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

Sivers Fcn from Back2Back AnalysisMeasurement of 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 hadronsThe fragmentation smears out the asymmetryNot sensitive to Collins function because the effect integrates out.

AN Predictions from Boer and VogelsangOn left are some theoretical guesses on expected magnitude of AN from Sivers

(i)

(ii)

(iii)

(iv)Boer and Vogelsang, PRD69:094025,2004Anselmino, DAlesio, Murgia PRD 67 (2003) 074010, with = 2.5 GeV for gluonsFrom fits to E704 Data

Sensitivity EstimateFor PHENIX central armP*Maximal di-hadron SiversMinimal di-hadron SiversProjected Errors for Run07 Transverse p+p with 5.0/pb

For PHENIX central arm acceptanceprocess contribution to 0Using central arms at low pT we have access to gluon Sivers functionUsing MPC at forward rapidity to measure 0 we have access to quark Sivers functionWith both measurements we should be able to disentangle quark and gluon Sivers functionPartonic Cross-Sections for central and forward regions

MPC Locations

PHENIX Muon Piston Calorimeter UpgradeSmall cylindrical hole in Muon Magnet Piston, Radius 22.5 cm and Depth 43.1 cm

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 CondensateAble to look at low xBj (gluon saturation)Longitudinal SpinALL measurement (g) at lower xBjTransverse SpinBack to back hadron azimuthal asymetryFull 2 Azimuthal CoverageMore acceptance of hadron for azimuthal asymmetry measurement

0 energy spectrum from one hour of data takingMay 11 2006, 1st 0 peakAbout 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 * 106 0 events (not taking into account detector inefficiencies) with which we can do at proof of principle analysis

SummaryUsing back to back hadrons we will measure the Sivers functionCentral arms will measure mainly gluon contribution to the Sivers functionUsing the MPC we will be able to measure the quark contributionWith enough statistics we will be able to disentangle the gluon and quark contributions to the Sivers function

Back-Up Slides

Fwd 0 xF distribution, Run06 62 GeV62.4 GeVAt 200 GeV, PYTHIA gives same cross-section as that measured by STARAt 62 this is not yet known if PYTHIA also matches the forward 0 cross-sectionThis 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.PYTHIA based study, 0.02/pb

PHENIX Muon Tracker Station I3

Next, North MPCInconvenient, but unused space!Inconvenient, but unused space!

North MPC DesignRed Box: new crystals that were added to the north design because of different constraintsBlue Boxes: Crystals that were in South but not in North

Sivers Fcn from Back2Back AnalysisBoer and Vogelsang, Phys.Rev.D69:094025,2004, hep-ph/0312320Non-Zero Sivers function means that there is a left/right asymmetry in the kT of the partons in the nucleonFor a positive Sivers 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 jetsThere 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 doesnt have to be a leading particle, but does have to be a good jet proxyThen look at distribution of away side particles

AN Reduction 1: PolarizationPolarization P < 1 just reduces AN by PBesides 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 axisSTj1j2

AN Reduction 2: Di-Hadron vs. Di-Jetsupdownunpolarizedaway side partonANdi-hadrondi-jetSince we dont 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

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

Run06 Actual Cent Arm Sivers Estimate0.27/pb, radial pol of 57%

Collins Effect?0PHENIX Acceptanceedge on viewof jetCollins Effect averages to 0 in back-to-back d di-hadron measurement as long as there is no net longitudinal component of outgoing quark spindistribution of hadrons around away side hadron R. Seidl, Belle Collaboration

South MPC AcceptanceGenerated 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

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 scopenote: 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.pulse shapes

fully installed mpc.s

-3 -2 -1 0 1 2 3 rapidity0 f coverage 2pEMCALEMCALPresent & Future PHENIX Acceptance for Calorimetry 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 coveredAlong with Nose-Cone Calorimeter, it would give PHENIX very good calorimetry coverage.

FermiLab Test Beam ResultsFNAL MTBF: Secondary beam with electron/hadron identificationEnergy Resolution is at worst 14%/EAnalysis is ongoing Improved Calibrations, Shower Shape extractionFNAL Meson Test Beam Facility

South MPC Run06 MIP and 0 PeakPbWO4 -dE/dx = 13 MeV/cm MIP peak sits at ~234 MeVAlong with 0, mass peak position, should allow us to set and confirm energy scale

MPC Left-Right Transverse AsymmetryAsymmetry seen in yellow beam (positive xF), but not in blue (negative xF)Only 10% of total statistics from 62 GeV Transverse RunSimple 3x3 tower sum clustering, with no overlap shower splittingCuts: mass>0.01 && mass

Summary and StatusNew electromagnetic calorimeter (MPC) has been installed into PHENIX for Run06 on a short time scale, giving coverage for 0 at forward rapiditiesVery important to confirm results from other experimentsData Sets from Run06200 GeV Transverse (~0/pb) Very little useful data, due to late arrival of electronics200 GeV Longitudinal (7.5/pb) forward 0 ALL, di-hadron ALL62 GeV Transverse (20/nb) Raw Asymmetries seen from 2-3 days data, commissioning as a local polarimeter62 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).