 Production at forward Rapidity in d+Au Collisions at 200 GeV The STAR Forward TPCs Lambda Reconstruction Lambda Spectra & Yields Centrality Dependence Summary Frank Simon, MPI Munich, Germany for the STAR collaboration SQM 2004, September , 2004, Cape Town, South Africa Outline

 Production at forward Rapidity in d+Au Collisions at 200 GeV Frank Simon The Solenoidal Tracker At RHIC Au d West East

 Production at forward Rapidity in d+Au Collisions at 200 GeV Frank Simon The STAR FTPCs coverage 2.5 < |  | < FTPCs in STAR 10 rows per detector 960 pads per row => channels inner radius 8 cm, outer radius 30 cm 150 cm < |z| < 270 cm true radial electron drift magnetic field 0.5 T: tracking with momentum and charge determination no particle ID from dE/dx (maximum 10 points on track), momentum resolution ~ 15%

 Production at forward Rapidity in d+Au Collisions at 200 GeV Frank Simon Why go forward? Why d+Au? Anti-  /  ratio < 1 at mid- rapidity (0.84 ± 0.05): Indicative of stopping Forward rapidity: Sensitive to baryon transport Asymmetry in d+Au collisions: Probe normally dense and cold medium on the Au side Multiple collisions of two constituents on deuteron side PHOBOS d+Au minbias, PRL 93, (2004) ~ 25 tracks~ 10 tracks Aud

 Production at forward Rapidity in d+Au Collisions at 200 GeV Frank Simon Forward  s: Signal Extraction Identification of  candidates (V0) by searching for a possible secondary vertex of a positive/negative pair Apply geometric cuts on pairs to reduce combinatoric background: separation of tracks (daughter dca) < 0.25 cm Proton dca < 2 cm Pion dca > 2.5 cm/ 3 cm dca of resulting  candidate < 1 cm decay length > 5 cm main vertexdecay vertex

 Production at forward Rapidity in d+Au Collisions at 200 GeV Frank Simon Acceptance for  candidates Acceptance as a function of y and p t Rapidity is the relevant physical variable Selected rapidity window 2.75 ± 0.25

 Production at forward Rapidity in d+Au Collisions at 200 GeV Frank Simon Forward  s: Signal and Background , GeV/c 2, BR 64% p    36% n    c  ~ 7.8 cm) No particle ID: K 0 s are the major source of background, contribution taken from HIJING simulations, K 0 s analysis feasible Signal shape is reproduced by simulations , FTPC d background subtraction

 Production at forward Rapidity in d+Au Collisions at 200 GeV Frank Simon Invariant Mass Background subtracted invariant mass for  and Anti-  in both detectors Slight shift to lower mass (about 5 MeV/c 2 ) for FTPC Au, probably due to residual background at low p t

 Production at forward Rapidity in d+Au Collisions at 200 GeV Frank Simon Corrections Efficiency & Acceptance Determined by embedding  s in d+Au events, and running those through the analysis code Efficiency for primary  s ~ 4% Feed down from particle decays  0 -> , BR ~100%: Cannot be resolved, so  s from  0 decays are included in primary  s  - ->  , BR ~ 100%: Measured at mid-rapidity  0 ->  , BR ~100%: Not measured, but the yield is assumed to be the same as for  - It is assumed that the ratio  does not change with rapidity

 Production at forward Rapidity in d+Au Collisions at 200 GeV Frank Simon Minimum Bias Spectra Yield and inverse slope determined from m t exponential fit 65% of the total yield covered Problematic first bin on FTPC Au, background & efficiency problems Temperature parameter Deuteron side  : 241 ± 4 (stat) ± 11 (syst) MeV d side Anti-  : 242 ± 5 (stat) ± 15 (syst) MeV Au side  : 232 ± 5 (stat) ± (syst) MeV Au side Anti-  : 210 ± 4 (stat) ± (syst) MeV

 Production at forward Rapidity in d+Au Collisions at 200 GeV Frank Simon Anti-  and  yields Anti-  consistent for all models  more tricky: Two production mechanisms, associated production NN ->  K N and pair production NN -> NN  Anti-  Baryon transport through multiple collisions and rescattering

 Production at forward Rapidity in d+Au Collisions at 200 GeV Frank Simon peripheral (40% - 100%) Deuteron side  : 232 ± 5 (stat) ± 10 (syst) MeV Au side  : 232 ± 7 (stat) ± (syst) MeV mid-central (20% - 40%) Deuteron side  : 239 ± 6 (stat) ± 15 (syst) MeV Au side  : 232 ± 6 (stat) ± (syst) MeV central (top 20%) Deuteron side  : 257 ± 6 (stat) ± 13 (syst) MeV Au side  : 233 ± 6 (stat) ± (syst) MeV Centrality Dependence Yield increases by a factor of 2.4 on the d and by a factor of 6 on Au side Temperature parameter on the d side increases with centrality Temperature parameter:

 Production at forward Rapidity in d+Au Collisions at 200 GeV Frank Simon Centrality: Temperature Parameter Increase of the temperature parameter on the West side with increasing centrality due to higher number of collisions of the deuteron nucleons Significant:  2 /ndf for linear rise: 1.2, for constant: 5.2

 Production at forward Rapidity in d+Au Collisions at 200 GeV Frank Simon Centrality: Yield Comparison to HIJING Asymmetry increases with centrality The majority of the events in the most peripheral bin have one spectator nucleon from the d

 Production at forward Rapidity in d+Au Collisions at 200 GeV Frank Simon Net  Anti  Only associated production/baryon transport, very low at mid- rapidity Even on Au side: baryon transport over more than 2 units in rapidity minbias Aud

 Production at forward Rapidity in d+Au Collisions at 200 GeV Frank Simon Model Comparisons Deuteron side well described by HIJING/BbarB, EPOS, AMPT Gold side well described by EPOS and AMPT On the Au side, hadronic transport is necessary to reproduce the data, HIJING plus additional baryon transport by junctions is not sufficient Thanks to L.W. Chen, C.M. Ko, Z.W. Lin, V. Topor-Pop, K. Werner for help, results and discussions

 Production at forward Rapidity in d+Au Collisions at 200 GeV Frank Simon Anti-  /  Ratio Asymmetry d/Au side: Nucleons from the deuteron suffer multiple collisions, more baryon transport Less transport on the Au side, each Au nucleon participates only in one collision, but additional rescattering causes transport minbias Aud

 Production at forward Rapidity in d+Au Collisions at 200 GeV Frank Simon Summary Forward  production in d+Au collisions at RHIC as signal to investigate stopping Asymmetry of d+Au: Multiple collisions of the two deuteron constituents while each participating gold nucleon is involved only once Anti-  /  shows strong contributions from baryon transport, more pronounced on the deuteron side Hadronic rescattering phase on the gold side The centrality dependence of the temperature parameter in agreement the multiple collision picture