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 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 ^ ^ .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. 5 m. f. p. deep lead calorimeter. Nikolsky and his co- workers^® have also determined Cpltdr *or hadrons energy 15,000 GeV by studying the zenith angle distribution of these hadrons. Inel This method of determining • ^ is independent of the shape of the primary proton energy spectrum and depends only weakly on the composi tion of charged hadrons at the observational level. A further refinement of the experimental results for the purpose of determining tT ^^ir ^ also 1,6611 achieved by Maryland group8 through a direct, measurement of the proton content of the charged.hadron - 270 flax. Since this is a new and interesting development it is appropriate to describe this measurement in seme detail. As is well-known the conventional methods like magnetic bending, ionisation measurements etc. for measuring the particle mass have severe practical limitations for hadrons of energies greater than about 300 GeV. The phenomenon of transition radiation, on the other hand, starts becoming interesting for this purpose at only these energies. The transition radiation is emitted when a charged particle traverses an interface between two media of different dielectric properties. The intensity and the energy spectrum of the emitted radiation depends on the Lorentz factor Y (= E/m) of the particle. For a single interface between vacuum and dielectric medium the intensity is proportional to Y and is equal to | • t\u*p • Y where e( is the fine structure constant, «p is the plasma frequency of the medium and "ft is the Plaint's constant. For vacuum-mylar interface this intensity is only 0.178 keV for Y = 3000 400 GeV) and hardly detectable in any detector in presence of the ionisation by the particle itself. The TR intensity can be Increased by using a large . number of interfaces, for example, by using large stack of stretched mylar foils. But in such a stack, due to interference between radiation emitted at different interfaces and due to absorption of the radiation in the medium itself, the TR yield is no longer proportional to Y and increases only slowly with Y . However the fact that for same total 271 energy ia seven times Yp helps in distingoishing pions from protons. The Maryland group^, *^ constructed a transition radiation detector consisting of a sandwich of 24 layers of styrofoam radiator and multiwire proportional chambers. The TR emissivity for this particular type of foam was measured by Fabjans (1975) at ISR. Also a small area 15 but otherwise identical 3 layer detector was calibrated directly at BNL using electrons. The complete experimental system including TR detector, calorimeter, spark chambers etc. as used at Sunspot to measure the unaccompanied charged hadron flux and the pion to proton ratio is shown in figure 2. A typical hadron interaction and cascade development in the calorimeter as shown by spark chamber picture is shewn in figure 3. Using this system the pion to proton ratio has been measured*6 to be 0.96 + 0.14 for hadrons of energy 400-800 GeV and 0.45 + 0.25 for hadrons of energy > 800 GeV. Another interesting result obtained by the Maryland group from 17 the same experiment concerns the measurement of instrumental effects which could have led to wrong identification of protons as o( -particles and heavier nuclei by Grigorov and his colleagues, in their satellite experiment. Ellsworth et al*? have reported that due to back scattered particles (particularly neutrons) from interactions inside the calorimeter the electronic detectors like scintillation detectors and multiwire - 272 proportional chambers located above the calorimeter give pulses of amplitude much larger than expected for singly charged particles. Thus it has been shown that the identification of protons by proportional chambers alone is' highly suspect and that this error increases with increasing energy. Though an exact quantitative correction to the results of Akimov-et al cannot be deduced from the studies made by Ellsworth 17 ’ et al due to different geometrical arrangement of detectors, it is quite clear (fig. 4) that the steepening in the proton energy spectrum is partly, if hot fully, due to instrumental effects. With these new measurements of unaccompanied charged hadron 8 flux in the energy range t 7 200-50,000 GeV by Siohan et al and Nam et al® a consistent picture of the energy dependence of O ^adr T of Q"pp can be obtained using for primary proton spectrum an extrapolation of the measurements of Ryan et al® to energies of about 4 g 10 GeV. In figure 5 are shown the results obtained by Siohan et al on Inel G“ air usin8 the experimentally measured "*t>/p ratio. As seen in Inel fig. 5 the 0*p-air ^lues obtained by the Maryland group are in good agreement with Ln^s extrapolation of ISR measurements of C pp Inel Inel and converted to (J'p-air. Also shown in this figure is the CS"p a with proper corrections* are shown in figure 7 along with recent results obtained by Amaldi et al*® (1977) at ISR. Also shown in the figure is the curve fitted by Amaldi et al*® to their measurements which is represented by the expression V - EJ)-,,t» 0S - (24.2. 1.1) E-0 55! 0 02] pp U , 2. 10+ 0.10 + (27.0+ 1.0)+(0.17 + 0.08) • 018 18 It should be noted that Amaldi. et al have also measured the energy dependence of 0( , the ratio of real to imaginary part of the scattering amplitude, and the best fit represented by the expression given above has been obtained through a simultaneous fit procedure for both Qt T T "9 and - The It is quite clear that the N^. - Ne data does net agree with T this result and requires (T*pp to be almost independent of energy in 5 8 the 10 -10 GeV energy range. Apart from some systematic uncertain* ties in measuring for air showers with small number of }Judetectors, / - 274 - Inel the G” p-air values obtained from N^*. - Ne data require some reinterpretation in the light of recent results about composition of primary cosmic, rays at air shower energies. As discussed in the next section, there are strong indications from air shower data that composi- 47 tion of primary cosmic rays in the 10 -10 GeV energy range is becoming enriched in iron group nuclei with increasing energy. Therefore Inel the Nikolsky and his colleagues*® have also measured hadron-lead nuclei inelastic cross-sections and deduced proton-lead cross-section at energies of 5 and 15 TeV. Compared to a value of 1780 + 18 mb for Inel IQ inel O'p-pb at 200 GeV, Nam et al have measured Cp.pb to be 1840 + 50 mb at 5 TeV and 1915 + 140. mb at 15 T eV . These m easurem ents i* Inel suggest an increase of (5. 6 + 3.0) % in G"p_pb from 200 GeV to 15 TeV, an increase consistent with a tn^s increase in ^*pp and Glauber theory; Another new measurement of cross-section reported recently 19 T by Maryland group1 yields the energy dependence of in the TC-P 19 150-1250 GeV energy range. MacFall et al have measured through Inel standard transmission method G"h-Fe lor **adr°118 energy 150-1250 GeV. Using the measured composition of hadron beam and its dependence on energy, they have deduced the pion-iron nuclei inelastic Inel Inel cross-section Gtc-Fe- They find that is increasing with energy by 7.7 + 3.4% from 150 to 1250 GeV. Using calculations of 4 Inel Gaisser et al this observed increase in 0"^_pe implies an increase T of about 10% for ^ over the same energy range. Figure 8 shows the measurements of 18 reported by MacFall et al1®. It is of interest to compare the cross-section values predicted by Glauber theory for interactions with various nuclei using the observed T Cj h_p values at machine energies and the experimentally measured G'tf-A * This comParison' ahown 18 Fig. 9, reveals clearly the success ^ .In e l T of Glauber formalism for converting 0* h-A 8140 ®*h-p since ratio of expected to measured value.is close to unity (+10%) for all the measurements. It is appropriate to remark here that the sensitivity of Inel t T Crp_A for changes in 0 ”pp reduces with increasing 0~pp 88 shown by Barger et al^1 (1974). Their result (^ .1 0 ) indicates that measurements Inel of. tr*p_A have to achieve higher and higher accuracy with increasing . T energy to obtain tT pp with given accuracy. - 276 - SCALING VIOLATION AT HIGH ENERGIES There are many experimental results obtained from air shower studies which have been interpreted as indicating a violation of scaling characteristics at air shower energies (10®- 10® GeV). Some of these observations have been interpreted in terms of a rather rapid increase 1. ( ~ E 2) of particle multiplicity with increasing energy. However these interpretations are not unique since they depend on the assumed composi tion of primary cosmic rays at very high energies. I would discuss briefly three of these observations. The first observation concerns the longitudinal development of air showers. Suga and colleagues (LaPointe et al'22 ) measured the .epth of shower maximum for various primary energies using constant intensity method (fig. 11). They concluded from these observations that showers develop much faster than expected from calculations based on the scaling model. Similarly Kalmykov and Khristiansen®® have observed the variation of N ^ ( > 10 GeV) with shower size Ne and have found Nj*. to be much larger than expected (fig. 12). Vatcha and Sreekantan®* have studied high energy hadrons in , air showers and find too few hadrons (fig. 13) compared to the predictions using scaling-model. All these three observations require violation of scaling characteristics to varying extent. However recently it has been 25 shown that the first two observations can be interpreted in terms of a .*%«.»•.» i » i. V. i/rnil • I* i : it «>*.. ’ .a.*, utjx. .* scaling model if the primary composition at energies of 10®-10® GeV is assumed to be purely iron group nuclei. The hadron observations ' 24 also would require much less drastic changes in interaction characteristics if the primaries are all iron group nuclei. The possibility that iron group nuclei may dominate at energies above 10 GeV5 was first suggested experimentally by the measurements on primary composition by the Goddard group^6 in early 70’s, They had found that while the energy spectra of protons, oL -particles, CNO group nuclei etc. had an energy exponent of about -2.75, the iron group nuclei had a much flatter spectrum with an exponent of about -2.2 in the energy range of 5-100 GeV/n" Recently the Maryland group 27 (Goodman et al 1978) have presented evidence on the basis of arrival time distribution of hadrons in air showers for enrichment of primary cosmic rays with iron group nuclei with increasing energy'.1 They find that the observed hadron flux accompanied with small showers and the proportion of delayed hadrons require that the exponents for the energy spectrum of protons and iron group nuclei in the 1-100 TeV/n energy range be -2.71+0.06 and - 2l. 36 + 0.06 respectively. These results suggest that Iron group nuclei Would be the dominant component 6 of primary cosmic rays at energies 10 GeV. These results also 22 support the interpretations of the longitudinal development of air showers , Njju’ - Ne variation 23 • , and hadron component studies in terms24 of iron group nuclei thus weakening the evidence for large scale violation of scaling characteristics at air shower energies. - 278 - ’ There are of course some problems about this interpretation S * e I since the observations of Srinivasa Rao and his colleagues on high £ { energy muons ( > 220 GeV) in small sise air showers do not seem to i • • I agree with Iren nuclei dominated composition (fig. 4). However the fact that at about 10** eV the Iron nuclei may constitute less than 40% of primaries and that there are relatively large statistical errors in | the high energy muon data28 suggest that these observations may be | consistent with the primary composition indicated by the measurements of Goodman et al*7. HEW PARTICLES OR PHENOMENA (I) Long flying component: \ _ Nikolsky and his colleagues** (Aaeikin et al 1975) have studied the absorption of high energy cascades in their large area lead calorimeter. They determine the absorption length of the cascade after it has reached ' the maximum by fitting an exponential decay curve to the cascade from 300 to 1400 g. cm'* (Fig. 15a). Surprisingly they find that Aabs changes from a value of 685 + 85 g. cm for hadron energies of le ss than 40 TeV to a value Of 1100 + 100 g. cm** for hadrons of energy above 40 TeV (fig. 15b). This change in is seen for single hadrons incident on the calorimeter as well as for air shower cores.~~ Aseikhret al*® interpret - 279 - these observations as due to the production of some new particles at energies > 40 TeV which have different interaction characteristics (either small interaction cross-section or small inelasticity or both). No other cosmic ray group has such a large area calorimeter to observe a significant number of very high hadrons in reasonable amount of time. Also most other calorimeters use iron as absorber where dependence on energy may be different since equilibrium between electro magnetic and hadronie component is reached faster in lead calorimeters compared with iron calorimeters. These results on are very interesting indeed and need to be studied in detail with different experimental techniques. > • (ii) Centauro_events: . The Broxlt-Japan Emulsion Chamber collaboration group^® has reported observation of 5 events which show very unusual characteristics. All 5 events have very large multiplicities, about 70 to 90, and have 6 primary energies > 10 GeV. The details about these events are given in the table below. The almost complete absence of V-rays from the main interaction is a peculiar feature of these events. These 5 events are out of a total of 44 events having > 200 TeV. Figures 16a and 16b show schematic - 280 - TABLE : Interesting features of Centauro Events Event Number I II in IV V Chamber Number CH-15 CH-17 CH-17 CH-17 CH-16 Height of main Intn (m) 50 80 230 500 - Observed Multiplicity Pb jets 20 23 29 25 19 C jets 29 9 8 13 8 Total 49 32 37 38 27 Calculated total Multiplicity 74 - 71 76 90 - Multiplicity Y -rays arriving,the chamber 0 0 17 51 34 Produced in A-jets - - 17 47 - Multiplicity of V - rays produced in main inttf 0 0 0 4 illustrations of Centauro I and IV events. It has been suggested that only baryons may have been produced in these ultra high energy interactions. While no satisfactory and detailed explanation has been offered so far for these events it is clear that very interesting phenomenon is taking place at energies /v* 10® GeV. (iii) Delayed particles: * In 1971 the Ooty group 31 of Tata Institute had reported observation - of some very energetic hadronic type of events in their calorimeter which were delayed relative to shower particles incident above the calorimeter by more than 25 nanoseconds. In a preliminary experiment using cloud 32 chamber Tonwar et al also reported observation of 2 such events with measurable cascades seen in the chamber. In a recent experiment using 2 the large area (4 m ) calorimeter having wide gap spark chambers, the 33 Maryland group has studied the arrival time distribution of hadrons associated with small air showers. They have also observed three interesting events whose energies can be estimated to be more than about 50 GeV which are.delayed by 30 nanoseconds or more. Figure 17 shows 33 the observations of Goodman et al as a diplot of pulse height in terms of equivalent particles from a scintillation detector located inside the calorimeter and time delay of this signal relative to the signal from the shower particle detectors located above the calorimeter. No such event is expected from known particles or processes including fluctuations as shown by detailed Monte Carlo simulations of air showers in the atmosphere. However such events could be interpreted as due to production of some 2 new type of massive particles with mass in the range of 5-20 GeV/c . Since the observed flux of such particles is about (4.3 + 1. 3) x 10"** cm -2 sec 1 sr 1 , the production cross-section required to explain the observations is about 10-100 yu-b depending on the assumed energy dependence of the cross-section above threshold. - 282 - These observations of delayed energetic events by Goodman et al 33 and by Tonwar et al 31 ’ 32 earlier imply the existence of new -7 massive relatively long lived ( ^ 10 sec.) particles which are produced 14 only at very high energies ( > 10 eV). Detailed information about the production and interaction characteristics of such particles can be obtained through air shower studies using visual detectors. Such a study 34 is now being carried out by the Ooty group using the large multiple cloud chamber with two scintillation detectors placed inside the chamber (fig. 18). The arrival time of the particle producing the cascade is measured by these two detectors relative to shower particles detected by two similar detectors located above the lead layer shielding the chamber. The energy of the partible is estimated from the observed cascade by track counting method. (iv) High energy cascades in underground experiment: " 35 Recently Krishnaswamy et al (1977) have reported observation of 4 high energy ( > 1000 GeV) cascades in their experiments being carried out deep underground in Kolar Geld Mines. The detectors used were large area vertical and horizontal telescopes and magnet spectrographs having scintillation detectors and neon llash tubes with a variety of absorbers. In addition to detection of single and multiple muons of very high energies, the telescopes record showers of different sizes generated either in the - 283 - rock enveloping the detectors or the absorbers Inside the telescopes. Most of these showers are due to normal electromagnetic interactions of atmospheric muons near the detector. Of the high energy showers -2 observed 2 have been seen in the detector located at a depth of 3375 hg cm and two have been seen at 7000 hg cm‘‘ level, suggesting depth independence of the phenomenon responsible for these events. No event of such high ■ energy is expected in the given exposure area factor from any known process. The observed features suggest that they are produced by a highly penetrating and isotropic component such as the cosmic ray neutrinos. However it is difficult to account for the observed frequency of these events unless the neutrino interaction cross-section for such processes is much higher than the extrapolated values from lower energies. Observations at various depths underground with improved detection system are continuing and further detailed observations are awaited with great interest. (v) Charm hadron production in hadron collisions: i ■ : ; : ' Charm particle production was probably first seen in cosmic ray experiment in 1952 by Kaplon et al36 but was obviously not recognised. Niu. et al3^ (1971) and Sugimoto et al3® (1975) reported observations of very interesting events in cosmic ray interactions at high energies ( > 10 TeV) which can now be easily explained as due to production of a pair of charm hadrons. Figure 19 and 20 show, schematically the events 37 38 39 seen by Niu et al 1 and Sugimoto et al respectively. Recent searches for charm hadrons in accelerator experiments at 200-400 GeV have given the production cross-section of about 100 job. The cross-section is estimated to be about 1 mb at energy of about 10 TeV. It is interesting to note the continuing rise in charm production cross-section from 400 GeV to 10 TeV... If the cross-sections continue to. rise with increasing energy by an order of magnitude, charm production may be playing a dominant role for some of the observed features like muon component in air showers. Therefore a determination of charm production cross-section at energies of ~ 100 TeV will be,of considerable significance for cosmic ray experiments. NEW EXPERIMENTS Cosmic ray experiments continue to provide interesting information about high energy physics since the present generation of accelerators have highest equivalent laboratory energy of only about 2 TeV (ISR).' However, in next,3 to 4 years,this situation would be changing with CERN/SPS and FLAB/MR facilities providing ]p-p interactions of as high an energy as 10*4 eV and interaction rates of about 10® per second. Therefore many of the experimental techniques presently being used by cosmic ray experimen ters would require considerable improvement to enable them to explore - 285 - successfully the very high energy region above 10 15 eV. The experiments would necessarily have to be large scale since the flux of cosmic ray 15 particles above energies of 3 x 10 eV (projected energy of FLAB/ED) is only about 0.2 m • 2 day-1. 1 Some experiments being planned or being started now are indeed looking forward to study high energy physics at energies > 10*6 eV. Two of these promising efforts are worth mention 40 here. One is the Akeno air shower project near Tokyo being implemented by a group whose members belong to various Universities in Japan. The main aim of this project is to study in detail all the components of air showers for primary energies of 10*® -10*® eV. Electron component, shower arrival direction, and shower front curvature would be measured using an EAS array of a large number ( ~ 500) of detectors spread over few square kilometers. The muon component would be sampled for each 2 shower by detectors of nearly 500 m area spread around with muon energy thresholds of 0.5 and 1 GeV. This would enable the muon density to be measured accurately for distances of 50-500 meters from shower axis and would yield an accurate value.of Nj*. ( > 0.5 GeV) and Np. ( > 1.0 GeV) for the shower.. The energy flow in the shower core would also be measured 2 by a large area system of shielded detectors. A 90 m area 8 m .f. p. deep calorimeter using concrete as absorber would measure the energy in the hadron component. For obtaining an accurate estimate of the energy loss in - 286 - the atmosphere which is a good measure of the primary energy/'Cerenkev light produced by the shower particles in the atmosphere would be measured by a complex set of Cerenkov detectors (2m diameter mirrors viewed by 19 photomultipliers each). The Akeno experiment should yield good data IE ifl on high energy physics in the 10 - 10* eV energy region. The other promising project is the Fly's Eye experiment of the group** at University of Utah. The experiment aims to detect and measure the air fluorescence light generated by air shower particles passing through the atmosphere. The detector system will consist of an array of specially fabricated UV sensitive photomultiplier tubes clustered in the focal plane of a large number of 1. 5 meter diameter parabolic mirrors. The mirrors with their photomultiplier arrays, mounted on a geodesic-like structure will be exposed to the night sky on clear moonless nights. This design enables measurements on a shower at different stages of development through the atmosphere. The timing system measures the shower trajectory. The effective selection area of the detector system increases with .increasing energy of the shower ■ since higher energy showers being brighter in terms of air fluorescence can be detected at larger distances. The estimates of Bergeson et al 4 1 on indicate that showers of energy 5 x 10 eV striking as far away as 50 Km from the Fly's Eye system could be detected.' A prototype consisting of 3 mirrors with 12 photomultipliers each was operated by Elbert et 43 in association with the large Volcano Ranch array of John Linsley The results of the measurements with this prototype system have been very encouraging. The complete Fly's Eye system holds great promise for giving new information on high energy physics in 1017 - 10^® eV energy range. Another very interesting and rather large scale experiment 1 being planned for by an International collaboration group 44 is the „ DUMAND (Deep Underwater Muon and Neutrino Detector)Project. Basically the experimental system would consist of a very large array of detectors immersed 5.5 Km under water in Pacific Ocean. In its Gigaton (1 Km3) version the experimental plan envisages a detector array of about 1200 strings, each 630 m eters long with 18 sensors equally spaced vertically. Many experimental and theoretical studies are being conducted to optimise the detection system. One possible system can be optical detection by photomultipliers of Cerenkov light produced by relativistic charged particles'in water. Sonic detectors are also being considered for detection of high energy particles and cas cades though early tests indicate energy threshold for such detectors 15 to be rather high ( > 10 eV). The potential of an experimental system like DUMAND for high energy physics and astrophysics is tremendous. For example, it can yield very valuable information on intermediate - 288 - vector boson and other new particles, neutrino oscillations, muon interactions at very high energies, cosmic ray composition at high energies, neutrino bursts etc. As expected the financial requirements for this experiment are rather large. Therefore it could be some time before the whole system gets assembled and starts giving new and exciting physics. In the discussion above I have attempted to give a flavour of some of the new interesting results that have been obtained in last few years in cosmic ray experiments and of some of the new experiments which may add valuable knowledge and.help in improving our under standing of high energy phenomenon. It is clear that information about 15 high energy processes for energies above 10 eV can be obtained only from experimental studies using cosmic rays since machines of energies 10*** eV are unlikely to be built in next two decades. New and bold ideas about possible experiments at these superhigh energies are being actively discussed by various cosmic ray research groups. - 289 - REFERENCES 1. G.B. YODH, YASH PAL, and J.S. TREFIL, Phys. Rev. Lett. 28 (1972) 1005. 2. T. KANEKO et al. Conference Papers, 12th Int. Conf. Cosmic Rays, Hobart, Australia, 7 (1971) 2759. 3. S.N. GANGULI and A. SUB RAMAN IAN, Conference Papers, 14th k Int. Conf. Cosmic Rays, Miinchen, Germany, 7 (1975) 2235 ; S.N. GANGULI, R. RAGHAVAN, and A. SUB RAMAN IAN, Pram ana 2 (1974 ) 348 ; S.N. GANGULI, Invited Talk, 2nd High Energy Physics Symposium, Santiniketan, India;(1974) 63. 4. T .K . GAISSER, G.B. YODH, V. BARGER and F. HALZEN, Conf. P apers, 14th Int. Conf. Cosmic Rays, Miinchen, Germany, 7 (1975) 2161. 5. 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Cosmic Rays, Munchen, Germany, 9 (1975) 3284. 13. J.R . MACFALL, Ph.D . Thesis, Univ. of Maryland (1976) Unpublished. 14. C. FAB JANS, Private Communication. 15. R .E . STREITMATTER et al, P reprint (1976) Unpublished. 16. J.R. MACFALL et al, Conf. Papers, 15th Int. Conf.Cosmic Rays, Plovdiv, Bulgaria, Late Papers Volume (1977). 17. R.W . ELLSWORTH et al, A str. Sp.Scl., 52, (1977) 415. 18. U. AMALDI et al, Phys. Lett. 66B (1977) 390. 19. J.R. MACFALL et al, Preprint (1978) To be published. 20. G.B. YODH, Invited talk, VUth Int. Colloquium mi Multiparticle Reactions, TUTZING, Germany (1976). 21. V. BARGER, F. HAL ZEN, T .K . GAISSER, C .J. NOBLE and G .B. YODH, Phys. Rev. Lett. 33 (1974) 1051. - 291 22. M. LAPOINTE et al, Can. J. Phys. 46 (1968) S 68 . 23. N.N. KALMYKOV and G.B. KHRISTIANSEN, Conf. P lie r s 14th Int. Conf. Cosmic Rays, Munchen, Germany, 8 (1975) 2861. 24. R.H . VATCHA and B. V. SREEKANTAN, J. Phys. A: M ath., Nucl. Gen., 6 (1973) 1078, ibid, J. Phys. A. M ath., Nucl. Gen. (1973) 1050 ; ibid, J. Phys.A : Math. , Nucl. Gen. 6 (1973) 1067. 25. T.K . GAISSER, R .J. PROTHEROE, K .E. TURVER, and T . J. L. McCOMB, Rev. Mod. P h y s., 50 (1978) 859. 26. V.K. BALASUBRAHMANYAN and J .F . ORMES, A p .J., 186 (1973) 109. 27. J. A. GOODMAN et al, Preprint (1978) To be published ; J.A . GOODMAN, Ph.D. Thesis, Univ. of Maryland (1978) Unpublished. 28. B. S. ACHARYA et al, Conference Papers, 15th Int. Conf. Cosmic Rays, Plovdiv, Bulgaria (1977). 29. V.S. ASEDCIN, G. Ya. GORYACHEVA, S. L NIKOLSKY, and V .I. YAKOVLEV, Conference Papers, 14th Int. Conf. Cosmic Rays, Munchen, Germany, 7 (1975) 2462. 30. M. TAMADA et al, Nuovo Cimento, 41B (1977) 245 ; J.A . CHINELLATO et al-, Preprint (1978). 31. S.C. TONWAR, S. NARANAN and B. V. SREEKANTAN, J. Phys. A. Gen. Phys. JS_(1972) 569. 32. S. C. TONWAR, B. V. SREEKANTAN and R. H. VATCHA, Pram ana, _8_(1977) 50. 33. J.A . GOODMAN et al, P reprint (1978) to be published. - 292 34. S. C. TONWAR, Invited talk on 'Delayed P articles in A ir Showers', Workshop on Charm Production and Lifetimes, Univ. of Delaware, Newark, USA (1978) ; S. C. TONWAR et al, Paper presented at 4th High Energy Physics Symposium, Jaipur (1978). 35. &LR. KRISHNASWAMY et al, Conf. Papers, 15th Int. Conf. Cosmic Rays, Plovdiv, Bulgaria, 6 (1977) 137. 36. M. KAPLON et al, Phys. Rev. 85 (1952) 900. 37. K. NIU et al, Prog. Theor. Phys. 46 (1971) 1644. 38. H. SUGIMOTO et al, Prog. Theor. Phys. 53 (1975) 1541 ; 39. C. RUBBIA, Summary Talk, Topical Conf. on Cosmic Rays and P article Physics above 10 TeV, Univ. of Delaware, Newark, USA (1978). 40. K. KAMATA, Invite ' Talk, Topical Conf. on Cosmic Rays and Particle Physics above 10 TeV, Univ. of Delaware, Newark, USA (1978). 41. H .E. BERGESON, J.C . BOONE, and G. L. CASSIDAY, Conf. Papers, 14th Int. Conf. Cosmic Rays, Munchen, Germany, 8 (1975) 3059 ; G. L. CASSIDAY et al, Conf. P apers, 15th Int. Conf. Cosmic Rays, Plovdiv, Bulgaria, 8 (1977) 270. . 42. J.W, ELBERT et al, Conf. Papers, 15th Int. Conf. Cosmic Rays, Plovdiv, Bulgaria, 8 (1977) 264. 43. J. LINSLEY, Conf. Papers, 15th Int. Conf. Cosmic Rays, Plovdiv, Bulgaria, 8 (1977 ) 206. • ■ x 44. A. ROBERTS, Invited Talk, Topical Conf. on Cosmic Rays and Particle Physics above 10 TeV, Univ. of Delaware, Newark, USA (1978).' 45. S. P . DENISOV e ta l, Phys. Lett. 36B (1971) 528 ; S. P . DENISOV e ta l, Nucl. Phys. B61 (1973) 62. 46. W. BUSZA et al, Phys. Rev. Lett. 34 (1975) 836. - 293 - Captions for the Figures Fig. 1 Variation of q -1*161 with energy deduced by Ganguli p -air Subramanian (1975). Points shown for energies below 10® GeV are based on measurements of unaccompanied charged hadron flux and have been obtained using the primary proton energy spectrum as given by,Ryan et al ( if ) or as given by Akimov et al ( 4 ). Points shown for energies above 10® GeV are obtained from Nj*. -Ne data. Fig; 2 : The experimental arrangement at. Sacramento Ridge Cosmic Ray Laboratory, Sunspot (Siohan et al, 1978). Fig. 3 : - Photograph of spark chamber system used by Yodh and Colleagues showing a typical unaccompanied charged hadron cascade. Fig. 4 Integral energy spectrum for primary protons reported by Akimov et al, with and without correction for back- scattered particles Fig. 5 : Lower bounds to the proton-air inelastic cross-section. Shaded areas reflect statistical uncertainties in experi mental data. Points if are based on composition corrected charged hadron flux. Point $ is based on zenith angle distribution (Nam et al. 1975). Solid curve is the expected variation of cr1” , with energy based w p -air on ISR measurements. Broken curve is a straight line eye fit to the 3 points. Fig. 6 : Variation of q*|f a*r with energy based on measurements of unaccompanied charged hadron flux at Tien-Shah (Nam et al, 1977). Points if are obtained using an extrapolation of primary proton energy spectrum given by Ryan et al (1972). Points ^ are obtained using an extrapolation of primary proton energy spectrum given by Ryan et al (1972). Point if are obtained using the energy spectrum given by Akimov et al (1970). _ . 294 T Fig. 7 Variation of with energy. The ISR measurements PP and the fitted curve are as given by Amaldi et al, (1977). Points ^ are C'pp values by Nam et al (1977) from their measurements of charged hadron flux.. Point $ at 16 TeV is the computed q-T value obtained using the PP zenith angle distribution of hadrons measured by Nam et al (1975). Fig. 8 Variation of with energy (MacFall et al, 1978). For comparison, a c c e p to r datS*Denisov et al4** (1971) and Busza et al 4 (1975) are also shown in the figure. Fig. 9 A comparison of the computed inelastic hadron nuclei cross-section r r using z-rT as m easured at h-A PP ISR energies and Glauber formalism for multiple scattering inside a nucleus (A) with the experimentally measured ^"hA a* var^ous energies. The ratio ^.Theory j ^ -E x p t is close to unity (within about 10%) for energies upto about 104 GeV (Yodh 1976). Fig. 10 Variation of the sensitivity of hadron-nuclei absorption cross-section rr - 31)8 to change in as a function X ~ h-A 6 ° P P of zr- 1 . U PP Fig. 11 Variation of the depth of shower maximum with primary energy. Cbmputed curves using (A = 56) nuclei as primaries are seen to give better agreement with experimental data. Fig. 12 Variation of the number Nj* of muons of energy > 10 GeV per shower with shower size Ne. Computed curves with iron nuclei as primaries seem to give better fit to the experimental data. Fig. 13 Integral energy spectrum of hadrons in air showers. Scaling model calculations do not agree with data. Fig. 14 Lateral distribution of high energy ( > 220 GeV) muons in air showers of size (1-4) x 104. The curves labelled 1 to 5 show the expected lateral distribution for various assumptions about primary composition. 1 I - 295 - Fig. 15a Typical cascade curve observed by Aseikin et al (1975) for single hadrons inTien-Shan lead calorimeter. Fig. 15b : Variation of the absorption length with energy for single hadrons and air shower cores. Fig: 16a - : Schematic illustration of Centauro event I. " Fig. 16b : Schematic illustration of Centauro event IV. Fig. 17 : A diplot of pulse height in terms of equivalent number of particles from a scintillation detector located inside the calorimeter and the arrival time delay of this signal relative to arrival time of shower particles (Goodman ’ e ta l, 1978). i Fig. 18 Schematic drawing of particle detectors located inside the large multiplate cloud chamber operating at Ooty (Tonwar 1978). Fig. 19 Schematic illustration of the new particle event seen by Niu et al (1971). Fig. 20 Schematic illustration of the new particle event seen, by Sugimoto et al (1975). **** 296 - Enar^ <«• GoV FIS - 1 TOO SENSITIVE VOLUME S * C * L COSMIC m v FLUI OETECTO* SCINT 0■ I< 2i S« «I » I FEET FIG. 2 . Integral Proton In te n sity (p a rtic le s/c m 2, sr, sec) sn Ti (pe limit) (upper i, T using it) lim er (low PCI, using Hi spectrum Spectrum after correction correction after Spectrum correction r te f a m ectru p S exps. 1*2-3 proton observed to it F I ! . FIS. 4- FIS. 9 - 297 - nry (GeV) Energy l » I / / I . I J ~ - 29a - 2 6 0 W* E C^»v) FIG. 5 a . eecA. ^ -smiftt ^ - (MaiitflA. uaveg B y * e ta l * ^e d n im , 1 5 ^ - cMbiiraA. u» w ^ A kuwn a t a l l s^ ^ ti s I t to* Enarg^ tew GeV F 1 G .G - 299 - 60 5 S l 6 0 40 So 100 3 0 0 VI GeV F16.7 ° w . vs- Energv 7 0 0 ■ „ ^ 6 0 0 ■ .1 t= x Denisov ▲ Buszo • This Expt 5 00 - 10* 10 Energy (GeV) F IS .8 300 - L l 0 8 *V7 ENEMY, w 6eV f i g .9 <3 F IS . 10, t - 301 - 800 Protons 11) Protons, present ,'e . work, a increasing » 600 ; -t E IGoisser E r 1974) 1 e 400 2 0 0 - FI6.11 Fe. . GG P. KK P.GG p. CM - 302 - 1 *5 IDFB sI Hodron energy (£*)(5eV) F IG .13 » COW MfMU (• m.). FIG. 14- Absorption Length (g/cm2) NO.Of PARTICLES 10 10 1200 1600 800 400 4 5 • 0 0 4 0 0 2 NSLE HADRONS N O R D A H E L S IN S PIS.ISb E (TeV) (TeV) E 0 - 303 - FIS. 154. FIS. DEPTH DEPTH -SlHetEi HADRONS* £ _ ftA S CORE CORE S ftA _ £ 2 . 0 0 6 9/cm •400m - 305 - 1 0 0 .0 0 | *0.00^ 2 8 0 .0 0 ^ ui 1 7 0 .0 0 d 6 0 .0 0 < 50.00 O * 0 .0 0 (£ Mi:::::!?)) 3$ 3 0 .0 0 Z 2 0 .0 0 _- D6LAT FIS. 17 LEAD N CLOUD CHAMBER Fe PLATES 14 g. cm "* each FIG. IB EVENT «B-a 1 f r r n r | i u n n i i i i n m n i imijection. - 307 - DISCUSSION T. Das : Among the various total cross-section data that you have presented, some (like the Echo Lake data) do not seem to extrapolate smoothly to the ISR energies. Do you think this difference is serious ? Or in other words, is anything drastic expected between the accelerator and the cosmic ray energies ? S. C. Tonwar : Inel / The differences seen between the cr data as obtained p -a ir from Echo Lake experiment and the expectation from ISR measurements are mainly due to non-inclusion of the correctum for the composition of the hadron beam. Some systematic effects also are present due to different criteria used by various groups for selecting unaccompanied events. The experimental data corrected for these effects agree well with extrapolation from ISR energies. D.S. Narayan : The scaling violation you reported, I want to know whether the violation takes place in the central region or in the fragmentation region. S. C. Tonwar : The rapid longitudinal development of air showers and also the observed variation of N^. ( > 10 GeV) with shower size Ne have been interpreted as due to scaling violation in central region assuming primaries to be protons. K. V .L . S arm a: i) How direct is the evidence for the absence of charged pitins in the Centauro events ? ii) Could the large angle cascades observed deep underground in the Indo-Japanese Collaboration experiment be some kind of Centauro events initiated by Neutrinos ? - 308 - S.C. Tonwar: i) There is really no direct evidence for the absence of charged pions in the Centauro events. However this absence is indicated by the fact that very few high energy gamma-rays are observed in these events suggesting the absence of neutral pions. ii) Regarding possible similarity of high energy cascades seen by Krishnaswamy et al with Centauro events, may be Dr Ito would like to comment ? N. Ito : The anomalous cascades observed at KGF do not have any penetrating particles among them. Hence it is difficult to understand them as due to Centauro type of events in neutrino interactions. M. V. S. Rao : By Monte Carlo simulation of air shower cores we find that some 'Centauro' events in which considerable number of gamma- rays are observed can be understood as due to fluctuated air shower cores. Thus the fraction of Centauro events is perhaps smaller by a factor of about 2. S.C. Tonwar : It is very interesting to know that Dr Rao and his colleagues have been able to generate two events out of a total of about 140 simulated air shower cores which have great similarity to Centauro event IV. If their interpretation is right, there should be some more particles around the main event with decreasing lateral density away from the core. This can be experimentally checked by Prof. Fujimoto and colleagues. However it may be mentioned that Centauro event IV is really the least striking event as compared to the first three events since for about same total energy the observed number of Y -rays striking the upper emul sion chamber is 51 for event IV compared to 0, 0, and 17 for first three events respectively. Also the observed 5 events are out of a total of 44 high energy events suggesting rather frequent occurrence of this type of phenomenon at very high energies.