christof roland/mitmoriond,march, 2001 -1- results from the phobos experiment at rhic christof...
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Christof Roland/MITMoriond,March, 2001 -1-
Results from the PHOBOS experiment at RHIC
Christof Roland (MIT)for the
PHOBOS Collaboration
Christof Roland/MITMoriond,March, 2001 -2-
Year 1: The Big Picture
Q: Entropy Production Hadro-Chemistry Thermal
Equilibration Multiplicity Charged Particle Density
Event Anisotropy Flow
Particle Ratios
Au+Au Collisions @ s = 130 GeV
Christof Roland/MITMoriond,March, 2001 -3-
PHOBOS Collaboration
ARGONNE NATIONAL LABORATORY
BROOKHAVEN NATIONAL LABORATORY
INSTITUTE OF NUCLEAR PHYSICS, KRAKOW
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
NATIONAL CENTRAL UNIVERSITY, TAIWAN
UNIVERSITY OF ROCHESTER
UNIVERSITY OF ILLINOIS AT CHICAGO
UNIVERSITY OF MARYLAND
Birger Back, Nigel George, Alan Wuosmaa
Mark Baker, Donald Barton, Alan Carroll, Stephen Gushue, George Heintzelman, Robert Pak, Louis Remsberg, Peter Steinberg,Andrei Sukhanov
Andrzej Budzanowski, Roman Holynski, Jerzy Michalowski,Andrzej Olszewski, Pawel Sawicki , Marek Stodulski, Adam Trzupek,Barbara Wosiek, Krzysztof Wozniak
Wit Busza (Spokesperson), Patrick Decowski, Kristjan Gulbrandsen, Conor Henderson, Jay Kane , Judith Katzy, Piotr Kulinich, Johannes Muelmenstaedt, Heinz Pernegger, Corey Reed,Christof Roland, Gunther Roland, Leslie Rosenberg, Pradeep Sarin,Stephen Steadman, George Stephans, Gerrit van Nieuwenhuizen,Carla Vale, Robin Verdier, Bernard Wadsworth, Bolek Wyslouch
Willis Lin, Jaw-Luen Tang
Joshua Hamblen , Erik Johnson, Nazim Khan, Steven Manly,Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs
Russell Betts, Clive Halliwell, David Hofman, Burt Holzman,Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter
Richard Bindel, Edmundo Garcia, Alice Mignerey
Christof Roland/MITMoriond,March, 2001 -4-
PHOBOS Detector
Ring Counters
Paddle Trigger Counter
Spectrometer
TOF
Octagon+Vertex
• 96000 Silicon Pad channels
• 4 Multiplicity Array • Mid-rapidity Spectrometer• Scintillator Paddles + Zero Degree Calorimeter for triggering• TOF wall for high-momentum PID
Christof Roland/MITMoriond,March, 2001 -5-
First RHIC physics result: Back et al., PRL 85 (2000) 3100
Multiplicity at =0 vs Energy
RESULTs Npart56 GeV 330 +/- 4 +10/-15
130 GeV 343 +/- 4 +7/-14
s dN/d 56 GeV 408 +/- 12 +/-30130 GeV 555 +/- 12 +/-35
s 2dN/d /Npart
56 GeV 2.47 +/-.10 +/-.25130 GeV 3.24 +/-.10 +/-.25
Ratio: 1.31 +/-.04 +/-.05
Au+Au @ 130 GeV:• 40% increase from p+p to central Au+Au• 70% increase from CERN-SPS
6% most central
Christof Roland/MITMoriond,March, 2001 -6-
Multiplicity at =0 vs Npart
Npart
Yellow band: Systematic uncertainty
Preliminary
dNch
/d/
(0.5
*Npa
rt) Physics run July-Sept 2000
10 centrality bins for upper 45% of cross section
Q: How does dNch/d@=0 evolve from 2.3 (p+p) to 3.25 (Au+Au) per participant pair?
• EKRT Saturation disfavored• Good agreement with previous PHOBOS point• Neither HIJING nor EKRT describe data well
Christof Roland/MITMoriond,March, 2001 -7-
Multiplicity in 4(Hit counting)
Occupancy correction (assuming Poisson statistics)
dNch
d =hits
O(,b) ×fB(,b)
A(ZVTX)
Rings Octagon Rings
Acceptance Factor
Backgroundcorrection
Christof Roland/MITMoriond,March, 2001 -8-
dNch/d vs Centrality Preliminary
Statistical errors only - 10-20% systematical uncertainty
Christof Roland/MITMoriond,March, 2001 -9-
Evolution of dNch/d vs Npart
• <Nch> = 4100 +/- 410 for 3% most central• Additional particle production near =0• Wider + more particles relative to HIJING
Preliminary
(dN
ch/d
)/(
½N
pa
rt)
Data
HIJING
Npart=356
Npart=215
Npart=103
(dN
ch/d
)/(
½N
pa
rt)
Statistical errors only
Npart
PHOBOS Prelim.
±10% Systematic Uncertainty±10% Systematic Uncertainty
HIJING
Nch
(||
<5.
4)
Christof Roland/MITMoriond,March, 2001 -10-
Collective Effects: Elliptic Flow
Q:
Does the initial space
anisotropy translate into
final state momentum
space anisotropy?
b (reaction plane)
dN/d(R ) = N0 (1 + 2V1cos (R) + 2V2cos (2(R ) ) + ... )
Christof Roland/MITMoriond,March, 2001 -11-
• Systematic error ~ 0.007
• Large V2 signal compared to lower energy
• Centrality Dependence close to Hydro.
• V2 drops for || > 1.5
Elliptic Flow Results
V2 PHOBOS STAR (PRL) Hydro. model
V2
Normalized Paddle Signal
SPSAGS
Preliminary
|| < 1.0 Averaged over centrality
Christof Roland/MITMoriond,March, 2001 -12-
Hadro Chemistry: Particle Ratios
p
K
p-
Preliminary
Thermal Model Estimte : B ~ 50 MeV Central region not net baryon-free!
Q: Baryo-Chemical Potential, Baryon Stopping
.)syst(..)stat(..
.)syst(..)stat(..
ppK
K
10050540
10090910
.)syst(..)stat(.. 050010011
Centrality =12 %<Npart> ~ 310
Christof Roland/MITMoriond,March, 2001 -13-
• dNch/d @=0 per participant• 70% higher than SPS for central Au+Au
• 40% higher than p+p at RHIC energy
• Npart evolution between HIJING and EKRT
• dNch/d in 4-• <Nch> = 4100 +/- 410 (||< 5.4) for 3% central
• Additional particle production near =0 for central events
• Wider than HIJING
• Elliptic flow• V2 up to 0.06 – close to hydrodynamic limit
• larger than SPS
• V2 drops for || > 1.5
• Particle ratios• p/p ratio 0.54 +/- 0.1
• Central region not baryon free
Summary
Christof Roland/MITMoriond,March, 2001 -14-
Outlook I: 2001
• >100x statistics• Physics:
• low-pT physics
• Spectra• HBT
• Resonances (at low pT
• Event-by-Event physics
• Both arms completed • Energy systematics• Species systematics