Centrality Dependence of Charged Antiparticle to Particle Ratios Near Mid-Rapidity in d Au Collisions at vsNN = 200 GeV

1
Centrality Dependence of Charged Antiparticle to
Particle Ratios Near Mid-Rapidity in dAu
Collisions at vsNN 200 GeV

• Abigail Bickley
• Univ. of Maryland, Chemistry Dept.
• for the
• Collaboration

September 22, 2003
2
Collaboration
Birger Back, Mark Baker, Maarten Ballintijn,
Donald Barton, Bruce Becker, Russell Betts,
Abigail Bickley, Richard Bindel, Wit Busza
(Spokesperson), Alan Carroll, Patrick Decowski,
Edmundo Garcia, Tomasz Gburek, Nigel George,
Kristjan Gulbrandsen, Stephen Gushue, Clive
Halliwell, Joshua Hamblen, Adam Harrington, Conor
Henderson, David Hofman, Richard Hollis, Roman
Holynski, Burt Holzman, Aneta Iordanova, Erik
Johnson, Jay Kane, Nazim Khan, Piotr Kulinich,
Chia Ming Kuo, Jang Woo Lee, Willis Lin, Steven
Manly, Alice Mignerey, Gerrit van Nieuwenhuizen,
Rachid Nouicer, Andrzej Olszewski, Robert Pak,
Inkyu Park, Heinz Pernegger, Corey Reed,
Christof Roland, Gunther Roland, Joe Sagerer,
Pradeep Sarin, Iouri Sedykh, Wojtek Skulski,
Chadd Smith, Peter Steinberg, George Stephans,
Andrei Sukhanov, Marguerite Belt Tonjes, Adam
Trzupek, Carla Vale, Robin Verdier, Gábor Veres,
Frank Wolfs, Barbara Wosiek, Krzysztof Wozniak,
Alan Wuosmaa, Bolek Wyslouch, Jinlong Zhang
ARGONNE NATIONAL LABORATORY BROOKHAVEN
NATIONAL LABORATORY INSTITUTE OF NUCLEAR
PHYSICS, KRAKOW MASSACHUSETTS INSTITUTE OF
TECHNOLOGY NATIONAL CENTRAL UNIVERSITY,
TAIWAN UNIVERSITY OF ILLINOIS AT
CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF
ROCHESTER
3
Outline

• Motivation
• Specifics of the detector
• Changes implemented for Run 2003
• Spectrometer acceptance
• Analysis details
• Particle identification
• Corrections systematic errors
• Centrality determination
• Final ratios vs Centrality
• dAu and AuAu ratios comparison
• Model comparison
• Implications of results

4
Motivation
Initial State
Final State Interactions

• In dAu collisions little reinteraction is
  expected thus the ratios should reflect the
  initially produced yields
• Recent results suggest conditions in AuAu
  collisions are different than those observed in
  dAu collisions
• Do these different conditions influence the
  measured particle ratios?

5
Centrality Dependence

• The more collisions a participating nucleon
  suffers the greater the baryon number transport
  to mid-rapidity

6
?p?/p Ratio vs Centrality

• If the total proton yield is equal to the sum of
  the transported and produced components ?

7
PHOBOS Detector 2003
TOF Walls
mini-pCal
SPECTRIG

• New T0 Cerenkov detectors
• DAQ upgrade (x10)
• Forward proton calorimeters
• Moved TOF walls back
• New on-line high pT Spectrometer Trigger

pCal
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Spectrometer
?

• Reversible 2T magnetic field
• Two symmetric spectrometer arms

• Two independent measurements
• Acceptance and efficiency cancel

• Proximity to interaction point reduces
  secondaries and feed-down products
• Particle tracking expanded to include outer
  spectrometer wing ? results in extended
  acceptance

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Magnetic Field Reversals

• Bending toward beampipe h-B-, hB

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Particle Identification

• Cut bands lie 3 RMS deviations from the expected
  mean
• Cutoffs minimize contamination from other
  particle species

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Spectrometer Acceptance

• Contours represent where the acceptance has
  fallen to 10 of the maximal value

12
Raw Ratios Acceptance Corrected

• Assumptions the following must be the same for
  antiparticles and particles for each bending
  direction and centrality bin
• Acceptance and tracking efficiency
• Field strength (B/B-) agree within 0.2
• Centrality Fractions (ERing) agree within 1
• Kinematic distributions
• ?pT?, ?pT2? and ?y? agree within 2

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Corrections

• Protons
• Absorption ? 3.5 1.4 (syst.)
• Secondary ? 1.6 0.3 (stat.) 0.2 (syst.)
• Feed-down ? -0.5 1 (syst.)
• Kaons total correction lt1
• Pions total correction lt0.5

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Corrections
Counts
cut position
dca of track to beam orbit (cm)
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Systematic Uncertainties

• Kaon and Proton Ratios
• Centrality Measure 2
• Kinematic Acceptance (pT and y) 1
• Proton Ratios
• Dead hot spectrometer channels 0.5
• Spectrometer arm asymmetries 1
• Polarity-dependent vertex correction 1
• Pion Ratios
• Electron Contamination lt 0.1

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Trigger Elements
Negative Paddles
Positive Paddles
Positive T0s
Negative T0s
d
Au
PN
T0N
T0P
PP

• Normal Trigger (dAVertex)
• 30M events collected
• required T0 coincidence and vzlt50cm
• Peripheral Trigger (dAPeriph)
• 20M events collected
• required dAVertex and Paddle occupancy lt50

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Measuring Centrality in dAu
HIJING Simulation
dN/dh
Energy (arb. units)
Pseudorapidity
Trigger Centrality ?Ncoll? ??? ???
dAVertex 60-100 2.9(1.7) 2.2(1.3) 0.20
dAVertex 30-60 7.0(3.0) 4.0(1.8) 0.61
dAVertex 10-30 12(3.6) 6.1(1.8) 0.78
dAVertex 0-10 16(4.0) 8.1(2.0) 0.84
dAPeriph 60-100 2.8(1.7) 2.2(1.3) 0.18
dAPeriph 30-60 6.2(2.7) 3.7(1.6) 0.24

• Glauber Calculation
• Hijing 1.383
• Hulthen w.f.
• ?inelastic 41mb
• Full GEANT Simulation

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Particle Ratios vs Centrality

• Any final state effects in AuAu collisions do
  not modify the
• produced meson yields

• AuAu proton ratio is significantly lower than
  dAu ratios

• All dAu particle ratios appear to be
  independent of centrality

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Baryon Transport
?

• dAu vs AuAu comparison
• ?central dAu gt ?central AuAu
• BUT !!
• (p/p)central dAu gt (p/p)central AuAu
• Relative fraction of transported protons in
  central dAu collisions is half that in central
  AuAu collisions!

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Model Comparison
dAu

• Models agree with the expectation that baryon
  transport increases
• with increasing ? thus resulting in a decreased
  ?p/p? ratio
• Data does not exhibit this behavior

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Conclusions

• dAu and AuAu ? and K ratios are consistent ?
  any final state interactions in AuAu
  collisions do not modify the ratio of initially
  produced meson yields
• Relative fraction of transported protons in
  central dAu half that in central AuAu
  collisions ? may be evidence
  of collective behavior in AuAu collisions that
  affects baryons
• dAu particle-antiparticle ratios show a
  surprising lack of centrality dependence
• Results are in clear disagreement with AMPT,
  HIJING and RQMD predictions
• nucl-ex/0309013

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Backup Slides
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Raw Particle Yields
Trigger Centrality Evts (M) ?- ? K- K p p Evt(M) ?- ? K- K p p
dAVertex 60-100 1.0 2787 13879 163 537 310 556 1.1 15320 3087 524 157 543 421
dAVertex 30-60 2.9 14963 74941 824 2732 1604 3494 3.1 81368 16164 2930 1011 2998 2282
dAVertex 10-30 2.4 19663 95755 1113 3660 2198 4558 2.6 103027 20641 3780 1237 3824 2903
dAVertex 0-10 1.3 13628 64357 803 2497 1549 3077 1.4 69664 14303 2675 864 2649 1958
dAPeriph 60-100 3.0 8255 40530 455 1416 866 1841 3.2 42931 8797 1509 461 1564 1085
dAPeriph 30-60 3.0 13666 65799 737 2353 1461 3182 3.3 71542 14435 2449 821 2707 2009

• dAVertex 30M evts required T0 coincidence and
  vzlt50cm
• dAPeriph 20M evts required dAVertex and Paddle
  occupancy lt50

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Final Particle Ratios
Trigger Centrality ??? ?? -?/?? ? ?K -?/?K ? ?p?/?p?
dAVertex 60-100 2.2 (1.3) 0.995?0.015?0.017 0.97?0.07?0.03 0.84?0.04?0.04
dAVertex 30-60 4.0 (1.8) 1.004?0.007?0.017 0.95?0.03?0.03 0.80?0.02?0.03
dAVertex 10-30 6.1 (1.8) 1.008?0.006?0.017 0.97?0.02?0.03 0.83?0.02?0.03
dAVertex 0-10 8.1 (2.0) 1.016?0.007?0.017 0.97?0.03?0.03 0.86?0.02?0.03
dAPeriph 60-100 2.2 (1.3) 0.996?0.008?0.017 1.02?0.04?0.04 0.86?0.03?0.03
dAPeriph 30-60 3.7 (1.6) 1.014?0.007?0.017 0.97?0.03?0.04 0.82?0.02?0.03
AuAu 0-12 5.2 1.025?0.006?0.018 0.95?0.03?0.03 0.73?0.02?0.03
Superscript statistical uncertainty
Subscript systematic uncertainty