The project of upgrading of the Pamir and the Hadron experimental setups currently operating at high mountain altitudes is proposed. The setups are designed for comprehensive investigations of the primary cosmic rays (PCR)as well as nuclear interactions in the energy range 

1–1000 PeV where some new phenomena beyond the conventional conceptions of nuclear cascade processes have been recently

observed

Slavatinsky, S.A.

English

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IL NUOVO CIMENTO Vol. 24 C, N. 4-5 Luglio-Ottobre 2001Investigation of unusual phenomena in cosmic rays withTien Shan and Pamir experimental setups at energyhigher than 1 PeV - II(∗)S. A. Slavatinsky(∗∗)P. N. Lebedev Physical Institute, Russian Academy of SciencesLeninskii Prospekt 53, 117924 Moscow, Russia(ricevuto il 24 Ottobre 2000; approvato il 12 Febbraio 2001)Summary. — The project of upgrading of the Pamir and the Hadron experimentalsetups currently operating at high mountain altitudes is proposed. The setups aredesigned for comprehensive investigations of the primary cosmic rays (PCR) as wellas nuclear interactions in the energy range 1–1000 PeV where some new phenomenabeyond the conventional conceptions of nuclear cascade processes have been recentlyobserved.PACS 13.85.Tp – Cosmic-ray interactions.PACS 96.40.De – Composition, energy spectra, and interactions.PACS 96.40.Pq – Extensive air showers.PACS 01.30.Cc – Conference proceedings.1. – Main goals of experiments with the Pamir and the Hadron-M experi-mental setupsAt present, a dramatic situation exists in cosmic ray physics at energies above 1 PeV.On the one hand, numerous phenomena beyond the conventional concepts of nuclearcascade processes in the atmosphere are observed mainly in the EAS core region. Onthe other hand, modern accelerator experiments still provide no evidence for any seriousdeviations from the Standard Model of strong interactions [1].One may suppose that unusual particles, e.g., strangelets or even more exotic onesmay be present in the PCR flux at energies above several units of PeV and their existencecould be the origin of the observed anomalous phenomena in experiments with cosmicrays.(∗) Paper presented at the Chacaltaya Meeting on Cosmic Ray Physics, La Paz, Bolivia,July 23-27, 2000.(∗∗) On behalf of the Pamir and Tien Shan Collaboration.c© Societa` Italiana di Fisica 563564 S. A. SLAVATINSKYFig. 1. – a) A layout of detector location of the Hadron-M setup at Tien Shan (3340 m a.s.l.).b) Dissection of the central detector of the Hadron-M setup.To promote this study we propose to perform a series of experiments which couldconsiderably contribute to the solution of this dramatic situation. These experimentsare necessary not only to increase the statistics of anomalous events but also to improvethe reliability and variety of experimental data on each of the events. With this objectin view, we intend– to employ an X-ray emulsion chamber of a new type specially designed for certainphysical problems at the Pamirs in the framework of the Pamir-Chacaltaya experiment;– to upgrade the setup which is now in operation at the Tien Shan Mountain Station.The main point of this upgrading which will result in assembling a new Hadron-M setupis the employment of a radically new detector, namely, a ionization neutron calorimeter(INCA) of large area.The idea to associate ionization calorimeter and neutron supermonitor in one device(INCA) by including neutron counters with neutron moderators in the calorimeter wasproposed ago by Dr. A. P. Chubenko [2]. This technique essentially enlarges the range ofmeasured energies, improves the accuracy of energy determination and makes it possibleto separate primary particles of electromagnetic origin from nuclear ones by neutronnumber in a single cascade. The validity of the assumptions was confirmed by acceleratorexperiments with stretching beams of 70 GeV protons and with 3 GeV pion beams aswell as with 550 MeV electron beams.2. – The present status of the Hadron setup and its upgradingThe Hadron setup consists of the following detectors and instruments (fig.1a):– In the center, there is an XREC with ionization chambers of 160 m2 in sensitivearea. A correlation with EAS is established by coincidence of space coordinates andangular characteristics of electron-photon cascades in XREC with those signals detectedby ionization chambers positioned in a cross-way manner. The ionization chambersmeasure also the sum energy of electron-photon component distributed over the wholeINVESTIGATION OF UNUSUAL PHENOMENA IN COSMIC RAYS ETC. - II 565area of the XREC. The spatial resolution of ionization channels is 0.11 by 0.11 m2.– The ground surface shower array of 120 scintillation detectors for recording EASelectron-photon component. The arrangement of the detectors make it possible to recordEAS inside a circle of 200 m in radius positioned in the center of the setup and thus torefine lateral distribution functions (LDF) at large distances.– The Chronotron system for determination of EAS arrival angles by measuring thedelay of the EAS front arrival in various points of the shower array.– Fifteen spectrometers of complete absorption on the basis of ionization chambersfor measuring the energy flux of the electron-photon component; these detectors areregularly distributed within a circular area of 40 m radius.– Underground central muon detector of 100 m2 sensitive area for recording muonswith energy Em > 5 GeV.– For measuring direction and time of arrival of single muons with respect to EASfront, there is a MUON-T central underground setup consisting of 18 wide-gap sparkchambers with nanosecond electronic recording channels.– The neutron supermonitor 18 NM-64 located at 34 m from the center and connectedwith the EAS recording system for measuring the energy flux of the hadron componentwith Eh > 50 MeV.– The VEGA system consisting of 13 photomultipliers without mirrors for recordingEAS Cherenkov radiation in the atmosphere.The main trends of upgrading of the HADRON-M central part are as follows:– Replacing the existent old-type ionization impact recording facility in the centralpart of the Hadron setup with the INCA (fig.1b).– Replacing the old-type electronics with modern one.3. – Statistics within 3-year exposition of the Hadron-M setup and expectedresultsThe problems which could be solved as a result of 3-year exploitation of the Hadron-Msetup are listed beneath with short description of the applied techniques for their solution:1) The conclusion of the diffusion model on the nature of the PCR energy spectrumbend at energy of 3-4 PeV will be confirmed or rejected. For this purpose, the partialenergy spectra for the main PCR nucleus groups (protons, α-particles, middle nuclei withZ = 6–8, heavy nuclei with Z = 10–25 and iron nuclei) in the energy range 0.5–100 PeV,i.e. in the range before and above the first energy bend, will be determined for the firsttime.The total number of recorded EAS with axes within the INCA borders will be as highas ∼ 105 events after 3-year setup operation term. For all such events, the EAS energywill be determined by the most reliable method as an integral of energy densities releasedin the setup detectors by each of the main EAS components, i.e. electron-photon, muonand hadron one. The expected accuracy of the EAS energy determination is 10–15%while the expected uncertainty in the primary energy is ∼ 30% assuming the validityof the Standard Model of hadron interactions. The nature of primary particle for eachparticular event can be established from the collection of several EAS characteristics and,in some cases, it can be determined using the characteristics of the corresponding gamma-family recorded by XREC [3]. To reconstruct the mass composition of PCR particles fromthe characteristics of induced EAS we shall apply the technique of an inverse problem566 S. A. SLAVATINSKYsolution and multivariate analysis [4] exploited for image recognizing. We might expectthat the reliability of attribution of recorded events to the specified five groups of PCRparticles will be high enough and an error of nucleus nature determination will be within20–30% due to high mountain elevation of the setup. The expected numbers of eventsfor each specified group of PCR particles will be near 104.Thus the information on existence of PCR partial spectrum bends will be originallyobtained in the experiment. The comparison of these data with predictions of variousdiffusion model versions will make it possible to draw conclusion on applicability of themodel version under consideration. In any case such an information will clarify not onlythe spectrum bend nature but perhaps the existence of some cosmic ray source nearbythe Galaxy which can produce irregularities in the PCR composition around the Earth.2) The search for local gamma-ray sources and the study of diffuse gamma-radiationin a weakly explored energy range of 0.2–10 PeV will be performed. For this purpose,intensity and shape of energy spectrum of muon-less, hadron-less and, especially, neutron-less EAS will be measured in the specified energy range. The performed acceleratorexperiments and appropriate estimations give the value of coefficient for rejection ofhadron induced showers as low as 10−5.In the 3-year term of HADRON-M operation, it is expected to observe 1200 EASin the 0.2–10 PeV energy range. It will be possible not only to discover the source ofprimary gamma-quanta but also to determine their energy spectrum.Besides, the flux value for the primary diffuse gamma-quanta with energy higher than200 TeV will be established.3) Unique information on unusual phenomena and events previously observed in cos-mic rays will be obtained due to EAS recording both in the calorimeter and by scin-tillation and neutron counters; this makes it possible not only to measure the primaryenergy E0 reliably and accurately enough but also to effectively determine the nature ofthe primary particle producing each of the event.Such information may be crucial for interpretation of the following formerly observedunusual events:a) Events with coplanar divergence of secondary particles of highest energies. At EASenergies above 10 PeV, the total number of 4-core coplanar events will be about 10. It issignificant that, for all these events, a complete information will be obtained both on theprimary particle generating the EAS and on the properties of the EAS itself. Besides, afew dozens of 3-core coplanar events in multi-core EAS will be observed.b) Events related to production of “halos”, i.e. large diffuse darkened spots onX-ray films produced by high-energy hadrons. The expected number of these eventswill amount 25± 5. Note that information on the primary particle nature and its energyis of particular importance for interpretation of these events. More over, it is hard toexclude that the nature of these primary particles is unusual, namely, it may be relatedto production of strangelets. In this case, the corresponding EAS will have also unusualcharacteristics. For instance, they will produce extended hadron shower cores in the deepcalorimeter [5].c) In the HADRON-M operation term we expect to detect several Centauro andAnti-Centauro events, but their recording will be supplied with information of mainimportance, i.e. primary particle nature and its energy. Perhaps the energy thresholdfor their observation is higher than available at accelerators.d) Knowledge of nature of the primary particle will make it possible to performINVESTIGATION OF UNUSUAL PHENOMENA IN COSMIC RAYS ETC. - II 567Fig. 2. – The Pamir XREC designed for the study of penetrating particle absorption.detailed analysis of EAS characteristics in order to discover the signature of quark-gluonplasma in heavy nuclei interactions (e.g., Fe-air).e) Physics processes responsible for appearance of abnormally delaying for 500 andmore microseconds intensive neutron component in EAS cores originated from primaryparticle with energy higher than 3 PeV will be established.4) The problem of existence of the second (“reverse”) bend in the PCR energy spec-trum at energies higher than 50 PeV will be solved. The expected number of EAS withenergies higher than 50 PeV drastically depends on the presence or absence of the secondbend and will amount to 600 and 200, respectively, after 3 years of operation.4. – XRECs of the Pamir Experiment: status, upgrading and expectedstatisticsAn extensive experimental site destined for exposition of large-area XREC at elevationof 4370 m above sea level at the Pamirs was constructed by the Pamir ExperimentCollaboration in the past years (fig. 2).At present a steel frame 36 m2 in area is constructed at Pamirs. The frame makesit possible to assemble an XREC consisting of two lead blocks separated in the verticaldirection by 2.5 m air gap. The total depth of lead absorber amounts to 50 cm. Ifthe effect of weak absorption arises from charmed Λc and D-meson production, thecorresponding absorption curve which is expected after 3-year exposition must have aclear bump.The absence of the bump will favor the presence of a new type of hadrons withproduction cross-section about one order less than nuclear one. It is quite evident thatthe discovery of such particles, probably consisting of quarks of higher color symmetries,would be of fundamental importance for physics.In conclusion, we are glad to invite all cosmic ray physicists to take part in theseexperiments with the Pamir and Tien Shan setups.∗ ∗ ∗The work is supported by Russian Foundation for Basic Research, project No. 00-02-17271.568 S. A. SLAVATINSKYREFERENCES[1] Slavatinsky S. A., Nucl. Phys. B (Proc. Suppl.), 52 (1997) 56.[2] Antonova V. A., Chubenko A. P. et al., Nucl. Phys. B (Proc. Suppl.), 75A (1999) 333.[3] Chadranian L., Roinishvili N. et al., Nucl. Phys. B (Proc. Suppl.), 75A (1999) 180.[4] Danilova T. V. et al., Russ. J. Nucl. Phys., 54 (1991) 137.[5] Dremin I. M. and Yakovlev V. I., in Proceedings of the 17th Conference on MultiparticleDynamics, Seewinkel 1986, 1 (1986) 849.

Investigation of unusual phenomena in cosmic rays with Tien Shan and Pamir experimental setups at energy higher than 1 PeV (part II)

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Investigation of unusual phenomena in cosmic rays with Tien Shan and Pamir experimental setups at energy higher than 1 PeV (part II)

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