# Presentation: 383291

## Jet-like Correlations between forward- and mid-rapidity 

- Fuqiang Wang
- For the STAR Collaboration

## FTPC associated with TPC trigger

- trigger on main TPC high pT particles (|η| < 1)
- and look at FTPC associated particles (2.7 < |η| < 3.9).** **

- trigger

- assoc.

- assoc.

## Why do we want to do it?

**Why do we want to do it?**

- Jet correlations are measured in the main TPC (|η| < 1). Significant modification has been observed.Is there jet correlation at forward rapidity? Hwa, Yang, nucl-th/0605037.If there is, is the correlation different from mid-rapidity?
- could be different due to different pathlengths.
- could be identical if Bjorken boost invariance.

- STAR, PRL 95, 152301 (2005)

## Why do we want to do it?

**Why do we want to do it?**

- Probing different kinematics, and g vs. q jets?

- x=0.05

- x=0.05

**g**

**g**

**g**

**g**

- x=0.05

- x=0.7

**g**

**q**

**q**

**g**

## FTPC v2 correction

- Centrality: 70-20%

- FTPC v2: STAR, Phys. Rev. C 72, 014904 (2005).** **

- Different methods give similar v2 results for the FTPC data.
- Parameterize v2 in pT and .
- Centrality dependence measured by STAR (preliminary).

## Au-side / d-side difference

- corrected for efficiency*acceptance. normalized per trigger particle.
- Background normalized to near-side ||<1.

- |trig|<1, 2.7<|assoc|<3.9

- 

- dN/d

## Au+Au minimum bias

- Major systematic uncertainties from v2:
- MTPC v2: v2{RP} and v2{4} bracket the uncertainty.
- FTPC v2: from v2{2}. uncertainty assumed to be as same as MTPC v2 uncertainty. Conservative estimate.

- Normalization fixed at |±1|<0.2

- Background normalization
- uncertainty in dashed lines.

- |trig|<1, 2.7<|assoc|<3.9
- 3<pTtrig<10 GeV/c, 0.2<pTassoc< 2 GeV/c

- 

- dN/d

- raw signal

- bkgd subtracted

- Near-side consistent with zero.
- Broad away-side correlation.

## Au+Au centrality variation

- |trig|<1, 2.7<|assoc|<3.9
- 3<pTtrig<10 GeV/c, 0.2<pTassoc< 2 GeV/c

- Normalization fixed at |±1|<0.2. Systematic uncertainty plotted for 10-0% data.

- dN/d

- 

- Near side
- consistent with
- zero.
- Away-side broad
- correlation in
- central collisions.

## Double-Gaussian fit

- Systematic errors from
- v2 uncertainties.

## Compare FTPC to MTPC

**Compare FTPC to MTPC**

- dAu

- AuAu 10-0%

- AuAu 80-60%

- 3<pTtrig<4 GeV/c
- FTPC: 0.2<pTassoc< 2 GeV/c
- MTPC: 0.2<pTassoc< 3 GeV/c

- Away-side correlations are
- very similar.

- 

- 

## Inclusive and correlated dN/d

**Inclusive and correlated dN/d******

- inclusive
- yield
- PHOBOS, PRL93, 082301 (2004)

- correlated
- yield within
- ||<2.1

- 

## Summary

- Sizeable away-side jet correlation signal in FTPC with a TPC trigger particle.
- Correlation magnitude smaller at forward rapidity than at mid-rapidity.
- d+Au: correlated yield in Au-direction ~ 2 x d-direction.
- Near-side  ridge extended to forward rapidity?Systematic uncertainty too large to conclude.
- Away-side correlation broadens with centrality.
- three-particle correlation analysis?
- Correlation shapes similar: mid- **≈** forward-rapidity:
- dE/dx so large that the  or pathlength does not really matter?
- dE/dx so large that q- and g-jet difference does not really matter?

## v2 parameterization

- C*{1-exp[-(pT/A)B]}

- D*exp[-(/E)2/2]

- v2(centrality, , pT) = v2cent(centrality) * v2() * v2pT(pT)

- pT  (GeV/c)

- 

- v2   (%)

- v2  (%)

## eta smearing

- eta = 2.7, 3.3, 3.9         theta = 2, 4, 8 degree