# Presentation: 277332

## First measurement of double-spin asymmetry 

**at RHIC**
- Abhay Deshpande
- RIKEN-BNL Research Center
**For PHENIX collaboration**
- December 10th, 2003
- University of Illinois

**A****LL****(********0****)**

## Plan of this talk....

-  Brief history of spin
-  Relativistic Heavy Ion Collider: as a *Polarized Collider*
-  **Beam polarization measurement**
-  **PHENIX Spin Physics program and the detector**
-  Double spin asymmetry measurement for 0 production
-  Longitudinal beams at PHENIX and sign of polarization
-  Relative luminosity issues
-  **Asymmetry**
-  Background estimate and asymmetry of the background
-  Systematic checks
-  **Result and comparison with theory**
-  **Summary & future prospects of spin at RHIC**

## Past experiments & results

-  Past experiments: Deep Inelastic Scattering (DIS)
-                                 Fixed target experiments
-  **EMC, SMC at CERN: **
**  ****-- polarized muon beams (~190 GeV/c) **
**      ******** ****on polarized solid state targets**
** ****SLAC(E80,E130,E142,E143,E154,E155,X)**
**  ****-- polarized electron beams (~10********49 GeV/c)**
**      ******** ****on polarized solid/gaseous targets**
** ****HERMES at DESY**
**  ****-- polarized electron/positron beam (~27 GeV/c)**
**      ******** ****on polarized gas/jet targets**
-  Confirmed the violation of Ellis-Jaffe Spin sum rule: p,n too small
-  Confirmed Bjorken Spin sum rule: p-n=Constant*f(Q2)
-  **Where is the nucleon spin? ******** Gluons?**

## B. Adeva et al., SMC, PRD58, 112002(1998)

**1/2=(1/2)**************+**********G+L****q****+L****g**

**Proton Spin Puzzle remains unsolved!**

** ****constrained, need  to measure**** **

**Gluon Spin Contribution:**

**Quark Spin Contribution:**

**1/2=(1/2)**************+**********G+L****q****+L****g**

- Extensive uncertainty studies

***Similar results from E154 and many theoretical groups....***

## Relativistic Heavy Ion Collider

- Au + Au collisions at **200** GeV/u
- p + p collisions up to 500 GeV
- spin polarized protons (70%)
- lots of combinations in species and energy in between

_**Performance**_**        **_**Au + Au **_**          **_**p+p**_
******s****nn****	****                200 GeV       500 GeV**
**L [cm****-2**** s ****-1**** ]           2 x 10****26            ****2 x 10****32 **
**Cross-section       7 barns        60 mbarn**
** ****Interaction rates  14 kHz         12 MHz**

**Design Parameters:**

**RHIC Capabilities**

**AGS**

**LINAC**

**BOOSTER**

- Pol. Proton Source
- 500 A, 300 s

**Spin Rotators**

- Partial Siberian Snake

- Siberian Snakes

- 200 MeV Polarimeter

- AGS Internal Polarimeter

- Rf Dipoles

- RHIC pC Polarimeters

- Absolute Polarimeter
-              (H jet)

- 2  1011 Pol. Protons / Bunch
-  = 20  mm mrad

- RHIC accelerates heavy ions to 100 GeV/A
- and polarized protons to 250 GeV

**Relativistic Heavy Ion Collider**

## Siberian Snakes at RHIC

- Depolarizing Resonance:
- Spin tune = no. of spin kicks
- Imperfection resonances:
-  --magnet errors & misalignements
- Intrinsic resonances:
-  --vertical focusing fields
- Effect of depolarizing resonances
- averaged out by rotating spin by
- large angles on each  turn

- 4 helical dipoles  S. snake
- 2 snakes in each ring
-    -- axes orthogonal to each other

- RIKEN/BNL

- (Funded by RIKEN Institute in Japan)

## Proton beam polarimetry (I)

- ANL, BNL, Kyoto, RIKEN/RBRC &
**Yale** Collaboration

- (AGS-E950 Experiment 1999/2000)

## Polarization Run III & beyond

| RUN | #proton/bunch
[x109] | 
#bunch | 
Beta*
(m) | 
Emittance
(m) | 
Luminosity
1030 cm-2s-1 | 
Pol.
(%) |
| --- | --- | --- | --- | --- | --- | --- |
| 2001-
2002 | 70 | 55 | 3 | 25 | 1.8 | 15-25 |
| 2002-2003 | 100 | 55 | 1 | 25 | 16 | 25-35 |
| 2005- | ?
 | 112 | 1 | ? | ? | 50 |
| Design | 200
 | 112 | 1 | 20 | 80 | 70 |

**Presently:** ~30% relative error
- From unknown analyzing power:
- Lack of experimental points in high
- Energy region.
*Absolute pp gas jet polarimeter 2004*
*Will reduce this to ~5% (goal)*

##  12 Countries;  57 Institutions;  460 Participants

**  ****USA   Abilene Christian University, Abilene, TX **
**             ****Brookhaven National Laboratory, Upton, NY **
**             ****University of California - Riverside, Riverside, CA**
**             ****University of Colorado, Boulder, CO**
**             ****Columbia University, Nevis Laboratories, Irvington, NY**
**             ****Florida State University, Tallahassee, FL**
**             ****Georgia State University, Atlanta, GA**
**             ****University of Illinois Urbana Champaign,  IL**
**             ****Iowa State University and Ames Laboratory, Ames, IA**
**             ****Los Alamos National Laboratory, Los Alamos, NM**
**             ****Lawrence Livermore National Laboratory, Livermore, CA**
**             ****University of New Mexico, Albuquerque, NM **
**             ****New Mexico State University, Las Cruces, NM**
**             ****Dept. of Chemistry, Stony Brook Univ., Stony Brook, NY**
**             ****Dept. Phys. and Astronomy, Stony Brook Univ., Stony Brook, NY  **
**             ****Oak Ridge National Laboratory, Oak Ridge, TN**
**             ****University of Tennessee, Knoxville, TN  **
**             ****Vanderbilt University, Nashville, TN****	****                                                                                                **

**Brazil        University of São Paulo, São Paulo**
**China        Academia Sinica, Taipei, Taiwan**
**                  ****China Institute of Atomic Energy, Beijing**
**                  ****Peking University, Beijing**
**France      LPC, University de Clermont-Ferrand, Clermont-Ferrand**
**                  ****Dapnia, CEA Saclay, Gif-sur-Yvette**
**                  ****IPN-Orsay, Universite Paris Sud, CNRS-IN2P3, Orsay          **
**                  ****LLR, Ecòle Polytechnique, CNRS-IN2P3, Palaiseau**
**                  ****SUBATECH, Ecòle des Mines at Nantes, Nantes**
**Germany  University of M****ü****nster, M****ü****nster**
**Hungary   Central Research Institute for Physics (KFKI), Budapest**
**                  ****Debrecen University, Debrecen**
**                  ****Eötvös Loránd University (ELTE), Budapest **
**India          Banaras Hindu University, Banaras**
**                  ****Bhabha Atomic Research Centre, Bombay**
**Israel         Weizmann Institute, Rehovot**
**Japan       Center for Nuclear Study, University of Tokyo, Tokyo**
**                  ****Hiroshima University, Higashi-Hiroshima **
**                  ****KEK, Institute for High Energy Physics, Tsukuba **
**                  ****Kyoto University, Kyoto**
**                  ****Nagasaki Institute of Applied Science, Nagasaki**
**                  ****RIKEN, Institute for Physical and Chemical Research, Wako**
**                                               ****RIKEN-BNL Research Center, Upton, NY              **
**                  ****University of Tokyo, Bunkyo-ku, Tokyo**
**                  ****Tokyo Institute of Technology, Tokyo**
**                  ****University of Tsukuba, Tsukuba **
**                  ****Waseda University, Tokyo                    **
**S. Korea   Cyclotron Application Laboratory, KAERI, Seoul**
**                  ****Kangnung National University, Kangnung**
**                  ****Korea University, Seoul **
**                  ****Myong Ji University, Yongin City **
**                  ****System Electronics Laboratory, Seoul Nat. University, Seoul**
**                  ****Yonsei University, Seoul**
**Russia       Institute of High Energy Physics, Protovino **
**                   ****Joint Institute for Nuclear Research, Dubna **
**                   ****Kurchatov Institute, Moscow**
**                   ****PNPI, St. Petersburg Nuclear Physics Institute, St. Petersburg**
**                   ****St. Petersburg State Technical University, St. Petersburg**
**Sweden     Lund University, Lund**

*** ******12 Countries;  57 Institutions;  460 Participants***

## The Detector: Run 1  Run 2

- Run-1 (2000-1)

## Run 3 Configuration

**Central Arm Tracking**
-       Drift Chamber
-       Pad Chambers
-       Time Expansion Chamber
**Muon Arm Tracking**
-       Muon Tracker:  **North Muon Tracker**
**Calorimetry**
-       PbGl
-       PbSc
**Particle Id**
-       Muon Identifier: **North Muon Identifier**
-       RICH
-       TOF
-       TEC
**Global Detectors**
-       BBC
-       ZDC/SMD  **Local Polarimeter**
**      ****Forward Hadron Calorimeters**
-       NTC
-       MVD
**Online Calibration and Production**

## RHIC Spin Physics Program

-  0,+,-  Production

- Heavy Flavors

- Prompt Photon

- Gluon Polarization

- Flavor  Decompsition

- Transverse
- single/double
- spin physics

- W physics
- Longitudinal single spin physics

- Transversity:
- Sivers vs. Collins effects
- & physics of higher twists;
- Pion interf. Fragmentation

- Transverse single spin physics
- Phenix-Local Polarimetry

##  Scattering processes in polarized p+p

- Hard Scattering Process

## Analyzing powers

**NLO corrections are now known for all relevant reactions **

- LO

- LO

## Leading hadrons as jet tags

- Hard Scattering Process

- qg+gq

- qq

- gg

**Fraction of ********0**** produced**

- p**T** (GeV)

## Double spin asymmetry 0production

- (P) Polarization -- absolute scale and “longitudinal”ness
- (L) Relative Luminosity -- bunch to bunch variation
- (N) Number of pi0s -- triggers and efficiencies etc.

- ++ same helicity
- + opposite helicity

## Beam polarization in PHENIX

- With RHIC CNI polarimeter
- Uncertainty estimated to be  ~30%
- Theory uncertainty ~20%
-  Other experimental sources estimated to 10-15%
- This error does not change the significance of ALL, because it scales both value and error in the same way
**Spin direction confirmation **
**With Spin Rotators commissioning**
**Confirmed with PHENIX local polarimeter**
**Long. component of the spin direction monitor **
**PHENIX local polarimeter**

**Beam polarization in PHENIX**

**Notes:**
Explain the problem here... what the stable direction of the proton spin is in the collider and that it needs to be rotated by 90 degrees longitudinally. Done by spin rotator magnets. Accelerator guys tell us not to worry, and trust their calculations. Not good enough. Look for single spin transverse effects. They should vanish if the spin rotators are doing their job. 
Looked for pi0 production in very forward region (pT < 0.3 GeV). Saw nothing. STAR saw an asymmetry in inclusive pion production. We saw a large analyzing power in forward neutron production. Not know the origin of it, but know it exists, probably because of the Delta or Lambda production. Clear correlation with beam polarization and as a function of Phi the azimuth a sine way seen.

## PHENIX Local Polarimeter 2003

- ~1800cm

- 10cm

- (±2mrad)

**PHENIX Collision Point**

- Dx magnet

**Blue beam**

**Yellow beam**

- beam

**Zero Degree Calorimeter (ZDC)**
- Tungsten-Fiber Sandwich
- 5.1T, 149 X0         3 ZDCs each side

- SMD

**Shower Max Detector **
**(SMD)**
- Plastic Scint. strips
- (0.5cm x 3)
- 10 and 15 cm long
- 7 x 1.5cm columns
- 8 x 1.5cm rows
-       Read by
-       Hamamatsu M16

**Notes:**
We realized this could be used to measure the spin orientation at PHENIX
PHENIX was planning to include this in our detector any way, so WE USED THE EXISTING STRUCTURE FOR WHAT WE WANTED TO DO.

## Run 3: Loc.Pol. Operation

**Run 3: Loc.Pol. Operation**

- Energy/SMD strip  Energy Deposit Profile  hit position
-              determine left/right and up/down & on the  plot
- Max Amplitude at  = /2, –/2
-             Left/Right asymmetry  Transverse
- Max Amplitude at  = 0
-             Up/Down asymmetry   Transverse  radial
- Flat curve  No asymmetry   Longitudinal

## Longitudinal Polarization

- Spin Rotators OFF
- Vertical polarization

- Spin Rotators ON
- Correct Current !
- Longitudinal polarization!

- Spin Rotators ON
- Current Reversed
- Radial polarization

## How do we know the direction?

-  To compensate for this precession, the spin rotator currents are set
-   to have the beam spin direction rotated by ~40 degrees in the accelerator
-   plane.
-  How well do we know the components in x,y,z directions....

## How do we know the direction?

- Blue, connection **correct**

- Blue, connection **IN-correct**

## Longitudinal component of spin

- Up-Down asymmetry

- Left-Right asymmetry

**Longitudinal component of spin**

## Relative luminosity (I)

- Counts live trigger _in each bunch crossing_
- 4 inputs – for syst. error study:                          Beam Beam Counter and Zero Degree Calorimeter used – different kinematical region, different physics signals
- Systematic error study through comparison of counts from different detectors
-  look at ratio of 2 detector scalars crossing-by-crossing:
- a(i) = NA(i)/NB(i)
- Ratio should be the same for all crossings (constant)
- B is always the counts from the Beam-Beam Counter (BBCLL1), A is one of the other scalars.
- Fit this by the expected pattern:
- a(i) = C[1+ALLP1(i)P2(i)]
- C, ALL are the fitting parameters.
-  2 is a very important check of systematic errors

- ALL vs fill

- 2/NDF  vs (ALL)

- 20

- 30

- 10

- Not so good, but ...

**Relative luminosity (I)**

**Notes:**
Product of polarization is “signed”

## Relative luminosity (II)

- ZDC/BBC vs z-vertex width

- ALL vs fill

- 2/NDF  vs (ALL)

- After vertex correction

- 2

- 3

- 1

- 

- Now 2/NDF1

- Vertex width affects
- Rel. Lum. measurements

**Relative luminosity (II)**

## Relative luminosity: Result

- Pessimistic estimation limited by ZDC statistics (30 times less than BBC statistics used in Rel. Lum. measurements)
- Rel. Lum. contribution for 0 ALL less than 0.2%
- For average beam polarizations of 26%
- ALL of BBC relative to ZDC consistent with 0 (<0.2%)
- Strong indication that both ALLs are zero (very different kinematical regions, different physics signals)

**Relative luminosity: Result**

## Data set: selection criteria

- Based on EMCal; Threshold ~1.4 GeV/c
- Rejection factor ~110
- Analyzed data sample: 	**42.7M events (~0.215 pb****-1****)**
**	****	****	****	****sqrt(<P****b****P****y****>)~26%**
- Minimum Bias data
- To obtain “unbiased” 0 cross section at low pT
- For high pT photon trigger efficiency study

**Data set: selection criteria**

## Central arm  and 0 trigger

**Trigger with a rejection power of > 100 at Level-1 needed in p+p**
- Reduce the 12MHz interaction rate to  1 KHz
**EMCal part has two sums to collect photon showers**
- 2x2 towers non-overlapping sum (low threshold ~ 0.8 GeV)
- Used in conjunction with RICH to form an electron trigger
- 4x4 towers overlapping sum (higher thresholds at 2 and 3 GeV)
- Used for  trigger

- 2x2 in 2001-2002 run.

**Central arm ******** and ********0**** trigger**

##   trigger efficiency for 0

- Data
- MC

- 0 efficiency plateaus for pT>4 GeV/c
- Limited efficiency at      pT<4 GeV/c:
- 	1-2 GeV/c: 6%
- 	2-3 GeV/c: 60%
- 	3-4 GeV/c: 90%
- 	4-5 GeV/c: 95%
- Monte Carlo reproduces Data well

- 0 pT (GeV/c)

** ******** ****trigger efficiency for ********0**

##  0: reconstruction

** ************0****: reconstruction**

##  0 cross section (2002 Run2)

- Favors a larger gluon-to-pion FF (KKP)
- Important confirmation of theoretical foundations for spin program
- Run3 results reproduce Run2 results
- Confirm the Run-3 data reliability and consistency
- Run3 data reaches even higher pTs; results will be finalized soon

**Phys. Rev. Lett. 91**
**241803 (2003)**

** ********0**** cross section (2002 Run2)**

##  0 reconstruction for ALL

- 2-3 GeV/c
- Bckgr=17%

- 3-4 GeV/c
- Bckgr=7%

- 4-5 GeV/c
- Bckgr=5%

- 1-2 GeV/c
- Bckgr=45%

- Results obtained for four pT bins from 1 to 5 GeV/c
- 0 peak width varies from 12 to 9.5 MeV/c2 from lowest to highest pt bins
- Background contribution under 0 peak for 25 MeV/c2 mass cut varies from 45% to 5% from lowest to highest pT bins

** ********0**** reconstruction for A****LL**

##  0 counting for ALL

**N********0****: **
- 25 MeV/c2 around 0 peak (and also 15 and 35 MeV/c2 for cross checks)
**N****bck1****: **
- Two 50 MeV/c2 wide areas adjacent to 0 peak
**N****bck2****: **
- 250 MeV/c2 wide area between  0 and  peaks

| pt
GeV/c | N0
15 MeV/c2 | N0
25 MeV/c2 | N0
35 MeV/c2 | Nbck1 | Nbck2
 |
| --- | --- | --- | --- | --- | --- |
| 1-2 | 1278k | 1777k | 2129k | 1470k | 3478k |
| 2-3 | 874k | 1059k | 1146k | 335k | 989k |
| 3-4 | 176k | 201k | 208k | 27k | 83k |
| 4-5 | 34k | 38k | 39k | 3.9k | 12k |

- N0 and Nbck accumulated statistics

** ********0**** counting for A****LL**

## ALL measurement

- Collect *N* and *L *for ++ and + configurations (sum over all crossings) and calculate ALL for each fill
- Average ALL over fills; use 2/NDF to control fit quality; use “bunch shuffling” to check syst. errors

- ++ same helicity
- + opposite helicity

**A****LL**** measurement**

## ALL vs. fill # for different pT

- ALL averaged over fills

**3-4 GeV/c**

**1-2 GeV/c**

**4-5 GeV/c**

- 2**-3 GeV/c**

- 1-2 GeV/c
- ALL= -2.8%±1.2%
- 2/ndf = 64/48
- 2-3 GeV/c
- ALL= -2.2%±1.5%
- 2/ndf = 34/48
- 3-4 GeV/c
- ALL= -0.2%±3.3%
- 2/ndf = 49/48
- 4-5 GeV/c
- ALL= -2.3%±7.4%
- 2/ndf = 39/48

**A****LL**** vs. fill # for different p****T**

## Systematic check: bunch shuffling

- ALL

- 2-3 GeV/c

- All <2/NDF> are ~1

- Bunch shuffling = Randomly assigns helicity for each crossing

- 2/NDF

- 3-4 GeV/c

- 4-5 GeV/c

- 1-2 GeV/c

- Widths are consistent with obtained errors (ALL)

- 2-3 GeV/c

- 3-4 GeV/c

- 4-5 GeV/c

- 1-2 GeV/c

**Systematic check: bunch shuffling**

## Asymmetry of “background”

- ALL averaged over fills

- 1-2 GeV/c
- ALL= 0.4%±1.0%
- 2/ndf = 47/48
- <2/ndf> = 48/48
- 2-3 GeV/c
- ALL= -2.2%±1.7%
- 2/ndf = 35/48
- <2/ndf> = 50/48
- 3-4 GeV/c
- ALL= 1.9%±5.5%
- 2/ndf = 33/47
- <2/ndf> = 45/47
- 4-5 GeV/c
- ALL= 10%±14%
- 2/ndf = 47/44
- <2/ndf> = 41/44

**2-3 GeV/c**

**3-4 GeV/c**

**4-5 GeV/c**

**1-2 GeV/c**

**Asymmetry of “background”**

## ALL Results

| pt
GeV/c | 

15 MeV/c2 | 

25 MeV/c2 | 

35 MeV/c2 |  | 
 |
| --- | --- | --- | --- | --- | --- |
| 1-2 | -0.0230.014 | -0.0280.012 | -0.0240.011 | -0.0060.014 | 0.0040.010 |
| 2-3 | -0.0270.016 | -0.0220.015 | -0.0220.014 | -0.0350.027 | -0.0220.017 |
| 3-4 | -0.0170.035 | -0.0020.033 | -0.0010.032 | 0.0940.092 | 0.0190.055 |
| 4-5 | -0.0140.079 | -0.0230.074 | -0.0130.073 | 0.380.24 | 0.100.14 |

**A****LL**** Results**

## ALL

- 0+bck
- 35 MeV/c2

- 0+bck
- 15 MeV/c2

- Bck2

- 0+bck
- 25 MeV/c2

- Bck1

**A****LL**

## Checks.....

| pt
GeV/c | 
++ vs   | 
+  vs  + |
| --- | --- | --- |
| 1-2 | 0.0070.017 | -0.0130.017 |
| 2-3 | 0.0020.021 | 0.0050.021 |
| 3-4 | 0.0610.046 | -0.0270.046 |
| 4-5 | -0.0860.105 | -0.0670.104 |

- PID = Shower profile cut (**0>96%)

- Consistent with 0 within 1.5

- PID check

| pt
GeV/c | 

noPID | 

PID |
| --- | --- | --- |
| 1-2 | -0.0310.010 | -0.0280.012 |
| 2-3 | -0.0190.014 | -0.0220.015 |
| 3-4 | -0.0040.032 | -0.0020.033 |
| 4-5 | -0.0390.073 | -0.0230.074 |

- ++ vs  and + vs +

- The same results

**Checks.....**

**Notes:**
Shower profile cut (data vs. MC electrons/photons)
Time of Flight

## AL check for “yellow” beam

| pt
GeV/c | 

15 MeV/c2 | 

25 MeV/c2 | 

35 MeV/c2 |  |  |
| --- | --- | --- | --- | --- | --- |
| 1-2 | 0.0010.004 | 0.0000.003 | 0.0000.003 | 0.0020.004 | 0.0000.003 |
| 2-3 | 0.0010.004 | 0.0000.004 | 0.0000.004 | 0.0020.007 | 0.0020.005 |
| 3-4 | 0.0070.009 | 0.0110.009 | 0.0080.009 | -0.0330.025 | -0.0100.015 |
| 4-5 | -0.0010.021 | 0.0040.020 | 0.0080.020 | 0.0200.064 | 0.0500.039 |

- All are zeros within 1.5

**A****L**** check for “yellow” beam**

## AL check for “blue” beam:

| pt
GeV/c | 

15 MeV/c2 | 

25 MeV/c2 | 

35 MeV/c2 |  |  |
| --- | --- | --- | --- | --- | --- |
| 1-2 | -0.0010.004 | 0.0010.003 | 0.0000.003 | -0.0020.004 | -0.0000.003 |
| 2-3 | 0.0010.004 | 0.0000.004 | 0.0020.004 | 0.0090.007 | 0.0000.005 |
| 3-4 | 0.0040.009 | 0.0060.009 | 0.0060.008 | -0.0040.024 | -0.0360.015 |
| 4-5 | -0.0240.021 | -0.0160.020 | -0.0160.019 | -0.0110.062 | 0.0130.038 |

- All are zeros within 1.5, except

**A****L ****check for “blue” beam:**

## ALL(0) at 200 GeV CME

| pT
GeV/c | 
(rbck) |  | 
(Bck
subtracted) |
| --- | --- | --- | --- |
| 1-2 | -0.0280.012 (45%) | -0.0060.014 | -0.0460.025 |
| 2-3 | -0.0220.015 (17%) | -0.0350.027 | -0.0190.019 |
| 3-4 | -0.0020.033 (7%) | 0.0940.092 | -0.0090.036 |
| 4-5 | -0.0230.074 (5%) | 0.380.24 | -0.0450.079 |

- Polarization scaling error ***P *~30%: is not included
- Enters the ALL quadratically
- Analyzing power AN(100 GeV) ~ AN(22GeV) is assumed
***P*~30%: combined stat. and syst. error for AN(22GeV) (AGS E950)
- pT smearing correction is not included

**A****LL****(********0****) at 200 GeV CME**

## Our result vs. Theory

- GRSV Curves from B.Jaeger e al., PRD67, 054005 (2003)

**Our result vs. Theory**

## 0 Production and G

- Jager, Schafer, Stratmann, Vogelsang

** ************ ****can be used to determine ********G with limited ****L**** & ****P**

## Polarized pp development & Physics

**2002:** first acceleration of polarized protons to 100 GeV (snakes work)
-  Single spin asymmetries for local polarimetry ideas
**2003:** first collisions with longitudinal polarized protons (spin rotators work)
- First double spin asymmetry result from PHENIX (STAR expected)
**2004/5:** New AGS weak snake, search new betatron tune
- Gluon spin measurement from neutron and charged pions
- First transversity measurements
**2006/7:** New AGS strong snake, new vacuum pumping for RHIC, first trial for 250 GeV beams
- First glimpse of gluon polarization using other probes (direct photons)
- Transversity measurement
- Engineering run for W physics
**2008/9** and onwards: high luminosity, high polarization and higher energy
- Other (rare) probes of polarized gluon distribution (silicon vertex detector)
- W physics with PHENIX detector (trigger upgrade)
**Beyond this is RHIC II and eRHIC construction.....(?)**

## Summary

- RHIC is functioning as a polarized collider
- Learnt a lot: Polarimetry, Single spin asymmetries (neutrons, neutral pions), local polarimetry, pp******0**** **total cross section....
**PHENIX not only took longitudinally polarized data, but also has done a very fast analysis for double longitudinal asymmetry in ************ production**
- Uncertainties are large
- Data are consistent with the the previous pQCD fits at NLO of the Deep Inelastic Scattering & with zero ALL
***PHENIX is ready for higher luminosity and higher polarization!***
- Figure of Merit: P12 * P22 * L so improvements are expected fast.... *A modest increase in polarization and luminosity will make a world of difference!*
**Annual beam time for polarization and luminosity development essential**
**Future of Spin at RHIC looks very bright! **
**RHIC Spin: other paths to ********G, quark/anti-quark distributions, transversity.....**
**eRHIC is gaining momentum as a next spin physics faciility!**

## eRHIC: http://www.bnl.gov/eic

- A polarized electron/positron beam facility to collide with RHIC
- High intensity (0.45 A current) and high energy ~ 10 GeV/c (Sqrt(s) = 100 GeV for e-p)
- A mini-HERA but in addition:
- Polarized proton, helium beams and polarized electrons/positrons
- Heavy ion beams from deuteron to Uranium
- 100 times larger luminosity compared to HERA
- Broad international interest is developing in the eRHIC from Spin and heavy ion DIS communistgy;  including recent studies in europe on possible experiment(s) at eRHIC from the HERA-III community
**US DoE’s list of 28 “must-do” projects**
- If it were only technology: 2009 could be a good time to begin construction
**BNL management plans to pursue 2010 as the target date for begin construction**
- WG: Accelerator, IR, Physics/Detector
- Next meeting at BNL January 29,30,31, 2004
- All are welcome to attend; contact me

- (eRHIC: _**e**_lectron-_**i**_on _**c**_olllider at RHIC)

## Discussion

-  hep-ph/0310197 Jager,Schafer,Stratmann,Vogelsang
- A detailed discussion of the possibility of negative ALL: IS IT POSSIBLE?
- Asymmetry could be negative but its magnitude has to be small 10-3
- A negative ALL does not mean a negative contribution of G
- Analysis of charged pion data would be essential

## Bunch fitting approach

- 2-3 GeV/c

- 3-4 GeV/c

- 4-5 GeV/c

- 1-2 GeV/c

- 2/NDF from bunch fitting for each fill
- All 2/NDF ~ 1 => no problem seen within fills

- 2/NDF

- Collect *N* and *L *for each crossing *i* and fit *A**LL** *from* N(i)/L(i)=C*{*1+A**LL**P**B**(i)P**Y**(i)*} for each fill;* *use 2/NDF to control fit quality

**Bunch fitting approach**

## ALL from bunch fitting....

- ALL averaged over fills

- 2-3 GeV/c

- 3-4 GeV/c

- 4-5 GeV/c

- 1-2 GeV/c

- 1-2 GeV/c
- ALL= -2.8%±1.2%
- 2/ndf = 62/48
- <2/ndf> = 51/48
- 2-3 GeV/c
- ALL= -2.2%±1.5%
- 2/ndf = 35/48
- <2/ndf> = 48/48
- 3-4 GeV/c
- ALL= -0.7%±3.3%
- 2/ndf = 56/48
- <2/ndf> = 56/48
- 4-5 GeV/c
- ALL= -7.2%±7.6%
- 2/ndf = 46/48
- <2/ndf> = 56/48

**A****LL**** from bunch fitting....**

***Consistent!***

## Luminosity vs. bunch fitting

| pt
GeV/c | N0
Bunch fit | N0
Luminosity |
| --- | --- | --- |
| 1-2 | -2.81.2
1.06 | -2.81.2
1.04 |
| 2-3 | -2.21.5
0.99 | -2.21.5
1.01 |
| 3-4 | -0.73.3
1.17 | -0.23.3
1.07 |
| 4-5 | -7.27.6
1.17 | -2.37.4
0.90 |

- Results are identical at lower pt bins
- Results start to deviate at higher pt bins
- Pure statistical effect: too low statistics in each crossings to be used in bunch fitting
- Confirmed from simple MC: deviations may be comparable to stat. error

- We use luminosity approach for final ALL for all pt bins

**Luminosity vs. bunch fitting**

## Statistical uncertainty on N0

- Nbck2

- N0

| pt
GeV/c | N0
15 MeV/c2 | N0
25 MeV/c2 | N0
35 MeV/c2 | Nbck1 | Nbck2
 |
| --- | --- | --- | --- | --- | --- |
| 1-2 | 1.134 | 1.220 | 1.302 | 1.360 | 1.708 |
| 2-3 | 1.047 | 1.081 | 1.114 | 1.178 | 1.406 |
| 3-4 | 1.015 | 1.026 | 1.037 | 1.101 | 1.222 |
| 4-5 | 1.008 | 1.015 | 1.021 | 1.059 | 1.162 |

- In multi-0 events:
- Comparison to naïve approach:

- d*k*/d*N**ev*

- d*k*/d*N**ev*

- Fluctuation enhancement (squared) due to multi-particle events

**Statistical uncertainty on N********0**

## Proton beam polarimetry (II)

- Injection with Spin Flipped: Asymmetry Flipped
- Adiabatically Snake on: Horizontal polarization
- Accelerate equivalent to 180o rotation: 180o rotated

**Successful Single**
**Snake Operation !**

## Polarization at RHIC Runs III