A Novel Shakedown of the Proton Spin Breakdown

  • View
    37

  • Download
    0

Embed Size (px)

DESCRIPTION

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. - PowerPoint PPT Presentation

Text of A Novel Shakedown of the Proton Spin Breakdown

  • A Novel Shakedown of the Proton Spin BreakdownHow the Field has Become Wider with a Polarized Proton ColliderUniversity of Massachusetts AmherstChristine AidalaSeptember 13, 2007Old Dominion University

    C. Aidala, ODU, September 13, 2007

  • Nucleon Structure: The Early Years1933: Estermann and Stern measure the protons anomalous magnetic moment indicates proton not a pointlike particle!1960s: Quark structure of the nucleonSLAC inelastic electron-nucleon scattering experiments by Friedman, Kendall, Taylor Nobel PrizeTheoretical development by Gell-Mann Nobel Prize

    C. Aidala, ODU, September 13, 2007

  • Deep-Inelastic Scattering: A Tool of the TradeProbe nucleon with an electron or muon beamInteracts electromagnetically with (charged) quarks and antiquarksClean process theoreticallyquantum electrodynamics well understood and easy to calculate!

    C. Aidala, ODU, September 13, 2007

  • (Unpolarized) Proton Structure and Bjorken-xHalzen and Martin, Quarks and Leptons, p. 201xBjorkenxBjorken1xBjorken111/31/3xBjorken1/31ValenceSeaA point particle3 valence quarks3 bound valence quarks3 bound valence quarks and some slow sea quarksSmall xWhat momentum fraction would the scattering particle carry if the proton were made of

    C. Aidala, ODU, September 13, 2007

  • Decades of DIS DataWealth of data largely thanks to proton-electron collider, HERA, in Hamburg, which shut down in July this yearRich structure at low xHalf protons linear momentum carried by gluons!PRD67, 012007 (2003)

    C. Aidala, ODU, September 13, 2007

  • And a (Relatively) Recent Surprise From p+p, p+d CollisionsFermilab 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!PRD64, 052002 (2001)New techniques let us continue to find surprises in the rich linear momentum structure of the proton, even after > 40 years!What about the protons angular momentum structure?

    C. Aidala, ODU, September 13, 2007

  • The Quark Spin Contribution SLAC: 0.10 < xSLAC
  • Decades of Polarized DIS2000 ongoing2007 ongoing Quark Spin Gluon Spin Transverse Spin GPDs Lz

    SLAC E80-E155

    CERN EMC,SMC COMPASS

    DESY HERMES

    JLAB Halls A, B, C

    So far no polarized electron-proton collider. R&D for future Electron-Ion Collider in current Long-Range Plan for Nuclear Physics.But what could you learn from a polarized proton-proton collider?

    C. Aidala, ODU, September 13, 2007

  • A Polarized Proton Collider:Opportunities . . .Proton-proton collisions Direct access to the gluons via gluon-quark, gluon-gluon scatteringHigh energy provided by a collider allows production of new probesW bosonsHigh energy allows use of new theoretical toolsFactorized perturbative quantum chromodynamics (pQCD) (more on this later!)IF Can find a way to maintain polarization of proton beamsthrough 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

  • 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

  • Hydrogen-Jet Polarimeter for Beams at Full EnergyUse transversely polarized hydrogen target and take advantage of transverse single-spin asymmetry in elastic proton-proton scatteringOnly consider single polarization at a time. Symmetric process! Know polarization of your targetMeasure analyzing power in scatteringThen use analyzing power to measure polarization of beam

    C. Aidala, ODU, September 13, 2007

  • The Relativistic Heavy Ion Collider at Brookhaven National Laboratory

    C. Aidala, ODU, September 13, 2007

  • RHIC as a Polarized p+p ColliderAGSLINACBOOSTER Polarized SourceSpin Rotators 200 MeV Polarimeter AGS Internal Polarimeter Rf Dipole RHIC pC PolarimetersPHENIXPHOBOSBRAHMS & PP2PPSTARAGS pC PolarimeterPartial SnakeSiberian SnakesSiberian Snakes Spin FlipperVarious equipment to maintain and measure beam polarization through acceleration and storage

    C. Aidala, ODU, September 13, 2007

  • News to Celebrate

    C. Aidala, ODU, September 13, 2007

  • RHIC PhysicsBroadest possible study of QCD in A+A, p+A, p+p collisionsHeavy ion physicsInvestigate nuclear matter under extreme conditionsExamine systematic variations with species and energyProton spin structureGluon polarization (DG)Sea-quark polarization Transverse spin structureMost 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

  • Flavor-Separated Sea Quark Polarizations Through W Production Parity violation of the weakinteraction in combination withcontrol over the proton spin orientation gives access to theflavor spin structure in the proton!For W- interchange u and d.

    C. Aidala, ODU, September 13, 2007

  • Spin Physics at RHICThree experiments: STAR, PHENIX, BRAHMSFuture running only with STAR and PHENIXLongitudinal 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

  • Single-Spin Asymmetries for Local Polarimetry:Confirmation of Longitudinal PolarizationSpin Rotators OFFVertical polarizationfAN

    C. Aidala, ODU, September 13, 2007

  • A Polarized Proton Collider:Opportunities . . . and ChallengesProton-proton collisions Direct access to the gluons via gluon-quark, gluon-gluon scatteringHigh energy provided by a collider allows production of new probesW bosonsHigh energy allows use of new theoretical toolsFactorized perturbative quantum chromodynamics (pQCD)Challenge: No longer dealing with the clean processes of QED!

    C. Aidala, ODU, September 13, 2007

  • RHIC Spin: Proton Structure with Quark and Gluon ProbesAt ultra-relativistic energiesthe proton represents a jetof quark and gluon probesNeed QCD now, not QED!

    C. Aidala, ODU, September 13, 2007

  • Hard Scattering in p+p:Factorization and UniversalityHard 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

  • pQCD in Action at s=200 GeVFraction pions producedh~0p0

    C. Aidala, ODU, September 13, 2007

  • Prompt g Production at s=200 GeVGluon Compton scattering dominatesAt LO no fragmentation functionSmall contribution from annihilation Will be an important channel for DG!

    C. Aidala, ODU, September 13, 2007

  • Probing the Gluon Polarization at RHIC++ same helicity+- opposite helicityN: yieldR: luminosity++/luminosity+-With factorized pQCD in hand as a theoretical tool, can probe DG via double-helicity asymmetry measurementsNow for some results . . .

    C. Aidala, ODU, September 13, 2007

  • The Pion Isospin Triplet, ALL and DGAt transverse momenta > ~5 GeV/c, midrapidity pions dominantly produced via qg scatteringTendency 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 measurablyOrder of asymmetries of pion species can allow us to determine the sign of DG

    C. Aidala, ODU, September 13, 2007

  • ALL of at s=200 GeVPHENIX Run-06 charged pions coming soon!

    C. Aidala, ODU, September 13, 2007

  • 2005 dataGluon Polarization from Inclusive Hadrons and Jets in Polarized p+p

    C. Aidala, ODU, September 13, 2007

  • Update on G vs ALL0 in PHENIX from 2006 DataCalc. by W.Vogelsang and M.Stratmannstd scenario, G(Q2=1GeV2)=0.4, is excluded by data on >3 sigma level: 2(std)2min>9Only exp. stat. uncertainties included (syst. uncertainties expected to be small)Uncertainties from functional form g(x) not included.Sasha Bazilevsky, AGS&RHIC Users Meeting, June 2007

    C. Aidala, ODU, September 13, 2007

  • Transverse Momentum vs. xgluon Limited sensitivity to x-dependence of Dg(x)Currently no sensitivity to low x and little to x>~0.3Log10(xgluon)NLO pQCD: 0 pT=29 GeV/c xgluon=0.020.3GRSV model: G(xgluon=0.020.3) ~ 0.6G(xgluon =01 )

    Each pT bin corresponds to a wide range in xgluonData is not sensitive to functional form of g(xgluon) Quantitative analysis must include impact of different function form g(xgluon) shape

    C. Aidala, ODU, September 13, 2007

  • Extending x Range is Crucial!Gehrmann-Stirling parameterizationsGSC: G(xgluon= 01) = 1 GRSV-0: G(xgluon= 01) = 0 GRSV-std: G(xgluon= 01) = 0.4 Current data is sensitive to G for xgluon= 0.020.3

    C. Aidala, ODU, September 13, 2007

  • Spin Crisis Came Out of a Low-x Measurement SLAC: 0.10 < xSLAC
  • Extend x RangeUpgrade 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