How to plot direct photon data
to learn something quantitative
and something new
M. J. Tannenbaum
Brookhaven National Laboratory
Upton, NY 11973 USA
December 7, 2006
How to plot direct photon data
M. J. Tannenbaum 1
LO-QCD in 1 slide
How to plot direct photon data
M. J. Tannenbaum 2
LO-QCD in 1 slide
C
A
B
f aA (x1 )
f bB (x 2 )
a
b
D
d
dtˆ
C /c
c
d
X
D
D/d
How to plot direct photon data
M. J. Tannenbaum 2
Relationship to DIS
How to plot direct photon data
M. J. Tannenbaum 3
Relationship to inclusive high pT production
in hadron collisions
How to plot direct photon data
M. J. Tannenbaum 4
ab(cos *) and Spin Asymmetry -Fundamental predictions of QCD
How to plot direct photon data
M. J. Tannenbaum 5
Paris1982-first measurement of QCD
subprocess angular distribution using
0-0 correlations
DATA: CCOR NPB 209, 284 (1982)
QCD
How to plot direct photon data
M. J. Tannenbaum 6
Paris1982-first measurement of QCD
subprocess angular distribution using
0-0 correlations
DATA: CCOR NPB 209, 284 (1982)
QCD
How to plot direct photon data
M. J. Tannenbaum 6
Application to direct photon production
See the classic paper of Fritzsch and Minkowski, PLB 69 (1977) 316-320
q
g
q
q
q
g
Compton
isolated
photons
Annihilation
small-ignore
Compton distribution is much flatter than scattering and peaked backwards from gluon
Substitution and Jacobean gives:
How to plot direct photon data
M. J. Tannenbaum 7
For AB collisions, taking the ratio to p-p
cancels everything but the structure functions
How to plot direct photon data
M. J. Tannenbaum 8
Semi-Inclusive measurements-I
How to plot direct photon data
M. J. Tannenbaum 9
Semi-Inclusive measurements-II
How to plot direct photon data
M. J. Tannenbaum 10
Semi-Inclusive measurementssomething new
How to plot direct photon data
M. J. Tannenbaum 11
There have been a few theory papers
• Ramona Vogt and collaborators have touched on this issue in a
few theory papers:
S. R. Klein and R. Vogt, PRL 91 (2003) 142301,
Emel’yanov, Khodinov, Klein,Vogt PRC 61 (2000) 044901
and a few previous papers cited in the above references
How to plot direct photon data
M. J. Tannenbaum 12
Our Beautiful
Data
How to plot direct photon data
M. J. Tannenbaum 13
Direct photon spectrum in d+Au collisions
Run-3 d+Au
Subtraction (pt<5 GeV)
and tagging (pt>5 GeV)
methods
Data agrees with
pQCD predictions
in entire pt range
=> No indication
for nuclear effects
NLO pQCD calculations from W.Vogelsang
How to plot direct photon data
M. J. Tannenbaum 14
Direct photon cross section
in p+p s = 200GeV
•
PHENIX Year-3 final result.
Submitted to PRL
hep-ex/0609031
•
Good agreement with
theoretical calculation (NLO
pQCD) within the error and
theoretical uncertainty.
How to plot direct photon data
M. J. Tannenbaum 15
RHIC-PHENIX year-5
direct photon cross-section
•
•
•
How to plot direct photon data
PHENIX Year-5
preliminary result.
pT region is extended up to
24GeV/c.
Good reference for the
evaluation of nuclear effect
for high-pT direct photon
production at RHIC.
M. J. Tannenbaum 16
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%.
How to plot direct photon data
Data
Fit
M. J. Tannenbaum 17
Direct photon spectra
in Au+Au sNN= 200GeV
Phys. Rev. Lett. 94, (2005) 232301
•
Run4 large amount of
Au+Au data make it
possible to extend the
pT range up to 20GeV/c.
How to plot direct photon data
M. J. Tannenbaum 18
Direct photon spectra
in Au+Au sNN= 200GeV
scaled232301
p+p cross-section
Phys.Blue
Rev.line:
Lett.N
94,
coll(2005)
•
Run4 large amount of
Au+Au data make it
possible to extend the
pT range up to 20GeV/c.
How to plot direct photon data
M. J. Tannenbaum 18
Re-plotting or
re-labelling the data
How to plot direct photon data
M. J. Tannenbaum 19
RdA in d+Au at sNN=200 GeV
d+Au Direct PHENIX Prelim
Both Direct and 0 consistent with 1
How to plot direct photon data
M. J. Tannenbaum 20
Direct is“EMC effect” for gluons
Nuclear Modification Factor-Min Bias
2
A
= Rg (x,Q )
Eskola, Kolhinen, Vogt hep-ph/0104124
100 xT
Consistent with 1 No modification within the error
This is first measurement of ‘EMC effect’ for gluons
How to plot direct photon data
x pT(RHIC) pT (LHC)
0.02 2 GeV/c 60 GeV/c
0.002 0.2 GeV/c 6 GeV/c
M. J. Tannenbaum 21
Direct photon RAA in Au+Au
•
Nuclear modification factor
Yield from hard processes can be scaled with N
coll
(# of collisions).
divided by expected (binary scaled) yield from p+p
data.
d 2Y AA /dpT dy
RAA ( pT ) =
TAA d 2 NN /dpT dy
TAA = N coll / inel.
•
•
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?
R
using pQCD shows different tendency.
AA
First data using p+p data
as reference!
Thanks to the more
accurate p+p/Au+Au data.
How to plot direct photon data
M. J. Tannenbaum 22
Direct photon RAA in Au+Au
•
Nuclear modification factor
Yield from hard processes can be scaled with N
coll
(# of collisions).
divided by expected (binary scaled) yield from p+p
data.
d 2Y AA /dpT dy
RAA ( pT ) =
TAA d 2 NN /dpT dy
TAA = N coll / inel.
•
•
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?
R
using pQCD shows different tendency.
AA
First data using p+p data
as reference!
Thanks to the more
accurate p+p/Au+Au data.
How to plot direct photon data
M. J. Tannenbaum 22
Direct photon RAA in Au+Au
•
Nuclear modification factor
Yield from hard processes can be scaled with N
coll
(# of collisions).
divided by expected (binary scaled) yield from p+p
data.
d 2Y AA /dpT dy
RAA ( pT ) =
TAA d 2 NN /dpT dy
TAA = N coll / inel.
•
•
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?
R
using pQCD shows different tendency.
AA
First data using p+p data
as reference!
Thanks to the more
accurate p+p/Au+Au data.
How to plot direct photon data
M. J. Tannenbaum 22
Direct photon RAA in Au+Au
•
Nuclear modification factor
Yield from hard processes can be scaled with N
coll
(# of collisions).
divided by expected (binary scaled) yield from p+p
data.
d 2Y AA /dpT dy
RAA ( pT ) =
TAA d 2 NN /dpT dy
TAA = N coll / inel.
•
•
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?
R
using pQCD shows different tendency.
AA
First data using p+p data
as reference!
Thanks to the more
accurate p+p/Au+Au data.
How to plot direct photon data
M. J. Tannenbaum 22
Direct photon RAA in Au+Au
•
Nuclear modification factor
Yield from hard processes can be scaled with N
coll
(# of collisions).
divided by expected (binary scaled) yield from p+p
data.
d 2Y AA /dpT dy
RAA ( pT ) =
TAA d 2 NN /dpT dy
TAA = N coll / inel.
•
•
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?
R
using pQCD shows different tendency.
AA
First data using p+p data
as reference!
Thanks to the more
accurate p+p/Au+Au data.
How to plot direct photon data
M. J. Tannenbaum 22
Direct photon RAA in Au+Au
•
Nuclear modification factor
Yield from hard processes can be scaled with N
coll
(# of collisions).
divided by expected (binary scaled) yield from p+p
data.
d 2Y AA /dpT dy
RAA ( pT ) =
TAA d 2 NN /dpT dy
TAA = N coll / inel.
•
•
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?
R
using pQCD shows different tendency.
AA
First data using p+p data
as reference!
Thanks to the more
accurate p+p/Au+Au data.
How to plot direct photon data
M. J. Tannenbaum 22
Direct photon RAA in Au+Au
•
Nuclear modification factor
Yield from hard processes can be scaled with N
coll
(# of collisions).
divided by expected (binary scaled) yield from p+p
data.
d 2Y AA /dpT dy
RAA ( pT ) =
TAA d 2 NN /dpT dy
TAA = N coll / inel.
•
•
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?
R
using pQCD shows different tendency.
AA
First data using p+p data
as reference!
Thanks to the more
accurate p+p/Au+Au data.
How to plot direct photon data
M. J. Tannenbaum 22
Direct photon RAA in Au+Au
•
Nuclear modification factor
Yield from hard processes can be scaled with N
coll
(# of collisions).
divided by expected (binary scaled) yield from p+p
data.
d 2Y AA /dpT dy
RAA ( pT ) =
TAA d 2 NN /dpT dy
TAA = N coll / inel.
•
•
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?
R
using pQCD shows different tendency.
AA
First data using p+p data
as reference!
Thanks to the more
accurate p+p/Au+Au data.
How to plot direct photon data
M. J. Tannenbaum 22
Direct photon RAA in Au+Au
•
Nuclear modification factor
Yield from hard processes can be scaled with N
coll
(# of collisions).
divided by expected (binary scaled) yield from p+p
data.
RAA with pQCD
d 2Y AA /dpT dy
RAA ( pT ) =
TAA d 2 NN /dpT dy
TAA = N coll / inel.
•
•
RAA is consistent with Ncoll scaled p+p
reference.
RAA of very high-pT direct photons is
below one.
RAA with p+p data
A hint of jet-quenching effect for fragmentation
photons?
R
using pQCD shows different tendency.
AA
First data using p+p data
as reference!
Thanks to the more
accurate p+p/Au+Au data.
How to plot direct photon data
M. J. Tannenbaum 22
A Better Theory Comparison using RAA
Au+Au minimum bias
Eskola,Kolhinen,Ruuskanen
Nucl. Phys. B535(1998)351
100 xT
Do the structure function ratios actually drop
by ~20% from x=0.1 to x=0.2?
How to plot direct photon data
M. J. Tannenbaum 23
Central Collisions---no theory counterpart-yet
Au+Au Central Collisions
Theorists, HELP!
??
100 xT
Nobody has yet measured nor calculated structure
function ratios as a function of centrality!!!
How to plot direct photon data
M. J. Tannenbaum 24
This could be the biggest result at QM2006
QM2005
-I wanted to make a T-shirt
QM2006If RAA= RAA the whole
concept of energy loss changes
How to plot direct photon data
M. J. Tannenbaum 25
Suggestions for other plots with the same data
1. Plot /0 for Au+Au vs centrality and compare to p-p. It would
be interesting to see whether /0 increases with pT in p-p and
whether it keeps increasing, plateaus or turns over in Au+Au.
2. Plot
This directly divides by the pT dependent point-like reference in
Au+Au eliminating the most of the uncertainty in initial state
structure function effects as well as eliminating the systematic
error from the uncertainty in the normalization of the p-p cross
section. It is similar to J/Psi/Drell Yan vs centrality favored by
NA50. Klaus Reygers defined GAA and made such a plot at
HP2004 in his talk, but it didn’t make the proceedings which
were very restricted in length.
How to plot direct photon data
M. J. Tannenbaum 26
Possible Explanations
• Issues with cluster merging at high pT and large centrality? This
must be studied in detail.
• Inadequate attention to Z/A for structure functions in AuAu, d, p
in our expectations. More d quarks at x > 0.1 would suppress
photons relative to pizeroes in Au+Au cf. d+Au and p-p. Also, if
we measure RAuAu, we actually want the measured F2Au/197F2p with
no correction for isospin, as typically done to get F2N.
• Initial state energy loss of incident partons in back half of the Au
nuclei when hitting the hot medium formed by the front half of the
Au nuclei? Depends crucially on formation and thermalization
times.
• Total lack of attention by DIS experiments so far to centrality
dependence of structure functions in nuclei.
• This is clearly very exciting. Any other wild guesses?
How to plot direct photon data
M. J. Tannenbaum 27