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Recent Results in Spin Physics at and

Recent Results in Spin Physics at and . Anselm Vossen Center for Exploration of Energy and Matter. (Re)Stating the Obvious: Motivation for Studying Q C D. QCD successful in describing high energy reactions BUT No consistent description of hadronic sector

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Recent Results in Spin Physics at and

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  1. Recent Results in Spin Physics at and Anselm Vossen Center for Exploration of Energy and Matter

  2. (Re)Stating the Obvious: Motivation for Studying QCD • QCD successful in describing high energy reactions • BUT No consistent description of hadronic sector • Many phenomena that are not understood • No consistent description of fundamental bound state of the theory • Compare to QED: • Bound state: QED: atom • Stringent tests of QED from study of spin structure of hydrogen • g-2 of the electron • Lamb shift (Nobel prize 1955) • Vacuum effects: Polarization, Casimir • Atomic physics • QCD: • Phenomena fundamentally richer • Fundamental bound state proton • QCD binding energy : most of the visible energy in the universe • Nucleon Sea, Theta vacua transitions related to EW Baryogenesis • Use transverse spin to study QCD on amplitude level with interference • Tools: Light source p-p Collider

  3. (Re)Stating the Obvious: Motivation for Studying QCD Millenium Prize • QCD successful in describing high energy reactions • BUT No consistent description of hadronic sector • Many phenomena that are not understood • No consistent description of fundamental bound state of the theory • Compare to QED: • Bound state: QED: atom • Stringent tests of QED from study of spin structure of hydrogen • g-2 of the electron • Lamb shift (Nobel prize 1955) • Vacuum effects: Polarization, Casimir • Atomic physics • QCD: • Phenomena fundamentally richer • Fundamental bound state proton • QCD binding energy : most of the visible energy in the universe • Nucleon Sea, Theta vacua transitions related to EW Baryogenesis • Use transverse spin to study QCD on amplitude level with interference • Tools: Light source p-p Collider

  4. RHIC: The QCD Machine • Outline • RHIC and the STAR detector • Highlights of the longitudinal Spin Program at STAR • Gluon Polarization • Sea Quark Polarization • Transverse polarization of quarks in the proton • Measuring Spin Dependent Fragmentation Functions in e+e- at Belle

  5. RHIC: The QCD Machine Absolute Polarimeter (H jet) RHIC pCPolarimeters ANDY/ BRAHMS E-Lens and Spin Flipper Siberian Snakes Siberian Snakes PHENIX STAR Spin Rotators (longitudinal polarization) Spin Rotators (longitudinal polarization) Pol. H- Source LINAC EBIS BOOSTER Helical Partial Siberian Snake AGS 200 MeV Polarimeter AGS pC Polarimeter Strong AGS Snake • Versatility: • Polarized p+pSqrt(s) collisions at 62.4 GeV, 200 GeV and 500 GeV • Recent Spin Runs: • 2011 500 GeV, longitudinal at Phenix, transverse at STAR ~30 pb-1 sampled • 2012 200 GeV, Phenix and STAR, transverse ~20 pb-1 sampled (STAR: ~x10 statistics)

  6. STAR

  7. The STAR Detector in 2010 Time Projection Chamber (TPC) Charged Particle Tracking |η|<1.3 Endcap Electromagnetic Calorimeter: 1<η<2 Forward EMC 2<η<4 Barrel Electromagnetic Calorimeter (BEMC): |η|<1 h = - ln(tan(q/2))

  8. Central Region (-1<h<1) • Identified Pions, h • Jets • Endcap (1<eta<2) • Pi0, eta, (some) jets • FMS (2<eta<4) • Pi0, eta Full azimuth spanned with nearly contiguous electromagnetic calorimetry from -1<h<4  approaching full acceptance detector PID (Barrel) with dE/dx, in the future: ToF pi/K separation up to 1.9 GeV

  9. 10 20 30 pT(GeV) Proton Spin Structure with Quark and Gluon Probes at ultra-relativistic energies the proton represents a beam of quark and gluon probes jet Hard Scattering Process Dominates at RHIC: Jet production provides directprobe of gluon content

  10. DG2 DGDq Dq2 Gluon Polarization Measurement Polarized DIS: ~ 0.3 Poorly constrained Hard Scattering Process The related double spin asymmetry: experimental double spin asymmetry DIS pQCD ? Dominates at RHIC ~ probe gluon content in jet production

  11. Jets: Proven Capabilities in p+p, pQCD regime B.I. Abelev et al. (STAR Coll.), Phys.Rev.Lett. 97, 252001, 2006 SPIN-2010: Matt Walker/Tai Sakuma, for the collaboration Jets well understood in STAR, experimentally and theoretically

  12. STAR Improved precision from 2006 to 2009 Substantially larger figure of merit (P4 x L) than in all previous runs combined

  13. New global analysis with 2009 RHIC data Special thanks to the DSSV group! DSSV++ is a new, preliminary global analysis from the DSSV group that includes 2009 ALL measurements from PHENIX and STAR First experimental evidence of non-zero gluon polarization in the RHIC range (0.05 < x < 0.2)

  14. Probing sea quark polarization through Ws • Weak interaction process • Only left-handed quarks • Only right-handed anti-quarks • Perfect spin separation Parity violating single helicity asymmetry AL • Complementary to SIDIS measurements • High Q2 ~ MW2 • No fragmentation function effects

  15. Δu Δd High precision W asymmetry era PHENIXandSTAR through 2013 run First preliminary results from 2012 already provide substantial sensitivity Future results will provide a dramatic reduction in the uncertainties

  16. Discovery of Large Asymmetries in p+p Test of QCD: Asymmetries for transverse spin are small at high energies (Kane, Pumplin, Repko, PRL 41, 1689–1692 (1978) ) Experiment (E704, Fermi National Laboratory): π+ π0 π-

  17. Discovery of Large Asymmetries in p+p Test of QCD: Asymmetries for transverse spin are small at high energies (Kane, Pumplin, Repko, PRL 41, 1689–1692 (1978) ) Experiment (STAR, Brookhaven National Laboratory): Effect persists at high energies (pQCD valid)

  18. Possible AN Explanations: Transverse Momentum Dep. Distributions Sivers Effect:Introduce transverse momentum of parton relative to proton. Collins Effect:Introduce transverse momentum of fragmenting hadron relative to parton. SP SP kT,p p p p p Sq kT,π Correlation between Proton spin (Sp) and parton transverse momentum kT,p Correlation between Proton spin (Sp) and quark spin (Sq) + spin dep. frag. function Intrinsic transverse momentum challenges Current QCD framework Number of Citations:

  19. Possible AN Explanations: Transverse Momentum Dep. Distributions Sivers Effect:Introduce transverse momentum of parton relative to proton. Collins Effect:Introduce transverse momentum of fragmenting hadron relative to parton. SP SP kT,p p p p p Talk about this next time;-) Sq kT,π Next Time Correlation between Proton spin (Sp) and parton transverse momentum kT,p Correlation between Proton spin (Sp) and quark spin (Sq) + spin dep. frag. function Intrinsic transverse momentum challenges Current QCD framework Number of Citations:

  20. Parton Distribution Functions The three leading order, collinear PDFs q(x) f1q (x) unpolarized PDF quark with momentumx=pquark/pprotonin a nucleon well known – unpolarized DIS helicity PDF quark with spin parallel to the nucleon spinin a longitudinally polarized nucleon known – polarized DIS q(x) g1q(x) transversity PDF quark with spin parallel to the nucleon spin in a transversely polarized nucleon Helicity – transversity: direct measurement of the nonzero angular momentum components in the protons wavefunction Tq(x) h1q(x) chiral odd, poorly known Cannot be measured inclusively

  21. γ* e- u,d,s   + + + + Probability to Find Polarized Quark Optical Theorem: s=-Im(Aforward scattering)

  22.    ↑ ↓ ↓ ↑ ↑ ↑ ↑ ↑ Transversity is Chiral Odd • Transversity base:   _ _ + = _ + Difference in densities for ↑, ↓ quarks in ↑ nucleon • Helicity base: chiral odd • Needs chiral odd partnerFragmentation Function • Does not couple to gluons adifferent QCD evolution than g1(x) • Valence dominatedaTensor charge gT comparable to Lattice calculations

  23. _ Chiral odd FFs Collins effect + * * _ + q N _ + : Collins FF

  24. Lz Lz-1 _ Chiral odd FFs Interference Fragmentation Function + * * _ + q N _ +

  25. Collins effect in quark fragmentation J.C. Collins, Nucl. Phys. B396, 161(1993) q Collins Effect: Fragmentation with of a quark qwith spin sqinto a spinless hadron h carries an azimuthal dependence:

  26. Mid-Rapidity Collins Asymmetry Analysis at STAR • STAR provides the full mid-rapidity jet reconstruction and charged pion identification • Look for spin dependent azimuthal distributions of charged pions inside the jets! First proposed by F. Yuan in Phys.Rev.Lett.100:032003. • Measure average weighted yield: pbeam S⊥ ΦS pπ jT Φh –pbeam PJET

  27. Mid-rapidity Collins analysis Run 12 Projections

  28. 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:

  29. Di-Hadron Correlations : Angle between polarisation vector and event plane Bacchetta and Radici, PRD70, 094032 (2004)

  30. c b X Interference Fragmentation Function in p-p fR-fS X a fS : Angle between polarisation vector and event plane

  31. NEW: STAR shows significant Signal!

  32. Strong Rapidity Dependence • STAR upgrades will cover h<2 in the near future • <xBj>0.25 (current)0.45: Not probed in SIDIS yet! • Proposed Forward upgrade:h<4 p+/p- p+/p- Additional precision data from last years run + increased kinematic reach Explore p0/p+-channels

  33. Spin Dependent FF in e+e- : Need Correlation between Hemispheres ! • Asymmetry is • Need fragmentation function • 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!

  34. z2 z1 Measuring spin dependent FFs in e+e- Annihilation into Quarks • Spin dependence in e+e- • quark fragmentation • will lead to (azimuthal) • asymmetries in • correlation measurements! • Experimental requirements: • Small asymmetries  • very large data sample! • Good particle ID to high • momenta. • Hermetic detector electron q1 q2 quark-2 spin quark-1 spin z1,2 relative pion pair momenta positron Here for di-hadron correlations:

  35. Measurement of Fragmentation Functions @ • KEKB: L>2.11 x 1034cm-2s-1 • Asymmetric collider: • 8GeV e- + 3.5 GeV e+ • √s=10.58 GeV ((4S)) • e+e-(4S)BB • Integrated Luminosity: > 1000 fb-1 • Continuum production: 10.52 GeV • e+e-(u, d, s, c) • >70 fb-1 => continuum Belle detector KEKB Anselm Vossen 35 35

  36. He/C2H6 Large acceptance, good tracking and particle identification! Collins Asymmetries in Belle 36 36

  37. 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 • ~100 fb-1~1000 fb-1 0.5 0.8 1.0

  38. Interference Fragmentation– thrust method e+e-(p+p-)jet1(p+p-)jet2X Find pion pairs in opposite hemispheres Observe angles j1+j2between the event-plane (beam, jet-axis) and the two two-pion planes. Theoretical guidance by papers of Boer,Jakob,Radici[PRD 67,(2003)] and Artru,Collins[ZPhysC69(1996)] Early work by Collins, Heppelmann, Ladinsky [NPB420(1994)] j2-p p-j1 • Model predictions by: • Jaffe et al. [PRL 80,(1998)] • Radici et al. [PRD 65,(2002)]

  39. Transverse Spin Dependent FFs: Cuts and Binning • Full off-resonance and on-resonance data (7-55): ~73 fb-1 + 588 fb-1 • Visible energy >7GeV • PID: Purities in for pion pairs > 90% • Opposite hemisphere between pairs pions • All 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 >0.2

  40. Asymmetry extraction Amplitude a12 directly measures ( IFF ) x ( -IFF ) (no double ratios) • Build normalized yields: • Fit with: or

  41. (z1x m1) Binning arXiv:1104.2425 AV et. al, PRL 107, 072004(2011)

  42. (m1x z1) Binning arXiv:1104.2425 AV et. al, PRL 107, 072004(2011)

  43. Comparison to theory predictions Red line: theory prediction + uncertainties Blue points: data • Mass dependence : Magnitude at low masses comparable, high masses • significantly larger (some contribution possibly from charm ) • Z dependence : Rising behavior steeper

  44. 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)

  45. Measurement at Belle leads to first point by point extraction of Transversity M. Radici at FF workshop, RIKEN, 11/2012 See also: Courtoy: Phys. Rev. Lett. 107:012001,2011 Is Soffer Bound violated? h(x)<|f(x)+g(x)|/2

  46. Handedness Correlations   Thrust direction L R   L/R

  47. QCD Vacuum Transitions carry Chirality QN The QCD Vacuum Difference in winding number: Net chirality carried by Instanton/Sphaleron • Vacuum states are characterized by “winding number” • Transition amplitudes: Gluon configurations, carry net chirality • e.g. quarks: net spin momentum alignment • Similar mechanism to EW baryogenesis

  48. QCD Vacuum Transitions carry Chirality QN arXiv:0909.1717v2 [ Kharzeev, McLerran and Warringa, arXiv:0711.0950, Fukushima, Kharzeev and Warringa, arXiv:0808.3382

  49. Handedness Correlations Expect negative correlation for local p-odd effect   Thrust direction L R Q=1   L/R

  50. q Unpolarized Fragmentation Functions Precise knowledge of upol. FFs necessary for virtually all SIDIS measurements e- γ* e+ q h First FF extraction including uncertainties (e+e-):Hirai, Kumano, Nagai, Sudoh (KEK)Phys. Rev. D 75, 094009 (2007) Dπ+i

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