Government & Politics

Pion, kaon, proton and anti-proton transverse momentum distributions from p+p and d+Au collisions at sqrt(sNN) = 200 GeV

Description
Pion, kaon, proton and anti-proton transverse momentum distributions from p+p and d+Au collisions at sqrt(sNN) = 200 GeV
Published
of 7
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Share
Transcript
    a  r   X   i  v  :  n  u  c   l  -  e  x   /   0   3   0   9   0   1   2  v   5   2   3   J  u  n   2   0   0   5 Pion, kaon, proton and anti-proton transverse momentum distributions from p+p andd+Au collisions at  √  s NN   = 200  GeV J. Adams, 3 M.M. Aggarwal, 29 Z. Ahammed, 43 J. Amonett, 20 B.D. Anderson, 20 D. Arkhipkin, 13 G.S. Averichev, 12 S.K. Badyal, 19 Y. Bai, 27 J. Balewski, 17 O. Barannikova, 32 L.S. Barnby, 3 J. Baudot, 18 S. Bekele, 28 V.V. Belaga, 12 R. Bellwied, 46 J. Berger, 14 B.I. Bezverkhny, 48 S. Bharadwaj, 33 A. Bhasin, 19 A.K. Bhati, 29 V.S. Bhatia, 29 H. Bichsel, 45 J. Bielcik, 48 J. Bielcikova, 48 A. Billmeier, 46 L.C. Bland, 4 C.O. Blyth, 3 B.E. Bonner, 34 M. Botje, 27 A. Boucham, 38 A.V. Brandin, 25 A. Bravar, 4 M. Bystersky, 11 R.V. Cadman, 1 X.Z. Cai, 37 H. Caines, 48 M. Calder´on de la Barca S´anchez, 17 J. Castillo, 21 O. Catu, 48 D. Cebra, 7 Z. Chajecki, 44 P. Chaloupka, 11 S. Chattopadhyay, 43 H.F. Chen, 36 Y. Chen, 8 J. Cheng, 41 M. Cherney, 10 A. Chikanian, 48 W. Christie, 4 J.P. Coffin, 18 T.M. Cormier, 46 J.G. Cramer, 45 H.J. Crawford, 6 D. Das, 43 S. Das, 43 M.M. deMoura, 35 A.A. Derevschikov, 31 L. Didenko, 4 T. Dietel, 14 S.M. Dogra, 19 W.J. Dong, 8 X. Dong, 36 J.E. Draper, 7 F. Du, 48 A.K. Dubey, 15 V.B. Dunin, 12 J.C. Dunlop, 4 M.R. Dutta Mazumdar, 43 V. Eckardt, 23 W.R. Edwards, 21 L.G. Efimov, 12 V. Emelianov, 25 J. Engelage, 6 G. Eppley, 34 B. Erazmus, 38 M. Estienne, 38 P. Fachini, 4 J. Faivre, 18 R. Fatemi, 17 J. Fedorisin, 12 K. Filimonov, 21 P. Filip, 11 E. Finch, 48 V. Fine, 4 Y. Fisyak, 4 K. Fomenko, 12 J. Fu, 41 C.A. Gagliardi, 39 L. Gaillard, 3 J. Gans, 48 M.S. Ganti, 43 L. Gaudichet, 38 F. Geurts, 34 V. Ghazikhanian, 8 P. Ghosh, 43 J.E. Gonzalez, 8 O. Grachov, 46 O. Grebenyuk, 27 D. Grosnick, 42 S.M. Guertin, 8 Y. Guo, 46 A. Gupta, 19 T.D. Gutierrez, 7 T.J. Hallman, 4 A. Hamed, 46 D. Hardtke, 21 J.W. Harris, 48 M. Heinz, 2 T.W. Henry, 39 S. Hepplemann, 30 B. Hippolyte, 18 A. Hirsch, 32 E. Hjort, 21 G.W. Hoffmann, 40 H.Z. Huang, 8 S.L. Huang, 36 E.W. Hughes, 5 T.J. Humanic, 28 G. Igo, 8 A. Ishihara, 40 P. Jacobs, 21 W.W. Jacobs, 17 M. Janik, 44 H. Jiang, 8 P.G. Jones, 3 E.G. Judd, 6 S. Kabana, 2 K. Kang, 41 M. Kaplan, 9 D. Keane, 20 V.Yu. Khodyrev, 31 J. Kiryluk, 22 A. Kisiel, 44 E.M. Kislov, 12 J. Klay, 21 S.R. Klein, 21 D.D. Koetke, 42 T. Kollegger, 14 M. Kopytine, 20 L. Kotchenda, 25 M. Kramer, 26 P. Kravtsov, 25 V.I. Kravtsov, 31 K. Krueger, 1 C. Kuhn, 18 A.I. Kulikov, 12 A. Kumar, 29 R.Kh. Kutuev, 13 A.A. Kuznetsov, 12 M.A.C. Lamont, 48 J.M. Landgraf, 4 S. Lange, 14 F. Laue, 4 J. Lauret, 4 A. Lebedev, 4 R. Lednicky, 12 S. Lehocka, 12 M.J. LeVine, 4 C. Li, 36 Q. Li, 46 Y. Li, 41 G. Lin, 48 S.J. Lindenbaum, 26 M.A. Lisa, 28 F. Liu, 47 L. Liu, 47 Q.J. Liu, 45 Z. Liu, 47 T. Ljubicic, 4 W.J. Llope, 34 H. Long, 8 R.S. Longacre, 4 M. Lopez-Noriega, 28 W.A. Love, 4 Y. Lu, 47 T. Ludlam, 4 D. Lynn, 4 G.L. Ma, 37 J.G. Ma, 8 Y.G. Ma, 37 D. Magestro, 28 S. Mahajan, 19 D.P. Mahapatra, 15 R. Majka, 48 L.K. Mangotra, 19 R. Manweiler, 42 S. Margetis, 20 C. Markert, 20 L. Martin, 38 J.N. Marx, 21 H.S. Matis, 21 Yu.A. Matulenko, 31 C.J. McClain, 1 T.S. McShane, 10 F. Meissner, 21 Yu. Melnick, 31 A. Meschanin, 31 M.L. Miller, 22 N.G. Minaev, 31 C. Mironov, 20 A. Mischke, 27 D.K. Mishra, 15 J. Mitchell, 34 B. Mohanty, 43 L. Molnar, 32 C.F. Moore, 40 D.A. Morozov, 31 M.G. Munhoz, 35 B.K. Nandi, 43 S.K. Nayak, 19 T.K. Nayak, 43 J.M. Nelson, 3 P.K. Netrakanti, 43 V.A. Nikitin, 13 L.V. Nogach, 31 S.B. Nurushev, 31 G. Odyniec, 21 A. Ogawa, 4 V. Okorokov, 25 M. Oldenburg, 21 D. Olson, 21 S.K. Pal, 43 Y. Panebratsev, 12 S.Y. Panitkin, 4 A.I. Pavlinov, 46 T. Pawlak, 44 T. Peitzmann, 27 V. Perevoztchikov, 4 C. Perkins, 6 W. Peryt, 44 V.A. Petrov, 13 S.C. Phatak, 15 R. Picha, 7 M. Planinic, 49 J. Pluta, 44 N. Porile, 32 J. Porter, 45 A.M. Poskanzer, 21 M. Potekhin, 4 E. Potrebenikova, 12 B.V.K.S. Potukuchi, 19 D. Prindle, 45 C. Pruneau, 46 J. Putschke, 23 G. Rakness, 30 R. Raniwala, 33 S. Raniwala, 33 O. Ravel, 38 R.L. Ray, 40 S.V. Razin, 12 D. Reichhold, 32 J.G. Reid, 45 G. Renault, 38 F. Retiere, 21 A. Ridiger, 25 H.G. Ritter, 21 J.B. Roberts, 34 O.V. Rogachevskiy, 12 J.L. Romero, 7 A. Rose, 46 C. Roy, 38 L. Ruan, 36 R. Sahoo, 15 I. Sakrejda, 21 S. Salur, 48 J. Sandweiss, 48 M. Sarsour, 17 I. Savin, 13 P.S. Sazhin, 12 J. Schambach, 40 R.P. Scharenberg, 32 N. Schmitz, 23 K. Schweda, 21 J. Seger, 10 P. Seyboth, 23 E. Shahaliev, 12 M. Shao, 36 W. Shao, 5 M. Sharma, 29 W.Q. Shen, 37 K.E. Shestermanov, 31 S.S. Shimanskiy, 12 E Sichtermann, 21 F. Simon, 23 R.N. Singaraju, 43 G. Skoro, 12 N. Smirnov, 48 R. Snellings, 27 G. Sood, 42 P. Sorensen, 21 J. Sowinski, 17 J. Speltz, 18 H.M. Spinka, 1 B. Srivastava, 32 A. Stadnik, 12 T.D.S. Stanislaus, 42 R. Stock, 14 A. Stolpovsky, 46 M. Strikhanov, 25 B. Stringfellow, 32 A.A.P. Suaide, 35 E. Sugarbaker, 28 C. Suire, 4 M. Sumbera, 11 B. Surrow, 22 T.J.M. Symons, 21 A. Szanto de Toledo, 35 P. Szarwas, 44 A. Tai, 8 J. Takahashi, 35 A.H. Tang, 27 T. Tarnowsky, 32 D. Thein, 8 J.H. Thomas, 21 S. Timoshenko, 25 M. Tokarev, 12 T.A. Trainor, 45 S. Trentalange, 8 R.E. Tribble, 39 O.D. Tsai, 8 J. Ulery, 32 T. Ullrich, 4 D.G. Underwood, 1 A. Urkinbaev, 12 G. VanBuren, 4 M. van Leeuwen, 21 A.M. Vander Molen, 24 R. Varma, 16 I.M. Vasilevski, 13 A.N. Vasiliev, 31 R. Vernet, 18 S.E. Vigdor, 17 Y.P. Viyogi, 43 S. Vokal, 12 S.A. Voloshin, 46 M. Vznuzdaev, 25 W.T. Waggoner, 10 F. Wang, 32 G. Wang, 20 G. Wang, 5 X.L. Wang, 36 Y. Wang, 40 Y. Wang, 41 Z.M. Wang, 36 H. Ward, 40 J.W. Watson, 20 J.C. Webb, 17 R. Wells, 28 G.D. Westfall, 24 A. Wetzler, 21 C. Whitten Jr., 8 H. Wieman, 21 S.W. Wissink, 17 R. Witt, 2 J. Wood, 8 J. Wu, 36 N. Xu, 21 Z. Xu, 4 Z.Z. Xu, 36 E. Yamamoto, 21 P. Yepes, 34 V.I. Yurevich, 12 Y.V. Zanevsky, 12 H. Zhang, 4 W.M. Zhang, 20 Z.P. Zhang, 36 R. Zoulkarneev, 13 Y. Zoulkarneeva, 13 and A.N. Zubarev 12  2(STAR Collaboration) , ∗ 1 Argonne National Laboratory, Argonne, Illinois 60439  2  University of Bern, 3012 Bern, Switzerland  3  University of Birmingham, Birmingham, United Kingdom  4 Brookhaven National Laboratory, Upton, New York 11973  5  California Institute of Technology, Pasadena, California 91125  6  University of California, Berkeley, California 94720  7  University of California, Davis, California 95616  8  University of California, Los Angeles, California 90095  9  Carnegie Mellon University, Pittsburgh, Pennsylvania 15213  10  Creighton University, Omaha, Nebraska 68178  11 Nuclear Physics Institute AS CR, 250 68  ˇ Reˇz/Prague, Czech Republic  12  Laboratory for High Energy (JINR), Dubna, Russia  13  Particle Physics Laboratory (JINR), Dubna, Russia  14 University of Frankfurt, Frankfurt, Germany  15  Institute of Physics, Bhubaneswar 751005, India  16  Indian Institute of Technology, Mumbai, India  17  Indiana University, Bloomington, Indiana 47408  18  Institut de Recherches Subatomiques, Strasbourg, France  19  University of Jammu, Jammu 180001, India  20  Kent State University, Kent, Ohio 44242  21 Lawrence Berkeley National Laboratory, Berkeley, California 94720  22  Massachusetts Institute of Technology, Cambridge, MA 02139-4307  23  Max-Planck-Institut f¨ ur Physik, Munich, Germany  24 Michigan State University, East Lansing, Michigan 48824 25  Moscow Engineering Physics Institute, Moscow Russia  26  City College of New York, New York City, New York 10031 27  NIKHEF, Amsterdam, The Netherlands  28  Ohio State University, Columbus, Ohio 43210  29  Panjab University, Chandigarh 160014, India  30  Pennsylvania State University, University Park, Pennsylvania 16802  31 Institute of High Energy Physics, Protvino, Russia  32  Purdue University, West Lafayette, Indiana 47907  33  University of Rajasthan, Jaipur 302004, India  34 Rice University, Houston, Texas 77251 35  Universidade de Sao Paulo, Sao Paulo, Brazil  36  University of Science & Technology of China, Anhui 230027, China  37  Shanghai Institute of Applied Physics, Shanghai 201800, China  38  SUBATECH, Nantes, France  39  Texas A&M University, College Station, Texas 77843  40  University of Texas, Austin, Texas 78712  41 Tsinghua University, Beijing 100084, China  42  Valparaiso University, Valparaiso, Indiana 46383  43  Variable Energy Cyclotron Centre, Kolkata 700064, India  44 Warsaw University of Technology, Warsaw, Poland  45  University of Washington, Seattle, Washington 98195  46  Wayne State University, Detroit, Michigan 48201 47  Institute of Particle Physics, CCNU (HZNU), Wuhan 430079, China  48  Yale University, New Haven, Connecticut 06520  49  University of Zagreb, Zagreb, HR-10002, Croatia  (Dated: February 8, 2008)Identified mid-rapidity particle spectra of   π ± ,  K  ± , and  p (¯  p ) from 200 GeV p+p and d+Au colli-sions are reported. A time-of-flight detector based on multi-gap resistive plate chamber technologyis used for particle identification. The particle-species dependence of the Cronin effect is observedto be significantly smaller than that at lower energies. The ratio of the nuclear modification fac-tor ( R dAu ) between protons (  p  + ¯  p ) and charged hadrons ( h ) in the transverse momentum range1 . 2  < p T   <  3 . 0 GeV/c is measured to be 1 . 19 ± 0 . 05(stat) ± 0 . 03(syst) in minimum-bias collisions andshows little centrality dependence. The yield ratio of (  p  + ¯  p ) /h  in minimum-bias d+Au collisionsis found to be a factor of 2 lower than that in Au+Au collisions, indicating that the Cronin effectalone is not enough to account for the relative baryon enhancement observed in heavy ion collisionsat RHIC. PACS numbers: 25.75.Dw, 25.75.-q, 13.85.Ni  3Suppression of high transverse momentum (  p T  ) hadronproduction has been observed at RHIC in central Au+Aucollisions relative to p+p collisions [1, 2, 3, 4]. This sup-pression has been interpreted as energy loss of the en-ergetic partons traversing the produced hot and densemedium [5]. At intermediate  p T  , the degree of sup-pression depends on particle species. The spectra of baryons (protons and lambdas) are less suppressed thanthose of mesons (pions, kaons) [6, 7] in the  p T   range2  < p T   <  5 GeV/c. The baryon content in the hadronsat intermediate  p T   depends strongly on the impact pa-rameter (centrality) of the Au+Au collisions with about40% of the hadrons being baryons in the minimum-biascollisions and 20% in very peripheral collisions [6, 7].Hydrodynamics [8, 9], parton coalescence at hadroniza-tion [10, 11, 12] and gluon junctions [13] have been sug-gested as explanations for the observed particle-speciesdependence.On the other hand, the hadron  p T   spectra have beenobserved to depend on the target atomic weight ( A ) andthe produced particle species in lower energy p+A colli-sions [14, 15, 16]. This is known as the “Cronin Effect”, ageneric term for the experimentally observed broadeningof the transverse momentum distributions at intermedi-ate  p T   in p+A collisions as compared to those in p+pcollisions [14, 15, 16, 17, 18]. The effect can be charac-terized as a dependence of the yield on the target atomicweight as  A α . At energies of   √  s  ≃  30 GeV,  α  dependson  p T   and is greater than unity at high  p T   [14, 15], indi-cating an enhancement of the production cross section.The effect has been interpreted as partonic scatteringsat the initial impact [17, 18]. Thus, the Cronin effectis predicted to be larger in central d+Au collisions thanin d+Au peripheral collisions [19]. At higher energies,multiple parton collisions are possible even in p+p colli-sions [20]. This combined with the hardening of the spec-tra with increasing beam energy would reduce the Cronineffect [18]. At sufficiently high beam energy, gluon sat-uration is expected to result in a relative suppression of hadron yield at high  p T   in both p+A and A+A collisionsand in a substantial decrease and finally in the disap-pearance of the Cronin effect [21].Recent results on inclusive hadron production fromd+Au collisions indicate that hadron suppression at in-termediate  p T   in Au+Au collisions is due to final-stateeffects [4, 22, 23]. The rapidity dependence of the particleyield at intermediate  p T   shows suppression in forward ra-pidity (deuteron side) and enhancement in the backwardrapidity (Au side) in d+Au collisions at RHIC [24, 25].A study of particle composition will help understand thesrcin of the rapidity asymmetry [10]. In order to furtherunderstand the mechanisms responsible for the particledependence of   p T   spectra in heavy ion collisions, and toseparate the effects of initial and final partonic rescatter- ∗ URL:  www.star.bnl.gov ings, we measured the  p T   distributions of   π ± ,  K  ± ,  p  and¯  p  from 200 GeV d+Au and p+p collisions. In this letter,we discuss the dependence of particle production on  p T  ,collision energy, and target atomic weight.The detector used for these studies was the SolenoidalTracker at RHIC (STAR). The main tracking device isthe Time Projection Chamber (TPC) which providesmomentum information and particle identification forcharged particles up to  p T   ∼  1 . 1 GeV/c by measuringtheir ionization energy loss ( dE/dx  ) [26]. Detailed de-scriptions of the TPC and d+Au run conditions havebeen presented in Ref. [22, 26]. A prototype time-of-flight detector (TOFr) based on multi-gap resistive platechambers (MRPC) [27] was installed in STAR for thed+Au and p+p runs. It extends particle identificationup to  p T   ∼ 3 GeV/c for  p  and ¯  p . In p+p and d+Au col-lisions, the  dE/dx  resolution from TPC was found to bebetter than 8% and there is 2  ∼  3 σ  separation betweenthe  dE/dx  of pions at relativistic rise and the  dE/dx  of kaons and protons at  p T > ∼ 2 GeV/c [26]. By combiningthe particle identification capability of   dE/dx  from TPCand Time-of-Flight from TOFr, we are able to extendpion identification to ∼ 3 GeV/c [26, 28]. MRPC technol-ogy was first developed by the CERN ALICE group [29]to provide a cost-effective solution for large-area time-of-flight coverage.TOFr covers π/ 30 in azimuth and − 1 <η< 0 in pseudo-rapidity at a radius of   ∼  220 cm. It contains 28 MRPCmodules which were partially instrumented during the2003 run. Only particles from  − 0 . 5  < η <  0 are se-lected where most of the MRPC modules were instru-mented. Each module [27] is a stack of resistive glassplates with six uniform gas gaps. High voltage is ap-plied to electrodes on the outer surfaces of the outerplates. A charged particle traversing a module gener-ates avalanches in the gas gaps which are read out by6 copper pickup pads with pad dimensions of 31 . 5 × 63mm 2 . The MRPC modules were operated at 14 kV witha mixture of 95%  C  2 H  2 F  4  and 5% iso-butane at 1 at-mosphere. In d+Au collisions, TOFr is situated in theoutgoing Au beam direction which is assigned negative η . The average MRPC TOFr timing resolution alone forthe ten modules used in this analysis was measured tobe 85 ps for both d+Au and p+p collisions. The “start”timing was provided by two identical pseudo-vertex po-sition detectors (pVPD), each 5.4 m away from the TPCcenter along the beamline [30]. Each pVPD consists of 3detector elements and covers ∼ 19% of the total solid an-gle in 4 . 4  < | η | <  4 . 9 [30]. Due to the low multiplicity ind+Au and p+p collisions, the effective timing resolutionof the pVPDs was 85 ps and 140 ps, respectively.Since the acceptance of TOFr is small, a special trig-ger selected events with a valid pVPD coincidence andat least one TOFr hit. A total of 1.89 million and 1.08million events were used for the analysis from TOFr trig-gered d+Au and non-singly diffractive (NSD) p+p colli-sions, representing an integrated luminosity of about 40 µ b − 1 and 30 nb − 1 , respectively. The d+Au minimum-  4 p (GeV/c) 0 0.5 1 1.5 2 2.5 3 3.5           β    1   / 0.60.811.21.41.61.82 pK π e   2 ) 2 (GeV/c 2 Mass -0.5 0 0.5 1 1.5    C  o  u  n   t  s 0100200300400500<1.4 GeV/c T 1.2<p pK π FIG. 1: 1 /β   vs. momentum for  π ± ,  K  ± , and  p (¯  p ) from 200GeV d+Au collisions. Separations between pions and kaons,kaons and protons are achieved up to  p T   ≃ 1 . 6 and 3 . 0 GeV/c,respectively. The insert shows  m 2 =  p 2 (1 /β  2 − 1) for 1 . 2  < p T   <  1 . 4 GeV/c. Clear separation of pions, kaons and protonsis seen. bias trigger required an equivalent energy deposition of about 15 GeV in the Zero Degree Calorimeter in theAu beam direction [22]. Minimum-bias p+p events weretriggered by the coincidence of two beam-beam coun-ters (BBC) covering 3 . 3  <  | η |  <  5 . 0 [1]. The NSDcross section was measured to be 30 . 0 ±  3 . 5 mb by avan der Meer scan and PYTHIA [31] simulation of theBBC acceptance [1]. A small multiplicity bias (  < ∼ 10% ind+Au and 18% in p+p) at mid-rapidity was observed inTOFr triggered events due to the further pVPD triggerrequirement and was corrected for using minimum-biasdata sets and PYTHIA [31] and HIJING [32] simulations.The effect of the trigger bias on the mid-rapidity parti-cle spectra was found to be independent of particle  p T  at  p T   > 0.3 GeV/c [33]. Centrality tagging of d+Au col-lisions was based on the charged particle multiplicity in − 3 . 8  < η <  − 2 . 8, measured by the Forward Time Pro- jection Chamber in the Au beam direction [22, 34]. TheTOFr triggered d+Au events were divided into three cen-tralities: most central 20%, 20 − 40% and 40 − ∼  100%of the hadronic cross section. The average number of binary collisions   N  bin   for each centrality class and forthe combined minimum-bias event sample is derived fromGlauber model calculations and listed in Table I.The TPC and TOFr are two independent systems.In the analysis, hits from particles traversing the TPCwere reconstructed as tracks with well defined geome-try, momentum, and  dE/dx   [26]. The particle trajec-tory was then extended outward to the TOFr detectorplane. Fig. 1 shows inversed velocity (1 /β  ) from TOFrmeasurement as a function of momentum (  p ) calculatedfrom TPC tracking in TOFr triggered d+Au collisions.The raw yields of   π ± ,  K  ± ,  p  and ¯  p  are obtained fromGaussian fits to the distributions in  m 2 =  p 2 (1 /β  2 − 1)in each  p T   bin. For  π ± at  p T   > 1.8 GeV/c, an addi-tional cut on  dE/dx  was applied at 50% efficiency [28].The  dE/dx  distribution was measured by selecting on   -   2    d  y   )   (   G  e   V   /  c   )    T    d  p    T   p -4 10 -3 10 -2 10 -1 101  dAu Minbias-0.5<y<0.0 - π   -  Kp  dAu Minbias-0.5<y<0.0 + π +  K p 0 0.5 1 1.5 2 2.5 3 3.5      π    N   /   (   2    2    d -4 10 -3 10 -2 10 -1 101  pp NSD-0.5<y<0.0 - π -  Kp  (GeV/c) T p 0 0.5 1 1.5 2 2.5 3 3.5 pp NSD-0.5<y<0.0 + π   +  K p FIG. 2: The invariant yields of   π + (filled circles),  K  + (opensquares),  p  (filled triangles) and their anti-particles as a func-tion of   p T   from d+Au and NSD p+p events at 200 GeV. Therapidity range was  − 0 . 5  < y <  0 . 0 with the direction of theoutgoing Au ions as negative rapidity. Errors are statistical. pure pion and proton samples from TOFr. The uncer-tainty of this cut was evaluated by systematically study-ing the yield as a function of the cut. Acceptance andefficiency were studied by Monte Carlo simulations andby matching TPC track and TOFr hits in real data. TPCtracking and MRPC hit matching efficiencies were bothabout 90%. Weak-decay feeddown (e.g.  K  0 s  →  π + π − )to pions is  ∼  12% at  p T   < 1 GeV/c and  ∼  5% at higher  p T  , and was corrected for using PYTHIA [31] and HI-JING [32] simulations. Inclusive  p  and ¯  p  production ispresented without hyperon feeddown correction.  p  and ¯  p from hyperon decays have the same detection efficiencyas primary  p  and ¯  p  [35] and contribute about 20% to theinclusive  p  and ¯  p  yield, as estimated from the simulation.The invariant yields  d 2 N/ (2 πp T  dp T  dy ) of   π ± ,  K  ± ,  p and ¯  p  from both NSD p+p and minimum-bias d+Auevents are shown in Fig. 2. The average bin-to-bin sys-tematic uncertainty was estimated to be of the order of 8%. The systematic uncertainty is dominated by the un-certainty in the detector response in Monte Carlo simu-lations ( ± 7%). The normalization uncertainties in d+Auminimum-bias and p+p NSD collisions are 10% and 14%,respectively [1, 22]. The charged pion yields are consis-tent with  π 0 yields measured by the PHENIX collabora-tion in the overlapping  p T   range [2, 23].Nuclear effects on hadron production in d+Au col-lisions are measured through comparison to the p+pspectrum, scaled by the number of underlying nucleon-nucleon inelastic collisons using the ratio R dAu  =  d 2 N/ (2 πp T  dp T  dy ) T  dAu d 2 σ  ppinel / (2 πp T  dp T  dy ) , where  T  dAu  =   N  bin  /σ  ppinel  describes the nuclear geom-etry, and  d 2 σ  ppinel / (2 πp T  dp T  dy ) for p+p inelastic colli-sions is derived from the measured p+p NSD cross sec-tion. The difference between NSD and inelastic differ-  5    d   A  u    R 0.40.60.811.21.41.61.82dAu Minbias-0.5<y<0.0 π  K p  (GeV/c) T p 0 0.5 1 1.5 2 2.5 30.40.60.811.21.41.61.82dAu 0-20%  (PHENIX) CP Au+Au R 0 π  p FIG. 3: The identified particle  R dAu  for minimum-bias andtop 20% d+Au collisions. The filled triangles are for  p  + ¯  p ,the filled circles are for  π + + π − and the open squares are for K  + + K  − . Dashed lines are  R dAu  of inclusive charged hadronsfrom [22]. The open triangles and open circles are  R CP   of   p +¯  p and  π 0 in Au+Au collisions measured by PHENIX [7]. Errorsare statistical. The gray band represents the normalizationuncertainty of 16%. ential cross sections at mid-rapidity, as estimated fromPYTHIA [31], is 5% at low  p T   and negligible at  p T   >  1 . 0GeV/c. Fig. 3 shows  R dAu  of   π + +  π − ,  K  + +  K  − and  p +¯  p  for minimum-bias and central d+Au collisions. Thesystematic uncertainties on  R dAu  are of the order of 16%,dominated by the uncertainty in normalization. The R dAu  of the same particle species are similar betweenminimum-bias and top 20% d+Au collisions. In bothcases, the  R dAu  of protons rise faster than  R dAu  of pi-ons and kaons. We observe that the spectra of   π ± ,  K  ± ,  p  and ¯  p  are considerably harder in d+Au than those inp+p collisions.The  R dAu  of the identified particles has charactersticsof the Cronin effect [14, 15, 16, 18] in particle produc-tion with  R dAu  less than unity at low  p T   and aboveunity at  p T > ∼ 1 . 0 GeV/c. On the contrary, the  R CP   (nu-clear modification factor between central and peripheralcollisions) of identified particles in Au+Au collisions at √  s NN   = 200 GeV as measured by PHENIX and STARcollaborations [6, 7] do not have the above features. The R CP   of   p + ¯  p  follows binary scaling and that of   π 0 showslarge suppression of meson production in central Au+Aucollisions [7] as depicted in the bottom panel of Fig. 3.It is notable that the  R dAu  of proton and anti-protonare greater than unity in both central and minimum-biasd+Au collisions while the proton and antiproton produc-tion follows binary scaling in all centralities in Au+Aucollisions [7].Fig. 4 depicts (  p +¯  p ) /h , the ratio of protons (  p +¯  p ) overinclusive chargedhadrons ( h ) as a function of   p T   in d+Auand p+p minimum-bias collisions at  √  s NN   = 200 GeV,and Au+Au minimum-bias collisions at  √  s NN   = 130GeV [7]. The systematic uncertainties on these ratioswere estimated to be of the order of 10% for  p T < ∼ 1 . 0 TABLE I:  N  bin  from a Glauber model calculation, (  p +¯  p ) /h averaged over the bins within 1 . 2  < p T   <  2 . 0 GeV/c (leftcolumn) and within 2 . 0  < p T   <  3 . 0 GeV/c (right column)and the  R dAu  ratios between  p + ¯  p  and  h  averaged over 1 . 2  < p T   <  3 . 0 GeV/c for minimum-bias, centrality selected d+Aucollisions and minimum-bias p+p collisions. A p+p inelasticcross section of   σ inel  = 42 mb was used in the calculation.For  R dAu  ratios, only statistical errors are shown and thesystematic uncertainties are 0.03 for all centrality bins.centrality   N  bin   (  p + ¯  p ) /h R p +¯ pdAu /R hdAu min. bias 7 . 5 ± 0 . 4 0 . 21 ± 0 . 01 0 . 24 ± 0 . 01 1 . 19 ± 0 . 050–20% 15 . 0 ± 1 . 1 0 . 21 ± 0 . 01 0 . 24 ± 0 . 02 1 . 18 ± 0 . 0620–40% 10 . 2 ± 1 . 0 0 . 20 ± 0 . 01 0 . 24 ± 0 . 02 1 . 16 ± 0 . 0640– ∼ 100% 4 . 0 +0 . 8 − 0 . 3  0 . 20 ± 0 . 01 0 . 23 ± 0 . 02 1 . 13 ± 0 . 06p+p 1 . 0 0 . 17 ± 0 . 01 0 . 21 ± 0 . 02 — GeV/c, decreasing to 3% at higher  p T  . At RHIC en-ergies, the anti-particle to particle ratios approach unity(¯  p/p  = 0 . 81 ± 0 . 02 ± 0 . 04 in d+Au minimum-bias colli-sions) and their nuclear modification factors are similar.The (  p  + ¯  p ) /h  ratio from minimum-bias Au+Au colli-sions [7] at a similar energy is about a factor of 2 higherthan that in d+Au and p+p collisions for  p T > ∼ 2 . 0 GeV/c.This enhancement is most likely due to final-state effectsin Au+Au collisions [5, 8, 9, 11, 12, 13]. The ratios showlittle centrality dependence in d+Au collisions, as shownin Table I. The identified particle yields can also provideimportant information and constraints for other studieseven when our measurements are in a limited rapidityrange (-0.5 < y < 0.0). Our measurement of (  p  + ¯  p ) /h ratio shows that baryons account for only about 20% of the total inclusive charged hadrons with little central-ity dependence. Therefore, the measurement of rapid-ity asymmetry of inclusive charged hadrons around mid-rapidity by the STAR collaboration [24] is unlikely dueto a change in particle composition or baryon stopping.For  p T   <  2 . 0 GeV/c, the (  p  + ¯  p ) /h  ratio in p + ¯p col-lisions at  √  s NN   = 1 . 8 TeV [36] is very similar to thosein d+Au and p+p collisions at  √  s NN   = 200 GeV. Alsoshown are  p/h + ratios in p+p and p+W minimum-biascollisions at  √  s NN   = 23 . 8 GeV [14, 15]. Although therelative yields of particles and anti-particles are very dif-ferent, the Cronin effects are similar. At  √  s <  40 GeV,there is a general trend of decreasing Cronin effect of allparticles with beam energies at high  p T   [15, 16], however,the Cronin effects of ¯  p  data are less conclusive [16].The difference between  R dAu  at  √  s NN   = 200 GeV for  p  + ¯  p  and  h  can be obtained from the (  p  + ¯  p ) /h  ratiosin d+Au and p+p collisions. Table I shows  R  p +¯  pdAu /R hdAu determined by averaging over the bins within 1 . 2  < p T   < 3 . 0 GeV/c. Alternatively, we can study Cronin effectof the identified particles by comparing the  α  parame-ters of protons and pions. At lower energy, the  α  pa-rameter in the power law dependence on target atomicweight  A α of identified particle production falls with √  s  [15, 16] at high  p T   (  p T   ≃  4 . 6 GeV/c). From theratios of   R dAu  between  p + ¯  p  and  π + + π − , we may fur-
Search
Similar documents
View more...
Tags
Related Search
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks
SAVE OUR EARTH

We need your sign to support Project to invent "SMART AND CONTROLLABLE REFLECTIVE BALLOONS" to cover the Sun and Save Our Earth.

More details...

Sign Now!

We are very appreciated for your Prompt Action!

x