# Presentation: 589124

## The RHIC Experiments: 

***what can they do (forward)?***

**Kenneth N. Barish**
**UC Riverside**

**Forward physics at RHIC workshop**
**2004 RHIC/AGS Users Meeting, BNL**
**14 May, 2004**

## Regions of a nucleus

- x

-  **Q (GeV)**

- 1

- 10-1

- 10-3

- 10-2

- 10-4

- CGC

- CQF

- 1

- 10

- 100

- QCD

- Y~0

- Y~4

- Y~2

**Regions ****of a nucleus**

- pQCD

- CGC boundary
- QS2 =QS(y=0) 2 ey
- ~0.3
- CQF boundary
- QS2 =QS(y=0) 4

**BULK**

- pQCD

**CENTRAL**

**BRAHMS**

## Understanding proton spin structure

**Understanding proton spin structure**

**Need to understand dynamics of the nucleon spin:**
**Contribution of gluons to proton spin (********G)**
**Gluon feed-down to quark sea (measure ********q/q and ********q/q)**
**W production unique in providing theoretically clean access**
**A****N**** possibly gives us access to the transversity distribution, orbital angular momentum, and higher twist effects**

## Flavor decomposition 

_**Drell-Yan production of lepton pairs**_
**Maximal parton level asymmetry**: *a**LL*= -1
**Possible severe background from semi-leptonic decays of open charm productions – can be improved with forward silicon tracking.**

_**W production**_
**Produced in parity violating *****V-A***** process**
** ****Chirality / helicity of quarks defined**
**Couples to weak charge**
** ****Flavor almost fixed: flavor analysis possible**
** ****Flavor ID reduces uncertainty in current pol-PDF models.**
**E.g., PHENIX-Muon Arms**

## G and forward detectors

**prompt photon**

## Experimental access to low-x gluons

**Gluons at low-x**
- pp & pA
- * , ee
- Prompt photons
- Open Charm
- Hadrons
- J/ production
- correlations
**Map out previous diagrams**

## Coverage of experiments

**NCC**

- 0        1         2        3         4        5
- Rapidity

**PHENIX **
******Si endcap **

- pp2pp

- STAR
- FPD
- FTPC

- PHENIX CENTRAL

- STAR
- TPC
- EMC

- STAR
- ENDCAP

**BRAHMS**

**Coverage of experiments**

**PHOBOS **
**spectrometer**

**************jets, e, ******** ********, charm/beauty, e******

**************jets, charm/beauty**

**************L********LL**

**************L********LL**

********

**charged hadrons**

**Au**

**d**

**Large ******** coverage is needed**

## PHOBOS Detector System

** ****New trigger system**
**for d+Au PID spectra**

**TOF**

**TOF**

**SpecTrig**

## Pseudorapidity Distributions at 200 GeV  

**Pseudorapidity Distributions at 200 GeV  **

-  p + p at 200 GeV

-  d + Au at 200 GeV Min-Bias

- arXiv:nucl-ex/0311009 andSubmitted to PRL

- PHOBOS Preliminary

## Cronin Effect as a Function of  (d+Au)

- Cronin Effect as a Function of  (d+Au)

## The data at forward rapidities was collected with FFS at 4o ( ~3) and 12o (~2)

**INEL**
**2.47<********<5.29**

- The data at forward rapidities was collected with FFS at 4o (**** ~3) and 12o (******~2****)**

## High pT suppression for different ‘s

**High p****T ****suppression for different ********‘s**

- Where does the high pt suppression come form?
- Initial State (property of cold nucleus)
- Final state (QGP)
- dA

- same effect at  >2

## STAR Detector

**Forward ************ ****Detector (FPD) **
** ****Pb-glass EM calorimeter**
** ****Shower-Maximum Detector (SMD)**
** ****Preshower**

-  **TPC: -1.0 ****< ******** < 1.0**
** ****FTPC: 2.8 < ******** < 3.8**
** ****FPD: |********| ******** 3.8 (p + p)**
**          ****|********| ******** 4.0 (p + p and d + Au)**

- Endcap EMC
- 1< <2 = 2

## Forward 0 Inclusive Cross Section

**STAR data consistent with Next-to-Leading Order pQCD calculations**
**in contrast to data at lower ********s (Bourelly and Soffer, hep-ph/0311110)**

** **STAR data at
- = 3.8 (hep-ex/0310058, accepted to PRL, in press)** **
-  = 3.3 (hep-ex/0403012, Preliminary)** **
** **NLO pQCD calculations at fixed  with equal factorization and renormalization scales = pT
-  Solid and dashed curves differ primarily in the g   fragmentation function

- Forward** ********0**** **Inclusive Cross Section

## AN for forward π0 production at s=200GeV

-  In agreement with several models including different dynamics:

- Sivers: spin and k correlation in initial state (related to orbital angular momentum?)
- Collins: Transversity distribution function & spin-dependent fragmentation function
- Qiu and Sterman (initial-state) / Koike (final-state) twist-3 pQCD calculations

- STAR collaboration, hep-ex/0310058, accepted by Phys. Rev. Lett. (in press)

-  pT dependence?
-  xF<0?
- AN with mid-rapidity correlation?

-  Spin dependence in jet?
-  Heavy flavors??
-  Related to “gluon saturation”???

- AN for forward π0 production at s=200GeV

## STAR

**STAR**
**Large rapidity gap**** ********0****+h****±**** ****correlation data**

**35<E********<45GeV**

**Midrapidity h******** tracks**** ****in TPC**
**   ****-0.75 < ********< +0.75**

**Trigger by forward ************ **

-  **E****p**** > 25 GeV**
** **************** ******** ****4**

- Coicidence Probability
-  [1/radian]

****

- Beam View

- Top View

**Large rapidity gap ********0**** +h correlation data are suppressed in d+Au relative to p+p at small <xF> and <pT,p>      **
**Consistent with CGC picture**

## Forward Upgrades to PHENIX

-      Muon trigger for highest luminosities in p-p, d-A and A-A
-      and with robustness against beam and collision related
-      backgrounds.

- Trigger chambers
- new lvl1-trigger
- electronics

- Nosecone Calorimeters

- Forward Sillicon
- Tracking detectors

- Coverage 1<<3
- Jets direction and energy
- photons
- 0’s
- electrons
- detached vertices for charm and bottom

- Central arm upgrades
- Aerogel Counter-PID
- RPC – for TOF
- Barrel Sillicon tracking
- Hadron Blind Detector
-       –Datliz rejection

## PHENIX Forward Upgrade Components

**PHENIX Forward Upgrade Components**

**Endcap Vertex Tracker **
- silicon pixel detectors
**Nosecone Calorimeter**
- W-silicon  (only 20cm long)
- shower max (Si)

**Muon trigger**
- U-tracker (RPC or MuTr)
- D-tracker (RPC’s)

## Space is tight ...

**Challenges:**
**-only 40 cm apart from collision point ... **
**-only 20 cm of space is available**

## Design thoughts

**Good ********/********0**** separation**
**Good position resolution**
**e/h separation**
**Reasonable jet measurements**
**Triggering capability**
**Notes:.**
**AuAu is challenging**
**Shower max layers required**
**Need upstream tracking to recover J/******** resolution in AuAu**

**Calorimeter****: ~****	****40 L****rad ****/ 1.6 L****abs**
**Lateral **** ****seg.****       ****	****1.5 x 1.5 cm****2**
**EM section:****        ****	****10 Lrad**
******/********0**** identifier:****   ****	****at a depth ~ 5Lrad (two layers of ~2x60 mm****2****  silicon strips)**

**PHENIX preliminary design:**
_***14 cm of W absorber ***_
***+***
_***6 cm  Si readout***_

**Design thoughts**

**This is a huge challenge, but not completely crazy!!**

**Q****2**

**Log(x****2****)**

**0.5 pb****-1 ****pAu (run 12)**
******log(x****2****) ********Q****2****=0.1x1 GeV****2**

**1000 **
**event/bin**

**500**

**100**

**20**

**Coverage of NCC at 200 GeV**

**Direct photon**

## Level-1 triggering scheme

## Summary

**NCC**

- 0        1         2        3         4        5
- Rapidity

**PHENIX **
******Si endcap **

- pp2pp

- STAR
- FPD
- FTPC

- PHENIX CENTRAL

- STAR
- TPC
- EMC

- STAR
- ENDCAP

**BRAHMS**

**Summary**

**PHOBOS **
**spectrometer**

**************jets, ******** ********, charm/beauty, e******

**************jets, charm/beauty**

**************L********LL**

**************L********LL**

********

**charged hadrons**

## Extra slides ...

## Semi-inclusive DIS

**Semi-inclusive DIS**

- In addition to the scattered electron, one measures in addition, the hadronic final state(s) – leading K’s and ****’s
- Access to flavor separated parton distributions

- Comments:
- Treated only at LO so far
- Q2 of 2.5 GeV2 is a concern
- Higher twist effects not included
- u-quark “dominance” limits precision of d and s-quark  (and anti-quark) polarized distributions.
- “Hadron taging” technique relies on knowledge of fragmentation functions
**Measurements at the highest Q****2 ****(RHIC) are important.**
**W production (at RHIC) is an independent and eloquent technique**

- Hermes: Phys.Rev.Lett 92 (2004) 012005

## Sensitivity goal: flavor decomposition  

- 70% polarization,
- 800 pb-1, 104 detected W’s

**N. Saito**

- AL(W+) → u/u(x1)   @x1>>x2
- AL(W+) → –d/d(x1) @x2>>x1

- (W+ and W-- have a different acceptance)

- The measurement of inclusive single spin muon asymmetries is the least biased way to probe q/q, q/q.
- Complete theoretical treatment from first principles by Nadolsky and Yuan using re-summation and NLO techniques [NuclPhysB 666(2003) 31].
- PHENIX is in the process of re-evaluating their sensitivities using their NLO code.
- Measurement requires a trigger with rejection ~10,000.
- Present muon trigger has a rejection of 250 (run 3).
- Upgrade needed ... requires momentum determination at level-1 to reject background due to hadron-decay’s into ’s and beam related backgrounds.
- Nose-cone calorimeter important to help reject hadron jets off-line