high p t charged hadron suppression at s =200 gev
DESCRIPTION
High p T Charged Hadron Suppression at s =200 GeV. Jiangyong Jia State University of New York at Stony Brook. Introduction Detectors Charged hadron analysis Background Correction High p T Results and Discussion Charged Hadron Spectra and Suppression - PowerPoint PPT PresentationTRANSCRIPT
1
High pT Charged Hadron Suppression at s =200 GeV
Introduction Detectors Charged hadron analysis
Background Correction
High pT Results and Discussion Charged Hadron Spectra and Suppression d-Au results: Suppression is Final State Effect Details of the Suppression Patterns Collision Geometry and Jet absorption
Summary and outlook
Jiangyong JiaState University of New York at Stony Brook
2
Quark Gluon Plasma
QCD coupling constant is “asymptotically free” s 0 as r 0
Lattice QCD predicts a deconfined phase Quarks and gluons are freed Quark Gluon Plasma TC ~ 155-175 MeV C ~ 0.3-1.0 GeV/fm3
Achieve in the laboratory by colliding heavy-ions Relativistic Heavy Ion Collider at BNL Estimate from measured transverse energy ET
20
1~ TdEEV dycR
Formation time = 0.3-1fm/c
i ~ 5 - 15 GeV/fm3 Tc ~ 250-350 MeV
2%
Tnn
y 0
dE580GeV at s 200GeV
dy
RHIC
How can we confirm the existence and study the properties of QGP?
3
The Experimental Probe for QGP
Use Hard Scattering or “Jets” as the probe Example : p—p collisions
proton
proton
q
q
hadronsleadingparticle
leading particle
schematic view of jet production
hadrons
p+p->0 + X s= 200 GeV
Jet dominate pT>2 GeV/c
Calibrated probe: Jet cross section can be calculated in pQCD for nucleon-nucleon collisions
4
Calibrated probe
Incoming quarks and gluons (a,b) described by Parton Distribution Function PDF deduced from experimental data
Scatter with large momentum transfer “Hard scattering”and create c,d Early in the collision (t ~ 1/Q2) With large momentum (jets) Calculable in pQCD
c,d fragment and create hadrons Fragmentation functions from data
Fragmentation Theorem
AB hX fa/A(xa,Q
2a) fb/B(xb,Q
2b) a b cd
Dh/c(zc,Q2
c)
5
Medium Modification of Jets
Initial production rate is proportional to the number of independent binary nucleon nucleon collisions Nbinary
Participants
hard hardAA NNbinaryN A
A
spectators
q
q
hadrons
hadrons
leadingparticle
jet production in quark matter
leadingparticle
Created early 0~1/E~0.2fm/c for 1 GeV parton
Experience the full time scale of the medium Strongly interact and lose significant amount of energy (~ GeV/fm)
Attenuation or absorption of jets
“jet quenching”
dydpNdN
dydpNdR
TNN
binary
TAA
AA 2
2:factor onmodificatiNuclear
Suppression of high pT hadrons
By definition, processes that scale with Nbinary will produce RAA=1.
q
q
hadronsleadingparticle
jet production in quark matter
6
High pT suppression at s=130 GeV
First observation of high pT hadron suppression in Au-Au at s = 130 GeV PHENIX collaboration PRL
88 (2002) 22301
130GeV
Detailed pT and centrality dependence of charged hadrons PLB 561 (2003) 82 Peripheral RAA 1 Central RAA saturates ~ 0.6 at
pT >2GeV/C
PHENIX
More statistics from RUN-2. Higher in pT and more detailed centrality dependence
7
Pioneering High Energy Nuclear Interaction eXperiment (PHENIX)@Relativistic Heavy Ion Collider (RHIC)
2 counter-circulating rings, 3.8 km circumference
Any nucleus on any other. Top energies (each beam):
100 GeV/nucleon Au-Au. 250 GeV polarized p-p.
Maximal Set of Observables Photons, Electrons, Muons, ID-hadrons
Highly Selective Triggering High Rate Capability. Rare Processes.
8
PHENIX Setup for Au-Au at s = 200 GeV in Year 2001
Background Rejection and Subtraction Pad Chamber 2:PC2
RPC1 = 4.2 m
Pad Chamber 3:PC3RPC1 = 4.9 m
Ring Image Cerenkov Detector:RICHRRICH = 2.5-4.1 m
Charged particle Tracking||<0.35, =
Drift Chamber :DCRDC = 2-2.4 m
Pad Chamber 1:PC1RPC1 = 2.4 m
Trigger and CentralityBeam-Beam Counters:BBC3.0<||<3.9, = 2
Zero-Degree Calorimeters: ZDC|| > 6, |Z|=18.25 m
9
Centrality Selection
BBC charge is participants ZDC energy is sensitive to
spectators.
Define centrality classes: ZDC vs BBC
bEZDC
QBBC
0-5%
15-20%10-15%
0-5%
5-10%
Centrality classes defined by cut on the BBC_Q and ZDC_E
Extract Npart, Ncoll from Glauber model simulation
27 million minimum bias events used
10
Track reconstruction by DC-PC1
Drift Chamber measure trajectory in (x,y) plane Give the bending angle after magnetic field
T
Kp
pP
δp%1%7.0
Measured momentum resolution is
x
y
r
PC1 hits combined with the collision vertex fix the polar angle .
sin( )Tpp
z
r
0
11
Backgrounds include
1. e+/e- from conversion of in materials
2. Weak decays, mostly K±
These tracks have small , consequently large apparent pT
Backgrounds in Charged Hadron measurement
Tracks with matching cut at PC2 and PC3
Overwhelmed by background at high pT
12
Background under the matching distribution
Matching in r-plane at PC Plot the residual distribution Tails are the background Asymmetric shape due to residual bend
Different charge bend in opposite direction
e produce Cerenkov light in RICH, and detected by PMT.
Tracks can be divided into two categories according to RICH response:
NPMT >0 ( e background and high pT )NPMT <0 (decay background and high pT k,p )
a) Define the shape from a sample of background
b) Normalize the background outside the matching window
c) Subtract to get the signal
13
6<pT<7GeV/c
Conversion Background Estimate
Tracks with RICH hit contains both electron background and primary pions e NPMT follows Poisson distribution with mean of 4.5 Pions begin to fire RICH at pT >4.8 GeV/c, <NPMT> < 3 at pT <10 GeV/c
e background subtraction from the matching distribution Require NPMT>4 to tag pure electron backgrounds Normalize electron background and subtract it Monte-Carlo reproduce the conversion background matching distribution.
14
Decay Background Estimate
Tracks do not fire RICH (NPMT<0)contains decay background and
primary K±,P± Tracks at pT >10 GeV/c are dominated by decay background This sample of tracks gives the background matching distribution For each pT bin, normalize to background in 3-9 region and subtract Monte-Carlo reproduce the decay background matching distribution
6<pT<7GeV/c
15
Signal/background ratio
Signal/All-bg ~ 1 at 7 GeV/c and ~0.3 at 10GeV/c.
SignalConversionDecay
Signal/bg
16
Corrections
Monte-Carlo simulation of single particles through PHENIX detector
Plateau is given by geometrical acceptance and efficiency yellow band show the systematic
error At high pT dominated by
background subtraction
Embed single particle into real events to estimate occupancy correction correction for most central collision is
1.35 ± 6%
pT and centrality dependence factorize
17
Charged hadron spectra and evolution
pT spectra out to 10 GeV/c Characteristic power-law tail
“Peripheral”
Particle
Physics
“Central”
Nuclear
Physics
Ratio of each centrality to minimum bias spectra Peripheral central Concave Convex High pT shape is almost centrality independent
18
Suppression of charged hadron in Central collisions
Central RAA suppressed by factor of 4.5
Peripheral RAA ~ 1
Consistent with hard-scattering
*
19
Suppression: An Initial State Effect?
Multiple elastic scatterings (Cronin effect) Wang, Kopeliovich, Levai, Accardi Nuclear enhancement observed in pA and
AA at lower energies
Nuclear shadowing Relevant for x<0.01 Not reached at RHIC
Gluon Saturation (CGC) Wavefunction of low x gluons overlap;
Gluon fusion ggg saturates the density of gluons in the initial state. (gets Nch right!)
Gribov, Levin, Ryshkin, Mueller,
Qiu, Kharzeev, McLerran,
Venugopalan, Balitsky,
Kovchegov, Kovner, Iancu …
1AAR
1AAR
Broaden pT :
xG(x,Q2)
QSx
20
Jet Quenching: A Final State Effect?
Hadronic absorption of fragments: Gallmeister, et al. PRC67,044905(2003) Fragments formed inside hadronic medium
Energy loss of partons in dense matter Gyulassy, Wang, Vitev, Baier, Wiedemann…
PCM & clust. hadronization
NFD
NFD & hadronic TM
PCM & hadronic TM
CYM & LGT
string & hadronic TM
Hadron gas
1AuAuR d+Au is the “control” experimentFinal state effect: no suppressionInitial state effect: suppression dAu AuAuR R RdAu~ 0.7
D.Kharzeev et al., hep-ph/0210033
Gluon saturation model::
21
First d-Au Results from RHIC
d-Au control experiment:
Initial state effects present in Au nucleusMedium volume too small for jet quenching
d-Au Result:
No suppression of high pt hadron yieldsPronounced “Cronin enhancement”
RHIC at too high x for shadowing and gluon saturation!
PHENIX
*
22
Centrality Dependence
Different and opposite centrality evolution of Au+Au experiment from d+Au control
Centrality dependence is consistent with Cronin effect
Au + Au Experiment d + Au Control Experiment
Preliminary Datanucl-ex/0308006
Jet suppression is clearly a final state effect
A.Accardi
*
23
Beam Energy Dependence
Expect xT scaling for hard processes: Spectrum shape depends only on
Normalization by
Empirically n=6.3
( )n T
dE G xdp s
3
3
1
TT
px
s
2
n
s
Compilation of neutral pion data
24
Test xT Scaling for Au-Au
Compare data from 130 and 200 GeV beam energy Central & peripheral 0 data consistent with n=6.3 Peripheral h data consistent with n=6.3 Small deviation for central h data consistent with proton enhancement
Expected s dependence for hard scattering processes
25
Particle Composition: Charged-to-Pion Ratio
Intermediate pT region h/ centrality dependent ~ 1.6 for peripheral collisions Reaches ~ 2.5 for central events
Proton enhancement in central collisions
High pT region (pT > 4.5 GeV/c) h/ ~ 1.6 Independent of centrality Same value as found in pp
Particle composition likeJet fragmentation
hard
protons
26
Centrality Dependence of Jet Quenching
Hard region: pT > 4.5 GeV/c Suppression depends on centrality but not on pT Characteristic features of
jet fragmentation independent of centrality
xT scaling h/0 constantpQCD spectral shape
softhard
Soft and intermediate region: pT < 4.5 GeV/c Extends > 2 GeV/c into pQCD region Changing particle composition unlike jet
fragmentation pT dependent suppression
Have jet quenching but
particle production from
jet fragmentation
27
Centrality Dependence of Suppression(I)
High pT yield per binary collision: pT > 4.5 GeV/c continuous decrease with centrality Identical for charged hadrons and 0
peripheral to central factor ~ 4
High pT yield per participant pT > 4.5 GeV/c Initially increases like collision scaling Decreases above Npart~100 by ~1.5
Approximate participant scaling???
*
28
Centrality Dependence of Suppression(II)
Surface emission givesapproximate Npart scaling:
part
part part
part
NyieldN N
event N
23
43
Jet absorption + nuclear geometry
suggested by Bjorken 1982
Energy loss (B.Mueller, nucl-th/0208038)Energy loss (X.N.Wang,nucl-th/0307036)jet absorption with Woods-Saxon geometry (next)
STAR data from nucl-ex/0305015
Hadron yield above 4.5 GeV/c peripheral data scale with Ncoll deviation for Npart > 50
*
29
max~17/fm2
Central collisions (0-5%)
Ncoll ~ 1000
Peripheral collisions (75-80%)
Ncoll ~ 10
max<1/fm2
very dilute surface
Modeling the Hard Scattering
Number of hard scattering proportional to collision density Ncoll (x,y)
Number of collisions determined from the nuclear overlap Woods-Saxon nuclear density distribution Project into plane transverse to beam and divide by transverse area
probability of hard scattering Ncoll (x,y)
30
max~4/fm2
Central collisions (0-5%)
Npart ~ 350
Peripheral collisions (75-80%)
Npart ~ 10
max<0.7/fm2
Modeling the Matter Density Matter density proportional to participant density Npart (x,y)
Number of participants calculated from collision geometry Participant density related to energy density
23
2 3
20
2~ 2.5 / ~ 5 15 /central
Npart Bjorken
Afm GeV fm
r A
31
Jet Absorption Picture
Npart(x,y)
Ncoll(x,y)
Generate dijet isotropicly according to binary collision profile
Density of matter in transverse plane determined by participant density
dl
f e Interpretation: - static source absorption l
Jets are absorbed in dense reaction volume according to:
is the absorption parameter (only free parameter)fix to give f = 0.22 for central collisions
in static limit corresponds to absorption length ~ 2.9 fm
Neglect any pT dependence and jet fragmentation
32
10
I = dl ρ (x,y)
20
I = dl l ρ (x,y)
03
00
lI = dl ρ (x,y)
l +l
Centrality Dependence of High pT Yields
Compare to jet absorption picture describes centrality
dependence of yield Not very sensitive to
absorption pattern used
1. Centrality dependence consistent with jet absorption in extremely opaque medium
2. Centrality dependence of yield reflects mostly collision geometry
- static source absorption l- static source absorption l2
- expanding source absorption l
*
33
Jet-Jet Azimuthal Correlations(I)
Di-jet are correlated in azimuth direction Leading particle + angular correlation Strong near side and far side correlation in p-p collisions
AA
yield(AuAu) backgroundI =
expected
Back jet are easier to be quenched in medium
34
Jet-Jet Azimuthal Correlations (II)
Compare STAR data 4 < pT < 6 GeV/c to absorption picture by construction, same side jet (~0) will always give unity Away side jet () suppression by factor ~ 7 well described by jet
absorption and collision geometry Away side jet have almost factor of 2 more suppression than single
hadron suppression, consistent with surface emission
Near side
Away side
centrality dependence of yield reflects mostly collision geometry
*
35
Azimuthal Anisotropy(I)
Different direction have different energy loss Jet are more likely to be emitted in plane than
out of planeIn plane
Out plane
Centrality dependence of v2 at pT > 4 GeV/c from data Measured v2 for different methods are quite different v2
2-particle-cumulant>= v2BBC-reaction-plane> v2
4-particle-cumulant
The difference comes from contributions that do not correlate with reaction plane
4 particle cumulant method is less affected by non-flow contribution
36
Azimuthal Anisotropy(II)
Comparing to jet absorption calculation largest v2 from jet absorption picture 5-10% 1 from v2
4-particle-cumulant
Sensitive to the energy loss assumption and dynamic evolution of the medium
37
Nuclear profile dependence
Woods-Saxon matter density has defuse surface
v2 increase by using hard sphere or cylindrical nuclear geometry May imply that the medium has a different shape other than Woods-Saxon
However, it misses the centrality dependence of the suppression
38
Summary
Charged hadron pT spectra measured out to 10 GeV/c with bg rejection
Rich high pT phenomena observed at RHIC
Jet quenching well established experimentally Suppression of high pT hadron yields d-Au data indicate it is an final state effect Consistent with jet quenching and surface emission
xT scaling of pion production similar to pp
Particle composition at high pT are like pp
pT >4-5 GeV/c, suppression is ~ constant, spectra shape like pp
Jet absorption picture and collision geometry works reasonably well Describe general features of jet quenching
Consistent with suppression of hadron yieldsConsistent with back-to-back jet correlation
Azimuthal anisotropy described qualitatively
39
Outlook
Suppression is a well established effect. What is future of high pT physics?
s dependenceSPS s = 17.2 GeV i =3 GeV/fm3 RHIC s = 200 GeV i ~ 5 GeV/fm3
where the jet quenching set in? or does it already happen in SPS? Hadron pT>20 GeV/c
At certain pT, jet should penetrate the medium again. More details on the Jet modification pattern:
RAA for baryon at high pT back-to-back correlation High pT v2 for identified particle
Jet absorption
40
Track reconstruction by DC-PC1
Drift Chamber provides 12 hits in (x,y) plane. Give the bending angle after magnetic field,
which provide the initial momentum measurement
TT
R
rRq
pcGeVmrad
p
dLBr /087.0
PC1 hits combined with the collision vertex fix the polar angle .
pP
δp%1%7.0
Measured momentum resolution is
)sin(Tpp
41DC
PC1 PC2PC3
r-BVe
x
y
r-at PC2 and PC3 are correlated Define optimized matching variables:
D+ and D-
42
Nucleon-Nucleon Reference
PHENIX p-p data at 200 GeV 0 data out to 14 GeV/c consistent with NLO pQCD
calculation charged hadron results not available
yet
Comparison to fit of UA1 data UA1 data at 200GeV PHENIX 0 spectra scaled by
1.6(ISR result)
Charged hadron N-N reference Use 0 data to constrain fit systematic uncertainty ~ 20%
43
xT-scaling in pp
Charged hadrons s = 23-1800 GeV Approximate xT scaling with n = 6.3
Deviation from xT scaling for pT < 1-2 GeV/c
32
3 ( , )
1( )
T
pTxT sn x s
dE Gdp s
44
Neutral pions s = 39-540 GeV Approximate xT scaling with n = 6.3
No data for pT < 1-2 GeV/c
xT-scaling in pp (II)
45
Testing xT scaling with 130 and 200 GeV Au-Au
xT scaling can be used to test pQCD in heavy-ion collisions Shadowing and gluon saturation is basically a scaling effect Partonic final state medium effect may or may not scale Hadron absorption and parton coalesce probably does not scale
Scaled by6.3( / 200)s
46
xT scaling power n from 200/130 ratio
)130log()200log())200(/log())130(/log( 3333
)( GeVpdEdGeVpdEd
Txn
n=6.410.250.49
n=7.530.180.4
n=6.330.390.37
n=6.120.330.36
n= ncent-nperi = 1.410.43proton “enhancement” up to 4 GeV