illuminating rhic matter with the multi-purpose direct photon

Illuminating RHIC Matter with the Multi-purpose Direct Photon

Justin Frantz(A member of PHENIX on behalf of RHIC)

Quark Matter’ 06 Shanghai, ChinaNovember 16th, 2006

November 16, 2006 Justin Frantz Quark Matter ’06 2

Greater Picture

Soft Spectrum Hard SpectrumpQCD/Jet Suppression ControlQGP/Hadron Thermal

HBT

Direct Photon v2?

-h (jet) Ratesv2 Control (0!)

-jet Shapes

Virtual

Pseudo-Cronological Progression of Direct Photon Theory/Studies/Measurements in HIA healthy and expanding sub-field !

Di-photons?

Intermediate pT Jet-medium


time

Forward CGC

Multi-purpose!!!


Greater Picture

Soft Spectrum Hard SpectrumpQCD/Jet Suppression ControlQGP/Hadron Thermal

HBT

Non-0 Direct v2?

-h (jet) Ratesv2 Control (0!)

-jet Shapes

Virtual

Pseudo-Cronological Progression of Direct Photon Theory/Studies/Measurements in HIA healthy and expanding sub-field !

Di-photons?


time

Forward - CGC

Multi-purpose!!!


Other Uses (Deprecated)…

• Many bad puns– e.g. “Illuminating” RHIC Matter with the Multi-

purpose Direct Photon - Justin Frantz QM06

-Charles Gale hep-ph/0609301


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%


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


Start w/ Low pT Precision…

• Published PHENIX Result:• Calorimeter Result, statistical

“cocktail” comparison

• Double Ratio R = tot/dec

• = 1+ Sdirect/Bdecay

• Absolute precision on gdir degrades as S/B decreases, R ~ 1

• Only upper limits constrained within 12% R systematics..


Still Many therm 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

• 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• … • …

Most Complete?


Still Many therm 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)


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


QM’06: Enter STAR into the game…

• PHENIX has 2 calorimeters, but still same experiment (sharing aspects of clustering/ data analysis/ triggering)– E/E = 8%/√E + 2%, seg = 0.01, || < 0.35

• Great to have independent confirmations from STAR

•STAR Calorimeter:

• E/E = 16%/√E + 2%,

• seg = 0.05, w/ a shower max detector 0.007

•0< < 1


2 Experiments: ~√2 x the Precision?

• Also good for averaging completely indep. measurements to reduce errors a la PDG

STAR p+p well underway as well (Martijn Russcher talk)

Now: Errors in 6-10 GeV Region STAR 16% PHENIX 12% -- combined: 9.5 %

In the future?: STAR 10% PHENIX 8% -- combined 6%

PHENIX Preliminary

d+Au 200 GeV


Improving Precision: Low pT

• Calorimeter measurements limits: – Resolution gets worse @ low pT

– Hit clustering problems (splitting/merging)

• Turn to several other methods– External Conversion Methods– New: Internal Conversion Method– HBT

E/E

Res

olu

tion

(%

)

pT (GeV/c)

e+

e-

EMCal

Tracking


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)

r = mass vs

rPHENIX Beam Pipe

Run4 data

STAR TPC


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

What happened? looked promising.

:nucl-ex/0401008


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 * 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


Virtual = Real ?• Theoretical Uncertainty

– e.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)


@ Very low pT : 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…


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

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

PHENIX Final

Run4 Au+Au 200 GeV


Jet-Medium Photons: Two Types

• -jet Conversion– Model: q jets traversing q/g bath convert (Kinematics: small u

dominates: p ≈ pq) First calc Fries, et. al./ more complete treatment w/ Turbide,Gale et. al.

• Fragmentation (Brems.) – Jet Eloss implies suppression of Frag but Zakarov/others predict

enhancement (New paper from E. Wang et. al.) also included by the above authors.

w/o suppresion


Jet-Medium Photons Two pT Regions

• Fragmentation (Brems.) -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


Direct Photon v2

• Jet-medium sources /(& jet suppression also should cause non-zero direct v2

• Measure the Reaction Plane R,

Particle production at ( – R) → v2

• PHENIX Paper: Indications of direct photon in inclusive (decay + direct) flow?– QM’06 STAR Poster on this as well

(G.Lin)

• Jet-medium interactions -> non-0 v2 (admixture includes negative)

PHENIXnucl-ex/0508019


Direct Photon v2

In 40-60% disagreement above 3 GeV—all points positive

0-20% also disfavors though slightly

Still inconclusive within the PHENIX uncertainties?

First measurement: Run 7/8 Au+Au systematics reduceable

Turbide, et.al

PHENIX Preliminary

PHENIX Preliminary


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→+Xp+p→direct+X


PHENIX Au+Au High pT Data

• With new p+p PHENIX makes real direct RAA …

PHENIX Parallel talk by TadaAki Isobe


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


Jet-medium Enhancement tested…• …allowing a quantative test of Jet-medium

enhancement predictions

• At high pT data favors standard suppression predictions, not enhancement


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 S…)– Interpretation of the partonic medium?

• Is there suppression in high pt direct? Still need more precision at high pT


Other (deprecated) uses of RHIC , continued…

• Bad alliterative experiments…– “Phun with Photons” ????


Photon-Jet Has Arrived!!!• 2 particle Correlations

• Both STAR and PHENIX: First results p+p– PHENIX Au+Au Result, STAR work on d+Au– Au+Au signal cleaner p+p/d+A jet signal cleaner– 2 Parallel Talks: Subhasis Chattopadhyay, Jiamin Jin

STAR d+Au Preliminary

PTassoc. hadron > 1 GeV/c

C() jet-jet

0 0

-jet


-jet in Au+Au

• PHENIX Au+Au compared to p+p

See also poster by Matt Nguyen


Gamma-Jet Yields• Integrated Away-side yields:

• 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)

p+p


What will we now learn from -jet?

• Cleaner determination of fragmentation modification ~ better constrain Eloss models

I AA

w/ Eloss

F. Arleo hep-ph/0601075

Trigger don’t have surface bias, thus eventually should constrain Eloss geometry


Most Important Use of Direct

• Fitting the direct photon data into the overall picture we are constructing at RHIC…


Summary• Full entrance of STAR into RHIC direct 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 jet-medium enhancements @ intermediate pT (4-5 GeV/c)…

• …& favors “standard” frag suppression, disfavors enhancement to the highest pT’s

• Direct flow measurements inconclusive: but also favor “standard” frag 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


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

illuminating rhic matter with the multi-purpose direct photon

Documents

direct g v2

ti choicesrenk

w flowhbt hhg important

gh jet ratesv2 control

low pt thermal photons

w periph

quantitative result

precision scalelow precision