Transverse Single Spin Asymmetries at High x F

Transverse Single Spin Asymmetries at High x. F in Mickey Chiu

Transverse Single Spin Asymmetries Definition: where p is the 4 -momentum of a particle (hadron, jet, photon, etc. . . ) Experimentally, there a variety of (~equivalent) ways this can be measured. 1. Yield difference between up/down proton in a single detector Left Right This is susceptible to Rel. Luminosity differences 2. Or, take the left-right difference between 2 detectors This is susceptible to detector Relative Acceptance differences 3. Or, take the cross geometric mean (square-root formula) Mostly insensitive to Relative Luminosity and Detector Acceptance differences 2

Transverse Proton Spin Physics Polarized parton distribution functions quark helicity distribution – known gluon helicity distribution – poorly known transversity distribution – unknown Naïve LO, Leading Twist, p. QCD Result E 704 Helicity violation term due to finite quark masses 3

Transverse Proton Spin Physics • Various possible explanations have been proposed to explain these asymmetries • Transversity x Spin-dep fragmentation (e. g. , Collins effect or IFF), • Intrinsic-k. T in proton (Transverse Momentum Dep Functions) , • Eg, Sivers Function • Perturbative LO Twist-3 Calculations (Qiu-Sterman, Efremov, Koike) • These calculations have been related to the Sivers function A Unified picture for single transverse-spin asymmetries in hard processes, Ji, Qiu, Vogelsang, Yuan PRL 97: 082002, 2006 • Or some combination of the above • Caveat: The theory is still being actively worked out Anim. courtesy J. Kruhwel, JLAB 4

PHENIX at RHIC Spin STAR MPC PHENIX Transversely Polarized p+p Data Set • Central Arm Tracking | | < 0. 35, x. F ~ 0 • Drift Chamber (DC) • momentum measurement • Pad Chambers (PC) • pattern recognition, 3 d space point • Time Expansion Chamber (TEC) • additional resolution at high pt • Central Arm Calorimetry • Pb. Gl and Pb. Sc • Very Fine Granularity • Tower x ~ 0. 01 x 0. 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 • Pb. WO 4 Crystal • Forward Muon Arms 1. 2 < | | < 2. 4 Run 02 Run 05 Run 06 Run 08 s (Ge. V/c 2) 200 200 62. 4 200 Ldt (pb-1) 0. 15 2. 7 0. 02 5. 2 <P> 0. 15 0. 47 0. 50 ~0. 50 P 2 L 0. 0034 0. 033 0. 87 0. 05 1. 3 5

PHENIX Muon Piston Calorimeter Upgrade SOUTH Density 8. 28 g/cm 3 Size 2. 2 x 18 cm 3 Length 20 X 0, 0. 92 Weight 721. 3 g Moliere radius 2. 0 cm Radiation Length 0. 89 cm Interaction Length 22. 4 cm Light Yield ~10 p. e. /Me. V @ 25 C Temp. Coefficient -2% / C Radiation Hardness 1000 Gy Main Emission Lines 420 -440, 500 nm Refractive Index 2. 16 Small cylindrical hole in Muon Magnet Piston, Radius 22. 5 cm and Depth 43. 1 cm 6

Muon Piston Calorimeter Performance • Shower Reconstruction Using Shower Shape Fits All Pairs Mixed Events Background subtracted • Energy Scale Set by MIP • In Noisy Towers, Used Tower Spectrum MIP Peak • Photon Pair Cuts • Pair Energy > 8 Ge. V • Asymmetry |E 1 -E 2|/|E 1+E 2| < 0. 6 • Noisy Towers in Run 06 (up to 25% of MPC) Excluded • Width ~ 20 Me. V • Confirmed with 0, peaks 7

0 AN at High x. F p +p 0+X at s=62. 4 Ge. V/c 2 3. 0< <4. 0 PLB 603, 173 (2004) process contribution to 0, =3. 3, s=200 Ge. V • Large asymmetries at forward x. F • Valence quark effect? • x. F, p. T, s, and dependence provide quantitative tests for theories 8

RHIC Forward Pion AN at 62. 4 Ge. V E 704, 19. 4 Ge. V, PLB 261, (1991) 201 BRAHMS PRL 101, 042001 PHENIX Preliminary • Brahms Spectrometer at “ 2. 3 ” and “ 3. 0 ” setting < > = 3. 44, comparable to PHENIX all eta • Qualitatively similar behavior to E 704 data: pi 0 is positive and between pi+ and pi-, and roughly similar magnitude: AN(pi+)/AN(pi 0) ~ 25 -50% • Flavor dependence of identified pion asymmetries can help to distinguish between effects • Kouvaris, Qiu, Vogelsang, Yuan, PRD 74: 114013, 2006 • Twist-3 calculation for pions for pion exactly at 3. 3 • Derived from fits to E 704 data at s=19. 4 Ge. V and then extrapolated to 62. 4 and 200 Ge. V • Only qualitative agreement at the moment. Must be very careful in comparisons (between expt’s 9

Comparison to 0 at s = 200 Ge. V/c 2 STAR • Trend with seems to disagree with STAR result, but is consistent with theoretical predictions. • This might just be due to the different collision energy and p. T coverage? 10

Kinematic Cuts and AN Phys. Rev. D 74: 114013, 2006. 5 <3. a t e 5 >3. eta • Mean AN is measured to be lower for p. T>1, even though mean x. F is higher for this p. T bin, and higher x. F implies higher asymmetry • This implies that AN is dropping with pt for a given x. F slice • The cut, for a given x. F slice, splits that slice into high pt and low pt, with the lower eta selecting higher pt • This implies that AN at lower should be smaller, consistent with predictions of PRD 74: 114013 • However, at 62. 4 Ge. V the p. T are low (p. QCD invalid? ) • Cross-section is being analyzed now 11

Run 08 pi 0 E > 6 Ge. V Asymm<0. 6 • A LOT more data is expected from Run 08 • Currently the data processing is in progress at CC-Japan • As of this past Tuesday it was 80% done, still needs to be transferred • Results on pi 0 AN to be expected by early next year • There also other possibilites from this data set… 12

Sivers Fcn from Back 2 Back Analysis 1/Ntrig d. N/d (au) Run 03 -charged dn/d anti-aligned 2 MPC 0 • 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 antialigned 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 h, 0 j 1 Boer and Vogelsang, Phys. Rev. D 69: 094025, 2004, hep-ph/0312320 Bomhof, Mulders, Vogelsang, Yuan, PRD 75: 074019, 2007 ST j 2 13

Summary • Much new data coming from transversely polarized proton interactions • p +p (RHIC), but also e+p SIDIS (Hermes, Compass, JLab), e+e- (Belle) • Along with new data on the helicity distribution of partons in the proton (gluon spin), transversely polarized proton collisions could add a wealth of new information on proton structure • Transversity, Orbital angular momentum? 1 -dimensional • GPD’s may be cleanest way to OAM • However, strongest asymmetries are in p +p • PHENIX has measured the transverse asymmetry of 0, h , and J/ , covering an x. F from 0 to 0. 6 (at two different collision energies). • There also sizable asymmetries from proton wave-function forward neutrons out to x. F ~ 1. * • In the future, we expect ~25% of the polarized PHENIX preliminary p+p running will be in the transverse mode • Lots more data coming • New upgrade detectors should significantly enhance physics reach • Nose Cone Calorimeter • Silicon Detectors (SVTX and FVTX) * See Poster by M. Togawa 14

15

2 Future PHENIX Acceptance NCC MPC EMCAL f coverage EMCAL HBD 0 VTX & FVTX -3 -2 -1 0 1 2 3 • 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): Pb. WO 4 Electromagnetic Calorimeter • Hadron Blind Detector (2007 -2009): Cs. I Triple GEM Cerenkov Detector • Nose Cone Calorimeter (2010 -end): Tungsten-Silicon Electromagnetic Calorimeter with limited Jet Capabilities (1 arm, possibly 2 with funding) • SVTX (2009 -end): Central Arm Silicon Tracker • FVTX (2010 -end): Muon Arm Silicon Tracker 16

17