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Single-spin asymmetries in inclusive hadron electroproduction at HERMES

Single-spin asymmetries in inclusive hadron electroproduction at HERMES. Klaus Rith University of Erlangen-Nürnberg & DESY.

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Single-spin asymmetries in inclusive hadron electroproduction at HERMES

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  1. Single-spin asymmetries in inclusive hadron electroproduction at HERMES Klaus Rith University of Erlangen-Nürnberg & DESY SPIN 2010, FZ-Jülich September 30, 2010

  2. Outline Motivation: AN in inclusivepp scattering HERMES Results Comparison to pp, DIS and model predictions Summary 2

  3. AN in pp AN =[()-()]/[()+()] E704 p+ ( ) p0 Large AN has been observed in p p h X reactions at ANL, BNL, FNAL, RHIC for s = 4.9–200 GeV p- Possible origins: Sivers DF (was invented to explain AN) Collins FF + transversity DF Twist-3 Combinations of above Possible connection to orbital angular momentum L ? For consistent partonic description: Need flavor dependent AN(E, xF, pT), CMS xF = plong/plong,max 3

  4. AN for identified hadrons in pp s = 200 GeV K+ p+ K- p- AN(+)positive  - AN(-) negative AN(K+)  AN(K-) positive (in disagreement with expectation from valence quark fragmentation) AN(p)  0, AN(p) positive More data and theoretical input needed p p 4

  5. AN for identified hadrons in pp I. Arsene et al., Phys. Rev. Lett. 101 (2008) 042001 62.4 GeV 200 GeV preliminary 5

  6. STAR AN for 0 in pp Negative xF Positive xF Consistent with zero for all pT 6

  7. Inclusive hadron electroproduction k = (E, k) k‘ = (E‘, k‘) Scatteredleptonl‘ remainsundetected l x l ‘ q = k – k‘ x h Detected hadron p l + p h + X Relevant kinematic variables: Feynman variable xF = phlong/phlong,max (in ep CMS) Transverse hadronmomentumpT(w.r.tedirection) 7

  8. HERMES Experiment Data taking: 1995-2007 27.6 GeV e+/e- beam of HERA polarisation  60 % Internal gas targets polarized : 1H, 1H , 2H, 3He unpolarized: 1H, 2H, 3He, 4He, N, Ne, Kr, Xe 8

  9. HERMES Spectrometer tracking: p/p~2%, <0.6 mrad, 40-220 mrad e e‘ h PID: RICH, TRD, Preshower, Calorimeter lepton-hadron separation > 98% 9

  10. hadron separation Aerogel n=1.03 C4F10 n=1.0014 Hadron:  ~ 98%, K ~ 88% , P ~ 85% HERMES spectrometer – RICH Two radiators 10

  11. HERMES front view Measure N()(xF,i, pT,i, i) i 220 mrad k‘ 40 mrad k Spinflip every 90 sec acceptance effects cancel  target spin vector S 11

  12. TSA in inclusive hadron electroproduction TSA: Tranverse target single-spin asymmetry Inclusivehadronelectroproduction: ep  h X + - K+ K- Scattered leptonnot detected: quasi-real photoproduction 66.4 M 56.8 M 5.5 M 3.0 M Azimuthal asymmetry: Asymmetry amplitude AXY UT (xF, pT, ) A(xF, pT, ) = = AUTsin(xF, pT) sin beam target UU (xF, pT) polarisation L -  R 2 AN = = AUTsin(left-rightasymmetry) L +  R  12

  13. Single-spin azimuthal asymmetry polarisation-weighted luminosity luminosity acceptance d3N () =  L() d3UU + (-) LP() d3UT ] (xF, pT, ) dxFdpTd = d3UU  L() + (-) LP() AUT sin(xF, pT) sin] (xF, pT, ) N/LP -N/LP AUT( xF, pT, ) =  AUT sin(xF, pT) sin N/L +N/L Acceptance effects cancel for small bin size or asymmetry 13

  14. Inclusive hadron TSA p+ positive positive K+ p- slightly negative compatible with 0 K- xF dependence 14

  15. Inclusive hadron TSA Increase with pTat low pT Decrease at high pT p+ K+ p- K- pT dependence 15

  16. Inclusive hadron TSA Sign change for - K- p- K+ p+ positive for xF0 pT dependence for different xF intervalls 16

  17. Comparison to DIS Sivers Collins HERMES HERMES + + p+ 0 0 p- - - PL B693 (2010) 11 ANresembles Sivers PRL 103 (2009) 152002  M. Diefenthaler (HERMES)  A. Richter (COMPASS) 17

  18. Comparison to pp K+ p+ K- p- +, -, K+: AN similar to pp K-: AN rather different from pp 18

  19. Inclusive hadron TSA Interpretation: non-trivial due to missing hard scale - except for high pT(factorisation?) Model predictions: M. Anselmino et al., PRD 81 (2010) 034007 Sivers Collins 19

  20. Conclusion HERMEShasmeasuredwithhighprecisionsingle-spinasymmetriesin inclusivehadronelectroproduction, e + p h + X,from atransverselypolarisedprotontarget Substantial single-spin asymmetries are observed for positive pions and kaons Asymmetries for negative pions and kaons are small and show interesting dependence on xF The dependence on pT is similar to that observed in pp The dependence on pT resembles the behaviour of the Sivers asymmetry in DIS 20

  21. STAR AN for 0 and  in pp Very large asymmetry for  7

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