# Presentation: 815512

## Recent Spin Results from STAR

**From                   Collaboration**

**OGAWA, Akio**

- Working Group Meeting on “Future pp and Spin Physics at RHIC”
- 7 Oct 2005, BNL

## The Relativistic Heavy Ion Collider

-  at Brookhaven National Laboratory

**R-HI **
- New state of matter
- QGP
- De-confinement
- ...
**polarized proton**
- Nucleon Spin Structure
- Spin Fragmentation
- pQCD
- ...
- RHIC is a QCD lab

## Polarized Proton Operation at RHIC

| pp Run  | 2002  | 2003 | 2004 |   2005                                                      |  > 2006 LongTermGoals |  |
| --- | --- | --- | --- | --- | --- | --- |
| CM Energy |                                  200 GeV |  |  |  | 200 GeV | 500 GeV |
| <Pb> and direction at STAR | 0.15  T       | 0.30 T/L | 0.40  L | 0.45  L/T | 0.7 L/T | 0.7  L/T |
| Lmax [ 1030 s-1cm-2 ] | 2 |  6 | 6 | 16 | 80 | 200 |
| Lint    [pb-1 ] at STAR | 0.3  | 0.5 / 0.4 | 0.4 | 9 | 320  | 800  |

## The               Collaboration

**615 collaborators**
**52 institutions**
**12 countries**

**S****olenoid ****T****racker ****A****t ****R****HIC**

## Nucleon Spin

- 1/2 = 1/2  + G + LL

- “Spin Sum Rule”

## STAR detector   

- Solenoidal Magnet
- B = 0.5 T

- Tracking Detectors
- Time Projection Chamber   ||<1.6
- Forward TPC              2.5<||<4.0
- Silicon Vertex Tracker        ||<1

- Trigger Detectors
- Beam-Beam Counters   3.4<||<5
- Zero-Degree Calorimeter     ||~6

- + E-M Calorimeters - installation in stages
- to be completed before 2006
- Barrel EMC                         ||<1
- Endcap EMC                1.0<  <2.0
- Forward Pion Detector  3.3<|<4.1

- STAR is adding lots of EM calorimetry to detect high-energy   , e, 0                              TPC+EMC for _jet reconstruction_                                                                                                                                     BBC + scaler board system for relative luminosity and polarization monitoring

- STAR detector**   **

- + STAR Upgrade Plans:  Time of Flight, Forward Meson Spectrometer, Forward Tracker, Micro-Vertex Detector

- CTB

- ZDC

- ZDC

- (BBC)

- Cutway side view of the detector

- where pseudorapidityln tan

- 5

- Yellow(proton)
-  beam

- Blue(proton)
-  beam

## Jet reconstruction at STAR

- - via TPC pT for charged hadrons+EMC ET for e-m showers

- 2) Trigger used in this analysis - High Tower:
- ET > 2.4 GeV deposited in one tower** **( x = (0.05 x 0.05)
- + additional requirement of BBC coincidence.

- 3) Cuts on:
-   charged tracks || < 1.6  and  pT >0.1 GeV/c
-   jets: pT jet > 5 GeV/c , 0.2< jet  (det) <0.8
-   background:  Ejet(neutral)/Ejet(total)< 0.9 (2004)  and < 0.8  (2003)
-   |z-vertex| < 75cm (2003) and < 60cm (2004)
-  tower ET>3.5 GeV software threshold (only 2004 cross section)

- 1) Jets reconstruction - midpoint cone algorithm (Tevatron II)
- seed energy = 0.5 GeV, cone angle R = 0.4 in splitting/merging fraction f=0.5

- 5) Final statistics (after cuts) for:
-   cross section :   42k jets (2004)
-   ALL asymmetry:   125k (2003) and  162k (2004) jets

- 4) Data set: 0.4 pb-1 (2003 and 2004) recorded luminosity
-                  <Pb> =0.3 (2003) and <Pb> = 0.4 (2004)

- EMC on-line event displaydi-jet event

## Uncorrected per-event yield

- Reasonable agreement between data/MC
- 10 weighted pythia samples
- Slope difference:
- Short term: incorporated into sys. uncertainty
- Long term: iterative re-weighting of MC sample

- Allows data/MC comparison before luminosity
- For HT, include trigger pre-scale:

- DNP2005 M.Miller,MIT

## Data vs. MC

- pt (jet) >10 GeV/c

- Red  pythia + gstar
- Black  data
- All error bars statistical

- R

- 

- EM energy

- charged energy

- DNP2005 M.Miller,MIT

## Cross section for inclusive jet production

- ~25% ± 5%
- From simulations. Consistent result  obtained from di-jet evts

- Bins of width 1-sigma (resolution)    “purity” of ~35% over range on the diagonal.
- Motivates application of bin-by-bin correction factors:

- (MC)

- DNP2005 M.Miller,MIT

## Bin-by-bin correction factors

- MB data statistics limited
- More advanced unfolding techniques currently under study

***************et*** : decreases *c(p**T**)*
***resolution****: *increases *c(p**T**)*
*********Trig***: ~1 e-2 at *p**T-jet* =   5 GeV
-              ~1 at *p**T-jet* = 50 GeV

*“**measured”*

*“**true”*

- Simulation

- DNP2005 M.Miller,MIT

## Preliminary results for the cross section in inclusive jet production in p+p at sqrt(s)=200 GeV vs NLO Calculation

-  50% systematic uncertainty from  energy-scale (dominant) shown.
-  Other sources of systematic uncertainties  (smaller, not shown):  normalization, BBC trigger efficiency, background contribution, ...
*Agreement (within systematics) over 7 orders of magnitude*

-  MB and HT data agree in overlap region
-  NLO QCD - Fortran code from:                    hep-ph/0404057 (Jager et al.)
- Rcone=0.4,  CTEQ 6.1 ***F*= ***R* =*p**T*

- DNP2005 M.Miller,MIT

## Double Longitudinal Spin Asymmetry Measurements

- Require concurrent measurements:
-   magnitude of beam polarization, *P**1(2)                                                    *RHIC polarimeter(s)
*  *direction  of  polarization vector  at interaction point
-   relative luminosity of bunch crossings with different
-    spin directions:                                                                   STAR
-   spin dependent yields of process of interest: Ni and Nij

- Statistical significance:

## Double spin asymmetry ALL(preliminary) results

- Sources of systematic uncertainties: background contribution, trigger bias, relative luminosity,  residual (non-longitudinal) asymmetries, bunch to bunch systematic variations (random pattern analysis) + beam polarization

- Double spin asymmetry ALL(preliminary) results
- in inclusive jet production in p+p collisions at sqrt(s)=200GeV

-  Consistent results from 2003 and 2004 analyses
-  Results limited by statistical precision
-  Total systematic uncertainty ~0.01 (STAR) + beam polarization (RHIC)

- DNP2005 J. Kiryluk,MIT

## Total systematic uncertainty ~0.01 (STAR) + beam pol. (RHIC)  

- Results limited by statistical precision
- Total systematic uncertainty ~0.01 (STAR) + beam pol. (RHIC)

- jet cone=0.4,  0.2<jet<0.8

- *) Predictions:
- B.Jager et.al, Phys.Rev.D70(2004) 034010

- *)

- Double spin asymmetry ALL(preliminary) results
- in inclusive jet production in p+p collisions at sqrt(s)=200GeV

- DNP2005 J. Kiryluk,MIT

## Cross checks - e.g. (2004) parity violating asymmetries 

- Consistent with zero - as expected
- All other xcheck asymmetries were found consistent with zero

- Cross checks - e.g. (2004) parity violating asymmetries

- DNP2005 J. Kiryluk,MIT

## Run5 data under analysis right now and Run6 STAR projection

- Run5 data under analysis right now and Run6 STAR projection

- 2005

- 2006

- Start collecting di-jet sample + developing necessary  - 0 discrimination algorithms for future direct photon and +jet measurements.

## Lambda polarization in longitudinally polarized p+p collisions at STAR 

-   reconstruction at STAR via decay channel:p+(Br=64%)
- - combining TPC tracks with opposite charges
-   cuts for tracks and decay vertex topology
-   |<xF>|~0.008    <pT> ~1.5 GeV/c
-  Data sample (after all cuts) 2003+2004
- ~30k Lambda and ~30k anti-Lambda

- Lambda polarization in longitudinally polarized p+p collisions at STAR

- See: talk by Q. Xu, LBNL & Shandong Univ. (tomorrow!)

## STAR Detector

-  **TPC: -1.0 ****< ******** < 1.0**
** ****Forward-TPC: 2.8 < ******** < 3.8**
** ****BBC : 2.2 < ******** < 5.0**
** ****FPD: |********| ~ 4.1 and ~3.6**

**Upgraded Forward ************ ****Detector (FPD) **
** ****Pb-glass EM calorimeter**
**  ****(from IHEP Protovino, used in E704)**
** ****Shower-Maximum Detector (SMD)**
** ****Preshower**

## Mass resolution ~ 20MeV

**Mass resolution ~ 20MeV**
**We understand gain ~2% level**
**Efficiencies is almost purely**
**geometrically determined**

## Forward  production in hadron collider 

**                  ****NLO pQCD**
**Jaeger,Stratmann,Vogelsang,Kretzer**

**Forward**** ************ ****production in hadron collider**

-  **Large rapidity ******** production ************~4******** probes asymmetric partonic collisions**
-  Mostly **high-x valence quark**** + ****low-x gluon**
* ***0.3***** < x*****q****<  0.7**** **
-  **0.001*****< x*****g ****< 0.1**
-  <z> nearly constant and high  0.7 ~ 0.8
-  **Large-x quark polarization is known to be large from DIS**
** ****Directly couple to gluons = A probe of low x gluons**

**p**
**d**

**p**
**Au**

********

- q

- g

**E****N**

**x****q****p**

**x****g****p**

- 

********

**E****N**

- (collinear approx.)

## ppX cross sections at 200 GeV

- The  inclusive differential cross section for 0  production is consistent with NLO pQCD calculations at 3.3 < η < 4.0
- The data at low pT are more consistent with the Kretzer set of fragmentation functions, similar to what was observed by PHENIX for  production at midrapidity.

- ppX cross sections at 200 GeV

- D. Morozov (IHEP),
- XXXXth Rencontres de Moriond - QCD,
- March 12 - 19, 2005

- NLO pQCD calculations by Vogelsang, et al.

- pQCD applicability / factorization / scale dependence?

## pQCD scaling of cross section 

**pQCD scaling of cross section **

**p****T****, x****F**** and ********s dependences of cross section**
**and pQCD scaling**
-    Similar to ISR analysis J. Singh, et al Nucl. Phys.
-     B140 (1978) 189.

- pQCD scaling gives B=4  (FF modification of Pt will increase B)

- STAR published and
- preliminary 0 cross sections in
- forward rapidity at s=200GeV

- Run5 online 0 reconstruction
- on s= 410GeV data

## Large Analyzing Powers at RHIC

**Large Analyzing Powers at RHIC**

**First measurement of A****N**** for forward ****π****0**** production at ********s=200GeV**** **

- Similar to **FNAL E704** result at s = 20 GeV
- 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
-    suppressed? (hep-ph/0408356)
- Qiu and Sterman (initial-state) / Koike (final-state) twist-3 pQCD calculations

- STAR collaboration, hep-ex/0310058, Phys. Rev. Lett. **92** (2004) 171801

**First shown**
**at spin2002**

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

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

## Measurement of AN for mid-rapidity leading charged particle production at s=200GeV

**  ****primary track multiplicity >3**
** ****average polarization  P= - 8% , Q= - 14% **

- Not sensitive to L monitor

- PRELIMINARY

**Measurement of A****N**** for mid-rapidity**** leading charged particle production at ********s=200GeV**

- Spin2002 J. Balewski(IUCF)

## BBC (Preliminary) Results 

-    Unexpected AN of unknown origin measured with the BBC
-    Strong pseudorapidity dependence of AN for xF>0   and AN = 0 for xF<0
-    (syst) < (stat)

- AN BBC <cos > = p1 ANCNI +p0

- AN BBC =0.67(8)x AN  CNI ~ 1%
-         3.9 <  < 5.0

- AN BBC = 0
- 3.4 <  < 3.9

- Transverse Single Spin Asymmetries
- BBC (Preliminary) Results** **

- (BBC) (x10-3)

- (BBC) (x10-3)

- (CNI) (x10-3)

- (CNI) (x10-3)

- Spin2004 J. Kiryluk (UCLA/MIT)

## AN(xF) in run5 at √s=200 GeV

- AN(xF) in run5 at √s=200 GeV

- _Run5 data:_
- PBeam~45%(online), L~0.4 pb-1
-  Using online Polarization
- AN consistent with run3 data
- Nonzero effect at xF>0.4
- Zero for negative xF

- _Analysis includes:_
- Clustering analysis
- Fit to parameterized shower shape
- Applying cuts:
- Etot > 20 GeV
- Nγ ≥ 2
- Zγγ = |E1-E2|/(E1+E2) < 0.7
- Fiducial volume > 1/2 cell from edge
- 0.07 < mγγ < 0.3 GeV/c2
- Gains are determined from π0 peak position for each tower
- Energy dependent gain correction
- Run/Luminosity dependent gain correction
- MC to data comparison

-        _*To do:*_
- Study of systematic errors
- Include single arm data for consistency

- Spin2005 D. Morozov(IHEP)

## AN(pT) in run3+run5 at √s=200 GeV

- Combined statistics from run3 and run5 allowed to distinguish nonzero effect in AN(pT) plot
- There is an evidence on C/pT dependence at xF>0.4
- Fit – C = 0.07 ± 0.01
- Theoretical prediction’s  needed to compare – constrain on Sivers function?
- To do: systematics study

- Online calibration of CNI polarimeter

- Spin2005 D. Morozov(IHEP)

## Separating xF and pT dependence

-  ~10 week of transverse polarization running at STAR in run6 expect to yield L *dt * 10pb-1 with 50% beam polarization   reduce statistical errors AN by >4 compared to run-3 data
-  enables measurement of AN(pT) at fixed *x*F with FPD++
- Calculations of fixed-*x*F AN(pT) by U.d’Alesio and F. Murgia (private communication) based on work described in PRD **70** (2004) 074009

## “Semi-inclusive” pp

**Inclusive hadron production = Collins + Sivers** **Mixed **
**Sivers DF measurements**
-    Di-jet & far side di-hadron kT balance
-    Jet AN     (one 40GeV 0 .vs. two 20GeV 0)
-    Photon AN
-    Heavy meson AN
**Transversity measurements**
-    Near side di-hadron correlation (with Collins FF from Belle)
-    Jet/hadron ATT
-    DY

## Gluon Sivers function from di-jet kT balance            Directly measuring initial state kT by looking at 2 jets                   leads to 1/pT none-suppressed signal for Sivers function

- Gluon Sivers function from di-jet kT balance            Directly measuring initial state kT by looking at 2 jets                   leads to 1/pT none-suppressed signal for Sivers function

- D. Boer and W. Vogelsang, Phys.Rev. D **69** (2004) 094025
- T. Henry, J. Phys. **G30**, S1287 (2004).

- 10/pb, P=50% (run6)

- Jet #2

- AN ST  k

- Jet #1

## What can a larger calorimeter do?

- With FPD++ module size and electronic dynamic range, have >95% probability of detecting second photon from  decay.
- --> Capabilities for Direct photon & particle correlation / jet & heavier mesons measurements

## Forward Meson Spectorometer (FMS) Physics GoalsThese we know we can do from FPD analysis of π0

- 1. Measure gluon distributions xg(x) in protons and gold nuclei from 0.001<xb<0.1
- Check universality of xg(x) in region of overlap with DIS (0.02<xb<0.1)
- 2. Characterize correlated pion distributions as a function of Q2 to search for onset of saturation effects
- Is Au a Color Glass Condensate (CGC)?
**3. Resolve the origin of large transverse spin asymmetries in p********+p -> ********0****+x for forward ********0 ****production**

## Probing the low-x gluon density in the Au nucleus

- Showed suppression of forward π0 in dAu

- G. Rakness, for STAR [hep-ex/0507093]

## STAR forward upgrade plan

## New FMS Calorimeter

- Lead Glass From FNAL E831
- 804 cells of 5.8cm5.8cm60cm
- Schott F2 lead glass

- Loaded On a Rental Truck for Trip To BNL

## Conclusions

-  **First preliminary results for jet cross section and jet A****LL**
** ****Preliminary Lambda polarization study at mid rapidity is shown  **
** ****More results from forward ********0**** production **
** ****Expect more physics with upcoming runs with improved luminosity & polarization, together with upgrades of detectors**
** ****Full BEMC ready for run6, together with trigger upgrades **
** ****FPD++ in run6, FMS run7 at forward rapidity**
** ****RUN6 STAR request :**
** ****10/pb transverse spin**
** ****20/pb longitudinal spin**
** ****Some AuAu if pp goal is archived early**
** ****DAQ upgrade (run8) & Tracking upgrades (run9/10)**