named CREDO, after Cosmic-Ray Extremely Distributed Observatory [34]. The CREDO project was initiated by the author of this proposal. The Inauguration Meeting was held on 30 August 2016 in Karkow and gathered nearly 50 participants from all over the world [34]. The aim of CREDO is to look for time coincidences between the cosmic-ray signal received by very distant stations, on a globe scale. As far as large scale time correlations are the experimental goal, the size of the CREDO network and the number of detecting stations has a critical importance. One of the key ideas to make CREDO as large as possible is to involve in the experiment also non-scientists and their pocket devices: smartphones. The idea of using a smartphone as a portable cosmic-ray detrector has been practically explored by two collaborations: DECO [35] and CRAYFIS [36]. DECO offers a free cosmic-ray-detection app already now, CRAYFIS is still in the beta phase. Both DECO and CRAYFIS were asked to contribute to CREDO and both are positive: the CRAYFIS representative gave a talk during the CREDO Inauguration Meeting and DECO locations were used to prepare the first simulations of CREDO performance. The perspectives are bright: there are a number of colleagues attending the Inauguration ready to contribute to the CREDO tasks, there is also a number of cosmic-ray experiments, including large collaborations, ready to share their data or considering a participation (e.g. the Pierre Auger Collaboration, Baikal-GVD, ATLAS and MAGIC – all represented during the CREDO Inauguration).

A worldwide network of cosmic-ray detectors will not only be a unique tool to study fundamental physics laws, it will also provide a number of other opportunities, including spaceweather or geophysics studies. Among the latter one has to list the potential to predict earthquakes by monitoring the rate of low energy cosmic-ray events. An indication of such a potential comes from the Pierre Auger Observatory where an abnormal increase of the low energy signal rate was noted hours before the devastating earthquake in Chile in 2010 [37]. The infrastructure composed of the Pierre Auger Observatory and many other detectors, no matter how large or small, would give an obviously larger chance to identify cosmic-ray-based earthquake precursors. The mechanism  potentially responsible for a connection between the earthquakes and cosmic-ray can be the inverse magnetostrictive effect: the change of magnetic properties of a material when exposed to a mechanical stress. Such an effect should occur during the tectonic movements preceeding an earthquake. The inverse magnetostrictive effect should be reflected in the variation of the local geomagnetic field vector and hence also in the change of the local detection rate of low energy cosmic-rays.

A potential to predict earthquakes does not only give a hope to save human lives with fundamental physics research, it will also strenghten fundamental physics reaserach: the smartphone users in the territories exposed to the high earthquake risk should more readily download the cosmic-ray app (if the earthquake prediction potential is clear to them) and contribute to the CREDO strategy more efficiently than the others living in the earhquake-free areas. There one should count mostly on science enthusiast and their will to undestand better the Universe.


The first and the easiest way to identify a super-preshower is to analyse the already available data, e.g. the resources collected by the Surface Detector of the Pierre Auger Observatory. It migh be a very difficult task in case of SPS A/B. As explained above, if SPS-induced showers are present in the available data, the currently used set of observables might be not enough to identify SPS properly if the SPS A/B primaries can mimic well the nuclei. A more optimistic perspective can be sketched for SPS C/D in the Pierre Auger Observatory or any other large instrument. To give an example let us consider an SPS C/D with most of the particles below the event trigger level of a big observatory. In this case, the low energy secondary particles arriving at the surrface array are noticed if there is no event-level trigger at the same time. These particles are considered a background and the corresponding data are processed only within a working buffer, they are not stored later if there is no standard event found. This disregarded background can serve as a signal within the SPS C/D strategy: at the same time when the standard trigger algorithm looks for a group of neighbor stations receiving the signal simulatneously one can ask about a group of isolated stations receiving the signal within the same or a similar time window. Given the design and the low level trigger rate of the Pierre Auger Observatory one would expect that already 10 isolated and simultaneoulsy triggering stations would give a unique signature, clearly distinguishable from the random noise. Moreover, if the simulateous signal in isolated tanks comes from one source, eg. from a super-preshower with a flat front, the arrival times should be correspondingly ordered in time – reflecting the geometry of the arrival direction of the front. Taking this into account one would expect that the number of the stations required for a clearly non-random signal will be even lower than 10. How much lower? This should be studied in detail using Monte Carlo simulations of super-preshowers, subsequent air showers and the detector response. The above analysis/trigger idea is illustrated in Fig. 7 [18]. The author of this proposal is the member of the Pierre Auger Collaboation so the studies on an SPS-dedicated trigger in Auger will be a natural research direction, unexplored so far. This research is actually on the way, the trigger strategy described above, named mT2 – for multi-2nd level trigger, has already been poposed during the last Auger Analysis Meeting in Karlsruhe and it was received well, with encouragements to continue the study. The result of the initial discussion during the mentioned meeting was that mT2 in its basic version should not interfere with the current Auger trigger setup and hardware capabilities, which means that the analysis can be started as soon as properly trained manpower is available. If this application is successful the new SPS task including the mT2 study will naturally be led within the Pierre Auger Collaboration by the Krakow group.

Fig. 7: The SPS triggering strategy (right panel): look for n isolated stations receiving the signal simulatenously. The comparison is made to the standard triggering scheme (left panel): look for a group of neighbor stations receiving the signal simulatneously. [18]

The mT2 trigger strategy can be implemented in a straightforward way in the worldwide infrastructure like CREDO. Of course one has to work on optimizing details: temporal and geographical windows, checking various arrival directions and front geometries of SPS, considering possible delays in time, etc., but the key analysis idea should remain unchanged: we are looking for clearly non-random signal arrival time patterns extending over an area larger than in case of a single extensive air shower.

Justification for tackling specific scientific problems by the proposed project

What is the nature of Dark Matter? How to explain the existence of particles of energies greater than 1020 eV? There can be just one explanation of these two mysteries: Super Heavy Dark Matter decay or annihilation. It is assumed that a production of supermassive (i.e. mass ≥ 1023 eV) particles could occur in the early Universe, during the inflation phase. Such particles could annihilate or decay presently leading to the production of jets containing mainly photons, also of extremely high energies, even 1020 eV. Such photons could reach Earth unaffected or they might initiate electromagnetic cascades well above the Earth atmosphere. The latter option is presently a scientific terra incognita. Identifying a scientific terra incognita fully justify undertaking the appropriate research. Pioneer configuration of the existing cosmic-ray infrastructure and a novel data analysis on a global scale is proposed here to initiate an exploration of a potentially new observation channel of the Universe: the super-preshower channel.

The wide super-preshower hypothesis can be considered a candidate scenario for a number of unexplained cosmic-ray measurements. The examples include Smith et al. 1983 (32 TeV EAS within 5 minutes while only one such event would have been expected) [38] and Fegan et al. 1983 (simultaneous increase in the cosmic-ray shower rate at two recording stations 250 km apart) [39]. On one hand the mentioned measurements were single observations, not seen by other groups, but on the other nobody approached what is going to be done withing this project: establishing a meta-structure composed of the detectors used by different groups in all the available energy range. It will give a chance to confirm the historical reports and maybe to find new physics effects.

Given the lack of convincing experimental evidence in the super-preshower channel, a number of additional applications of the proposed experimental setup (CREDO) and its high social and educational potential, the success of the project proposed here is more than likely – it also strongly motivates undertaking the study.

Pioneering nature of the project

 Super-preshowers, as a potential manifestation of SHDM interactions and other fundamental physical processes, pointing back to the physics in the GUT energy range, appear as a new, unexplored sub-field of cosmic ray physics, putting a simple genaralizing transofrmation: n=1 → n>1, where n denotes the number of primary particles arriving simultaneously at the Earth. This new sub-field can be considered a potentially new channel of the observation of the Universe, very well compatible with the most reasonable startegy dedicated to solving the mysteries of the Universe: take all the information channels we have and analyse them together. This multi-channel approach is now being execuded for n=1 with the AMON network [40], processing information from the cosmic-ray, neutrino, gamma-ray, and gravitational wave observatories. Generalization described above opens a new channel: super-preshowers.  All the reasearch undertaken in this new channel is therefore automatically pioneer, requiring a novel approach to data and promises a success: new contribution to our knowledge about the Universe. Either observation or non-observation of SPS will be meanignful and constraining (pointing to) the existing theories in a novel way. It is also obvious, that since the reasearch we are going to undertake is on the edge of unknown, one cannot be surprised if a completely unexpected fundamental discovery will be made – something which does not fit to any of the models that are presently in reach of our imagination.

 Although the infrastructure proposed here to look for super-preshowers is going to be composed, at least at the beginning, of the already existing detectors, organizing these detectors within a worldwide network will be an unprecedented technical and scientific challenge. Various difficulites can be foreseen: identifying an SPS signal in the random noise, accessing all the stations in real time, pre-classification of temporal patterns by machines (not to loose important things having no idea what is important), organizing the alerting,  communication within a large collaboration, and many others. An efficient handling of all the difficulties will require a novel approach in many fields and a dedicated effort of not only one group but a whole collaboration. Such a collaboration has already been formed, it is called CREDO and it was initiated by the author of this proposal. The group to be formed after this project receives funding should take the natural lead in CREDO, the lead in the pioneer research addressing fundamental physics questions.

 The impact of the project results on the development of the research field and scientific discipline, civilisational impact

 Pursuing the research strategy proposed in this application will have large impact on astroparticle physics and possibly also on fundamental physics. The new observation channel of the Universe will be open – super-preshowers. If SPS are seen, they could point us back to the interactions at energies close to the GUT scale. This will mean an unprecedented chance to test experimentally dark matter models and scenarios, probe the interaction models, the spacetime properties – all in the close-to-GUT enrgy regime. If SPS are not observed it will valuably constrain the theories we have and narrow the search for a breakthrough in science. Apart from addressing fundamental physics questions the project proposed here will have a number of additional appplications: alerting the astroparticle community on SPS candidates to enable a multi-channel data scan, the explained above potential to predict earthuaquakes, integrating the scientific community (variety os science goals, and detection techniques, wide cosmic-ray energy ranges, etc.), helping non-scientists to explore the Nature on a fundamental but still understandable level – and many more.  The high social and educational potential of the project gives a hope for a contribution not only to a progress in physics but also for a civilizational development.

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