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Measurement of Collins Asymmetries in e + e - Annihilation at the KEK B-Factory

Measurement of Collins Asymmetries in e + e - Annihilation at the KEK B-Factory. M. Grosse Perdekamp. Illinois. XII Workshop on High Energy Spin 2007 Joint Institute for Nuclear Research, Dubna, September 6 th. D. Gabbert Illinois and RBRC M. Grosse Perdekamp Illinois and RBRC

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Measurement of Collins Asymmetries in e + e - Annihilation at the KEK B-Factory

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  1. Measurement of Collins Asymmetries in e+e- Annihilation at the KEK B-Factory M. Grosse Perdekamp. Illinois XII Workshop on High Energy Spin 2007 Joint Institute for Nuclear Research, Dubna, September 6th D. Gabbert Illinois and RBRC M. Grosse Perdekamp Illinois and RBRC K. Hasuko RIKEN and RBRC S. Lange Frankfurt M. Leitgab Illinois D. Mertens Illinois A. Ogawa BNL and RBRC R. Seidl Illinois and RBRC V. Siegle RBRC for the Belle Collaboration

  2. Motivation Collins FF for global QCD analysis of single transverse asymmetries in pp and SIDIS Collins Asymmetries from e+e- LEP first work on Delphi data in the 90s: Bonivento, Matteuzzi, Kotzinian, (DELPHI note,1995), Efremov, Smirnova, Tkachev (Nucl. Phys. Proc. Suppl. 74, 1999) Experimental technique Results Future Plans Spin dependent observables Precision measurement of spin averaged hadron fragmentation functions ----------- Outline ------------ Collins Asymmetries in Belle

  3. Why is the Collins Fragmentation Function Interesting? o Very basic QCD process: Fundamental test case for any approach to solve QCD at soft scales. o Tests of universality and factorization between e+e-, DIS and p-p collisions o Symmetry properties o Evolution is fundamental QCD prediction o Connection between microscopic and macroscopic observables:  Probe/analyzer for transverse quark spin critical input for transverse proton spin program at DESY, CERN, JLab and RHIC Collins Asymmetries in Belle

  4. MotivationTransversity Quark Distributions δq(x)from Collins- (CFF) and Interference-Fragmentation (IFF) Latest HERMES results for Collins Asym- Metries, M. Diefenthaler, DIS 2007, Munich Collins- and IFF- asymmetries in semi-inclusive deep inelastic scattering (SIDIS) and pp measure ~ δq(x) x CFF(z) ~ δq(x) x IFF(z) Collins- and IFF- asymmetries in e+e- annihilation are of the form ~ CFF(z1) x CFF(z2) ~ IFF(z1) x IFF(z2)  global QCD analysis Collins Asymmetries in Belle

  5. Global Analysis: Extract Transversity Distributions RBRC Transversity Workshop 2000 Factorization + Universality ?! e+e- ~ CFF(z1) x CFF(z2) ~ IFF(z1) x IFF(z2) SIDIS ~ δq(x) x CFF(z) ~ δq(x) x IFF(z) pp  jets ~ G(x1)xδq(x2) x CFF(z) pp  h+ + h- + X ~ G(x1)xδq(x2) x IFF(z) pp  l+ + l- + X ~ δq(x1) x δq(x2) Transversity, δq(x) Tensor Charge Theory Lattice QCD: Tensor Charge Collins Asymmetries in Belle

  6. First QCD Analysis of SIDIS + e+e- ! Anselmino, Boglione, D’Alesio, Kotzinian, Murgia, Prokudin, Turk Phys. Rev. D75:05032,2007 Fit includes: HERMES SIDIS + COMPASS SIDIS + Belle e+e- transversity dist. + Collins FF Collins Asymmetries in Belle

  7. The Preliminary DELPHI Collins Result Efremov, Smirnova, Tkachev (Nucl. Phys. Proc. Suppl. 74, 1999) Sample: 3.5 x 106 events at √s=MZ0 Analysis: di-hadron correlation for leading hadrons endcaps endcaps 35<θ2<135 • First result on Collins Asymmetries in e+e- • Monte Carlo for acceptance corrections • Un-estimated (large) systematic errors • DELPHI result e+e- compatible with HERMES+ BELLE (Efremov, Goeke, Schweitzer) 15< θ2 <175 Collins Asymmetries in Belle

  8. Measurement of Collins Asymmetries In e+e- at KEK B with the Belle Phys.Rev.Lett.96:232002,2006 and update at Spin 2006 in Kyoto

  9. Collins Effect in Quark Fragmentation J.C. Collins, Nucl. Phys. B396, 161(1993) q Collins Effect: Fragmentation of a transversely polarized quark q into spin-less hadron h carries an azimuthal dependence: Collins Asymmetries in Belle

  10. General Form of Fragmentation Functions Number density for finding hadron h from a transversely polarized quark, q: unpolarized FF Collins FF Collins Asymmetries in Belle

  11. Collins FF in e+e- : Need Correlation between Hemispheres ! • Quark spin direction unknown: measurement of • Collins function in one hemisphere is not possible • sin φ modulation will average out. • Correlation between two hemispheres with • sin φi Collins single spin asymmetries results in • cos(φ1+φ2) modulation of the observed di-hadron • yield. • Measurement of azimuthal correlations for pion pairs • around the jet axis in two-jet events! Collins Asymmetries in Belle

  12. Collins Effect in di-Hadron Correlations In e+e- Annihilation into Quarks! • Collins effect in e+e- • quark fragmentation • will lead to azimuthal • asymmetries in di-hadron • correlation measurements! • Experimental requirements: • Small asymmetries  • very large data sample! • Good particle ID to high • moments. • Hermetic detector electron q1 z2 z1 q2 quark-1 spin quark-2 spin z1,2 relative pion momenta positron Collins Asymmetries in Belle

  13. KEKB Asymmetric collider 8 GeV e- + 3.5 GeV e+ Ös = 10.58 GeV , e+e-  ϒ(4S)  BB Off-resonance: 10.52 GeV e+e-  qq (u,d,s,c) Integrated Luminosity: 547 fb-1 (on resonance) 60 fb-1 (off-resonance) KEKB: L>1.6 x 1034cm-2s-1 !! Belle detector KEKB • Average Trigger rates: • U(4S)BB 11.5Hz • qq 28 Hz • mm + tt 16 Hz • Bhabha 4.4 Hz • 2g 35 Hz 1.5 x 109 hadronic events in analysis ~ 430 x DELPHI … Collins Asymmetries in Belle

  14. Luminosity vs time for 24 hours at KEKB Continuous Injection  Constant Collision Rate high energy ring - beam current HER lifetime low energy ring - beam current LER lifetime ∫Ldt vs day time ∫Ldt =1fb-1/day 24 hours Collins Asymmetries in Belle

  15. Large acceptance, good tracking and particle identification! Collins Asymmetries in Belle

  16. Hadronic Events observed with Belle  1.5 x 109 hadronic events in analysis Off resonance: 29fb-1 , √s=10.52 GeV (published) On resonance: 547fb-1 , √s=10.58 GeV (preliminary) ~ 0.5 Thrust ~ 1 Collins Asymmetries in Belle

  17. Measuring Light Quark Fragmentation Functions on the ϒ(4S) Resonance e+e-qq̅, q∈uds e+e-cc̅ • small B contribution (<1%) in high thrust sample • >75% of X-section continuum under • ϒ(4S) resonance • 29 fb-1 547 fb-1 • several systematic errors reduce with more • statistics • Charm-tagged Data sample also increases 0.5 0.8 1.0 Collins Asymmetries in Belle

  18. Originally off-resonance data, now also on-resonance data (29.1  547 fb-1) Track selection: pT > 0.1GeV vertex cut:dr<2cm, |dz|<4cm Acceptance cut -0.6 < cosqi< 0.9 Event selection: Ntrack  3 Thrust > 0.8 Z1, Z2>0.2 Applied Cuts, Binning z2 1.0 3 6 8 9 0.7 2 5 7 8 0.5 1 5 4 6 0.3 0 1 2 3 0.2 z1 0.2 0.3 0.5 0.7 1.0 • Hemisphere cut • QT < 3.5 GeV • Pion PID selection Collins Asymmetries in Belle

  19. Event Structure at Belle e+e- CMS frame: Near-side Hemisphere: hi , i=1,Nn with zi e- <Nh+,-> = 6.4 Q e+ Jet axis: Thrust Spin averaged cross section: far-side hemisphere: hj , j=1,Nf with zj Collins Asymmetries in Belle

  20. Collins Fragmentation: Angles and CrossSection: cos(f1+f2) Method (e+e- CMS frame) Observable: yield, N12(φ1+φ2)of π+π- pairs j2-p e- Q j1 j2 j1 e+ 2-hadron inclusive transverse momentum dependent cross section: Net anti-alignment of transverse quark spins Collins Asymmetries in Belle

  21. Collins Fragmentation: Angles and Cross Sectioncos(2f0) Method (CMS Frame) Observable: yield, N0(2φ0) of π+π- pairs e- Q Independent of thrust-axis Convolution integralI over transverse momenta [Boer,Jakob,Mulders:NPB504(1997)345] j0 e+ 2-hadron inclusive transverse momentum dependent cross section: Net anti-alignment of transverse quark spins Collins Asymmetries in Belle

  22. Complication: Radiative Contribution to the Di-Hadron Cross Section same cos(2Φ0) dependence as Collins effect … QT e- e+ Frame: z1 z2 Collins Asymmetries in Belle

  23. Examples of Fits to Azimuthal Asymmetries 2a0 R0 R12 2a12 N0(f0)/<N0> N12(Φ1+Φ2)/<N12> 2f0 (f1+f2) a0 and a12contain Collins + radiative effects + acceptance effects D1 : spin averaged fragmentation function, H1: Collins fragmentation function Collins Asymmetries in Belle

  24. Large Radiative and Acceptance Effects ! Example: a0 for unlike-sign pion pairs: a0U generated uds-MC vs reconstructed uds-MC vs data (Difference MC-data: charm contribution) a0 for like-sign pion pairs: a0L generated uds-MC vs reconstructed uds-MC vs data (Difference MC-data: charm contribution) generated uds-MC reconstructed uds-MC data generated uds-MC reconstructed uds-MC data Collins Asymmetries in Belle

  25. Method to eliminate gluon contributions: Double ratios for unlike- and like sign pions (I) radiative effects are charge independent and cancel. (II) Acceptance effects cancel. (III) RUL and RL depend depend on Hfav and Hdis differently.  A12 retains sensitivity for the Collins effect! Cross checked against subtraction RUL-RL with identical results. Form double ratios for unlike and like-sign pion pairs: Collins Asymmetries in Belle

  26. Unlike-sign pion pairs (U): (favored x favored + unfavored x unfavored) Like-sign pion pairs (L): (favored x unfavored + unfavored x favored) p±p0 pairs (favored + unfavored) x (favored + unfavored) A. Efremov et al. ([hep-ph/0603054]): charged pp pairs are similar (and easier to handle) (C): (favored + unfavored) x (favored + unfavored) Two Double Ratios Double ratios unlike/like-sign not very sensitive in separating favored and disfavored Collins functions  look at unlike-sign/charge-sum UL UC Observables: A12(UL), A12(UC) A0(UL) , A0(UC) published and input to fit by Anselmino et al. Collins Asymmetries in Belle

  27. Consistency Checks for Double Ratio (0) Check that Monte Carlo Double asymmetries are 0. (1) Calibrate with “known” physics asymmetry: Weak decays produce azimuthal asymmetries. Showed that double ratio method give correct asymmetry for tau-sample. (2) Comparison of Double Ratio with Subtraction Method leads to identical results. (3) Observe polar angle dependence (4) Smaller asymmetry for lower thrust sample (5) Null tests: (a) mixed events give 0 asymmetry (b) single side asymmetries average to 0 Collins Asymmetries in Belle

  28. Double Ratios From Monte Carlo Monte Carlo knows Radiative and accep- tance effects! Do they cancel in the final double ratio? Assign largest observed average MC double ratio + statistical error as systematic error <A0UL>=0.0013∓0.0009  0.0022 Collins Asymmetries in Belle

  29. Nonzero quark polarization ~ sin2 q Unpolarized de-nominator ~ 1+cos2q Clear linear behavior seen when using either thrustz or 2nd hadron as polar angle Better agreement for thrust axis (~approximate quark axis) UC plots similar Collins Asymmetries: sin2q/(1+cos2q) Binning (UL) PRELIMINARY thrustz q2 Collins Asymmetries in Belle

  30. Beam Polarization zero? cos(2f) asymmetries for jets or gg False asymmetries from weak decays  estimate charm contribution through D tagging False asymmetries from misidentified hemispheres  QT or polar angle cut False asymmetries from acceptance Cancels in double ratios, can be estimated in charge ratios from data, fiducial cuts Correlations from decays lower z cut Other Experimental Issues Collins Asymmetries in Belle

  31. Significant non-zero asymmetries Rising behavior vs. z UL/C asymmetries about 40-50% of UL/L asymmetries First direct measurements of the Collins function UL/L data published Final Charm Corrected Results for e+ e-p p X (29fb-1, off-resonance Data) Phys.Rev.Lett.96:232002,2006 Collins Asymmetries in Belle

  32. Significance largely increased Behavior unchanged Reduced systematics Precise measurements of the Collins function Preliminary Charm Corrected Results for e+ e-p p X (547 fb-1,on-resonance) Preliminary Collins Asymmetries in Belle

  33. Tau contributions PID systematics* MC double ratios Charged ratios (p+p+ /p-p- ) Higher order terms Double ratio-subtraction method Improved Systematic Errors (UC) A0 (cos(2f0)) moments A12 (cos(f1 +f2)) moments Reweighting asymmetries: underestimation of cos(f1+f2) asymmetries rescaled by 1.21 Correlation studies: statistical errrors rescaled by 1.02 (UL) and 0.55 (UC) Collins Asymmetries in Belle

  34. 547 fb-1 charm corrected data sample, UL and UC double ratios Collins Asymmetries I: 4x4 z1, z2 binning A0 (cos(2f0)) moments A12 (cos(f1 +f2)) moments PRELIMINARY PRELIMINARY Collins Asymmetries in Belle

  35. First QCD Analysis of SIDIS + e+e- ! Anselmino, Boglione, D’Alesio, Kotzinian, Murgia, Prokudin, Turk Phys. Rev. D75:05032,2007 Fit includes: HERMES SIDIS + COMPASS SIDIS + Belle e+e- transversity dist. + Collins FF Collins Asymmetries in Belle

  36. Observation of large azimuthal asymmetries in light quark frag-mentation. Updated statistics: ∫Ldt = 29 fb-1  547 fb-1 Double ratios reliably cancel contributions from detector acceptance and gluon radiation. Important input for the transverse spin physics programs at RHIC, HERMES, COMPASS and JLab. Fundamental test case for QCD at soft scales! Summary & Outlook • Future spin dependent FFs:  update Collins FF  measure pT dependence  interference fragmentation  Collins FF for VMs  Lambdas • Precision measurement of spin averaged fragmentation func-tions as input to RHIC program with inclusive hadrons and future precision measurements in SIDIS. Collins Asymmetries in Belle

  37. Motivation ∆G from QCD Analysis of ALL for inclusive hadrons: π0,+,-, η, K+,- PHENIX π0 cross section a |η|<0.35 Phys.Rev.Lett.91:241803,2003 Idea: QCD analysis of LEP and Belle data will fix uncertainty in know- ledge of FFs (gluon FF, flavor separation) Deviation connected to uncertainties in FFs  gluon FF! Collins Asymmetries in Belle

  38. What is Known Experimentally in e+e- ? Hirai, Kumano, Nagai, Sudo hep-ph/0612009 (including errors!) Earlier work: Kretzer Binnewies, Potter, Albino Kniehl, Kramer, Potter Albino, Kniehl, Kramer Most recent work: De Florian, Sassot, Stratmann Collins Asymmetries in Belle

  39. Input also for precision measurements of quark helicity distributions in SIDIS, in particular at a possible future electron- polarized proton collider. Belle Impact on the Knowledge of FFs Belle: Charged h+/-, pions, kaons, protons Compilation of data available for the char- ged hadron FF FF • h+,- • pions • kaons • protons Belle MC FF <1% of data sample work in progress precision at high z! Collins Asymmetries in Belle

  40. Reduced asymmetries in low thrust sample At low thrust significant B contribution (for t<0.8 ~20 % B for t>0.8 < 1 % B) A12 thrust axis dependent High QT (>3.5 GeV) asymmetries from beam related BG UC plots similar Collins Asymmetries III: QT Binning (UL) PRELIMINARY Thrust>0.8 Thrust<0.8 (not corrected for heavy quark contributions) Collins Asymmetries in Belle

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