# Presentation: 844340

## Jet Energy Loss and Correlations from STAR

- Fuqiang Wang
- for the STAR Collaboration

**Pre-Meeting Workshop: Properties and Signatures of sQGP**
**2006 Division of Nuclear Physics Annual Meeting**
- Nashville, Tennessee
- October 25, 2006

## Outline

- “punch-through” at high pt
- “disappearance” at intermediate pt
- enhancement at low pt
- three-particle jet-like correlation

## results not covered

- identified hadron jet-like correlation.
- near-side  correlation (ridge).
- forward-0 and mid-rapidity h± correlation.
- forward- and mid-rapidity h± correlation.
-  -h correlation.
- e-h correlation.

## “punch-through” at high pt

- clear away side peak even in central Au+Au for high trigger pT
- background reduced for higher associated pT
- little modification of near-side yield
- suppression of away-side yield apparent in central Au+Au

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

- STAR, nucl-ex/0604018, PRL 97 (2006) 162301.

## width of away-side peaks

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

- away-side widths similar for central and peripheral, also for different pt.
- yield suppressed x5 in central w.r.t. dAu.

- finite prob. of not interacting: fragmentation as in vacuum?
- fragment in medium, then hadrons lose energy with insignificant broadening at large pt?
- lose some energy, and then fragment?

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

- Au+Au 40-80%

- Magestro, QM 2005.

## “disappearance” at intermediate pt

- near-side correlation unchanged
- away-side peak suppressed in central Au+Au
- consistent with surface emission
- distributions in d+Au similar to p+p
- suppression is final state effect
- more intuitive hint for “jet” suppression, but quantitatively much more difficult

## “disappearance” has RP dependence 

- Evidence of less suppression in-plane than out-of-plane, consistent with energy loss picture.

- STAR, PRL93 (2004) 252301.

## Enhancement at low pt

- STAR, PRL95 (2005) 152301.

- Enhanced and broadened away-side distribution at low pT.

## Low pt trigger, modest pt associated

- trigger pT =2.5-4 GeV/c, associated pT =1.0-2.5 GeV/c

- STAR Preliminary

- 0-5%

- 5-10%

- 10-20%

- 20-40%

- 40-60%

- 60-80%

- PHENIX, PRL97 (2006) 052301.

- J.G. Ulery (STAR), nucl-ex/0510055.

## Low pt trigger, modest pt associated

- Au+Au top 5%

- Au+Au top 5%

-  (rad)

- pTtrig=2.5-4 GeV/c, pTassoc=1-2.5 GeV/c

- Double-peak structure more pronounced with lower trigger pt.

- J.G. Ulery (STAR), nucl-ex/0510055.

- PHENIX, PRL97 (2006) 052301.

## Partial thermalization

- Two sources of particles:
- hard: hard scattering products.
- soft: bulk medium constituents.
- Very different as seen in peripheral.
- Become similar in central.

- <pT> from away jets

- <pT> from medium decay

- Away side <pT> (GeV/c)

- hard-soft: approach thermalization.
- soft-soft (larger x-section): higher degree of thermalization.

- STAR, PRL 95 (2005) 152301.

- g

- g

## <pt> is not peaked (even dipped at )

- <pt> is not peaked (even dipped at )

- Novel dip at  in away <pT> for pTtrig<6 GeV/c.
- Hadrons in the double-hump are harder – shock wave push?

- number
- correlation

- pT-weighted
- correlation

- pTtrig=4-6 GeV/c
- pTassoc=0.15-4 GeV/c

- Angular dependence of <pt>

- F. Wang (STAR), nucl-ex/0508021.

## Sound shock waves – sonic boom

- Mach Cone

- _[Supersonic Jets ](file:///f-18flyby.mpg)_

## Nuclear shock waves

- Many recent studies:
- H. Stoecker, nucl-th/0406018.
- Muller, Ruppert, nucl-th/0507043.
- Chaudhuri, Heinz, nucl-th/0503028.
- Y.G. Ma, *et al.* nucl-th/0601012.

- Casalderrey-Solana, Shuryak, Teaney,
- hep-ph/0411315
- Casalderrey-Solana and Shuryak, hep-ph/0511263

- Scheid, Muller, Greiner, Phys. Rev. Lett. 32, 741 (1974)
- Hofmann, Stoecker, Heinz, Scheid, Greiner, PRL 36, 88 (1976)

- cS ~ 0.33, Mach angle = 70o

## Do we see it?

**near-side**
**trigger**

**away-side jet axis**

- Di-hadron azimuthal correlation

- 

- projection

- 

## Are they shock wave conical flow?

- Jets deflected by radial flow:
- In each single event, the away jet is deflected to the side by radial flow.
- When many events are summed up, double-peak structure may appear.

- Or preferential selection of jet particles:
- -	those directed inwards are harder to get out because of energy loss.
- those directed outwards are easier to get out.

- Rudy Hwa

- Double-peak structure can be also generated by deflected jets.

## So how are we going to see it?

- Need 3-particle correlation to discriminate conical flow vs deflected jets.

## Raw 3-particle correlation

- Δ1

- Δ

- pTtrig=3-4 GeV/c
- pTassoc=1-2 GeV/c

- What one gets:(jet+bkgd) x (jet+bkgd).
- To get (jet x jet),one must subtract (jet x bkgd) and (bkgd x bkgd).

- J.G. Ulery (STAR), Hard Probes 2006, nucl-ex/0609047.

## Background x Background (Soft-Soft)

- Δ1

- Δ2

- Constructed by mixing a random trigger particle with soft particle pairs in min-bias events.
- Contains correlations between soft particle pairs that are not associated with the trigger particle.

- J.G. Ulery (STAR), Hard Probes 2006, nucl-ex/0609047.

## Jet x Background + trigger v2

- Δ

- Δ1

- Δ2

- Red is Jet + Background
- Black is Background and open black is scaled background (such that Red - Open Black is zero within |Δ±1|<0.2).
- Jet x Background term is created by folding 2-particle jet signal with 2-particle background.
- (Red – Open Black) x Open Black + Open Black x (Red – Open Black)

- J.G. Ulery (STAR), Hard Probes 2006, nucl-ex/0609047.

## Final 3-particle correlation signal

**-**

- =

**-**

- raw

- jet x bkgd

- bkgd x bkgd

## as a function of centrality

*pp*

- d+Au

- Au+Au
- 50-80%

- Au+Au
- 30-50%

- Au+Au
- 10-30%

- Au+Au
- 0-10%

- J.G. Ulery (STAR),
- Hard Probes 2006, nucl-ex/0609047.

## Signal Strengths

- Δ2

-   Evaluate signals by calculating average signals in the boxes.
-   Near-side, Away-side, Cone, and Deflected.

- J.G. Ulery (STAR), Hard Probes 2006, nucl-ex/0609047.

## Cone position

- Optimum placement of boxes can be determined from varying the placement and from fits.
- Fit fails for 0-10% Au+Au.
- 1.3 radians from π was chosen.

- Radians from π

- Average Cone Signal

- Au+Au Central 0-12% Triggered

**Average Signal in 0.7x0.7 Squares**

- Stat. error only

- J.G. Ulery (STAR),
- Hard Probes 2006,
- nucl-ex/0609047.

## Signals

- Signals taken from average in 0.7x0.7 squares.
- Open symbols are ZDC triggered data and are shifted to the left.
- Large source of systematic errors comes from flow.
- Another significant source is background normalization.
- Signal consistent with Mach cone at about π±1.3 in more central Au+Au collisions.

- J.G. Ulery (STAR), Hard Probes 2006, nucl-ex/0609047.

## Conclusions

- Dijets reappear in heavy ions at sufficiently high pt. Angular distribution little modified, dijet yield is still strongly suppressed.
- At intermediate pt, dijets strongly suppressed (and broadened) that no appreciable dijets survive.
- Rich phenomena at low pt: broadening (even double-peaked) in away-side correlation and <pt>.
- Three-particle jet-correlation results consistent with Mach-cone shock-waves or Cerenkov radiation. Active work is on-going.

## backups

## Re-appearing at low pT

- Re-appearing at low pT

- High pT

- Low pT

- _Definition:_
- near side: ||<1, ||<1.4 away side: ||<2.1, ||<1

- Separation at 1 radian.

## Associated particles pT distributions

- syst. error

- Associated particles pT distributions

_**Near side:**_
- overall
- enhancement
- from pp to AA
- larger initial
- parton energy
- (and modest
- energy loss)?

_**Away side:**_
_** **_
- softening of
- spectra from pp
- to central Au+Au
- energy from
- initial parton
- converted to
- low pT particles.
- energy loss in
- medium!

- 4 < pTtrig < 6 GeV/c

## Conditions for Mach-cone shock waves at RHIC

- Supersonic speed: jets (speed of light)
- A hydrodynamic medium: speed of sound
- The bulk appears equilibrated at T=170 MeV (LQCD-predicted TC).
- Initial stage high pressure and energy density.
- Large elliptic flow is large, described by hydrodynamics within 20-30%.
- Number of constituent quarks scaling; hadronization via coalescence and perhaps quark deconfinement.
- Strong interaction: shock waves (large energy deposition in short time, pressure disturbance)
- High pt suppression (factor of 5)
- Di-jet suppression at high pt.
- Low pt jet-correlation enhanced and broad; partial equilibration between jets and the bulk.

- RHIC has created a perfect fluid of hot and dense matter!
- speed of sound, supersonic jets, energy loss.
- RHIC seems to have all the conditions for Mach-cone shock waves.

## Anisotropic flow

- Previous term contains flow between the two soft particles, but flow correlations between the trigger and soft particles are lost in event-mixing.
- Top plot contains terms of v2trig * v2assoc.
- Bottom plot contains terms of v2*v2*v4 with v4 = 1.15*v22.
- v2 is taken as average of reaction plane and 4-particle measurements.

- Δ1

- Δ1

- Δ2

- Δ2

- Jason Ulery (STAR), Hard Probes 2006.

## Flow systematics

- Flow is varied between the modified reaction plane result and the 4- particle cumulant result.
- Result is robust with the variation in v2.

- reaction plane v2

- 4-particle cumulant v2

- Jason Ulery (STAR), Hard Probes 2006.

## Background normalization systematic

- Normalization within |Δ±1|<0.175 assuming zero yield at minimum.
- Default uses a normalization range of 0.35.
- Normalization range of 0.70 used to check systematic.
- Result is robust with respect to normalization range.

- default

- wide norm. region

- Jason Ulery (STAR), Hard Probes 2006.

## cumulant vs jet-like with no flow

- J.G. Ulery, FW, nucl-ex/0609017.

## cumulant vs jet-like with flow

- J.G. Ulery, FW, nucl-ex/0609017.