results from phobos at rhic david hofman university of illinois at chicago for the collaboration...
TRANSCRIPT
Results from PHOBOS at RHICDavid Hofman
University of Illinois at Chicago
For the Collaboration
European Physical SocietyHEP2005 International Europhysics Conference
on High Energy Physics EPS (July 21st-27th 2005) in Lisbon, Portugal
HEP2005 2
What PHOBOS has studied so far…
• Relativistic Heavy Ion Collisions of – Au+Au
• √sNN = 19.6, 55.9, 62.4, 130.4 200.0 GeV
– Coming soon: • Cu+Cu (√sNN = 22.5, 62.4 and 200.0 GeV)
• “Benchmark” Collisions of – d+Au
• √sNN = 200.7 GeV
– Coming soon: • p+p (√sNN = 200, 410 GeV)
HEP2005 3
What PHOBOS has measured so far…
• Centrality dependence of primary charged particle production vs.– (dN/d out to |<5.4)
– – R (flow)
– pT (0.2 – ~5 GeV/c)
• Identified charged particles– antiparticle/particle ratios
– low pT yields of ,K,p (0.03 – 0.2 GeV/c)
– Spectra for pT = 0.3 – ~4 GeV/c
HEP2005 4
What PHOBOS has observed so far…
• We have created a state of matter at RHIC with high energy-density, that is nearly net-baryon free and interacting very strongly.
• Transition to this high-energy state of matter does not create abrupt changes in observables at RHIC energies.
• The data exhibit many “simple” scaling behaviors.
• The data exhibit a remarkable factorization of collision energy and geometry.
“White Paper”: nucl-ex/0410022, Nucl. Phys. A 757, 28
HEP2005 5
The Collaboration (June 2005)
Burak Alver, Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Richard
Bindel, Wit Busza (Spokesperson), Zhengwei Chai, Vasundhara Chetluru, Edmundo García,
Tomasz Gburek, Kristjan Gulbrandsen, Clive Halliwell, Joshua Hamblen, Ian Harnarine, Conor
Henderson,
David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Jay Kane,
Piotr Kulinich, Chia Ming Kuo, Wei Li, Willis Lin, Steven Manly, Alice Mignerey,
Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Corey Reed,
Eric Richardson, Christof Roland, Gunther Roland, Joe Sagerer, Iouri Sedykh, Chadd Smith,
Maciej Stankiewicz, Peter Steinberg, George Stephans, Andrei Sukhanov, Artur Szostak,
Marguerite Belt Tonjes, Adam Trzupek, Sergei Vaurynovich, Robin Verdier, Gábor Veres,
Peter Walters, Edward Wenger, Donald Willhelm, Frank Wolfs, Barbara Wosiek, Krzysztof
Woźniak, Shaun Wyngaardt, Bolek Wysłouch
ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORYINSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY
NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGOUNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER
HEP2005 6
The PHOBOS Detector (2005)
NIM A 499 (2003) 603
TOF
T0 Trigger Counter
• Triggering & Centrality Determination• 4- Multiplicity Detector• Magnetic Spectrometer + ToF
Spectrometer
pCAL
Paddle Trigger Counter
SpecTrig
ZDC
Vertex
Octagon Rings
SpecCal
Properties of this “State of Matter”
HEP2005 8
High Energy Density & Approaching a Baryon-Free Environment
PHOBOS nucl-ex/0405003Energy Density Estimate:
Largest Uncertainty is the Time to Equilibration.
Conservative estimates put eq ~ 2 fm/c & RHIC > 3 GeV/fm3
Energy Density ~6x energy density inside nucleons (20x for nuclei)
B ~ 27 MeV at full RHIC energy, a factor ~10x smaller than at SPS.
Particle Ratios:
Approaching Unity
PHOBOS PRC 67, 021901R
HEP2005 9
Strongly Interacting Matter
• Elliptic flow reaches hydro limit• Suppressed high-pT production• No enhanced low-pT production
PHOBOS nucl-ex/0407012
FLOW
PHOBOS PRC 70, 051901(R)low-pT
00
0.5
1.0
1.5
RA
A, R
dA
u
Au+Au 0-6%
d+Au 0-20%
high-pT PHOBOS PRL 91, 072302
200 GeV Au+Au, 0-50%
hydro
200 GeV Au+Au
pT (GeV/c)
Gradual Transition to this “State of Matter”
HEP2005 11
Smooth Evolution of Mid-rapidity dNch/dEnergy Centrality
200 GeV (measured UA5)
19.6 GeV (interpolated ISR)pp pp
90 % C.L.
PHOBOS nucl-ex/0410022 PHOBOS PRC 70, 021902(R)
Au+Au data
Au+Au & Pb+Pb data
HEP2005 12
Au+Au 0-40% central
Smooth Evolution of Bulk Elliptic Flow IENERGY
v 2v 2
PHOBOS PRL 94, 122303 PHOBOS PRL 94, 122303
HEP2005 13
Smooth Evolution of Bulk Elliptic Flow IICentrality
PHOBOS nucl-ex/0407012 PHOBOS nucl-ex/0407012
Au+Au @ 200 GeV
HEP2005 14
Smooth RAA Evolution I
PHOBOS PRL 94, 082304
ENERGY
RA
A
0
1
2
pT
62.4 GeV200 GeV
HEP2005 15
Smooth RAA Evolution II
CENTRALITY
Red = 62.4 GeVBlue = 200 GeV PHOBOS PRL 94, 082304 & PLB 578, 297
line for illustration only
“Simple” Scaling Behaviors
1) Extended Longitudinal Scaling
HEP2005 17
p + p inel.
dN
/d
beamy
Reminder: Limiting Fragmentation in p+pData: UA5 (Alner et al.),Z.Phys.C33, 1 (1986)
Ansatz: At high collision energy, d2N/dy’dpT and particle mix, reach a limiting value and become independent of energy around beam rapidity (i.e. in the fragmentation region).
Ansatz: Benecke, Chou, Yang, Yen, Phys. Rev. 188, 2159 (1969)
Shift to Rest Frame of Beam
HEP2005 18
dN/d: Extended Longitudinal ScalingAu+Au
PHOBOS PRL 91, 052303 & preliminary 62.4
HEP2005 19
v2 flow: Extended Longitudinal ScalingAu+Au
PHOBOS PRL 94, 122303
HEP2005 20
dN/d: Extended Longitudinal Scalingd+Au
dAu & pEmulsion per incident nucleon and approx. same Npart
PHOBOS nucl-ex/0409021 (accepted PRC-RC)
“Simple” Scaling Behaviors
1) Extended Longitudinal Scaling
2) The Importance of Npart
HEP2005 22
Npart Participants
Ncoll Binary Collisions
Npart/2 ~ A
L~A1/3
Ncoll ~ A4/3
Participants (Npart) and Collisions (Ncoll)
b
HEP2005 23
Collisions per Participant Pair
Glauber Monte Carlo
Au+Au
HEP2005 24
Extracting <Nch> in Au+Au and d+Au
PHOBOS arXiv:nucl-ex/0409021 (accepted PRC-RC)
PHOBOS PRL 91, 052303
Utilize PHOBOS broad coverage (and the observed extended longitudinal scaling) to extract <Nch>
HEP2005 25
PHOBOS PRL 91, 052303
Npart scaling for Nch in Au+Au
Total charged particle yield per participant pair is flat with centrality Reduction at mid-rapidity balanced by increase at larger rapidity
PHOBOS arXiv:nucl-ex/0301017
HEP2005 26
Npart scaling for Nch in d+Au
arXiv:nucl-ex/0409021 (accepted PRC-RC)
HEP2005 27
NpartRAA at 62.4 and 200 GeV
PHOBOS 62.4 GeV200 GeV
PHOBOS PRL 94, 082304
Ncoll
Ncoll
(Nco
ll sc
aled
)
Yields normalized by Npart are less centrality-dependent
Au+Au
Ncoll
“Simple” Scaling Behaviors
1) Extended Longitudinal Scaling
2) The Importance of Npart
3) Universality of Total Charged Particle Production
HEP2005 29
Nch production in pp, dA, AA and ee
PHOBOS nucl-ex/0301017 & nucl-ex/0410022
“Match” for d+Au & p+p
e+e-
200 GeV
130 GeV
20 GeV
“Match” for Au+Au & e+e-
HEP2005 30
Universal Curve for Nch vs (s) at RHIC Energies
PHOBOS nucl-ex/0301017 & nucl-ex/0410022
When pp and dA “corrected” for energy loss to leading baryon
Au+Au
PHOBOS d+Au (@ √s/2)
Factorization of CollisionEnergy and Geometry
HEP2005 32
Factorization of Energy and Centrality Dependence for Mid-rapidity dNch/d
PHOBOS PRC 70, 021902R
PHOBOS PRC 65, 061901R
Preliminary: 62.4 GeV
NNpartNNpartmid sfNfsNR 21,
Au+Au Collisions
HEP2005 33
Factorization: pT Dependence
TNNpartTNNpartmid psfNfpsNR ,,, 21
Centrality factorization appears to be pT independent
Au+Au: Ratio 200/62.4 GeV
lines for illustration only
PHOBOS Data PRL 94, 082304 & PLB 578, 297
HEP2005 34
RAA Evolution with Centrality… Universal?
PHOBOS 62.4 GeV200 GeV
Npart
Ncoll
Ncoll
PHOBOS PRL 94, 082304
HEP2005 35
RAA Evolution with Centrality… Universal?
PHOBOS 62.4 GeV200 GeV
Npart
TNNTpartNPC
NAA psfpNRR partpart ,,
• Energy-independent
• Weak function of Npart, pT
• Energy-dependent
• Strong function of √s, pT
Ncoll
Ncoll
PHOBOS PRL 94, 082304
HEP2005 36
What has PHOBOS learned so far?
• We have created a state of matter at RHIC with high energy-density, that is nearly net-baryon free, and that is strongly interacting.
• Transition to this high-energy state of matter does not create abrupt changes in observables at RHIC energies.
• The data exhibits “simple” scaling behaviors and factorizations that unite the data. → suggests strong global constraints and illustrates the importance of the collision geometry in the initial state and the very early evolution of the colliding system.
• Waiting for Cu+Cu results!→ test these features in a smaller system.