# Presentation: 664588

## Recent Transverse Spin Results in Polarized p+p Collisions at   

- Han Liu
- Los Alamos National Lab

- RHIC/AGS Annual User's Meeting

- June 19, 2007

## Outline

- Introduction
- The PHENIX Experiment
- Single Spin Asymmetry Measurements
-      -- Mid-rapidity π0 and charged hadrons
- --  Forward π0 (MPC, Run6)
- --  Forward J/Ψ
- --  Forward neutron
- Summary and Outlook

- RHIC/AGS Annual User's Meeting

- June 19, 2007

## A Brief History...

- -- Kane, Pumplin, Repko ‘78
- At leading twist and with collinear
- factorization, pQCD predicts small
- analyzing powers in transversely
- polarized p+p collisions

- -- FermiLab E704 experiment
- Found strikingly large transverse
- single-spin effects in p+p fixed-
- target collisions with 200 GeV
- polarized proton beam

- RHIC/AGS Annual User's Meeting

- June 19, 2007

## Theoretical efforts

- Four different mechanisms have been proposed to explain this asymmetries
- Sivers effect
-  --  Transverse momentum dependent quark and gluon distributions give rise to correlation between transverse proton spin and the transverse momentum kT of quarks and gluons
- Collins effect
-  -- Transversity distributions + spin dependent fragmentation functions
- Higher-twist effects
-  -- Quark gluon field interference
-        * Sterman and Qiu   Initial State Twist 3
-       * Koike  Final State Twist 3
- A coherent treatment of the Sivers effect and quark gluon correlations at higher twist has been provided
- by Ji, Qiu, Vogelsang and Yuan (**PRL97**:082002,2006)
- Or some combination of above

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- June 19, 2007

## RHIC as a Polarized p+p Collider

**AGS**

**LINAC**

**BOOSTER**

-   Polarized Source

- Spin Rotators

-   200 MeV Polarimeter

-  AGS Internal Polarimeter

-   Rf Dipole

-  RHIC pC Polarimeters

**P****HENIX**

**P****HOBOS**

**B****RAHMS & PP2PP**

**S****TAR**

- AGS pC Polarimeter

- Partial Snake

- Siberian Snakes

- Siberian Snakes

-  Spin Flipper

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## Proton Spin Structure at PHENIX

**Single Spin Asymmetries A****N**

- Inclusive Hadron Production

**Transverse Spin**

**A****LL****(gg,gq********h+X)**

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## The PHENIX Detectors for Spin Physics

**Central Arm Tracking        |********| < 0.35, x****F**** ~ 0**
- Drift Chamber (DC)
- momentum measurement
- Pad Chambers (PC)
- pattern recognition, 3d space point
- Time Expansion Chamber (TEC)
- additional resolution at high pt
**Central Arm Calorimetry**
- PbGl and PbSc
- Very Fine Granularity
- Tower x ~ 0.01x0.01
- Trigger
**Central Arm Particle Id**
- RICH
- electron/hadron separation
- TOF
- /K/p identification
**Global Detectors (Luminosity,Trigger)**
- BBC                           **3.0 < |********| < 3.9**
- Quartz Cherenkov Radiators
- ZDC/SMD  (**Local Polarimeter)**
- Forward Hadron Calorimeter
**Forward Calorimetry**         **3.1 < |********| < 3.7**
- MPC
- PbWO4 Crystal
**Forward Muon Arms        **
**                 **South arm: -2.0 <η < -1.2
-                  North arm: 1.2 < η < 2.4

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## Recent PHENIX AN Measurements

-  Mid-rapidity π0/ h±
-  Forward π0 with Muon Piston Calorimeter
-  Forward rapidity J/ Ψ
-  Forward neutron

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## PHENIX polarized-proton runs

| Year | s [GeV] | Recorded L | Pol [%] | FOM (P4L) |
| --- | --- | --- | --- | --- |
| 2003 (Run 3)  | 200 | .35 pb-1 | 27 | 1.5 nb-1 |
| 2004 (Run 4) | 200 | .12 pb-1 | 40 | 3.3 nb-1 |
| 2005 (Run 5) | 200 | 3.4 pb-1 | 46 | 150 nb-1 |
| 2006 (Run 6) | 200 | 7.5 pb-1 | 62 | 1100 nb-1 |
| 2006 (Run 6) | 62.4 | .08 pb-1  | 48 | 4.2 nb-1  |

**Longitudinally Polarized Runs**

**Transversely Polarized Runs**

| Year | s [GeV] | Recorded L | Pol [%] | FOM (P2L) |
| --- | --- | --- | --- | --- |
| 2001 (Run 2) | 200 | .15 pb-1 | 15 | 3.4 nb-1 |
| 2005 (Run 5) | 200 | .16 pb-1 | 47 | 38 nb-1 |
| 2006 (Run 6) | 200 | 2.7 pb-1 | 57 | 880 nb-1 |
| 2006 (Run 6) | 62.4 | .02 pb-1  | 48 | 4.6 nb-1  |

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## Asymmetry calculation

- Square root formula
- Luminosity formula

- P – Beam polarization (CNI)
- R – Relative luminosity (BBC, ZDC)

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## π0 and charged hadrons at Mid-rapidity

- Why Measure AN of Different Particle Species at Mid-rapidity in PHENIX?
- -- Different kinematic regions
- -- Currently dominated by gg and gq
- scattering, mainly probes the Sivers
- effect
- -- Future measurements will be
- dominated by quark scattering, more
- sensitive to transversity + Collins

- Fraction of pion production

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## Mid-Rapidity 0 and charged hadron Cross Section Measurements at s = 200 GeV

- * NLO QCD Calculation Cross-sections consistent with Data
-  --- CTEQ6M pdf
-  --- KKP and Kretzer Fragmentation Fcns
- * Necessary Confirmation that pQCD can be used successfully at RHIC to extract spin dependent pdf’s

- arXiv:0704.3599 [hep-ex]

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## 0 and charged hadrons  at Mid-rapidity

- PRL 95(2005)202001

- AN for both charged
- hadrons and neutral
- pions at mid-rapidity
- consistent with zero
- to within a few percent

- Run2: 0.15 pb-1, P ~15%

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## Update on charged hadrons 

- Update on charged hadrons

- pT (GeV/c)

- || < 0.35

- Run5

- AN h+/h-

- Improved polarization
- P=15% in 2001/02
- P=47% in 2005

- AN is zero within 1% 
- contrast with forward pions

- Can be used to provide upper limit on the gluon Sivers distribution             Anselmino et al, **PRD74**:094011,2006

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## Constraints on Gluon Sivers?

- Anselmino et al, **PRD74**:094011,2006

- PHENIX 0, PRL 95, 202001 (2005)

- LO QCD Transverse Momentum Dependent parton scattering calculations
- Thin Red: valence u and d Sivers alone
- Cyan: Gluon Sivers Function at positivity bound, no sea quark Sivers
- Thick Red: Gluon Sivers parameterized to be 1 sigma from PHENIX 0 AN, no sea quark Sivers
- Blue: valence + sea quark Sivers at positivity bound
- Green: Gluon Sivers function and  valence + sea quark at positivity bound  the largest gluons Sivers function compatible with our data

- Normalized GSF

- vanishing sea quark contribution

- Valence + sea quark contributions at positivity bound

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## Forward 0 at s=62 GeV

- New calorimeter (Muon Piston Calorimeter) added in Run6
- 192  2.2x2.2x18 cm3 PbWO4 crystals, 220 cm from vertex (behind Beam-Beam counter)
- 3.1 < || < 3.65 (Region of large observed asymmetries)
- Only south arm in Run6
- Expect 200GeV longitudinal and 62.4GeV longitudinal & transverse results (very little useful 200GeV transverse data due to late electronics)

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##     0  AN at large xF

- Asymmetry seen in yellow beam (positive xF), but not in blue (negative xF)
- Large asymmetries at forward xF    Valence quark effect?
- xF, pT, s, and  dependence provide quantitative tests for theories

- process contribution to 0, =3.3, s=200 GeV

- PLB **603**,173 (2004)

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## RHIC Forward Pion AN at 62.4 GeV

- RHIC Forward Pion AN at 62.4 GeV

- Brahms Spectrometer at “2.3” and “3.0” setting  <> = 3.44, comparable to PHENIX all eta
- Qualitatively similar behavior to E704 data: pi0 is positive and between π+ andπ- , and
-   roughly similar magnitude: AN(π+)/AN(π0) ~ 25-50%
- Flavor dependence of identified pion asymmetries can help to distinguish between effects
- Kouvaris, Qiu, Vogelsang, Yuan, PRD74:114013, 2006
- Twist-3 calculation for pions (  exactly at 3.3)
- Derived from fits to E704 data at s=19.4 GeV and then extrapolated to 62.4 and 200 GeV
- Only qualitative agreement at the moment.  Must be very careful in comparisons (between experiments and theories) that kinematics are matched, since AN is a strong function of pT and xF

- PHENIX and Brahms Preliminary

**E704, 19.4 GeV, PLB 261, (1991) 201 **

- Solid line: two-flavor (*u*, *d*) fit
- Dashed line: valence + sea, anti-quark

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## Comparison to 0 at s = 200 GeV

- -- The apparent opposite trend in theηdependence between STAR and PHENIX may result from the difference in collsion energy and pT coverage
- -- Theoretic calculations for √s = 200 GeV appear to disagree with the experimental results

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## J/Ψ production at forward rapidity

- J/Ψ production at forward rapidity

- Why J/ Ψ?
- Eliminate Collins’ effects
-     * J/Ψ production dominated by gluon gluon fusion at RHIC energy
-                    Pythia 6.1 simulation
-     * gluon has zero transversity
- A perfect channel for gluon Sivers function
- Important to understand the origin of observed large AN at large xF

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## Like/Unlike charge signed dimuon mass spectra

- Run6 Lvl2 data

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## AN vs. xF

- Theoretical prediction:
- Only available for open charm production
- --quark Sivers function set to its maximum
-    gluon Sivers function set to 0
- --gluon Sivers function set to its maximum
-    quark Sivers function set to 0

- *How does J/Ψ production affect prediction?
-   Waiting for theoretical calculation
- * If AN comes form the initial state Disfavor the maximum contribution of gluon Sivers function

- pT=1.5GeV/c

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## Forward neutron Asymmetries

*A**N* measurement at IP12 (Y.Fukao et.al., hep-ex/0610030)
- large *A**N* was discovered for forward neutrons
-  Local polarimeter at PHENIX
- ZDC + position sensitive counters to measure the neutron *A**N*
- understand the forward neutron production mechanism

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## Cross section Measurement

-  Cross section result is consistent with ISR data

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## Forward Neutrons at 200GeV

- AN consistent with zero for xF<0
- Large asymmetry for xF>0
- No xF dependence observed

- detecting charged particles
- in BBC (3.0<|η|<3.9)

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## Finite asymmetry persists at 62 and 410GeV

**√****s = 62.4 GeV**

**√****s = 410 GeV**

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## Why such large asymmetries?

- AN is produced via interference of spin non-flip and spin-flip amplitudes
- In Regge theory
-      -- A spin non-flip amplitude contribution can be described due to Reggeon and Pomeron exchange
-      -- We need spin-flip amplitude –> one pion exchange amplitude
- One pion exchange model (OPE) may explain the result
-     -- OPE has been used to describe exclusive diffractive neutron production
-      -- The cross-section at ISR is well described by spin-flip OPE

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- June 19, 2007

## Summary 

- Much new data coming from transversely polarized proton interactions
- PHENIX has measured the transverse asymmetry of 0, h,  J/ and neutron at two different collision energies (200GeV and 62GeV)
- -- In central rapidity, AN ~ 0 within statistics
-            may provide information on gluon Sivers effects
- -- π0  AN at large rapidity consistent with low energy results
- -- First measurement  in J/Ψ production at xF≈±0.1
-    gluon-fusion dominates, possibly sensitive to gluon's sivers effects
- -- Large negative asymmetry in neutron production at  forward rapidity and
-    backward asymmetry consistent with zero
-   diffractive-like processes

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## Outlook

- Central Arms
-      -- Two-hadron back-to-back correlations
-     (**Boer and Vogelsang, Phys.Rev.D69:094025,2004)**
-      Idea: Non-zero Sivers function implies spin-dependence in kT distributions of partons within proton and would lead to an asymmetry in  of back-to-back jets
- Muon Arms
-      -- Single Muons
-           Stopped hadrons  π, K
- 	     Prompt muons     Open charm
-      -- B2B dimuons   open beauty and open charm
- New upgrade detectors should significantly enhance physics reach
-       -- Nose Cone Calorimeter
-       -- Silicon Detectors (SVTX and FVTX)

- RHIC/AGS Annual User's Meeting

- June 19, 2007

## Backup Slides

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## Future PHENIX Acceptance

**-3              -2             -1                 0                1               2               3    ******

****** ****coverage                 2******

**EMCAL**

**EMCAL**

- History – PHENIX is a small acceptance, high rate, rare probes (photons, J/Psi, etc.) detector
- Future – Add acceptance and add some new capabilities (hadron blind, displaced vertex)
- Muon Piston Calorimeter (2006-end): PbWO4 Electromagnetic Calorimeter
- Hadron Blind Detector (2007-2009): CsI Triple GEM Cerenkov Detector
- Nose Cone Calorimeter (2010-end): Tungsten-Silicon Electromagnetic Calorimeter with limited Jet Capabilities
- SVTX (2009-end): Central Arm Silicon Tracker
- FVTX (2010-end): Muon Arm Silicon Tracker

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## Comparison with forward neutron

- p

- N*(*)  n+X

- Y

-  Diffractive-like picture

- AN(X) < 0, AN(Y) > 0

- p

- n

- X

-  kick-out/recoil picture

- AN(X) > 0, AN(Y)??

- * Asymmetry is 0 when data is selected by BBC only.
- * Measure AN of coincident particles at BBC
- --- Forward neutron, backward BBC (2.28±0.55±0.10)*10-2 >0     4σ
- --- Forward neutron, forward BBC (-4.50±0.50±0.22)*10-2 <0       9σ
- --- No significant asymmetry for backward ZDC tagged data or in top-bottom asymmetry
- * Systematic error doesn’t include ANCNI error

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## Sivers Fcn from B2B jets Analysis

**Boer and Vogelsang, Phys.Rev.D69:094025,2004, hep-ph/0312320**

- Boer and Vogelsang find that this parton asymmetry will lead to an asymmetry in the  distribution of back-to-back jets
- There should be more jets to the left (as in picture to the left)
- Should also be able to see this effect with fragments of jets, and not just with fully reconstructed jets?
- Take some jet trigger particle along ST axis (either aligned or anti-aligned to ST)
- Trigger doesn’t have to be a leading particle, but does have to be a good jet proxy
- Then look at  distribution of away side particles

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## AN Reduction: Di-Hadron vs. Di-Jets

- AN Reduction: Di-Hadron vs. Di-Jets

- up
- down
- unpolarized

- away side parton

- AN

- di-hadron
- di-jet

- No full jet reconstruction 
- Use di-hadron correlations to measure jet
- Smears out di-hadron AN relative to di-jet AN, with smearing function g (assumed here to be Gaussian)

-  *Broadens and lowers the asymmetry, but still measurable*

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## Muon Candidates

- Punch-through hadrons

- The muon arm is at the forward rapidities of       1.2 < || < 2.4

- Stopped hadrons

- Decay muons

- Prompt Muons

- Candidate Tracks:

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