# Presentation: 483435

## Properties of a hot dense matter explored by electro magnetic probes at RHIC

- Takao Sakaguchi, for the PHENIX Collaboration
- Brookhaven National Laboratory

- Outline:
- EM probes emission and their origin
- Hard photon related observables
- Soft photon related observables
- Summary of what we learned

- T. Sakaguchi, JPS Fall meeting

## Emitted at all stages then surviving unscathed strongly ( s, almost transparent to medium)

- Electro-magnetic probe emission

- Emitted at all stages then surviving unscathed strongly ( **********s**, almost transparent to medium)

***Cartoons from G. David, Hard Probe 2006, and C. Gale in PHENIX Coll. Meeting, 2008***

- T. Sakaguchi, JPS Fall meeting

## Production Process
Compton and annihilation (LO, direct)
Fragmentation (NLO)

Carry thermodynamical information of the state
Temperature, Degrees of freedom, formation time.

- Compton and annihilation (LO, direct)
- Fragmentation (NLO)
- Carry thermodynamical information of the state
- Temperature, Degrees of freedom, formation time.

- Electro-magnetic probe basics

**Gordon and Vogelsang, PRD48, 3136 (1993)**** **

**Small Rate: Yield********s**

**[photons]**

**[dileptons]**

- T. Sakaguchi, JPS Fall meeting

## High pT single hadrons in Au+Au

- RAA extended to 20GeV/c
- Significant suppression as high as a factor of ~4
- Integrated RAA proved that the energy loss is consistent with fractional (increases with pT)

_***arXiv:0801.4020***_

- T. Sakaguchi, JPS Fall meeting

## Experiments meet with theories

- First quantitative discussion of model parameter constraint
- Not only <qhat> (PQM model parameters), but also gluon and initial energy density, are constrained

- <qhat>=13.2 (+2.1/-3.2) GeV2/fm

_*Matter is opaque! Is it blackdisk?*_

_**PRC77, 062907 (2008)**_

- T. Sakaguchi, JPS Fall meeting

## Matter geometry?

- Possibilities other than density gradient picture

- Tangential emission
- 2+1 correlation would help?

- Probabilistic process of punch-through jets. Matter density is not necessarily uniform

- T. Sakaguchi, JPS Fall meeting

## Subtract -h, -h from (incl -h

If the result is true, the jet-emission is not always tangential.
 is not necessarily the “direct”. Fragment, bremsstrahlung, Jet-conversion photons could significantly contribute
similar to h-h correlation? Isolation of “direct photons” would be needed
Ridge structure, same RAA and IAA

- If the result is true, the jet-emission is not always tangential.
-  is not necessarily the “direct”. Fragment, bremsstrahlung, Jet-conversion photons could significantly contribute
- similar to h-h correlation? **Isolation** of _**“direct photons”**_ would be needed
_***Ridge structure, same R***__***AA***__*** and I***__***AA***_

- -Jet correlation

**Red points integrated R****AA**** from single ********0**** measurement (pT>5GeV/c)**
**Blue points: Same (integrated away side yield: I****AA****) from ********-h measurement (Assoc. pT>5GeV/c)**

****

- T. Sakaguchi, JPS Fall meeting

## Low mass Dilepton  internal conversion of direct photons
Any excess above expected hadron decay contribution should be from direct photon internal conversion
M<<pT, F~1

Excess ratio in certain mass region is converted to the excess of total direct photons to total hadron decay contribution
Using Kroll-Wada formula

- Any excess above expected hadron decay contribution should be from direct photon internal conversion
- M<<pT, F~1
- Excess ratio in certain mass region is converted to the excess of total direct photons to total hadron decay contribution
- Using Kroll-Wada formula

- Temperature from direct photons

_*Fit results*_
- Cent.   dN/dy(pT>1GeV/c)   T(MeV)    2/DOF
- 0-20%   1.100.200.30    2212318   3.6/4
- 20-40%  0.520.080.14   2152015   5.2/3
- MB        0.330.04 0.09   2241619   0.9/4

**arXiv:0804.4168 (nucl-th)**

- T. Sakaguchi, JPS Fall meeting

## Time scan of temperature ~dileptons~

**Known hadron decay components (cocktail) in lines**
**Caveat: cocktail calculation here does not include contribution from internal conversion of direct photons**
**2-components fits**
**m****T****-scaling of ********0**** (good approximation of cocktail) + exponential**
**Intermediate mT****: ~200MeV consistent with direct photon result.**
**Reasonable given internal conversion of photons are not subtracted**
**increasing with mass, consistent with radial flow**
**Low mT****: **
**inverse slope of ~ 120MeV**

**2 single exponential fits:**
**Low-pT: 0<mT<1 GeV**
**High-pT: 1<mT<2 GeV**

- T. Sakaguchi, JPS Fall meeting

## Direct photons to dilepton ratio could  cancel out normalization problems

A prediction: the ratio weekly depends on Tc, EOS, but rather strongly on Ti

- A prediction: the ratio weekly depends on Tc, EOS, but rather strongly on Ti

- Another quantities

***Nayak et al. PRC78,034903(2008)***

*R**em* as a function of mass range

*R**em* as a function of Tc

- _(under Born approx.)_

_*Analysis using PHENIX real data is on-going*_

- T. Sakaguchi, JPS Fall meeting

## Property summary

- Matter is opaque, but is not sure whether it is uniform
- Single hadron spectra shows significant suppression, and deduced the fact that the matter is very opaque
- However, Jet emission geometry, density profile unknown
- -Jet analysis does not answer the question at this moment because fragment photons would have been triggered ( is not necessarily direct)
- Temperature of matter:
- By exponential fits
- Low pT(mT) region: ~120MeV, med pT(mT): ~200MeV
- Follows system expansion
- Consistent between direct photon and dileptons
- Contribution from internal conversion of direct photons is not subtracted yet.
- Wait for final publication.
- Ratio of direct photons and dileptons could deduce much direct info on initial temperature
- Above temperature might depend on EOS

- T. Sakaguchi, JPS Fall meeting

## Backup

- T. Sakaguchi, JPS Fall meeting

## Direct photon v2 in Au+Au collisions

- Hadron decay photon subtracted from inclusive photon v2.
- Reached up to ~8GeV/c, no significance for pT<3GeV/c
- Tends to be positive?
- Uncertainty of meas/bkgd dominates error here.
- It is not due to v2 measurement of inclusive photons or 0
- Could be improved by internal conversion method?

- T. Sakaguchi, JPS Fall meeting

## pT dependency of dileptons

**Single exponential fit:**
**Low-p****T****: 0<m****T****<1 GeV**
**High-p****T****: 1<m****T****<2 GeV**
**2-components fits**
**2exponentials**
**m****T****-scaling of ********0**** + exponential**
**Intermediate pT****: inverse slope increase with mass, consistent with radial flow**
**Low pT****: **
**inverse slope of ~ 120MeV**

- T. Sakaguchi, JPS Fall meeting

## Motivation of the work (Revisit)

- Two papers from Indian theorists:
- J. K. Nayak et al., arXiv:0806.0447, arXiv:0705.1591
- Also, QM presentation
- _[http://www.veccal.ernet.in/~pmd/qm2008/webpage/Program/9Feb/Session_XXIII/j.k.nayak.ppt](http://www.veccal.ernet.in/~pmd/qm2008/webpage/Program/9Feb/Session_XXIII/j.k.nayak.ppt)_
- Taking the ratio of direct photons to dileptons would deduce the initial temperature
- Rem
- I am not big fan of any theoretical model, but the idea of taking ratio sound promising
- Theorists say that the ratio very weakly depends on Tc and is independent of flow and medium effects.
- The ratio has 1-dim parameter space rather than 4-dim in spectra prediction

- _(under Born approx.)_

- T. Sakaguchi, JPS Fall meeting

## Correlation Structures @ low pta 

- There are two interesting  points in this plot:
- The shoulder indeed does appear to be present upon adding the new stats and rebinning
- The yields look like they disfavor a ridge yield—shown in blue is John Chen’s Ridge yield from 5-7 x 1-2

- For the ridge yield I took his d/eta value, multiplied by the deta acceptance factor (1.4)  (isn’t it 0.7?) and since lookn at his plots, it seems to extend 1 rad, mult iply by d/d=1
- Need triangle acceptance factor 1/2 ?  Check w/ John

- T. Sakaguchi, JPS Fall meeting

## Yields and Slopes

**Intermediate p****T****: inverse slope increase with mass, consistent with radial flow**
**Low p****T****: **
**inverse slope of ~ 120MeV **
**accounts for most of the yield **

**SLOPES**

- T. Sakaguchi, JPS Fall meeting

## Correlation Structures @ low pta 

- There are two interesting  points in this plot:
- The shoulder indeed does appear to be present upon adding the new stats and rebinning
- The yields look like they disfavor a ridge yield—shown in blue is John Chen’s Ridge yield from 5-7 x 1-2

- For the ridge yield I took his d/eta value, multiplied by the deta acceptance factor (1.4)  (isn’t it 0.7?) and since lookn at his plots, it seems to extend 1 rad, mult iply by d/d=1
- Need triangle acceptance factor 1/2 ?  Check w/ John

- T. Sakaguchi, JPS Fall meeting

## Sources of photons:

- Hard direct photons. pQCD with shadowing
- Non-thermal

- Fragmentation photons. pQCD with shadowing
- Non-thermal

- Thermal photons
- Thermal

-  Jet in-medium bremsstrahlung
- Thermal

-  Jet-plasma photons
- Thermal

- T. Sakaguchi, JPS Fall meeting

## Direct photon v2 ~a photon source detector~

- Direct photon v2 ~a photon source detector~

- Depending the process of photon production, angular distributions
-      of direct photons vary
- Jet fragmentation (v2>0), Jet-photon conversion, in-medium bremsstrahlung (v2<0), **Turbide, et al., PRL96, 032303(2006), etc..**
- Thermal photon v2 ~ Quark v2 (>0), (based on hydro calculation)
**Chatterjee, et al., PRL 96, 202302(2006), Kopeliovich et al., arXiv:0712.2829, etc..**

**Turbide et al., arXiv:0712.0732**

- T. Sakaguchi, JPS Fall meeting

## arXiv:0801:4555 (Cu+Cu 22, 62, 200GeV)

- c.m.s. energy dependence of RAA
- 22GeV p+p reference is from a parameterization.
- Cronin enhancement at 22GeV

_*PPG084, Chair: K. Reygers*_

- T. Sakaguchi, JPS Fall meeting

## The information carried by EM probes

- Emission rates:

- [photons]

- [dileptons]

- The electromagnetic spectra will be direct probes of the in-medium
-   photon self-energy
- They are ***hard probes:***
***EM signals as probes for hadronic tomography***
**Need a model for the dynamics of the HI collision**

- McLerran, Toimela (85), Weldon (90), Gale, Kapusta (91)

- T. Sakaguchi, JPS Fall meeting

## Quenching = Jet-Plasma interaction. Does this have an EM signature?

- The plasma mediates a jet-photon conversion

- Fries, Mueller & Srivastava, PRL **90**, 132301 (2003)

- T. Sakaguchi, JPS Fall meeting

## pT dependency II 

**p+p: follows the cocktail for all the mass bins**
**Au+Au: significantly deviate at low p****T**** **

**p+p**

**Au+Au**

- T. Sakaguchi, JPS Fall meeting

## Something we may have missed..

- Initial multiple scattering effect should exist...?
- : kT broadening, 0: kT broadening + recombination.
- Detail study of p+A or d+A should help

*Russcher (STAR), QM06*

**STAR, d+Au********meas****/********bkgd**

**PHENIX, d+Au, R****AA**

*Peressounko (PHENIX), QM06*

- T. Sakaguchi, JPS Fall meeting

## A calculation tells that even in low pT region(pT~2GeV/c), jet-photon conversion significantly contributes to total

What do we expect naively? (or guessively?)
Jet-Photon conversions  Ncoll  Npart  (s1/2)8  f(xT), “8” is xT-scaling power
Thermal Photons   Npart  (equilibrium duration)  f( (s1/2)1/4 )
Bet: LHC sees huge Jet-photon conversion contribution over thermal?

Together with v2 measurement, the “thermal region” would be a new probe of medium response to partons

- My LHC favorite

- A calculation tells that even in low pT region(pT~2GeV/c), jet-photon conversion significantly contributes to total
- What do we expect naively? (or guessively?)
- Jet-Photon conversions  Ncoll  Npart  (s1/2)8  f(xT), “8” is xT-scaling power
- Thermal Photons   Npart  (equilibrium duration)  f( (s1/2)1/4 )
***Bet: LHC sees huge Jet-photon conversion contribution over thermal?***
- Together with v2 measurement, the “thermal region” would be a new probe of medium response to partons

**Turbide et al.,**
**arXiv:0712.0732**

- T. Sakaguchi, JPS Fall meeting

## Low pT photons in Au+Au and p+p are measured using internal conversion method

p+p agrees with NLO pQCD well, and Au+Au has excess over the calculation 

**Theoretical fit results are:**
**   ****- 0.15 fm/c, 590 MeV**
**     ****(d’Enterria, Peressounko)**
**   ****- 0.2 fm/c, 450-660 MeV**
**      ****(Srivastava et al.)**
**   ****- 0.5 fm/c, 300 MeV**
**      ****(Alam et al.)**
**   ****- 0.17 fm/c, 580 MeV**
**      ****(Rasanen et al.)**
**   ****- 0.33 fm/c, 370 MeV**
**      ****(Turbide et al.)**

- Low pT photons in Au+Au and p+p

**See: Dahms, Session XV**

- Low pT photons in Au+Au and p+p are measured using internal conversion method
- p+p agrees with NLO pQCD well, and Au+Au has excess over the calculation

***Shorter ************0****** increases total yield and temperature Result also strongly depends on EOS.***

**Lines are NLO pQCD**

- T. Sakaguchi, JPS Fall meeting

## Towards a consistent tomography of matter under extreme conditions with electromagnetic radiation

- Hard probes, (some) hard facts; perfect fluids, and sticky issues...

**PHENIX Collaboration Meeting ****University of Illinois at Urbana-Champaign ***  ****~ July 17-19 2008, Urbana, IL ~***

- T. Sakaguchi, JPS Fall meeting

## Outline

- Information revealed by photon measurements
- Dynamics of heavy ion collisions: link between the soft and hard sectors
- Details of photon measurement @ RHIC
- Photon azimuthal anisotropy
- Photon tagged-jets: a clean probe of jet energy loss?
- Conclusions

- T. Sakaguchi, JPS Fall meeting

## What is tomography and what is it good for?

- Medical diagnostics tool: Medical Imaging
- Recreation of an object (2D-3D) from a series of X-ray images
- Properties of the source are known and calibrated
- Probes propagate through the medium. Interaction is known, medium is known and stable
- Image(s) reconstructed

- T. Sakaguchi, JPS Fall meeting

## The “patient” here is hot and dense strongly interacting matter. Trying to get info about the QCD phase diagram

- S. B. Ruster et al., PRD 72, 034004 (2005)

- F. Karsch, E. Laermann, hep-lat/0305025

- T. Sakaguchi, JPS Fall meeting

## Caution: not all dynamical models are the same...

- Microscopic transport models (UrQMD, HSD...)
- Hydrodynamic models
- Thermal fireball models
- Those differ in details (symmetry assumptions, chemical potentials, freezeout conditions, cross sections...)
- Need to be constrained by hadronic observables!

- T. Sakaguchi, JPS Fall meeting

## Sources: Electromagnetic radiation from QCD 

- First approaches

- McLerran, Toimela (1986); Kajantie, Kapusta, McLerran, Mekjian (1986)
- Baier, Pire, Schiff (1988); Altherr, Ruuskanen (1992)

- Rates diverge:

- HTL
- resummation

- T. Sakaguchi, JPS Fall meeting

## AMY, Arnold, Moore, and Yaffe, JHEP 12, 009 (2001); JHEP 11, 057 (2001): incorporates LPM; photon rates complete to leading order in αs

- Going to two loops:  Aurenche, Kobes, Gelis, Petitgirard (1996)
- 		          Aurenche, Gelis, Kobes, Zaraket (1998)

- Co-linear singularities:

- AMY, Arnold, Moore, and Yaffe, JHEP **12**, 009 (2001); JHEP **11**, 057 (2001): incorporates LPM; photon rates complete to leading order in αs

- Can be expressed in terms of the solution to a linear integral equation

- T. Sakaguchi, JPS Fall meeting

## Electromagnetic radiation (photons) from hadrons at the SPS used to make predictions for RHIC

- Details in Turbide, Rapp, Gale, PRC (2004)
- Same spectral densities as used for dileptons
- Low momentum radiation from thermal sources

- Hadronic sources: WA98 & NA60

- T. Sakaguchi, JPS Fall meeting

- Photons and dileptons at the SPS: significant progress in nailing down details of the Spectral Densities and dynamical modeling
- CERN Dec 07
- HP 2008

- Turbide, Rapp & Gale
- PRC 2004

- 	Ruppert *et al. *PRL 2008

- T. Sakaguchi, JPS Fall meeting

## RHIC: jet-quenching

- 	Azimuthal correlation:
- Shows the absence of “away-side” jet.

- T. Sakaguchi, JPS Fall meeting

## Jet-quenching = tomography 

- Jet-quenching = tomography

- Dominant source of energy loss: medium-induced gluon
- bremsstrahlung? However, see later...

- T. Sakaguchi, JPS Fall meeting

## Quenching = Jet-Plasma interaction. Does this have an EM signature?

- The plasma mediates a jet-photon conversion

- Fries, Mueller & Srivastava, PRL **90**, 132301 (2003)

- T. Sakaguchi, JPS Fall meeting

## Sources of photons:

- Hard direct photons. pQCD with shadowing
- Non-thermal

- Fragmentation photons. pQCD with shadowing
- Non-thermal

- Thermal photons
- Thermal

-  Jet in-medium bremsstrahlung
- Thermal

-  Jet-plasma photons
- Thermal

- T. Sakaguchi, JPS Fall meeting

## A theoretical connection between jet energy loss and the electromagnetic emissivity

- Use again the approach of Arnold, Moore, and Yaffe
- 	JHEP **12**, 009 (2001); JHEP **11**, 057 (2001)
- Incorporates LPM
- Complete leading order in S
- Inclusive treatment of collinear enhancement, photon and gluon
- 	emission

- Can be expressed in terms of the solution to a linear integral equation

- T. Sakaguchi, JPS Fall meeting

## E loss/gain: some systematics

- Includes E gain
- Evolves the whole
-   distribution function

- T. Sakaguchi, JPS Fall meeting

## Time-evolution of a parton distribution

- T. Sakaguchi, JPS Fall meeting

## PHENIX hadronic data

- B. Cole, QM 05

- T. Sakaguchi, JPS Fall meeting

## Photons: establishing a baseline

- QCD @ NLO, Aurenche *et al*., NPB **286**, 553 (1987)
- See also Gordon & Vogelsang

- Turbide, Gale, Frodermann, Heinz, PRC (2008)*.*

- Photons from AA in a couple of slides...

- T. Sakaguchi, JPS Fall meeting

## But: other signature of jet-photon conversion? 

- Jet-plasma photons will come out of the
- 	hadron-blind region. “Optical” v2 < 0

- Suggestion & high pT: Turbide, Gale, Fries PRL (2006)
- Low pT: Chatterjee *et al., *PRL (2006)
- All pT: Turbide *et al., *PRC (2008)

- T. Sakaguchi, JPS Fall meeting

## Data: Results from PHENIX

- v2: small! Consistent with zero (within errors)

- T. Sakaguchi
- RHIC/AGS 07

- T. Sakaguchi, JPS Fall meeting

## AZHYDRO (Heinz & Kolb)(c.f. Quark Gluon Plasma III)

- Tc=164 MeV,     =0.2 fm/c, Tfo=130 MeV
- Good modeling of bulk dynamics
- Small values of momentum anisotropies
- Geometric anisotropy shrinks rapidly

- T. Sakaguchi, JPS Fall meeting

## Results: Spectra 

- Results: Spectra

- Window for thermal effects at low to intermediate pT
- Same dynamical model as hadronic data
- NO additional parameters in the EM fits, over the hadronic fits
- The preliminary experimental data is being finalized

- S. Turbide *et al., *PRC (2008)

- T. Sakaguchi, JPS Fall meeting

## Results: RAA

- Results: RAA

- The discrimination between models is dependent
- on the high pT photons

- See also F. Arleo, JHEP (2007)

- S. Turbide *et al., *PRC (2008)

- T. Sakaguchi, JPS Fall meeting

## Results: v2

- S. Turbide *et al., *PRC (2008)

- T. Sakaguchi, JPS Fall meeting

## Results: v2 sensitivity

- Good news: high pT photon v2 sensitive to
- details of initial conditions (geometric isotropy)

- Some additional resolution with correlation analyses:

- Jet bremsstrahlung/fragmentation correlated with hadrons
- Jet-plasma & thermal, uncorrelated

- S. Turbide *et al., *PRC (2008)

- T. Sakaguchi, JPS Fall meeting

## Dileptons?

- Dusling & Zahed, arXiv:0712.1982 * *

- E. L. Bratkovskaya, W. Cassing,
- O. Lynnyk, arXiv:0805.3177 * *

- H. van Hees, QM08

- T. Sakaguchi, JPS Fall meeting

## Energy loss systematics with collisional energy loss (along with radiative).

- What next? New development

- G. Qin, J. Ruppert, C. Gale, S. Jeon,
- G. D. Moore,
- M. G. Mustafa, PRL (2008)

- There is (some) room to re-examine the effect on EM emission

- T. Sakaguchi, JPS Fall meeting

## Photon-tagged jets: photon-hadron correlations

- X.-N. Wang, Huang, Sarcevic., Phys. Rev. Lett. 77, 231 - 234 (1996)

- At LO the photon is strongly correlated with the away-side jet

- LO

- Proposed advantage:

- Calibrated probe of the QGP.

_**At LO:**_

- How does it look
- in a full calculation?

- T. Sakaguchi, JPS Fall meeting

## But, recall sources of photons:

- Hard direct photons. pQCD with shadowing
- Non-thermal

- Fragmentation photons. pQCD with shadowing
- Non-thermal

- Thermal photons
- Thermal

-  Jet in-medium bremmstrahlung
- Thermal

-  Jet-plasma photons
- Thermal

- T. Sakaguchi, JPS Fall meeting

## Some definitions...

- The hadron spectrum, given
- a trigger photon

- Joint probability for producing
- a back-to-back pair

- Initial distribution of away-side jet before
- evolution in the medium

- Yield per trigger in AA collisions/yield per trigger in
- pp collision

- Inclusive fragmentation function in AA/ (...) in pp

- T. Sakaguchi, JPS Fall meeting

## 3D Hydro results

- address data in the soft sector with one consistent approach

- Nonaka & Bass: PRC75, 014902 (2007)

- T. Sakaguchi, JPS Fall meeting

## Results (with coll. E loss)

- The initial momentum distribution of the
- away-side jet (direct component not shown)
- in central Au – Au @ RHIC

- Different  contributions to yield per trigger
- for photon-tagged 0 in central Au – Au @
- RHIC

- Results (**with** coll. E loss)

- Qin *et al., in preparation*

- T. Sakaguchi, JPS Fall meeting

## Results: pp

- T. Sakaguchi, JPS Fall meeting

## Results: AA

- T. Sakaguchi, JPS Fall meeting

## Results: AA

- IAA for photon-triggered hadrons as a function of
- centrality

- Yield per trigger on the away-side as a
- function of centrality

- T. Sakaguchi, JPS Fall meeting

## What is the quantitative importance of the additional processes in correlation studies?

- Data can’t (at this point) make a statistically
- significant difference...

- T. Sakaguchi, JPS Fall meeting

## More phun with photons: discriminate between dynamical approaches? 

- 2D – Azhydro
- (Kolb & Heinz)

- 3D hydro
- (Nonaka & Bass)

- Turbide *et al. PRC *(2008)

- Qin *et al., *in preparation

- T. Sakaguchi, JPS Fall meeting

## Conclusions

- Photons and hard probes (e.g. jets) can and should be treated together and consistently
- The RHIC data is compatible with a picture where jets loose energy (radiative + elastic), and where plasma channels participate in both energy loss and photon production
- Photon and hard probes help in the modeling of *soft* matter
- Viscosity?
- Do dileptons (in progress)
- LHC (in progress)
- Jet-Jet correlations at NLO
- The future is bright for correlation measurements involving EM variables, and calculations!

- T. Sakaguchi, JPS Fall meeting