Results from the

Experiment at RHIC

Abigail BickleyUniversity of Maryland

For the Collaboration

Topics in Heavy Ion CollisionsJune 25-28, 2003, Montreal

Collaboration (May 2003)

Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Bruce Becker, Russell Betts,

Abigail Bickley, Richard Bindel, Andrzej Budzanowski, 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, Aaron Noell, Rachid Nouicer, Andrzej Olszewski,

Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Louis Remsberg, Christof Roland,

Gunther Roland, Joe Sagerer, Pradeep Sarin, Pawel Sawicki, Iouri Sedykh, Wojtek Skulski,

Chadd Smith, Peter Steinberg, George Stephans, Andrei Sukhanov, Ray Teng,

Marguerite Belt Tonjes, Adam Trzupek, Carla Vale, Robin Verdier, Gábor Veres, Bernard

Wadsworth, Frank Wolfs, Barbara Wosiek, Krzysztof Wozniak, Alan Wuosmaa, Bolek Wyslouch,

Jinlong Zhang

ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORYINSTITUTE OF NUCLEAR PHYSICS, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGYNATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGO

UNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER

PHOBOS Detector in 2002

(12m)

Broad Capabilities of the Phobos Spectrometer

• Low pT: PID

– Stopping in Si (pT<0.2 GeV/c)

– dE/dx versus p (pT<1GeV/c)• Particle Ratios (Au+Au)

• High pT: Non-PID– Charged particle spectra

• Au+Au compared to d+Au

Particle Identification

Based on dE/dx measurements in Si sensors

Au+Au Au+Aup

k

π

Particle Ratios: Energy Dependence

p/p

K–/K+

pT = 0.07 – 1.0 GeV/c

PHOBOS 130 GeV PRL 87, 102301, 2001

PHOBOS 200 GeV PRC 67, 021901(R), 2003

At RHIC see a rapidly decreasing net baryon density near midrapidity.

A+A central collisions

K-/K+

€

p p

Energy evolution of BUsing measured <K–>/<K+>,<p>/<p> and statistical model

of F. Becattini et al., (PRC64,024901,2001) with Tch 160 – 170 MeV

Estimated baryochemical potential at sNN = 200 GeV: B = 26 2 MeV

Fit:P.Braun-MunzingerNP. A697, 902, 2002.

Centrality and pT dependence

Ratios are independent of pT and Npart

PHOBOS preliminary

Au+Au 200 GeV

10% most central

p/p

K–/K+

/+

PHOBOS preliminary

p/p

K–/K+

/+

Systematic Errors not shown

Phobos Preliminary

PT Distribution of Charged Particles

Particle ratios dominated by particles with pT<1GeV/c; “Soft” part of spectrumWhat about high pT particle production? Look at the “Hard” part of the spectrum.

65 ± 4

93 ± 5

138 ± 6

200 ± 8

276 ± 9

344 ± 12<Npart>

45-50%

35-45%

25-35%

15-25%

6-15%

0-6%

Centrality

Transverse Momentum Distributionsfor Au+Au @ 200 GeV

0.2<y <1.4

nucl-ex/0302015: Submitted to Phys Lett B

Ratio of Au+Au and pp Spectra at 200 GeV

• Observe a significant change in the spectral shape between pp and Au+Au collisions already for mid-peripheral events.

• Central Au+Au collisions show a strong violation of (expected) collision scaling at high pT.

mid-peripheral

central

Npart = 65 ± 4

Npart = 344 ± 12

pp from UA1: Nucl.Phys.B335, (1990) 261.

Transverse Momentum Distributionsfor d+Au @ 200 GeV

0.2<<1.4

Centrality Determination:Energy in Silicon Ring Counters

Energy (arb. units )

Cou

nts

3.0<||<5.4

Transverse Momentum Distributions

0 – 20%

20 – 40%

40 – 70%70 – 100%

3.3 ± 1.0

6.7 ± 0.9

10.9 ± 0.915.5 ± 1.0

<Npart>

70-100%

40-70%

20-40%

0-20%Centrality

nucl-ex/0306025: Submitted to PRL

pp from UA1:Nucl.Phys.B335,

(1990) 261

Phobos d+Au Results

€

dAuR =σ

pp inel

< collN >

dAud2NTdp dη

d2σ (UA1)pp

Tdp dηPHOBOS d+Au: nucl-ex/0306025

central Au+Au

Spectrometer Results

• Low Pt– Au+Au particle ratios: show that a net baryon free

region is being approached at RHIC

• High Pt– Au+Au spectra: central spectrum shows strong

suppression relative to collision scaling– d+Au spectra: suppression observed in Au+Au

spectra is not due to initial state effects