# Presentation: 004107

## Some Striking NewSTAR Results

**Some Striking New*****STAR***** Results**

**Carl A. Gagliardi**
- Texas A&M University
- for the               **Collaboration**

- A **few** of the **most important**, **qualitatively new** results from ***STAR***.

## As we left Oakland 

- Phys. Rev. Lett. 91, 072304 (2003).

- In central Au+Au collisions:
- Strong suppression of inclusive hadron production
- Disappearance of the away-side jet
- d+Au looks like p+p
- Jet quenching in the dense medium

## Limitations of RAA

- Limitations of RAA

- K.J. Eskola et al., NP A747, 511

- Central RAA Data

- RAA  at  10 GeV/c

- Leading hadrons preferentially arise from the surface
- Limited sensitivity to the region of highest energy density
- Need more penetrating probes

- (proportional to gluon density)

## Charm and electron RAA and v2

- Identified D0 consistent with binary scaling at low pT
- Non-photonic electrons arise primarily from c and b
- Large charm suppression and v2 at intermediate pT

- F. Laue, sect 5a

- H. Zhang, sect 5c

## What happens as we raise the pT?

- 	In central Au+Au collisions, non-photonic electrons are very strongly suppressed at high pT

- J. Bielcik, sect 5c

**Notes:**
New plots without grid ans w/o d+Au in centrality 2 3. Shaded region reflecting d_Nbin

## How suppressed is suppressed?

- High-pT electron suppression is comparable to inclusive charged hadron suppression

- Gluons and light quarks

- Heavy quarks

## Not what we expected!

- Data agree with c  e predictions if the density is quite high
- But b  e should be there, too
- Is our understanding of c and b production correct?
- Is our understanding of partonic energy loss correct?
- How strong are the in-medium interactions?
- How dense is the medium?

## Di-jets at much higher pT

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

***STAR*** Preliminary

- pT(assoc)>6 GeV

- Clear emergence of the away-side jet

- No background subtraction!

- D. Magestro, sect 3b

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

## Di-jets and the interaction mechanism

- ~0.54

- ~0.25

**Scaling factors relative to d+Au**

- 	Direct measurement of the medium modification (and lack thereof) of the away-side jet
- Away-side width and fragmentation function
- Can partonic energy loss models describe these simultaneously?

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

- D. Magestro, sect 3b

## Di-jets and the medium

- 	Yield provides a better upper limit on the density of the medium
- Constrain the number of active degrees of freedom?
-       [Müller, Rajagopal, hep-ph/0502174]

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

## Putting the pieces together

- Poster by Dainese, Loizides and Paic

- RAA ≈ IAA ≈ 0.20-0.25

- From M. Van Leeuvan

## How does the medium respond?

- 	Measure low-pT associated hadrons
- Away-side particles increase in number and soften in pT
- Away-side flat or small dip for intermediate pTtrig

***STAR*** Preliminary

- J. Ulery, sect 3c

- M. Horner, poster #70

## Conical flow?

****1

****2

****1

****2

- Does a shock wave form?
- Three-particle correlations
**Conical flow**:  associated particles may appear on opposite sides of Δφ = π
**Deflected jets**:  associated particles on the same side of Δφ = π

- Casalderrey-Solana, Shuryak and Teaney, hep-ph/0411315
- Stocker, NP A750, 121
- Ruppert and Muller, PL B618, 123

## Three-particle correlations in d+Au and Au+Au

- Elongated along
- diagonal: kT effect?
- deflected jets?
- Distinctive features
- of conical flow are
- not seen in present
- data with these pT
- windows.

- Difference in Au+Au
- average signal per radian2:
- center – corner =
-    0.3 ± 0.3 (stat) ± 0.4 (syst)
- center – cone =
-    2.6 ± 0.3 (stat) ± 0.8 (syst)

- J. Ulery, sect 3c

## Conclusion

**Suppression of non-photonic ****electron yield **at high-pT, and
**Re-emergence of the ****away-side jet** at high-pT
- Improved **upper and lower limits** on the energy density
**Severe test** of our understanding of partonic energy loss
**Three-particle correlations** with an intermediate-pT trigger
- kT effects or deflected jets, or ...
- Characteristic signature of conical flow is **not** **observed**
- Overall, ***STAR*** has a wealth of new data!
- Answer questions we’ve been asking
- Help us ask questions we weren’t smart enough to ask before
- The answers to those questions will tell us
- What is the strongly interacting matter that we are creating at RHIC?
- What are its properties?

## The STAR Collaboration

**The *****STAR***** Collaboration**

**U.S. Labs:****   ****	**
**	****Argonne,  Lawrence Berkeley,  and Brookhaven National Labs**
**U.S. Universities:****    **
**	****UC Berkeley, UC Davis,  UCLA,  Caltech, Carnegie Mellon, Creighton,  Indiana, Kent State, MIT, MSU,  CCNY, Ohio State, Penn State,  Purdue,  Rice, Texas A&M, UT Austin, Washington, Wayne State, Valparaiso, Yale**
**Brazil:****	****    **
**	****Universidade de Sao Paolo**
**China:****	****    **
**	****IHEP - Beijing, IPP - Wuhan, USTC,**
**	****Tsinghua, SINAP, IMP Lanzhou**
**Croatia:****	****    **
**	**** ****Zagreb University**
**Czech Republic:****	****    **
**	**** ****Nuclear Physics Institute**
**England:**
**	****University of Birmingham**

**France:****     **
**	****Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes**
**Germany:****  **
**	****Max Planck Institute – Munich University of Frankfurt**
**India:**
**	****Bhubaneswar, Jammu, IIT-Mumbai, Panjab, Rajasthan, VECC**
**Netherlands:**
**	****NIKHEF/Utrecht**
**Poland:**
**	****Warsaw University of Technology**
**Russia:****  **
**	****MEPHI – Moscow,  LPP/LHE JINR – Dubna,  IHEP – Protvino**
**South Korea:**
**	****Pusan National University**** **
**Switzerland:**
**	****University of Bern**
**	**

**Notes:**
Let me put up the most important slide: the STAR collaboration, 
and I want to thank my STAR colleagues to give me the opportunity to present this talk on their behalf. 
Thank you for your attention.

## Slide 17

## Identified particle RCP

- Barannikova, sect 1a; Cai, sect 1a; Salur, sect 5a

-  Φ definitively follows K0 at intermediate pT : mass is not the source
-  All particles consistent for pT > ~5-6 GeV/c

**Notes:**
Make a link to fragmentation picture: origin of v2 at high pt, if due to fragme

## Charm production

- Zhang, sect 5c

- First direct measurement of open charm in Au+Au Collisions
- Total charm cross-section in Au+Au: Nbinary scaling from d+Au

## STAR and PHENIX non-photonic electron RAA measurements agree very well

- STAR and PHENIX non-photonic electron RAA measurements agree very well

- PHENIX figure from Vicki Greene’s talk

## Electron RAA predictions with lower densities

- N. Armesto et al, private comm.

- M. Djordjevic et al., nucl-th/0507019

## Alternative scenario: collisional contribution

- 	Large collisional (not radiative) interactions also produce large suppression and v2

- AMPT:
- (C.M. Ko)

- ← σ=10 mb

- ← σ=3 mb

- ← pQCD

- Moore & Teaney, hep-ph/0412346

## Centrality dependence of near and away-side yields

- Near-side yields consistent within errors
- Away-side yields decrease monotically with increasing NPart
- Suppression pattern similar for two pT(assoc) ranges!

- Fit scaledby x2

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

- D. Magestro, sect 3b

## Surface emission for dijets?

- Poster by Dainese, Loizides and Paic

- Emission points for dijets also show surface bias, tangential emission
- IAA dominated by tangential pairs for large

## Hadron-triggered fragmentation functions

- Away-side D(zT) suppressed, but shape unchanged

- ~0.54

- ~0.25

**Scaling**
_**factors**_

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

- D. Magestro, sect 3b

## An upper bound on energy density?

- Müller and Rajagopal: From entropy and jet quenching to deconfinement  hep-ph/0502174
- The number of degrees of freedom can be determined independently of direct measurements of temperature

- Energy density:

- Entropy:

- Degrees of freedom:

- A lower bound on (T) is constrained by an upper bound on energy density

## Mean pT

- <pT>=pt-weighted correlation / number correlation.
- <pT> is more robust.
- Some of the systematic errors cancel.
- Dip on the away side in central Au+Au for moderate pTtrig.
- Appears more thermalized with medium.

- J. Ulery, sect 3c