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Nathan Means (Stony Brook University) For the PHENIX Collaboration

Measuring Azimuthal Asymmetries in Back-to-Back Hadrons Using Polarized PP Collisions at RHIC with the MPC. Nathan Means (Stony Brook University) For the PHENIX Collaboration. Single Transverse Spin Asymmetries.  s = 200 GeV. P hys. R ev. L ett. 92 (2004) 171801. P T =0.5~2 GeV/c. E704.

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Nathan Means (Stony Brook University) For the PHENIX Collaboration

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  1. Measuring Azimuthal Asymmetries in Back-to-Back Hadrons Using Polarized PP Collisions at RHIC with the MPC Nathan Means (Stony Brook University) For the PHENIX Collaboration

  2. Single Transverse Spin Asymmetries s = 200 GeV Phys.Rev.Lett. 92(2004) 171801 PT=0.5~2 GeV/c E704

  3. 2 0  h Sivers Fcn from Back2Back Analysis • Measurement of δΦ between back-to-back jets is sentive to the Sivers function (Boer and Vogelsang, PRD69:094025,2004) • Difficult to measure jets with PHENIX acceptance and so will use back to back hadrons • The fragmentation smears out the asymmetry • Not sensitive to Collins function because the effect integrates out.

  4. AN Predictions from Boer and Vogelsang Boer and Vogelsang, PRD69:094025,2004 Anselmino, D’Alesio, Murgia PRD 67 (2003) 074010 • On left are some theoretical guesses on expected magnitude of AN from Sivers • (i) • (ii) • (iii) • (iv) From fits to E704 Data , with <kT2> = 2.5 GeV for gluons

  5. Sensitivity Estimate For PHENIX central arm P* Maximal di-hadron Sivers Minimal di-hadron Sivers Projected Errors for Run07 Transverse p+p with 5.0/pb

  6. Partonic Cross-Sections for central and forward regions process contribution to 0 For PHENIX central arm acceptance process contribution to π0 Using central arms at low pT we have access to gluon Sivers function Using MPC at forward rapidity to measure π0 we have access to quark Sivers function With both measurements we should be able to disentangle quark and gluon Sivers function

  7. South Muon Magnet North Muon Magnet MPC Locations

  8. PbWO4 Scintillating Crystals Density 8.28 g/cm3 Size 2.2x2.2x18 cm3 Length 20 X0, 0.92  Weight 721.3 g NORTH SOUTH Moliere radius 2.0 cm Radiation Length 0.89 cm Interaction Length 22.4 cm Light Yield ~10 p.e./MeV @ 25 C Temp. Coefficient -2% / C Radiation Hardness 1000 Gy Main Emission Lines 420-440, 500 nm Refractive Index 2.16 PHENIX Muon Piston Calorimeter Upgrade Small cylindrical hole in Muon Magnet Piston, Radius 22.5 cm and Depth 43.1 cm

  9. Why the MPC? • Access to Forward Physics (pseudo rapidity of 3.1 – 3.7 for south and 3.1 – 3.9 for north?) • Color Glass Condensate • Able to look at low xBj (gluon saturation) • Longitudinal Spin • ALL measurement (Δg) at lower xBj • Transverse Spin • Back to back hadron azimuthal asymetry • Full 2π Azimuthal Coverage • More acceptance of hadron for azimuthal asymmetry measurement

  10. May 11 2006, 1st0 peak π0 energy spectrum from one hour of data taking • About 28(?) nb-1 of data with an average beam polarization of 57% were collected in Run-6 (~3 days of data) • This gives us ~ 1.3 * 106π0 events (not taking into account detector inefficiencies) with which we can do at “proof of principle analysis”

  11. Summary • Using back to back hadrons we will measure the Sivers function • Central arms will measure mainly gluon contribution to the Sivers function • Using the MPC we will be able to measure the quark contribution • With enough statistics we will be able to disentangle the gluon and quark contributions to the Sivers function

  12. Back-Up Slides

  13. Fwd 0 xF distribution, Run06 62 GeV PYTHIA based study, 0.02/pb 62.4 GeV • At 200 GeV, PYTHIA gives same cross-section as that measured by STAR • At 62 this is not yet known if PYTHIA also matches the forward 0 cross-section • This assumes a perfect detector, which the MPC is not (Run06 was commissioning run) • Acceptance includes smearing effect from z-vertex dist, and 30 cm cut, but not detector noisy/dead areas, or reconstruction efficiencies.

  14. PHENIX Muon Tracker Station I  APD PbWO4 3<η<4 South Muon Piston Calorimeter (SMPC) APD/pre amps Driver Boards Beam pipe

  15. Next, North MPC Inconvenient, but unused space! Inconvenient, but unused space!

  16. North MPC Design Blue Boxes: Crystals that were in South but not in North Red Box: new crystals that were added to the north design because of different constraints

  17. 2 0  h Sivers Fcn from Back2Back Analysis Boer and Vogelsang, Phys.Rev.D69:094025,2004, hep-ph/0312320 • Non-Zero Sivers function means that there is a left/right asymmetry in the kT of the partons in the nucleon • For a positive Siver’s function, there will be net parton kT to the left (relative to direction of proton, assuming spin direction is up). • Boer and Vogelsang find that this parton asymmetry will lead to an asymmetry in the  distribution of back-to-back jets • There should be more jets to the left (as in picture to the left). • Should also be able to see this effect with fragments of jets, and not just with fully reconstructed jets? • Take some jet trigger particle along ST axis (either aligned or anti-aligned to ST) • Trigger doesn’t have to be a leading particle, but does have to be a good jet proxy • Then look at  distribution of away side particles

  18. AN Reduction 1: Polarization • Polarization P < 1 just reduces AN by P • Besides that, most of the time the jet is not aligned exactly along the polarization axis, which means AN=AN(j1,) and also the polarization is reduced by cos(j1) • We can make a simple (though wrong) estimate for this effect by calculating the average polarization from a jet spread of /2 around the polarization axis j1 ST j2

  19. AN Reduction 2: Di-Hadron vs. Di-Jets AN away side parton up down unpolarized di-hadron di-jet • Since we don’t reconstruct jets fully, we have to use di-hadron correlations to measure jet . This smears out the di-hadron AN relative to the di-jet AN, with smearing function g (assumed here to be a gaussian, with jT=0.35). • The effect broadens and lowers (by just a little bit) the asymmetry

  20. Rediscovery of an Old Idea of Yuji’s http://www.phenix.bnl.gov/WWW/publish/goto/Polarimetry/pol1.html (and also Ken Imai)

  21. Run06 Actual Cent Arm Sivers Estimate 0.27/pb, radial pol of 57%

  22. N(f)/N0 Collins Effect? PHENIX Acceptance R. Seidl, Belle Collaboration 0 edge on view of jet distribution of hadrons around away side hadron Collins Effect averages to 0 in back-to-back d di-hadron measurement as long as there is no net longitudinal component of outgoing quark spin

  23. South MPC Acceptance =3.7 =3.1 • Generated 10K single photons of 10 GeV at South MPC, flat in phi and theta in PISA to look at the response. • Coverage is from 3.1<<3.7 with (almost) full acceptance in phi.

  24. pulse shapes • screenshots taken 2/12/06, from beam in yellow (first Run06 circulating beam in RHIC, no blue beam yet, so these are not from collisions… ie, they are from beam backgrounds) • signal (sky blue) is after our prototype receiver channel. the signal out of the twisted pair is not much different. signal into mondo chip is flattened out b/c of the integrater circuit at input of EMC FEM. • magenta, green, and blue are trigger bit signals, used to trigger the scope • note: preamp signal is different… above signal is after shaping in driver/receiver boards. I have led versions of the signals at every stage, if you want.

  25. fully installed mpc.s

  26. NCC NCC MPC MPC Present & Future PHENIX Acceptance for Calorimetry EMCAL 0 f coverage 2p EMCAL -3 -2 -1 0 1 2 3 rapidity • Addition of MPC increases PHENIX acceptance for calorimetry by a factor of 4 (with a detector more than 10 times smaller) • Especially important that the very forward region (>3) is covered • Along with Nose-Cone Calorimeter, it would give PHENIX very good calorimetry coverage.

  27. FermiLab Test Beam Results FNAL Meson Test Beam Facility • FNAL MTBF: Secondary beam with electron/hadron identification • Energy Resolution is at worst 14%/E • Analysis is ongoing… • Improved Calibrations, Shower Shape extraction

  28. MIP Peak South MPC Run06 MIP and 0 Peak • PbWO4 -dE/dx = 13 MeV/cm  MIP peak sits at ~234 MeV • Along with 0, mass peak position, should allow us to set and confirm energy scale

  29. MPC Left-Right Transverse Asymmetry yellow blue • Asymmetry seen in yellow beam (positive xF), but not in blue (negative xF) • Only 10% of total statistics from 62 GeV Transverse Run • Simple 3x3 tower sum clustering, with no overlap shower splitting • Cuts: mass>0.01 && mass<0.30 && high “energy”

  30. Summary and Status • New electromagnetic calorimeter (MPC) has been installed into PHENIX for Run06 on a short time scale, giving coverage for 0at forward rapidities • Very important to confirm results from other experiments • Data Sets from Run06 • 200 GeV Transverse (~0/pb) – Very little useful data, due to late arrival of electronics • 200 GeV Longitudinal (7.5/pb) – forward 0 ALL, di-hadron ALL • 62 GeV Transverse (20/nb) – Raw Asymmetries seen from 2-3 days data, commissioning as a local polarimeter • 62 GeV Longitudinal (80/nb) – Unique data set at RHIC. • Currently installing North MPC, with slightly larger acceptance, and with lessons from the South, to be ready for the beginning of Run07 (cooldown on Dec. 1).

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