Introduction Experimental setup and considerations Preliminary Physics results

1. Transverse Single-Spin asymmetries for p+ and p- production from pp collisions at _S = 200 GeV • Introduction • Experimental setup and considerations • Preliminary Physics results • Conclusion and Prospects F.Videbaek Single Spin Asymmetries in BRAHMS

2. Left Right Introduction An = (s+ - s-) / (s+ + s-) • Where the spin cross section is determined with the spin direction defined by kb x kpi • Early (naive) QCD predicted this effect to be small • Non-zero Single Transverse Spin Asymmetry (SSA/ An) requires Spin Flip Amplitude and phase difference in intrinsic states • Such studies may clarify properties of transverse quark structure of the nucleon • Sivers effect [Phys Rev D41 (1990) 83; 43 (1991) 261] Flavor dependent correlation between the proton spin , momentum and transverse momentum of the un-polarized partons inside the proton. • Collins effect [Nucl Phys B396 (1993) 161] Correlation between the quark spin, momentum and transverse momentum of the pion. Single Spin Asymmetries in BRAHMS

3. Background Low energy data (FNAL E704 ) show clear differences between p+- and p0. p+ D.L.Adams (E704) Phys.Lett B264,462(1991); Phys.Rev. D53, 4747 (1996). Recent STAR results on p0 also shows a significant SSA/ An at RHIC energies. Preliminary BRAHMS data was shown at DIS05. p0 p- Single Spin Asymmetries in BRAHMS

4. RHIC beam transversely polarized at BRAHMS detector Single Spin Asymmetries in BRAHMS

5. The BRAHMS Spectrometer

6. Kinematic Variables • The kinematic variables of interest are Feynman x (xF) and pT. • Shown is the BRAHMS acceptance for the data taken at  = 2.3 deg and the maximum field setting (7.2 Tm). • The acceptance is not straight in angle or h. Illustrated in this plot. Thus care should be taken when comparing to both other experiments and to theory. The momentum resolution is dp/p~1% at 22 GeV/c. Single Spin Asymmetries in BRAHMS

7. Determination of Asymmetries. • Asymmetries are determined from • An = (s+ - s-) / (s+ + s-) • Experimentally determined from • An = 1.0 /P (N+ - L*N-) / (N+ + L*N-), • where L = L+ / L- • Need to know • Beam Polarization • Bunch Luminosities • Pion rates in spectrometer Single Spin Asymmetries in BRAHMS

8. Bunch Polarization These are obtained from the CNI online polarimeter normalized to a Gas Jet Target measurements Single Spin Asymmetries in BRAHMS

9. Determination of Asymmetries. • Asymmetries are determined from • An = (s+ - s-) / (s+ + s-) • Experimentally determined from • An = 1.0 /P (N+ - L*N-) / (N+ + L*N-), • where L = L+ / L- • Need to know • Beam Polarization • Bunch Luminosities • Pion rates in spectrometer Single Spin Asymmetries in BRAHMS

10. Bunch Luminosities • Bad bunches with different intensity outside norm is rejected. • L+/L- ~ 1.05-1.15 typical factors • Run-5 have more systematic check with varying patterns. Since the up and down spin patterns alternate most time-dependent systematic errors are small. The main issue is determination of the L+ and L-. Single Spin Asymmetries in BRAHMS

11. Luminosityvariation vs. runs Single Spin Asymmetries in BRAHMS

12. Determination of Asymmetries. • Asymmetries are determined from • An = (s+ - s-) / (s+ + s-) • Experimentally determined from • An = 1.0 /P (N+ - L*N-) / (N+ + L*N-), • where L = L+ / L- • Need to know • Beam Polarization • Bunch Luminosities • Pion rates in spectrometer Single Spin Asymmetries in BRAHMS

13. PID using RICH Good track are selected in spectrometer; determining momenta. Pions identified from momentum and radius measured in a Ring Imaging Cherenkov Counter. The pion identification is clean up to 35 GeV. Measured radius vs. calculated showing the selected pions p P GeV/c Single Spin Asymmetries in BRAHMS

14. Hadron Spectra • pp p- spectrum over 7 orders of magnitude • Spectra for other charged hadrons are forth coming • Such spectra will provide a testing ground for pQCD Single Spin Asymmetries in BRAHMS

15. AN measurements for p- Measurements at 2.3 and 4 degrees. Results averages of pT range in each setting. Pz Single Spin Asymmetries in BRAHMS

16. Summary of pT dependence • 0.15-0.30 in Xf • AN(pi-) 0.078+-0.002 low pT • AN (pi-) 0.045+-0.003 higher pT • AN (pi+) 0.066+-0.002 low pT Systematic errors from online polarization is (presently estimated at ~20% [scale] ) Single Spin Asymmetries in BRAHMS

17. Twist 3 (initial state) calculations by J.Qiu and G.Sterman, Phys.ReV.D59,014004(98) Extrapolated to lower pT 2.3 deg Single Spin Asymmetries in BRAHMS

18. Comparison to data within acceptance. The AN for p+ in the theory is ~ AN for p- with opposite sign The theory does predict a lowering at higher pTand a nearly flat distribution with xF in the acceptance. Single Spin Asymmetries in BRAHMS

19. Other results. • Using polarization from opposite beam (yellow), we obtain AN equivalent to asymmetries for negative xF Brahms will also access other charged hadrons; p+-, K+-. Single Spin Asymmetries in BRAHMS

20. Conclusions • BRAHMS has obtained the preliminary result for single spin asymmetries for p+ and p- in 200 GeV pp collisions at RHIC in the xF range of 0.17 to 0.35 • The AN values for p+ and p- are significantly different with opposite sign • The absolute AN value for p- decrease with increasing pT • The sign of An is consistent with behavior from lower energy data • An at negative xF for p+ and p- are consistent with 0 The protons are found to have AN ~0 Single Spin Asymmetries in BRAHMS

21. The BRAHMS Collaboration I.Arsene7,12, I.G. Bearden6, D. Beavis1, S. Bekele6 , C. Besliu9, B. Budick5, H. Bøggild6 , C. Chasman1, C. H. Christensen6, P. Christiansen6, R. Clarke9, R.Debbe1, J. J. Gaardhøje6, K. Hagel7, H. Ito10, A. Jipa9, J. I. Jordre9, F. Jundt2, E.B. Johnson10, C.E.Jørgensen6, R. Karabowicz3, E. J. Kim4, T.M.Larsen11, J. H. Lee1, Y. K. Lee4, S.Lindal11, G. Løvhøjden2, Z. Majka3, M. Murray10, J. Natowitz7, B.S.Nielsen6, D. Ouerdane6, R.Planeta3, F. Rami2, C. Ristea6,9, O. Ristea9, D. Röhrich8, B. H. Samset11, D. Sandberg6, S. J. Sanders10, R.A.Sheetz1, P. Staszel3, T.S. Tveter11, F.Videbæk1, R. Wada7, H. Yang6, Z. Yin8,and I. S. Zgura12 1Brookhaven National Laboratory, USA, 2IReS and Université Louis Pasteur, Strasbourg, France 3Jagiellonian University, Cracow, Poland, 12Institute of Space Science,Bucharest 4Johns Hopkins University, Baltimore, USA, 5New York University, USA 6Niels Bohr Institute, University of Copenhagen, Denmark 7Texas A&M University, College Station. USA, 8University of Bergen, Norway 9University of Bucharest, Romania,10University of Kansas, Lawrence,USA 11 University of Oslo Norway 48 physicists from 11 institutions Single Spin Asymmetries in BRAHMS

22. Backup Single Spin Asymmetries in BRAHMS

23. Backup- STAR RHIC data Single Spin Asymmetries in BRAHMS

24. TMA BB BB CC/INEL Event characterization Global Detectors in use for luminosity measures, and inelastic pp cross section Triggers are defined with the CC,Inel ZDC and BB; p+p collisions were triggered with the INEL/CC detectors. Single Spin Asymmetries in BRAHMS

25. Vertex determination • Vertex Calculated from timing measurements in sets of counters CC position on each side of IP covering roughly 2 < |h| < 5.2. • Z-resolution is ~ 2 cm in Run-4 • The spectrometer accepts track weighted towards negative Z Single Spin Asymmetries in BRAHMS

26. Event Selection Criteria • Clean track through spectrometer and in time with the RHIC 108 nsec clock. • Momentum determined from 3 measurements. • -40< Z_Vertex <30 (Vertex from collision) determined from global detectors (INL, BB, ZDC) • Track points to collision vertex (in Z and Y) • Good Bunches Only (selected per store) • Select pions using RICH for particle identification. Single Spin Asymmetries in BRAHMS

27. Single Spin Asymmetries in BRAHMS