High Energy Hadron Polarimetry G. Bunce Polarized Sources and Targets, Polarimeters, September 2007 I would like to thank Hiromi Okada, Itaru Nakagawa, Les Bland, Werner Vogelsang, Abhay Deshpande, Sasha Bazilevsky, Matthias Grosse Perdekamp, and many others for their advice and plots.

I will first discuss proton and then neutron polarimetry. Along the way, I will connect these polarimetry measurements and goals to important present and future RHIC physics results and plans. Let’s start with the pp physics measurements.

EMC at CERN: J. Ashman et al., NPB 328, 1 (1989): polarized muons probing polarized protons “proton spin crisis”

Probing  G in pp Collisions pp  hX Double longitudinal spin asymmetry A LL is sensitive to  G

Measuring A LL (N) Yield (R) Relative Luminosity BBC vs ZDC (P) Polarization RHIC Polarimeter (at 12 o’clock) Local Polarimeters (SMD&ZDC in PHENIX and BBC in STAR) Bunch spin configuration alternates every 106 ns Data for all bunch spin configurations are collected at the same time  Possibility for false asymmetries are greatly reduced

Polarization Measurements 2006 Run

A LL : jets Run3&4: PRL 97, STAR Preliminary Run5 (  s=200 GeV) PHENIX Preliminary Run6 (  s=200 GeV) Run3,4,5: PRL 93, ; PRD 73, ; hep-ex A LL :  0 Bottom line: A_LL is small, < 1 sigma from 0.

Transverse spin: pion A_N --very large forward asymmetries A N (  ) at 62 GeV Kyoto Spin2006 STAR Many sigma significance observed!

unpol. u Expected start: 2009  q-  q at RHIC via W production Many sigma significance expected for this parity-violating asymmetry.

Now let’s look at the proton polarization uncertainty achieved so far.

RHIC Polarized Collider BRAHMS & PP2PP STAR PHENIX AGS LINAC BOOSTER Pol. H - Source Spin Rotators (longitudinal polarization) Siberian Snakes 200 MeV Polarimeter RHIC pC Polarimeters Absolute Polarimeter (H  jet) AGS pC Polarimeter Strong AGS Snake Helical Partial Siberian Snake PHOBOS Spin Rotators (longitudinal polarization) Siberian Snakes 2006: 1 MHz collision rate; P=0.6

P target from BRP P beam by H-Jet-polarimeter Effective A N pC of RHIC pC-polarimeter Fill by fill beam polarizations for experiments A N of pp  pp 1.Confirmation of the system works well. 2.Physics motivation. Stream of offline analysis  target,  beam  beam pC H-jet polarimeter RHIC pC polarimeter

H. Okada et al., PLB 638 (2006), Results of A N in the CNI 100 GeV/c |r 5 | =0 Driven by E-M Spin Flip: polarized proton anomalous magnetic moment.

2005 Jet Normalization Summary Blue Yellow  P(blue)/P(blue) = 5.9%  P(yellow)/P(yellow) = 6.2%  [P(blue) x P(yellow) ]/[P_b x P_y] = 9.4% A_N(2005) = A_N(2004) x (S +/-  A(jet stat)/A +/-  A(jet syst)/A +/-  A(pC syst)/A) A_N(05)=A_N(04)x( / / /-.005)  P/P(profile)=4.0% A_N(05)=A_N(04)x( / / /-.022)  P/P(profile)=4.1% Goal: 10%

Our goal for proton polarimetry was Delta P/P=+/- 5%, and a 10% uncertainty for 2 spin asymmetry measurements. Therefore we reached our goal of a 10% uncertainty due to the beam polarization for the A_LL measurements in 2005, and were near our goal of a 5% uncertainty for the A_N/L measurements.

RHIC spin measurements use the polarization to scale the measured asymmetry: A_LL = 1 /(P_1 x P_2) x epsilon_LL with epsilon_LL = [(N_++) - Rx(N_+-)]/[(N_++) + Rx(N_+-)], R = L’_++/L’_+- or A_N(L) = 1 /(P) x epsilon_N(L) with epsilon_N(L) = [(N_+) – Rx(N_-)]/[(N_+) + Rx(N_-)], R = L’_+/L’_-

The uncertainty for a non-zero * A_LL is: (Delta A_LL/A_LL)^2 = (2 x Delta P/P)^2 + (Delta epsilon/epsilon)^2 Therefore a 5% Delta P/P contributes 10% to the A_LL uncertainty, and its contribution is at the same level as a measured 10 sigma physics asymmetry.** Similarly, a 5% Delta P/P contributes 5% to the A_N/L uncertainty, and its contribution is at the same level as a 20 sigma physics asymmetry * For A_LL = 0, a 5% DP/P uncertainty increases Delta A_LL by 0.5%. ** We actually (mostly) independently measure P_1 and P_2.

Conclusion: the proton polarization uncertainty achieved for RHIC (5%) is reasonable and sufficient. Also, we expect to be able to reach 2% uncertainty or better with improved polarization profile measurements, coming from a greatly improved carbon target setup (in place for the 2008 run).

Now let’s discuss polarized neutrons at RHIC: physics and polarimetry: --why hasn’t this been a priority? --why do I use the past tense?

Ok, why haven’t neutrons been a priority? ---DIS polarized n and p results are used to separate u and d quark contributions; also test the Bj Sum Rule (see Abhay’s talk); for eRHIC also for W^+ and W^- exchange (parity violating g_5) ---RHIC uses parity violating production of W+ and W- to separate (u,dbar) from (d,ubar) and rapidity of lepton to separate quarks from antiquarks ---Polarized n vs. p results at RHIC would be trivial exchange of roles of u and d quarks…

And why do I use the past tense? ---RHIC, HERMES, COMPASS, and BELLE results have led to a renaissance of transverse spin physics  the “trivial” result that polarized n vs. p exchanges the u and d quarks implies that the dynamics of the observed spin asymmetries are from the valence quarks  fundamental prediction of sign reversal for Drell- Yan vs. DIS transverse spin asymmetry -- n vs. p Drell-Yan identifies u vs. d quark orbital angular momentum contribution to the spin of the proton

Transverse spin: pion A_N --forward asymmetries at RHIC A N (  ) at 62 GeV Kyoto Spin2006 STAR root(s) = 200 GeV root(s) = 62 GeV

Forward pion asymmetries at the ZGS and Fermilab (fixed target): Phys. Lett. B261(1991)201 Phys. Lett. B264(1991)462 Phys. Rev. D.18 (1978) root(s) = 5 GeVroot(s) = 20 GeV

pp   X Cornerstones to the RHIC Spin program To appear PRD Rapid, hep-ex Mid-rapidity: PHENIX Forward: STAR PRL 97, (2006)

√s=23.3GeV√s=52.8GeV But, do we understand forward  0 production in p + p? At  s << 200 GeV, not really…. 2 NLO collinear calculations with different scale: p T and p T /2 Bourrely and Soffer (hep-ph/ , Data references therein): NLO pQCD calculations underpredict the data at low  s from ISR  data /  pQCD appears to be function of , √s in addition to p T xFxF xFxF           Ed 3  dp 3 [  b/GeV 3 ] Data-pQCD difference at p T =1.5GeV

A Fundamental Test of Universality: Transverse Spin Drell Yan at RHIC vs Sivers Asymmetry in Deep Inelastic Scattering Important test at RHIC of recent fundamental QCD predictions for the Sivers effect, demonstrating… attractive vs repulsive color charge forces Possible access to quark orbital angular momentum Requires very high luminosity (RHIC II) Both STAR and PHENIX can make important, exciting, measurements Discussion available at

Simple QED example: DIS: attractive Drell-Yan: repulsive Same in QCD: As a result: Attractive vs Repulsive Sivers Effects Unique Prediction of Gauge Theory !

x Sivers Amplitude 0 0 Experiment SIDIS vs Drell Yan: Sivers| DIS = − Sivers| DY *** Probes QCD attraction and QCD repulsion *** HERMES Sivers ResultsRHIC II Drell Yan Projections Markus Diefenthaler DIS Workshop Munich, April 2007

Concluding Remarks Proton polarimetry has met goals, and probably good to go to the future (expect also eRHIC) Very good reasons to develop polarized neutrons for RHIC as well as eRHIC/EIC Transverse spin renaissance! Polarized deuteron beams attractive for transverse spin (but absence of g-2 also complicates polarimetry) Polarized 3-He beam: can we use similar polarimetry techniques as for protons? Important step: theoretical guidance— workshop similar to RBRC Workshop #1 that started the CNI polarimetry for protons!---work presented here by L. Trueman

H. Okada et al., PLB 638 (2006), Results of A N in the CNI 100 GeV/c |r 5 | =0

A N and r 5 results at 24 GeV/c Set r 5 as free parameter  Im r 5 =    Im r 5 =    Re r 5 =    Re r 5 =     2 /ndf = 2.87/7   2 /ndf = 2.87/7 preliminary |r 5 |=0 0.8 M events

Contribution to theoretical understanding of A N Input: A N pC at 24GeV/c, 100GeV/c A N pp at 100GeV/c Prediction: A N at 24GeV/c -t (GeV/c) 2 ANAN Prediction by L. Trueman (BNL) A N 24GeV/c Data vs. prediction

p-^3He Elastic Scattering (from L. Trueman) pol. p--^3He p—pol ^3He No Hadron helicity flipHadron helicity flip