Multiparticle Production at High Multiplicities
aa r X i v : . [ h e p - ph ] J u l MULTIPARTICLE PRODUCTION AT HIGH MULTIPLICITIES
E.S. Kokoulina , † , A.Y. Kutov , : for SVD-2 Collaboration LPS, GSTU, Belarus , LPP, JINR, Russia DM UrD,RAS,Russia † E-mail: [email protected]
Abstract
Theoretical and experimental studies of high multiplicity events are analyzed.Some interesting phenomena can be revealed at high multiplicities. Preliminaryresults of project
Thermalization are reported.
The multiparticle production (MP) study at high energies is one of the actual topicsof high energy physics. The different theoretical approaches and the experimentalprograms are developed. The Quark-Gluon Matter search is the complicated prob-lem of hadron and nucleus interactions [1]. We consider that our MP study at lowerenergies may be useful. The purpose of the ”
Thermalization ” experiment [2] is toinvestigate the collective behavior of MP particles in proton and proton-nucleusinteractions p + p ( A ) → n π π + 2 N (1)at the proton energy E lab = 70 GeV. We use modernized setup SVD-2 - Spectrom-eter with Vertex Detector (SVD). It was created to study of production and decayof charm particles, but had the basic components necessary for performance of thephysical program of the Thermalization project.At present multiplicity distributions (MD) at this energy is measured up to thenumber of charged particles n ch = 18 ([3]-[4]). In the region of high multiplicity(HM) n ch >
20 we expect [5]: formation of high density thermalized hadronic sys-tem, transition to pion condensate or cold QGP, increase of partial cross section σ ( n ) is expected in comparison with commonly accepted extrapolation, enhancedrate of direct soft photons. We will be continue to search for new phenomena: Bose-Einstein condensate (BEC), events with ring topology (Cherenkov gluon radiation).The available MP models and MC codes (PYTHIA) are distinguished consider-ably at the HM region. We also research hadronization mechanism and connectedquestions [6].The review is organized as follows: section 2 presents a description of setupSVD-2, section 3 gives alignment results, section 4 informs about of new phenomenasearching and our preliminary data of 2002 run. We summarize in section 5. The layout of the SVD installation at U −
70 accelerator is shown on Figure 1. Thebasic requirements to the equipment consisted in the following: The study is carried out on the extracted beam of protons with energy 70 GeVand intensity ∼ in a cycle of the accelerator. ∗ The liquid hydrogen target is used. ∗ Installation is capable to detect of events with HM of charged particles and γ quanta. Multiplicity of photons makes up to ≤ ∗ The HM trigger system is capable to select rare events with multiplicity n π =20 ÷
30. The suppression factor of events with low multiplicity n π <
20 is 10 . ∗ The magnetic spectrometer has the momentum resolution δp/p ≈ .
5% in theinterval p = 0 . ÷ . Figure 1: Schematic of the SVD installation at U-70.
For a target accommodation in the design of installation there is a space along abeam only 7 cm. Design and manufacture of liquid hydrogen target is under a acomplete JINR responsibility. The target has 7 cm thick and 3.5 cm in diametervassal of liquid hydrogen. Thermostat is equipped with a thin (200 µm ) lavsanwindows to suppress background scattering. Successful tests of a whole target sys-tem had indicated to advanced reduction of helium consumption in which resultingfactor is expected in order of 1.5. Straw tube chamber system is a new addition of SVD setup. This detector hasbeen designed in the department of V. Peshehonov from LPP of JINR . It imple-ments front end boards with preamplifiers produced in Minsk (NC PHEP BSU) andTDC modules produced in Protvino (IHEP) allowing to detect several pulses, con-sequently coming from the anode on each trigger signal. Typical plane dimensionis 70 x 70 cm . The total of channels is about 2400. .4 HM trigger Our experiment owes to carry out at suppression of low multiplicity events by atrigger. It is urgent request for it. For this purpose the scintillation hodoscope orHM trigger was designed and manufactured. It suppresses interactions with trackmultiplicity below 20. Beyond this it is as so thin as not distorts an angular andmomentum resolution of the setup to any kind fake signal. The scintillator counterarray may operate at higher counting rate and more resistant to many kinds ofnoise.
The vertex detector (VD) is necessary constituent of SVD setup because it allowsto vertex position identify. Vertex front-end uses a integrated circuit called GAS-SIPLEX. As the GASSIPLEX is 16-channel design, only 1280 channels of detectormay be placed on one board. For 50 µm pitch detector the largest sensitive areadimension is 64 mm . To overcome this restriction the Collaboration had taken thedecision to use integrated 128-channel circuits VIKING. JINR provides importanttechnical support in this development. Now we had purchased a requisite consign-ment of these circuits and are installing in VD. The magnet MC-7A having length on the beam 3 m is used in spectrometer. Magnetfield in the center is equal to 1.1 T at a current 4000 A . The detection system of thespectrometer includes 18 planes of proportional chambers (PC). The data analysisgive the following characteristics of the spectrometer: average PC efficiency is 80%;coordinate accuracy on the reconstructed tracks is 1 mm ; the momentum resolutionon beam tracks (p=70 GeV/c) is 3 %; the momentum resolution on the secondarytracks is ∼ required for Thermalization project.The gamma-detector consists of 1536 full absorption Cherenkov counters. Ra-diators from a lead glass have the size 38 × × mm and are connected withPMT-84-3. Total fiducial area of the detector is 1 . × . m . The energy resolutionon 15 GeV electrons is 12%. Accuracy of the γ quantum coordinate reconstruc-tion is ∼ mm . At run 2007 the gamma-detector calibration was carried out andgamma- quantum events were recorded. The importance task of any experiment is to provide reconstruction of chargedparticle tracks. Spatial characteristics and geometric position of detector modulescan be differ from its design values. Possible reasons of detector misalignmentsare the limited accuracy of initial hardware, inaccuracies in placing of detectorsand their internal dimensions. The alignment procedure intends to compensatesuch misalignment by a mathematical way. We use for alignment procedure more obust, efficient and high precision method based on the Linear Least Squares (LLS)[7]. At 2006 technical run we had obtained data on hydrogen target. We had pickedout some events with good identification of 787 (single) space tracks on hits in vertexdetector and carried out alignment. Histograms of χ /n df for local fits before andafter alignment procedure are in Figure 2. At present it is continued data processing c c Figure 2: χ /n df for tracks: (left) before and (right) after alignment. and high multiplicity event searching. One of such events is shown on Figure 3.Preliminary multiplicity distribution of charged particles was obtained based on Z, mm1300 1350 1400 1450 1500 1550 X , mm -30-20-100102030 Run=358 pp X vs Z Nevent=16517 Ntracks=21
Z, mm1300 1350 1400 1450 1500 1550 Y , mm -30-20-100102030 Run=358 pp Y vs Z Nevent=16517 Ntracks=21
Figure 3: Event with multiplicity 21.
VERTEX detector data. It is shown on Figure 4.
The HM region study is important, because MP models and Monte-Carlo gener-ators are differed at high multiplicity ( n > n ( s )) very considerably. There arethe theoretical predictions about manifestation such phenomena as Cherenkov-like ntries 33984Mean 4.741 Nch0 5 10 15 20 25 30110 Entries 33984Mean 4.741
Multiplicity for pp E=50 Gev view X
Entries 33984Mean 6.586
Nch0 5 10 15 20 25 30110 Entries 33984Mean 6.586 =50 Gev for view Y p Multiplicity for pp E
Figure 4: Preliminary MD in pp at HM region. (gluon) radiation [8], Bose-Einstein condensation (BEC) of pions [9, 10], excess ofsoft photon rate [11] and other collective phenomena. We like to reveal their in ourfindings.For multiparticle dynamics insight and the MD description in hadron interac-tions we had proposed the Gluon Dominance model (GDM) [12]. In the frameworkof this model we research quark-gluon matter and hadronization stage detail by us-ing MD of the charged and neutral particles and their moments [13]. GDM bases onthe essentials of QCD and phenomenological scheme of hadronization. Our modelstudies had shown: valent quarks of initial protons are staying in leading particles(from 70 to 800 GeV/c and higher). MP is realized by gluons. We called themactive ones.Some of active gluons ( ∼ pp interactionsat 70 GeV/c and higher. In project Thermalization we plan to verify these. Thereare many of experimental and theoretical results, which evidence of cluster natureof MP by significant short-range multiplicity correlations [15], the observed scalingof the dynamical fluctuations of mean transverse-momentum [16].In GDM the evaporation of gluon sources may be realized by single gluons andalso groups consisted from two or more fission gluons. The superposition of themexplains the shoulder structure of MD at ISR and higher energies [12]. Our approach ives the possible interpretation of soft and semi-hard components [17].We modified GDM by including of the intermediate quark topologies to explainthe experimental differences between pp and pp inelastic topological cross sectionsand second correlation moment behavior at few GeV/c [18]. The high multiplicityin this process originates from ”4” or ”6”-topologies. Our scheme of hadronizationdescribes well MD for hadron interactions at 70 GeV and higher and could be useto study the central nuclear collisions at low and high energies. Entries 37764Mean 3.378 h Entries 37764Mean 3.378
Pseudorapidity for View X Ntr>18 Entries 15590Mean 3.457 h Entries 15590Mean 3.457
Pseudorapidity for View Y Ntr>18
Figure 5: The pseudorapidity spectra in pP b at n > The Cherenkov type radiation can be emitted in the projectile and target par-ticles. This leads to two peaks of dense groups of particles (spikes) distribution inrapidity phase-space. At the same time the particle distribution at the azimuthalangle is uniform. Study of the spike center distribution [19] in central C-Cu colli-sions at 4.5 GeV/c/A (all charged particles) and Mg-Mg collisions at 4.3 GeV/c/A(only negative charged particles) were found to be in agreement with the hypothesisof mesonic Cherenkov radiation. For this goal it was used transformation of pseu-dorapidity spectra from η variable to ˜ η with the uniform spectrum. In each casethe distance between peaks for these experiments is in agreement with Cherenkovradiation hypothesis, the charged-dependence was absent.The ring-like substructures of secondary in P b at 158 A GeV/c and Au at 11.6 GeV/c induced interactions with Ag(Br) nuclei in emulsion detector wereinvestigated [20]. The good agreement was obtained with idea of Cherenkov radia-tion.It must be emphasized that such events are rare, and represent at about 1% offull statistics. Therefore high luminosity and high multiplicity trigger of SVD setupagrees to collect enough statistics to study this phenomenon. The preliminary indi-cations to the manifestation of the ring events are in Figure 5. This pseudorapidityspectra for pP b -interactions at high multiplicity ( n >
18) shows up such behavior.As it was mentioned the Bose-Einstein condensation is very interesting phe-nomenon. The considerable efforts are necessary to confirm it experimentally. AtHM events the plentiful number of pions (charged and neutral) are produced. All ofthem are bosons. When the multiplicity increase moments of them are approachingto zero. In the case of relativistic ideal Bose gas the pion number fluctuations maygive a clear signal of approaching the BEC point [10]. When the temperature T decreases, the chemical potential increases and becomes equal to µ π = m π at BEC emperature T = T C . At this point the total number of particles takes up the lowestenergy state.M.I. Gorenstein and V.V. Begun had viewed the case of HM events in p + p interactions with beam energy of 70 GeV [10]. The volume of pion system wasestimated as, V = E/ε ( T, µ π ), and the number of pions was determined as, N π = V ρ π ( T, µ π ). In the vicinity of the BEC point they revealed an abrupt and anomalousincrease of the scaled variance of neutral and charged pion number fluctuations.Our experiment permits to experimental test of this phenomena. We are expectedto take a lot of high multiplicity event statistics with reconstructed by gammaquantum neutral mesons and study scaled variance of neutral and charged pionnumber fluctuations, We are continueing our work to making of program packets for data processing andnew phenomena study at HM region.
Author E.K. is glad to thank the NPQCD-2007 Org.Committee for partial financialsupport and warm working atmosphere created.These researches implemented into framework of project ”Thermalization” ispartially supported by RFBR grant − − − Bel a . References [1] David d , Enterria. Quark-Gluon Matter. Submitted to: J.Phys. G:Nucl.Part.Phys. (nucl-ex/0611012).[2] V.V. Avdeichikov et al. Multiparticle production processes in p p interactionwith high multiplicity at E ( p ) = 70 GeV. Proposal ”Termalization”. (In Rus-sian) JINR-P1-2004-190, 45pp (2005).[3] V.V.Babintsev et al. IHEP preprint M-25, Protvino (1976).[4] M.Yu. Bogolyubsky et al. The methodic of film information handling in theexperiment E-161. (In Russian) IHEP-INP-MSU-JINR E-161 Collaboration .IHEP-97-50, 9pp. (1997).[5] P.F. Ermolov et al. Proton-proton interaction with high multiplicity at energyof 70 GeV (proposal). Phys.At.Nucl., , 157-161 (1979). .M. Dremin. Ring-like events: Cerenkov gluons or Mach waves? Nucl.Phys. A767 , 233-247 (2006).[9] J.Zimanyi, G.Fai and B.Jacobsson. Bose-Einstein condensation of pions in en-ergetic heavy ion collisions? Phys.Rev.Lett. , 1705-1707 (1979);I.N. Mishustin et al. Pion production and Bose enhancement effects in rela-tivistic heavy ion collisions. Phys.Lett. B276 , 403-408 (1992);R.Lednicky et al. Multiboson effects in multiparticle production. Phys.Rev.,
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