We present a phenomenological model which describes the formation of a
Centauro fireball in nucleus-nucleus interactions in the upper atmosphere and
at the LHC, and its decay to non-strange baryons and Strangelets. We describe
the CASTOR detector for the ALICE experiment at the LHC. CASTOR will probe, in
an event-by-event mode, the very forward, baryon-rich phase space 5.6 < \eta <
7.2 in 5.5 A TeV central Pb + Pb collisions. We present results of simulations
for the response of the CASTOR calorimeter, and in particular to the traversal
of Strangelets.Comment: 4 pages, 4 figures, to appear in the proceedings of the 26th ICR

Angelis, A. L. S.

Bartke, J.

Bogolyubsky, M. Yu.

Filippov, S. N.

Gladysz-Dziadus, E.

Kharlov, Yu. V.

Kurepin, A. B.

Maevskaya, A. I.

Mavromanolakis, G.

Panagiotou, A. D.

Sadovsky, S. A.

Stefanski, P.

Wlodarczyk, Z.

English

arXiv

Presentation made at the 26th International Cosmic Ray Conference, ICRC'99We present a phenomenological model which describes the formation of a Centauro fireball in nucleus-nucleus interactions in the upper atmosphere and at the LHC, and its decay to non-strange baryons and Strangelets. We describe the CASTOR detector for the ALICE experiment at the LHC. CASTOR will probe, in an event-by-event mode, the very forward, baryon-rich phase space 5.6eta7.2 in 5.5xA TeV central Pb+Pb collisions. We present results of simulations for the response of the CASTOR calorimeter and, in particular, to the transversal of Strangelets.We present a phenomenological model which describes the formation of a Centauro fireball in nucleus-nucleus interactions in the upper atmosphere and at the LHC, and its decay to non-strange baryons and Strangelets. We describe the CASTOR detector for the ALICE experiment at the LHC. CASTOR will probe, in an event-by-event mode, the very forward, baryon-rich phase space 5.6 < \eta < 7.2 in 5.5 A TeV central Pb + Pb collisions. We present results of simulations for the response of the CASTOR calorimeter, and in particular to the traversal of Strangelets

Angelis, A.L.S.

Bogolyubsky, M.Yu.

Filippov, S.N.

Kharlov, Yu.V.

Kurepin, A.B.

Maevskaya, A.I.

Panagiotou, A.D.

Sadovsky, S.A.

CERN Document Server

hep-ph/9908210   1 Aug 1999HE.6.2.02Formation of Centauro and Strangelets in Nucleus–NucleusCollisions at the LHC and their Identification by the ALICEExperiment 1A.L.S. Angelis1, J. Bartke2, M.Yu. Bogolyubsky3, S.N. Filippov4, E. Gładysz-Dziadus´2,Yu.V. Kharlov3, A.B. Kurepin4 , A.I. Maevskaya4, G. Mavromanolakis1, A.D. Panagiotou1,S.A. Sadovsky3, P. Stefanski2 and Z. Włodarczyk51Division of Nuclear and Particle Physics, University of Athens,Greece.2Institute of Nuclear Physics, Cracow, Poland.3Institute for High Energy Physics, Protvino, Russia.4Institute for Nuclear Research, Moscow,Russia.5Institute of Physics, Pedagogical University, Kielce, Poland.AbstractWe present a phenomenological model which describes the formation of a Centauro fireball in nucleus-nucleusinteractions in the upper atmosphere and at the LHC, and its decay to non-strange baryons and Strangelets.We describe the CASTOR detector for the ALICE experiment at the LHC. CASTOR will probe, in an event-by-event mode, the very forward, baryon-rich phase space 5.6    7.2 in 5.5A TeV central Pb + Pbcollisions. We present results of simulations for the response of the CASTOR calorimeter, and in particular tothe traversal of Strangelets.1 Introduction:The physics motivation to study the very forward phase space in nucleus–nucleus collisions stems fromthe potentially very rich field of new phenomena, to be produced in and by an environment with very highbaryochemical potential. The study of this baryon-dense region, much denser than the highest baryon densityattained at the AGS or SPS, will provide important information for the understanding of a Deconfined QuarkMatter (DQM) state at relatively low temperatures, with different properties from those expected in the highertemperature baryon-free region around mid-rapidity, thought to exist in the core of neutron stars.The LHC with an energy equivalent to 1017 eV for a moving proton impinging on one at rest, will be thefirst accelerator to effectively probe the highest energy cosmic ray domain. Cosmic ray experiments havedetected numerous most unusual events which have still not been understood. These events, observed in theprojectile fragmentation rapidity region, may be produced and studied at the LHC in controlled conditions.Here we mention the “Centauro” events and the “long-flying component”. Centauros (Lates, Fugimito &Hasegawa 1980) exhibit relatively small multiplicity, complete absence (or strong suppression) of the electro-magnetic component and very high hpTi. In addition, some hadron-rich events are accompanied by a stronglypenetrating component observed in the form of halo, strongly penetrating clusters (Hasegawa & Tamada 1996,Baradzei et al. 1992) or long-living cascades, whose transition curves exhibit a characteristic form with manymaxima (Arisawa et al. 1994, Buja et al. 1982).2 A model for the formation of Centauro and StrangeletsA model has been developed in which Centauros are considered to originate from the hadronization ofa DQM fireball of very high baryon density (b& 2 fm 3) and baryochemical potential (b>> mn),produced in ultrarelativistic nucleus–nucleus collisions in the upper atmosphere (Asprouli, Panagiotou &Gładysz-Dziadus´ 1994, Panagiotou et al. 1992, Panagiotou et al. 1989). In this model the DQM fireballinitially consists of u, d quarks and gluons. The very high baryochemical potential prohibits the creation of uuand dd quark pairs because of Pauli blocking of u and d quarks and the factor exp ( q=T) for u and d anti-1 To appear in the proceedings of the 26th International Cosmic Ray Conference, 17-25 August 1999, Salt Lake City.Further information at: http://home.cern.ch/angelis/castor/Welcome.htmlquarks, resulting in the fragmentation of gluons into ss pairs predominantly. In the hadronization which followsTable 1. Average characteristic quantities of Centauroevents and Strangelets produced in Cosmic Rays andexpected at the LHC.Centauro Cosmic Rays LHCInteraction “Fe +N” Pb+ Pbps & 6.76 TeV 5.5 TeVFireball mass & 180 GeV  500 GeVyproj 11 8.67  104' 300cent9.9 ' 5.6cent1 ' 0.8< pT> 1.75 GeV 1.75 GeV (*)Life-time 10 9 s 10 9 s (*)Decay prob. 10 % (x  10 km) 1 % (x  1 m)Strangeness 14 60 - 80fs(S/A) ' 0.2 0.30 - 0.45Z/A ' 0.4 ' 0:3Event rate & 1 % ' 1000/ALICE-year“Strangelet” Cosmic Rays LHCMass ' 7 - 15 GeV 10 - 80 GeVZ . 0 . 0fs' 1 ' 1(*) assumedthis leads to the strong suppression of pi-ons and hence of photons, but allows kaonsto be emitted, carrying away strange anti-quarks, positive charge, entropy and tem-perature. This process of strangeness dis-tillation transforms the initial quark matterfireball into a slightly strange quark matterstate. The finite excess of s quarks and theirstabilizing effects, in addition to the largebaryon density and binding energy and thevery small volume, may prolong the life-time of the Centauro fireball, enabling it toreach mountain-top altitudes (Theodoratou &Panagiotou 1999). In the subsequent decayand hadronization of this state non-strangebaryons and strangelets will be formed.Simulations show that strangelets could beidentified as the strongly penetrating parti-cles frequently seen accompanying hadron-rich cosmic ray events (Gładysz-Dziadus´ &Włodarczyk 1997, Gładysz-Dziadus´ & Pana-giotou 1995).In this manner, both the basic characteris-tics of the Centauro events (small multiplic-ities and extreme imbalance of hadronic to photonic content) and the strongly penetrating component arenaturally 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 cosmicray interactions and for nucleus–nucleus interactions at the LHC.3 Design of the CASTOR detectorWith the above considerations in mind we have designed the CASTOR (Centauro And STrange Ob-ject Research) detector (Angelis et al. 1997) for the ALICEheavy ion experiment at the LHC, in order to study the veryforward, baryon-dense phase space region. CASTOR willcover the pseudorapidity interval 5:6    7:2 and willprobe the maximum of the baryon number density and en-ergy flow. It will identify any effects connected with theseconditions and will complement the physics program pursuedby the rest of the ALICE experiment in the baryon-free mid-rapidity region. Figure 1 depicts the net baryon number pseu-dorapidity distribution as predicted by the HIJING Monte-Carlo generator for an average central Pb + Pb collision atthe LHC, with the acceptance of CASTOR superimposed onthe plot.The CASTOR calorimeter is azimuthally symmetric aroundthe beam pipe and is shown schematically in figure 2. It com-prises electomagnetic and hadronic sections and is longitudi--20246810-10 -8 -6 -4 -2 0 2 4 6 8 10ηFigure 1: Average net baryon number pseu-dorapidity distribution obtained from 50 cen-tral Pb+ Pb HIJING events.nally segmented so as to measure the profile of the formation and propagation of cascades. The calorimeteris made of layers of active medium sand-wiched between tungsten absorber plates.The active medium consists of planes ofsilica fibres and the signal is the Cherenkovlight produced as they are traversed by thecharged particles in the shower. The fi-bres are inclined at 45 degrees relative tothe incoming particles in order to maxi-mize the light output. The calorimeter isazimuthally divided into 8 self-supportingoctants. In the current stage of the design  CALORIMETERInt. Point Beam pipeH	EMFigure 2: Schematic representation of the CASTOR calorimeter.each octant is longitudinally segmented into 80 layers, the first 8 (' 14.7 X0) comprising the electromagneticsection and the remaining 72 (' 9.47 I) the hadronic section. The calorimeter will be read out via air lightguides made out of stiff plastic, internally painted with UV reflecting paint. The produced Cherenkov photonswill propagate along the silica fibres to the lateral surfaces of the calorimeter where they will exit into the lightguides. Inside the light guides they will be directed to PM tubes equipped with quartz photocathode entrywindows to optimally match the wavelength of the Cherenkov light. It is envisaged to couple together thelight output from groups of 4 consecutive active layers into the same light guide, giving a total of 20 readoutchannels along each octant.4 Simulation of the CASTOR calorimeter performanceWe have made detailed GEANT simulations of the response of the CASTOR calorimeter. Figure 3 showsthe total number of Cherenkov photons produced, retainedand propagated inside the fibres, as a function of the in-cident particle energy for incident photons and hadronsfrom one central LHC Pb + Pb HIJING event. About210 Cherenkov photons per GeV are obtained for incidentphotons and 129 Cherenkov photons per GeV for incidenthadrons. The accurate measurement of both the electro-magnetic and hadronic energy components is a prereq-uisite for an effective Centauro search and the CASTORcalorimeter is optimized in that respect.In addition we have simulated the interaction of aStrangelet with the calorimeter material, using the simpli-fied picture described in (Angelis et al. 1998, Gładysz-Dziadus´ & Włodarczyk 1997). As an example figure 4shows the response of the calorimeter to one central LHCPb + Pb HIJING event, to which has been added aStrangelet of Astr=20, Estr=20 TeV and quark chemicalpotential str=600 MeV (energy conservation has beentaken into account). Figure 4a shows the energy deposi-tion along the octant which contains the Strangelet, whilefigure 4b shows the average of the energy deposition along0500010000150002000025000300003500040000450000 20 40 60 80 100 120 140 160 180 200 (a) Incident Photons       Nc/GeV = 210 (b) Incident hadrons       Nc/GeV = 129 E incident [GeV] NcFigure 3: Simulation of the total number ofCherenkov photons produced, retained and propa-gated inside the fibres vs. incident particle energy:(a) For incident photons, (b) For incident hadrons.the remaining seven octants.The study of such simulated events shows that the signal from an octant containing a Strangelet is muchlarger than the average of the remainder, while its transition curve displays long penetration and many maximastructure such as observed in cosmic ray events.010203040502 4 6 8 10 12 14 16 18 20 R.O. Layer [GeV] E visible [GeV] (a) Sector with Strangelet (b) Average of    other SectorsFigure 4: Simulation of the energy deposition in the readout layers (couplings of 4 consecutive samplinglayers) of the CASTOR calorimeter: (a) In the octant containing the Strangelet, (b) Average of the otheroctants.5 ConclusionsWe have developed a model which explains Centauro production in cosmic rays and makes predictionsfor Pb + Pb collisions at the LHC. Our model naturally incorporates the possibility of Strangelet formationand the “long-flying component” frequently seen accompanying hadron-rich cosmic ray events is assimilatedto such Strangelets. We have designed a detector well suited to probe the very forward region in Pb + Pbcollisions at the LHC, where very large baryon number density and energy flow occur. CASTOR will identifyany effects connected with these conditions, while it has been particularly optimized to search for signatures ofCentauro and for long-penetrating objects. We have simulated the passage of Strangelets through the CASTORcalorimeter and we find large energy deposition, long penetration and many-maxima structures similar to thoseobserved in cosmic ray events.AcknowledgementsThis work has been partly supported by the Hellenic General Secretariat for Research and TechnologyENE 1361.1674/31-1/95, the Polish State Committee for Scientific Research grants 2P03B 121 12 andSPUB P03/016/97, and the Russian Foundation for Fundamental Research grant 96-02-18306.ReferencesAngelis, A.L.S. et al. 1998, INP 1800/PH, Krako´w 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-Dziadus´, 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-Dziadus´, E. & Włodarczyk, Z. 1997, J. Phys. G: Nucl. Part. Phys. 23, 2057.Gładysz-Dziadus´, 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 .

Formation of Centauro and Strangelets in Nucleus-Nucleus Collisions at the LHC and their Identification by the ALICE Experiment

Formation of Centauro and Strangelets in Nucleus-Nucleus Collisions at
  the LHC and their Identification by the ALICE Experiment

Formation of Centauro and Strangelets in Nucleus-Nucleus Collisions at the LHC and their Identification by the ALICE Experiment

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