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New Results from Cosmic Rays

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New Results from Cosmic Rays 0 NEW RESULTS FROM COSMIC RATS S.C. Tonwar Tata Institute of Fundamental Research Hoasi BhaSsha RoasS, Bombay-400 005 I wish to discerns here some of the interesting results that have become available In last few years fro m experiments carried out using cosmic ray beam. These results provide information about particle physics at energies well above these available at particle accelerators. I have also included in this discussion some experimental results which were obtained many years back but have been reinterpreted recently in the light of our present knowledge of high energy processes v . , and cosmic ray composition. I must emphasize right in the beginning that most of the interesting results obtained in cosmic ray experiments suffer from poor statistics due to very low luminosity of the cosmic ray beam at high energies. Further the interpretations of observed phenomena, in some cases, are not unique due to our lack of precise knowledge of the composition of primary cosmic rays at these'energies. Therefore, the cosmic ray experiments, by their very nature, can provide in some cases only a glimpse of the interesting phenomenon which may be occurring at very high energies. An idea of the statistical problems faced by a cosmic ^ray^physicist may be given by a comparison of the cosmic ray particle flux with the beam luminosity obtained, say, at ISR machine. For - 262 - - 263 - energies above 2000 GeV (2 TeV) the proton flux at the top of atmosphere is about 70 m"^sr"*hr“l and only about 0.5 m '^sr^day*1 at mountain altitude (730 g. cm*^). On the other hand one can observe about 10® interactions per second at any of the ISR intersections. Of course these difficulties do not really discourage a cosmic ray physicist because they are more than compensated by the excitement due to the possibility of observing completely new phenomenon at very high energies. The new results discussed here, can be conveniently grouped into three categories : (i) Results on hadron-nuclei and hadron-hadron interaction cross-sections, (ii) Results concerning possible violation of scaling behaviour at high energies, and (iii) Results on New Particles and New Phenomenon. Though most of the results discussed here belong to hadron physics, interesting phenomenon observed recently in underground experiments at Kolar Gold Fields has also been included in the discussions on new phenomenon. Finally I plan to mention briefly some of the new experiments being planned which would provide certainly new and possibly • exciting information about high energy processes at super high energies. , - 264 INTERACTION CROSS-SECTIONS AT HIGH ENERGIES Most cosmic ray experiments measure hadron-nude us Inel inelastic cross-sections O^-A corresponding value for taadron- T proton total cross-section is then deduced using Glauber theory of multiple scattering. There are basically two methods which have been Inel used for determination of <Th-A . The first method is the standard transmission method where attenuation of a hadron beam through inter­ actions in a multilayered absorber is studied in laboratory. In the second method the attenuation of primary cdsmic ray proton flux through the atmosphere is studied using the atmosphere above the observational level as a slab of absorber. I would discuss here the recent developments and new results obtained in last few years using both these methods. Since interesting information on the energy dependence of total proton-protan cross-section has been deduced from measurements using the second method, I would first discuss the present situation regarding these measurements. Around 1975 there were basically two viewpoints regarding the T energy dependence of CTp.p which suggested very different behaviour T of (Tp.p at very high energies. The first viewpoint was represented by the -results obtained by Yodh, Pal and Trefil* in 1972 indicating that T 1 2 CTp-p is increasing with energy as I n s , s being the c*.m. energy.* - 265 - This result was obtained by comparing the expected attenuation of primary proton flux through the atmosphere and the measured flux at Mt. Chacattaya (550 g. cm ) as given by Kaneko et al (1971) of . unaccompanied charged hadrons. The second viewpoint was later given by Ganguli and Subramanian^ in 1975 who reanalysed the same data using a different primary energy spectrum and also added information obtained from Njjl, -Ne measurements at air shower energies. They concluded T that CTp_p is increasing slowly with energy as Ins and might become constant at high energies. The basic difference between these two view­ points, obtained using essentially the same experimental data in the 2-20 TeV energy range, was due to the assumption of different shapes for the primary proton energy, spectrum at energies above 2 TeV, apart from small corrections. The primary proton.energy spectrum Np (E,0) enters in the calculation of O'pi air through the expression: „ . 2.4 xlO4 11161 (E) = —— — - • In„ |r ---”------------ j 1 mbarns ° p - a ir x L n ? ( E . , ) J s 2 where Np(E, x) is the surviving proton flux at depth x g. cm- in the atmosphere. Since - 266 - Inel = Total _ Elastic Op-air ~ Op-air " ®"p-air _ Total Elastic ' T and <T* . and ry are related to ry . a p -a ir ' y p - a ir . PP measurement of tr-1”61 leads to a determination of u p -a ir PP through calculations using Glauber theory of multiple scattering. ^ ^ .a ir (o. r, fpp) 0-p.TC = 1 d5 ' lFP-air<^.r, fpp) * j d 2 ' I Here Fp.gir is the elastic scattering amplitude which is related to the proton-proton scattering amplitude fpp, nuclear radius r and momentum transfer A and Can be computed using reasonable assumptions about nuclear parameters and the formalism developed by Glauber for multiple scattering. The proton-proton scattering amplitude fpp is given by here oC is the ratio of real to imaginary part of the scattering amplitude, b is the diffaractive width, k is the proton momentum and t is the momentum transfer. The energy dependence of o( and b is assumed as given by the experiments at machine energies. V - 267 - Inel Apart from the crucial dependence of fT p .^ and hence of T the deduced 0~pp on 016 assumed shape of the primary proton energy spectrum, corrections are also necessary for the fact that experiments measure the unaccompanied charged hadron flux which include secondary hadrons (p, ic , K etc.) produced by higher energy primary cosmic rays higher up in the atmosphere. Thus Np " Nch - NP ' % " N* However Np and Nr are negligible in proportion to among secondary hadrons and correction needs to be applied only for the pion content of the unaccompanied charged hadron flux. Note that the error Inel in determination of CTp-air is quite small for even a large error in measured flux due to the logarithmic factor. The measured value of 0*ptair using the flux (NCh - ) also needs to be corrected for quasi­ elastic scattering, diffaractive excitation and inelastic screening processes 4 as discussed in detail by Gaisser et al . There have been only two direct measurements of primary proton energy spectrum. The measurement using balloon borne calorimeter by 5 Ryan et al (1972) gave the integral energy spectrum as Np(E.O) = 1.14E‘1,75cm-2sec-1 for 20 < E< 2000 GeV . The measurements by Grigorov and his colleagues®*7 gave the energy 1 - 268 - spectrum for primary protons as Np(E, O) = 3 x 10’4 (-™ -)1' 62 • Q + (--y0-)2j cm-2sec-1 for 20< E< 20,000. These measurements have been made in a series of experiments using satellite borne calorimeters. Surprisingly the measurements of 7 Akimov et al show the proton energy spectrum to be steepening for energies greater than 1500 GeV. This particular feature has invited lot of attention and criticism to these measurements since such a bend in the proton energy spectrum has not revealed itself in any of the measurements at higher energies of various cosmic ray components at mountain or airplane altitudes or muon energy spectrum at sea level. Yodh et al* have therefore used an extrapolation of the spectrum 5 given by Ryan et al in their analysis for obtaining energy dependence of ^"^air °* G"pp' ®n 016 other hand Ganguli and Subramanian^ P 7 have used the proton energy spectrum as given by Akimov et al . They Inel have also included in their analysis the results on deduced from - Ne data obtained at air shower energies. The air shower date" shows the O '^^ir t0 near*y independent of energy and therefore a slow increase as Ins of a-*116* is suggested by Ganguli and p -air Subramanian from their analysis shown in figure 1. - 269 This picture has gone considerable change in last 3 years due to a series of new measurements with much improved detector systems. These measurements have come mainly from two groups: Yodh and colleagues from University of Maryland at College Park. (USA) and Nikolsky and co-workers from Lebedev Institute in Moscow (USSR). 8 The Maryland group (Siohan et al , 1978) has measured the unaccompanied charged hadron energy spectrum in the 100-10,000 GeV range at mountain 2 2 altitude of 730 g. cm (Sunspot, New Mexico). They have used a 4 m area 8 m. f. p. deep iron calorimeter having wide gap spark chambers 9 inside as well as above. Similarly the Lebedev Institute group (Nam et al , 1977) measured the unaccompanied charged hadron energy spectrum in O the energy range 2000-50,000 GeV at 700 g. cm" (Tien-Shan) using a 2 36 m area, 4.
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