# Presentation: 118601

## Spin Physicswith the PHENIX Detector

- 21st Winter Workshop on Nuclear Dynamics, Breckenridge

- Mickey Chiu
- University of Illinois at Urbana

## Nucleon Spin Physics

## Polarised PDFAsymmetry Analysis Collaboration M. Hirai, S. Kumano and N. Saito, PRD (2004)

- Valence Dist’s are determined well
- Sea Distribution poorly constrained
- Gluon can be either pos, 0, neg!

## RHIC Spin Evolution

**BRAHMS & PP2PP**

**STAR**

**AGS**

**LINAC**

**BOOSTER**

- Pol. Proton Source
- 500 A, 300 s

- Partial Siberian Snake

**Siberian Snakes**

- 200 MeV Polarimeter

- AGS Internal Polarimeter

- Rf Dipoles

**PHOBOS**_*** ***_

**RHIC**

**PHENIX**

**RHIC *****p*****C CNI Polarimeter**

## What Do We Measure at RHIC?

- We measure spin asymmetries for cross sections
*A*LL: double helicity asymmetry
- Useful in extracting *g*(*x*), *q*(*x*) etc.

***A******TT*****: Transversity**

***A******N*****:****Twist-3 etc **

***A******L******:*****Parity Violation**

## RHIC Spin: L and P Progress

- RHIC Spin: *L* and *P* Progress

- Run 2: *A*N
- ~7 nb-1/day
- (0.15/pb),PB~15%
- Run-3:*A*LL
- 10 nb-1/day 0.35/pb,PB~26%
- (AGS) 40%
- Run-4:*A*LL
- Only Machine Studies
- 30nb-1/day
- 0.12/pb,PB~40%
- (AGS) 50%
- Run-5 :*A*LL
- ~11 weeks

## Mid-Rapidity 0 and charged hadron Production in p+p  at s = 200 GeV

- NLO QCD Calculation Cross-sections consistent with Data
- CTEQ5M pdf
- KKP and Kretzer Fragmentation Fcns
- Necessary Confirmation that pQCD can be used successfully at RHIC to extract spin dependent pdf’s.
- Same comparison fails for lower energies

## Getting Polarization Information 

- Getting Polarization Information

- AN = 0.108±0.0087

- preliminary

- Large Neutron AN was discovered at IP12
- Cause not yet well understood
- A possible diffractive process?
- Charge Exchange?
- ZDC/SMD can make a local polarimetry measurement at PHENIX
- Allows us to measure independently the polarization

## Measuring ALL

- To determine g, look at ALL:
- R is the relative luminosity, and can be measured (to some accuracy) at PHENIX using the BBC or ZDC.
- Our Goal: dR/R < 0.1% for each fill                           dALL < 2×10-3(expected ALL for pions ~ 3×10-3 @pT=3 GeV/c)

## Constraints on g(x) w/ 0 Production

- Constraints on *g*(*x*) w/ 0 Production

*pp*  0 *X* is sensitive to *gg**gg* and  *gq**gq*

- PHENIX Results from Run-3
- To Appear in PRL

## Other Probes of g

| reaction | LO subprocesses | partons probed |
| --- | --- | --- |
| pp  jets X   X  | qq,qq,qg,ggjetX | q, g |
| pp   X | qgq, qqg  | g |
| pp  QQ X | ggQQ, qqQQ | g |

- See Talks by Takao Sataguchi, Youngil Kwon, Sergey Butsyk

- G(x)

- x

- cceX

- bbeX

- J/

- GS95

- prompt photon

- hadrons

## Single Transverse SpinAsymmetries

- Transversity x Spin-dep fragmentation (Collins effect), or
- Intrinsic-*k*T imbalance (Sivers effect) , or
- Higher-twist effects
- Sterman and Qiu Initial State Twist 3
- Koike Final State Twist 3
- Or combination of above

- left

- right

- Fermilab E-704 reported Large Asymmetries *A*N in pion productions

## Look for left-right asymmetry with respect to beam spin and direction

OR look either on left or right side and compare 0 production for + and - spin states

Two methods provide important check of systematic errors

- OR look either on left or right side and compare 0 production for + and - spin states
*Two methods provide important check of systematic errors*

- Calculating AN

*R**acc* = relative acceptance
- of left and right detectors

*R**lumi* = relative luminosity
- of + and - spin states

## AN of Neutral Pions and Non-Identified Charged Hadrons

- AN of Neutral Pions and Non-Identified Charged Hadrons

## Sivers and Why it is Interesting

- Non-Zero Sivers function means that there is a left/right asymmetry in the kT of the partons in the nucleon
- Probes space-time structure of nucleon wave-function
- Testable kT dependence of nucleon wave-function testable
- Sivers requires quark orbital angular momentum
- Centrality dependent effects
- Quark Shadowing in central region causes kT asymmetry?
- Red Shift/Blue Shift effects in peripheral regions?
- ST  (P  kT) is T-odd and naively thought to vanish
- FSI effects found by Brodsky et.al. that allow T-odd function to be non-zero

- J=1/2

- <LZ> = ?

## Sivers Fcn from Back2Back 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

## Unpolarized Results from Run03 p+p

- anti-aligned

- aligned

- Asymmetry
- numerator is difference between aligned and anti-aligned  dist’s, where aligned means trigger jet and spin in same direction
- denominator is simply unpolarized  distribution
- On left are some theoretical guesses on expected magnitude of AN from Siver’s
- On right are gamma-charged hadron  dist’s from Run03 p+p
- 2.25 GeV gamma’s as jet trigger, 0.6-4.0 GeV charged hadrons to map out jet shape
- Dotted lines are schematic effect on away side  dist due to Siver’s Fn (not to scale)

- Run03 -charged dn/d

- Boer and Vogelsang, PRD69:094025,2004

- 1/Ntrig dN/d (au)

## Estimated AN from Run03 p+p

- Parametrized AN with                                                                 , A=0.08, =0.8
- Used this to calculate AN using unpolarized gamma-charged Run03 p+p dN/d
- Put asymmetry into distribution and then calculate AN
- On right shows statistical significance from Run03 p+p (0.35/pb).
- Assumed Poisson statistics (but k factor only ~10% different?)
- Note that area around =0 can be used as a systematic check (it should be flat)
- Also note that AN from Boer/Vogelsang paper is idealized, and the real signal will be reduced

- parametrized AN

- -

## AN Reduction 1: Polarization

- AN Reduction 1: Polarization

- Polarization P < 1 just reduces AN by P

- Besides that, most of the time the jet is not aligned exactly along the polarization axis, which means AN=AN(j1,) and also the polarization is reduced by cos(j1)

- We can make a simple (though wrong) estimate for this effect by calculating the average polarization from a jet spread of /2 around the polarization axis

- ST

- j1

- j2

## AN Reduction 2: Di-Hadron vs. Di-Jets

- AN Reduction 2: Di-Hadron vs. Di-Jets

- up
- down
- unpolarized

- away side parton

- AN

- di-hadron
- di-jet

- Since we don’t reconstruct jets fully, we have to use di-hadron correlations to measure jet .  This smears out the di-hadron AN relative to the di-jet AN, with smearing function g (assumed here to be a gaussian, with jT=0.35).
- The effect broadens and lowers (by just a little bit) the asymmetry

## Combined Effects

- Full di-jet Sivers
- Reduced by lower <P>, di-hadron smearing
- Run03 p+p gamma-charged, 0.35/pb

- Given 0.35/pb of data, we should be able to get 1% statistical significance in AN using gamma-charged measurements of jet dphi
- Expected raw AN could be 3.5%
- Could also be as low as 0.5%, or as large as 10%
- Effects from P=0.5, jet angle not aligned with transverse polarization, and fragmentation to dihadrons reduces raw AN to ~1.0%
- Have not evaluated systematic errors yet (underlying event...)
- Can also do this in Longitudinal collisions (Collins effect?)

## Some Future Measurements

- Anomalous Parity Violation in Jet Production
- Contact Interaction (Scale  ~ 3.3 GeV at RHIC)
- New Gauge Boson Z’

- Upgrades
- Muon Trigger for W Bosons (Wei)
- Measure sea quark polarization
- Nose Cone Calorimeter (Vasily)
-  + jet  G, extends x-range
- Silicon Vertex Tracker (Gerd)
- heavy flavor and jet reconstruction

## Summary

- There are a variety of QCD phenomena that are not well understood in our most basic QCD object, the proton
- QCD is complicated
- PHENIX Has Measured 0 ALL out to pt ~ 5 GeV/c
- Demonstration of ability to do spin physics
- First constraints on g(x)
- 10 times statistics for 0, h, , c, b ALL expected in upcoming run
- 0 and charged AN at xF = 0 is 0
- Start of transverse physics program
- Have access to Sivers function via back-to-back di-hadrons
- Possibly probes orbital angular momentum

## Backup Slides

## AN Systematic Errors

- Measured asymmetry of background
- Immediately outside the 0 mass peak
- In the mass region between the 0 and the 
- Compared independent measurements for two polarized beams
- Compared results for left and right sides of detector
- Compared minimum bias and triggered data samples
- Examined fill-by-fill consistency of asymmetry values
- Used the “bunch shuffling” technique to check for systematic errors
- Randomly reassign the spin direction to each bunch in the beam
- Recalculate the asymmetry
- Repeat many times (1000) to produce a “shuffled” asymmetry distribution centered around zero
- Compare width of shuffled distribution to statistical error on physics asymmetry

- In  addition to calculating the asymmetry using more than one method, potential systematic errors have been investigated in the following ways:

## AN of Neutral Pions and Non-Identified Charged Hadrons at Midrapidity

- Mainly sensitive to g-g and g-q
- interactions

- AN of Neutral Pions and Non-Identified Charged Hadrons at Midrapidity