Hall A Technical Report

Single and Double Spin Asymmetry Measurements in Semi-Inclusive DIS on Polarized 3He Vincent SulkoskyMassachusetts Institute of Technology

XX International Workshop on Deep-Inelastic Scattering and Related Subjects

28 March 2012, University of Bonn, Germany

1TMD PDFs link Intrinsic motion of partons Parton spinSpin of the nucleonMulti-Dimension structureProbes orbital motion of quarksA new phase of study, fast developing fieldGreat advancement in theories (factorization, models, Lattice ...)Not systematically studied until recent yearsSemi-Inclusive DIS (SIDIS): HERMES, COMPASS, Jlab-6GeV, ...p-p(p_bar) process : FNAL, BNL, ...

Transverse Momentum Dependent (TMD) Parton Distributions

! Read experiment names

A crucial innovation in this new phase of investigation of the fundamental structure of matter is looking at, and studying, physical observables which are sensitive to the transverse structure of the nucleon. This information is encoded in the so-called Transverse Momentum Dependent partonic Distributions or TMDs, which link the intrinsic motion of partons to their spin and the spin of the parent nucleon. TMDs can be used to construct a three-dimensional picture of partons inside hadrons in momentum space and may be related to the orbital angular momentum of partons. Here is a nave picture why OAM and TMD are correlated: in DIS, since the momentum transfer is large, nucleon contracts into a pancake. However, on the transverse plane, which is perpendicular to that of virtual photon momentum transfer, transverse motion of the quark is conserved. Therefore if quark carries OAM in side this polarized nucleon, transverse momentum will be non-zero. Therefore TMD opened a new phase of study. There was few studies of TMD until a decade ago. But this field are fast developing in both theory and experimental ways ... 2Quark polarizationUnpolarized(U)Longitudinally Polarized (L)Transversely Polarized (T)Nucleon PolarizationULTLeading-Twist TMD PDFsf1 =

f 1T =Sivers

Helicityg1 =

h1 =Transversity

h1 =Boer-Mulders

h1T =Pretzelosity

h1L =

Worm Gear(Kotzinian-Mulders): Survive trans. Momentum integrationNucleon SpinQuark Spin

g1T =

Worm Gear! relate g1, f1 -> collinear w/ pT dep.

Say: Noval new information on structure of nucleon, spin-orbital cor and multi-parton cor.Beside the three parton distribution functions which survive the integration over the quark transverse momentum there are five more transverse momentum dependent distribution functions at leading twist.Here is a table of all the 8 leading twist TMDs, the cartoons on the right hand side of each name tell you the meaning of each TMDs. Again, the virtual photon is supposed to go out of the paper and thats our longitudinal direction. The red circle and arrow are the quark and its spin, and black circle and arrow are the nucleon and its spin. The blue arrow shows the momentum direction of the quark.An important information these 5 new TMDs will tell you is the quark oribtal angular motion. They will vanish without orbital angular momentum.

In particular, the Sivers function directly tells you the quark orbital angular momentum in a transverse polarized target, Boer-Mulder tells you the correlation of the quark orbital momentum and its spin inside a unpolarized nucleon and Pretzelosity, in certain model context, direct measures the relativistic nature of the nucleon.

Blue: no kt dependence and T-evenRed: T-odd with kt dependenceOther: kt dependence and T-even

3Quark polarizationUnpolarized(U)Longitudinally Polarized (L)Transversely Polarized (T)Nucleon PolarizationULTLeading-Twist TMD PDFsf1 =

f 1T =Sivers

Helicityg1 =

h1 =Transversity

h1 =Boer-Mulders

h1T =Pretzelosity

g1T =

Worm Gearh1L =

Worm Gear(Kotzinian-Mulders): Probed by E06-010Nucleon SpinQuark Spin

! relate g1, f1 -> collinear w/ pT dep.

Say: Noval new information on structure of nucleon, spin-orbital cor and multi-parton cor.4

TransversityCharacteristics of Transversity h1T = g1L for non-relativistic quarks No gluon Transversity in nucleon Chiral-odd difficult to access in inclusive DISSoffers bound |h1T| Sivers effectNo GPD correspondencea genuine sign of intrinsic transverse motionFirst TMDs in Pioneer Lattice calculation arXiv:0908.1283 [hep-lat], arXiv:1011.1213 [hep-lat]Worm-Gear Functions g1T

Worm Gearg1T =

TOTg1T (1)S-P int.P-D int.Light-Cone CQM by B. Pasquini B.P., Cazzaniga, Boffi, PRD78, 2008

! Say Boer-Mulders, Sivers measured, complementary picture

7

Detect one hadron from fragmentation of the struck quark in coincidence with the scattered electronFlavor tagging possible through fragmentation functionz = Eh/ at least > 0.2

Access TMDs through SIDISHadrons tag flavor dependence of quarks.z hadron energy fraction8Access TMDs through SIDISSL, ST: Target Polarization; e: Beam Polarization

UnpolarizedPolarizedTargetPolarizedBeam andTargetBoer-MulderSiversTransversity/CollinsPretzelosity

Worm Gear9

Separation of TMDs

Separate different effects through angular dependenceCollins asymmetry:

Sivers asymmetry:

Pretzelosity:

Double-spin asymmetry:

Jefferson Lab CEBAF

ABC

CEBAF: Continuous Electron Beam Accelerator Facility

acceleratingstructuresCHL

RF separatorsProperties Emax6.0 GeV Imax200mA Pe 85% Beam To 3 Halls

Re-circulating arcsE06010 Experiment SetupSuccessful data taking 2008-09Polarized electron beam ~80% polarizationFast Flipping of helicity at 30Hz (for g1T)Charge asymmetry: controlled by online feed back at PPM levelPolarized 3He targetBigBite at 30 as electron armDipole magnet, Pe = 0.7 ~ 2.2 GeV/c MWDC/shower-preshow/scintillatorHRSL at 16 as hadron armQQDQ config, Ph = 2.35 GeV/cScintillator/drift chambers/Cherenkov/RICH/ lead glass

Beam Polarimetry(Mller + Compton)

LuminosityMonitor

Whats new:Neutron TargetHelicity Flip -> Cancel drift/cancel false asym.Beam charge feed back -> PPM level Charge Asym13Angular Coveragecolor coded for each target spin direction: up, down, left and right.

Collins:Sivers and Worm-Gear:

Target spin orientations: up-down and left-right(increases angular coverage)Finite Acceptance w/ Spin Flip -> Larger one

14HRS and BigBite Spectrometers

Particle Identification

Hadron Identification from HRSElectron Identification from BigBite

Kaon and proton data can be separated by coincidence/TOF and the RICH detector: both provide K/ ~ 4 separationCombined pion rejection 99.9%should simply point out which particle you want to keep, which one to reject.16 Effectively a polarized neutron targetImproved figure of meritRb+K hybrid mixture cellNarrow bandwidth lasersCompact size: No cryogenic support needed

Polarized 3He Target

Beam3HeCell~90% ~1.5% ~8%

Technical break through 1: hybrid cell17

History of Figure of Merit of Polarized 3He TargetHigh luminosity: L(n) = 1036 cm-2 s-1Record high steady ~ 60% polarization with 15 A beam with automatic spin flip every 20 minutes 18Performance of 3He Target

Average 3He pol. = 55%18

SSA check: HRS single-arm 3He SSA(Witness channels on 3He, not corrected for target polarization and dilution)

False asymmetry < 0.1%K. Allada Univ. of Kentucky2010.3He Target Single-Spin Asymmetry in SIDIS

~87% ~8% ~1.5%

3He Sivers SSA:negative sign for +, consistent with zero for - 3He Collins SSA are not large (as expected).

After correction of N2 dilution (dedicated reference cell data)Blue band: model (fitting) uncertainties Red band: other systematic uncertainties

Phys. Rev. Lett. 107 (2011) 072003Results on NeutronCollinsasymmetries are not large, except at x=0.34Siversagree with global fit, and light-cone quark model. Consistent with HERMES/COMPASS

favors negative

Independent demonstration of negative d-quark Sivers function. Blue band: model (fitting) uncertainties Red band: other systematic uncertaintiesRadiative correction: bin migration + uncer. of asy.Spin-dependent FSI estimated 1GeV2W>2.3GeVz=0.4~0.6W>1.6GeVx bin 1234 ~ 2.0 GeV2 ~ 2.8 GeV ~ 0.5

29Raw DataFarm ProductionCoincidence AsymmetryWitnessAsymmetryEvent SelectionPhysicsAnalysisDetector calibrationScalersTarget polarizationRun data baseSpectrometeropticsPID cutsLumi Cuts Beam CutsReconstruction CutsCorrections: luminosity, DAQ deadtime, detector efficiency, .Transversity Data Analysis FlowTwo independent teams: Blue vs Red.N2 Dilution correctionBackgroundSeparation of Collins vs Sivers3He to neutron correction30Hadron Particle IdentificationGas Cherenkov and lead glass:separate hadrons from electronsAerogel Cherenkov:separates pions and other hadrons

Kaon and proton data can be cleaned up by coincidence/TOF and the RICH detector: both provide K/ ~ 4 separationCombined pion rejection 99.9%Particle Identification for Kaons

33Analysis: Target Single-Spin AsymmetryTarget single-spin asymmetry from normalized yields, need to consider :beam charge, target density, DAQ life time, detector efficiency etc. Automatic target spin flip once every 20 minutes.

2845 target spin local pairsBeam Charge + vs Beam Charge - Beam charges are well-balanced between the pairs

33Two teams carried out independent analysisRed Team: Maximum Likelihood MethodBlue Team: Local Pair-Angular Bin-Fit MethodDo not share any code.Many cross checks on intermediate results. Analysis of Asymmetry

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Two team independent asymmetry analysesMany cross checks on intermediate asymmetries. Red team.

Blue team.

Blue team implementedRed teams method.

Correction for N2 Dilution

Cross section ratios determined through reference cell N2 and 3He data.

From 3He to Neutron

very small (< 0.003)Cross section ratios determined through reference cell H2 and 3He data.

DSA Consistency Checks

MLE vs Local Spin Pair Methods

Successful asymmetry extraction from simulated dataTest bias and efficiency of MLE method at E06-010 statisticsSIMC: E06-010 Monte Carlo