25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow ...
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Transcript of 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow ...
25.01.2007 RELNP seminar, ITEP, S.Kiselev 1
Direct photons. Data review.Sergey Kiselev, ITEP Moscow Introduction Before QM’06
p+p: prompt γA+B: experimental methods
Subtraction method Momentum correlations methodInternal conversion method
QM’06high-pt
low-pt
elliptic flow v2
γ-h azimuthal correlation Conclusions
25.01.2007 RELNP seminar, ITEP, S.Kiselev 2
Introduction Direct photons: not from hadron decays Quark gluon level:
qq gγ, qg qγ, qq(g) qq(g)γ. Initial hard NN collisions, pQCD prompt γ.
Thermalised QGP stage thermal γ from QGP.
25.01.2007 RELNP seminar, ITEP, S.Kiselev 3
Introduction – cont. Hadron level:
meson scatterings: ππ ργ, πρ πγ, πK K* γ, Kρ Kγ, KK* πγ, πK* Kγ, . . .
Thermalised hadron stage thermal γ from hadron gas Decay photons:
Long lived (c » cAB ~ 50-100 fm) π0 γγ, γγ, ’ ργ/ωγ/2γ
Shot lived (c cAB ~ 50-100 fm) ω πγ, a1 πγ, Δ Nγ, K* Kγ, γ, ρ ππγ, . . .
25.01.2007 RELNP seminar, ITEP, S.Kiselev 4
Prompt : pp data A Compilation of Data, J. Phys. G, 23 (1997) A1 Data fit: D.Srivastava, Eur.Phys.J, C22 (2001) 129
25.01.2007 RELNP seminar, ITEP, S.Kiselev 5
Prompt : data fit
25.01.2007 RELNP seminar, ITEP, S.Kiselev 6
Prompt : other data fit PHENIX
hep-ph/0609037 d3σ/dyd2pT = (√s)5 ·
F(xT,y)
25.01.2007 RELNP seminar, ITEP, S.Kiselev 7
Prompt : data/theoryP.Aurenche et.al, PR D73, 094007 (2006), with PHENIX, D0 dataThe data can be described (accuracy ~ 50%) within the NLO QCD (JETPHOX code), except E706 experiment.
25.01.2007 RELNP seminar, ITEP, S.Kiselev 8
Experimental methods for direct photons
Last years: large progress in experimental techniques to extract direct photons
Direct photons have been revealed by methods: Subtraction method, WA98/2000, PHENIX/2005 Momentum correlation method, WA98/2004 Internal conversion method, PHENIX/2005 External conversion method, PHENIX/2006, QM’06
25.01.2007 RELNP seminar, ITEP, S.Kiselev 9
Subtraction method Direct photon measurement
by the subtraction method: WA98 PRL 85 (2000) 3595, PHENIX PRL 94 (2005) 232301
WA98 subtracted from measured photons those from known hadronic source: from decays of reconstructed o, and other hadrons (with some assumption of its yield and spectrum)
At pt > 0,5 GeV/c from o from from from ’
25.01.2007 RELNP seminar, ITEP, S.Kiselev 10
Subtraction – WA98
25.01.2007 RELNP seminar, ITEP, S.Kiselev 11
Subtraction – PHENIXPRL 94, 232301 (2005)
.
2
2
//
/)(
inelcollAA
TNN
AA
TAA
TAA
NTddpNdTddpNdpR
25.01.2007 RELNP seminar, ITEP, S.Kiselev 12
Momentum correlations method momentum
correlations, WA98 PRL 93 (2004) 022301, STAR nucl-ex/0511055 correlations
direct photons direct photons
correlation provide the system sizes at all stages of heavy-ion collisions
Needs larger statistics
25.01.2007 RELNP seminar, ITEP, S.Kiselev 13
Momentum correlations – WA98 Rinv (≈ 6 fm ≈
Rinv ( emitted in the late,
hadron gas, stage of the collision
Thermal calculations substantialy underestimate the data.
25.01.2007 RELNP seminar, ITEP, S.Kiselev 14
Internal conversion method A novel technique
(QM’05): internal conversion of direct photons into e+e-, PHENIX, nucl-ex/0511041 any source of real
emits also virtual with very low-mass
directdirectincl.) incl.
Electrons in the central arms were identified by matching charged particle tracks to clusters in the ECAL and to rings in the RICH
25.01.2007 RELNP seminar, ITEP, S.Kiselev 15
Internal conversion - details
32
2222
2
2
2
112141321 )
Mm()m(F
m)
mm(
mm
dmdN
Nee
eeeeee
e
ee
e
ee
ee
Main assumption: the Kroll-Wada (KW) formula, Phys.Rev.98(1955)1355A given reaction produces, instead of real γ, γ* e+e-. For decays:
Nγ – number of real γπo γγ πo γγ* γe+e- I=KW = 0.0059η γγ η γγ* γe+e- I=KW = 0.0081γdirect γ*direct e+e- I=KW = 0.0162 phase space factor =1, if pee
T » mee
25.01.2007 RELNP seminar, ITEP, S.Kiselev 16
Internal conversion – cont. Measurement for 1 < pT < 5
GeV/c consistent with calculations when thermal photon emission is taken into account (at high pT > 5 it is consistent with a NLO pQCD calculation).
25.01.2007 RELNP seminar, ITEP, S.Kiselev 17
RAA vs pT for direct photons
.
2
2
//
/)(
inelcollAA
TNN
AA
TAA
TAA
NTddpNdTddpNdpR
QM’05:High pT direct photonsare not suppressed strong suppression of mesons is not an initialeffect, but a final stateeffect
25.01.2007 RELNP seminar, ITEP, S.Kiselev 18
Quark Matter 2006 PHENIX data High-pT direct photon
Hard scattering Talk by T.Isobe
Low-pT direct photon Thermal emission from
QGP. Talk by D. Peressounko
Azimuthal anisotropy of direct photon Talk by V.S. Panteuev
γ- h azimuthal correlations Talk by J. Jin
Enter STAR into the game…
Run Year Species s1/2 [GeV ] Ldt
01 2000 Au+Au 130 1 b-1
02 2001/2 Au+Au 200 24 b-1 p+p 200 0.15 pb-1
03 2002/3 d+Au 200 2.74 nb-1 p+p 200 0.35 pb-1
04 2003/4 Au+Au 200 241 b-1 Au+Au 62 9 b-1
05 2004/5 Cu+Cu 200 3 nb-1 Cu+Cu 62 0.19 nb-1 Cu+Cu 22.5 2.7 b-1 p+p 200 3.8 pb-1
06 2006 p+p 200 93.3 pb-1 ?
p+p 62 1.1 pb-1 ?
07 2007 Au+Au 200
25.01.2007 RELNP seminar, ITEP, S.Kiselev 19
Systematic Study of High-pT Direct Photon Production with the PHENIX Experiment at RHIC
Tadaaki Isobe (CNS, Univ. of Tokyo)for the PHENIX Collaboration
The 19th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions
at Shanghai, China
25.01.2007 RELNP seminar, ITEP, S.Kiselev 20
High-pT direct photons: where are we?
p+p: agreement with NLO pQCD.
Run2 high-pT direct photons in Au+Au: consistent with binary scaled NLO pQCD.
Binary scaling is not obvious. 70% prompt photon + 30% jet
fragmentation at high-pT. Fragmentation photons are
suppressed by jet-quenching effect at RHIC?
Compensated by other contribution?
30% contribution from jet frag.
Phys. Rev. Lett. 94, (2005) 232301
25.01.2007 RELNP seminar, ITEP, S.Kiselev 21
Fraction of fragmentation photons Fraction of fragmentation photons
is evaluated in terms of the fraction of isolated photons in 200GeV p+p collisions.
If energy of cone around a target photon is much less than the energy of photon, the photon is defined as isolated photon.
Isolation cut removes fragmentation (Bremsstrahlung) photons.
Data are consistent with theoretical expectation within the error. hep-ex/0609031
Jet
Theoretical predictions where PHENIX acceptance is taken into account
25.01.2007 RELNP seminar, ITEP, S.Kiselev 22
Parameterization of the p+p data For the calculation of nuclear
modification factor, p+p reference is parameterized using a fitting function.
The fitting works well to parameterize the p+p photon data.
The parameterized photon data show enhancement comparing with NLO pQCD expectation by a factor of more than 20%.
Data Fit
25.01.2007 RELNP seminar, ITEP, S.Kiselev 23
Interaction of hard-scattered parton with dense matter. Compton scattering (jet-photon
conv.) R.J. Fries, Phys.Rev. C72
(2005) 041902 Over estimation at high-pT
S. Turbide, Phys.Rev. C72 (2005) 014906
Reproduce data well Bremsstrahlung
B.G. Zakharov, JETP Lett. 80 (2004) 1
If it is observed, it can be used as hard probe of bulk matter.
Medium induced high-pT direct photons
Jet-quenching effect for fragmentation photons are estimated with AMY formalism.
QGP-ThermalJet-photon
NLO-pQCD
All
Hard scattered parton interacts with gluon in bulk matter
25.01.2007 RELNP seminar, ITEP, S.Kiselev 24
Direct photon RAA
Nuclear modification factor Yield from hard processes can be
scaled with Ncoll (# of collisions). divided by expected (binary scaled)
yield from p+p data.
RAA is consistent with Ncoll scaled p+p reference.
RAA of very high-pT direct photons is below one. A hint of jet-quenching effect for
fragmentation photons? RAA using pQCD shows different
tendency.
.
2
2
//
/)(
inelcollAA
TNN
AA
TAA
TAA
NTddpNdTddpNdpR
First data using p+p data as reference!
Thanks to the more accurate p+p/Au+Au data.
RAA with pQCD
RAA with p+p data
.
2
2
//
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inelcollAA
TNN
AA
TAA
TAA
NTddpNdTddpNdpR
25.01.2007 RELNP seminar, ITEP, S.Kiselev 25
Comparison of RAA with theoretical calculation Turbide et al.
Phys. Rev. C72 (2005) 014906 + Private communication. AMY formalism for jet-
quenching effect for fragmentation photons.
Systematically data points are below theoretical prediction.
F. Arleo JHEP 0609 (2006) 015
High-pT suppression due to isospin effect, in addition to jet-quenching and shadowing. BDMPS for jet-
quenching. Medium induced jet-photon is
not taken into account. The suppression of very high-pT
photon is well reproduced.
25.01.2007 RELNP seminar, ITEP, S.Kiselev 26
Summary/T.Isobe Direct photons in 200GeV p+p collisions.
Published final year-3 p+p data. Preliminary year-5 data. Consistent with NLO pQCD within uncertainty.
Direct photons in 200GeV Au+Au collisions. Clear signal of direct photon at high-pT thanks to the strong
suppression of neutral hadrons. Spectra up to 20GeV/c.
First direct photons RAA in 200GeV Au+Au collisions with p+p reference. Almost consistent with binary scaled p+p data. RAA seems to be below one at very high-pT region.
25.01.2007 RELNP seminar, ITEP, S.Kiselev 27
Direct photons at low pt measured in PHENIX
D.Peressounko RRC “Kurchatov institute”
for the PHENIX collaboration
25.01.2007 RELNP seminar, ITEP, S.Kiselev 28
Subtraction and Tagging methods
Measure photon spectrum and remove those photons which make 0 mass with any other
Correct direct photon candidate sample for contribution from 0 decay photons with missing partner and for direct photons with fake partners
Subtract contribution from , etc. decays
Measure yield of inclusive photons corrected for hadron contaminations, conversion, efficiency and acceptance.
Measure spectrum of 0, , etc.
Calculate yield of decay photons and subtract it from the inclusive yield.
Ndir = N
incl - Ndecay
Subtraction Tagging
25.01.2007 RELNP seminar, ITEP, S.Kiselev 29
d+Au collisions: Double ratio
• Internal conversion method provides smaller systematic errors • But not as small as in the case of Au+Au collisions in Run-4 (Large background of external conversion on MVD detector in Run-3)
25.01.2007 RELNP seminar, ITEP, S.Kiselev 30
d+Au collisions: Spectrum
Internal conversion extends range of significant points to pt > 2 GeV
Data agrees with pQCD predictions in full pt range
=> No indication for nuclear effects
25.01.2007 RELNP seminar, ITEP, S.Kiselev 31
Au+Au collisions: External conversion
Combining this photon with others measured in EMCAL with loose PID cut, estimate proportion of photons coming from 0 decays
Correct for missing 0 decay partners Subtract , , ’ decay photons Calculate ratio N
all/Ndecay
Use very tight PID cut on EMCAL photons to produce very clean photon sample
Use external photon conversion in beam pipe to produce very clean photon sample
External conversion Tagging
no pair cutwith pair cut
Dal
itz
Conversion
Uses very pure photon sample avoid explicit calculation of 0 spectrum
=>reduce systematic errors
25.01.2007 RELNP seminar, ITEP, S.Kiselev 32
Comparison: Au+Au, central collisions
Spectra agree within errors in entire pt range
Systematic errors are still too large to extract thermal photons.There is room for thermal photons
This is consistent with excess above pQCD reported previously
25.01.2007 RELNP seminar, ITEP, S.Kiselev 33
Two-photon correlations
1
2
1
2rec
e-
e+
External conversion:• No close cluster interference• No hadron contamination
C2 calculated in EMCAL and converted+EMCAL agree =>both effects are under control
25.01.2007 RELNP seminar, ITEP, S.Kiselev 34
Conclusions/D.Peressounko Measurement of direct photon yield at small pt
is very interesting but extremely complicated task
PHENIX has developed a variety of methods for direct photon extraction in p+p, d+Au and Au+Au collisions producing consistent results
Because of the large systematic errors comparison of binary scaled d+Au spectrum with Au+Au does not allow to make a statement on the origin of the excess above pQCD observed in Au+Au.
More precise data are coming…
25.01.2007 RELNP seminar, ITEP, S.Kiselev 35
PHENIX measurements of reaction plane dependence of high pT photons and pions in Au+Au collisions
Vladislav Pantuev, University at Stony Brookfor PHENIX collaboration
25.01.2007 RELNP seminar, ITEP, S.Kiselev 36
Compton AnnihilationIn p+p Hard photons:direct component
q + g + q q + q + g
Photons in A+A
Direct Photons Decay Photons
hard thermal hard+thermal
QGP Hadron gasdirect fragmentation
Preequilibriumphotons
jet--conv.
Medium induced bremsstr.
In A+A picture is much more complicated:
V2=0V2<0V2<0
V2>0V2>0V2>0
25.01.2007 RELNP seminar, ITEP, S.Kiselev 37
There are theoretical predictions with a sizable azimuthal parameter v2 :
S.Turbide, C.Gale, R.J.Fries, PRL 96 032303 (2006)R. Chatterjee et al., PRL 96, 202302 (2006)
Thermal photons are produced throughout the expansion history and reflect quark anisotropy
Jets lose more energy where the medium is thicker - more jet-photon conversions (v2<0), + photons from fragmentation of quenched jets (v2>0)
4
25.01.2007 RELNP seminar, ITEP, S.Kiselev 38
How does PHENIX measure direct photons and v2?
Measure inclusive photon yield, Ninc Measure hadron contribution components 0 and By Monte Carlo calculate and decay background in
inclusive sample, Nbg Calculate direct photon excess over hadron decays, R Measure inclusive and hadron v2 by reaction plane
method Calculate direct photon v2 as R * v2
inc – v2BG
R = N inc / NBG
v2dir =
R – 1Use large statistics Run 4 Au+Au data set
See also poster 86 by Kentaro Miki
5
25.01.2007 RELNP seminar, ITEP, S.Kiselev 39
Step by step calculations:
PHENIX preliminary
PHENIX preliminary
PHENIX preliminary
PHENIX preliminary
6
25.01.2007 RELNP seminar, ITEP, S.Kiselev 40
PHENIX direct photon v2 result
Within statistical and systematic errors v2 is consistent with zero. v2=0 or cancellation of different contributions?
Systematic errors dominantly from R:
Enormous background of decay photons at low pT
7
25.01.2007 RELNP seminar, ITEP, S.Kiselev 41
PHENIX Measurement on High pT h-h and -h Azimuthal Correlations
Jiamin Jin
For the PHENIX collaborationQuark Matter 2006, ShanghaiNov. 18, 2006
25.01.2007 RELNP seminar, ITEP, S.Kiselev 42
Method Construct inclusive -h yield Construct decay -h yield via:
Pair by pair weighted summation convolutes all 0-h pair
contributions from higher pT Weight reflects probability from
kinematics for 0 at given pT to decay into photon in given pT range
Subtraction via:
hdecYhincRYRhdirY
11
# inclusive # inclusive ##decay decay
p+p
R=R=
25.01.2007 RELNP seminar, ITEP, S.Kiselev 43
First direct -h yield in p+p, cmp with PYTHIA!p+p: important baseline measurement!p+p: important baseline measurement!
• data PYTHIA PYTHIA 6.1 kT = 2.5 GeV
• A nice confirmation of our method
PHENIX Preliminary PHENIX Preliminary
25.01.2007 RELNP seminar, ITEP, S.Kiselev 44
•v2 modulated bkgd for inclusive/decay subtracted from each corr. fn under ZYAM assumption (v2 from single measurements)•Near side yield consistent with 0 small fragmentation photon yield
• Away side yield also small, suppressed!?
Au+Au: study medium induced modification!Au+Au: study medium induced modification!
First direct -h yield in Au+Au!1/
Ntri
gdN/
d
(rad) (rad)
1/N
trigdN
/d
25.01.2007 RELNP seminar, ITEP, S.Kiselev 45
Comparison btw Au+Au and p+p
• Hint of away side modification in AuAu!
Black: Au+Au Red: p+p
1/N
trigdN
/d
(rad)
1/N
trigdN
/d
(rad)
25.01.2007 RELNP seminar, ITEP, S.Kiselev 46
Away side integrated yield• trigger pT dependence• assoc. h pT dependence• centrality dependence + pp
• p+p shows a systematic trend of having higher yields in the away side than Au+Au!
25.01.2007 RELNP seminar, ITEP, S.Kiselev 47
Conclusions/J.Jin
First measurements of high pT direct -h yields in Au+Au/p+p collisions Near side yield ~ 0 Hint of suppression of away side jets in Au+Au Need more statistics to make conclusive
statement Upcoming Au+Au run
25.01.2007 RELNP seminar, ITEP, S.Kiselev 48
Conclusions High-pt: RAA in 200GeV Au+Au collisions seems to
be below one at very high-pT region. Low-pt: more methods, but errors are still too large.
More precise data are coming… Elliptic flow v2: within statistical and systematic
errors v2 is consistent with zero. γ-h azimuthal correlations: near side yield ~ 0, hint
of suppression of away side jets in Au+Au, need more statistics.
Multi-purpose Direct Photons