Elastic pp scattering, A N and r 5

1. Elastic pp scattering, AN and r5 • Mainly : • Data analysisfor the ~one-week run with roman-pots in 2009 (physics with tagged forward proton) • Results on AN & r5 Kin Yip Collider-Accelerator Department Brookhaven National Lab. Nov. 16, 2011, STAR Collaboration Meeting

2. Physics with Tagged Forward Protons p + p  p + X + p Double Pomeron Exchange (DPE) diffractive X= particles, glueballs Discovery Physics QCD color singlet exchange: C1, C1 azimuthal rapidity p + p  p + p elastic Single Diffraction Dissociation (SDD) Kin Yip

3. Helicity amplitudes for spin ½ ½  ½ ½ Kin Yip

4. AN and Nuclear Coulomb Interaction In the absence of hadronic spin-flip contributions, AN is exactly calculable. [Kopeliovich & Lapidus, Sov. J. Nucl. Phys. 19, 114 (1974).] Our data reach N.H. Buttimore, et al., Phys. Rev. D 59 (1999) 114010. Kin Yip

5. Previous AN measurements in the CNI region with hadronic spin-flip no hadronic spin-flip HJet@RHIC PRD79(09)094014 HJet@RHIC PRD79(09)094014 no hadronic spin-flip E704@FNAL s = 19.4 GeV PRD48(93)3026 pp2pp@RHIC s = 200 GeV PLB632(06)167 no hadronic spin-flip Kin Yip

6. Silicon Detector Performance in the 2009 run After excluding (3) edge strips and hot/dead strips • Only 5 dead/noisy strips per ~ 14000 active strips (active area limited by acceptance) • Overall plane efficiency > 99%. • Excellent detector efficiencies allow us to have clean data. Kin Yip

7. 2009 run and main Selection Cuts • Data was taken in 5 days ~July 2009 >70 million triggers • Elastically triggered ( ~33 million events) • Outside sequencer (DAQ) reset time window • Valid hit/strip with ADC  pedestal_per_channel + 5  • A Cluster: ≤5 valid consecutive hits with ADC sum separated from the pedestal (depending on size) • Clusters in A/C and B/D strips are within < 200 m (2 strips) • A track on each side (a track is formed by at least a cluster on each Roman Pot) • Collinearity (between the scattering angles in the East and West) • Timing-vertex cut • Fiducial cuts and getting rid of hotspots in the RP’s nearest to the beam (~tail of the beam) •  ~21 million events (before considering the spin combinations) Kin Yip

8. Collinearity cuts – mean &  (position) determined from each run A typical distribution of x = [x(West) x(East)] and y = [y(West)- y(East)] for a run is shown here. Width here is consistent with the beam divergence. Kin Yip

9. Calculation of single-spin asymmetry AN • Square root formula for raw asymmetry () using  and  :  = where can be ignored. • False asymmetry using  and  : . Kin Yip

10. Polarization Error (just for illustration) From Sasha’s official polarization page, http://www4.rcf.bnl.gov/~cnipol/pubdocs/Run09Offline/ and his advice: The overall average polarization PB+PY for all stores (i’s) are calculated as : = 1.224 where Li is the luminosity for each store i. And the overall statistical and systematic error for the PB+PY is found from:  PB+PY= 0.03833 In addition, there is a global error of PB+PY(global)/PB+PY = 4.4%. As a result, the total polarization error is 0.06610, or = 5.4%.

11. But really, what I use are the polarizations for each store (from the same afore-mentioned webpage): • For each run/store, I divide the asymmetry in each  bin by (Pb+Py), ie. /(Pb+Py) ~ AN  cos(). Kin Yip

12. Just one of the –t bins as an example : Raw asymmetry  False asymmetry  Kin Yip

13. Finalizing the analysis … Kin Yip • We have focused our efforts to figure out the best and most accurate transport for the RHIC configuration that we have used during the 2009 run. • Cross-checked the transport and the off-axis effects by established software such as MADX and Turtle (to arrive at the same result). • Determined (eg.) the signs of angles and magnet strengths related to our experiment with the help of accelerator physicists and dedicated new/old beam experiments. • Determining the best way to determine the scattering angle from positions in the RP’s (using MC simulation to tell us the accuracies). • We have spent a lot of time in alignment by detector position surveys in the RHIC tunnel and using the (over-)constraints from the elastic data to better align the detector geometry. • Quite a few systematic checks have been done. Eg.:

14. East Only (all –t) West Only (all –t)  ()  ()  ()  () Kin Yip

15. STAR 2009 The AN curve would be scaled up or down by larger or smaller polarization. Kin Yip

16. Kin Yip AN & r5 fit • Used the final transport matrix (Sep. 29, 2011), alignment correction and the crossing angle corrections (including hotspot/fiducial cuts). • Errors in   0.03 radians and t/t errors are as follows: • Systematic errors include those of beam divergence & offset, geometry and Leff .which are estimated using the full Hector beam transport simulation. • Re(r5) = 0.00124  0.00255 Im(r5) = 0.00751  0.04124 • Compared with when a flat t/t ~10% (and no error in ) : Re(r5) = 0.00124  0.00312 Im(r5) = 0.00719  0.04834

17. Contours (of 1/2/3 ’s) on r5: • Indicate no hadronic spin-flip • High precision measurement: x10 improvement compared to 2003 pp2pp data No polarization error included. 3  2 1 2003 (pp2pp) Phys. Lett.B 632 (2006) 167 Kin Yip

18. Comparisons Theoretical calculations from B.Z. Kopeliovich, arXiv:hep-ph/0211061. Kin Yip

19. To summarize: Kin Yip • >20 million good elastic events recorded in 5 days of data taking with RP’s in 2009 at s=200 GeV and special machine optics *=21 m. • Currently, we’re finalizing the systematic studies. • Upon completion, we should have the most precise measurement of AN in this energy range. • We’re preparing publication on AN and r5 and the knowledge gained is directly applicable to the other analyses: • double-spin asymmetries ANN and ASS • elastic scattering - spin averaged dN/dt => slope b etc.