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Future Perspectives on Transverse Single Spin Asymmetries at RHIC

Future Perspectives on Transverse Single Spin Asymmetries at RHIC. Disclaimer: the realities and perspectives to be presented are my own, although may be shared by others.

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Future Perspectives on Transverse Single Spin Asymmetries at RHIC

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  1. Future Perspectives on Transverse Single Spin Asymmetries at RHIC Disclaimer: the realities and perspectives to be presented are my own, although may be shared by others. Forewarning: my perspective is that spin is best probed in a polarized p+p collider in the forward direction. (Pause before starting so you can decide…) L.C. Bland Brookhaven National Laboratory INT Workshop on 3D parton structure of the nucleon Seattle, September 2009

  2. Conclusions and Summaryfrom Overview of Transverse Single Spin Asymmetry Measurements at RHIC • Transverse spin asymmetries are present at RHIC energies • Transverse spin asymmetries are present at large h • Particle production cross sections and correlations are consistent with pQCD expectations at large h where transverse spin effects are observed • Essential to go beyond inclusive (meson)production to disentangle dynamical origins 3D parton structure, INT

  3. L polarization observables at large x Going Beyond Inclusive Meson ProductionFuture Transverse Single Spin Asymmetry Measurements at RHIC(pending additional forward instrumentation+run time) Drell-Yan/virtual photon production at large y Direct photon production at large h (+ away-side jet) Large h jet production (+ p0 correlation in forward jet) Increasing impact Increasing experimental accessibility 3D parton structure, INT

  4. Comments About Present Realities… 3D parton structure, INT

  5. RHIC pC Polarimeters Absolute Polarimeter (H jet) Siberian Snakes Siberian Snakes PHENIX STAR Spin Rotators (longitudinal polarization) Spin Rotators (longitudinal polarization) Pol. H- Source LINAC BOOSTER Helical Partial Siberian Snake AGS 200 MeV Polarimeter AGS pC Polarimeter Strong AGS Snake RHIC is the First (Only) Polarized Proton Collider • GOALS • reference: RHIC Spin Plan (2008) http://spin.riken.bnl.gov/rsc/report/spinplan_2008/spinplan08.pdf • Determination of polarized gluon distribution (DG) using multiple probes • Determination of flavor identified anti-quark polarization using parity violating production of W • Transverse spin: connections to partonic orbital angular momentum (Ly) and transversity (dS) 3D parton structure, INT

  6. RHIC is a Unique Collider… Source: http://www.agsrhichome.bnl.gov/RHIC/Runs/ • …capable of colliding essentially all positive ions over a broad range of s • …with a broad and diverse physics program aimed at important questions • What is quark-gluon plasma?  heavy-ion collisions • How does the proton get its spin?  polarized proton collisions • Does the gluon density saturate in a heavy nucleus?  d+Au/p+Au collisions 3D parton structure, INT

  7. Plans for future runs at RHIC have been written… Reference: http://www.bnl.gov/npp/docs/RHIC%20Run%2010%20Plan_r1a.pdf This is the only transverse spin science goal written in the plan for the next 5 years 3D parton structure, INT

  8. LuminosityRun-9 performance Source: RHIC Collider Projections, W. Fischer et al. (2009) • Challenges remain to be overcome to realize the best-case scenarios • Luminosity increases at s=500 GeV relative to s=200 GeV were realized • Depolarizing resonances in RHIC will require new tunes to reduce their impact 3D parton structure, INT

  9. LuminosityFuture Projections Source: RHIC Collider Projections, W. Fischer et al. (2009) • Luminosity projections for s = 500 GeV are sufficient for transverse-spin DY • Improved polarization is important to achieve sufficient accuracy 3D parton structure, INT

  10. STAR Detector Forward Meson Spectrometer commissioned/operated in RHIC run 8. Cluster-pair triggered readout of Forward Time Projection Chamber in RHIC run 9. (Spatial resolution and pileup suppression adequate?) FTPC will be removed before RHIC run 11. • STAR and PHENIX are primarily instrumented near mid-rapidity • Forward direction can be viewed at STAR, but present instrumentation is limited and not completely compatible with high luminosity polarized p+p collisions • All experiments at RHIC are challenging, even with existing apparatus 3D parton structure, INT

  11. Influence of STAR SolenoidImpact on charged particles produced in the forward direction Charges see increasing radial fringe field as pT increases Interaction point FMS poletip • Radial and Azimuthal fields impart impulses in the Φ direction • These impulses are small and in opposite directions (they partially cancel each other) • Field effects on forward charged particles are small • Determining charge sign will require additional instrumentation 3D parton structure, INT

  12. Forward p+p J/ψ – 2-Cluster AnalysisRHIC Run-8 Result Reconstructed 2-cluster invariant mass / (~ 6 pb-1 Sampled Luminosity) C.Perkins, QM09 arXiv:0907.4396 • Fit with Gaussian + Offset • Gaussian Fit Parameters: • μ = 3.080 ± 0.020 GeV/c2 • σ = 0.082 ± 0.026 GeV/c2 • χ2/d.o.f. = 20.83/26 • Significance from fit • 4.5 σ • Cuts Applied: • E_pair > 60.0 GeV • Zγγ < 0.7 • Isolation Radius: • 0.4 Dh-Df • pT_cluster > 1.0 GeV/c • high-xF J/ may have implications for intrinsic charm at large Bjorken-x in proton • use to benchmark simulations for future transverse-spin Drell-Yan experiment 3D parton structure, INT

  13. Forward p+p J/ψ – 3-Cluster AnalysisRHIC Run 8 Result • Reconstructed invariant mass of candidate χC → J/ψ + γ events • Peak Counts = 8.40 ± 2.88 • 2.9 σ Significance • μ = 2.97 ± 0.025 GeV • σ = 0.070 ± 0.025 GeV • χ2/d.o.f. = 0.7 with 14 points fit. • Significance depends on background model • 2.9 σ significance with currently estimated background. 3D parton structure, INT C.Perkins, QM09 arXiv:0907.4396

  14. Attempts at realizing future transverse single-spin asymmetry measurementsA bottoms-up approach 3D parton structure, INT

  15. Future Physics Goal (I) p+pp0+X, s = 500 GeV • Motivations for measurement: • Strong evidence that large-xF AN persists over a broad range of √s  exploit existing capabilities to establish if this continues to √s = 500 GeV • There are prospects for a transverse spin DY measurement at RHIC. Likely best done at √s = 500 GeV. Persistence of pion AN to √s = 500 GeV is one physics requirement for transverse-spin DY • Requirements: • Capabilities to robustly identify p0 production to >100 GeV. Existing shower maximum detector in east FPD enables this identification (see backup) • Best estimates based on xF,pT scaling of sp, and limits on xT scaling, suggest precision comparable to largest pT measurements at √s=200 GeV can be achieved with Lint=7 pb-1 with Pbeam=55% • http://drupal.star.bnl.gov/STAR/system/files/20090203.3.pdf 3D parton structure, INT

  16. Future Physics Goal (II) p+p jet + X, s = 500 and 200 GeV • Motivations for measurement: • Expectation that jets, with their p0 fragments, will enable separation of contributions from Collins+Sivers(+other?), by analogy to semi-inclusive DIS • Published calculations suggest strong interest as a test of present understanding • Requirements: • Measurement of jet energy (see below)  addition of Forward Hadron Calorimeter behind existing FMS at STAR • Addition of hadronic+electromagnetic energy at trigger level to eliminate bias • Anticipate need for modest Lint, Pbeam concurrently achieved with other goals 3D parton structure, INT

  17. Forward Upgrade (I)Proposed Forward Hadron Calorimeter 3D parton structure, INT

  18. Forward Jets with FMS + FHCImportance of hadronic and EM jet fragments • Detectable hadrons and photons within acceptance of FMS+FHC are used for summed-energy trigger and for cone-based jet reconstruction • Fraction of energy of reconstructed jet is a nearly uniform distribution 3D parton structure, INT

  19. Forward Jets with FMS + FHCMeasuring the Jet Energy • Detectable hadrons and photons within acceptance of FMS+FHC are used for summed-energy trigger and for cone-based jet reconstruction. Results also checked via “trigger on scattered parton into finite solid angle” • Photon-only jets do not measure the scattered parton energy. • Combining hadronic + EM energy does measure the scattered parton energy, limited mostly by fragmentation effects. • Many jets are not particularly “jetty”, meaning only few hadrons are within the acceptance. Jets with few hadrons do not give a good measure of the scattered parton energy. Invariant mass from the FMS+FHC can discriminate “jetty” versus “non-jetty” fragmentations. 3D parton structure, INT

  20. Future Physics Goal (III) p+p g (+ jet) + X, s = 200 GeV • Motivations for measurement: • Test predictions that AN for forward photon production will be negative • DOE milestone as an experimental test of theoretical understanding • Requirements: • Without a SMD, must be done at √s = 200 GeV to ensure single g/diphoton separation at large xF. • Requires robust performance from FMS, to ensure sufficient acceptance to suppress backgrounds from p0, h, … decays • Correlated g+jet will require development of trigger, to handle the rates • Lint=30 pb-1 with Pbeam=65% at √s = 200 GeV 3D parton structure, INT

  21. Forward Direct Photons References: RHIC spin plan / STAR run-10 beam-use request • Suppress contributions from p0,h decays by requiring candidate direct photon in yellow-shaded annulus, and by requiring effective isolation of the candidate using the remainder of the FMS as an effective veto. This could be implemented at the trigger level via masks. • Primary background remains fragmentation photons. • For inclusive direct photons, it is expected that isolation can be improved with FHC behind the FMS. The need to separate the FMS complicates spin-dependent correlation measurements. 3D parton structure, INT

  22. Future Physics Goal (IV) p+p L + X, s = 500 • Motivations for measurement: • Lambda reveals its polarization through the weak interaction • Induced polarization measurement would be ~10x higher in s than from ISR • DNN is sensitive to transversity without transverse-momentum dependent fragmentation • Requirements: • Addition of FHC behind FMS • Trigger on hadronic cluster, tagged as neutral by BBC match • Ability to detect soft photons from Lp0nggn 3D parton structure, INT

  23. Reconstructed versus simulated decay vertex for events with Lp0n Reconstructed versus simulated vertex for triggered events Can L be reconstructed via p0n? With the vertex, Mggn can be reconstructed. Backgrounds mostly from Lg final states. • Forward Lp0n reconstruction appears feasible with FHC + FMS • Yields are model dependent, and may require elimination of hadronic showering in FMS 3D parton structure, INT

  24. Future Physics Goal (V) p+p e+e- + X, s = 500 • Motivations for measurement: • The world is waiting to see if there is a sign change relative to SIDIS… • Most robust test of present understanding • Requirements: • Charge-sign determination for DY daughters  restoration of tracking in interval spanned by FTPC + FMS shower-maximum detector • Robust understanding of forward dilepton spectrum at √s=500 GeV • Establish that transverse spin effects persist to √s=500 GeV • Lint ~ 250 pb-1 with Pbeam > 50% at √s=500 GeV 3D parton structure, INT

  25. Rapidity and Collision EnergyTransverse Spin Asymmetries for the DY Processhttp://spin.riken.bnl.gov/rsc/write-up/dy-final.pdf Light mass DY, Mg*> 4 GeV/c2 Rapidity distributions for different s Large rapidity acceptance required to probe valence quark Sivers function, also where p+pp+X transverse spin asymmetries are found to be large at RHIC. 3D parton structure, INT

  26. Forward Upgrade (II)Shower Maximum Detector (SMD) for FMS • FMS-SMD is required for direct photon physics at large xF for s=500 GeV p+p collisions. Scope can be limited to annular acceptance. • DY requires good space point at FMS and track near vertex to get charge sign. Feasibility of DY needs to be established, and run-9 multi-cluster triggered slow events can help. If feasible, restoration of tracking coverage of FTPC is required. Larger area coverage of FMS would then be required by FMS-SMD. • Fiber/scintillator-strip factories are mostly gone, and would need to be restored to build FMS-SMD. • Scope of FMS-SMD must be established before proceeding. 3D parton structure, INT

  27. p0, Jet, photon, DY Lint requirements Probe s Lint (pb-1) Pbeam Physics p+pp0+X 500 7 55 s dependence p+pjet+X 200 ~5 55 Sivers/Collins p+pg(+jet)+X 200 30 65 AN sign change p+pDY+X 500 250 55 AN sign change • RHIC spin plan involved mix of longitudinal/transverse polarization • FHC addition enables jet measurements, and could be done at s=500 GeV in run 11 during time to measure p+pp0+X with east FPD. • Feasibility tests of p+pL+X needed to establish Lint, Pbeam requirements 3D parton structure, INT

  28. Summary • Measurements of transverse single spin asymmetries beyond inclusive meson production in the forward direction will require additional instrumentation + run time • The experiment with the greatest impact is transverse spin DY. Realizing such an experiment will require demonstrated accelerator performance, additional instrumentation and run time. 3D parton structure, INT

  29. Backup 3D parton structure, INT

  30. Why does high-xF intrinsic heavy flavor matter? • Diffractive Higgs production at the LHC via QQ in proton • May provide a clear signal for Higgs production due to small background • How can high-xF intrinsic heavy flavor happen? • Not from Gluon Splitting (extrinsic heavy flavor) • Heavy quarks are expected to be multi-connected to the valence quarks within a proton and appear at large x via… Phys.Rev. D73 (2006) 113005 QED QCD • Can intrinsic heavy flavor expectations be tested experimentally? 3D parton structure, INT

  31. Shower Maximum Detector lead converter 7x7 matrix of lead glass cells preshower (7 Pb-glass cells) Example of event identified as a diphoton by the matrix and only a single photon by the SMD East FPD Events from run 9 Existing east FPD layout… • event requirements • >1 cluster • Egg > 50 GeV • single g/diphoton separation for matrix shown by GSTAR analysis to be robust to E~55 GeV • SMD response enables single g/diphoton separation to E>100 GeV • Plan is to add this performance to FMS in the future for √s=500 GeV operation 3D parton structure, INT

  32. Status/Plan of Large-xF DY • Large-xF J/ production has been observed from bare large-y calorimeter response in RHIC run 8. • Cluster-pair trigger is operational for acquiring large-y tracking data in RHIC run-9. Pending analysis, requirements for future DY can be established (e.g., fast-tracking inside solenoid, space points in front of FMS). • Sufficient luminosity for p+p s=500 GeV collisions has been established; further development of polarization is required, as is measurement of AN(xF) for p+pp0+X at s=500 GeV and measurement of large-xF J/ and U production at s=500 GeV, to bracket light-mass DY region. • Technical solutions exist for fast tracking inside solenoid (GEM trackers) and space points in front of FMS (forward meson preshower). Construction to span 2.5<h<4 region is required, and could be completed in ~2 years, pending approval. • RHIC schedule is oversubscribed  DY would be after RHIC run 11 (>2011). • Run-10 will be Au+Au energy scan for deconfinement critical point search, and Au+Au at sNN=200 GeV. • Run-11 is expected to be polarized p+p, with unknown mix of s=200,500 GeV and longitudinal/transverse polarization. 3D parton structure, INT

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