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

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Presentation on theme: "Recent Results in Spin Physics at and Anselm Vossen Center for Exploration of Energy and Matter."— Presentation transcript:

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 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 Millenium Prize

4 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 Versatility: Polarized p+p Sqrt(s) collisions at 62.4 GeV, 200 GeV and 500 GeV Recent Spin Runs: GeV, longitudinal at Phenix, transverse at STAR ~30 pb -1 sampled GeV, Phenix and STAR, transverse ~20 pb -1 sampled (STAR: ~x10 statistics)

6 STAR 6

7 Time Projection Chamber (TPC) Charged Particle Tracking |η|<1.3 Barrel Electromagnetic Calorimeter (BEMC): |η|<1 Endcap Electromagnetic Calorimeter: 1<η<2  = - ln(tan  2)) The STAR Detector in Forward EMC 2<η<4

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

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

10 10 ~ probe gluon content in jet production The related double spin asymmetry: Gluon Polarization Measurement experimental double spin asymmetry pQCD DIS ? G2G2 GqGq q2q2 Hard Scattering Process Dominates at RHIC Polarized DIS: ~ 0.3 Poorly constrained

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

12 Improved precision from 2006 to Substantially larger figure of merit (P 4 x L) than in all previous runs combined STAR

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

14 Probing sea quark polarization through Ws 14 Weak interaction process  Only left-handed quarks  Only right-handed anti-quarks Perfect spin separation Parity violating single helicity asymmetry A L Complementary to SIDIS measurements –High Q 2 ~ M W 2 –No fragmentation function effects

15 High precision W asymmetry era 15 First preliminary results from 2012 already provide substantial sensitivity Future results will provide a dramatic reduction in the uncertainties ΔuΔuΔdΔd PHENIX and STAR through 2013 run

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) ) π+π+ π-π- π0π0 Experiment (E704, Fermi National Laboratory):

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 A N Explanations: Transverse Momentum Dep. Distributions 18 SPSP k T,p p p SPSP p p SqSq k T, π Sivers Effect: Introduce transverse momentum of parton relative to proton. Collins Effect: Introduce transverse momentum of fragmenting hadron relative to parton. Correlation between Proton spin (S p ) and quark spin (S q ) + spin dep. frag. function Correlation between Proton spin (S p ) and parton transverse momentum k T,p Number of Citations: Intrinsic transverse momentum challenges Current QCD framework

19 Possible A N Explanations: Transverse Momentum Dep. Distributions 19 SPSP k T,p p p SPSP p p SqSq k T, π Sivers Effect: Introduce transverse momentum of parton relative to proton. Collins Effect: Introduce transverse momentum of fragmenting hadron relative to parton. Correlation between Proton spin (S p ) and quark spin (S q ) + spin dep. frag. function Correlation between Proton spin (S p ) and parton transverse momentum k T,p Talk about this next time;-) Number of Citations: Intrinsic transverse momentum challenges Current QCD framework

20 20 The three leading order, collinear PDFs Parton Distribution Functions q(x) f 1 q (x)  q(x) g 1 q (x)  T q(x) h 1 q (x) chiral odd, poorly known Cannot be measured inclusively unpolarized PDF quark with momentum x=p quark /p proton 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 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

21 21 Probability to Find Polarized Quark γ*γ*γ*γ* u,d, s e-e-e-e- Optical Theorem:  =- I m( A forward scattering ) + ++   +

22 22 Transversity is Chiral Odd _ + _   + ↑ ↑↑   ↑ ↓ ↑↑   ↓  _ Difference in densities for ↑, ↓ quarks in ↑ nucleon Transversity base :

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

24 24 Chiral odd FFs + _ + _   + q N _ L z -1LzLz Interference Fragmentation Function

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

26 26 Mid-Rapidity Collins Asymmetry Analysis at STAR ΦhΦh –p beam p beam S⊥S⊥ pπpπ P JET jTjT ΦSΦS  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:  Measure average weighted yield:

27 Run 12 Projections Mid-rapidity Collins analysis

28 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 29 Bacchetta and Radici, PRD70, (2004) : Angle between polarisation vector and event plane

30 30 b X a X Interference Fragmentation Function in p-p c SS R-SR-S : Angle between polarisation vector and event plane

31 NEW: STAR shows significant Signal!

32 Additional precision data from last years run + increased kinematic reach Explore      channels +/-+/- +/-+/- Strong Rapidity Dependence STAR upgrades will cover  <2 in the near future 0.25 (current)  0.45: Not probed in SIDIS yet! Proposed Forward upgrade:  <4

33 33 o Asymmetry is oNeed 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 φ Ri single spin asymmetries results in cos(φ R1 +φ R2 ) modulation of the observed di-hadron yield. Measurement of azimuthal correlations for di-pion pairs around the jet axis in two-jet events! Spin Dependent FF in e + e - : Need Correlation between Hemispheres !

34 34 q1q1 quark-1 spin 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 Measuring spin dependent FFs in e + e - Annihilation into Quarks electron positron q2q2 quark-2 spin z 1,2 relative pion pair momenta z2z2 z1z1 Here for di-hadron correlations:

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

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

37 Measuring Light Quark Fragmentation Functions on the ϒ (4S) Resonance 37 small B contribution (<1%) in high thrust sample >75% of X-section continuum under ϒ  (4S) resonance ~100 fb -1  ~1000 fb -1 e + e -  qq̅, q ∈ uds e + e -  cc̅ s “off”

38 Interference Fragmentation – thrust method 38 e + e -  (  +  - ) jet1 (     ) jet2 X Find pion pairs in opposite hemispheres Observe angles  1 +  2 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)]  2   1 Model predictions by: Jaffe et al. [PRL 80,(1998)] Radici et al. [PRD 65,(2002)]

39 Transverse Spin Dependent FFs: Cuts and Binning 39 Full off-resonance and on-resonance data (7-55): ~73 fb 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 (  ) <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 Z had1 >0.2

40 Asymmetry extraction Build normalized yields: Fit with: or Amplitude a 12 directly measures ( IFF ) x ( -IFF ) (no double ratios)

41 41 (z 1 x m 1 ) Binning arXiv: AV et. al, PRL 107, (2011)

42 (m 1 x z 1 ) Binning arXiv: AV et. al, PRL 107, (2011) 42

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

44 Subprocess contributions (MC) 44 8x8 m 1 m 2 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 M. Radici at FF workshop, RIKEN, 11/2012 See also: Courtoy: Phys. Rev. Lett. 107:012001,2011 Measurement at Belle leads to first point by point extraction of Transversity Is Soffer Bound violated? h(x)<|f(x)+g(x)|/2

46 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 Kharzeev, McLerran and Warringa, arXiv: , Fukushima, Kharzeev and Warringa, arXiv: arXiv: v2 [

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

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

51 KEKB/Belle  SuperKEKB, Upgrade 51 Aim: super-high luminosity ~10 36 cm -2 s -1 (~40x KEK/Belle) Upgrades of Accelerator (Microbeams + Higher Currents) and Detector (Vtx,PID, higher rates, modern DAQ) Significant US contribution First data in 2016

52 52

53 Highlights for FF Measurements Kaon efficiency > 95% over relevant kinematics, fake rate < 5% Vertex resolution improved by order of magnitude Obviously more statistics

54 Belle II Status

55 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 Q 2 region  Contribution to A N  Evolution of k T dependent Collins FF  Soffer bound, tensor charge Belle is the ideal machine to study quark fragmentation  Unpolarized Fragmentation functions  Charged pions and kaons  Vector mesons and di-hadrons  Polarized fragmentation functions in correlation between hemispheres  IFF in charged pion pairs  IFF with neutral pions  Collins in charged pion pairs  Collins in charged kaons,  0, , 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

56 Backup

57 Jet Reconstruction Detector GEANT PYTHIA Particle Data JetsMC Jets Midpoint Cone Algorithm: Adapted from Tevatron II (hep- exp/ Cone radius = √(Δη 2 +Δφ 2 ) = 0.7 Split / Merge fraction = 0.5 Anti-K T 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 measurements 57

58 58 Spin Decomposition of the Proton Naïve quark model – 3 valence quark CERN, SLAC, DESY, JLAB:   0.30 …and orbital angular momentum… QCD:..additional contributions from gluons and gluon splitting, sea quarks… GΣ  ΔG, Δ/ Σ = ?


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