1 / 28

Transversity Signals in Two-Hadron Production at COMPASS

Christian Schill Universit ät Freiburg. Transversity Signals in Two-Hadron Production at COMPASS. On behalf of the COMPASS Collaboration. Transverse spin physics at COMPASS Azimuthal asymmetries in two-hadron production Results for identified ππ , π K and KK pairs on the deuteron

meris
Télécharger la présentation

Transversity Signals in Two-Hadron Production at COMPASS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Christian Schill Universität Freiburg Transversity Signals in Two-Hadron Production at COMPASS On behalf of the COMPASS Collaboration • Transverse spin physics at COMPASS • Azimuthal asymmetries in two-hadron production • Results for identified ππ, πK and KK pairs on the deuteron • Discussion and Outlook DIS 2007, Munich, April 18

  2. Transverse Spin Physics q(x) f1(x) Dq(x) g1(x) DTq(x) = q↑↑(x) - q↑↓(x) h1(x) 3 distribution functions are necessary to describe the spin structure of the nucleon at LO: momentum distribution well known - unpolarized DIS helicity distribution known - polarized DIS transversity distribution still unknown DTq(x) decouples from inclusive DIS: helicity flip of quark  SIDIS experiment

  3. Transversity: How to measure it in SIDIS? Transversity Tq (x) chiral odd: observable effect only in combination with chiral odd fragmentation function • Suggested quark polarimeters in SIDIS: • Azimuthal distribution of single hadrons • Collins fragmentation function • Azimuthal dependance of the plane • containing a hadron pair • 2-hadron interference fragmentation • function • Measure transverse polarization of Λ • fragmentation function q Λ • COMPASS results Talk by A. Bressan • This talk • COMPASS results

  4. The COMPASS Spectrometer at CERN • Beam: 160 GeV µ+ (2 · 108 µ+ / 5s spill) • Polarized target • Particle identification: • RICH MuonWall SM2 E/ H CAL E/ H CAL 50 m SM1 Polarised Target MuonWall SciFi Straws RICH Silicon Drift Chambers Micromegas MWPC GEMs µ+ beam

  5. The polarised 6LiD-Target 3He – 4He dilution refrigerator Superconducting Dipole (0.5 T) Two 60 cm long target cells with opposite polarisation Vertex distribution: T=50mK Polarization: 50 % Dilution factor: 0.38 Transverse target polarization: Reversed one a week

  6. The polarised 6LiD-Target 3He – 4He dilution refrigerator Superconducting Dipole (0.5 T) Two 60 cm long target cells with opposite polarisation Vertex distribution: T=50mK Polarization: 50 % Dilution factor: 0.38 Transverse target polarization: Reversed one a week

  7. Ring Imaging Cherenkov Detector 3 m 6 m Mirror wall 5 m CsI MWPC Radiator: C4F10 Identification of π, K and protons Cherenkov thresholds:π ≈ 3 GeV/c K ≈ 9 GeV/c p ≈ 17 GeV/c 2σπ/K separation at 43 GeV/c

  8. Transversity Data Sample transversely polarised deuteron target ~ 20% of the running time 2002 2002 11 days 11 days of data taking (19), of data taking 2 periods trigger (large x, Q2) + PID (ECAL, RICH) 2003 2003 9 days 9 days of data taking (14), of data taking 1 period 2004 2004 14 days 14 days of data taking (24), of data taking 2 periods reconstructed reconstructed DIS events DIS events (10 (10 ) ) 6 6

  9. The Coordinate System 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) RS= R - S´ = R + S - π R (A. Bacchetta, M. Radici, hep-ph/0407345) (X. Artru, hep-ph/0207309)

  10. Azimuthal asymmetry for two-hadron production Target single spin asymmetry ARS(x,z,Mh2): z=z1+z2 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 presently unknown can be measured in e+e- (BELLE) expected to depend on the hadron pair invariant mass (X. Artru, hep-ph/0207309)

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

  12. RICH hadron identification all hadron pairs: 5.3 M 0.1 M (1.6%) 3.7 M (70%) 0.25 M (4.5%) 0.3 M (5.8%)

  13. Results for π+π- pairs

  14. Results for π+ K- pairs

  15. Results for K+π- pairs

  16. Results for K+ K- pairs

  17. sin Dependance Cross section σUT for two-π fragmentation depends on sin: (Interference of s- and p-wave of the 2π-state) (A. Bacchetta and M. Radici, hep-ph/0212300)  : Angle of h1 in the two-hadron CMS to the direction of Ph=Ph1+Ph2 <sin> = 0.95 <sin> = 0.90  small contribution in the kinematic region of COMPASS

  18. Discussion • First results for two identified hadron pair asymmetries • Asymmetries are small for all hadron pairs ππ, πK, and KK • Systematic effects are considerably smaller • than the statistical error Comparison with theoretical models 

  19. Comparison with Theory Model calculations for COMPASS kinematics (M. Radici, QCDN 06, hep-ph/0608037): Model for transversity: • Soffer, Stratmann, Vogelsang, • P.R. D65 (02) 114024 • Korotkov, Nowak, Oganessian, • E.P.J. C18 (01) 639 • Schweitzer et al., • P.R. D64 (01) 034013 • Wakamatsu • P.L. B509 (01) 59 ΔTq(x) xBj Prediction for COMPASS: • small asymmetries on the deuteron combination of isospin- symmetric target and properties of dihadron- fragmentation function Hqh(z) ARS Mh

  20. Outlook • Complementary measurements with proton target planned this year • Data (of comparable statistics) will be collected on a transversely • polarized proton target (NH3) and will allow flavour separation Predictions for two-hadron asymmetries on the proton at COMPASS: • Soffer, Stratmann, Vogelsang, • P.R. D65 (02) 114024 • Korotkov, Nowak, Oganessian, • E.P.J. C18 (01) 639 • Wakamatsu • P.L. B509 (01) 59 - ARS (M. Radici, hep-ex/0608037)

  21. Thank you!

  22. Results for two unidentified hadrons all combinations of +ve (h1) and –ve (h2) hadrons 2002-2004 COMPASS data 2002-2004 COMPASS data

  23. Partial wave expansion of Hqh(z) A. Baccetta, hep-ph/0708037 cos-Distributions of our data:

  24. Frame independant definition of φR • A. Baccetta, • hep-ph/0608037 where P1T and P2T are the transverse components of the hadron momenta with: we define:

  25. Double Ratio Method double ratio: Nup/down: upstream / downstream target cell N: target polarization vector pointing up / down fit function: final asymmetry:

  26. COMPASS kinematic region

  27. Transverse Λ Polarization

  28. Transverse Λ Polarization

More Related