Recent Results from PHOBOS

David Hofman – UIC

For the Collaboration

AGS/RHIC Users MeetingMay 15-16, 2003, BNL

AGS/RHIC Users Meeting 2003 2

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 Hołyński, 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 Woźniak, Alan Wuosmaa, Bolek Wysłouch,

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

Pradeep Sarin

AGS/RHIC Users Meeting 2003 3

The PHOBOS Detector in 2002137000 Silicon Pad Channels

1m

Nearly 4 Coverage

0 +3-3 +5.4-5.4

Octagon

Ring Counters

Spectrometer

ZDC

Triggering

ZDC

AGS/RHIC Users Meeting 2003 4

PHOBOS Data on dN/din Au+Au

vs. Centrality and s

dN

/d

19.6 GeV 130 GeV 200 GeVPHOBOS PHOBOS PHOBOS

Typical systematic band (90%C.L.)

Extensive systematic multiplicity data set.

AGS/RHIC Users Meeting 2003 5

Au+Au

Surprising: ratio of hard/soft collisions is the same.

Charged Particle Production at Midrapidity

Energy and Centrality Dependence

19.6 GeVpreliminary

130 GeV

200 GeVMidrapidity||<1

collpppartpp NxnNnxd

dN )1(

Published at 130 and 200 GeV: PRC 65, 061901(R) (2002); 19.6 GeV in Preparation

dN

ch/d

two component fit with x~ 0.1pp

19.6 GeVpreliminary

130 GeV200 GeV

Data is normalized by corresponding pp value for each energy.

pp

AGS/RHIC Users Meeting 2003 6

Charged Particle Production (dN/d)

Scale by <Npart>/2 & shift to =- ybeam

PHOBOS Au+Au

dN

ch/d

Systematic errors not shown

PHOBOS Au+Au

dN

ch/d

/<

Np

art>

/2

6% central

beamy

p + p inel.

UA5, Z.Phys.C33, 1 (1986)d

N/d

beamy Growth of the Fragmentation Region with sNN

Status: In Print for PRL

AGS/RHIC Users Meeting 2003 7

Centrality dependence of Nch

Error bands due to high- extrapolation

(preliminary)

Total charged particle production ~ Npart and consistent with e+e-

Au+Au

AGS/RHIC Users Meeting 2003 8

Comparison <Nch> vs. Energy

Surprising agreement at high energy

nucl-ex/0301017; Submitted for Publication

AGS/RHIC Users Meeting 2003 9

Preliminary v2200

Final v2130

PHOBOS Au-Au

v 2

200

130

<Npart>~190

Elliptic Flow (v2) at 130 and 200 GeV

PRL 89, 222301

PRELIMINARY 200 GeV results very similar to 130 GeV

130 GeV Data Published in PRL 89, 222301 (2002)

See Poster by Carla Vale for 200 GeV Track-based Results

AGS/RHIC Users Meeting 2003 10

Systematic Errors not shown

Phobos Preliminary

PT Distribution of Charged Particles

Phobos has capabilities to measure from pT, = 0.030 – 5 GeV/c

AGS/RHIC Users Meeting 2003 11

Invariant yields of very low pT particles

(+

+)

(K+

+K–)

(p+p)

PHOBOS preliminary

pT

[GeV/c]

1/

(2p

T)d

2N

/dyd

pT

X[c

m]

ABCDE F

Z[cm]

Beam pipe0

10

20

Z [cm] 0 10 20

→ Mass measurement by ‘energy-range’ method in 5 planes of silicon.

Unique: Can measure down to very low pT.

Status of Experimental Result: In Preparation for Publication

pT = 0.03 – 0.20 GeV/c

AGS/RHIC Users Meeting 2003 12

Interest in RHIC data is extremely high;

Preliminary Data already ‘Published’P. Kolb and R. Rapp; PRC 67 044903

AGS/RHIC Users Meeting 2003 13

Particle Ratios: Energy dependence

p/p

K–/K+

pT = 0.07 – 1.0 GeV/c

PHOBOS 130 GeV

PRL 87,102301,2001

(B~45 MeV)PHOBOS 200 GeV

(B~27 MeV)

Rapidly decreasing net baryon density near midrapidity

200 GeV Result is published: PRC 67, 021901(R) (2003)

A+A central collisions

AGS/RHIC Users Meeting 2003 14

At 200 GeV, minimum bias pp reference data exist for comparison.

Transverse Momentum Distributions for Au+Au @ 200

GeV

0.2<y<1.4

AGS/RHIC Users Meeting 2003 15

Comparing Au+Au spectra to pp

Excess yield at 2 GeV/c BUT, at higher energy the particle yields appear to come back ‘down’ to the pp value.

AGS/RHIC Users Meeting 2003 16

Ratio of Au+Au and pp spectra at 200 GeV

• We observe a significant change in the spectral shape between pp and Au+Au collisions.

• Central Au+Au collisions show an approximate scaling with the number of participants for low and high pT.

mid-peripheral

central

Npart = 65 ± 4

Npart = 344 ± 12

AGS/RHIC Users Meeting 2003 17

Evolution with Centrality (Au+Au)

• Divide spectra by fit to mid-peripheral 45-50% centrality bin.

• Gradual change of shape.

• Peak develops at 1.5 GeV/c.

• Low and high pT ‘matches’ the mid-peripheral yields.

mid-peripheral

centralYie

ld/<

Np

art/2

>/

mid

-per

iph

eral

fit

AGS/RHIC Users Meeting 2003 18

Centrality scaling in pT bins (Au+Au)

• Spectra normalized to a fit at mid-peripheral 45-50% bin.

Over the centrality range studied, for low and high pT, the Au+Au data scale approximately with number of

participants.

nucl-ex/0302015; Submitted for Publication

AGS/RHIC Users Meeting 2003 19

This Year: PHOBOS Detector 2003

Moved TOF walls back ~ 5 m from interaction point

Installed new spectrometer trigger detector that selects on high pT tracks

Installed new “time-zero” (T0) Cerenkov detectors to provide triggering and on-line vertexing as well as a start time for our TOF walls.

Proton calorimeter on Gold and Deuteron “going” sides for dA run

SPECTRIG

T0

T0

mini-pCal

pCal

x15 high pT data

See Poster By C. Henderson, J. Kane and G. Veres

pCal

Sum Energy (a.u.)

See Posters by A. Iordanova and R. Hollis

AGS/RHIC Users Meeting 2003 20

PHOBOS Preliminary Results from d+Au

• Four centrality bins based on energy in our Silicon Ring detectors

0.2<<1.4 Centrality Determination:Energy in Silicon Ring Counters

Energy (arb. units )

Cou

nts

3.0<||<5.4

Transverse Momentum Distributions in d+Au

PHOBOS d+Aupreliminary

0 – 20%

20 – 40%

40 – 70%70 – 100%

AGS/RHIC Users Meeting 2003 21

PHOBOS Preliminary Results from d+Au

PHOBOSpreliminary

PHOBOSpreliminary

PHOBOSpreliminary

PHOBOSpreliminaryR

dA

u Rd

A

u

Yie

ld/<

Np

art/2

>/p

+p

fit

Yie

ld/<

Np

art/2

>/p

+p

fit

peripheral

central

AGS/RHIC Users Meeting 2003 22

Summary and Outlook

• 5 papers (3 published and 2 submitted) since last AGS/RHIC Users’ Meeting.

• 5 additional papers from Au+Au data are in progress.

• First look at new results for d+Au shows qualitatively different features as compared to Au+Au!

• Exciting times at RHIC and PHOBOS. Many thanks to the entire RHIC crew for supplying us the beams.

AGS/RHIC Users Meeting 2003 23

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