arXiv:hep-ph/9908210v1 1 Aug 1999 oe o h omto fCnar n and Centauro of formation the for model A 2 1982). al. et Buja 1994, transi al. whose et cascades, (Arisawa long-living maxima or 1992) al. strongl halo, et of Baradzei form the in observed component penetrating antccmoetadvr high co very and “long-flying component the com magnetic multiplicity, and small relatively events exhibit “Centauro” 1980) Hasegawa the mention produced be we b may Here not region, still rapidity have fragmentation co which projectile energy events unusual highest most the numerous probe detected effectively to accelerator first eprtr aynfe einaon i-aiiy thou mid-rapidity, around dif region with -free temperatures, temperature low informati relatively important at provide state will (DQM) SPS, Matter or AGS produc re the be baryon-dense at to this attained of phenomena, study new The of potential. field baryochemical rich very potentially the ntal ossso ,dqak n los h eyhg ba high very The gluons. and and quarks d Panagiotou u, 1992, of consists initially al. et Panagiotou collision 1994, Gładysz-Dziadu´s nucleus–nucleus ultrarelativistic in produced Introduction: 1 Strangelets. respo of the traversal for the simulations of results present We collisions. 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In the hadronization which follows this leads to the strong suppression of pi- ons and hence of photons, but allows kaons Table 1. Average characteristic quantities of Centauro to be emitted, carrying away strange anti- events and Strangelets produced in Cosmic Rays and quarks, positive charge, entropy and tem- expected at the LHC. perature. This process of strangeness dis- Centauro Cosmic Rays LHC tillation transforms the initial quark matter Interaction “F e + N” P b + P b fireball into a slightly strange quark matter √s & 6.76 TeV 5.5 TeV state. The finite excess of s quarks and their Fireball mass & 180 GeV 500 GeV ∼ stabilizing effects, in addition to the large yproj 11 8.67 ≥ baryon density and binding energy and the γ 104 300 ≥ ≃ very small volume, may prolong the life- ηcent 9.9 5.6 ≃ time of the Centauro fireball, enabling it to ∆ηcent 1 0.8 ≃ reach mountain-top altitudes (Theodoratou & 1.75 GeV 1.75 GeV (*) Panagiotou 1999). In the subsequent decay Life-time 10−9 s 10−9 s (*) and hadronization of this state non-strange Decay prob. 10 % (x 10 km) 1 % (x 1 m) baryons and strangelets will be formed. Strangeness 14≥ 60 -≤ 80 Simulations show that strangelets could be fs (S/A) 0.2 0.30 - 0.45 ≃ identified as the strongly penetrating parti- Z/A 0.4 0.3 ≃ ≃ cles frequently seen accompanying hadron- Event rate & 1% 1000/ALICE-year ≃ rich cosmic ray events (Gładysz-Dziadu´s& “” Cosmic Rays LHC Włodarczyk 1997, Gładysz-Dziadu´s& Pana- Mass 7 -15GeV 10 - 80 GeV giotou 1995). Z ≃ . 0 . 0 In this manner, both the basic characteris- fs 1 1 ≃ ≃ tics of the Centauro events (small multiplic- (*) assumed ities and extreme imbalance of hadronic to photonic content) and the strongly penetrating component are naturally explained. In table 1 we compare characteristics of Centauro and strongly penetrating components (Strangelets), either experimentally observed or calculated within the context of the above model, for cosmic ray interactions and for nucleus–nucleus interactions at the LHC. 3 Design of the CASTOR detector With the above considerations in mind we have designed the CASTOR (Centauro And STrange Ob- ject Research) detector (Angelis et al. 1997) for the ALICE heavy ion experiment at the LHC, in order to study the very forward, baryon-dense phase space region. CASTOR will 10 cover the pseudorapidity interval 5.6 η 7.2 and will 8 probe the maximum of the baryon number≤ ≤ density and en- ergy flow. It will identify any effects connected with these 6 conditions and will complement the physics program pursued by the rest of the ALICE experiment in the baryon-free mid- 4 rapidity region. Figure 1 depicts the net baryon number pseu- dorapidity distribution as predicted by the HIJING Monte- 2 Carlo generator for an average central P b + P b collision at 0 the LHC, with the acceptance of CASTOR superimposed on the plot. -2 The CASTOR calorimeter is azimuthally symmetric around -10 -8 -6 -4 -2 0 2 4 6 8 10 the beam pipe and is shown schematically in figure 2. It com- η Figure 1: Average net baryon number pseu- prises electomagnetic and hadronic sections and is longitudi- dorapidity distribution obtained from 50 cen- tral P b + P b HIJING events.

nally segmented so as to measure the profile of the formation and propagation of cascades. The calorimeter is made of layers of active medium sand- CALORIMETER wiched between tungsten absorber plates. The active medium consists of planes of silica fibres and the signal is the Cherenkov Beam pipe light produced as they are traversed by the Int. Point charged particles in the shower. The fi- bres are inclined at 45 degrees relative to the incoming particles in order to maxi- mize the light output. The calorimeter is H EM azimuthally divided into 8 self-supporting octants. In the current stage of the design Figure 2: Schematic representation of the CASTOR calorimeter. each octant is longitudinally segmented into 80 layers, the first 8 ( 14.7 X0) comprising the electromagnetic ≃ section and the remaining 72 ( 9.47 λI) the hadronic section. The calorimeter will be read out via air light guides made out of stiff plastic,≃ internally painted with UV reflecting paint. The produced Cherenkov photons will propagate along the silica fibres to the lateral surfaces of the calorimeter where they will exit into the light guides. Inside the light guides they will be directed to PM tubes equipped with quartz photocathode entry windows to optimally match the wavelength of the Cherenkov light. It is envisaged to couple together the light output from groups of 4 consecutive active layers into the same light guide, giving a total of 20 readout channels along each octant. 4 Simulation of the CASTOR calorimeter performance We have made detailed GEANT simulations of the response of the CASTOR calorimeter. Figure 3 shows the total number of Cherenkov photons produced, retained and propagated inside the fibres, as a function of the in- cident particle energy for incident photons and hadrons

45000 Nc from one central LHC P b + P b HIJING event. About (a) Incident Photons 210 Cherenkov photons per GeV are obtained for incident 40000 Nc/GeV = 210 photons and 129 Cherenkov photons per GeV for incident 35000 hadrons. The accurate measurement of both the electro- 30000 magnetic and hadronic energy components is a prereq- uisite for an effective Centauro search and the CASTOR 25000 calorimeter is optimized in that respect. 20000 In addition we have simulated the interaction of a 15000 Strangelet with the calorimeter material, using the simpli- 10000 fied picture described in (Angelis et al. 1998, Gładysz- (b) Incident hadrons Dziadu´s& Włodarczyk 1997). As an example figure 4 5000 Nc/GeV = 129 shows the response of the calorimeter to one central LHC 0 0 20 40 60 80 100 120 140 160 180 200 P b + P b HIJING event, to which has been added a E incident [GeV] Strangelet of A =20, E =20 TeV and quark chemical str str Figure 3: Simulation of the total number of potential µ =600 MeV (energy conservation has been str Cherenkov photons produced, retained and propa- taken into account). Figure 4a shows the energy deposi- gated inside the fibres vs. incident particle energy: tion along the octant which contains the Strangelet, while (a) For incident photons, (b) For incident hadrons. figure 4b shows the average of the energy deposition along the remaining seven octants. The study of such simulated events shows that the signal from an octant containing a Strangelet is much larger than the average of the remainder, while its transition curve displays long penetration and many maxima structure such as observed in cosmic ray events. ] ] 50 GeV GeV [ [

40 30 (a) Sector with Strangelet 20 E visible 10 (b) Average of other Sectors 0 2 4 6 8 10 12 14 16 18 20 R.O. Layer Figure 4: Simulation of the energy deposition in the readout layers (couplings of 4 consecutive sampling layers) of the CASTOR calorimeter: (a) In the octant containing the Strangelet, (b) Average of the other octants. 5 Conclusions We have developed a model which explains Centauro production in cosmic rays and makes predictions for P b + P b collisions at the LHC. Our model naturally incorporates the possibility of Strangelet formation and the “long-flying component” frequently seen accompanying hadron-rich cosmic ray events is assimilated to such Strangelets. We have designed a detector well suited to probe the very forward region in P b + P b collisions at the LHC, where very large baryon number density and energy flow occur. CASTOR will identify any effects connected with these conditions, while it has been particularly optimized to search for signatures of Centauro and for long-penetrating objects. We have simulated the passage of Strangelets through the CASTOR calorimeter and we find large energy deposition, long penetration and many-maxima structures similar to those observed in cosmic ray events. Acknowledgements This work has been partly supported by the Hellenic General Secretariat for Research and Technology ΠENE∆ 1361.1674/31-1/95, the Polish State Committee for Scientific Research grants 2P03B 121 12 and SPUB P03/016/97, and the Russian Foundation for Fundamental Research grant 96-02-18306. References Angelis, A.L.S. et al. 1998, INP 1800/PH, Krak´ow 1998. Angelis, A.L.S. et al. 1997, CASTOR draft proposal, Note ALICE/CAS 97–07. Arisawa, T. et al. 1994, Nucl. Phys. B424, 241. Asprouli, M.N., Panagiotou, A.D. & Gładysz-Dziadu´s, E. 1994, Astropart. Phys. 2, 167. Baradzei, L.T. et al. 1992, Nucl. Phys. B370, 365. Buja, Z. et al. 1981, Proc. 17th ICRC, Paris Vol.11 p.104. Gładysz-Dziadu´s, E. & Włodarczyk, Z. 1997, J. Phys. G: Nucl. Part. Phys. 23, 2057. Gładysz-Dziadu´s, E. & Panagiotou, A.D. 1995, Proc. Int. Symp. on Strangeness & Quark Matter, eds. G. Vas- siliadis et al., World Scientific, p.265. Hasegawa, S. & Tamada, M. 1996, Nucl. Phys. B474, 225. Lates, C.M.G., Fugimito, Y. & Hasegawa, S. 1980, Phys. Rep. 65, 151. Panagiotou, A.D. et al. 1989, Z. Phys. A333, 355. Panagiotou, A.D. et al. 1992, Phys. Rev. D45, 3134. Theodoratou, O.P. & Panagiotou, A.D. 1999, 26th ICRC .