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A Novel Shakedown of the Proton Spin Breakdown

A Novel Shakedown of the Proton Spin Breakdown. How the Field has Become Wider with a Polarized Proton Collider. Christine Aidala. University of Massachusetts Amherst. Old Dominion University. September 13, 2007. Nucleon Structure: The Early Years.

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A Novel Shakedown of the Proton Spin Breakdown

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  1. A Novel Shakedown of the Proton Spin Breakdown How the Field has Become Wider with a Polarized Proton Collider Christine Aidala University of Massachusetts Amherst Old Dominion University September 13, 2007

  2. Nucleon Structure: The Early Years • 1933: Estermann and Stern measure the proton’s anomalous magnetic moment  indicates proton not a pointlike particle! • 1960’s: Quark structure of the nucleon • SLAC inelastic electron-nucleon scattering experiments by Friedman, Kendall, Taylor  Nobel Prize • Theoretical development by Gell-Mann  Nobel Prize C. Aidala, ODU, September 13, 2007

  3. Deep-Inelastic Scattering: A Tool of the Trade • Probe nucleon with an electron or muon beam • Interacts electromagnetically with (charged) quarks and antiquarks • “Clean” process theoretically—quantum electrodynamics well understood and easy to calculate! C. Aidala, ODU, September 13, 2007

  4. (Unpolarized) Proton Structure and “Bjorken-x” What momentum fraction would the scattering particle carry if the proton were made of … 3 bound valence quarks A point particle 1/3 1 1 xBjorken xBjorken 3 bound valence quarks and some slow sea quarks Sea 3 valence quarks Valence 1/3 1 Small x xBjorken 1/3 1 xBjorken Halzen and Martin, “Quarks and Leptons”, p. 201 C. Aidala, ODU, September 13, 2007

  5. Decades of DIS Data • Wealth of data largely thanks to proton-electron collider, HERA, in Hamburg, which shut down in July this year • Rich structure at low x • Half proton’s linear momentum carried by gluons! PRD67, 012007 (2003) C. Aidala, ODU, September 13, 2007

  6. And a (Relatively) Recent Surprise From p+p, p+d Collisions • Fermilab Experiment 866 used proton-hydrogen and proton-deuterium collisions to probe nucleon structure via the Drell-Yan process • Anti-up/anti-down asymmetry in the quark sea, with an unexpected x behavior! New techniques let us continue to find surprises in the rich linear momentum structure of the proton, even after > 40 years! What about the proton’s angular momentum structure? PRD64, 052002 (2001) C. Aidala, ODU, September 13, 2007

  7. The Quark Spin Contribution ΔΣ SLAC: 0.10 < xSLAC <0.7 CERN: 0.01 < xCERN <0.5 0.1 < xSLAC < 0.7 A1(x) EMC (CERN), Phys.Lett.B206:364 (1988) 1349 citations in SPIRES! 0.01 < xCERN < 0.5 “Proton Spin Crisis” x-Bjorken C. Aidala, ODU, September 13, 2007

  8. HERMES PRL92, 012005 (2004) Decades of Polarized DIS Quark Spin – Gluon Spin – Transverse Spin – GPDs – Lz SLACE80-E155 CERN EMC,SMC COMPASS DESY HERMES JLAB Halls A, B, C But what could you learn from a polarized proton-proton collider? 2000 ongoing 2007 ongoing So far no polarized electron-proton collider. R&D for future Electron-Ion Collider in current Long-Range Plan for Nuclear Physics. C. Aidala, ODU, September 13, 2007

  9. up quarks gluon sea quarks down quarks A Polarized Proton Collider:Opportunities . . . • Proton-proton collisions  Direct access to the gluons via gluon-quark, gluon-gluon scattering • High energy provided by a collider allows production of new probes • W bosons • High energy allows use of new theoretical tools • Factorized perturbative quantum chromodynamics (pQCD) (more on this later!) • IF— • Can find a way to maintain polarization of proton beams • through acceleration to high energies (O(102 GeV)) and • during storage in a ring. • Can create tools to measure the degree of beam polarization • at various points in the process of acceleration and storage. C. Aidala, ODU, September 13, 2007

  10. RHIC PHENIX STAR LINAC AGS “Siberian Snakes” To Maintain Polarization Effect of depolarizing resonances averaged out by rotating spin by 180 degrees on each turn • 4 helical dipoles in each snake • 2 snakes in each ring • - axes orthogonal to each other C. Aidala, ODU, September 13, 2007

  11. scattered proton (polarized) proton beam polarized proton target recoil proton Hydrogen-Jet Polarimeter for Beams at Full Energy • Use transversely polarized hydrogen target and take advantage of transverse single-spin asymmetry in elastic proton-proton scattering • Only consider single polarization at a time. Symmetric process! • Know polarization of your target • Measure analyzing power in scattering • Then use analyzing power to measure polarization of beam C. Aidala, ODU, September 13, 2007

  12. The Relativistic Heavy Ion Collider at Brookhaven National Laboratory C. Aidala, ODU, September 13, 2007

  13. Absolute Polarimeter (H jet) Helical Partial Snake Strong Snake RHIC as a Polarized p+p Collider RHIC pC Polarimeters Siberian Snakes BRAHMS & PP2PP PHOBOS Siberian Snakes Spin Flipper PHENIX STAR Spin Rotators Various equipment to maintain and measure beam polarization through acceleration and storage Partial Snake Polarized Source LINAC AGS BOOSTER 200 MeV Polarimeter Rf Dipole AGS Internal Polarimeter AGS pC Polarimeter C. Aidala, ODU, September 13, 2007

  14. News to Celebrate C. Aidala, ODU, September 13, 2007

  15. RHIC Physics Broadest possible study of QCD in A+A, p+A, p+p collisions • Heavy ion physics • Investigate nuclear matter under extreme conditions • Examine systematic variations with species and energy • Proton spin structure • Gluon polarization (DG) • Sea-quark polarization • Transverse spin structure Most versatile hadronic collider in the world! Nearly any species can be collided with any other, thanks to separate rings with independent steering magnets. C. Aidala, ODU, September 13, 2007

  16. Flavor-Separated Sea Quark Polarizations Through W Production For W- interchange u and d. Parity violation of the weak interaction in combination with control over the proton spin orientation gives access to the flavor spin structure in the proton! C. Aidala, ODU, September 13, 2007

  17. Transverse spin only (No rotators) Spin Physics at RHIC • Three experiments: STAR, PHENIX, BRAHMS • Future running only with STAR and PHENIX Longitudinal or transverse spin Longitudinal or transverse spin 2006 accelerator performance: Avg. pol 62% at 200 GeV (design 70%). Achieved 3.5x1031 cm-2 s-1 lumi (design ~5x this). C. Aidala, ODU, September 13, 2007

  18. Blue Yellow Spin Rotators ON Current Reversed! Radial polarization Blue Yellow Spin Rotators ON Correct Current Longitudinal polarization! Blue Yellow Single-Spin Asymmetries for Local Polarimetry:Confirmation of Longitudinal Polarization AN Spin Rotators OFF Vertical polarization f C. Aidala, ODU, September 13, 2007

  19. A Polarized Proton Collider:Opportunities. . . and Challenges • Proton-proton collisions  Direct access to the gluons via gluon-quark, gluon-gluon scattering • High energy provided by a collider allows production of new probes • W bosons • High energy allows use of new theoretical tools • Factorized perturbative quantum chromodynamics (pQCD) • Challenge: No longer dealing with the “clean” processes of QED! C. Aidala, ODU, September 13, 2007

  20. RHIC Spin: Proton Structure with Quark and Gluon Probes At ultra-relativistic energies the proton represents a jet of quark and gluon probes Need QCD now, not QED! C. Aidala, ODU, September 13, 2007

  21. q(x1) Hard Scattering Process Hard Scattering Process X X g(x2) Universality Hard Scattering in p+p:Factorization and Universality • “Hard” probes have predictable rates given: • Parton distribution functions (need experimental input) • pQCD hard scattering rates (calculable in pQCD) • Fragmentation functions (need experimental input) C. Aidala, ODU, September 13, 2007

  22. |h| < 0.35 PRL 95, 202001 (2005) STAR STAR pQCD in Action at Ös=200 GeV p0 Fraction pions produced h~0 C. Aidala, ODU, September 13, 2007

  23. g DgDq DqDq Prompt g Production at Ös=200 GeV • Gluon Compton scattering dominates • At LO no fragmentation function • Small contribution from annihilation Will be an important channel for DG! C. Aidala, ODU, September 13, 2007

  24. e+e- ? pQCD DIS Probing the Gluon Polarization at RHIC With factorized pQCD in hand as a theoretical tool, can probe DG via double-helicity asymmetry measurements Now for some results . . . N: yield ++ same helicity +- opposite helicity R: luminosity++/luminosity+- C. Aidala, ODU, September 13, 2007

  25. Fraction pions produced The Pion Isospin Triplet, ALL and DG • At transverse momenta > ~5 GeV/c, midrapidity pions dominantly produced via qg scattering • Tendency of p+ to fragment from an up quark and p- from a down quark and fact that Du and Dd have opposite signs make ALL of p+ and p- differ measurably • Order of asymmetries of pion species can allow us to determine the sign of DG C. Aidala, ODU, September 13, 2007

  26. STAR STAR ALL of ±at Ös=200 GeV PHENIX Run-06 charged pions coming soon! C. Aidala, ODU, September 13, 2007

  27. Gluon Polarization from Inclusive Hadrons and Jets in Polarized p+p 2005 data C. Aidala, ODU, September 13, 2007

  28. Update on ΔG vs ALL0 in PHENIX from 2006 Data Sasha Bazilevsky, AGS&RHIC Users’ Meeting, June 2007 • “std” scenario, G(Q2=1GeV2)=0.4, is excluded by data on >3 sigma level: 2(std)2min>9 • Only exp. stat. uncertainties included (syst. uncertainties expected to be small) • Uncertainties from functional form Δg(x) not included. Calc. by W.Vogelsang and M.Stratmann C. Aidala, ODU, September 13, 2007

  29. Transverse Momentum vs. xgluon • Limited sensitivity to x-dependence of Dg(x) • Currently no sensitivity to low x and little to x>~0.3 • NLO pQCD: 0 pT=29 GeV/c  xgluon=0.020.3 • GRSV model: G(xgluon=0.020.3) ~ 0.6G(xgluon =01 ) • Each pT bin corresponds to a wide range in xgluon • Data is not sensitive to functional form of g(xgluon) • Quantitative analysis must include impact of different function form g(xgluon) shape Log10(xgluon) C. Aidala, ODU, September 13, 2007

  30. GSC: G(xgluon= 01) = 1 G(xgluon= 0.020.3) ~ 0 GRSV-0: G(xgluon= 01) = 0 G(xgluon= 0.020.3) ~ 0 GRSV-std: G(xgluon= 01) = 0.4 G(xgluon= 0.020.3) ~ 0.25 Extending x Range is Crucial! Gehrmann-Stirling parameterizations GSC: G(xgluon= 01) = 1 GRSV-0: G(xgluon= 01) = 0 GRSV-std: G(xgluon= 01) = 0.4 Current data is sensitive to G for xgluon= 0.020.3 C. Aidala, ODU, September 13, 2007

  31. Quark-Parton Model expectation! E130, Phys.Rev.Lett.51:1135 (1983) 415 citations Spin Crisis Came Out of a Low-x Measurement SLAC: 0.10 < xSLAC <0.7 CERN: 0.01 < xCERN <0.5 0.1 < xSLAC < 0.7 A1(x) EMC (CERN), Phys.Lett.B206:364 (1988) 1349 citations in SPIRES! 0.01 < xCERN < 0.5 “Proton Spin Crisis” The history of the field teaches us that low x is important! x-Bjorken C. Aidala, ODU, September 13, 2007

  32. Extend to higher x at s = 62.4 GeV Extend to lower x at s = 500 GeV present x-range s = 200 GeV Extend x Range • Upgrade PHENIX and STAR detectors with forward coverage (observe collisions of low-x parton in one beam with high-x parton in other) • Measure at different center-of-mass energies •  lower x at s = 500 GeV. Expected to start in 2009. •  higher x at s = 62.4 GeV. Done in 2006! C. Aidala, ODU, September 13, 2007

  33. arXiv:0708.3060 p0 ALL at s=62.4 GeV Converting to xT, we can see the significance of the s=62.4 GeV data set compared to the Run-5 200-GeV preliminary data. Not bad for 2 weeks of 62-GeV running! Theory curves by W. Vogelsang pQCD is earning its keep down to lower energies! - Resummed calculation by de Florian, Vogelsang, and Wagner C. Aidala, ODU, September 13, 2007

  34. xgluon Inclusive 0 200 500 101 GeV N.B. x-range sampled depends on g(x,Q2) ! -- M. Stratmann 102 0 10 30 20 pT (GeV) Going Beyond Inclusive Measurements • Inclusive channels suffer from integration over x model-dependent DG extraction • Improved accelerator and detector performance will allow jet-jet and g-jet coincidence measurements, placing better constraints on partonic kinematics Note: Jets and prompt photons both carry total energy of scattered parton. Don’t need any fragmentation functions . . . C. Aidala, ODU, September 13, 2007

  35. Hard Scattering Process X Universality Reminder: Factorized pQCD • “Hard” probes have predictable rates given: • Parton distribution functions (need experimental input) • pQCD hard scattering rates (calculable in pQCD) • Fragmentation functions (need experimental input) C. Aidala, ODU, September 13, 2007

  36. Fragmentation Functions (FF’s):Improving Our Input for Inclusive Hadronic Probes • FF’s not directly calculable from theory—need to be measured and fitted experimentally • The better we know the FF’s, the tighter constraints we can put on the polarized parton distribution functions! • Traditionally from e+e- data—clean system! • Framework now developed to extract FF’s using all available data from deep-inelastic scattering and hadronic collisions as well as e+e- • de Florian, Sassot, Stratmann: PRD75:114010 (2007) and arXiv:0707.1506 C. Aidala, ODU, September 13, 2007

  37. h h Dg2 DgDq Dq2 An Example: Cross Section and ALL of h Meson h fragmentation function not yet available! No theoretical comparisons currently possible . . . C. Aidala, ODU, September 13, 2007

  38. Parameterizing the h FF Using e+e- and PHENIX p+p Data MARK II Once FF is available, asymmetry data will provide additional constraint on DG! L3 HRS OPAL CA, J. Seele, M. Stratmann, W. Vogelsang C. Aidala, ODU, September 13, 2007

  39. RHIC Data and Global Fits • Global fits of measurements sensitive to different processes and different kinematics essential to place tight constraints on nucleon pdf’s • World DIS results will be combined with RHIC measurements of various probes • Pions, jets, prompt photons, heavy flavor, gamma-jet and jet-jet correlations, . . . • Two global fit papers published so far including PHENIX p0 ALL data from RHIC • M. Hirai et al., Phys. Rev. D74, 014015 (2006) • Navarro and Sassot, Phys. Rev. D74, 011502 (2006) Still a long road ahead of us . . . C. Aidala, ODU, September 13, 2007

  40. Conclusions and Prospects • RHIC has been an exciting place to study nucleon spin structure for the past six years! • Very stimulating place to be an accelerator physicist, too! • Availability of a polarized proton collider has expanded breadth of field, attracted new members to the nucleon structure community • Moving into new era where RHIC will make decisive contributions to knowledge of polarized gluon distribution and more Nearly 20 years later, the proton spin crisis remains unresolved! But there’s a large and diverse community of people—at RHIC and complementary facilities—continuing to coax the secrets out of one of the most fundamental building blocks of the world around us. C. Aidala, ODU, September 13, 2007

  41. Extra Slides C. Aidala, ODU, September 13, 2007

  42. RHIC Specifications • 3.83 km circumference • Two independent rings • Up to 120 bunches/ring • 106 ns crossing time • Energy: • Up to 500 GeV for p+p • Up to 200 GeV for Au+Au(per N+N collision) • Luminosity • Au+Au: 2 x 1026 cm-2 s-1 • p+p : 2 x 1032 cm-2 s-1(70%polarized) C. Aidala, ODU, September 13, 2007

  43. Polarized Collider Development C. Aidala, ODU, September 13, 2007

  44. RHIC Polarimetry • Proton-carbon (pC) polarimeter • For fast measurements (< 10 s!) of beam polarization • Take several measurements during each fill • Polarized hydrogen-jet polarimeter • Dedicated measurements (weeks) to calibrate the pC polarimeter • Three-fold purpose of polarimeters • Measurement of beam polarization to provide feedback to accelerator physicists • Measurement of beam polarization as input for spin-dependent measurements at the various experiments • Study of polarized elastic scattering C. Aidala, ODU, September 13, 2007

  45. RHIC Performance, Longitudinal Polarization(PHENIX integrated luminosities shown) ** initial estimate C. Aidala, ODU, September 13, 2007

  46. PHENIX Polarized-Proton Runs: Transverse Polarization ** initial estimate C. Aidala, ODU, September 13, 2007

  47. STAR Improving Forward Coverage at RHIC • STAR Forward Meson Spectrometer will provide full azimuthal coverage for range 2.5  h  4.0 • Broad acceptance in xF-pT plane for inclusive p0 , getc…production in p+p and d(p)+Au • Broad acceptance for g-p0 and p0-p0 from forward jet pairs to probe low-x gluon density in p+p and d(p)+Au collisions PHENIX Muon Piston Calorimeter will provide full azimuthal coverage for range 3.1  h  3.7 and 2 < E(p0) < 25GeV Raw AN(f) of p0 from Run-6 MPC, 62.4 GeV C. Aidala, ODU, September 13, 2007

  48. 104 Central arms prompt  103 Q2 NCC prompt  102 10 1 200 GeV 10-1 10-3 1 10-2 10-5 10-1 10-4 x Prompt Photons with PHENIX Nosecone Calorimeter • γ-jet is: • Very clean way to measure the gluon • Measuring the angle of the jet gives you access to xgluon x C. Aidala, ODU, September 13, 2007

  49. W Production in Polarized p+p Collisions Single Spin Asymmetry in the naive Quark Parton Model Parity violation of the weak interaction in combination with control over the proton spin orientation gives access to the flavor spin structure in the proton! Experimental Requirements:  tracking at high pT event selection for muons difficult due to hadron decays and beam backgrounds  control of all backgrounds W Z C. Aidala, ODU, September 13, 2007

  50. Gluon Polarization from Photon-Gluon Fusion in DIS • golden channel: charm production • hadron production at high PT Photon-Gluon Fusion(PGF) Favors small ΔG(x≈0.1) C. Aidala, ODU, September 13, 2007

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