production at forward rapidity in d+au collisions at 200 gev the star forward tpcs lambda...

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, Germanyfor the STAR collaboration

SQM 2004, September 15 - 20, 2004, Cape Town, South Africa

Outline

16.09.2004 Production at forward Rapidity in d+Au Collisions at 200 GeVFrank Simon 2

The Solenoidal Tracker At RHIC

Au

d

West

East


The STAR FTPCs

coverage 2.5 < || < 4.0

2 FTPCs in STAR 10 rows per detector 960 pads per row => 19200 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%


Why go forward? Why d+Au?Anti- / ratio < 1 at mid-rapidity (0.84 ± 0.05): Indicative of stoppingForward 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, 082301 (2004)

~ 25 tracks ~ 10 tracks

Au d


Forward s: Signal ExtractionIdentification of candidates (V0) by searching for a possible secondary vertex of a positive/negative pairApply geometric cuts on pairs to reduce combinatoric background:

separation of tracks (daughter dca) < 0.25 cmProton dca < 2 cmPion dca > 2.5 cm/ 3 cmdca of resulting candidate < 1 cmdecay length > 5 cm

main vertex decay vertex

daughter dca

pion dca

V0 dca

proton dca

pion

proton

candidate

d e c a y l e n g t h

prim ary vertex decay vertex


Acceptance for candidates

Acceptance as a function of y and pt

Rapidity is the relevant physical variable

Selected rapidity window 2.75 ± 0.25


Forward s: Signal and Background

, 1.116 GeV/c2, BR 64% p 36% nc~ 7.8 cm)No particle ID: K0s are the major source of background, contribution taken from HIJING simulations, K0s analysis feasibleSignal shape is reproduced by simulations

, FTPC d

background

subtraction


Invariant Mass

Background subtracted invariant mass for and Anti- in both detectorsSlight shift to lower mass (about 5 MeV/c2) for FTPC Au, probably due to residual background at low pt


Corrections

Efficiency & AcceptanceDetermined by embedding s in d+Au events, and running those through the analysis codeEfficiency for primary s ~ 4%

Feed down from particle decays0 -> , BR ~100%: Cannot be resolved, so s from 0 decays are included in primary s- -> , BR ~ 100%: Measured at mid-rapidity0 -> , 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


Minimum Bias Spectra

Yield and inverse slope determined from mt exponential fit

65% of the total yield coveredProblematic first bin on FTPC Au, background & efficiency problems

Temperature parameter

Deuteron side : 241 ± 4 (stat) ± 11 (syst) MeVd side Anti-:242 ± 5 (stat) ± 15 (syst) MeV

Au side : 232 ± 5 (stat) ± 14 + 18 (syst) MeV Au side Anti-: 210 ± 4 (stat) ± 14 + 23 (syst) MeV


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


peripheral (40% - 100%)

Deuteron side : 232 ± 5 (stat) ± 10 (syst)

MeV

Au side : 232 ± 7 (stat) ± 14 + 18 (syst) MeV

mid-central (20% - 40%)


MeV


central (top 20%)


MeV


Centrality Dependence

Yield increases by a factor of 2.4 on the d and by a factor of 6 on Au sideTemperature parameter on the d side increases with centrality

Temperature parameter:


Centrality: Temperature Parameter

Increase of the temperature parameter on the West side with increasing centrality due to higher number of collisions of the deuteron nucleonsSignificant: 2/ndf for linear rise: 1.2, for constant: 5.2


Centrality: Yield

Comparison to HIJING Asymmetry increases with centralityThe majority of the events in the most peripheral bin have one spectator nucleon from the d


Net Anti

Only associated production/baryon transport, very low at mid-rapidityEven on Au side: baryon transport over more than 2 units in rapidity

minbias

Au d


Model Comparisons

Deuteron side well described by HIJING/BbarB, EPOS, AMPTGold 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


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

Au d


SummaryForward 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

production at forward rapidity in d+au collisions at 200 gev the star forward tpcs lambda...

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