# Presentation: 465893

## The RHIC Photon Feast

- Justin Frantz
- SUNY Stony Brook
- RHIC/AGS Users Meeting Photon Workshop June 21, 2005

**BBQ**

****

- Justin Frantz RHIC/AGS Users Mtg 2005

## A Succesful BBQ Starts With Flavors and Ingredients...

**Properly Aged:**   Theoretical techniques well established and have perhaps reached a milestone of maturity ?
**Healthy:**  A lot of activity by many different groups, theoretical community actively pursuing many new avenues (e.g. HBT)
**Organically Grown:  **Some tuning on SPS data possible
**Fresh:**  Medium Induced sources generating fresh excitement

- Justin Frantz RHIC/AGS Users Mtg 2005

**Notes:**
-attacking problems from new angles new observables, not just the pure rates
-tuning from other measurements 
-generating fresh outlook & some uniquely identifiable signals

## Ingredients: Hard Scattering Rates

- Perturbative QCD NLO predictions solid for years (*Phox*)
- At RHIC high pT  and works well...
- However predicted rates still have scale, FF (0) uncertainties unconstrained by the data
- Quantitative ~50%? getting larger as we go down
- NNLL/O gluon resummation not quite yet (see hep-ph/0504115), but maybe not *too* important @ RHIC

- PHENIX Final

- Justin Frantz RHIC/AGS Users Mtg 2005

**Notes:**
21 years 1984
Paper in april by Italian group 
Not too important...given the agreement so far

## Ingredients: Thermal Rates

- QGP: perturbative Thermal QCD
- Hard Thermal Loop (HTL) calculations “complete”?  Resummation of all order loops with LPM performed by A.M.Y.  Reliable fit in “the large  E/T range” (Aurenche hep-ph/0410282)  “Full result to LO in S”.
- Factor of 2 enhancement to previous
- What systematic should we assign? 50%?
- Hadron Gas (HHG):  pQuantum Hadro-Dynamics
- Also mature calculations
- However, including process X? (                      via                etc...)
- New processes usually can potentially change rates by factor of ~2 but often turn out to be less:  stable?  +/- 50-100%

- Justin Frantz RHIC/AGS Users Mtg 2005

**Notes:**
Seems to be consensus
See any of these papers for the AMY references
Hot
Still awaiting lattice rates:

## The New Ingredient: Jet-Medium Induced Photons

- Specific pT region ~3-7 GeV, just where the hard rates become truly hard
- Assumes QG degrees of freedom, equilibrium, different dependence than thermal rates
- Two possible components: multiple scattering, Bremmstrahlung
- Non-zero flow pattern!

- Turbide, et.al. hep-ph/0502248

- 

- 

- 

- Justin Frantz RHIC/AGS Users Mtg 2005

**Notes:**
-Multiple scattering not important for energy losssmall rate: but small rate for large number of q/g leads to sizable enhancement to the small rate of photon
-As input quark/gluon distributions e.g. thermal distributions
-No prediction yet on flow pattern

## Spices, Marinates, Prepwork

- Putting it all together!   Rates folded against:
- Realistic Phase Space Distributions and Evolutions
- Initial State or other state points
- Hydrodynamics, uRQMD, Parton Cascade Models
- Mixed phase, pre-equilibrium effects:
- Hydro-based “Complete” Evolution Models:
- Renk, et.al. fireball: flow / HHG important
- Turbide, Gale, Rapp fireball, but HHG not important:
- d’Enterria & Peresseunko: 2+1D Expansion, includes peripheral prediction
- Previous include no Jet-Medium, [< 4 GeV]
- Turbide, Gale, Jeon, Moore Jet Medium
- Bass, et.al.  PCM + Bjorken Expansion

- Differences?

- Justin Frantz RHIC/AGS Users Mtg 2005

**Notes:**
Marinate our steaks or tofu!  Bobby Flay the Iron Chef America
These rates are combined with real and momentum space distributions ... like freezeout
From the papers I couldn’t see the difference?

## Must have the proper BBQ Utensils

- The Grill:    RHIC

- AGS

- RHIC

- Justin Frantz RHIC/AGS Users Mtg 2005

**Notes:**
And others.... We have many!

## Single  Rate Measurements

- EM Calorimeter “Base Method”: Count Cal Hits
- PHENIX Calorimeters (seg. )  PbSc/Gl MidRap
- STAR Calorimeters (BC seg.  MidRap, ECC ForwardRap seg smaller )

- Limitations at low pT
- Hadronic showers (50% @ pt < 1GeV)
- Resolution (E/E = A/√E+B )
- Cluster splitting effects
- acceptance for 0

- Systematic errors for photon 10-15%,  14-18%
- Dominated by Energy Scale and Efficiency at high pT
- At very low pT by large hadron contamination

- Justin Frantz RHIC/AGS Users Mtg 2005

**Notes:**
Most important grilling tool: tongs, counting calorimeter actually clusters
Including decay photon contribution
Large hadronic shower contribution, still lower punch through
Resolution gets worse
Detector effects and p0 main background although measuring charge pions helps

## Singles Rate, Conversion Method

- Both PHENIX and STAR can measure photons via →*e**+**e**-* conversion
- Slightly different methods
- Opening angle cuts, Dalitz removal, Electron ID
- Totally different systematics: charge tracks

-    Beam-pipe Conversions

- PHENIX

- r = m2

- x

- y

- STAR TPC

- Justin Frantz RHIC/AGS Users Mtg 2005

**Notes:**
Pointy shaped forks: I don’t know what they’re really called, but you usually use them when you can’t find your tongs.
Marcia STAR, PHENIX though “unrealeased” 
Dalitz removal for phenix

## Singles Rate, Conversion Method

- Energy Resolution has opposite behavior
- Scale uncertainty slightly smaller, combine with Cal to reduce
- Electron ID runs out (e.g @ 5 Gev/c)
- Total systematics 13% (STAR)

- PHENIX Emcal

- PHENIX Tracking

-  E/E Resolution (%)

- pT (GeV/c)

- STAR
- Phys. Rev. C **70** (2004) 044902

- PHENIX

- Raw Yields 

- Arbitrary Units

- 62.4 GeV

- Justin Frantz RHIC/AGS Users Mtg 2005

**Notes:**
In particular energy resolution...
Combine, assuming they are consistent
An initial conservative estimation is higher but....
Even if similar sized errors : sqrt 2 reduction

## The Statistical Method. Tagging & Isolation Cuts:

- Extract Direct  from inclusive :  Subtract decay  (cocktail) contribution
- Cocktail based on measured meson (0) rates
- Double Ratio R:  Stat==syst error gets smaller in Run4
- Anti-Tagging 0 increases S/B
- As does isolation cut*
- In Au+Au apply isolation cut in peripheral bins

- -dAu data  -Pythia

**associated  pT**

- = A+B/p**T**

-     Jet Rejection

- w/ tagging

- w/o

*p+p*!

- Justin Frantz RHIC/AGS Users Mtg 2005

**Notes:**
Cocktail based mostly on Pi0 
So far mT scaled, but as our eta measurement becomes more 
Trade systematic for syst.  : automatic reduction for run4
Tagging reduction by a factor of two in the plot in p=P
-isolation*  because change physics source, removing Bremmstralong.

## Photon (Non?) Flow

- Measure reaction plane (PHENIX new MVD measurement)
- Indications of direct photon in inclusive (decay + direct)  flow?
- Repeat direct  Stat. Method vs. R

-  0 RAA

- R

-   PHENIX Preliminary

- Suppression of background like in central events

- Justin Frantz RHIC/AGS Users Mtg 2005

**Notes:**
Less flow for direct photon--Possibly negative flow
Even without reducing our systematics, Should see something interesting at phi_R = 90%:  in 50-60% Au+Au results were consistent with 0, because of overall S/B

## Photon-Jet Correlations

- Motivation:  Direct Photon (e.g. Energy) Cleanliness: **high p****T**
- Convenient for triggering
- Subtract  decay photon trigger distribution - use charge pions
- Azimuthal correlations: separate (jet-medium) Brems and Compton direct on the near side:
- Fragmentation Function dN/dz  using clean E

- 0/Brems

- Compton 

- M.Chiu

- QM’02

- Au+Au

- d+Au

- Justin Frantz RHIC/AGS Users Mtg 2005

**Notes:**
Just to remind, we’ve been trying this since day 1, albeit low pT trigger
Identified charge pions
Two distinct shapes for the two sources of photons
Yields would be interesting: Marcia
Holy grail dN/dz  still be statistics limited, as predicted by X.N. Wang but that doesn’t mean there can’t be ANY measurement

##   Interferometry / HBT

- HBT real correlation at very low pT. Tie down total **rate** with 1D Qinv
- Shape for  vs Minv different from , other contributions (e.g.detector)
- Could be performed with conversions too
- Au+Au 3D spacetime geo. Qout,side,etc...Info?  Large combinatorics!

- 1 GeV/c

- dN/Minv vs Minv

- ’

- Combinatric bkg.

- Justin Frantz RHIC/AGS Users Mtg 2005

**Notes:**
Couldn’t think of more grilling utensils
Generated interest because so far none of the theorectical sources can generate: 
How Hi in pT?  Two low for any theory to be applicable
Detector effects—cluster splitting

## Follow the Recipes to Make  Meals!

- A few of my own personal receipes:...

- Justin Frantz RHIC/AGS Users Mtg 2005

## Recipes:  @ high pT more precision

*p+p* Preliminary Comparison between isolation/non-iso method:  negative Brems?
- pQCD Brems ~ 30%
- Plenty of room in those systematics
- Make real RAA (with p+p it’s all there!) More precise also look for nuclear effects (kT, Cronin)?

- Justin Frantz RHIC/AGS Users Mtg 2005

**Notes:**
nail down things like Brems
Monique already discussed, but... why aren’t these consistent?  This gives an idea of true quantitative uncertainties in the QCD prediction

## Recipe: Use Conversion Measurements, too

- Use the conversion measurement:
- At low pT < ~3 GeV systematics probably smaller
- Factor of 102-4 loss in statistics won’t hurt in Run4
- In the region of overlap with the Calorimeter measurements, reduce  energy scale uncertainty by “combining” rate normalization
- extend *p+p*  measurement to lower pT ?
**Meal:** Constrain thermal model rates below 4 GeV  **and** confirm or deny jet-medium enhancement

- Justin Frantz RHIC/AGS Users Mtg 2005

**Notes:**
Because there’s less hadronic contamination, smaller resolution, cluster splitting not a problem
p+p there’s no reason at least for upper limits, but then the question of how small are systematics
Assuming they are consistent!
--confirm or deny: along these lines...

## Recipe: Focus on Reaction Plane for Jet-Medium pT

- Perform Reaction Plane dependent direct photon statistical analysis (under way @ PHENIX)
- Also with conversions where possible
- Measure direct  flow directly (may be 0)
- Meal: Combine with HBT and other measurements to constrain space time geometry, path dependencies

- Justin Frantz RHIC/AGS Users Mtg 2005

**Notes:**
Calorimeter based photon analysis can already be done and is being done.

## Other Recipes:

**Study ********-h correlations:**  separate angular jet shape differences btw Brems., Compton  bkg
- Also difference in flow portion of -h angular correlation shape
- Any of your “family favorites”?

- Justin Frantz RHIC/AGS Users Mtg 2005

## Conclusions

- No BBQ is complete without some good libations!
- Exciting time in the RHIC photon world!
- Not quite time yet:  More time needed in front of the grill.
- But as our meals are slowly served, there will certainly be much to celebrate!

- Justin Frantz RHIC/AGS Users Mtg 2005

**Notes:**
Didn’t

## Back-up possible kT effects (e.g. nuclear?)

- Justin Frantz RHIC/AGS Users Mtg 2005