Spin transfer coefficient K LL’ in photoproduction at HERMES D. Veretennikov On behalf of the...

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Transcript of Spin transfer coefficient K LL’ in photoproduction at HERMES D. Veretennikov On behalf of the...

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Spin transfer coefficient KLL in photoproduction at HERMES

D. VeretennikovOn behalf of the HERMES collaborationDIS08, London decay and spin transfer coefficient is self-analyzing particle due to its parity violation p - decay

Spin transfer coefficient SLL KLL from longitudinally polarized target KNN from transversely polarized target DLL from longitudinally polarized beam DNN from transversely polarized beamL is primary axis along target or beam polarizationL is secondary axis along momentumUnpolarized cross-sectionangle between proton momentum in the rest frame and the spindecay constant, 0.642 (), -0.642 ()

Angular distribution of protons (in rest frame)Study of polarization at HERMESDIS, e + p e + + XDLL spin transfer from longitudinally polarized e+/e- beam in semi-inclusive reaction / Published P.R. D 64 (2001), P.R. D 74 (2006) /Quasi-real photoproduction, e + p + XKLL spin transfer from longitudinally polarized targetDLL spin transfer from longitudinally polarized e+/e- beamKNN spin transfer from transversely polarized targetPn transverse (spontaneous) polarization / Publish P.R. D 76 (2007) /e + * ( Q2 0 GeV2 ) photoproduction mechanism in PYTHIAAccording to PYTHIA is produced due to diquark fragmentation or due to quark fragmentation

Most of events are within photoproduction peak (for 80% events Q2 < 0.05 GeV2, 15 GeV)Such that photon is quasi-real

HERMES experimentPolarized lepton (e-/e+) beam Ee = 27.5 GeV , monthly spin flip ( DLL )Long. / trans. polarized gas targets (H, D) , spin flip every 90 s ( KLL , KNN )Detector is up / down symmetric ( Pn )

Background suppression cuts forleading rejection (in HERMES acceptance proton is always leading) :Threshold Cherenkov det. 1996-1997Ring imaging Cherenkov 1999-2000h+h- pair background rejection :Vertex separation d(V1,V2) > 15 cm

() event reconstruction

Data sample for longitudinally polarized target ( 1996 - 2000 )

Formalism extraction of KLLNo MC simulation needed

Helicity balanced data sample

Moment method

Background subtraction

7

Photoproduction kinematics

Better separate production channelsValue of t allows for easy comparison with other experiments

KLL seems to be increasing at small t (diquark fragmentation?)KLL is pt independent (0 < pt < 1.2 GeV) Kinematical dependences of KLL for

Statistics for is not enough to see dependences on t or pt

Kinematical dependences of KLL for

Spin transfer for and , world dataFNAL, E704pp collisions with transversely polarized beamRICH, STARpp collisions with longitudinally polarized beam

World data compilation for spin transfer

FNAL result confirms a trend to increase spin transfer at small tConclusionLongitudinal spin transfer from polarized target to the is measured for the first time in quasi-real photoproductionKLL = 0.026 0.009stat 0.005systSpin transfer is increasing at small tKLL is pt independentLongitudinal spin transfer to is compatible with zero for available statisticsKLL = 0.002 0.022stat 0.008syst