25-jun-15jan rak1 jet properties from dihadron and photon hadron correlations at s=200 gev jan rak...
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Apr 18, 2023 Jan Rak 1
Jet properties from dihadron and Jet properties from dihadron and photon hadron correlations at photon hadron correlations at
s=200 GeVs=200 GeV
Jet properties from dihadron and Jet properties from dihadron and photon hadron correlations at photon hadron correlations at
s=200 GeVs=200 GeV
Jan RakJan RakJyvaskyla University & HIP, Finland
for the PHENIX collaboration
Jan RakJan RakJyvaskyla University & HIP, Finland
for the PHENIX collaboration
Apr 18, 2023 Jan Rak 2
Single inclusive vs two particle Single inclusive vs two particle correlations correlations
Inclusive distributions - despite the great success in the theoretical understanding RAA there is somewhat limited sensitivity to details of parton interaction with QGP–Energy loss, surface bias - different models similarity vs p RAA quark vs gluon RAA similarity vs direct gamma RAA similarity–Light vs heavy quark RAA (non-photonic electron) similarity
Two particle correlations - more detailed view into a nature of parton interactions with QCD medium. Access to parton intrinsic momentum kT -> soft pQCD radiation, jet shape parameters jT -> induced radiation, fragmentation function -> energy loss.–Di-hadron correlations and conditional yields–Direct photons-hadron correlations in p+p @ s=200 GeV
Apr 18, 2023 Jan Rak 3
Medium tomography: T. Renk, K. Eskola hep-ph/0610059
nucl-ex/0611018 (Phys. Rev. Lett.)
Eskola et al. NPA696 (2001) 729
gluons in Pb / gluons in p
x
AntiShadowing
Shadowing
Apr 18, 2023 Jan Rak 4
Elastic vs Radiative energy lossElastic vs Radiative energy lossS. Wicks et al., nucl-th/0512076
Partonic Energy Loss
Radiative 2N processes. Final state QCD radiation as in vacuum (p+p coll) - enhanced by QCD medium.
Elastic 22 LO processes
8 LO subprocesses
q ′q → q ′q 49
s2 +u2
t2
qq→ qq 49
s2 +u2
t2+
s2 + t2
u2
⎡
⎣⎢
⎤
⎦⎥
qq→ q ′q 49
t2 +u2
s2
......
8 LO subprocesses
q ′q → q ′q 49
s2 +u2
t2
qq→ qq 49
s2 +u2
t2+
s2 + t2
u2
⎡
⎣⎢
⎤
⎦⎥
qq→ q ′q 49
t2 +u2
s2
......
Elastic E models predict stronger broadening of away-side correlation peak - not seen in the data. Also various models differ significantly in radiative/elastic fraction.
Apr 18, 2023 Jan Rak 5
ppTT broadening only in broadening only in DIS?DIS?
Pasquale Di Nezza HERMES
??
away-side widths similar for central and peripherald+Au 0.24+-0.07 radAu+Au 20-40% 0.20+-0.02 radAu+Au 0-5% 0.22+-0.02 rad
away-side widths similar for central and peripherald+Au 0.24+-0.07 radAu+Au 20-40% 0.20+-0.02 radAu+Au 0-5% 0.22+-0.02 rad
STAR Phys.Rev.Lett.97:2006
8 < pT(trig) < 15 GeV/c
Apr 18, 2023 Jan Rak 6
Inclusive nuclear suppression factor RAA is not quite sensitive to the particular dE/dx mechanism - is it due to the surface bias?
Light and heavy quarks suppression looks similar:
Quarks and gluons suppression looks similar:
Direct photon suppression at high pT looks similar:
Some of the open questions Some of the open questions
RAAc−quark ≈RAA
u,d
RAAquark ≈RAA
gluon
RAAq,g ≈RAA
gamma
It is evident that the detailed understanding of unmodified parton properties
CRUTIAL
Apr 18, 2023 Jan Rak 7
pQCD quenching - modification pQCD quenching - modification of D(z) of D(z)
1( )
1 1 1
zD z D
E E E
⎛ ⎞≈ ⎜ ⎟− −⎝ ⎠
%
Wang, X.N., Nucl. Phys. A, 702 (1) 2002
( ) / ; ( ) / ( )D z dN dz z p fragment p jet≡ =
=ln(EJet/phadron)
pThadron~2 GeV for
Ejet=100 GeV
Borghini and Wiedemann, hep-ph/0506218
• MLLA: parton splitting+coherence angle-ordered parton cascade. Theoretically controlled, experimentally verified approach
• Medium effects introduced at parton splitting
Apr 18, 2023 Jan Rak 8
Azimuthal correlation function in Azimuthal correlation function in pp++pp @ @ s=200 GeVs=200 GeV
d+Au
Phys.Rev.D74:072002,2006
N
A
N jT jet fragmentation transverse momentum
F kT parton transverse momentum
YA folding of D(z) and final state parton dist.
p + p jet + jet
Apr 18, 2023 Jan Rak 9
Jet shape evolution with trigger and Jet shape evolution with trigger and assoc. assoc. ppTTAu+Au / p+p s = 200 GeV
arXiv:0705.3238 [nucl-ex]
Per-trigger yield vs. for various trigger and partner pT (pA
T pBT), arranged by
increasing pair momentum (pAT + pB
T)
• Flat region:
celebrated b2b disappearance
• Punch through region (HR):
reappearance at high-pT
• Shoulder region (SR):
Medium induced “Mach cone”
•Low pT:
Enhancement in SR & suppression in HS
•High pT:
Reappearance of away-side jet not due to merging of side peaks
Apr 18, 2023 Jan Rak 10
Dihadron correl. AuDihadron correl. Au++AuAu @ @ s=200 GeVs=200 GeV
RHS =Yjet( )d
HR∫Yjet( )d
SR∫
RHS =Yjet( )d
HR∫Yjet( )d
SR∫
Truncated mean 1<pTa<5 GeV/cTruncated mean 1<pTa<5 GeV/c
The width and the truncated pT of the shoulder peak are more **similar to the near peak** rather to the away side one
The width and the truncated pT of the shoulder peak are more **similar to the near peak** rather to the away side one
Apr 18, 2023 Jan Rak 11
Mach cone ?Mach cone ?
Consistent with p+p
Narrower by 20%
Mach cone significantly narrower (by 20%) as compared to peripheral away peak. Is Mach cone narrower than Delta function??
Mach cone significantly narrower (by 20%) as compared to peripheral away peak. Is Mach cone narrower than Delta function??
Apr 18, 2023 Jan Rak 12
Details on two-particle Details on two-particle correlations in correlations in pp++pp
Fragmentation function D(z) and
Intrinsic momentum kT
Fragmentation function D(z) and
Intrinsic momentum kT
Apr 18, 2023 Jan Rak 13
Soft + hard QCD Soft + hard QCD radiationradiation
k kTT phenomenology phenomenology
dd
=δ( −) dd)qT
pTγ=δ()qT −pTγ )
dd
=δ( −) dd)qT
pTγ=δ()qT −pTγ )
Back-to-back balanced
Soft QCD radiationSoft QCD radiation
dd
∝Gauss( ) dd)qT
pTγ∝Gauss(pTγ )
dd
∝Gauss( ) dd)qT
pTγ∝Gauss(pTγ )
dd
∝1
−n dd)qT
pTγ∝
1pTγ
−n
dd
∝1
−n dd)qT
pTγ∝
1pTγ
−n
Hard NLO radiationHard NLO radiation
q + g→ quark( )qT ) +photon(pTγ )Compton photo-production
Apr 18, 2023 Jan Rak 14
kT2 =
2
pT ,pair2 = kT
2
intrinsic+ kT
2
soft+ kT
2
NLOkT
2 =2
pT ,pair2 = kT
2
intrinsic+ kT
2
soft+ kT
2
NLO
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Phys. Rev., 1981, D23, 604
PHENIX
Resummation techniques:D. Boer and W. Vogelsang,Phys. Rev. D69 (2004) 094025 J. Qiu and I. Vitev,Phys. Lett. B570 (2003) 161
dd)qT
pTγ∝ exp(−)qT
2 ) ⊗ )qT−n
dd)qT
pTγ∝ exp(−)qT
2 ) ⊗ )qT−n
Apr 18, 2023 Jan Rak 15
Correl. fcn width - Correl. fcn width - kkTT and and acoplanarityacoplanarity
€
pout = 2 kTy
pTa
ˆ p Ta
⇒ pout2 = zt kT
2 xh
ˆ x h
pT,pair Lorentz boost preserves
€
M inv2 = 4 ˆ p T
2 = 2 ˆ p Ttˆ p Ta − 2 ˆ
r p Tt
ˆ r p Ta
€
ˆ x h =ˆ p Ta
ˆ p Tt
xh =pTa
pTt
€
ˆ x h−1 zt kT
2 = xh−1 pout
2 − jTy2 (1+ xh
2)partonic hadronic
Jet momenta imbalance due to kT smearing
Lab frame
Hard scattering rest frame
From an analysis of associated yield
Apr 18, 2023 Jan Rak 16
Assoc. yield - “Averaged” pQCD Assoc. yield - “Averaged” pQCD approachapproach
Assumptions (Phys.Rev.D74:072002,2006 for details) :
1. Invariant mass of mass-less partons in hard-scattering CMS and in LAB is the same -> non-Gaussian kT-smearing
2. Effective FS parton distribution:
3. Effective Fragmentation function:
,,γ to be extracted from fit to gamma-h or LEP
One can then evaluate:
1. Inclusive 0 cross section
2. Trigger 0 associated dist.
1'
2
1( ) ( )
T
TQ
T T x
d dz pD z
p dp z z = ⋅ ⋅Σ∫
1'
2
1( ) ( )
T
TQ
T T x
d dz pD z
p dp z z = ⋅ ⋅Σ∫
( ) (1 ) (1 )D z z z z γ= ⋅ − ⋅ +( ) (1 ) (1 )D z z z z γ= ⋅ − ⋅ +
€
ΣQ ( ˆ p T )∝ ˆ p T−n
€
ΣQ ( ˆ p T )∝ ˆ p T−n
M inv2 =4 p̂T
2 =2 p̂Tt p̂Ta −2 ˆrpTt ˆ
rpTa M inv
2 =4 p̂T2 =2 p̂Tt p̂Ta −2 ˆ
rpTt ˆ
rpTa
Apr 18, 2023 Jan Rak 17
Trigger associated spectra are Trigger associated spectra are insensitiveinsensitive to to D(z)D(z)
LEP data MJT Approximation - Incomplete Gamma function when assumed power law for final state PDF and exp for D(z)
xE =
rpTa ⋅
rpTtr
pTt2 =−
pTa
pTt
cosφ≈−pTa
pTt
yield
d
dpTt
=1
pTtn−1 dztzt
n−2
xTt
1
∫ e−b.zt ≈ m (n−1)1)xh
1+xE)xh
⎛
⎝⎜⎞
⎠⎟
−n
Apr 18, 2023 Jan Rak 18
Unavoidable Unavoidable zz-bias in di-hadron -bias in di-hadron correlationscorrelations
z-bias; steeply falling/rising D(z) & PDF(1/z)
ztrig
zassoc
Varying pTassoc with pTtrigger kept fixed leads to variation of both trigger and associated jet energies.
Fixed trigger particle Fixed trigger particle momentummomentum
does notdoes not fixfix
the the jet energyjet energy!!
Angelis et al (CCOR):Nucl.Phys. B209 (1982)Angelis et al (CCOR):Nucl.Phys. B209 (1982)
Apr 18, 2023 Jan Rak 19
kkTT bias bias
pT ,γ ∝Gauss( kT
2 )⊗1)pT8
Small kT (Gauss) and large pT power law
less probable than
Large kT (Gauss) and small pT power law
Even at relatively high photon momentum (10 GeV/c) γ-h pairs still not fully in power law pQCD regime.
Apr 18, 2023 Jan Rak 20
kk22TT and and zztt in p+p @ 200 GeV from in p+p @ 200 GeV from
00-h CF-h CFPhys.Rev.D74:072002,2006
For D(z) the LEP date were used. Main contribution to the systematic errors comes from unknown ratio gluon/quark jet => D(z) slope.
Base line measurement for the kT broadening - collisional energy loss. Direct width comparison is biased.
Still, we would like to extract FF from our own data -> direct photon-h correl.
Apr 18, 2023 Jan Rak 21
High pHigh pTT: ref. for HI, : ref. for HI, resummation, detailed NLO testsresummation, detailed NLO tests
PHENIX measured pTpair=3.360.090.43GeV/c
extrapolation to LHC k2T36 GeV2/c2
G.G. Barnaföldi, P.Levai
Apr 18, 2023 Jan Rak 22
Avoidable in Direct Photons Avoidable in Direct Photons CorrelationsCorrelations
q
qg
γ q
q g
γ
Compton Annihilation
q
q
q
q
g
g
g
γγ
Bremsstrahlung
Direct Photon Processes
These two diagrams fix the jet energy scale
Up to the kT effect !
Fragmentation photons measured using isolation cut analysis
ztrig =1±kT / )pT Q2 ≈const dN/dzassoc ∝ D(z)
Apr 18, 2023 Jan Rak 23
Direct Direct γγ-h Correlations in PHENIX p+p -h Correlations in PHENIX p+p s=200 GeVs=200 GeV
Run 5 p+p @ 200 GeV
5-7 X 1-2 GeV/c 7-9 X 1-2 GeV/c
5-7 X 2-5 GeV/c 7-9 X 2-5 GeV/c 9-12 X 2-5 GeV/c
9-12 X 1-2 GeV/c
Statistical Subtraction method:
γdirect = γall - γdecay
Matthew Nguyen APS Spring Meeting, April 15,
2007
• Signature small near-side correlation signal apparent
• Yield sensitive to contribution at the near-side
• Still room for some fragmentation contribution
Apr 18, 2023 Jan Rak 24
0 Direct γ
PHENIX PHENIX s=200 GeV s=200 GeV 00 and dir- and dir-γγ assoc. assoc. distributionsdistributions
Run 5 p+p @ 200 GeVStatistical Subtraction Method
Arb
itrar
y N
orm
aliz
atio
n
Arb
itrar
y N
orm
aliz
atio
n
Matthew Nguyen APS Spring Meeting, April 15, 2007
Exponential slopes still vary with trigger γ pTγ.
If dN/dxEdN/dz then the local slope should be pTγ independent.
xE =
rpTa ⋅
rpTtr
pTt2 =−
pTa
pTt
cosφ≈−pTa
pTt
FF slope
Apr 18, 2023 Jan Rak 25
Pythia Initial/Final st. Pythia Initial/Final st. radiation & radiation & kkTT
Initial/Fina state radiation OFF, k
2T=0 GeV/c
Initial/Fina state radiation OFF, k
2T=0 GeV/c
Initial/Fina state radiation ON, k
2T=5 GeV/c
Initial/Fina state radiation ON, k
2T=5 GeV/c
Apr 18, 2023 Jan Rak 26
Photon associated yields - Photon associated yields - “averaged” pQCD“averaged” pQCD
P()pTt &
)pTa ) )
pT
)pTt +
)pTa)pTt
)pTa −)pT2
exp( )pTt +
)pTa)2 −4 )pT
2
2 kTx2
⎛
⎝⎜⎜
⎞
⎠⎟⎟
)pTt =gamma mom.
P()pTt &
)pTa ) )
pT
)pTt +
)pTa)pTt
)pTa −)pT2
exp( )pTt +
)pTa)2 −4 )pT
2
2 kTx2
⎛
⎝⎜⎜
⎞
⎠⎟⎟
)pTt =gamma mom.
dN
dpTa pTt
=D(zt)⊗ ΣQ' (
pTt
zt
)⊗ d∫ )pTt P()pTt &
)pTa) )pT
dN
dpTa pTt
=D(zt)⊗ ΣQ' (
pTt
zt
)⊗ d∫ )pTt P()pTt &
)pTa) )pT
kT bias still important, sensitivity to the D(z) shape as expected, the slope is also changing as in the data - parton imbalance.
PYTHIA
Apr 18, 2023 Jan Rak 27
LO in LO in S S and BDMPS quenching and BDMPS quenching weightweight
F. Arleo, hep-ph/0701207
Absolutely no matching between dNd/z and D(z). This is because of the important contribution of the fragmentation-photon channel, as well as the restricted kinematical z window.
Apr 18, 2023 Jan Rak 28
SummarySummaryInclusive and two-particle correlation measurement in the high-pT sector at RHIC opened a new window into a QGP physics. Inclusive measurements have limited discrimination power -> complementary multiparticle correlations are important. However, two-particle correlations are not bias-free either:
di-hadron correlations:
• kT and initial/final state QCD radiation, resummation vs NLO
• jT near-side jet shape modifications
• z-bias washes out the sensitivity of the associated xE yield to the Fragmentation Function.
direct photon-hadron correlations
• Fragmentation function can be extracted from the associated xE yield. However
• kT-bias still present - pushes the minimum photon-trigger pT above 10 GeV/c at RHIC.