Analysis of fixed target collisions with the STAR detector

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1 Analysis of fixed target collisions with the STAR detector Brooke Haag for the STAR Collaboration Hartnell College / University of California, Davis Presented at the Meeting of the California Section of the APS November 11, 2011

2 Creating mini-big bangs in the laboratory Goal: Use relativistic collisions of nuclei to create hot dense matter which reproduces the earliest stages of the universe ions about to collide ion collision 2 plasma creation hadron production

3 QCD phase diagram Temperature#(MeV)# 300# 200# 100# 0# 0# 200#GeV# 62.4#GeV# 39#GeV# 27#GeV# 19.6#GeV# Kine;c#FreezeEout# Hadronic#Gas# 11.5#GeV# 7.7#GeV# QuarkEGluon#Plasma# 250# 500# 750# 1000# Baryon#Chemical#Poten;al#µ B# (MeV)# Color## Super# conductor# We have created a new state of matter consistent with the QGP! In 2010 (and continuing through 2011) an extensive beam energy scan was undertaken at RHIC with a major goal to find the critical point. Fixed target collisions could extend the physics analysis to even lower s. 3

4 STAR has fixed target events gold beam ions collide with aluminum beam pipe atoms the events are asymmetrical acceptance is not optimal... 4

5 STAR detector array η=1.0 η=1.5 η=2.0 blue tracks = non central beampipe event Al Beam Pipe Be Beam Pipe Al Beam Pipe 5

6 Collision Energy (GeV) 19.6 Au+Au 11.5 Au+Au 7.7 Au+Au Kinematic Calculations Single Beam Energy (snn) = center of mass energy Single Beam Pz (GeV/c) Fixed Target s 4.47 Au+Al 3.53 Au+Al 2.99 Au+Al Single Beam Rapidity (snn) = (2m 2 + 2Em) m = GeV/c 2 ; E = 9.8 GeV (snn) = 4.47 GeV pz = (E 2 m 2 ) = 9.76 GeV/c Center of Mass Rapidity rapidity (y) ybeam = 0.5*[ln(E + pz)/(e pz)] ybeam = 3.0 ycm = 1.5 6

7 zvertex > 100 cm Event Selection Run AuAu collider data Au+Al (snn) = 4.5 GeV 137k events pass selection cuts from 146 M total events pion multiplicity > 10 zvertex > 100 cm 5 cm > rvertex > 2 cm centrality definition underway 7 Vy primary vertex y-position cm > rvertex > 2 cm Vx primary vertex x-position

8 Particle identification via de/dx negative particles positive particles de/dx de/dx de/dx de/dx He π 10 π d p p 0 p (GeV/c) κ t p (GeV/c) de/dx from beampipe events as per selection criteria in slide 8 particle bands are well separated 2 p

9 π spectra comparisons STAR Preliminary uncorrected STAR data points E895 PRC68, (2003) slopes of π spectra STAR data, AGS data, and UrQMD compare reasonably AGS yields are predictably above STAR for Au+Au (AGS) vs. Au+Al (STAR) 9

10 π + /π yield ratios Net positive charge in the collision zone expanding spherical source effective potential - + / Extracted parameters include initial ratio R and the full coloumb potential Vc STAR PRELIMINARY Coloumb potential (Vc) of the source modifies momentum distribution greater effect for low momentum π R primordial ratio from initial yields, unmodified by the coloumb source STAR Au+Al 8 AGeV y ycm < 0.1 E895 Au+Au 8 AGeV y ycm < 0.05 E866 Au+Au 10 AGeV y ycm < m T -m (GeV/c ) Coulomb Poten,al (Vc in MV): E895: / E866: / Au+Al: / Ra,os: E895: / E866: / Au+Al: /

11 Conclusions and Outlook We can do physics with STAR as a fixed target experiment! We have been able to extract pion spectra for fixed target collisions at lab rapidity working to understand detector efficiency at high rapidities via simulated events checking pion contamination, stability of multiplicity as a function of zvertex Yields and slopes compare favorably with published data in this energy range We can extend the search for the critical point to lower energies We have more fixed target data at (snn) of 3.0 and 3.5 GeV 11

12 Backup Slides 12

13 Source'Coulomb'Poten/al' Ra/o'as'a'func/on'of'transverse'kine/c'' energy'with'transformed'bde'distribu/on' Jacobian'of'the'transforma/on' Effec/ve'Coulomb'poten/al'accoun/ng'for'the' reduced'charge'seen'by'low'momentum'π' Maximum'kine/c'energy'of' the'corresponding'π'velocity' Net'posi/ve'charge'in'the'collision'zone' Expanding'spherical'source'!'effec/ve'poten/al' Coulomb'poten/al'(V c )'of'the'source'modifies'momentum'distribu/on' Greater'effect'for'lowDmomentum'π'' R' 'primordial'ra/o'from'ini/al'yields,'unmodified'by'the'coulomb'source' Extracted'parameters'include'ini/al'ra/o'R'and'the'full'coulomb'poten/al'V c' 13

14 π + /π yield ratios fit parameters - + / STAR PRELIMINARY STAR Au+Al 8 AGeV E895 Au+Au 8 AGeV E866 Au+Au 10 AGeV m T -m (GeV/c ) Coulomb Poten,al: E895: / E866: / Au+Al: / Ra,os: E895: / E866: / Au+Al: / EXT PARAMETER STEP FIRST NO. NAME VALUE ERROR SIZE DERIVATIVE 1 p e e e e-04 2 p e e e e-05 3 p e-01 fixed 4 p e+00 fixed 5 p e-01 fixed E866 Chi^ EXT PARAMETER STEP FIRST NO. NAME VALUE ERROR SIZE DERIVATIVE 1 p e e e e-05 2 p e e e e-07 3 p e-02 fixed 4 p e+00 fixed 5 p e-01 fixed E895 Chi^ EXT PARAMETER STEP FIRST NO. NAME VALUE ERROR SIZE DERIVATIVE 1 p e e e e-04 2 p e e e e-06 3 p e-02 fixed 4 p e+00 fixed 5 p e-01 fixed STAR Au+Al Chi^

15 The Basics matter in the universe is made of atoms nucleus = protons + neutrons proton nucleons are hadrons (made of quarks) mesons = 2 quarks baryons = 3 quarks 15

16 π spectra STAR Preliminary 16