Performance of the ALICE CASTOR Calorimeter in the Detection of Exotic Events J

The ALICE Experiment Laboratory PLO300108 153

Performance of the ALICE CASTOR Calorimeter in the Detection of Exotic Events J. Bartke, J. Blocki, E. ladysz-Dziadu, and P. ychowski

The motivation to study the very forward phase space in Pb+Pb collisions at the LHC stems from the potentially very rich field of the new phenomena to be produced in an environment of very high baryochemical potential. The study of this baryon-dense region in the laboratory will provide important information for the understanding of a QGP state at relatively low temperatures, with different properties from the one in the higher temperature baryon-free region around mid-rapidity. A small collaboration of several laboratories has been formed to carry out this study. The CAS- TOR detector for probing the very forward rapidity region in Pb+Pb collisions at the LHC and to complement the CERN heavy ion physics program pursued essentially in the baryon-free midrapidity region has been proposed. The schematic design showing the main components of the CASTOR detector: the silicon multiplicity detector and the deep multilayer calorimeter, can be found in the 1997 and 1998 Annual Reports, and more recent description of the detector in [1 2 The calorimeter will be azimuthally divided into 8 octants and longitudinally segmented into layers, each layer consisting of a tugsten absorber plate followed by a number of quartz fibre planes. It will be 10 i deep and will be placed at - 17 rn from the interaction point to cover the pseudorapidity range .6 < 72 where the baryon density is expected to be large. It will search mainly for exotic events with large imbalance in electromagnetic and hadronic content and for abnormally penetrating objects 3. In order to illustrate the detector's sensitivity to new effects we have done simulations of Centauro- type events by means of our Monte-Carlo event generator CNGEN 4 Fig. shows two-dimensional lego histograms which illustrate the probability of a strangelet production, as a function of a pseudorapidity and energy. The simulated Centauro and strangelet events have characteristics apparently different from those predicted by "classical" (e.g. HIJING) generators 3 5]. The different exotic species were also passed through the deep calorimeter by means of GEANT 321. We simulated transition curves produced in the CASTOR calorimeter by: DCC clusters (both neutral and charged), Centauros, strangelets (both stable and unstable) and so-called mixed events produced by baryons and strangelets being the remnants of the Centauro fireball explosion. To study the sensitivity of the calorimeter to abnormally penetrating objects a neutral network technique was also used 2 In Fig. 2 there are compared transition curves produced by different exotic phenomena. It appears that all these phenomena give different energy deposition patterns and could be distinguished as well as from the background of usual events as one from the other.

1 20O 1. CV 3(0 1.b I

Fig. 1: Probability of a strangelet production as a function of its energy and pseudorapidity for two different sets of initial state parameters. 154 The ALICE Experiment Laboratory

EXOTIC EVENTS (signal background) in comparison with HIJING X10 30000 10000 20000 5000 10000

0 0 0 20 40 60 80 0 20 40 60 80 Neutral DCC, 40 and 20 TeV Charged DCC, 40 and 20 TeV Fig. 2 Simulated signals pro- 20000 15000 - duced by different kinds of ex- 15000 otic events (lines) in compar- 10000 10000 ison with HIJING event his- 5000 5000 tograms). The deposit of en- 0 0 ergy in one sector (hit by 0 20 40 60 80 0 20 40 60 80 the exotic object) vs. layer STRANGELET, 20 TeV STRANGELET, 40 TeV number in the calorimeter is shown. 15000 15000 10000 10000 5000 5000 0 0 0 20 40 60 80 0 20 40 60 80 CENTAURO, 140 TeV STR+CENT, 106+2OTeV

Prototypes of the calorimeter have been constructed and tested with electron and pion beams at CERN. The last CASTOR calorimeter test took place in October 2001. The preliminary results and comparison with the NA52 and HI calorimeters, employing the similar technology are promising.

_(This work was partly supported by Polish State Committee for Scientific Research grant No: 2PO3B 011 18 and SPUB-MICERNIP031DZI199.) References: 1. A.L.S. Angelis et al., Nuovo Cirn. C24 2001) 755; A.L.S. Angelis et al., Nucl. Phys. Proc. Suppl. 97 2001) 227; 2. A.L.S. Angelis et al., 6th Intern. Conf. on Strange Quarks in Matter, Frankfurt, Germany, 2001, to be publ. in J. Phys. C: Nucl. Part. Phys.; 3. E. ladysz-Dziadug, Institute of Nuclear Physics Krak6w, IFJ Report no 1879/PH, www.ifj.edu.pl/reports/2001.html; hep-ph/0111163, submitted to Phys. Part. Nucl.; 4. E. Gladysz-Dziadu et al., Proc. Third Intern.Conf. on Physics and Astrophysics of Quark-Gluon Plasma, Jaipur 1997, eds Bikas C. Sinha et al., Narosa Publishing House, New Delhi, 1998, p. 554; 5. E. ladysz-Dziadu, ALICE Internal Note, ALICE/CAS-2001; A.L.S. Angelis, J. Bartke, E. Gladysz-Dziadu, and Z. Wlodarczyk, EPJdirect C9 2000) 1-18, DOI 10.1007/sIO105OOcOO09.