ICHEP 2002, AmsterdamGerrit van Nieuwenhuizen/MIT Scaling of Charged Hadron p T distributions in...

ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT

Scaling of Charged Hadron pT distributions in

Au+Au collisions at 200 GeV

Gerrit van NieuwenhuizenMIT

for the PHOBOS Collaboration

ICHEP 2002July 24-31, 2002, Amsterdam


Collaboration

ARGONNE NATIONAL LABORATORYBirger Back, Alan Wuosmaa

BROOKHAVEN NATIONAL LABORATORY Mark Baker, Donald Barton, Alan Carroll, Nigel George, Stephen Gushue, George Heintzelman, Burt Holzman, Robert Pak, Louis Remsberg, Peter Steinberg, Andrei Sukhanov

INSTITUTE OF NUCLEAR PHYSICS, KRAKOWAndrzej Budzanowski, Roman Hołyński, Jerzy Michałowski, Andrzej Olszewski, Pawel Sawicki, Marek Stodulski, Adam Trzupek, Barbara Wosiek, Krzysztof Woźniak

MASSACHUSETTS INSTITUTE OF TECHNOLOGYMaartin Ballintijn, Wit Busza (Spokesperson), Patrick Decowski, Kristjan Gulbrandsen, Conor Henderson, Jay Kane, Judith Katzy, Piotr Kulinich, Jang Woo Lee, Heinz Pernegger, Corey Reed, Christof Roland, Gunther Roland, Leslie Rosenberg, Pradeep Sarin, Stephen Steadman, George Stephans, Carla Vale, Gerrit van Nieuwenhuizen, Gábor Veres, Robin Verdier, Bernard Wadsworth, Bolek Wysłouch

NATIONAL CENTRAL UNIVERSITY, TAIWANChia Ming Kuo, Willis Lin, Jaw-Luen Tang

UNIVERSITY OF ILLINOIS AT CHICAGORussell Betts, Edmundo Garcia, Clive Halliwell, David Hofman, Richard Hollis, Aneta Iordanova, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter, Joe Sagerer

UNIVERSITY OF MARYLANDAbigail Bickley, Richard Bindel, Alice Mignerey,

Marguerite Belt Tonjes

UNIVERSITY OF ROCHESTERJoshua Hamblen, Erik Johnson, Nazim Khan, Steven Manly, Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs


The PHOBOS Apparatus

• 1 Layer 4 Multiplicity Array• Octagonal Barrel + Annular Rings

• 16 Layer 2-Arm Spectrometer

Trigger & Centrality• Paddle Counters• ZDCs

137000 Si Pad Channels


The PHOBOS Spectrometer

z

x

y

70 cm 10cm • Outer layers situated in 2T magnetic field

• High segmentation in bending direction

• Tracking within 10 cm of interaction point

• Coverage near mid-rapidity

• Phi acceptance of 3% per Arm


• Spectra corrected for • Acceptance/Efficiency• Ghost Tracks • Momentum resolution • Variable bin width• Secondaries

• At 200 GeV min. bias. pp reference data exists

PHOBOS-Spectra @ 200GeV

_

0.2<y<1.4


• Production of high pT particles dominated by hard scattering

• High pT yield prop. to Ncoll

(binary collision scaling)

• Compare to pp spectra scaled up by Ncoll

• Violation of Ncoll scaling observed at 130GeV(PHENIX/STAR publications)

• Jet quenching?

Comparing Au+Au and pp Spectra 1_

_Au+Au


Charged Particle Production

Total multiplicity scales with Npart

Total Multiplicity

Preliminary

from Peter Steinbergs talk


Comparing Au+Au and pp Spectra 2_


Scaled Spectra / pp-Fit

• Centrality range: • <b> from 10 to 3 fm• <> from 3 to 6

_

Centrality Npart

45-50% 65 ± 4

35-45% 93 ± 5

25-35% 138 ± 6

15-25% 200 ± 8

6-15% 276 ± 9

0-6% 344 ± 12

PHOBOS Preliminary


• Shape differs from pp already at Npart = 65

• Moderate change from Npart = 65 to Npart =344

Scaled Spectra / pp-Fit _

_

PHOBOS Preliminary


Centrality scaling in pT bins

UA1 200 GeV

Rel

ativ

e Y

ield

Spectra normalized to yield at Npart = 65Npart


Npart scaling describes data at pT = 4.25 GeV/c

Normalized to yield at Npart = 65

Npart Scaling at high pT

Ncoll-scaling

PHOBOS Preliminary


Evolution with Centrality

• Follow change of shape vs most peripheral bin

• Dominantly participant scaling

• Violated by about 30% for most central collisions

PHOBOS


• Measured h+,- pT spectra in 200 GeV Au+Au collisions• pT range: 0.2 < pT < 5 GeV/c

• Rapidity range: 0.2 < y< 1.4

• Centrality range: 65 < Npart < 344

• Data show:• Substantial difference in spectral shape between pp and

peripheral Au+Au (Npart ~ 65)

• Minor change from 65 to 344 participants

• Even at pT of 4 – 5 GeV/c, Npart -scaling from peripheral to central Au+Au

Summary

_


Comparison to Lower Energies

• Data taken at 130GeV shows similar trends

• Shape is consistent with measurements by STAR R

elat

ive

Yie

ld


How to compare spectra to pp?

• Observations:• Mid-rapidity multiplicity compatible with two

component model

• Total multiplicity shows Npart scaling

• How do spectra scale with centrality? • Does scaling change over the pT range?

• Crucial for physics interpretation

_


_pp

Au+Au

19.6 GeVpreliminary

130 GeV

200 GeV

Two Component Model:

Charged Particle Production Central Density

Data from PRC 65 061901R (2002)

collpppartpp NxnNnxd

dN )1(

= N

co

ll/(

Np

art/2

)


Number of collisions at different Energies

inel=42 mb(RHIC)

Glauber Monte Carlo

inel=33 mb (SPS)

inel=21 mb (AGS)


Integrated Yields vs Centrality

dN/d - Multiplicity data

dN/dy – Spectra Integral


Mean pT vs centrality


Centrality scaling in pT bins

UA1 200 GeV

Rel

ativ

e Y

ield

Spectra normalized to FIT to yield at Npart = 65Npart


CorrectionsG

ho

st f

ract

ion

pT [GeV/c] pT [GeV/c]

pT [GeV/c]


Systematic Errors


Triggering on Interactions

t (ns)

Eve

nts

Negative

Paddles

Positive Paddles

ZDC N

ZDC PAu Au

x

z

PPPN

ValidCollision

• Coincidence between

Paddle counters• Paddle + ZDC timing reject

background


Centrality Determination

Data

Paddle signal

Nparticipants

Data+MC

HIJING +GEANT Glauber calculation Model of paddle triggerPeripheral

b

Central

b

2

4

6

x 2


Particle Tracking In Spectrometer1. Road-following algorithm

finds straight tracks in

field-free region

2. The curved tracks in B-

field found by clusters in

(1/p, ) space

3. Find match of straight

and curved by ,

consistency in dE/dx and

fit in yz-plane

4. Covariance matrix track

fit for momentum

reconstruction and ghost

rejection

x10 cm

1

2

By

z

Bea

m


Spectrometer Performance

Data Sample Production Run 2001(200 GeV)• 7.8 M Au+Au Events, Min. Bias Trigger• 32 M reconstructed particles

Acceptance Momentum Resolution

ICHEP 2002, AmsterdamGerrit van Nieuwenhuizen/MIT Scaling of Charged Hadron p T distributions in...

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