N Institute of Nuclear Physics Krakow, Poland

PL9902702 The Henryk NiewoaniczansKi H n Institute of Nuclear Physics Krakow, Poland

Report N0.I8OO/PH

THE ENERGY DEPOSITION PATTERN AS THE UNCONVENTIONAL STRANGELET SIGNATURE AND ITS RELEVANCE TO THE CASTOR CALORIMETER

A.L.S. Angelis1, J.Bartke2, E.Gladysz-Dziadus2 and Z.Wlodarczyk3

Address: Main site: High Energy Department: ul. Radzikowskiego 152, ul. Kawiory 26 A, 31-342 Krak6w, Poland 30-055 Krakow, Poland e-mail: [email protected] e-mail: [email protected] 30- 50 Report N0.I8OO/PH

THE ENERGY DEPOSITION PATTERN AS THE UNCONVENTIONAL STRANGELET SIGNATURE AND ITS RELEVANCE TO THE CASTOR CALORIMETER

A.L.S. Angelis1, J.Bartke2, E.Gladysz-Dziadus2 and Z.Wlodarczyk3

'•University of Athens, Athens, Hellas

l'Institute of Nuclear Physics, Cracow, Poland

^Institute of Physics, Pedagogical University, Kielce, Pola.nd

July 1998 PRINTED AT THE HENRYK NIEWODNICZANSKI INSTITUTE OF NUCLEAR PHYSICS KRAK6W, UL. RADZIKOWSKIEGO 152

Xerocopy: INP Krakow copies. Abstract

It has been shown, by GEANT simulations, that the energy deposition pattern in deep calorimeters could be the spectacular and unconventional signature of different kinds of stable and unstable strangelets. The CASTOR calorimeter is shown to be the appropriate tool for detection of strongly penetrating objects, such as strangelets possibly produced in the baryon-rich region in central Pb-Pb collisions at LHC energies.

1 Introduction.

The possible way to produce a quark-gluon plasma in the laboratory is by collisions of heavy ions at ultrarelativistic energies. New forms of matter might be formed during the phase transition from hadronic matter to a deconfined plasma. The properties of some forms of hypothetical strange matter, as small lumps of strange quark matter (strangelets) or hyperon matter (metastable exotic multihy- pernuclear objects (MEMO'S)) have been recently discussed by many authors (see for example [1, 2]), with special emphasis on their relevance to the present and future heavy ion experiments. In nucleus-nucleus collisions, many kinds of strangelets might be produced with different quark contents. Calculations, based on QCD and the phenomenological bag model, [1, 2] (up to the baryonic number A = 40), suggest that strange quark matter may be metastable or even completely stable for a wide range of bag model parameter values {Bl/A ~ 150 - 170 MeV). Generally, for higher bag parameter values there are less long-lived strangelet candidates and they are shifted towards higher values of baryon number A, strangeness factor fs (fs = S/A) and towards higher negative charges. But even low mass objects can be sometimes stable against strong and weak hadronic decays because of shell effects. They are called "magic strangelets". Short - lived candidates can decay completely via strong processes, within the timescales typical for them (~ 10~20 —10~24 sec), into a mixture of nucleons and hy- perons. In addition a fission of a strangelet into another strangelet and an arbitrary number of hadrons can be expected. It might well be that single hadron decay is not possible while multiple hadron decay is due to shell effects. The cascade of strong decays shifts the strangelet to higher strangeness (/s ~ 1.4) where it can be subject to weak nucleon decays. Strangelets surviving strong and weak nucleon decays could reach a very high strangeness fraction (fs > 2.2) and fall into a valley of stability, where only the weak leptonic decays will be possible. Therefore a relatively long 4 lifetime can be expected (r0 ~ 10~ sec). There are a lot of present and future accelerator experiments [3, 4] looking for the strange quark matter. They are mostly, however, focussed on long-lived (r0 > 10 - 100 ns) candidates with a small charge and/or a high mass. The results are, so far, negative (except for one candidate found by the NA52 CERN experiment [4]).

1 On the other hand, in the cosmic ray mountain experiments appears a wide spectrum of exotic events [5, 6] which can hardly be explained in terms of standard ideas. In the past several years many interesting explanations for some of these anomalies have been proposed. Among them the model [7, 8], based on the hypothesis of the phase transition from nuclear to quark matter, in interactions induced by nuclear primaries, successfully explains most features of the Centauro events and predicts also the possible formation of strangelets in the hadron-rich events. Moreover, the simulations of the passage of strangelets through the typical thick lead chambers, used in the mountain experiments at Mt. Chacaltaya and the Pamirs, show [9] that in addition to unstable, metastable and stable strangelets could also produce in the chambers the long many-maxima transition curves resembling the observed long-lived cascades [6]. Thus the numerous hadron-rich families accompa- nied by highly penetrating cascades, clusters or halo could be explained by assuming the same mechanism of the formation of a strange quark matter fireball and its subsequent decay into predominantly baryons and strangelet(s). These results [8] suggest also a new and unconventional signature of the strangelet. Strangelets could be detected by their energy deposition pattern in a system of deep calorimeters. This idea seems to be very promising, as it gives the possibility to detect both unstable (short-lived) and stable (long-lived) strangelets independently of the strangelet charge. The purpose of this work is to investigate the ability of the CASTOR calorimeter, proposed as a subsystem of the ALICE experiment, to detect strangelets.

2 Strangelets in the CASTOR calorimeter

Predictions concerning the possibility of production and detection of Centauros and strangelets at LHC energies (\/sNN = 6.3 TeV) have been given in [8, 10]. In central Pb+Pb collisions the formation of the baryon rich region is predicted to be between 4 and 8 units of rapidity, which is the crucial condition for the formation of such objects. Production of a variety of strangelets, characterized by a wide spectrum of the baryonic number (Astr ~ 11-68, when assuming the temperature T ^ 130-190 MeV and quarkchemical potential /i S 600-1000 MeV) should be possible. The new detector system called CASTOR, as an addition to the ALICE detector in the very forward rapidity region (5.6 < v < 7.2) has been proposed [11] with the purpose of identifying such exotic events. The CASTOR is designed to measure the hadronic and photonic multiplicities by means of the charged particles and photon multiplicity detectors and hadronic and photonic energy contents of an interaction by means of the calorimeter. Besides that the deep calorimeter will be able to detect the strongly penetrating particles. The calorimeter will be located at a distance of 1740 cm from the interaction point. It consists of electromagnetic and hadronic sections, of a total thickness of 760 mm of a tungsten absorber (what corresponds to 1075 mm of effective thickness), segmented every 10 mm in the hadronic and every 5 mm in the electromagnetic part. The proposed calorimeter will be made of annular absorber discs, subdivided into octants, alternated with planes of active medium, which will be quartz fibres, to make use of the Cherenkov light produced by the traversing particles. A quartz fibre calorimeter with 45° orientation with respect to the entering particle maximizes the light production and works as a "shower core" detector, sampling mostly the hadronic part of the shower which lies effectively within a cone of ±10° in the direction of the particle. Thus, the energy of a hadronic shower can be reliably measured very close to the calorimeter's edge. The transverse profile of the hadron shower is about of ~ 7 mm wide (at 200 GeV). Continuing and extending our work [9] we have simulated, by GEANT, the passage of stable and unstable strangelets through the calorimeter. We have looked at the intensity, shape and longitudinal extension of the produced transition curves and their dependence on the strangelet parameters. The main purpose of the simulations was to determine what kind of strangelets can give transition curves apparently different from a hadronic shower caused by "normal" particles. The detection conditions offered by such calorimeters differ, however, from the deep emulsion chambers used in the cosmic ray experiments. The latter have very fine lateral resolution ( ~ lOOfim), allowing for the observation of the development of individual cascades through the whole calorimeter depth. In contrast, in the CASTOR calorimeter, the signal produced by a strangelet will be detected simulta- neously with that of other particles entering the same calorimeter octant. Thus, the additional question is intensity and shape of the possible background and ability to separate a strangelet signal from it. The question is of course connected with the background origin. If strangelets are produced as the remnants of the Centauro fireball explosion, according to the mechanism proposed in [8], then the expected background will be produced by nucleons coming from the isotropic decay of the Centauro fireball. This case has been preliminarily investigated in [8] and it has been shown that the proposed azimuthal segmentation of the calorimeter should give the acceptable signal-to-noise ratio. In this work we have investigated the scenario, in which strangelets are born among other conventionally produced particles. We have compared a strangelet signal with the background estimated by means of the HIJING generator.

2.1 Short-lived strangelets We call short-lived strangelets the unstable objects which can decay via strong 20 interactions (r0 < 10~ sec) or the metastable ones decaying via weak nucleonic. decays.1 The complete decay of a strangelet via strong processes or its fission into a daughter strangelet and arbitrary number of hadrons is possible. A daughter strangelet will be shifted to a higher strangeness factor /s. After surviving a strong and possibly also weak nucleonic decay it can reach the region of a very high strangeness factor (/s > 2.2) where it is expected to become a long-lived (stable) object. In our calculations we have assumed, for simplicity, that a strangelet decays only via neutron emission. We have neglected other less probable processes (as strong pion 2, proton or hyperon emission). It is important to note, that the shape of the resulting transition curves depends only very weakly on the nature of the evaporated particles. Both nucleon and hyperon bundles passing the calorimeter will give similar long-range cascades. Unstable strangelets decay very fast, practically at the point of their formation, thus the considered picture resolves into a simple case of a bundle of neutrons entering the calorimeter. Assuming additionally that all hadrons are evaporated with very similar momenta we get a bundle of very strongly collimated neutrons. This assumption seems to be justified, as we should expect rather small transverse momenta connected with the evaporation process. It is also experimentally supported by the small lateral spread of the cosmic-ray mini-clusters. It has been shown [9] that the scenario in which an unstable or metastable .strangelet, via strong or weak decays, produces the strongly collimated bundle of neutrons successfully describes the long-range many maxima cascades observed in the cosmic ray experiments. The successive maxima, seen in the structure of a transition curve could be the result of interactions of such neutrons in the apparatus. Here we have investigated the signals which could be produced by the short- lived "LHC" strangelets in the CASTOR calorimeter. The general conclusion is similar as in the study of the cosmic-ray strangelets. Bundles of collimated neutrons can give in the CASTOR calorimeter the unconventional many-maxima signal. Its longitudinal structure and extent depend, of course, on the strangelet energy and the number of evaporated neutrons Nn. Fig.l shows three examples of transition curves produced by bundles of 7 and 12 neutrons of energy En « 1.2 TeV and 20 neutrons of energy En m 1 TeV, evaporated by a short-lived strangelet with baryonk number Astr = 40. They are compared with the possible background (full line histogram), estimated by HIJING, assuming that the rest of the accessible energy (not consumed by a strangelet) is going into "normal" particle production. We use in this and also in subsequent figures both linear and semilog vertical scale. In the figures with the semilog scale the vertical axis starts at about 1000. It allows to show in the apparent

1 The lifetimes of metastable strangelets decaying via weak nonleptonic decays is still the matter of debate. If their lifetimes are shorter than ~ 10~10 sec they could decay before reaching the CASTOR calorimeter. 2In the very high baryochemical potential environment, where our strangelets are formed, the creation of uu and dd pairs is suppressed. way the significance of the strangelet signal in the very deep part of the calorimeter where the normal hadronic signal is negligible. We see that a bundle of several neutrons (Nn > 7) possessing sufficiently high energies (En > 1 TeV) produces in the calorimeter the signal which can be distin- guished from the "normal" event signal. The strangelet signal is higher, has longer longitudinal extent and reveals a many-maxima structure in contrast to the rather smooth background.

2.2 Long-lived strangelets We call long-lived strangelets the "stable" objects capable to reach and pass 8 through the apparatus without decay (r0 > 10~ sec in the case of the CASTOR calorimeter). The weak radiative decays (u+d <-> s+u+7) and weak leptonic decays (d <-> u + e~ + Ve, s «-> u + e~ + ve) are expected to be slower than weak neutron emission. In [1] it has been estimated that hyperstrange multiquark droplets, having the strangeness to baryon ratio /s = 2.2 - 2.6 can be the subject of only the weak leptonic decays and their lifetime is estimated to be longer than T$ ~ 10~4 sec. If a strangelet is stable against these decays also, then it can only decay by higher order weak decay (AS ±2), which results in lifetimes of days (super long lived strangelet) [2]- We have assumed that "stable" strangelets, passing without decay through the apparatus, can interact with the apparatus material. We have used the simplified picture [9] of their possible interaction in the calorimeter obsorber. The strangelet is considered as an object with the radius

R = where the rescaled radius is

and n and m are the chemical potential and the mass of the strange quark respectively and ac is the QCD coupling constant. The mean interaction path of strangelets in the tungsten absorber is

Aw • mN

Penetrating through the calorimeter a strangelet collides with tungsten nuclei. In each act of collision the "spectator" part of a strangelet survives (a strangelet is more strongly bound than a normal nucleus) continuing its passage through the calorimeter and the "wounded" part is destroyed. Particles, generated at the consecutive; collision points, interact with tungsten nuclei in the "normal" way, resulting in the electromagnetic - nuclear cascade which develops in the calorimeter matter. We have simulated the penetration of stable strangelets through the calorimeter, assuming ac = 0.3 and several different sets of the initial strangelet parameters: • quark chemical potential values: n = 600, 1000 MeV (/z= 600 MeV is the value estimated for cosmic-ray Centauros)

• strangelet baryonic numbers: Astr = 15, 20, 40

• total strangelet energy: Estr « 8 - 40 TeV (or 400 - 1000 GeV/n) The total energy of particles entering the CASTOR calorimeter (and generated by HIJING) J2E"lJ2? «150 TeV. Thus, the assumed values of strangelet energy mean that a strangelet takes ~ (5 - 30)% of the total energy accessible within the CASTOR acceptance. It is a reasonable value, as it is consistent with the cosmic ray data [6], where the strongly penetrating cascades carry a similar fraction of the visible energy of the events. Examples of transition curves produced in the CASTOR calorimeter, by different stable strangelets, are presented in Figs. 2-6. The curves are limited to one calorimeter octant containing a strangelet. The strangelet cascade profiles are compared with those of the "normal" background, produced by particles generated by HIJING (full line histogram), after the subtraction of the energy carried by the strangelet. The results are qualitatively consistent with our earlier simulations [9] and we can conclude that: 1. Stable strangelets can produce in the calorimeter long range many- maxima cascades.

2. The strangelet signal is manifestly different from that produced by background from a "normal" event, as it is: • higher • slower attenuated • further longitudinally extended (some strangelets give a strong signal even at the very end of the calorimeter, i.e. after penetration of more than 80 cm of a tungsten absorber (60 - 80 calorimeter layers), where the signal from a "normal" event is practically negligible) • has different shape (reveals many-maxima structure in contrast to the smooth background)

3. Penetrating power of the signal increases with the value of: • quarkchemical potential n

• strangelet baryonic number AstT

6 • strangelet energy (sometimes even low energy strangelets with EstT ~ 400 - 500 GeV/n reveal a strongly penetrating power and produce, very deeply in the calorimeter, a much higher signal than that predicted by HIJING, see Fig.6)

4. Longitudinal structure depends mainly on the strangelet baryonic number Astr (many maxima structure is more pronounced for smaller Astr)-

2.3 The CASTOR calorimeter sensitivity to strangelets. As it has been shown in the previous subsections, the CASTOR calorimeter is an appropriate tool for strangelet detection, independently of the strangelet lifetime. • Stable strangelets are expected to produce the spectacular long range signals.

• Transition curves generated by unstable strangelets have shorter longitudinal extent than those obtained for stable strangelets but in this case also the strangelet signal differs essentially from the one generated by "normal" events. If 7 - 20 strangelet decay products carry an amount of energy greater than ~ 10 - 20 TeV, the strangelet signal should be easily separated from the background of accompanying "normal" particle production.

• The calorimeter will be able also to detect the possible strangelet evolution when the strong nucleon emission process transforms a short-lived strangelet into a stable object. Fig. 7 shows the transition curve of a short-lived strangelet (Astr = 23, EstT = 23 TeV) which after evaporation of 7 neutrons, in the strong decay process, becomes a long-lived object.

The probability of strangelet detection in the calorimeter depends both on the strangelet and calorimeter parameters. Generally, such factors as a long depth, small sampling along the length and fine granularity (division into radial as well azimuthal sectors) improve the sensitivity to strangelet detection. Assuming the previously described picture of strangelet decay and interaction we expect that the proposed calorimeter will be sensitive to the detection of strangelets for a wide spectrum of their parameters. As it is seen from Figs. 2-6, the stable strangelets with total energy Estr > 10 TeV, or energy per baryonic number Estr > 500 GeV/n and baryonic number Astr > 15 can be easily identified. Sometimes even lower energy strangelets, because of favourable fluctuations, can produce very deep in the calorimeter a characteristic signal allowing their identification (Fig.6). The results presented here have been obtained assuming that a strangelet enters the calorimeter at the centre of the octant. In this case leakage of the strangelet signal to neighbouring azimuthal sectors is negligible. We have also checked less favourable situations, when strangelets enter the calorimeter close to the sector edge or the border between two sectors. As it should be expected for a calorimeter where the transverse spread of cascades is reduced to about 7 mm, the most significant part of the energy is detected in the sector hit by the strangelet and only a small part of it leaks to other sectors. This effect is illustrated in Fig.8. There are compared simulated signals produced by stable strangelets (Astr = 15, Estr = 15 TeV) in the first (full curve), second (dashed curve) and third (dotted curve) sectors. It was assumed that the strangelet enters the first sector, at a point at distance d from the second one (d = 15, 6, 2, 0.7 mm). We see that even strangelets hitting the calorimeter very close to the border between two sectors produce a very strong signal in the main "strangelet" sector. For d > 3 mm more than 70% of the total energy deposited in the calorimeter is detected in the "strangelet" sector and at the distance d = 2 mm the total energy deposited in the first octant is more than twice deposited in the neighbouring sector. Thus the "edge" effect can not change the calorimeter sensitivity in an apprecia- ble way. It can disturb only the detection of the lowest energy strangelets (Estr ~ 10 TeV) hitting the calorimeter very close to a sector edge or a two-sector border (d < 2 mm). This question could concern about 10% of all low energy strangelets. In order to identify any unusually penetrating component we should observe the development, intensity (energy content) and propagation of hadronic cascades as a function of calorimeter depth. To meet this requirement, the calorimeter must be sampled along its length, with appropriate sampling steps. The simulations presented here have been done for the sampling and reading planes placed every 5 mm (~ 1.94X0 of effective thickness) in the electromagnetic part and every 10 mm (~ 3.88Xo of effective thickness) in the hadronic part of the calorimeter. Such sampling is similar to that in the cosmic ray emulsion chambers where the many- maxima long range cascades have been observed. As it has been shown in the previous subsections, such sampling seems to be also suitable for observation of the many-maxima character of the transition curves produced by "LHC" strangelets. We have checked how a many-maxima structure changes with the increase of the sampling thickness. Fig.9 shows transition curves produced by a typical stable strangelet (AHr = 20, Estr = 20 TeV, /i = 600 MeV). Fig. 9a shows the signals produced by the strangelet and HIJING background, separately. Figs. 9b and 9c show the summed signal in the "strangelet" sector in comparison with the average of the other sectors. Fig. 9a and 9b show transition curves obtained with the sampling and reading step described above. Fig. 9c is the same picture obtained for readings done every 4 layers (i.e. every ~ I6X0). As it should be expected, by decreasing the number of reading steps the strangelet signal becomes smoother. The many-maxima structure becomes rather a wave-like structure but it is still visibly different from the still smoother background.

3 Summary

The analysis of the super high energy cosmic ray exotic events has suggested the new unconventional strangelet signature [9] - the transition curve pattern. This idea has been adapted to the LHC conditions. Simulations of the passage of strangelets through the CASTOR calorimeter have been done for different kinds of strangelets, characterized by:

• baryonic number Astr = 15-40 • quarkchemical potential \x — 600-1000 MeV

• energy per baryonic number Estr — 400-1200 GeV/n It has been shown that the CASTOR calorimeter will be sensitive to both stable and unstable strangelets for a wide range of their parameters. This is very important in the context of the current experiments which are mostly sensitive only to long-lived objects. Acknowledgment s This work was partly supported by Polish State Committee for Scientific Re- search grant No. 2P03B 121 12 and SPUB P03/016/97. References

[1] S.A. Chin and A.K. Kerman, Phys.Rev.Lett. 43(1979)1292.

[2] J. Schaffner-Bielich et al., Phys.Rev. C55(1997)3038.

[3] E864 Collaboration, K.N.Barish et al., J.Phys.G: Nucl.Part. Phys. 23(1997)2127; E814 Collaboration, J. Barrette et al., Phys.Lett. B252(1990)550; E858 Collaboration, A. Aoki et al., Phys.Rev.Lett. 69(1992)2345; E878 Collaboration, D. Beavis et al., Phys.Rev.Lett. 75(1995)3078.

[4] NA52 (NEWMASS)Collaboration, G.Ambrosini et al., J.Phys.G: Nucl. Part.Phys. 23(1997)2135; E886 Collaboration, A. Rusek et al., Phys.Rev. C54,R15(1996).

[5] C.M.G. Lattes, Y. Fujimato and S. Hasegawa, Phys.Rep. 65(1980)151; L.T. Baradzei et al., Nucl.Phys. B370(1992)365.

[6] Z. Buja et al., 17th ICRC (Paris 1981) Vol.ll,p.l04; T. Arisawa et al., Nucl.Phys. B424(1994)241.

[7] A.D. Panagiotou et al., Phys.Rev. D45(1992)3134.

[8] M.N. Asprouli, A.D. Panagiotou and E. Giadysz-Dziadus, Astroparticle Phys. 2(1994)167; E. Giadysz-Dziadus and A.D. Panagiotou, Intern.Symp. on Strangeness and Quark Matter, Krete (1994), World Scientific, ed's G. Vassiliadis et al., p.265. [9] E. Giadysz-Dziadus and Z. Wlodarczyk, ALICE/97-17, Internal Note/CAS, 1997; E. Giadysz-Dziadus and Z. Wlodarczyk, J.Phys.G: Nucl.Part.Phys. 23 (1997)2057.

[10] E. Giadysz-Dziadus and A.D. Panagiotou, Internal Note ALICE/PHYS 97-16; E. Giadysz-Dziadus et al., Third Intern.Conf. on Physics and Astrophysics of Quark-Gluon Plasma, Jaipur 1997, ed. Bikas C. Sinha et al., to be publ.; E. Giadysz-Dziadus et al., ALICE/97-06, Internal Note/PHY.

[11] A. Angelis et al., ALICE/97-07, Internal Note/CAS.

10 Figure captions:

Fig.l. Transition curves produced by bundles of 7 (dot-dash curve) and 10 (dotted curve) neutrons of energy En « 1.2 TeV and 20 (dashed curve) neutrons of energy En « 1 Tev evaporated by a short-lived strangelet. Full line histogram shows the HIJING estimated background (assuming Astr = 40).

Fig.2. Transition curves of stable strangelets with energy Estr = 40 TeV, baryon number Astr = 40, quark chemical potential /i = 600 MeV (dashed curve) and // = 1000 MeV (dotted curve). Full line histograms in Figs. 2-7 show the HIJING estimated background.

Fig.3. Transition curves of stable strangelets with Estr = 20 TeV, Astr = 20, fj, = 600 MeV (dashed and dotted curves) and fj, = 1000 MeV (dash-dot curve).

Fig.4. Transition curves of stable strangelets with Estr = 14-15 TeV. Dashed curve: AstT = 20, Estr « 700 GeV/n, /i = 600 MeV; Dotted: Astr = 20, Estr « 700 GeV/n, n = 1000 MeV; Dash-dot: Asir = 15, Estr » 1000 GeV/n, \i = 600 MeV;

Fig.5. Transition curves of stable strangelets with Estr « 10 TeV. Dashed curve: Astr = 20, Estr « 500 GeV/n, /i = 600 MeV; Dotted curve: i4str = 20, Estr as 500 GeV/n, // = 1000 MeV; Dash-dot curve: AstT = 15, Estr « 700 GeV/n, // = 600 MeV.

Fig.6. Transition curves of stable strangelets with Estr « 8 TeV. Dashed curve: Astr = 20, Estr « 400 GeV/n, /* = 1000 MeV; Dotted curve: Astr = 15, £str « 500 GeV/n, /u = 600 MeV;

Fig.7. Unstable strangelet (Astr = 22, Estr & 22 TeV) transformed into the stable one, after evaporation of 7 neutrons. Fig.8. Signals produced in three neighbouring calorimeter octants by stable strangelets (Astr = 15, Estr = 15 TeV), hitting the first octant at the points d = 15, 6, 2, 0.7 mm far from the second octant border. Signals in the first, second and third octants are marked by full, dashed and dotted curves respectively.

Fig.9. a) Transition curves produced by the stable strangelet (Astr = 20, Estr = 20 TeV, n = 600 MeV) and HIJING separately; b) Summed signal in the "strangelet" sector in comparison with the average of other sectors assuming readings every layer, i.e. every 5 mm in electromagnetic and 10 mm in hadronic sectors; c) readings every 4 layers.

11 Bundles of 7n, 1 2n (E= 1.2 TeV/n) and 20n (E= 1 TeV/n)

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17 Unstable strangelet tronsformed into the stable one (E = 22 TeV)

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Figure 9: