Results from the PHOBOS Experiment at RHIC - A Perspective Russell Betts – UIC for
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Results from the PHOBOS Experiment
at RHIC - A Perspective
Russell Betts – UIC
for
The PHOBOS Collaboration
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C o l l a b o r a t i o n ( O c t o b e r 2 0 0 4 )
B u r a k A l v e r , B i r g e r B a c k , M a r k B a k e r , M a a r t e n B a l l i n t i j n , D o n a l d B a r t o n , R u s s e l l B e t t s , A b i g a i l B i c k l e y , R i c h a r d B i n d e l , W i t B u s z a ( S p o k e s p e r s o n ) , A l a n C a r r o l l , Z h e n g w e i C h a i , V a s u n d h a r a C h e t l u r u ,
P a t r i c k D e c o w s k i , E d m u n d o G a r c í a , T o m a s z G b u r e k , N i g e l G e o r g e , K r i s t j a n G u l b r a n d s e n , C l i v e H a l l i w e l l , J o s h u a H a m b l e n , I a n H a r n a r i n e , C o n o r H e n d e r s o n , D a v i d H o f m a n , R i c h a r d H o l l i s ,
R o m a n H o ł y ń s k i , B u r t H o l z m a n , A n e t a I o r d a n o v a , J a y K a n e , N a z i m K h a n , P i o t r K u l i n i c h , C h i a M i n g K u o , W e i L i , W i l l i s L i n , S t e v e n M a n l y , A l i c e M i g n e r e y , G e r r i t v a n N i e u w e n h u i z e n ,
R a c h i d N o u i c e r , A n d r z e j O l s z e w s k i , R o b e r t P a k , H e i n z P e r n e g g e r , C o r e y R e e d , C h r i s t o f R o l a n d , G u n t h e r R o l a n d , J o e S a g e r e r , I o u r i S e d y k h , W o j t e k S k u l s k i , C h a d d S m i t h , M a c i e j S t a n k i e w i c z , P e t e r S t e i n b e r g , G e o r g e S t e p h a n s , A n d r e i S u k h a n o v , M a r g u e r i t e B e l t T o n j e s , A d a m T r z u p e k ,
C a r l a V a l e , S e r g e i V a u r y n o v i c h , R o b i n V e r d i e r , G á b o r V e r e s , P e t e r W a l t e r s , E d w a r d W e n g e r , F r a n k W o l f s , B a r b a r a W o s i e k , K r z y s z t o f W o ź n i a k , B o l e k W y s ł o u c h
A R G O N N E N A T I O N A L L A B O R A T O R Y B R O O K H A V E N N A T I O N A L L A B O R A T O R YI N S T I T U T E O F N U C L E A R P H Y S I C S P A N , K R A K O W M A S S A C H U S E T T S I N S T I T U T E O F T E C H N O L O G Y
N A T I O N A L C E N T R A L U N I V E R S I T Y , T A I W A N U N I V E R S I T Y O F I L L I N O I S A T C H I C A G OU N I V E R S I T Y O F M A R Y L A N D U N I V E R S I T Y O F R O C H E S T E R
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Outline of the Talk
•The PHOBOS Experiment
•The Data and Analysis
•The Nature of the Matter formed in AA Collisions
•Discovery of Simple Scaling Rules
The PHOBOS Perspective on Discoveries at RHICThe PHOBOS White Paper
nucl-ex/0410022
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Spectrometer
Paddle Trigger Counter
NIM A 499 (2003) 603
Octagon
TOF
SpecTrig
T0 counter
•44- Multiplicity Detector•MMagnetic Spectrometer + TOF
The PHOBOS Experiment (2004)
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Multiplicity and Trigger Detectors
Octagon Paddle Trigger Counter
Ring Counter
ZDC
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Counting Particles
Bulk of Particles pT<1GeV
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Vertex Tracklets (I)
= 1 – 2
= 1 – 2
Tracklets are two point tracks
that are constrained by
the event vertex.
|| < 0.04 || < 0.3
Vertex Detector Event Display
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Vertex Tracklets (II)
All Pairs of Hits
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Hit Counting (I)
Octagon, Ring and Vertex Detectors (unrolled)
Count Hits or Deposited Energy
0 +3-3 +5.5-5.5
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Discriminating BackgroundE
(“M
IP”)
20 64-2-6 -4
04
812
20 64-2-6 -4E
(“M
IP”)
04
812
Data Monte Carlo
Si
E vs. in the Octagon
From Vertex
Not from Vertex
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Measure the Occupancy
!)(
NeNP
N
N=number of tracks/pad=mean number of tracks/pad
The numbers of empty and occupied padsdetermine the occupancy as a function of ,b
Method: Assume Poisson statistics
Ntra
cks/h
it pa
d
0-3%
50-55%
Octagon
Rings(central)
(peripheral)
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Energy Loss Multiplicity
300 m Si
PRIM
TOTAL
i
NNiM
Measured S/N = 10 - 20 << Landau Width
Use Non-Hit pads - forCommon-Mode Noise Suppression
M = 240 ± 15 ± 5 ± CMN for one sensor (120 channels) at = 0
NoiseCommonNoiseRandomMLandauM 2i
2i
0.30 - 0.40
Energy deposited in ith pad (truncated)corrected for angle of incidence
Mean energy loss for oneparticle traversing pad RATIO OF TOTAL TRACKS
TO PRIMARY TRACKS
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Elliptic Flow
(reaction plane: R)
dN/d(R ) = N0 (1 + 2V1cos (R) + 2V2cos (2(R) + ... )
View along beamline
Fourier decomposition of the Azimuthal Multiplicity Distribution:
Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671
Best estimate event plane
iii
iii
w
w
2cos
2sintan
21 1
2
V2 = < cos (2(2)) > /cos(2(2a 2
b))> )1/2
Directed flow Elliptic flow
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Centrality Determination
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NPart and NColl (Au+Au)
Paddle Mean
NPart
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NPart and Ncoll (d+Au)
Multiplicity DistributionPseudorapidity
Glauber Calculation•Hijing 1.383
•Hulthen w.f.•41mb inelastic cross-section
•Full GEANT Simulation
HIJING Simulation
dN/d
Cou
nts
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The Data
Au+Au
d+Au
Also pp at 200 GeV
Au+Au at 62.4 GeV/u
Spectra – Talk by Adam Trzupek
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Particle Density near Mid-RapidityModels prior to RHIC
PRL 88, 22302 (2002)PRL 91, 052303 (2003)
PRL 85, 3100 (2000)
arXiv:nucl-ex/0405027
On the low side of
nearly all predictions
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Initially released Energy per Unit Volume 5 GeV/fm3
Note: Energy Density inside Proton ≈ 0.5 GeV/fm3
11
45
1000~alld
dN
Therefore total energy released in
|| < 1 is ~2000GeV
Num
ber
of P
artic
les P
r odu
ced
at y
=0
Energy of Collision
“Relevant” Initial Volume ~ R2 ( 1 fm) 2
<E> ~ 0.7 GeV
Data from: PRL 85, 3100 (2000); PRL 88, 22302 (2002); PRL 91, 052303 (2003); arXiv:nucl-ex/0405027
dNch
/d
Energy per Unit Volume
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The Energy Density is High (3-5 GeV/fm3)
and
Much Larger than Inside a Hadron
A Description in Terms of Hadronic Degrees of Freedom is
Inappropriate
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Baryon Free at Mid-Rapidity
PRC 67, 021901R (2003)
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Evidence from Flow
200 GeV Au+Au PHOBOS
preliminary
0 < < 1.50-55% central,
h+ + h-
PRL,89, 222301 (2002)Nucl. Phys.A715, 611c (2003)
Approaches Hydro Limit
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Evidence from Low pT Particles
In a large volume, weakly interacting system we
would expect the development of particles
with long wavelength
arXiv:nucl-ex/0401006
PHOBOS PHENIX
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Suppression of High-pT Particles
Au+Au
0-6%
200 GeV
PHOBOS d+Au 200 GeV
PRL 91, 072302 (2003)
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The System is Strongly Interacting
atEarly Times (2fm/c)
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PHOBOS
E895 E895 E8953.0 GeV Au+Au
BRAHMS
prel.NA49 NA49
3.6 GeV Au+Au
4.1 GeV Au+Au
8.8 GeV Pb+Pb
17.3 GeV Pb+Pb
200 GeV Au+Au
Plateau in Pseudorapidity Distributions is Misleading
Rapidity Distributions of Pions are Gaussian
PRL 91, 052303 (2003)
arXiv:nucl-ex/0403050
No Plateau in Rapidity Distributions
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PHOBOS Preliminary v2200
PHOBOS v2130
No Boost-Invariant Plateau for v2
PRL 89, 222301 (2002)
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Limiting Fragmentation in pp
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beamy PRL 91, 052303 (2003)
6% central
Au+Au
dNch
/d/<
Npa
rt>/
2
Scaling – Limiting Fragmentation
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PHOBOS
arXiv:nucl-ex/0403033
A Rest Frame p or d Rest Frame
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Submitted to PRL
arXiv:nucl-ex 0406021
Dependence of v2 on sNN and
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Limiting Fragmentation in v2
Submitted to PRL
arXiv:nucl-ex 0406021
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Longitudinal Scaling
•Originally expected boost-invariance in mid-rapidity region not observed.
•Scaling in fragmentation region seen in Au+Au, d+Au and (previously) in pp and p+A
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Nucl.Phys. A715 (2003) 65-74
PRL 91, 052303 (2003)
PHOBOS
Connection between Central and Fragmentation Regions
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pp pX pp X
provided Mx2 is the same
Brenner et al
In pp collisions, on average, approximately half the energy goes into the
leading baryon
A.Brenner et al.Phys.Rev.D26 (1982)1497l
How to Compare Au+Au, p+p, and d+Au
arXiv:nucl-ex/0301017
arXiv:nucl-ex/0403033
Au+Au higher than
pp and d+Au.
But……..
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Universal Curve for Nch vs (s)
arXiv:nucl-ex/0301017
When pp corrected
for leading baryon
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Npart scaling for:
A, KA, pA, dA, AA
10 GeV to 200 GeV
Npart from 2 to 350
E178: J.E.Elias et al., Phys.Rev.D22(1980) 13
arXiv:nucl-ex/0403033
Phobos and E178 data
Preliminary
pp chosen to have the same available
energy
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NPart Scaling of Total Particle Production – Independent of Nature of Collision System
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Factorization of Energy and Centrality Dependence
PRC 70 (2004) 021902R
Where are the Minijets?
NNpartNNpartmid sfNfsNR 21,
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arXiv:nucl-ex/0403033
Centrality Dependence of d+Au
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arXiv:nucl-ex/0403033
SAME SEEN IN p+A AT ENERGIES 50-200 GeV
Factorization into Geometric and Energy Parts
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arXiv:nucl-ex/0405003PHOBOS
62.4 GeV
200 GeV
Energy and Geometry Factorize – Independent of pT
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Summary and Conclusions•High Energy Density Strongly Interacting Matter – Description in Terms of Simple Hadronic Degrees of Freedom Inappropriate. ( No Direct Evidence of Color Deconfinement or Partonic d.o.f)
•The Matter is Strongly Interacting – Not the Weakly Coupled QGP Originally Envisioned
•Simple Scaling Rules Unite the Data. Suggest Global Constraints or Universality
The PHOBOS Perspective on Discoveries at RHICThe PHOBOS White Paper
nucl-ex/0410022