Transcript Direct Photons

Illuminating RHIC Matter with the
Multi-purpose Direct Photon
Justin Frantz
(A member of PHENIX on behalf of RHIC)
Quark Matter’ 06 Shanghai, China
November 16th, 2006
Greater Picture
Pseudo-Cronological Progression of Direct Photon Theory/Studies/Measurements in HI
A healthy and expanding sub-field !
Soft Spectrum
QGP/Hadron Thermal
g-g HBT
Hard Spectrum
pQCD/Jet Suppression Control
Intermediate
Intermediate
pTpT
Jet-medium
Jet-medium
v2 Control (0!)
g-h (jet) Rates
Virtual g
Di-photons?
g-jet Shapes
Forward g CGC
Direct Photon v2?
time
Multi-purpose!!!
November 16, 2006
Justin Frantz Quark Matter ’06
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Greater Picture
Pseudo-Cronological Progression of Direct Photon Theory/Studies/Measurements in HI
A healthy and expanding sub-field !
Soft Spectrum
QGP/Hadron Thermal
g-g HBT
Intermediate pT
Jet-medium
Hard Spectrum
pQCD/Jet Suppression Control
v2 Control (0!)
Virtual g
g-h (jet) Rates
Di-photons?
g-jet Shapes
Forward g - CGC
Non-0 Direct g v2?
time
Multi-purpose!!!
November 16, 2006
Justin Frantz Quark Matter ’06
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Other Uses (Deprecated)…
• Many bad puns
– e.g. “Illuminating” RHIC Matter with the Multipurpose Direct Photon - Justin Frantz QM06
-Charles Gale hep-ph/0609301
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How Use _ FUL _?
• Now into the first years of the post-celebritory (we found the signal!)
phase…
• ..What have we learned from direct photons at RHIC so far? (pre
QM’06)
• For now, in most cases it is driven by precision scale…
– Low Precision: Qualitative Result @ low pT thermal photons are
probably present (almost as much as WA98)
– Better Precision: Quantitative Result: At high pT prompt Direct photons
binary scale to within ~+/-20%
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The question of precision
• So far most direct g theoretical predictions cannot be
tested with any stringency due to low precision
• Some recent improvements in measurement techniques
as well as new avenues proposed by theory and
experimentalists alike have shown promise in rectifying
this situation.
• This QM reveals concrete (quantitatively tangible)
experimental steps made in nearly all available
directions
• Allows us to:
– in a few cases, add some items to “learned at RHIC”
– See what, in more definite terms, we will be able to learn in the
next several years
– To this end, in this talk I will try to lay out quantitative estimates
where I can
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Start w/ Low pT Precision…
• Published PHENIX Result:
• Calorimeter Result, statistical
“cocktail” comparison
• Double Ratio R = gtot/gdec
• = 1+ Sdirect/Bdecay
• Absolute precision on gdir
degrades as S/B decreases, R
~1
• Only upper limits constrained
within 12% R systematics..
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Still Many gtherm Models Possible
• Thus the theoretical predictions cannot be constrained…
• Complete models generally include: QGP/ Hadronic Gas
Rates, folded w/ hydrodynamic volume, EOS Assumption,
Initial state (ie Ti) choices
Most Complete?
•
•
•
•
•
•
•
•
•
Renk (2004) w flow/HBT HHG important Ti=110 MeV
d’Enterria & Peresseunko (2005) w/ periph. Ti=610
Bass,Renk,Sriv., et.al. (2004) PCM Only (no thermal)
Turbide, Gale, Rapp (2004) HHG not important Ti= 370
Gelis, Neimi, et.al. (2003) Ti=580
Alam, Sinha, et.al. (2001) Ti = 265
Srivastava (2001) Ti390-670
…
…
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Still Many gtherm Model Possible
•
•
•
•
•
•
•
Renk (2004) w flow/HBT HHG important Ti=110 MeV
d’Enterria & Peresseunko (2005) w/ periph. Ti=610
Bass,Renk,Sriv., et.al. (2004) PCM Only (no thermal)
Turbide, Gale, Rapp (2004) HHG not important Ti= 370
Gelis, Neimi, et.al. (2003) Ti=580
Alam, Sinha, et.al. (2001) Ti = 265
Srivastava (2001) Ti390-670
Not well constrained (hence the
continuing proliferation of models)
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Direct Photon Precision/Accuracy in
General (e.g. Particle Physics)
• Experience tells us more than 1
experiment cross checking is good
D0
CDF
From Peitzmann and Thoma: Physics Reports 364 (2002) 175–246
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QM’06: Enter STAR into the game…
• PHENIX has 2 calorimeters, but still same
experiment (sharing aspects of clustering/
data analysis/ triggering)
– sE/E = 8%/√E + 2%, DpDh seg = 0.01, |h| < 0.35
• Great to have independent confirmations
from STAR
•STAR Calorimeter:
• sE/E = 16%/√E + 2%,
• DpDh seg = 0.05, w/ a
shower max detector 0.007
•0< h < 1
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2 Experiments: ~√2 x the Precision?
• Also good for averaging completely indep.
measurements to reduce errors a la PDG
d+Au 200 GeV
PHENIX Preliminary
Now: Errors in 6-10 GeV Region STAR 16% PHENIX 12% -- combined: 9.5 %
In the future?: STAR 10% PHENIX 8% -- combined 6%
STAR p+p well underway as well (Martijn Russcher talk)
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Improving Precision: Low pT
• Calorimeter measurements limits:
– Resolution gets worse @ low pT
– Hit clustering problems (splitting/merging)
• Turn to several other methods
e+
e-
November 16, 2006
sE/E Resolution (%)
– External Conversion Methods
– New: Internal Conversion Method
– HBT
EMCal
Tracking
Justin Frantz Quark Matter ’06
pT (GeV/c)
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Photon Conversion Method
• Identify conversion pair
candidates
– STAR two-track vertices
– PHENIX mis-rec’d mom-- Mass
peak @ 0 moes to finite mass
• Electron systematics same or
smaller than EMCal
– Bkg. Norm. easier (di-electron ~<
1% syst.)
– Better Mom resolution @ low pT
– Abs. efficiency more difficult
– Independent measurement (error
reduction)
STAR TPC
PHENIX Beam Pipe
Run4 data
r
r = mass vs f
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New Result / Old Result
• First PHENIX Result Using this method:
Au+Au 200 GeV
“Old” STAR 130 GeV Au+Au Result
New PHENIX Result this week!
Talk by D. Peresseunko
Full Decay Photon Calculation not
included
:nucl-ex/0401008
What happened? looked promising.
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Internal Conversion Method
• Y. Akiba (PHENIX), Inventor
• All real photon sources make
virtual photon e+e- pairs
• Measure e+e- in mass region
where direct should dominate
over Dalitz →convert to total
excess of direct g* over Dalitz
• Au+Au Result from last QM’05
• Method applied to d+Au
• Feasibility in lower multiplicity
– Need reference esp. @ low pT
where soft may not != pQCD
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Virtual g = Real g?
• Theoretical Uncertainty
– e.g. g* longitudinal states
• Answer by going to even higher pT looking for
consistency w/ high pT calorimeter/(conversion)
result
• Next factor of 5-10 in statistics should do it
• Also repeat in p+p (w/o possible nuclear effects)
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@ Very low pT : g-g HBT
• Several theoretical works: important not just for
direct photon yield
• Direct Yield can be obtained from strength of
HBT Qinv peak
• STAR prelim result QM’05: detector effects?
• PHENIX work on this also…
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To Intermediate pT:The Kink
• There is kink in both the run2 and run4 datasets
in the same place…
Au+Au 200 GeV Run2 Final
PHENIX Final
Run4 Au+Au 200 GeV
This could easily just be a
systematic effect but it is at least a
little curious b.c. it’s not there in
other centralities
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Jet-Medium Photons:
Two Types
•
g-jet Conversion
– Model: q jets traversing q/g bath convert (Kinematics: small u
dominates: pg ≈ pq) First calc Fries, et. al./ more complete
treatment w/ Turbide,Gale et. al.
• Fragmentation (Brems.) g
– Jet Eloss implies suppression of Frag g but Zakarov/others predict
enhancement (New paper from E. Wang et. al.) also included by
the above authors.
w/o suppresion
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Jet-Medium Photons
Two pT Regions
• Fragmentation (Brems.) g-jet Conversion
Imply large (2x) at Intermediate pT
• But also as importantly out to the highest
pT: no suppression!
– i.e. wins out over expected jet suppression
Jeon, Jalilian-Marian, Sarcevic
nucl-th/0208012
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Direct Photon v2
• Jet-medium sources /(& jet
suppression also should cause nonzero direct g v2
• Measure the Reaction Plane fR,
Particle production at (f – fR) → v2
• PHENIX Paper: Indications of direct
photon in inclusive (decay + direct) g
flow?
– QM’06 STAR Poster on this as well
(G.Lin)
• Jet-medium interactions -> non-0 v2
(admixture includes negative)
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PHENIX
nucl-ex/0508019
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Direct Photon v2
Turbide, et.al
PHENIX
Preliminary
In 40-60% disagreement above 3
GeV—all points positive
0-20% also disfavors though slightly
PHENIX
Preliminary
Still inconclusive within the PHENIX
uncertainties?
First measurement: Run 7/8 Au+Au
systematics reduceable
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In order to test the rates…
• Better p+p reference needed to make definitive
statement
– In past Au+Au “fake” RAA w/ NLO pQCD
• More precise Run5 PHENIX now available, also work
from STAR in this direction
p+p→gdirect+X
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p+p→p0+X
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PHENIX Au+Au High pT Data
• With new p+p PHENIX makes real direct g
RAA …
PHENIX Parallel talk by TadaAki Isobe
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Jet-medium Enhancement Tested…
• …allowing a quantative test of Jet-medium
enhancement predictions
• At mid pT some enhancement may be
possible, but current predictions are strongly
disfavored
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Jet-medium Enhancement tested…
• …allowing a quantative test of Jet-medium
enhancement predictions
• At high pT data favors standard
suppression predictions, not enhancement
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Implications/Discussion
• Homework for theory:
• Bremstrahlung enhancement must exist (in however
small amount) if gluon radiative Eloss (GLV, BDPMS…) is
present
– can discrepancy be accounted for? Another constraint on
radiative picture?
•
g-jet conversion seems reasonable given a QGP, where
does it go wrong? (modified aS…)
– Interpretation of the partonic medium?
• Is there suppression in high pt gdirect? Still need more
precision at high pT
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Other (deprecated) uses of RHIC g,
continued…
• Bad alliterative experiments…
– “Phun with Photons” ????
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Photon-Jet Has Arrived!!!
• 2 particle Df Correlations
g-jet
jet-jet
C(Df)
0
p
0
• Both STAR and PHENIX: First results p+p
p
– PHENIX Au+Au Result, STAR work on d+Au
– Au+Au g signal cleaner p+p/d+A jet signal cleaner
– 2 Parallel Talks: Subhasis Chattopadhyay, Jiamin Jin
PTassoc. hadron > 1 GeV/c
STAR d+Au Preliminary
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g-jet in Au+Au
• PHENIX Au+Au compared to p+p
See also poster by Matt Nguyen
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Gamma-Jet Yields
• Integrated Away-side yields:
p+p
• STAR/PHENIX p+p yields roughly consistent (STAR
trigger bin higher)
• PHENIX Au+Au consistent with expected suppression!
– Next step, more precision, take Au+Au/p+p ratio (IAA)
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What will we now learn from g-jet?
• Cleaner determination of fragmentation
modification ~ better constrain Eloss models
IAA
F. Arleo hep-ph/0601075
w/ Eloss
Trigger g don’t have surface bias, thus
eventually should constrain Eloss
geometry
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Most Important Use of Direct g
• Fitting the direct photon data into the
overall picture we are constructing at
RHIC…
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Summary
• Full entrance of STAR into RHIC direct g measurement will
be and in fact is already beneficial
• Need for greater precision at low pT being addressed with
new measurements/methods
– New methods being employed: external (PHENIX/STAR), internal
(PHENIX) conversion methods, HBT (PHENIX/STAR)
– Cold matter references have likewise already been improved
• New RAA data (PHENIX) strongly disfavors large jetmedium enhancements @ intermediate pT (4-5 GeV/c)…
• …& favors “standard” gfrag suppression, disfavors
enhancement to the highest pT’s
• Direct g flow measurements inconclusive: but also favor
“standard” gfrag suppression more than jet-medium
• First measurement of p+p gdirect-jet 2-particle corr.’s
– Within large error bars we see the suppression effect
– Improved precision will allow quantitative study
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d+Au Internal Conversion
• pQCD not trusted at low pT
• There could be photon production from soft
physics in p+p/ p+A
– ~no theoretical guidance on this
• Thus reference result for low pT photon
production needed
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