# Presentation: 832298

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

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

- September 22, 2003

##                  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

**Notes:**
I am speaking today as a representative of the Phobos collaboration which consists of 60 members from 8 institutions and 3 countries.

## 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
- d+Au and Au+Au ratios comparison
- Model comparison
- Implications of results

## Motivation

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

**Initial State**

**Final State Interactions**

## Centrality Dependence

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

## p/p Ratio vs Centrality

- If the total proton yield is equal to the sum of the transported and produced components 

## PHOBOS Detector 2003

**PHOBOS Detector 2003**

- SPECTRIG

- mini-pCal

- pCal

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

- TOF Walls

**Notes:**
Emphasize spectrometer, magnetic field, octagon, rings, T0’s and paddles

## 			Spectrometer

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

- Reversible 2T magnetic field
- Two symmetric spectrometer arms

- 

- Two independent measurements
- Acceptance and efficiency cancel

**Notes:**
Particles of a given charge in a given magnetic field polarity have the same acceptance and efficiency as do oppositely charged particles in the opposite magnetic field

## Magnetic Field Reversals

- Bending toward beampipe:     	h-B-, h+B+

## Particle Identification

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

## Spectrometer Acceptance

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

**Notes:**
Particles of a given charge in a given polarity bend in the same direction as do oppositly charged particles in the opposite polarity 

## 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%

## 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 <1%
- Pions: total correction <0.5%

## Corrections

- Counts

- dca of track to beam orbit (cm)

- cut position

## 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: < 0.1%

## Trigger Elements

- Normal Trigger: (dAVertex)
- 30M events collected
- required T0 coincidence and |vz|<50cm
- Peripheral Trigger: (dAPeriph)
- 20M events collected
- required dAVertex and Paddle occupancy <50%

- Negative Paddles

- Positive Paddles

- d

- Au

- PP

- PN

- T0N

- T0P

- Positive T0s

- Negative T0s

## Measuring Centrality in d+Au

**Energy (arb. units)**

**Pseudorapidity**

_**Glauber Calculation**_
**Hijing 1.383**
**Hulthen w.f.**
******inelastic**** = 41mb**
**Full GEANT Simulation**

**HIJING Simulation**

**dN/d******

| 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 |

## Particle Ratios vs Centrality

-   Any final state effects in Au+Au collisions do not modify the
-    produced meson yields

-   Au+Au proton ratio is significantly lower than d+Au ratios

-   All d+Au particle ratios appear to be independent of centrality

## Baryon Transport

- d+Au vs Au+Au comparison:
- central d+Au > central Au+Au
- 				BUT !!
- (p/p)central d+Au  > (p/p)central Au+Au
- Relative fraction of transported protons in central d+Au collisions is half that in central Au+Au collisions!

- 

## Model Comparison

-  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

- d+Au

## Conclusions

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

## Backup Slides

## 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 |vz|<50cm
-  dAPeriph: 20M evts; required dAVertex and Paddle occupancy <50%

## 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 |
| Au+Au | 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