Report

Recent Results in Spin Physics at and Anselm Vossen Center for Exploration of Energy and Matter (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 (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 RHIC: The QCD Machine 4 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 RHIC: The QCD Machine Absolute Polarimeter (H jet) RHIC pC Polarimeters ANDY/ BRAHMS E-Lens and Spin Siberian Snakes Flipper Siberian Snakes PHENIX STAR Spin Rotators (longitudinal polarization) Pol. H Source LINAC BOOSTER EBIS Spin Rotators (longitudinal polarization) AGS 200 MeV Polarimeter Helical Partial Siberian Snake AGS pC Polarimeter Strong AGS Snake Versatility: • Polarized p+p Sqrt(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) STAR 6 The STAR Detector in 2010 Time Projection Chamber (TPC) Charged Particle Tracking |η|<1.3 7 Endcap Electromagnetic Calorimeter: 1<η<2 Forward EMC 2<η<4 Barrel Electromagnetic Calorimeter (BEMC): |η|<1 h = - ln(tan(q/2)) 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 8 PID (Barrel) with dE/dx, in the future: ToF pi/K separation up to 1.9 GeV Proton Spin Structure with Quark and Gluon Probe at ultra-relativistic energies the proton represents a beam of quark and gluon probes Hard Scattering Process P1 jet x 1 P1 x 2 P2 P2 9 10 20 Dominates at RHIC: Jet production provides direct probe of gluon content 30 pT(GeV) Gluon Polarization Measurement Polarized DIS: ~ 0.3 Poorly constrained Hard Scattering Process P1 The related double spin asymmetry: x 1 P1 x 2 P2 A LL P2 10 G2 Gq q2 Dominates at RHIC ~ probe gluon content in jet production N jet N jet N jet N jet experimental double spin asymmetry a LL ( qg qg ) pQCD a LL ( gg gg )... G ( x1 ) G ( x1 ) ? A1 ( x 2 ) DIS 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 Improved precision from 2006 to 2009 12 STAR Substantially larger figure of merit (P4 x L) than in all previous runs combined New global analysis with 2009 RHIC data Special thanks to the DSSV group! 13 DSSV++ is a new, preliminary global analysis from the DSSV group that includes 2009 ALL measurements from PHENIX and STAR 0 .2 0 . 05 0 . 06 g ( x , Q 10 GeV ) dx 0 . 10 0 .07 2 2 First experimental evidence of non-zero gluon polarization in the RHIC range (0.05 < x < 0.2) Probing sea quark polarization through Ws 14 ud W l u d W l Weak interaction process Only left-handed quarks Only right-handed anti-quarks Perfect spin separation Parity violating single helicity asymmetry AL A W L d ( x 1 ) u ( x 2 ) u ( x 1 ) d ( x 2 ) A W L u( x1 )d ( x 2 ) d ( x1 )u( x 2 ) • Complementary to SIDIS measurements – High Q2 ~ MW2 – No fragmentation function effects High precision W asymmetry era Δu 15 PHENIX and STAR through 2013 run Δd First preliminary results from 2012 already provide substantial sensitivity Future results will provide a dramatic reduction in the uncertainties 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) ) AN mq example, s m q 3 MeV , s 20 GeV , A N 10 Experiment (E704, Fermi National Laboratory): pp X π+ π0 s 20 GeV Observable : AN 1 R πL P R L 4 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) ) AN mq example, s m q 3 MeV , s 20 GeV , A N 10 Experiment (STAR, Brookhaven National Laboratory): pp Observable X : AN 1 R L P R L Effect persists at high energies (pQCD valid) 4 Possible AN Explanations: Transverse Momentum Dep. Distributions Sivers Effect: Collins Effect: Introduce transverse momentum of parton Introduce transverse momentum of relative to proton. fragmenting hadron relative to parton. SP SP kT,p p p p p Sq Correlation between Proton spin (Sp) and parton transverse momentum kT,p Number of Citations: kT,π Correlation between Proton spin (Sp) and quark spin (Sq) + spin dep. frag. function Intrinsic transverse momentum challenges Current QCD framework 18 Possible AN Explanations: Transverse Momentum Dep. Distributions Sivers Effect: Collins Effect: Introduce transverse momentum of parton Introduce transverse momentum of relative to proton. fragmenting hadron relative to parton. SP SP kT,p p p Talk about this next time;-) p p Sq Correlation between Proton spin (Sp) and parton transverse momentum kT,p Number of Citations: kT,π Correlation between Proton spin (Sp) and quark spin (Sq) + spin dep. frag. function Intrinsic transverse momentum challenges Current QCD framework 19 Parton Distribution Functions The three leading order, collinear PDFs q(x) f1q (x) q(x) g1q(x) unpolarized PDF quark with momentum x=pquark/pproton in a nucleon well known – unpolarized DIS helicity PDF quark with spin parallel to the nucleon spin in a longitudinally polarized nucleon known – polarized DIS transversity PDF Tq(x) h1q(x) 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 chiral odd, poorly known Cannot be measured inclusively 20 Probability to Find Polarized Quark 21 e- γ* u,d,s Optical Theorem: =-Im(Aforward scattering) + + + + Transversity is Chiral Odd • Transversity base: ↑ ↑ ↑ _ ↑ ↓ ↑ ↓ ↑ + + _ h1 _ Difference in densities for ↑, ↓ quarks in ↑ nucleon • Helicity base: chiral odd • Needs chiral odd partnerFragmentation Function • Does not couple to gluons adifferent QCD evolution than g1(x) • Valence dominateda Tensor charge gT = − comparable to Lattice calculations 22 Chiral odd FFs 23 Collins effect * H + + + : Collins FF _ _ q N 1 h1 _ * Chiral odd FFs 24 Interference Fragmentation Function * Lz H + + 1 _ _ q N + Lz-1 h1 _ ( ) * Collins effect in quark fragmentation J.C. Collins, Nucl. Phys. B396, 161(1993) sq q k sq ph ph h, ph k ph : quark momentum : quark spin : hadron momentum : transvers e hadron momentum zh Eh Eq 2 Eh s : relative hadron momentum 25 Collins Effect: Fragmentation with of a quark q with spin sq into a spinless hadron h carries an azimuthal dependence: (k p h s q sin Mid-Rapidity Collins Asymmetry Analysis at STAR S⊥ STAR provides the full mid-rapidity jet reconstruction and charged pion identification pπ Look for spin dependent azimuthal distributions of charged pions inside the jets! First proposed by F. Yuan in Phys.Rev.Lett.100:032003. jT Φh –pbeam Measure average weighted yield: A exp 2 N sin( C )d c PBeam N ΦS pbeam PJET d d 26 UU 1 A N sin( h s ) Mid-rapidity Collins analysis Run 12 Projections Interference FF in Quark Fragmentation sq q =2 / h1 R R h2 : quark momentum :quark spin : momentum difference ℎ1 − ℎ2 transverse hadron momentum difference = / : relative hadron pair momentum : hadron pair invariant mass 28 Interference Fragmentation Function: Fragmentation of a transversely polarized quark q into two spin-less hadron h1, h2 carries an azimuthal dependence: ( k RT s q sin Di-Hadron Correlations p+ p c.m .s. = lab fram e SB P A , P B : m om enta of protons P h1 P B 1 0 0 G eV 29 2RC P h 1 , P h 2 : m om enta of hadrons P C P h1 P h 2 P A 1 0 0 G eV R C ( P h1 P h 2 ) / 2 S B : proton spin orientation PC pp hhX hadron plane: P h 1 , P h 2 scattering plane: P C , P B P h2 R : from scattering plane S : from polarization vector to hadron plane to scattering plane ( S R ) AU T sin( S R ) AU T h1 H 1 : Angle between polarisation vector and event plane Bacchetta and Radici, PRD70, 094032 (2004) Interference Fragmentation Function in p-p R-S / 0 X c h1 p, S / 0 a ˆ b H f1 p X D ( S R ) AU T sin( S R ) AU T h1 H 1 S : Angle between polarisation vector and event plane 30 NEW: STAR shows significant Signal! 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 +/- +/- Additional precision data from last years run + increased kinematic reach 0 Spin Dependent FF in e+e- : Need Correlation between Hemispheres ! o Asymmetry is AU T h1 H 1 o Need fragmentation function o Quark spin direction unknown: measurement of Interference Fragmentation function in one hemisphere is not possible sin φ modulation will average out. o 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-jet33events! Measuring spin dependent FFs in e+e- Annihilation into Quarks electron ( ) z2 ( ) Spin dependence in e+equark fragmentation will lead to (azimuthal) asymmetries in correlation measurements! q1 Experimental requirements: q2 quark-2 spin z1,2 relative pion pair momenta z1 quark-1 spin Small asymmetries very large data sample! Good particle ID to high momenta. Hermetic detector positron Here for di-hadron correlations: 34 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 -1 ●Integrated Luminosity: > 1000 fb ●Continuum production: 10.52 GeV + - (u, d, s, c) ●e e -1 => continuum ●>70 fb ● 35 Anselm Vossen Belle detector KEKB 35 He/C2H6 Large acceptance, good tracking and particle identification! 36 36 Collins Asymmetries in Belle Measuring Light Quark Fragmentation Functions on the ϒ(4S) Resonance 37 e+e-qq̅, q∈uds 4s “off” e+e-cc̅ 0.5 0.8 1.0 • small B contribution (<1%) in high thrust sample • >75% of X-section continuum under ϒ (4S) resonance • ~100 fb-1 ~1000 fb-1 Interference Fragmentation – thrust method e+e- (+-)jet1()jet2X Find pion pairs in opposite hemispheres Observe angles j1+j2 between 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 Ph 1 Ph 2 Ph 1 Ph 2 j1 Model predictions by: •Jaffe et al. [PRL 80,(1998)] •Radici et al. [PRD 65,(2002)] A H 1 (z 1 , m 1 H 1 (z 2 , m 2 cos (j 1 j 2 38 Transverse Spin Dependent FFs: Cuts and Binning 39 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 Asymmetry extraction Build normalized yields: N ( 1 2 ) , N Fit with: a 12 cos( 1 2 ) b12 or a12 cos( 1 2 ) b12 c12 cos 2 (1 2 ) d 12 sin( 1 2 ) Amplitude a12 directly measures ( IFF ) x ( -IFF ) (no double ratios) (z1x m1) Binning arXiv:1104.2425 AV et. al, PRL 107, 072004(2011) 41 (m1x z1) Binning arXiv:1104.2425 AV et. al, PRL 107, 072004(2011) 42 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 43 Subprocess contributions (MC) 44 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) 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 Handedness Correlations Thrust direction L R + × − ⋅ Handedness: ∣ + ∣∣ − ∣ ? = sinΦ > 0 + − − C: + + + L/R Jet handedness: 46 − + 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 QCD Vacuum Transitions carry Chirality QN arXiv:0909.1717v2 [ Kharzeev, McLerran and Warringa, arXiv:0711.0950, Fukushima, Kharzeev and Warringa, arXiv:0808.3382 Handedness Correlations Thrust direction L R Q=1 + × − ⋅ Handedness: ∣ + ∣∣ − ∣ ? = sinΦ > 0 + − − C: + + + L/R Jet handedness: − + Expect negative correlation for local p-odd effect 49 Unpolarized Fragmentation Functions Precise knowledge of upol. FFs necessary for virtually all SIDIS measurements e- q γ* e+ q h Dq First FF extraction including uncertainties (e+e-): Hirai, Kumano, Nagai, Sudoh (KEK) Phys. Rev. D 75, 094009 (2007) h KEKB/BelleSuperKEKB, Upgrade 51 Aim: super-high luminosity ~1036 cm-2s-1 (~40x KEK/Belle) Upgrades of Accelerator (Microbeams + Higher Currents) and Detector (Vtx,PID, higher rates, modern DAQ) Significant US contribution http://belle2.kek.jp First data in 2016 52 Highlights for FF Measurements Kaon efficiency > 95% over relevant kinematics, fake rate < 5% Vertex resolution improved by order of magnitude Obviously more statistics Belle II Status Summary and Outlook RHIC is ideal machine to study gluonic properties of the nucleon First result indicating non-zero Gluon polarization in the proton Sea-quark polarization Investigation in surprising transverse spin effects Transversity in di-hadron Correlations and from Collins effect Investigate high x, high Q2 region Contribution to AN Evolution of kT dependent Collins FF Soffer bound, tensor charge Belle is the ideal machine to study quark fragmentation Unpolarized Fragmentation functions Polarized fragmentation functions in correlation between hemispheres Charged pions and kaons Vector mesons and di-hadrons IFF in charged pion pairs IFF with neutral pions Collins in charged pion pairs Collins in charged kaons, 0, h, vector mesons Theory of transverse single spin asymmetries is developing rapidly Tests will come from upgrades at STAR/PHENIX and Belle II STAR and Belle are in the middle of major upgrades Far Future: eSTAR at eRHIC Backup Jet Reconstruction , p , etc q, g GEANT e , MC Jets Midpoint Cone Algorithm: • Adapted from Tevatron II (hepexp/0005012 • Cone radius = √(Δη2+Δφ2) = 0.7 • Split / Merge fraction = 0.5 PYTHIA Particle Detector Data Jets Anti-KT Algorithm: • Radius = 0.6 • Less sensitive to underlying event affects STAR Detector has: • Full azimuthal coverage • Charged particle tracking from TPC for |η| < 1.3 • E/BEMC provide electromagnetic energy reconstruction for -1 < η < 2.0 STAR well suited for jet 57measurements Spin Decomposition of the Proton Naïve quark model – 3 valence quark 1 1 ( Δu v Δd v Δqs 2 2 Σ 1 ??? CERN, SLAC, DESY, JLAB: S ~ 0.30 QCD: ..additional contributions from gluons and gluon splitting, sea quarks… 1 1 Σ G 2 2 ΔG, Δ/Σ= ? …and orbital angular momentum… 1 JqJ g 2 1 Σ Lq 2 G58 Lg