1 / 31

James L. Drachenberg For the STAR Collaboration October 1, 2013

James L. Drachenberg For the STAR Collaboration October 1, 2013. Transverse Single-spin Asymmetries from p ↑ + p ⟶ jet + X and p ↑ + p ⟶ jet + π ± +X at √ s = 500 GeV at RHIC. OUTLINE Introduction Event Selection Analysis Description Systematic Uncertainties Preliminary Results

archer
Download Presentation

James L. Drachenberg For the STAR Collaboration October 1, 2013

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. James L. Drachenberg For the STAR Collaboration October 1, 2013 Transverse Single-spin Asymmetries fromp↑+ p ⟶ jet + Xandp↑+ p ⟶ jet + π± +Xat√s= 500 GeVat RHIC • OUTLINE • Introduction • Event Selection • Analysis Description • Systematic Uncertainties • Preliminary Results • Conclusions STAR

  2. Contributions to Proton Spin Structure Consider proton moving right Proton spin  Δq(x) Δg(x)   coming into focus: arXiv:nucl-ex/1304.0079 poorly constrained Polarized DIS: ~ 0.3 Spin sum rule: Proton spin  h1(x)   Transversity– data over limited kinematic range: xBj ≤ 0.3 Transverse-spin Jet Asymmetries - Drachenberg

  3. Sensitivity to Orbital Motion and Transversity? Sivers mechanism:asymmetry in the forward jet or γproduction Collins mechanism:asymmetry in the forward jet fragmentation ⟨Sq⋅ (p× kT,π) ⟩ ≠ 0 ⟨SP⋅ (p× kT,parton) ⟩ ≠ 0 SP SP kT,parton p p Sensitive to transversity(h1) Sensitive toproton spin–partontransverse motioncorrelations (needs Lz) p p π± Kinematic Variables z = pπ/pjet jT(kT, π)=πpTrelative to jet axis Sq kT,π Separate Sivers and Collins: Go beyond inclusive production - e.g. Jets, correlations, direct photons Sivers~ sin(φS) Collins ~ sin(φS-φh) φS—angle between spin and event planeφh—angle of hadron around jet axis Transverse-spin Jet Asymmetries - Drachenberg

  4. Transverse Jet Asymmetries Asymmetry moments sensitive to various contributions (analogous moments sensitive to gluon scattering) AUT – Transverse single-spin asymmetry (also written AN) Transverse Momentum Dependent (TMD) Approach Transversity • Boer-Mulders • FF Pretzelocity • Boer-Mulders • FF pbeam S⊥ ΦS Sivers • Boer-Mulders • Collins F. Yuan, PRL 100, 032003 (2008) D’Alesioet al., PRD 83, 034021 (2011) pπ Transverse-spin Jet Asymmetries - Drachenberg jT Φh –pbeam PJET

  5. Transverse Jet Asymmetries Asymmetry moments sensitive to various contributions (analogous moments sensitive to gluon scattering) AUT – Transverse single-spin asymmetry (also written AN) Transverse Momentum Dependent (TMD) Approach Transversity • Boer-Mulders • FF Pretzelocity • Boer-Mulders • FF pbeam S⊥ ΦS Sivers • Boer-Mulders • Collins F. Yuan, PRL 100, 032003 (2008) D’Alesioet al., PRD 83, 034021 (2011) pπ Transverse-spin Jet Asymmetries - Drachenberg jT Φh –pbeam PJET

  6. STAR Transverse Jet Asymmetries at Central Pseudorapidity Collins Asymmetry A ≣ 2<sin(ϕS – ϕh)> vs. z Collins Asymmetry A ≣ 2<sin(ϕS – ϕh)> vs. jT 0.1 2<sin(ϕS – ϕh)> R. Fersch, DNP2011 -0.1 0.2 0.4 0.6 0.8 z 10-1 1 10 jT (GeV) STAR measured transverse single-spin asymmetries for inclusive jet production at central pseudorapidity and √s = 200 GeV (2006) : consistent with zero : hints of non-zero asymmetry with charge-sign dependence Similarly, di-jet and π0 AN at central psuedorapidity and 200 GeV consistent with zero PRL 99, 142003, PRL. 95, 202001, arXiv:hep-ex/1108.0911 Phys. Rev. D 86 32006 (2012) Transverse-spin Jet Asymmetries - Drachenberg

  7. STAR Transverse Jet Asymmetries at Central Pseudorapidity 2012 STAR data provide opportunity for higher precision and greatly reduced systematic uncertainties at √s = 200GeV R. Fersch, DNP2011 2011 STAR data provide opportunity for first measurements of central pseudorapidity inclusive jet asymmetries at √s = 500GeV  Increased sensitivity to gluonicsubprocesses Aschenauer, JLab UGM 2013 pT [GeV/c] Transverse-spin Jet Asymmetries - Drachenberg

  8. Moments of Jet Asymmetries at 500 GeV Various contributions to polarized jet+π cross section (TMD approach) Phys. Rev. D 83, 034021 (2011) Transverse-spin Jet Asymmetries - Drachenberg

  9. Moments of Jet Asymmetries at 500 GeV Various contributions to polarized jet+π cross section (TMD approach) Phys. Rev. D 83, 034021 (2011) Negligible under maximized scenario! Transverse-spin Jet Asymmetries - Drachenberg

  10. Moments of Jet Asymmetries at 500 GeV Various contributions to polarized jet+π cross section (TMD approach) Phys. Rev. D 83, 034021 (2011) D’Alesio et al. Possible non-zero contributions, expected to be quite small e.g. Phys. Rev. Lett. 95, 202001 (2005); Phys. Rev. Lett 99, 142003 (2007); Phys. Rev. D 86, 032006 (2012); arXiv:hep-ex/1108.0911 projections for √s = 500GeV Transverse-spin Jet Asymmetries - Drachenberg

  11. Moments of Jet Asymmetries at 500 GeV Various contributions to polarized jet+π cross section (TMD approach) D’Alesio et al. “Collins-like” asymmetry: Sensitive to linearly polarized gluons Completely unconstrained! Phys. Rev. D 83, 034021 (2011) Maximized contribution for √s = 500 GeV Gluon helicity density matrix Off-diagonal terms related to linear polarization in (xy) plane at angle φ to x-axis Phys Rev. D 73, 014020 (2006) Transverse-spin Jet Asymmetries - Drachenberg

  12. Solenoidal Tracker at RHIC Jet reconstruction utilizes TPC + Barrel + Endcap EMC J. Zhou, M.S. Thesis • Minbias Trigger: coincidence in • vertex position detector (VPD) • Pb+plastic scintillator with PMT readout • 570 cm from interaction point • 4.24 < |η| < 5.1, Transverse-spin Jet Asymmetries - Drachenberg

  13. Jet Reconstruction in STAR STAR Di-jet event at detector-level Data jets MC jets GEANT Detector  e+   e- Particle  Anti-kTalgorithm JHEP 0804, 063 (2008) Radius parameter R = 0.6 PYTHIA Use PYTHIA + GEANT to quantify detector response Parton π± Kinematic Variables z – π momentum / jet momentum jT – πpT relative to jet axis Transverse-spin Jet Asymmetries - Drachenberg

  14. 2011 STAR Event Selection • Center of mass energy, √s = 500GeV • Total integrated luminosity of 25 pb-1 for all transverse runs • Polarization for present analysis: 54±3% • Good event vertex with |zvertex| < 30 cm • Jet Reconstruction: • Nhits, track > 12 • Track association with event vertex • Minimum track pT > 0.2 GeV/c • Minimum tower energy > 0.2 GeV • Jet requirements: • No charged particles with pT > 30 GeV/c • Total charged-particle pT> 0.5 • Neutral-energy fraction < 0.98 • |ηjet| < 1.0 (and within detector acceptance of BEMC+TPC) • 6 < pT,jet < 55 GeV/c • Pion Requirements: • Restriction on dE/dx: -1 < nσ(π) < 2.5 (contamination < 3%) • (ηjet-ηch)2 + (φjet-φch)2 > (0.1)2 • Nhits, dE/dx > 5 Transverse-spin Jet Asymmetries - Drachenberg

  15. Studies with Embedded Monte Carlo Systematic shifts in reconstructed kinematic variables and azimuthal resolutions evaluated by comparing to Monte Carlo embedded in real zero-bias data simulate effects of real, out-of-time pile-up Detector-level jets matched both to parton and particle jets with matched event vertex Kinematic shifts evaluated at particle level Corresponding parton-jet pT~0.6-1.4 GeV/c lower jet pT track jT track z Transverse-spin Jet Asymmetries - Drachenberg

  16. Sources of Systematic Uncertainty • Dominant systematic uncertainty from • reconstructed jets unassociated with parton jets •  Take difference between measured AUT and AUT assuming dilution • Further systematic uncertainties: • Resolution of relevant azimuthal angles •  corrected as dilution to measured asymmetry • “leak-through” of other moments of AUT • Pion contamination from K/p and e± (< 3%) • Polarization uncertainty (correlated vertical scale uncertainty, σ(P)/P = 5.6%) Angular resolution corrected as dilution Pion contamination < 3% Transverse-spin Jet Asymmetries - Drachenberg

  17. Asymmetry Measurements half of detector α and β yields are functions of integrated over For uniform acceptance: Transverse-spin Jet Asymmetries - Drachenberg

  18. Estimating Leak-through Systematic Assuming 10% Sivers asymmetry 0.2 < zreco < 0.3 For 10%, upper-limit ~ 0.0021 For 2%, upper-limit ~ 0.0004 Acceptance inefficiencies can allow non-zero effects to “leak through” and distort desired observable Quantify distortion by event-weighting unpolarized data yields and calculating resulting asymmetries Reasonable acceptance + small observed asymmetries  Small upper-limits on “leak-through” systematic Transverse-spin Jet Asymmetries - Drachenberg

  19. Sivers Asymmetries Asymmetries shown as function of particle-jet pT Corresponding parton-jet pT lower by 0.6-1.4 GeV/c Horizontal errors include uncertainties from statistics, calorimeter gains, efficiencies, track momentum, and tracking efficiency No sign of sizable azimuthal asymmetry in jet production at √s = 500GeV Consistent with expectation from inclusive jets, di-jets, and neutral pions at √s = 200GeV pT [GeV/c] Transverse-spin Jet Asymmetries - Drachenberg

  20. Sivers Asymmetries Asymmetries shown as function of particle-jet pT Corresponding parton-jet pT lower by 0.6-1.4 GeV/c Horizontal errors include uncertainties from statistics, calorimeter gains, efficiencies, track momentum, and tracking efficiency Measured asymmetries shown in η-bins No sign of sizable asymmetry pT [GeV/c] Transverse-spin Jet Asymmetries - Drachenberg

  21. Collins Asymmetries Increased gluonicsubprocesses at √s = 500 GeV lead to expectation of small Collins asymmetry until larger z D’Alesio et al. Present data do not have sufficient statistics at high-z to observe Collins asymmetry of order 1% Transverse-spin Jet Asymmetries - Drachenberg

  22. Collins Asymmetries Present model predictions expect negligible effects for AUT vs. jT integrated over z > 0.1 Measured asymmetries shown for xF > 0 (i.e. 0 < ηjet < 1) in z-bins No sign of non-zero asymmetry as a function of jT or jet pT Similarly, no sign of positive effect for backward region (xF < 0), as expected Transverse-spin Jet Asymmetries - Drachenberg

  23. Collins-like Asymmetries Maximized contribution for √s = 500 GeV D’Alesio et al. Model predictions shown for “maximized” effect, saturated to positivity bound Until now, Collins-like asymmetries completely unconstrained  Sensitive to linearly polarized gluons Transverse-spin Jet Asymmetries - Drachenberg

  24. Collins-like Asymmetries Measured asymmetries shown for -1 < η < 1 in z-bins Consistently below 2% maximum from model D’Alesio et al. Transverse-spin Jet Asymmetries - Drachenberg

  25. Collins-like Asymmetries Similarly, no large effect observed as a function of jet pT Measured asymmetries shown for -1 < η < 1 in z-bins Transverse-spin Jet Asymmetries - Drachenberg

  26. Summary • STAR data from 2011 provide first measurements of transverse spin asymmetries for jet production at central pseudorapidity and √s = 500GeV Transverse-spin Jet Asymmetries - Drachenberg

  27. Summary • STAR data from 2011 provide first measurements of transverse spin asymmetries for jet production at central pseudorapidity and √s = 500GeV • Increased gluonicsubprocesses at √s = 500 GeV provide unique sensitivity to Collins-like asymmetry from linearly polarized gluons Transverse-spin Jet Asymmetries - Drachenberg

  28. Summary • STAR data from 2011 provide first measurements of transverse spin asymmetries for jet production at central pseudorapidity and √s = 500GeV • Increased gluonicsubprocesses at √s = 500 GeV provide unique sensitivity to Collins-like asymmetry from linearly polarized gluons • No observation of large asymmetry from gluon Sivers effect, consistent with expectations from previous measurements of jet and π0 asymmetries at √s = 200 GeV Transverse-spin Jet Asymmetries - Drachenberg

  29. Summary • STAR data from 2011 provide first measurements of transverse spin asymmetries for jet production at central pseudorapidity and √s = 500GeV • Increased gluonicsubprocesses at √s = 500 GeV provide unique sensitivity to Collins-like asymmetry from linearly polarized gluons • No observation of large asymmetry from gluon Sivers effect, consistent with expectations from previous measurements of jet and π0 asymmetries at √s = 200 GeV • No observation of large asymmetry from Collins effect, consistent with expectations from decreased quark subprocesses at √s = 500 GeV Transverse-spin Jet Asymmetries - Drachenberg

  30. Summary • STAR data from 2011 provide first measurements of transverse spin asymmetries for jet production at central pseudorapidity and √s = 500GeV • Increased gluonicsubprocesses at √s = 500 GeV provide unique sensitivity to Collins-like asymmetry from linearly polarized gluons • No observation of large asymmetry from gluon Sivers effect, consistent with expectations from previous measurements of jet and π0 asymmetries at √s = 200 GeV • No observation of large asymmetry from Collins effect, consistent with expectations from decreased quark subprocesses at √s = 500 GeV • First measurements of Collins-like asymmetries will help place constraints on model predictions beyond maximal projections from positivity bounds Transverse-spin Jet Asymmetries - Drachenberg

  31. Looking Forward • Additional data from 2011 jet-patch triggers will allow much greater precision for higher jet pT (above 7 GeV/c) • High precision measurements from 2012 at √s = 200 GeV will allow greater sensitivity to effects from quark subprocesses STAR Preliminary Results at √s = 500 GeV Sivers Asymmetries Collins Asymmetries Collins-like Asymmetries Transverse-spin Jet Asymmetries - Drachenberg

More Related