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Measurements of Transverse Spin Effects in SIDIS

Measurements of Transverse Spin Effects in SIDIS. Outlook. Introduction Asymmetries Transversity DF from Single Hadron from Two Hadrons from Hyperons Sivers DF Other TMD Near/Far Future Conclusions. What you will w/not find. Review of all Deuteron Results w/not 2007 proton results

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Measurements of Transverse Spin Effects in SIDIS

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  1. Measurements of Transverse Spin Effects in SIDIS

  2. Outlook • Introduction • Asymmetries • Transversity DF • from Single Hadron • from Two Hadrons • from Hyperons • Sivers DF • Other TMD • Near/Far Future • Conclusions

  3. What you will w/not find • Review of all Deuteron Results • w/not 2007 proton results • They are on their way… • ½ PB of data processed • Data quality checks ongoing • Late Spring

  4. Spectrometer • longitudinally polarised muon beam • longitudinally or transversely polarised target • momentum and calorimetry measurements • particle identification MuonWall SM2 E/HCAL E/HCAL Straws SDC MWPC W45 SciFi Silicon Micromegas GEMs SM1 Polarised Target Muon Wall RICH mbeam • Beam: • Luminosity 5 . 1032 cm-2 s-1 • intensity 2 108 µ+/spill (4.8s/16.8s) • momentum 160 GeV/c

  5. 3He – 4He Dilution refrigerator (T~50mK) superconductive Solenoid (2.5 T) Dipole (0.5 T) Target solid state target operated in frozen spin mode • 2002-2004: 6LiD • dilution factor f = 0.38 polarization PT = 50%~20% of the time transversely polarised • during data taking with • transverse polarization • dipole field always  • polarization reversal in the 2 cells after ~ 5 days two 60 cm long cells with opposite polarisation (systematics) dN/dz 4000 2000 0 zvtx (mm) 0 -1000 1000

  6. Event Selection • DIS cuts: • Q2 > 1 (GeV/c)2 • 0.1 < y < 0.9 • W > 5 GeV/c2 • All hadron selection: • z > 0.20 • pt > 0.1 GeV/c • Plus for leading hadron: • zl > 0.25 • No signals in the CALOs from neutral particles with z > zl Statistics 2002 - 2004: 8.5 * 106 positive hadrons 7.0 * 106 negative hadrons

  7. Hadron Identification • Hadron identification is based on RICH response: several studies performed on the stability in time of the detector. • Cherenkov thresholds: π~ 2 GeV/c • K ~ 9 GeV/c • p ~ 17 GeV/c • 2 σπ/K separation at 43 GeV/c • In the leading hadron sample: • ~76% pions • ~12% kaons

  8. Kinematics – inclusive

  9. Kinematics - SI

  10. K0 Reconstruction Z(V0) – Z(prim. vtx.) > 10 cm ● angle of target pointing < 0.01 rad ● |Mpp– MK0| < 20 MeV/c² ● pt, arm > 0.025 GeV/c ● pt, K0 > 0.1 GeV/c K0 target pointing Armenteros S/B ~ 15

  11. TRANSVERSITY

  12. Transversity DF q=uv, dv, qsea quark with spin parallel to the nucleon spinin a transversely polarised nucleon DTq(x) = q↑↑(x) - q↑↓(x) h1q(x), dq(x), dTq(x) • Properties: • probes the relativistic nature of quark dynamics • no contribution from the gluons  simple Q2 evolution • Positivity: Soffer bound…………….. • first moments: tensor charge………. • sum rule for transverse spinin Parton Model framework………… • it is related to GPD’s • is chiral-odd: decouples from inclusive DIS Soffer, PRL 74 (1995) Bakker, Leader, Trueman, PRD 70 (04)

  13. How To the Transversity DF is chiral-odd: survives only by the product with another chiral-odd function can be measured in SIDIS on a transversely polarised target via “quark polarimetry”

  14. Single hadron asymms. Collins and Sivers terms in SIDIS cross sections depend on different combination of angles: • C = h- s’ • Collins angle S = h- sSivers angle hazimuthal angle of the hadron sazimuthal angle of the transverse spin of the initial quark s’ azimuthal angle of the transverse spin of the fragmenting quark s’ = p -s (spin flip)

  15. Collins Effect Collins effect: a quark with an upward (downward) polarization, perpendicular to the motion, prefers to emit the leading meson to the left (right) side with respect to the quark direction i.e. the fragmentation function of a transversely polarized quark has a spin dependent part And the resulting measured asymmetry

  16. Unidentified Hadrons • only statistical errors shown (~1%), systematic errors considerably smaller • small asymmetries compatible with 0 for both + and – hadrons • [NP B765 (2007) 31-70]

  17. Identified Hadrons

  18. Genova, 27 febbraio 2008 Naïve Interpretation (parton model, valence region) • proton data  unfavored Collins FF ~ – favored Collins FF at variance with unpol case u quark dominance (d quark DF ~ unconstrained) • deuteron data some (small) effect expected even if  cancellation between Tu (x) and Td (x) access to Td (x)

  19. Two Hadrons z-axis = virtual photon direction x-z plane = lepton scattering plane R= angle between lepton scattering plane and two-hadron plane S= azimuthal angle of initial quark versus lepton scattering plane S´= π - S (fragmenting quark) R RS= R - S´ = R + S - π (A. Bacchetta, M. Radici, hep-ph/0407345) (X. Artru, hep-ph/0207309)

  20. Azimuthal Asymmetries z=z1+z2 Target single spin asymmetry ARS(x,z,Mh2): and N±(RS): Number of events for target spin up (+) and down (-) f: Dilution factor ≈ 0.38 D: Depolarisation factor D=(1-y)/(1-y+y2/2) PT: Target polarisation ≈ 0.5 Under measurement in e+e- (BELLE) expected to depend on the hadron pair invariant mass (X. Artru, hep-ph/0207309)

  21. Selection • DIS cuts: • Q2 > 1 GeV2/c2 • 0.1 < y < 0.9 • W > 5 GeV/c2 • Hadron selection: • z1,2 > 0.1 (current fragmentation) • xF1,2 > 0.1 • z1+z2 < 0.9 (exclusive rho) • RICH identification of π, K

  22. Two hadron asymm.s Expected Small (Radici/Bacchetta, PRD74(2006)114007)

  23. Identified 2 Hadrons

  24. z-order two identified hadrons • Motivations: • Hadrons with higher relative energy carry more information about the fragmenting quark polarization • For leading hadron pairs signal enhancement is predicted PID with 2003-04 rich

  25. z-order two identified hadrons

  26. L Polarimetry

  27. Results

  28. SIVERS DF

  29. SIVERS Mechanism • The Sivers DF is probably the most famous between TMDs… • gives a measure of the correlation between the transverse momentum and the transverse spin • Requires final/initial state interactions of the struck quark with the spectator system and the interference between different helicityFock states to survive time-reversal invariance • Time-reversal invariance implies: • …to be checked • In SIDIS:

  30. Unidentified hadrons • only statistical errors shown (~1%), systematic errors considerably smaller • small asymmetries compatible with 0 for both + and – hadrons • [NP B765 (2007) 31-70]

  31. Identified Hadrons

  32. deuteron data preliminary 2002-2004 2 Naïve Interpretation • proton data asymmetry for p+ > 0, asymmetry for p-≈ 0 Sivers DF for d-quark ≈ - 2 Sivers DF for u-quark the measured asymmetriescompatible with zero suggest F. Bradamante

  33. Small SIVERS on D: hint for small Lg the measured asymmetry on deuteron compatible with zero has been interpreted as Evidence for the Absence of Gluon Orbital Angular Momentum in the Nucleon S.J. Brodsky and S. Gardner, PLB643 (2006) 22

  34. Other TMD’s

  35. Sidis Xsection From A. Bacchetta et al., JHEP 0702:093,2007. e-Print: hep-ph/0611265

  36. Results - LO g1Tis the only parton DF which is chiral-even, T-even, leading twist function in addition to the unpolarised DF and to the helicity DF

  37. Results - LO

  38. Transverse Target SSA for exclusive r (Q2>1) • Motivations: • Hard exclusive meson production (HEMP) is a way, complementary to DVCS, to access GPDs • Vector mesons Transverse Target Single Spin Asymmetry AUT(fh,fS) connected to GPD E • E allows flip of proton helicity, while quark helicity is not flipped → overall helicity is not conserved • angular momentum conservation implies transfer of orbital angular momentum Ji Sum Rule

  39. Selection • Besides standard DIS cuts: • Q2 > 1 GeV2/c2 • 0.1 < y < 0.9 • W > 5 GeV/c2 • Exclusive r selection: • only 3 outgoing particles m, p+, p- • 0.01 < pT2 < 0.5 [(GeV/c)2] • missing energy -2.5 GeV< Emiss<2.5 GeV • Inv. Mass -0.3 MeV/c2 < Mpp – Mr < 0.3 MeV/c2

  40. Results

  41. 2007 RUN

  42. Coupling hole Beam line Thermal screen Microwave power Cavity 1 Cavity 2 Cavity 3 Target in 2007 solid state target operated in frozen spin mode 2007: NH3 dilution factor f = 0.14 polarization PT = 90% 2 3 cells

  43. Projected errors for full statistics (45x1012m)

  44. Summary • precise deuteron data from COMPASS are now available • Collins and Sivers asymmetries h±, p±, K± • + other 6 TMDs [sin(3fh-fS), sin(fS), sin(2fh-fS), cos(fh-fS), cos(2fh-fS), cos(fh)] • Two hadron asymmetries pp, pK, KK • Transverse Lamba polarization • all the measured deuteron asymmetries are very small, and compatible with zero • COMPASS data on deuteron allows to determine the d-quark contribution • present phenomenological studies can describe at the same time the BELLE (FF), the HERMES (proton) and COMPASS (deuteron)…and have allowed a first extraction of the transversity distribution DTq • At the same way COMPASS and HERMES data have allowed a first extraction of the Sivers DF

  45. Coming Soon • Deuteron • Cahn and Boer-Muldersasymmetries  unpol • g2 • Proton • Collins + Sivers… • Little further in time… all the rest • Future programs • Drell-Yan [see … M. Chiosso talk] • Precision measurement … for better flavour separation and measurements of first moments…

  46. THAT’S ALL…(FOR NOW!)

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