The total of 23500 Extensive Air Showers (EAS) with the energy above  1016 eV have been detected during the
 3500 hours of Horizon-T (HT) detectors system operations before Aug 2016. Among these EAS, more than a
thousand had an unusual spatial and temporary structure that showed the pulses with several maxima (modals
or modes) from several detection points of the HT at the same time. These modes are separated in time from
each other starting from tens to thousands of ns. These EAS have been called multi-modal. Analysis shows that
the multi-modal EAS that have been detected by Horizon-T have the following properties:
1. Multi-modal EAS have energy above  1017 eV.
2. Pulses with several modes are located at large distances from EAS axis.
The overview of the collected data will be provided. General comments about the unusualities of the structure
of the multi-modal EAS will be presented

Baigarin, Kanat

Beisembaev, Rashid

Beisembaeva, Elena

Beznosko, Dmitriy

Dalkarov, Oleg

Ryabov, Vladimir

Sadykov, Turlan

Shaulov, Sergei

Stepanov, Aleksei

Vildanov, Nikolay

Vildanova, Marina

Zhukov, Valeriy

Nazarbayev University Repository

Extensive Air Showers with Unusual StructureDmitriy Beznosko1,?, Rashid Beisembaev2, Kanat Baigarin1, Elena Beisembaeva2, Oleg Dalkarov2, VladimirRyabov2, Turlan Sadykov3, Sergei Shaulov2, Aleksei Stepanov2, Marina Vildanova2, Nikolay Vildanov2 , and Va-leriy Zhukov21Nazarbayev University, Physics Department, Astana, KZ2P. N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow, Russia3LLP “Institute of Physics and Technology”, Almaty, KazakhstanAbstract.The total of 23500 Extensive Air Showers (EAS) with the energy above ∼1016 eV have been detected during the∼3500 hours of Horizon-T (HT) detectors system operations before Aug 2016. Among these EAS, more than athousand had an unusual spatial and temporary structure that showed the pulses with several maxima (modalsor modes) from several detection points of the HT at the same time. These modes are separated in time fromeach other starting from tens to thousands of ns. These EAS have been called multi-modal. Analysis shows thatthe multi-modal EAS that have been detected by Horizon-T have the following properties:1. Multi-modal EAS have energy above ∼1017 eV.2. Pulses with several modes are located at large distances from EAS axis.The overview of the collected data will be provided. General comments about the unusualities of the structureof the multi-modal EAS will be presented.1 IntroductionThe Horizon-T [1] detector system is located at Tien ShanHigh-altitude Science Station (TSHSS) of Lebedev Physi-cal Institute of the Russian Academy of Sciences at ∼3340meters above the sea level. It consists of eight charged par-ticle detection points separated by the distance up to onekilometer as well as optical detector subsystem to mea-sure the Vavilov-Cherenkov light from the EAS. The aerialview of the detector system is shown in Figure 1. The co-ordinates of each detection point with respect to the point1 are given in a table 1.Figure 1. Aerial view of Horizon-T detector system.HT is an innovative detector system constructed tostudy both the spatial and temporal distribution of the?e-mail: dmitriy.beznosko@nu.edu.kzcharged particles within the EAS in the energy rangeabove 1016 eV coming from a wide range of zenith an-gles (0o - 85o) with time resolution of few ns. This novelapproach allows to collect two-fold the data from each de-tection point (particle density and time of passage) and in-crease measurement precision of the EAS parameters suchas measuring the core position when it falls outside ofthe detector system area. The HT detector system con-sists of detectors of several different types: plastic scintil-lator [2] with MELTS [3] FEU49 model PMT, plastic scin-tillator with Hamamatsu [4] R7723 PMT assembly, glasswith R7723 PMTs and a Vavilov-Cherenkov radiation de-tector with both FEU49 and Hamamatsu H6527 PMT as-semblies. All detection points connect to Data Acquisition(DAQ) via cables that are being calibrated separately [5].Table 1. HT detection points coodrinatesStation # X, m Y, m Z, m R, m1 0 0 0 02 –445.9 –85.6 2.8 454.13 384.9 79.5 36.1 394.74 –55.0 –94.0 31.1 113.35 –142.4 36.9 –12.6 147.66 151.2 –17.9 31.3 155.47 88.6 178.4 –39.0 2038 221.3 262 160.7 374From the start of a first prototype to August 2016, thatis over ∼3500 hours of HT detector system operations,23500 EAS with the energy above ∼1016 eV, which is thethreshold energy for HT. Among these EAS, more than athousand had an unusual spatial and temporary structurethat showed the pulses with several maxima (also calledmodes) from several detection points of the HT at the sametime. These modes were separated from each other bytime from tens to thousands of ns. These EAS are calledthe also called Multi-Modal Events (MME). Initially at-tributed to delayed particles, they were first observed by J.Jelly and W. Whitehouse [6].2 Standard EAS definitionAs a solid starting point, the definition of the ’standard’EAS is required. For that, we adopt the output of the EASsimulation package CORSIKA [7]. The simulated EASserves as a reference that is simple to compare to, and al-lows to demonstrate certain simple properties of the EASdisk at the observation level.Firstly, every parent particle regardless of species andenergy gives rise to a single uniform EAS without anybreaks in the structure or large-scale fluctuations with sta-tistical significance.Secondly, the particle density drops smoothly with dis-tance when moving away from core. The symmetry is as-sumed here for the vertically incoming EAS disk. Thecharged particles distribution vs. the distance from coreis illustrated in Figure 2. These simulation results are sup-ported by the result of the experiment ’Hadron’ publishedearlier [8].Figure 2. Charged particles density vs. distance from EAS core.And, finally, the thickness of the EAS disk increaseswith the distance from the core. Additional characteristicsmay be sought from the simulated EAS but these threeseem to be vital ones to both standard definition and theillustration of the unusualities of the EAS detected. Forthe illustration of the disk widening, the particles arrivaltime distribution over the 4 m2 area at 50 and 100 metersis illustrated in Figure 3 and Figure respectively 4.Figure 3. Charged particles arrival time at 50 m from EAS core.Figure 4. Charged particles arrival time at 100 m from EAS core.In Figure 5 the event display of the standard EAS asdetected by the HT detector system is shown. We can seethat the EAS disk is arriving from the side of the detectorpoint 4 grazing it with its edge, then hits points 5, 1 and 6almost simultaneously with the core passing further thenpoint 7 following the arrival direction.Figure 5. Sample ’standard’ event as seen by HT detector sys-tem.3 EAS with Unusual StructureBesides the initial observation of the MME in 1953 [6],other scientists were trying to study these events at differ-ent times. Initially, the effect was attributed by many ofthem to a birth in the EAS of a very massive particle witha low γ factor that would get delayed and then start a newshower of its own, thus causing the multi-modality of thedetected signals.Over 60’s to 80’s, the MME events were studied byBritish and US physicists, such as Linsley J. [9], WatsonA.A. [10] and Yodh G.B. [11]. Since the 70’s, the delayedparticle effect is studied in Japan (Sakuyama H. [12], In-oue N. [13]). Starting from the 80’s, the studies of MMEwere continued by the Moscow State University [14] andin at Lebedev Physical Institute of the Russian Academyof Sciences [15] [16]. In the 90’s, the MME pulses wereregistered at the Yakutst detector system [17], and in the2000’s they were detected by the "TUNKA" detector sys-tem [18].Note that the delayed particle explanation, in orderto support the time delayed observed experimentally, re-quires frequent birth of the particles with the rest massesexceeding 1012 eV. Not only we don’t know such a parti-cle, but, according to the current gauge invariance theories,the probability of such a particle being born is inverselyproportional to the square of the mass contradicting thefrequency of observation. Thus, the MME researchershave always admitted that they have extreme difficultiesexplaining the multi-modality using the current physicsknowledge and that MME may indicate the existence ofa new physical phenomena.Figure 6. MME as seen by HT detector system.3.1 MME Example at HTMost MME events detected at HT seem to be parts of alarger event arriving far away from the detector system.However, there are several events recorded with the MMEaxis falling near one of the far periphery points, allowingto observe the complex structure of such an event. Anexample of such MME event is given below.The event in Figure 6 was detected on Jan. 26 2016at 3:51 UTC. The event display shows the very large sig-nal at detection point 2 and and the next pulse is visibleFigure 7. MME as seen by HT detector system.Figure 8. MME as seen by HT detector system.from the point 5, thus indicating that the MME axis hasarrived somewhere between these points much closed topoint 2. The amplitudes of pulses from other detectionpoints is much smaller and is not visible in this figure. Ifwe take pulses with highest amplitude and use them aswith a standard EAS analysis, then the axis of this eventis tilted at θ ∼ 50o and arrival direction is approximatelyalong the line, connecting detection points 2 and 3, deviat-ing towards point 5. Note also that is a pulse from point 2resembles what is expected from a standard EAS, the pulsefrom point 5 seems to start deviate from that expectationof a smooth pulse shape.Shown in Figure 7 are the pulses from detection points1 and 7 only. Note that these points are both located aboutthe same distance from the axis and further then the point5. Both have a complicated structure, with the signal frompoint 7 having the modes spread farther apart then forpoint 1 signal.The pulses from detection points 6 and 4 display fullmulti-modality (see Figure 8). The peaks are separated byhundreds of ns and feature at least one of the pulses eachhaving a complex shape.The pulses from the detection points 3 and 8 are shownin Figure 9. These points are farthest from the axis of thisevent and display the features similar to points 4 and 6,except that the pulses have further separated by severalhundreds of ns. Signal from the point 8 has the same 3distinct modes, however, point 3 has only 2 modes visible.It is also the farthest point from the axis of the event, andit is possible that some modes are too weak to be detected.Figure 9. MME as seen by HT detector system.From the pulses from all detection points we can inferthat this is a very high energy event as its radius is at least1 km. There are several clean events like this that havebeen observed at HT and they all follow the same pattern -a large single pulse (that may have structure that is just toofine to be resolved), then the complicated structure pulsesat intermediate distances and fully separated multi-peakedpulses at the farthest points from the event axis. It is alsoplausible that other MME events detected are just parts ofthe events that have the structure described above. Thefurther studies and analysis of such unusual events are inprogress.4 ConclusionA large number of MME events were detected at HT. Theobservations show large variety of shapes and delays be-tween the modes, thus discarding the hypothesis of the de-layed particles, because in this case all detection pointswould have shown a similar structure. There is a strong in-dication that all the variety of forms detected comes fromthe unified structure that was observed in several eventswith the axis close to the far periphery detection points,allowing observation of the event structure at different dis-tances.References[1] R U Beisembaev et al., arXiv:1605.05179, (2016)[2] A Baitenov et al., arXiv:1601.00086, (2016)[3] MELZ-FEU, 4922-y pr-d, 4c5, Zelenograd, g.Moskva, Russia, 124482 http://www.meltz-feu.ru[4] Hamamatsu Photonics, 314-5 Shimokanzo, Toyooka-village, Iwatagun, Shizuoka-ken, 438-0193 Japanhttp://www.hamamatsu.com[5] T Beremkulov et al., arXiv:1608.04312, (2016)[6] J.V. Jelly and W.J. Whitehouse, Proc. Phys. Soc. A66,454 (1953)[7] D. Heck et al., Forschungszentrum Karlsruhe ReportFZKA 6019[8] Adamov D.S. et al., ICRC. 460A, 5(1987)[9] Linsley J. and Scarsi L., Phys. Rev. 128, 2384 (1962)[10] Baxter A.J., Watson A.A. and Wilson J.G., Proc. 9ICRC. 2, 724 (1965)[11] Yodh G.B. et al., Proc. 18 ICRC. 11, 264 (1983)[12] Sakuyama H. et al., Proc. 16 ICRC.8, 135 (1979)[13] Inoue N. et al., Proc. 19 ICRC. 7, 316 (1985)[14] Atrashevich V. B. et al., RAS News Bul. 58 (12), 98(1994)[15] Beisembaev R.U. and Vavilov Yu.N. et al., Proc. 24ICRC. Roma 1, 454 (1995)[16] Beisembaev R.U. et al., Nuclear Physics T.72. 11, 1-4 (2009)[17] Glushkov A. B. et al., Letters to Journal of Experi-mental and Theoretical Physics 67 (6), 361 (1998)[18] Prosin V. V. et al., RAS Bulletin 73 (5), 627 (2009)

Extensive Air Showers with Unusual Structure

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Extensive Air Showers with Unusual Structure

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