# Presentation: 227025

## Hard Probes at RHIC: Past, Present, and Future

- James Dunlop
- Brookhaven National Laboratory

- BNL Colloquium James Dunlop

- 10/30/2007

## The Promise of Jet Tomography

- Simplest way to establish the properties of a system
- Calibrated probe
- Calibrated interaction
- Suppression pattern tells about density profile
- Heavy ion collisions
- Hard processes serve as calibrated probe
- Suppression provides density measure

- +

- =

- BNL Colloquium James Dunlop

- 10/30/2007

## Application to Heavy Ion Collisions: Initial Results 

- Strong suppression in Au+Au collisions, no suppresion in d+Au:
- 	Effect is due to interactions between the probe and the medium
- Established use as a probe of the density of the medium
- Conclusion (at the time): medium is dense (50-100x nuclear matter density)

***PHENIX: Phys. Rev. Lett. 91 (2003) 072301***
***STAR: Phys. Rev. Lett. 91 (2003) 072304***
***PHOBOS: Phys. Rev. Lett. 91 (2003) 072302***
***BRAHMS: Phys. Rev. Lett. 91 (2003) 072303***

- BNL Colloquium James Dunlop

- 10/30/2007

## Calibrated Probe: Hard Interactions

- Hard interactions well understood in perturbative QCD
- Factorization holds
- PDF (initial) x NLO x FF (final)
- Example: 0 production well reproduced down to 2 GeV
- Numerous other examples
-   in the forward direction,
- STAR PRL 92 (2004) 1718
- STAR PRL 97 (2006) 152302.
- proton production in p+p,  	STAR PLB 637, (2006)161.
- Direct  production
- PHENIX PRD 71 (2005) 071102
- Jet production in p+p,
- STAR PRL 97 (2006) 252001
- Significant uncertainties in the calculations, so for precision the baseline needs to be measured

- p+p→0+X

***S.S. Adler et al, Phys. Rev. Lett. 91 (2003) 241803***

- KKP Fragmentation

- (Data – pQCD)/pQCD

- BNL Colloquium James Dunlop

- 10/30/2007

## Calibrated Probe?  Initial state

- Initial conditions may not be trivial at forward y at RHIC, at mid-y at the LHC
- Definitive tests of CGC picture with in run 8 d+Au with the STAR FMS
- Wide pseudorapidity range for monojet search (-1 <  < 4, E up to 60 GeV/c)
- Covers xmin>10-3 in standard factorization; reach much lower x in CGC framework

*First look run 3, STAR PRL 97, 152302 (2006).*

- BNL Colloquium James Dunlop

- 10/30/2007

## The Limitations of RAA: “Fragility”

- The Limitations of RAA: “Fragility”

- Surface bias leads effectively to saturation of RAA with density
- Challenge: Increase sensitivity to the density of the medium

***K.J. Eskola, H. Honkanken, C.A. Salgado, U.A. Wiedemann, Nucl. Phys. A747 (2005) 511***

***A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38(2005) 461 ***

- BNL Colloquium James Dunlop

- 10/30/2007

## Black and White

- Medium extremely black to hadrons, limiting sensitivity to density
- Medium transparent to photons (white): no sensitivity
- Is there something grey?

***S.S. Adler et al, Phys. Rev. Lett. 94, 232301 (2005)***

- BNL Colloquium James Dunlop

- 10/30/2007

## Calibrated Interaction? Grey Probes

- Problem: interaction with the medium so strong that information lost: “Black”
- Significant differences between predicted RAA, depending on the probe
- Experimental possibility: recover sensitivity to the properties of the medium by varying the probe

***Wicks et al, Nucl. Phys. A784 (2007) 426***

- BNL Colloquium James Dunlop

- 10/30/2007

## Gluons vs Quarks: Method

**q jets or g jets**  **gluon jet contribution to protons is significantly larger than to pions at high p****T**** in p+p collisions at RHIC; pbar/******** < 0.1 from quark jet fragmentation at low beam energy .**** **STAR Collaboration, PLB 637, 161 (2006).
**From Kretzer fragmentation function, the g/q jet contribution is similar to AKK.** S. Kretzer, PRD 62, 054001 (2000).

- BNL Colloquium James Dunlop

- 10/30/2007

## Gluons vs. Quarks: No shade of gray

- Gluons should lose more energy than quarks
- Pions have larger quark contribution than protons
- SO, Protons should be more suppressed than pions
- Experimentally NOT observed: equal suppression for pT>6 GeV/c
- Perhaps: If medium already black to quarks, can’t be blacker than black
- Other methods to be tried: kinematics in  (as done in e.g. dijet Sivers)

- gluon  jet

- quark  jet

- quark  jet

- STAR Collaboration, PRL 97 (152301) 2006

- BNL Colloquium James Dunlop

- 10/30/2007

## Charm/Beauty: No shade of gray

- Unexpectedly strong suppression of non-photonic electrons a major issue
- Calls into question the calibration of the interaction of the probe with the medium
- Uncertainties in B contribution: need to measure c and b separately

*STAR,  PRL 98 (2007) 192301**	*

*PHENIX, PRL 98 (2007) 172301*

- BNL Colloquium James Dunlop

- 10/30/2007

## Mechanisms for Energy Loss

- QED: different momenta, different mechanisms
- Just beginning the exploration of this space in QCD

- Bremsstrahlung
- Radiative dE/dx

- “Passage of Particles through Matter”, Particle Data Book

- BNL Colloquium James Dunlop

- 10/30/2007

## Correlations

- WMAP: 10-5 level
- One sample
- Only photons
- Well-defined separation of sources

- RHIC: 10-1 to 10-3 level
- Multiple samples
- Multiple probes
- Model dependence in separation of sources
- quite a few “two-component” models, with different components

- BNL Colloquium James Dunlop

- 10/30/2007

## Interpreting Correlations

- Geometric biases:Hadrons: surface
- 	Di-hadrons: tangential, but depending on Eloss can probe deeply
- 	Charm-hadron, and especially Beauty-hadron(B): depends on Eloss
- 		Note: b and c produced in pairs, B and C decay into multiple hadrons
- 	Gamma-hadrons: Precise kinematics, back to surface
- Beyond reaction of probe to medium, also reaction of medium to probe

***T. Renk, Phys.Rev. C74 (2006) 024903***

- BNL Colloquium James Dunlop

- 10/30/2007

## Dijets from dihadrons 

- Dijets from dihadrons

- NOT background subtracted: no ambiguities from background model
- At high trigger pT, high associated pT:
- clear jet-like peaks seen on near and away side in central Au+Au

- 8 < pT(trig) < 15 GeV/c

- pT(assoc)>6 GeV

***STAR PRL 97 (2006) 162301***

- d+Au

- 1/Ntrig dN/d()

- Au+Au 20-40%

- Au+Au 0-5%

- BNL Colloquium James Dunlop

- 10/30/2007

**Notes:**
Start off with 2 assoc, then move to 6 assoc

## (Minimal) Modification of Clean Signals

- Away-side yield strongly suppressed
- 	(almost) to level of RAA
- No dependence on zT in measured range
- No modification in shape in transverse or longitudinal direction
- The jets you can see cleanly are also in some sense the least modified

***STAR PRL 97 (2006) 162301***

- BNL Colloquium James Dunlop

- 10/30/2007

## Where does the energy go?

- Lower the associated pT to search for radiated energy
- Additional energy at low pT BUT no longer collimated into jets
- 	Active area: additional handles on the properties of the medium?
- 	Mach shocks, Cherenkov cones ...
- 	e.g. Renk and Ruppert, Phys. Rev. C 73 (2006) 011901

**PHENIX preliminary**

***M. Horner, QM2006***

***STAR, Phys. Rev. Lett. 95 (2005) 152301***

- 0-12% 200 GeV Au+Au

- BNL Colloquium James Dunlop

- 10/30/2007

## - Correlations

- Phys. Rev. C73 (2006) 064907

- mid-central Au+Au
- pt < 2 GeV

**3 < p****T****(trig) < 6 GeV****2 < p****T****(assoc) < p****T****(trig)**

- 0.8< pt < 4 GeV
- STAR PRC 75(2007) 034901

- /√ref

**In Au+Au: broadening of the near-side correlation in ******** **
**Seen in multiple analyses**
**Number correlations at low p****T**
**PRC73 (2006) 064907**
**P****T**** correlations at low p****T****, for multiple energies**
**Major source of p****T**** fluctuations**
**J. Phys. G 32, L37 (2006)**
**J. Phys. G 34, 451 (2007)**
**Number correlations at intermediate p****T**
**PRC 75, 034901 (2007)**
**Number correlations with **
**   ****	****trigger particles up to 8 GeV/c**
**D. Magestro, HP2005**
**J. Putschke, QM2006**

- BNL Colloquium James Dunlop

- 10/30/2007

##  Two-Component Ansatz

- Simple ansatz
**near-side jet peak**
**near-side ridge**
**v2 modulated background**

**3<p****t,trigger****<4 GeV**
**p****t,assoc.****>2 GeV**

**Au+Au 0-10%**
- preliminary

-  Two-Component Ansatz

- BNL Colloquium James Dunlop

- 10/30/2007

## Two-component Model at High Pt: “Ridge” and “Jet”

**3<p****t,trigger****<4 GeV**
**p****t,assoc.****>2 GeV**

**Au+Au 0-10%**
- preliminary

**“****Jet” yield constant**
**with N****part**

**J****ö****rn Putschke, QM2006**

- Reminder from pT<2 GeV:
-  elongated structure already in minbias AuAu
-  elongation in p-p  to  elongation in AuAu.

*STAR, PRC 73, 064907 (2006)*

- p+p. low pT
- Number correlations

- Au+Au. low pT
- pT  correlations

- /√ref

- BNL Colloquium James Dunlop

- 10/30/2007

## How to interpret shape modifications?

**How to interpret shape modifications?**

**Hard-soft: **** away-side spectra approaching the bulk.**
**Deflected jets, Mach-cone shock waves, Cherenkov radiation, completely thermalized momentum conservation, or...?**

-  M. Horner, QM2006

- STAR Collaboration, PRL 95,152301 (2005)

- BNL Colloquium James Dunlop

- 10/30/2007

## Three particle correlations

- Two Analysis Approaches:
**Cumulant Method**
-     Unambiguous ***evidence for true three particle correlations***.
**Two-component Jet+Flow-Modulated Background Model**
**     ****Within a model dependent  analysis, evidence for conical emission **in central Au+Au collisions

**p****T****trig****=3-4 GeV/c **
**p****T****assoc****=1-2 GeV/c**

*C. Pruneau, QM2006*
*J. Ulery, HP2006 and poster, QM2006*

- BNL Colloquium James Dunlop

- 10/30/2007

## Future at RHIC: “RHIC II” or the fb era

- RHIC: luminosity + upgraded detectors for precision
- Beauty: last hope for a “grey” probe; needs detector upgrades to both STAR and PHENIX to isolate from charm
-  -jet: precision probe of energy loss
- Upsilon: precision tests of Debye screening with a “standard candle”

- Previous Au Run, year 4

- STAR HFT

- PHENIX VTX

- Current Au Run, year 7

- One year at RHIC II ~ 30 nb-1
- 30 nb-1*1972 =~ 1 fb-1 p+p equivalent

- BNL Colloquium James Dunlop

- 10/30/2007

## STAR Upgrades

**DAQ1000:DAQ and TPC-FEE upgrade**

**Heavy Flavor Tracking Upgrade**

** ****Pixel detector**

**Inner silicon tracker **

**Forward GEM tracker**

***initial conditions***

***heavy flavor***

***Critical Point Search***

- ~2010

- ~2009

- COMPLETED

- ~2010

- ~2010-2013

- BNL Colloquium James Dunlop

- 10/30/2007

## -Jet: Golden Probe of QCD Energy Loss

-   emerges unscathed from the medium
- Probes deeply into the medium: different surface bias from hadron, dihadron
- Fully reconstructed kinematics: measure real fragmentation function D(z)

- 

- h

- BNL Colloquium James Dunlop

- 10/30/2007

## Gamma-Jet: unique capability of RHIC II

- RHIC: Clean separation of  from 

**W.Vogelsang NLO**
**RHIC II**** ****L****= 20nb-1**
**   ****LHC: 1 month run**

******0**** ****suppression at**
**  ****RHIC & LHC**

- BNL Colloquium James Dunlop

- 10/30/2007

## Golden Probe: Towards -jet in Au+Au

- Golden Probe: Towards -jet in Au+Au

- Direct  does not couple to medium or fragment into jets
- No surface bias on trigger, full kinematics of hard collision
- But: luminosity hungry, and backgrounds from  0 and fragmentation 

***STAR QM05, T. Dietel, nucl-ex/0510046***

- From 30 ub-1
- Upgraded RHIC II: 30 nb-1/year

- DATA STATISTICS WILL INCREASE BY FACTOR of 1000 in one year at RHIC II

- BNL Colloquium James Dunlop

- 10/30/2007

## Gamma-Hadrons now:Spectra for DIRECT -tagged events in p+p

**Promising for future ********-jet **
**	****Reminder: spin will measure **
**	****asymmetries that are ~1%**
**	**
**From p+p 2 pb****-1****, half acceptance **
**Equivalent p+p luminosity in **
**30 nb****-1 ****Au+Au = 1 fb****-1****: **
**factor of 1000 in one year at RHIC II!**

- Use -enriched sample:
- plot away-side pT-spectra for photon-tagged events (after subtracting 0-hadron correlations)

***Subhasis Chattopadhyay,QM2006***

- Gamma-Hadrons now:Spectra for DIRECT -tagged events in p+p

- BNL Colloquium James Dunlop

- 10/30/2007

## Gamma-Hadrons in the fb era

- Needs RHIC II luminosity.

- Phys.Rev.C74:034906,2006.
- Phys.Rev.Lett.77:231-234,1996.

- Projections for PHENIX
- From J. Nagle, Galveston
- STAR has somewhat higher statistics

- BNL Colloquium James Dunlop

- 10/30/2007

## Heavy Flavor Correlations

- Isolate b from c
- Isolate production mechanism
- In medium: what is losing energy, and how much?

- gluon splitting/fragmentation

- 0

- 

- Flavor creation

- BNL Colloquium James Dunlop

- 10/30/2007

## Grey Correlations: Heavy Flavor in the fb era

- Identified heavy flavor correlations: promising, but statistical power still low
- RHIC II: many orders of magnitude (~x1000 with luminosity, S/B improvements)

- Light Hadrons

- Heavy flavor

- Inclusive Spectra

- Correlations

- From 5 pb-1

- BNL Colloquium James Dunlop

- 10/30/2007

## Jets in the fb era

- Jet reconstruction under optimization
- In hand: p+p, Cu+Cu, Au+Au
- From LHC: should work for Et>~20-30 GeV
- Nbin projection from p+p
- 	# Jets in bin at 40 GeV
- 	Run 6 Cu+Cu: ~50
- 	Run 7 Au+Au: ~1000 .
- 	RHIC II: 	~50, 000
- 			Precise D(z)

- 2 pb/GeV

- 40% precision with 0.3 pb-1, half barrel

*STAR PRL 97 (2006) 252001*

- BNL Colloquium James Dunlop

- 10/30/2007

## Quarkonium: Upsilon

- Sequential dissociation of quarkonia to measure energy density of plasma
- Requires full luminosity of RHIC II for definitive measurements

**RHIC**

- Proof of principle measurement: run 6 p+p

- Upsilon(1S+2S+3S)→e+e-

- BNL Colloquium James Dunlop

- 10/30/2007

## Other initiatives: Muons and dileptons

- Muon Tracking Detector: use magnet steel as absorber
**Physics: dileptons from intermediate mass up to quarkonia states**
**Best method for separating Upsilon states (a la CDF)**
**R+D stage: Brookhaven LDRD 2007-2008**
- Dielectrons using TOF for ID and HFT for background rejection

- BNL Colloquium James Dunlop

- 10/30/2007

## Conclusion

- Jet Quenching well established: “textbook” science
- Moving towards the quantitative
- Separate by parton species in search of a grey probe
- Track lost energy and its interaction with the medium with two- and multi-particle correlations
- Watershed in coming years from RHIC II luminosity upgrade and detector upgrades
- Precision studies with , b, c, and associated multi-hadron correlations
- Complementary, competitive, and in some ways superior, to LHC

- BNL Colloquium James Dunlop

- 10/30/2007

## Towards -jet: ( Correlation analysis

***See Subhasis Chattopadhyay, QM2006***

**Use “shower-shapes” in EMC: Create two samples**
**	****Enriched photon sample (mix ********, ********0****)**
**	****Enriched ********0**** sample (almost pure ********0****)**
**Reduction in near angle peak in Photon sample**
**	****Away-side yields only slightly reduced**
**Effect more prominent for larger Et****trigger**

******0**
**Mixed**
**Photon**

*From p+p collisions run 5, 2 pb*-1

- Towards -jet: ( Correlation analysis

- BNL Colloquium James Dunlop

- 10/30/2007

## Away-Side: pTtrig Dependence

**0-12%**

- 1.3 < pTassoc < 1.8 GeV/c

- 4.0 < pTtrig < 6.0 GeV/c

- 6.0 < pTtrig < 10.0 GeV/c

- Away-side:
- Structures depend on range of pT.
- becomes flatter with increasing pTtrig
- yield increases

- 3.0 < pTtrig < 4.0 GeV/c

**AuAu 0-12%**

**Central contribution to away-side**
**becomes more significant with **
**harder p****T****trig**** => fills dip**

- Away side

**Mark Horner, QM2006**

- BNL Colloquium James Dunlop

- 10/30/2007

## 10-20 GeV: Effects of the Medium Most Apparent

**energy loss by 20 GeV jets**
**   ****accessible at RHIC (& interpretable)**

**p****T**** trigger > 8 GeV/c**

- STAR PRL nucl-ex/0604018

- Majumder, et al. hep-ph/0611135

- BNL Colloquium James Dunlop

- 10/30/2007

##  Two-Component Ansatz

- Study near-side yields
- Study away-side correlated yields and shapes
- Components
**near-side jet peak**
**near-side ridge**
**v2 modulated background**

- _Strategy:_ Subtract  from  projection: isolate ridge-like correlation
-  _Definition of “ridge yield”:_
- ridge yield := Jet+Ridge()  Jet()
- Can also subtract large .

**3<p****t,trigger****<4 GeV**
**p****t,assoc.****>2 GeV**

**Au+Au 0-10%**
- preliminary

-  Two-Component Ansatz

- BNL Colloquium James Dunlop

- 10/30/2007

##       Annual yields at RHIC II & LHC

***from Tony Frawley***
*** ******RHIC Users mtg.***

***at LHC:  (10-50) x ************     ~10% of ******L******        25% running time***

- BNL Colloquium James Dunlop

- 10/30/2007

## Precision (and its limits)

**C. Loizides**
**hep-ph/0608133v2**

***J. Lajoie [PHENIX] QM2006***

- BNL Colloquium James Dunlop

- 10/30/2007

## PHENIX Upgrades

**-3              -2             -1                 0                1               2               3    rapidity**

****** ****coverage                 2******

**EMCAL**

**EMCAL**

**(i) ***********0****** and direct *********** with additional EM calorimeters (NCC, MPC)**
**(ii) *****heavy flavor***** with silicon vertex tracker (VTX, FVTX)**** **
**	**** ****(i)+(ii) for large acceptance ***********-jet ***
**(iii) *****low mass dileptons***** (HBD) **

- BNL Colloquium James Dunlop

- 10/30/2007