1 / 24

L. Nogach, IHEP, Protvino for the STAR Collaboration

STAR. Measurements of transverse spin effects in the forward region with STAR detector. L. Nogach, IHEP, Protvino for the STAR Collaboration. Outline: Motivation STAR detector Inclusive p 0 measurements More possibilities with the FMS 2009 run at √s=500 GeV Summary and outlook.

Download Presentation

L. Nogach, IHEP, Protvino for the STAR Collaboration

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.


Presentation Transcript

  1. STAR Measurements of transverse spin effects in the forward region with STAR detector L. Nogach, IHEP, Protvinofor the STAR Collaboration • Outline: • Motivation • STAR detector • Inclusive p0 measurements • More possibilities with the FMS • 2009 run at √s=500 GeV • Summary and outlook DSPIN-2009, September 1-5

  2. Motivation • Contrary to simple pQCD predictions, first measurements of  production in p↑p collisions found large transverse single spin asymmetries. Similar large effects have recently been found in e+e- and semi-inclusive deep-inelastic scattering. • Significant developments in theory in the past few years suggest common origins for these effects, but large transverse spin asymmetries inp↑+p →  + Xproduction are not yet fully understood. • More fundamental question: what is the underlying dynamics in kinematics where transverse spin effects are observed?

  3. Polarized pp collisions at RHIC RHIC pC Polarimeters Absolute Polarimeter (H jet) Siberian Snakes Siberian Snakes PHENIX STAR Spin Rotators (longitudinal polarization) Spin Rotators Pol. H- Source LINAC BOOSTER Helical Partial Siberian Snake AGS 200 MeV Polarimeter AGS pC Polarimeter FOM=P2L Strong AGS Snake

  4. STAR detector layout FMS TPC FPD BBC BEMC • FPD • Modular detector • Small xF-pT range compared to FMS FPD FMS FMS • 20x acceptance of previous forward detectors at STAR • Full azimuthal coverage for 2.5 < η < 4.0 • Array of 1264 Pb-glass cells

  5. Published measurements with the FPD (20022006) PRL 92, 171801 (2004) PRL 101, 222001 (2008) • AN at positive xF grows with increasing xF • xF dependence matches theoretical model expectations qualitatively • pT dependence at fixed xF is not consistent with 1/pT expectation of theoretical model calculations √s=200 GeV, <η> = 3.8 U.D’Alesio, F.Murgia Phys. Rev. D 70, 074009 (2004) arXiv:0712.4240 C.Kouvaris, J.Qiu, W.Vogelsang, F.Yuan, Phys. Rev. D 74, 114013 (2006) Asymmetry revealed at lower energies persists at √s=200 GeV

  6. Inclusive h AN measurements (2006) Asymmetry for h-mesons is larger than for p0 (similar to the E704 measurements): (AN)h = 0.361 ± 0.064 for 0.55<xF<0.75 arXiv:0905.2840

  7. Inclusive p0 AN with the FMS (2008) y x P arXiv:0901.2828 Octant subdivision of FMS for inclusive p0 spin sorting • Azimuthal dependence appears • to be as expected • AN is comparable to prior measurements with the FPD

  8. AN(pT) at |xF|>0.4 with the East FPD/FMS (2008) negative xF positive xF • AN for negative xF consistent with zero • Indication of AN for positive xF persists • up to pT ~5 GeV/c • Needs more transverse spin running arXiv:0901.2763+ A.Ogawa @CIPANP09

  9. High xF vector mesons 3 photon events to look forwp0g (BR= 8.9%) • pT(triplet)>2.5 GeV/c • E(triplet)>30 GeV • pT(photon cluster)>1.5 GeV/c • pT(p0)>1 GeV/c Background only MC Run8 FMS data Fit is Gaussian + p3  μ=0.784±0.008 GeV σ=0.087±0.009 GeV Scale=1339±135 Events Significant (10s) wp0g signal seen in the data => possibility to measure spin-1 meson AN arXiv:0906.2332

  10. First look at “jet-like” events in the FMS Eventselection: “Jet-shape” distribution of energy within jet-like objects in the FMS as a function of distance from the jet axis • >15 cells with energy > 0.4GeV in the event • (no single pions in the event) • cone radius = 0.5 (η-φ space) • “Jet-like” pT >1 GeV/c, xF > 0.2 • 2 perimeter fiducial volume cut (small/large cells) • “Jet shape” in data matches simulation well • Reconstructed mass does not match as well • High-tower trigger used in Run 8 biases jets arXiv:0901.2828

  11. Forward p0-p0 azimuthal correlations • Possible back-to-back di-jet/di-hadron Sivers measurement • Possible near-side hadron correlation for Collins fragmentation function/ • Interference fragmentation function + Transversity • Low-x / gluon saturation study – accessing lowest xBjgluon

  12. Benchmark for Drell-Yan: First look at J/ψ → e+ + e- in the FMS Reconstructed 2-cluster invariant mass • Fit with Gaussian + Offset • Gaussian fit parameters: • μ = 3.080 ± 0.020 GeV/c2 • σ = 0.082 ± 0.026 GeV/c2 • χ2/d.o.f. = 20.83/26 • Significance from the fit • 4.5 σ High-xF, high mass dilepton pairs are difficult to reconstruct • Cuts applied: • E_pair > 60.0 GeV • zγγ < 0.7 • Isolation radius: 0.4 η-φ • pT_cluster > 1.0 GeV/c First high-xFJ/ψmeasurement at √s > 62 GeV arXiv:0907.4396

  13. 2009 – first physics run at √s=500 GeV Luminosity: 56x56 bunches with 1.8x1011 intensity; 10 pb-1 integrated Polarization: ~30% (longitudinal) First look at poevent reconstruction in the FPD: • using matrix+preshower (no SMD data) • 20 GeV < Etotal < 80 GeV • fixed vertex (z=0), no minbias condition • Ng=2 Forward Pion Detector module schematic: Shower Maximum Detector lead converter 7x7 matrix of lead glass cells preshower (7 Pb-glass cells) fit by Gaussian+”gamma” function

  14. 2009 data at √s=500 GeV FPD measures energy up to ~200 GeV ═> SMD information is required to reconstruct pions above ~60 GeV Example of 2-photon event when two clusters significantly overlap in the matrix, but are clearly separated in the SMD

  15. Forward Hadron Calorimeter • Proposed to be staged at a minimal Dz from the FMS symmetrically of DX magnet • two matrices of 9x12 Pb-scintillator detectors • real jets physics with • FMS+FHC • polarization transfer coefficients • through measurement of •  polarization • in the n0 channel first simulations of L→np0

  16. Summary • Large transverse single spin asymmetries at large h are observed up to √s=200 GeV. • High precision inclusive p0AN measurements with the FPD allow for a quantitative comparison with theoretical models. • FMS allows to look at heavier mesons, “jet-like” events and particle correlations. • Essential to go beyond inclusive production to disentangle dynamical origins.

  17. Outlook • Measurements of AN in inclusive p0 production at √s=500 GeV (Run 11?). • Extend forward calorimetry to have hadronic capability (FHC) to measure full jets and to study inclusive L production. • Extend measurements of transverse single spin asymmetries from hadron production to prompt photon and jets. • Develop RHIC experiment for a future measurement of transverse single spin asymmetries for Drell-Yan production of dilepton pairs.

  18. Backups

  19. Definition: dσ↑(↓) – differential cross section of p0 when incoming proton has spin up(down) Two methods of measurements: Single arm calorimeter: R – relative luminosity (by BBC) Pbeam – beam polarization Two arm (left-right) calorimeter: No relative luminosity needed Left p0, xF<0 p0, xF>0 p  p Right Single Spin Asymmetry positive AN: more p0 going left to polarized beam

  20. Possible mechanisms • Sivers effect [Phys. Rev. D 41, 83 (1990); 43, 261 (1991)]: Flavor dependent correlation between the proton spin (Sp), proton momentum (Pp) and transverse momentum (kT) of the unpolarized partons inside. The unpolarized parton distribution function fq(x,kT) is modified to: • Collins effect [Nucl. Phys. B396, 161 (1993)]: Correlation between the quark spin (sq), quark momentum (pq) and transverse momentum (kT) of the pion. The fragmentation function of transversely polarized quark q takes the form: According to the latest theoretical developments, both mechanisms contribute to  AN

  21. Separating Sivers and Collins effects Sivers mechanism:asymmetry in the forward jet or g production Collins mechanism: asymmetry in the forward jet fragmentation SP SP kT,q p p p p Sq kT,π Sensitive to proton spin – parton transverse motion correlations Sensitive to transversity To discriminate between the two effects we need to go beyond p0 detection todirect photons orjet-like events

  22. p0 inclusivecross section Cross-section is consistent with NLO pQCD calculations PRL 97, 152302 (2006) nucl-ex/0602011

  23. Forward p0 – midrapidity azimuthal correlations • pQCD inspired “GSV cuts” (Guzey, Strikman and Vogelsang, hep-ph/0407201): • |ηTPC| < 0.9 ; 2.8 < ηFMS < 3.8 • 2.5(2.0)GeV < pTFMS • 1.5(1.0)GeV < pTTPC < pTFMS • |zγγFMS|< 0.7, 0.07 < Mγγ < 0.30 GeV • only leading particle considered, corrected for pile-up • as proposed in hep-ex/0502040 • Possible back-to-back di-jet/ di-hadron Sivers measurements • Low-x / gluon saturation study • Step-stone towards transverse spin forward photon-jet arXiv:0907.3473

  24. Future runs at RHIC

More Related