The transverse momentum spectra of identified charged particles have been
measured at very low and intermediate transverse momenta in Au+Au collisions at
sqrt(s_NN) = 62.4 GeV and d+Au collisions at sqrt(s_NN) = 200 GeV using the
PHOBOS detector at RHIC. New results on charged particle production at very low
p_T in central Au+Au collisions at sqrt(s_{NN) = 200 GeV in the centrality
intervals 0-6% and 6-15% are presented. A comparison of the PHOBOS low-p_T data
with predictions of a recent optical model is shown. The shapes of m_T spectra
for d+Au and Au+Au collisions are compared.Comment: Presented at the 18th International Conference on Ultra-Relativistic
  Nucleus-Nucleus Collisions, Quark Matter 2005, Budapest, Hungary, Aug. 4-9,
  200

Adam Trzupek

Adler

Back

Bjorken

Busza

Cramer

Kolb

Schnedermann

English

arXiv

Crossref

Particle production at very low and intermediate transverse momenta in d+Au and Au+Au collisions

The transverse momentum (p(T)) spectra of identified charged particles have been measured at very low and intermediate transverse momenta in Au+Au collisions at root(s(NN)) = 62.4 GeV and d+Au collisions at root(s(NN)) = 200 GeV using the PHOBOS detector at RHIC. New results on charged particle production at very low p(T) in central Au+Au collisions at root(s(NN)) = 200 GeV in the centrality intervals 0-6% and 6-15% are presented. A comparison of the PHOBOS IOW-PT data with predictions of a recent optical model is shown. The shapes of m(T) spectra for d+Au and Au+Au collisions are compared

Trzupek, A

and, PHOBOS Collaboration

Veres, GI

ELTE Digital Institutional Repository (EDIT)

arXiv:nucl-ex/0510039v1  12 Oct 2005Particle production at very low and intermediate transverse momenta ind+Au and Au+Au collisionsAdam Trzupek3 for the PHOBOS CollaborationB.Alver4, B.B.Back1, M.D.Baker2, M.Ballintijn4, D.S.Barton2, R.R.Betts6, A.A.Bickley7,R.Bindel7, A.Budzanowski3, W.Busza4, A.Carroll2, Z.Chai2, V.Chetluru6, M.P.Decowski4,E.Garcı́a6, T.Gburek3, N.George2, K.Gulbrandsen4, S.Gushue2, C.Halliwell6, J.Hamblen8,G.A.Heintzelman2, C.Henderson4, I.Harnarine6, D.J.Hofman6, R.S.Hollis6, R.Hołyński3,B.Holzman2, A.Iordanova6, E.Johnson8, J.L.Kane4, N.Khan8, W.Kucewicz6, P.Kulinich4,C.M.Kuo5, W.Li4, W.T.Lin5, C.Loizides4, S.Manly8, A.C.Mignerey7, R.Nouicer2,6,A.Olszewski3, R.Pak2, I.C.Park8, C.Reed4, L.P.Remsberg2, M.Reuter6, E.Richardson7,C.Roland4, G.Roland4, L.Rosenberg4, J.Sagerer6, P.Sarin4, P.Sawicki3, I.Sedykh2, W.Skulski8,C.E.Smith6, M.A.Stankiewicz2, P.Steinberg2, G.S.F.Stephans4, A.Sukhanov2, A.Szostak2,J.-L.Tang5, M.B.Tonjes7, A.Trzupek3, C.Vale4, G.J.van Nieuwenhuizen4, S.S.Vaurynovich4,R.Verdier4, G.I.Veres4, P.Walters8, E.Wenger4, D.Willhelm2, F.L.H.Wolfs8, B.Wosiek3,K.Woźniak3, A.H.Wuosmaa1, S.Wyngaardt2, B.Wysłouch41 Argonne National Laboratory, Argonne, IL 60439-4843, USA2 Brookhaven National Laboratory, Upton, NY 11973-5000, USA3 Institute of Nuclear Physics PAN, Kraków, Poland4 Massachusetts Institute of Technology, Cambridge, MA 02139-4 07, USA5 National Central University, Chung-Li, Taiwan6 University of Illinois at Chicago, Chicago, IL 60607-7059,USA7 University of Maryland, College Park, MD 20742, USA8 University of Rochester, Rochester, NY 14627, USAThe transverse momentum (pT ) spectra of identified charged particles have been measuredat very low and intermediate transverse momenta in Au+Au collisi ns at√sNN = 62.4 GeVand d+Au collisions at√sNN = 200 GeV using the PHOBOS detector at RHIC. New results oncharged particle production at very lowpT in central Au+Au collisions at√sNN = 200 GeV inthe centrality intervals 0-6% and 6-15% are presented. A comparison of the PHOBOS low-pTdata with predictions of a recent optical model is shown. Thes apes ofmT spectra for d+Auand Au+Au collisions are compared.1. IntroductionIn nucleus-nucleus collisions, an enhanced production of low-pT particles could signal newlong-wavelength physics phenomena [ 1, 2]. It is also expected that yields of particles withhigher masses, like protons and antiprotons can be modified du to collective transverse expan-sion of the system [ 3, 4]. Measurements at very lowpT can also provide a critical test formodels predicting a pronounced modification of the low-pT particle emission pattern, e.g. [ 5].12The PHOBOS experiment has the unique capability to measure charged particles at trans-verse momenta as low as 30, 90 and 140 MeV/c for charged pions,kaons and for protonsand antiprotons, respectively, using a multi-layer, magnetic spectrometer. Yields at very lowtransverse momenta are determined using a reconstruction procedure developed to look for par-ticles which range out in the fifth silicon layer of the PHOBOSspectrometer. A descriptionof the ”stopping algorithm” is presented in [ 6]. At intermediatepT , particle momentum andcharge are obtained from the curvature of particle trajectories in a 2T magnetic field and particleidentification is provided by the specific energy loss (dE/dx) in the spectrometer and by Time-of-Flight detectors. Details on tracking, particle identification, event selection and centralitydetermination in the PHOBOS detector can be found in [ 7].2. pT spectra in Au+Au collisions at√sNN = 62.4 GeVThe preliminary particle yields forπ±,K±, p and p̄ are presented in Fig. 1 forthree centrality intervals: 0-15%, 15-30%and 30-50%. The data are corrected fordetector effects (acceptance, efficiency,momentum resolution) and backgroundparticles including feed-down from weakdecays and secondary particles producedin the beam pipe and detector material.The rapidity coverage of measured yieldsextends from about 0.4 to 1.4 forπ±, from0.2 to 1.2 forK± and from 0.2 to 1.1 forpandp̄. The preliminary results on antipar-ticle to particle ratios have been obtainedfor the 15% most central collisions. Theresults of 0.84± 0.02(stat.)± 0.08(syst.)for K−/K+ and 0.37± 0.01(stat.) ±0.06(syst.) forp̄/p fit smoothly into theenergy evolution of antiparticle to parti-cle ratios from the AGS up to the highestRHIC energy.Low-pT yields of (π++π−), (K++K−)and (p + p̄) near mid-rapidity in Au+Aucollisions at√sNN = 62.4 GeV, correctedfor detector effects and background parti-cles, are shown in Fig. 2 in the same cen-trality bins. One can see that (K+ +K−)and (p+p̄) yields are quite consistent with-310-210-1101102100-15%+π +K p0-15%-π -Kp -310-210-11011021015-30% 15-30%0 1 2 3-310-210-11011021030-50%1 2 330-50%PHOBOS Preliminary Au+Au,62.4 GeV (GeV/c)Tp-2 (GeV/c)dyTdpN2 d Tpπ21Figure 1. pT spectra ofπ±, K±, p andp̄ nearmid-rapidity in Au+Au collisions at√sNN =62.4 GeV.extrapolations of blast wave functions (BWF) [ 4] fitted to the spectra at higher transversemomenta. Some disagreement between the measured yield of pions and BWF at lowpT couldbe attributed to a contribution from resonances which is noti cluded in the model. A similarbehavior was observed forpT yields measured in the 15% most central Au+Au collisions at3√sNN = 200 GeV [ 6], indicating that at both energies no significante hancement of particleproduction is observed at very lowpT . Also, a flattening of the (p + p̄) spectra down to verylow transverse momentum is observed. This could be a consequence of collective transverseexpansion of the medium created in heavy ion collisions at RHIC. [GeV/c]Tp-110 1]2/GeV2 [cTN/dydp2 d-1 ) Tpπ(2110210310)-π++π()-+K+(K)p(p+PHOBOS PreliminaryAu+Au, 62.4 GeV0-15% [GeV/c]Tp-110 1]2/GeV2 [cTN/dydp2 d-1 ) Tpπ(2110210310)-π++π()-+K+(K)p(p+PHOBOS PreliminaryAu+Au, 62.4 GeV15-30% [GeV/c]Tp-110 1]2/GeV2 [cTN/dydp2 d-1 ) Tpπ(2110210310 )-π++π()-+K+(K)p(p+PHOBOS PreliminaryAu+Au, 62.4 GeV30-50%Figure 2. (π+ + π−), (K+ + K−) and (p + p̄) yields at very lowpT in Au+Au collisions at√sNN = 62.4 GeV. Blast wave fits to the intermediatepT data (solid lines) are extrapolated tolow pT (dashed lines).3. Low-pT yields in central Au+Au collisions at√sNN = 200 GeVThe spectra of (π++π−), (K++K−) and (p+p̄) at very low transverse momentum in the 15%most central Au+Au collisions at√sNN = 200 GeV, measured in the PHOBOS experiment, arepresented in [ 6]. In order to confront the extrapolations from a recent optical model [ 5], whichwere available only for more central collisions, with measurements, the published data samplewas split into two finer centrality bins. Fig. 3 shows thepT yields, corrected for detector effectsand background particles, measured in the centrality intervals 0-6% and 6-15%. In Fig. 4,the pion yield measured in the 6% most central Au+Au collision is compared to the opticalmodel predictions for the spectrum of negative pions at mid-rapidity. The originally published [GeV/c]Tp0 0.1 0.2]2/GeV2 [cTN/dydp2 d-1 )Tpπ(210210310 )-π++π()-+K+(K)p(p+Au+Au, 200 GeV0-6%PHOBOS preliminary [GeV/c]Tp0 0.1 0.2]2/GeV2 [cTN/dydp2 d-1 )Tpπ(210210310 )-π++π()-+K+(K)p(p+Au+Au, 200 GeV6-15%PHOBOS preliminary [MeV/c]Tp0 20 40 60]2/GeV2 [cTN/dydp2 d-1 )Tpπ(2010002000PHOBOS PreliminaryAu+Au, 200 GeV0-6% )/2-π+ +π(Figure 3. (π+ + π−), (K+ + K−) and (p + p̄) yields atvery low pT in 0-6% and 6-15% central Au+Au collisionsat√sNN = 200 GeV.Figure 4. Optical model pre-dictions [ 5, 8] for pion spectraat low pT compared to PHO-BOS data (see text for details).4]2[GeV/cTm0 1 2 3 4]2[GeV/clocT0.20.4]2/GeV4 [cTN/dydm2 d-1 ) Tmπ(2-410-310-210-110110210310PHOBOS preliminaryd+Au, 200 GeV)-π++π()-+K+(K)p(p+ ]2[GeV/cTm0 1 2 3 4]2[GeV/clocT0.20.4]2/GeV4 [cTN/dydm2 d-1 ) Tmπ(2-410-310-210-110110210310 π K pPHOBOSPHENIXAu+Au, 200 GeV0-15%Figure 5.mT spectra of (π++π−), (K++K−) and (p+p̄) at very low and intermediatepT measured in d+Au (left plot) and central Au+Au collisions (right plot). Inverse localslope parameters ofmT spectra are shown in the lower panels of each figure.extrapolation is shown by the dashed curve, while the solid curve depicts the recently modifiedmodel calculations [ 5, 8].4. mT scalingIt is interesting to compare the particle yields at very low and intermediatepT in d+Au andcentral Au+Au collision at the same energy of√sNN = 200 GeV. Yields of (π+ + π−), (K+ +K−) and (p+ p̄) in d+Au collisions, corrected for detector effects and background particles, areshown in Fig. 5. One can see that in d+Au collisions (π+ + π−) and (p + p̄) mT spectra aresimilar while the (K+ +K−) spectrum is systematically lower (by a factor of about 2) due tostrangeness suppression. ThemT spectra for the 15% most central Au+Au collisions measuredby the PHOBOS [ 6] and PHENIX [ 9] experiments at very low and intermediate tranversemomenta, respectively, are also shown in Fig. 5. In order to compare the shapes of themTspectra, inverse local slope parameters were calculated byfitting locally exponential functionsto each spectrum (see bottom panels of Fig. 5). We can see thatfor d+Au collisions local slopesare similar for all particle species both at low and intermediatepT . In contrast, Au+Au spectralshapes are similar at higher transverse masses (mT > 1.7 GeV) while at lowmT a flattening of(K++K−) and (p+p̄) spectra is observed. This flattening of the (p+p̄) spectrum is significantlystronger than the one observed for the spectra of charged kaons. One can also see that themTdependence of the local slopes of the (π++π−) mT spectrum for Au+Au collision is consistentwith that found for the local slopes of (π+ + π−), (K+ + K−) and (p + p̄) spectra in d+Aucollisions.5. SummaryYields of pions, kaons and protons and antiprotons at very low and intermediatepT nearmid-rapidity in Au+Au collisions at√sNN = 62.4 and 200 GeV, measured in the PHOBOS5experiment, indicate that there is no evidence for enhancedpro uction of particles at very lowtransverse momentum. The pion low-pT data can constrain the recent optical model predictions.A significant flattening of the (p + p̄) mT spectrum down to very lowpT is observed in centralAu+Au collisions at both energies which could be a consequence of the collective transverseexpansion of the system. In d+Au collisions, no flattening isob erved and the shapes of themTspectra are similar at very low and intermediatepT .This work was partially supported by U.S. DOE grants DE-AC02-98CH10886, DE-FG02-93ER40802, DE-FC02-94ER40818, DE-FG02-94ER40865, DE-FG02-99ER41099, and W-31-109-ENG-38, by U.S. NSF grants 9603486, 0072204, and 0245011, by Polish KBN grant 1-P03B-062-27(2004-2007), by NSC of Taiwan Contract NSC 89-2112-M-008-024, and by Hun-garian OTKA grant (F 049823).REFERENCES1. W. Busza, ”Particle Production in Highly Excited Matter”, Plenum Press, New York, 1993,p. 149.2. J. Bjorken, Acta Phys. Pol. B28 (1997) 2773.3. P.F. Kolb and R. Rapp, Phys. Rev. C67 (2003) 044903.4. E. Schnedermann, J. Sollfrank and U. Heinz, Phys. Rev. C48(1993) 2462.5. J.G. Cramer, G.A.Miller, J.M.S. Wu and J. Yoon, Phys. Rev.L tt. 94 (2005) 102302.6. B.B. Back, et al., (PHOBOS Collab.), Phys. Rev. C70 (2004)051901(R).7. B.B. Back, et al., (PHOBOS Collab.), Nucl. Phys. A757 (2005) 28.8. B.B. Back, et al., (PHOBOS Collab.), nucl-ex/0506008, J.G. Cramer, 2005, (private com-munication, erratum to be published).9. S.S. Adler, et al., (PHENIX Collab.), Phys. Rev. C69 (2004) 34909.

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Particle production at very low and intermediate transverse momenta in
  d+Au and Au+Au collisions

Particle production at very low and intermediate transverse momenta in d+Au and Au+Au collisions

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