ICHEP 2002, AmsterdamGerrit van Nieuwenhuizen/MIT Scaling of Charged Hadron p T distributions in...
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Transcript of 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
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
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
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
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
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
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
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
• 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
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
• 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
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
Charged Particle Production
Total multiplicity scales with Npart
Total Multiplicity
Preliminary
from Peter Steinbergs talk
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
Comparing Au+Au and pp Spectra 2_
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
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
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
• Shape differs from pp already at Npart = 65
• Moderate change from Npart = 65 to Npart =344
Scaled Spectra / pp-Fit _
_
PHOBOS Preliminary
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
Centrality scaling in pT bins
UA1 200 GeV
Rel
ativ
e Y
ield
Spectra normalized to yield at Npart = 65Npart
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
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
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
Evolution with Centrality
• Follow change of shape vs most peripheral bin
• Dominantly participant scaling
• Violated by about 30% for most central collisions
PHOBOS
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
• 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
_
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
Comparison to Lower Energies
• Data taken at 130GeV shows similar trends
• Shape is consistent with measurements by STAR R
elat
ive
Yie
ld
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
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
_
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
_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
)
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
Number of collisions at different Energies
inel=42 mb(RHIC)
Glauber Monte Carlo
inel=33 mb (SPS)
inel=21 mb (AGS)
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
Integrated Yields vs Centrality
dN/d - Multiplicity data
dN/dy – Spectra Integral
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
Mean pT vs centrality
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
Centrality scaling in pT bins
UA1 200 GeV
Rel
ativ
e Y
ield
Spectra normalized to FIT to yield at Npart = 65Npart
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
CorrectionsG
ho
st f
ract
ion
pT [GeV/c] pT [GeV/c]
pT [GeV/c]
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
Systematic Errors
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
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
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
Centrality Determination
Data
Paddle signal
Nparticipants
Data+MC
HIJING +GEANT Glauber calculation Model of paddle triggerPeripheral
b
Central
b
2
4
6
x 2
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
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
ICHEP 2002, Amsterdam Gerrit van Nieuwenhuizen/MIT
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