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Measurement of (Interference) Fragmentation Functions in e + e - at

Measurement of (Interference) Fragmentation Functions in e + e - at. a nd Di-Hadron Correlations a nd . Anselm Vossen. DiFF Mini Workshop Pavia, Italy, September 5 th - 8 th 2011 . Outline. IFF measurements at Belle Observables Kinematic Distributions

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Measurement of (Interference) Fragmentation Functions in e + e - at

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  1. Measurement of (Interference) Fragmentation Functions ine+e- at and Di-Hadron Correlations and Anselm Vossen DiFF Mini Workshop Pavia, Italy, September 5th - 8th 2011

  2. Outline • IFF measurements at Belle • Observables • Kinematic Distributions • Flavor decomposition (Charm Contributions) • Results • Future Plans • Phenix • Experiment • Results • Star • Current status • Future possibilities

  3. Interference FF in Quark Fragmentation q Interference Fragmentation Function: Fragmentation of a transversely polarized quark q into two spin-less hadron h1, h2 carries an azimuthal dependence:

  4. Spin Dependent FF in e+e- : Need Correlation between Hemispheres ! • Quark spin direction unknown: measurement of • Interference Fragmentation function in one hemisphere is not possible • sin φ modulation will average out. • Correlation between two hemispheres with • sin φRi single spin asymmetries results in • cos(φR1+φR2) modulation of the observed di-hadron • yield. • Measurement of azimuthal correlations for di-pion pairs • around the jet axis in two-jet events!

  5. z2 z1 Measuring di-Hadron Correlations In e+e- Annihilation into Quarks • Interference 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 • momenta. • Hermetic detector • Observable:cos(φR1+φR2) modulation measures electron q1 φR1 φR2 q2 quark-2 spin quark-1 spin z1,2 relative pion pair momenta positron

  6. KEKB: L>2.11 x 1034cm-2s-1 !! Belle detector KEKB • Asymmetric collider • 8GeV e- + 3.5GeV e+ • √s = 10.58GeV (U(4S)) • e+e-U(4S)BB • Off-resonance production: 10.52 GeV • e+e-qq (u,d,s,c) • Integrated Luminosity: > 1000 fb-1 • >70 fb-1 => continuum 6

  7. He/C2H6 Large acceptance, good tracking and particle identification!

  8. Interference Fragmentation–thrust method • e+e- (+-)jet1()jet2X • transverse spin projection 2 q 1 8

  9. Similar to previous method Observe angles j1R+j2R between the event-plane (beam, two-pion-axis) and the two two-pion planes. Theoretical guidance by Boer,Jakob,Radici Interference Fragmentation – “f0“ method jR2 p-jR1

  10. Cuts and Binning Similar to Collins analysis, full off-resonance and on-resonance data (7-55): ~73 fb-1 + 588 fb-1 Visible energy >7GeV PID: Purities in for di-pion pairs > 90% Same Hemisphere cut within pair (p+p-), opposite hemisphere between pairs All 4 hadrons in barrel region: -0.6 < cos (q) <0.9 Thrust axis in central area: cosine of thrust axis around beam <0.75 Thrust > 0.8 to remove B-events  < 1% B events in sample zhad1,had2>0.1 z1 = zhad1+zhad2 and z2 in 9x9 bins mpp1 and mpp2 in 8x8 bins: [0.25 - 2.0] GeV New: Mixed binning

  11. Kinematics

  12. Opening Cut and Energy Flow Opening Cut of 0.8 Opening Cut of 0.9

  13. Zero tests: MC No opening cut Opening cut>0.7 Opening cut >0.8 Ph 13 A small asymmetry seen due to acceptance effect Mostly appearing at boundary of acceptance Opening cut in CMS of 0.8 (~37 degrees) reduces acceptance effect to the sub-per-mille level

  14. (z1x m1) Binning arXiv:1104.2425 PRL 107, 072004(2011)

  15. (m1x z1) Binning arXiv:1104.2425 PRL 107, 072004(2011)

  16. Subprocess contributions (MC) 8x8 m1 m2 binning tau contribution (only significant at high z) charged B(<5%, mostly at higher mass) Neutral B (<2%) charm( 20-60%, mostly at lower z) uds (main contribution)

  17. Subprocess contributions (MC) 9x9 z1 z2 binning tau contribution (only significant at high z) charged B(<5%, mostly at higher mass) Neutral B (<2%) charm( 20-60%, mostly at lower z) uds (main contribution)

  18. Accessing QCD vacuum fluctuations in Quark Fragmentation • QCD vacuum is superposition of theta vacua • On microscopic scale this could be accessible in experiments • First results in STAR • Planned measurements in Belle: • Needed as a ‘tie breaker’ • Model Calculations predict 2% effect • Access to nonperturpative properties of QCD • Transition instantons/sphalerons: Role in Early Universe, baryogenesis …

  19. Event Topology electron p- p+ q1 z2 z1 q2 Jet Axis quark-1 spin quark-2 spin : Spin : Momentum z1,2 relative pion momenta positron • Fragmentation in P-odd bubble leads to left right asymmetry • Difference in ‘Winding number’ gives effective increment in chirality • Spin alignment via chromomagnetic effect • Azimuthal event by event modulation • Measurement: Extract width of distribution of first moments • Analysis already underway: Is there a Di-hadron Analogue?

  20. Currently underway: • Belle II is a significant upgrade to Belle and will sample 2 orders of magnitude higher luminosity • High precision data will enable measurement of • P-odd FFs • Transverse momentum dependent FFs • Charm suppression possible • IU will develop FEE for Barrel KLM detector crucial for high precision FF measurement of identified particles

  21. Belle Fragmentation activity Black: about to start Green: ongoing Grey: finished

  22. Same Hemisphere Correlations? • Motivation: P-odd FF x Collins (in Single hadron) does not average out

  23. p+p complementary and increased kinematic reach in x, z • Kinematic reach of SIDIS data • Kinematic reach in p+p for single pions at 3<eta<4 • Relative hadron momentum z for p+p (3<eta<4) collisions and SIDIS (COMPASS), only single hadron, di-hadron z1+z2 ‘less different’ PT PT z pt Mean z: 0.64

  24. Definition of Vectors and Angles Bacchetta and Radici, PRD70, 094032 (2004)

  25. PHENIX Detectors used for IFF Analysis • Use 2 separate spectrometer arms at central rapidity,|h| < 0.35 • Azimuthal coverage: 90° + 90° • Electromagnetic Calorimeters • PbSC + PbGl • High granularity DhDf=0.010.01 • Tracking of charged particles • Drift chamber, pad chambers Little p_t dependence of x at mid rapidity, low x

  26. vs Invariant Mass of the Pair First measurement of IFF in pp Results and Projections From run 12+13

  27. Planned Transversity measurements at STAR • Measurements with current detector • Transversity in Di-Hadron correlations • p0 in FMS and Encap, p+ /p-inTPC • Sivers effect in jets in EEMC • Explore jet –jet and gamma –jet asymmetries Full azimuth spanned with nearly contiguous electromagnetic calorimetry from -1<h<4  approaching full acceptance detector

  28. FMS R&D for planned STAR forward upgrade ~ 6 GEM disks Tracking: 2.5 < η < 4 • Forward instrumentation optimized for p+A and transverse spinphysics • Charged Tracking upgrade covering FMS will enable di-hadron measurements and jet measurements • Star decadal plans calls additionally for PID (e.g. RICH) and pi0/gamma separation (preshower) • Transverse spin effect dominated by valence quarks accessed in forward direction proton nucleus

  29. Projections forBelle Measurements of IFF in STAR, Channel: (p+p0) (p+p0) a12 0.002 Hadron pair in second hemisphere: 0.77 GeV <Minv< 1.2 GeV 0 -0.002 -0.004 (580 fb-1 integrated luminosity) Errors one order of magnitude smaller than average asymmetry in (p+p-)

  30. Measuring Light Quark Fragmentation Functions on the ϒ(4S) Resonance e+e-qq̅, q∈uds 4s “off” e+e-cc̅ • small B contribution (<1%) in high thrust sample • >75% of X-section continuum under • ϒ(4S) resonance • 73 fb-1 662 fb-1 0.5 0.8 1.0 31

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