Constraining D g with p 0 ALL: Experimental issues

1. Constraining Dg with p0 ALL:Experimental issues Kieran Boyle Stony Brook University December 4, 2006

2. Tell them what you will tell them Outline • The Concept • p + p p0 + X • The Equation • ALL • The Measurement • Luminosity • How do you define a collision • Relative Luminosity • Why do we need it • What can go wrong • Polarization • Total Polarization • Quick and Dirty (CNI) • Slow and accurate (Hpol jet) • Local Polarimetry (Which way is Pol. Pointing?) • p0 yields • How to reconstruct • p0 background reduction • The Results • The “Theoretical” inputsWhat does the data say about Dg 2

3. Tell Them: The concept • One lesson we all surely learned at ECT: • How can we get Dg? with DS ~25%, Dg not well constrained, DL ? l, k’ (SI)DIS: Clean but mostly colorblind l, k h Dq Dg Hard Scattering Process p0 P+P: Dirty but colorful Dg2 DgDq Dq2 3

4. p+p  Dg ? • Theorist says: • is hard to calculate (LO, NLO, etc.) but with lots of effort it’s done • So theorist tell experimentalist to “simply” measure: - Ds = 4

5. where , is rapidity   p+p  Dg ? • Experimentalist replies: bias Trigger bias From experimental data geom Geometrical acceptance From MC reco Reconstruction efficiency (cut efficiencies) From MC or/and experimental data smear Smearing effect (due to finite resolutions): From MC Each efficiency has a systematic uncertainty (~1-10%), which makes measuring a (small) difference difficult where 5

6. p+p  Dg ? • Compromise • If Df = Dq, then we have this from pDIS • So roughly, we have From ep (&pp) (HERA mostly) From e+e- pQCD NLO +- = + = ++ + 6

7. But why is ALL any better? • We can write and that e can give large systematics • So then ALL = Assume f++ = f+- i.e. helicity independent 7

8. BRAHMS & PP2PP (p) PHENIX (p) STAR (p) Does f++ = f+- ? • Only if efficiencies don’t change between ++ and +- measurementdetector stability between Polarization flips. • Examples: • SMC: Solid or liquid targetflip takes 1 hour, so do it every 8 hours • Hermes: gas targetflip on the order of seconds(s) • RHIC: Polarized bunchflip every bunch=every 106ns RHIC CNI (pC) Polarimeters Absolute Polarimeter (H jet) RHIC allows a great reduction in systematics Spin Rotators Siberian Snakes Partial Siberian Snake LINAC BOOSTER Pol. Proton Source AGS AGS Internal Polarimeter 200 MeV Polarimeter Rf Dipoles 8

9. How Do We Actually Measure ALL? • The ingredients: • Luminosity (L): • How do we measure it?  Relative Luminosity (R) • How do we define a collision\event? • Measurement • Systematic uncertainty • Polarization (P) • Magnitude • Direction (Is it really longitudinal?) • p0 yield (N) • How do we get p0’s? 9

10. Luminosity

11. From Astrid Morreale LUMINOSITY Luminosity is the number of particles per unit area per unit time times the Opacity of the target, usually expressed in either the cgs units cm-2 s-1 or b-1 s-1. The integrated luminosity is the integral of the luminosity with respect to time. The luminosity is an important value to characterize the performance of an accelerator. Where • L is the Luminosity. • N is the number of interactions. • ρ is the number density of a particle beam, e.g. within a bunch. • σ is the total cross section. • dΩ is the differential solid angle. • is the differential cross section • For an intersecting storage ring collider: • f is the revolution frequency • n is the number of bunches in one beam in the storage ring. • Ni is the number of particles in each beam • A is the cross section of the beam. } n, A, N1, N2 all have uncertainty: stat. and systematic

12. Can we reduce uncertainty? • Well Luminosity can be written as • With this definition, we can use the same trick: What are you saying?!? Assume s++ = s+- for ppX i.e. helicity independent 12

13. Relative Luminosity

14. BBC How do you define an event? Calculate c*(T1-T2)/2 c=spd of light We call this Minimum Bias (minbias) trigger 2.887m 0.6m 14

15. 8 But Why Use Relative Luminosity? • Consider a game of pool (billiards) • There is no physical asymmetry in whether a collision can occur (If they get close enough they collide in both a and b). • However, we will see an asymmetry as there is more likelihood of collision on table a. a) High Luminosity “Bunch” a) Low Luminosity “Bunch” b) Low Luminosity Bunch 15

16. Relative Luminosity • Calculate Relative Luminosity using BBC defined collisions. • Due to a feature of RHIC, one spin pattern has 3 less bunches that the other, and so we end up with two “structures” in Relative Luminosity (one with ++ with more bunches, the other with +- with more bunches). • Statistical uncertainty <0.00001 A fill is defined as from beam injection to beam dump, ~7-8 hours long. 16

17. But does s++ = s+- • Not always (otherwise there is no point measuring ALL) • Consider two different luminosity detectors (here, the BBC and ZDC) • Assume each has some asymmetry in what they measure (ABBC and AZDC) • Look at ratio • Fit this with where ALL is the asymmetry in the ratio. • We find ALL consistent with zero, which implies: • ALL|BBC = ALL|ZDC • Now the physics measured by BBC (charged hadrons with 3<|h|<4) and ZDC (neutrons with |h|>6) are different. So it is unlikely for them to be non zero and equal. • Take uncertainty on ALL|BBC to be uncertainty in ALL of p0 from R. 17

18. Polarization—Magnitude (I am not an expert on this)

19. Forward scattered proton slow, low statistics but absolute Quick, high statistics, relative proton target BRAHMS & PP2PP (p) RHIC proton beam recoil proton measure! Carbon target PHENIX (p) 90º in Lab frame STAR (p) Recoil carbon Polarized proton Polarimetry at RHIC RHIC CNI (pC) Polarimeters Absolute Polarimeter (H jet) Spin Rotators Siberian Snakes Partial Siberian Snake LINAC BOOSTER Pol. Proton Source AGS AGS Internal Polarimeter 200 MeV Polarimeter 19 Rf Dipoles

20. and Carbon proton Hiromi Okada, Spin2006 Single spin asymmetry Double spin asymmetry Physics topics of pp elastic scattering in the CNI region • Described using Helicity Amplitudes 1~ 5 • Interaction matrix M; Nuclear + Coulomb force • Nuclear and Coulombforces become similar in size at –t~10-3 (GeV/c)2. • They interfere with each other Coulomb Nuclear Interference spin non–flip double spin flip spin non–flip double spin flip single spin flip Well known Unpolarized pp elastic scattering experiment  Very small No one photon exchange contribution to ANN.  Sensitive to 5had and 2had ! 20

21. Ultra thin Carbon ribbon Target (3.5mg/cm2) 6 1 3s Mass cut 15cm carbon 2 5 non-relativistic kinematics Time of Flight (ns) MC ~ 11.17 GeV sM ~ 1.5 GeV Si strip detectors (TOF, EC) 3 4 prompts alpha Thin dead layer for low energy carbon spectroscopy Invariant Mass 2mm pitch 12 strips Energy (keV) 10mm p+ implants ~150 nm depth With alternating spin pattern (+,-,+,-) square-root formula 72 strips in total CNI Detector setup • Particle ID (banana cut) • Clear separation from backgrounds using TOF measurement So we know Pbeam if we know AN 21

22. Forward scattered proton JET target FWHM ~6.5mm RHIC 24, 100GeV/c proton beam ~1mm Recoil particle JET 80cm left Si detectors Measuring AN: Two in One proton beam proton target Recoil proton goal scaling uncertainty right 22

23. Polarization—Direction

24. BRAHMS & PP2PP (p) PHENIX (p) STAR (p) Transverse Longitudinal Radial (Transverse) Use Spin Rotators Spin rotators are partial siberian snakes, and can rotate the polarization direction to many different orientations. RHIC CNI (pC) Polarimeters Absolute Polarimeter (H jet) Spin Rotators Siberian Snakes Partial Siberian Snake LINAC BOOSTER Pol. Proton Source AGS AGS Internal Polarimeter 200 MeV Polarimeter Rf Dipoles 24

25. ZDC Run 5 charged particles neutron But How Longitudinal is Longitudinal? • We have to check if we have or • Take a look at transverse spin asymmetries: • Charged/Neutral pion in forward (large xF) direction is seen, so why not use that? (STAR actually does something like this) • PHENIX cannot measure forward pions (before J. Koster et al. built MPC) • A. Bazilevsky et al. (hep-ex/0610030) found a very forward neutron asymmetry at RHIC. • When beam is longitudinal, asymmetry0 by parity 25

26. p p Charged particles Neutral particles Neutral particles How do you measure forward neutrons? • Using 3 ZDC units, we can measure the majority of the neutron shower, and remove photon showers by excluding events which do not deposit energy in each unit. Yellow Blue 26

27. Raw asymmetry SMD Raw asymmetry YELLOW BLUE f f Raw asymmetry Raw asymmetry YELLOW BLUE f f X Y How do you measure AN for neutrons? • To measure asymmetry, we need position. For this, we use a Shower Maximum Detector (SMD) • Detector consists of a grid of horizontal and vertical scintilator strips. • Get X,Y position and calculate f position. X Y 27

28. LR c2/NDF = 82.5/97 p0 = -0.00423±0.00057 c2/NDF = 88.1/97 p0 = -0.00323±0.00059 UD XF>0 XF>0 UD c2/NDF = 119.3/97 p0 = -0.00056±0.00063 c2/NDF = 81.7/97 p0 = -0.00026±0.00056 LR XF<0 XF<0 Measured Asymmetry During Longitudinal Running <PT/P>= 10.25±2.05(%) <PL/P> = 99.48±0.12±0.02(%) <PT/P>= 14.47±2.20(%) <PL/P> = 98.94±0.21±0.04(%) 28 Fill Number Fill Number

29. Remaining Transverse ComponentATT • Here • ATT • azimuthally independent double transverse spin asymmetry. • ALL background (e<0.01). • expected to be small, but previously unmeasured. • In Run5, PHENIX took a short transverse run specifically to measure ATT. • Consistent with zero. • Possible systematic contribution to ALL <0.07dALL. 29

30. p0 Yield

31. g g p0 p p X p0 • Why measure p0? • Very abundant in p+p collisions • Decay is 99.9% p0gg • PHENIX is designed for very good photon and electron measurements • p0 are easy to measure with our limited acceptance • Kinematics • Two clusters with energy E1 and E2 • Then  31

32. CARTOON # Combinatorial background Mgg p0 h g-g Invariant Mass Spectrum • We actually take all clusters that resemble photons, and calculate an invarient mass 32

33. h g Apply Some Cuts to the Data • Shower Shape: • Calculate c2 based on energy distribution. Remove clusters with less than 2% of being a photon. • Calibrated with test beam data • Time of Flight (ToF) • Can accurately measure collision time and detection time. • Remove slow (low E) hadrons. • Charge Veto • Some hadronic clusters survive shower shape and ToF. • Use detector of charged particles about 20 cm in front of EMCal to remove some remaining charged hadrons 33

34. g-g Invariant Mass Spectrum 34

35. p0 Cross Section • Consistent with previous PHENIX results. • NLO pQCD Theory is consistent with data over nine orders of magnitude. • As theory agrees well with our data, we can use it to interpret our results in terms of Dg 35

36. The Asymmetry

37. Calculating p0 ALL • Calculate ALL(p0+BG) and ALL(BG) separately. • Get background ratio (wBG) from fit of all data. • Subtract ALL(BG) from ALL(p0+BG): ALL(p0+BG) = wp0· ALL(p0) + wBG · ALL(BG) p0+BG region : ±25 MeV around p0peak BG region : two 50 MeV regions around peak 37

38. The Result and (Possible) Interpretation

39. Run6 p0 ALL (200 GeV) • Run6 Data set from filtered data requiring a high pT photon • Data below 5 GeV limited statistics due to filter, so must wait full production. • GRSV curves are parameterizations using different input parameters for Dg, at an input scale of Q2=0.4 GeV GRSV: M. Gluck, E. Reya, M. Stratmann, and W. Vogelsang, Phys. Rev. D 63 (2001) 094005. 39

40. What about Dg? • Confidence levels from a simple c2 test between our data and the four curves plotted. • Theoretical uncertainties are not taken into account (for now). Range is from varying ALL by polarization scale uncertainty * At input scale: Q2 = .4 GeV2 • Run 6 rules out maximal gluon scenarios. • Expect clearer statement when lower pT data from Run6 is available; possibly will allow differentiation between STD and Dg=0. 40

41. x p0 Does a Lot to Constrain Dg So if Dg>0, p0 provides a powerful constraint of Dg. AAC Or Not? 41

42. Conclusions (What I told you) • Experimentalist measure ALL to reduce systematic uncertainties. • Each element for measuring in ALL has been described. • Systematic uncertainties have been considered • Results for p0 ALL from 2005 and (partial) 2006 have been shown. • Simple c2 interpretation on the results clearly exclude Dg=g, and also exclude Dg=-g. • 2006 low pT will add to the current constraint on Dg. • AAC found that 2005 give a significant constraint on Dg if we assume Dg>0. 42