Charged particle multiplicity studies with PHOBOS Birger Back Argonne National Laboratory for the PHOBOS Collaboration.
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Charged particle multiplicity studies with PHOBOS
Birger Back
Argonne National Laboratory
for the
PHOBOS Collaboration
2
PHOBOS Collaboration
Burak Alver, Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Richard
Bindel,
Wit Busza (Spokesperson), Vasundhara Chetluru, Edmundo García, Tomasz Gburek, Joshua
Hamblen, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta
Iordanova, Chia Ming Kuo, Wei Li, Willis Lin, Constantin Loizides, Steven Manly, Alice Mignerey,
Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Corey Reed, Christof
Roland, Gunther Roland, Joe Sagerer, Peter Steinberg, George Stephans, Andrei Sukhanov,
Marguerite Belt Tonjes, Adam Trzupek, Sergei Vaurynovich, Robin Verdier, Gábor Veres, Peter
Walters, Edward Wenger, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, 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
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PHOBOS experiment: June 2000 – June 2005
-5.4 < < 5.40.5o < < 179.5o
Main emphasis:
4 multiplicity and
low pT particles
4
PHOBOS multiplicity measurements
System s1/2 (GeV)
Au+Au 200, 130, 62.4, 19.6
Cu+Cu 200, 62.4, 22.4
d+Au 200
p+p 200, 410
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dN/d basics
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What would an isotropic source look like?
Isotropic emission: 1/cosh2
Only 22% emittedwith pT > pL
Theseparticles carry information aboutthe densest regionformed in the collisions
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What happens to the original protons?
AGS
SPS
RHIC 62
RHIC 200
LHC 5500
(BRAHMS preliminary)
dN
/dy
I.Bearden (BRAHMS), QM2006
Net (original) protons move away from mid-rapidity region with increasing collision energy
Mid-rapidity region begins to look like a pure energy-density region reminiscent of the early universe
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dN/d @ =0
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Pre-RHIC theoretical predictions
PHOBOS, Nucl. Phys. A747, 28 (2005)
First RHIC
results
New dataPRC 74, 021901
(2006)
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Factorization of centrality and energy dependence
)N(g)s(fd
dNpart0
ch ||<1
Data: PHOBOS, PRL 97, 012301 (2006); PRC70, 021902(R) (2004); PRC65, 061901(R) (2002)
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Energy density
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Energy density estimates?
Absolute maximum:Total available energy:
Volume at instant of overlap:
Instantaneous energy density:Not equilibrated matter
Birger’s estimate:Isotropic energy:
Volume after 0 =1 fm/c:
Equilibrated energy density:
35,000GeV200/2350/2sNE NNparttot
3333 fm 14fm /100734
r34
V
/
33max0 GeV/fm 2,500GeV/fm 1435,000 /
GeV 1,2150.6/0.631275/fm NE chtisoch
isotot
30
2 fm 300249c2rV
33iso0 GeV/fm 4GeV/fm 3001,215 /
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Bjorken estimate of energy density
Phenix: ET measurement at 130 GeV
0 = 4.6 [GeV/fm3] PRL 87, 052301 (2001)
NA49: ET measurement at 17 GeV
0 = 3 [GeV/fm3] PRL 75, 3814 (1995)
Brahms
Conclusion: All reasonable estimates are substantially larger than thepredicted transition density of0 = 0.7-1.0 GeV/fm3
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CompletedN/d
distributions
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PHOBOS Au+Au Data
* PHOBOS PRL 91,52303 (2003)
PHOBOS, PRL 91, 052303 (2003); PRC 74, 021901 (2006)
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Cu+Cu data
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Centrality (%)
Npart
(total)
Npart
(Au)
Npart
(d)
0-20 15.5 13.5 2.0
20-40 10.8 8.9 1.9
40-60 7.2 5.4 1.7
60-80 4.2 2.9 1.4
80-100 2.7 1.6 1.1
d+Au centrality dependence
PHOBOS, Phys. Rev. C72, 031901(R) (2005)
d Au
Central: asymmetric
Peripheral: symmetric
Momentum conservation?
Peripheral
Central
>
~
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System size:Au+Au
vs.Cu+Cu
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Unscaled dN/d very similar for Au+Au and
Cu+Cu at same Npart
Scaling Laws
Cu+CuPreliminary
3-6%, Npart = 100
PHOBOS PHOBOS
62.4 GeV 200 GeV
Au+Au35-40%,Npart = 98
Cu+CuPreliminary
3-6%, Npart = 96Au+Au35-40%, Npart = 99
See poster by Richard Hollis
dN/d in Cu+Cu vs Au+Au for Npart ~ 100
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Unscaled dN/d very similar for Au+Au and Cu+Cu
at same Npart
Scaling Laws
Cu+CuPreliminary
15-25%, Npart = 61
PHOBOS PHOBOS
62.4 GeV 200 GeV
Au+Au45-50%,Npart = 62
Cu+CuPreliminary
15-25%, Npart = 60
Au+Au45-55%, Npart = 56
Also true for mid-central Cu+Cu vs peripheral Au+Au
dN/d in Cu+Cu vs Au+Au for Npart ~ 60
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Extended longitudinal scaling
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Extended longitudinal scaling – Au+Au
PHOBOS Phys. Rev. Lett. 91, 052303 (2003) / Nucl. Phys. A757, 28 (2005)
beamyydy
dN independent of energy
Works also for dN/d because:
)m/pln(y tt
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Scaling Laws
19.6 GeV 62.4 GeV 130 GeV 200 GeV
PHOBOS preliminary
preliminary preliminary preliminary preliminary
“Extended Longitudinal Scaling” of all longitudinal distributions
- ybeam
preliminary
PHOBOSAu+Au0-6%
Au+Au0-40%
Au+Au0-40%
200GeV130GeV62.4 GeV (prel)19.6 GeV
Extended longitudinal scaling – Au+Au
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Scaling Laws
Same for Cu+Cu
preliminarypreliminary
preliminary preliminaryPHOBOS
62.4 GeV 200 GeV
‘Extended Longitudinal Scaling’ also seen in Cu+CuPersists from p+p to Au+Au over large range in ’
preliminary
preliminary
PHOBOS
- ybeam
Cu+Cu0-6%
200GeV
62.4GeV
Cu+Cu0-40%
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Extended longitudinal scaling in p-A and d-A
PHOBOS, Phys. Rev. C72, 031901(R) (2005)
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Total charged particle multiplicity
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Total charged particle multiplicities in Au+Au
Nch Q Npart
Width x height = const
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Total multiplicity as a function of energyNch= dN/dx(2ybeam+0.3-dN/d/195)
height x width
width
hei
ght
PHOBOSPRL 91,52303 (2003)
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Energy dependence of Nch
0.31s0.77lndη
dNN
2
where
dηdN
1951
0.32ydη
dNN
2N2N
ch
part
chbeam
ch
partpart
ch
,
0-6% Central AuAu collisions
Npart=344
PHOBOS, PRL 91,52303 (2003)
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Universality – comparing AA to pp and e+e-
PHOBOS, PRC 74, 021902(R) (2006)
Shapes: Au+Au and e+e- “similar”Total Nch: Au+Au same as e+e-
p+p: leading hadron removes 50% of energy
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Evolution of Nch/Npp ratio vs Npart
Nch/(Npart/2) constant with centrality
d+Au also lower than Au+Au
d+Au data similar to low-energy p+A
NchdAu=0.5 Npart Nch
pp
(1 Deuteron = 2 protons)
d+Au: Centrality dependence of total Nch
PHOBOS, Phys. Rev. C72, 031901(R) (2005)
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Other new PHOBOS results (QM2006)
New data on antiparticle/particle ratios Identified particle spectra for 62.4 GeV Au+Au Event-by-event v2 measurement and flow fluctuations
Two-particle correlations and cluster size
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New Data: antiparticle/particle ratios
PHOBOS, QM2006
200, 62.4 GeV Cu+Cu 200 GeV Cu+Cu and Au+Au
Energy dependence for Cu+Cu System dependence at 200 GeV
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Identified particle spectra for 62.4 GeV Au+Au
First published identified spectra for 62.4 GeV Au+Au at RHIC(down to very low pT, a unique PHOBOS measurement)
blast-wave fits
PHOBOS, nucl-ex/0610001Accepted for PRC
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New Analysis: event-by-event v2 measurement
Measure v2 on an event-by-event basis
Average and compare to our standard analysis
Agreement with both hit and track based PHOBOS results
200 GeV Au+Au
PHOBOS, QM2006; arXiv:nucl-ex/0608025Submit to PRL this week
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Event-by-event flow: fluctuations
PHOBOS, QM2006Submit to PRL this week
v2 fluctuations
mirror
part fluctuations
(v2)/<v2> and (part)/<part> in 200 GeV Au+Au Collisions
PHOBOS part prediction
PHOBOS v2 result
90% CL
MC with nofluctuations
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Effective cluster size analysis
On average, particles produced in clusters with a size of 2-3.
Interesting centrality dependence – compare to other systems
p+p
scale error
2
Ke
ff =
eff
ecti
ve c
lust
er s
ize
PHOBOS, QM2006
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Summary and conclusion
Multiplicity
– PHOBOS have performed complete charged particle multiplicity measurements for Au+Au, Cu+Cu, d+Au, and p+p collisions
– Systen size dependence
– ‘Complete’ pseudorapidity distributions Midrapidity multiplicity
– Factorization of centrality and energy dependencies Limiting fragmentation – extended longitudinal scaling
– Seen for Au+Au, Cu+Cu, and d+Au
– Also observed in flow observables Total charged particle multiplicity
– Nch/Npart constant with centrality
– ‘Universality’ – compared to elementary e+e- collisions Future: Finish up many analysis and reviews
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Why mid-rapidity?
Emphasize producedor scatteredparticles
Triple Gaussianfit function
200 GeV Au+Au 0-6% central
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System size dependence - Au+Au vs. Cu+Cu
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Centrality dependence 200 GeV
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Cu+Cu elliptical flow – eccentricity scaling
PHOBOS, QM2006
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