direct photons and jet correlation in hi. integrated i aa (0.4
Post on 20-Dec-2015
213 views
TRANSCRIPT
Direct photons and Jet correlation in HI
Direct photons and Jet correlation in HI
DongJo Kim Feb 15 2007 Munster DongJo Kim Feb 15 2007 Munster
Integrated IAA(0.4<xE<1.0) similar with RAA!
• more suppression, as peripheral central • similar to 0 RAA values!
Promising solution: direct -jets
q g
Calibrated probe of the QGP – at LO, ET, = Pre-quenched ET,jet
No Surface Bias – clearer picture of jet fragmentation modification Hard process – pQCD calcs agree well with data
has no E-loss in medium!
Size of medium
But D(z) is effectively softened in opposing jet
How to construct direct -h yield i. Construct inclusive -h yield
ii. Construct decay -h yield via:– Pair by pair weighted
summation method i. convolutes all 0-h pair
contributions from higher pT
ii. Weight reflects the probability from kinematics for a 0 at given pT to decay into a photon in a given pT range
iii. Subtraction via:
)1
(/11
1hdechinchdir Y
RY
RY −−− −
−=
Assume two photon sources, ( = # photons in data sample):
directdecayincl +=
pT=5-7 GeV/c
pT=9-12 GeV/c
decaydirect
decay direct
Direct photons:
LO (compton, annihilation,…)
NLO (bremsstrahlung, fragmentation)
Hadronic decay photons:
2
2
each’decay
0
Measuring direct -jet yields (I)
Assume two photon sources, ( = # photons in data sample):
Let Y = per-trigger conditional jet pair yield (1/Ntrig)dNpairs/d():
Write in terms of R
decaydirectincl +=
decayincl
decaydir
incl
dirincl YYY
+=
decay
dir
decay
incl
simdecay
measincl
R
+=≅≡ )/()/(
)1(
1)
11(
−−
=→+−=
RYYR
YYR
YR
Y decayincldirdecaydirincl
Measuring direct -jet yields (I)
direct-h± in PYTHIA*
• (LO) prompt-h±
• (NLO) frag-h±
pT =7-9 GeV/c, pT
h =2-5 GeV/c 200GeV
Direct -h:
On near side, PYTHIA says only NLO s contribute.
*For amusement only. Not for serious quantitative predictions
Direct -h yield: Au+Au
• Near side yields consistent with 0 or very small from fragmentation photons
• Away side yields also small, suppressed!?
Away side Integrated yield
• p+p shows a systematic trend of having higher yields in the away side than Au+Au!
We expect that the proportion of direct photons is enhanced as the size of the medium increases, since R is sensitive to suppression.
If two different systems (e.g. Central Cu+Cu and mid-central Au+Au) suppress 0s and s by the same amount, then they should have comparable R values.
Component 2 of 3: “double ratio” R
Component 2 of 3: “double ratio” R
4444 84444 76%200%5030 −− ≈ partpart NCuCuNAuAu
Double ratio R measured in AuAu, but not yet in CuCu…
Use <Npart> scaling to map AuAu R CuCu.
We will refer to the quantity “(direct/decay)Au+Au interp.”
Full test of method in PYTHIA
Black: correlations with “true” direct photon triggers (ID’ed in event record)
Blue: direct photon correlations produced by subtraction method
The bias toward a low jet yield is worse for lower pT photon triggers, where R is smaller.
If one increases R by ~10%, the “true” correlation is roughly recovered. We use this 10% to gauge the systematic error from the subtraction method.
Magenta: direct g-jet per-trigger yield, subtraction method as above, but with R scaled up by 10%
R = 1.90
R = 1.1*1.90 *Please note: This bias is due to the method, not uncertainty in R!
-h+/- != decay-h+/- (can’t neglect ,…)
We are currently working hard to reduce this systematic error.
Dir
ect -
h p
airs
/tri
gg
er
Preliminary Cu+Cu Results: direct -h+/-
per-trigger jet pair yields: systematic from R
systematic from subtraction method
Cu+Cudirect-h+/- vs. -h+/- jet yields
per-trigger jet pair yields: systematic from R
systematic from subtraction method
Direct photons in 200GeV Au+Au
Blue line: Ncoll scaled p+p cross-section• 900M events
• Reached up to 18GeV/c
• Qualitatively well described by NLO pQCD calculations
Direct photon RAA in 200GeV Au+Au
• Used p+p data is the denominator– NLO pQCD as
denominator is shown as well for a reference
• For pT<10GeV, RAA is consistent with Ncoll scaled p+p reference.
• RAA seems to decrease at very high-pT
• Difference of NLO pQCD calcuation and p+p data affects quite a bit.
RAA with pQCD
RAA with p+p data
Comparison with some models
• 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.??
What is expected from structure function?
100 xT
Au+Au minimum bias
Structure function ratios drops by ~20% from x=0.1 to 0.2?
Eskola,Kolhinen,Ruuskanen Nucl. Phys. B535(1998)351
What is expected from isospin effect?
• Werner Vogelsang provided direct photon cross-section in p+p, p+n and n+n at 200 and 62.4GeV
• Minimum bias Au+Au can be calculated by:
)Z)-(A Z)-2Z(A (Z)(1/A /N nn2
pnpp22
collAA σσσσ ++×=
What is RAA for pure hard scattering
• Consistent with F. Arleo’s work.
• Werner’s comment: The isospin effect has to be bigger than for 0, because for 0 the qg channel is proportional to g(x1)*(u+d+ubar+dbar)(x2), among other things, which is flavor and isospin "blind"…
• 62GeV Direct photon would be a good measure of the effect
– The effect could be seen in lower pT region, where the analysis is rather established
• Interplay of jet-photon conversion and isospin effect in 4-6GeV/c region would be, though
One message: RAA<1 for direct photons does not necessarily mean that our messageof “0 suppression at high pT” changes
Direct photon v2 ~what we would see?~• pT>3GeV/c
– N-N and jet fragmentation (v2>0)– Jet-photon conversion, in-medium
bremsstrahlung (v2<0)– Higher the pT gets, lower the v2
become.
• pT<4GeV/c– Thermal photon v2 based on
hydro calculation (roughly 20-30% centrality)
• Quark flow ~ photon flow– dilepton v2 is also predicted, and
is in the same order
annihilationcomptonscattering
Bremsstrahlung (energy loss)
jet
jet fragment photon
v2 > 0
v2 < 0 Chatterjee et al. PRL 96, 202302 (2006)
Turbide, et al., PRL96, 032303(2006)
Direct photon v2 in Au+Au collisions• Hadron decay photon subtracted
from inclusive photon v2.
• Reached up to ~8GeV/c (~4GeV/c in Run2)
• Tends to be positive?
PHENIX PreliminarysNN=200GeV Au+Au
PHENIX PreliminarysNN=200GeV Au+Au
Finalizing systematic errors..
1
).().().( 22
2 −−×
=R
bkgdvinclvRdirv