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The QCD of PVDIS 12 GeV

The QCD of PVDIS 12 GeV. A clean measurement of CSV at the quark level, d/u for the proton, and (higher-twist) di-quarks. Thanks to Bosted, Brodsky, Chudakov, Kumar, Londergan, Meziani, Michaels, Reimer, Ramsey-Musolf, Paschke, Pitt, Zheng. P. A. Souder Syracuse University. OUTLINE.

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The QCD of PVDIS 12 GeV

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  1. The QCD of PVDIS 12 GeV A clean measurement of CSV at the quark level, d/u for the proton, and (higher-twist) di-quarks Thanks to Bosted, Brodsky, Chudakov, Kumar, Londergan, Meziani, Michaels, Reimer, Ramsey-Musolf, Paschke, Pitt, Zheng P. A.Souder Syracuse University The QCD of DIS Parity at 12 GeV P. A. Souder

  2. OUTLINE • PVDIS and the Standard Model: introduction and motivation for 1% data. • Discovery potential: CSV violation, di-quarks, and d/u for the proton. • Theoretical issues • Expected performance of proposed apparatus. The QCD of DIS Parity at 12 GeV P. A. Souder

  3. PV Asymmetries Weak Neutral Current (WNC) Interactions at Q2 << MZ2 Longitudinally Polarized Electron Scattering off Unpolarized Fixed Targets (gAegVT+gVegAT) • The couplings gT depend on electroweak physics as well as on the weak vector and axial-vector hadronic current • For PVDIS, both new physics at high energy scales as well as interesting features of hadronic structure come into play • A program with a broad kinematic range can untangle the physics The QCD of DIS Parity at 12 GeV P. A. Souder

  4. New Physics Reach: Qweak and Møller Kurylov, Ramsey-Musolf, Su To be relevant, new SM tests must have small enough errors to show up on plots like this The QCD of DIS Parity at 12 GeV P. A. Souder Examples:

  5. 1.0% Add data on PVDIS: ± 10% 10% -10% DIS-Parity requires a factor of 5-10 improvement In δA/A to be competitive with Qweak, Møller No 1-4sin2θW suppression of APV The QCD of DIS Parity at 12 GeV P. A. Souder

  6. Electron-Quark Phenomenology V A A V C1u and C1d will be determined to high precision by Qweak, Cs C2u and C2d are small and poorly known: one combination can be accessed in PV DIS New physics such as compositeness, leptoquarks: Deviations to C2u and C2d might be fractionally large The QCD of DIS Parity at 12 GeV P. A. Souder

  7. Hadronic Structure for PV Electron DIS e- e- * Z* X N fi(x) are quark distribution functions For an isoscalar target like 2H, structure functions largely cancel in the ratio: (2C2u-C2d)/(2C1u-C1d)=0.136 Especially for x>0.5 or so APV becomes independent of x, Q2, W, and depends only on y The QCD of DIS Parity at 12 GeV P. A. Souder

  8. Why should we believe PVDISwhen no one Believes NuTeV? The QCD of DIS Parity at 12 GeV P. A. Souder

  9. Assumptions for the Paschos-Wolfenstein Ratio PW Ratio depends on the following assumptions: • Isoscalar target (N=Z) • include only light (u, d) quarks • neglect heavy quark masses • assume isospin symmetry for PDFs • no nuclear effects (parton shadowing, EMC, ….) • no higher twist effects • radiative corrections OK? (γ-W boxes?) • no contributions outside Standard Model JLab 12 GeV issues Nobody believes that this is the problem The QCD of DIS Parity at 12 GeV P. A. Souder

  10. Use PV To Study hadronic structure? • PV might have the smallest errors:<1%, much better than cross section measurements • PV: Systematics are Pe and <Q2> • Cross sections: Systematics are target length, solid angle, etc. The QCD of DIS Parity at 12 GeV P. A. Souder

  11. Strategy: • measure or constrain higher twist effects at x ~ 0.5-0.6 • precision measurement of APV at x → 0.8 to search for CSV Search for CSV in PV DIS • u-d mass difference • electromagnetic effects • Direct observation of parton-level CSV would be very exciting! • Important implications for high energy collider pdfs • Could explain significant portion of the NuTeV anomaly For APV in electron-2H DIS: Sensitivity will be further enhanced if u+d falls off more rapidly than u-d as x  1 The QCD of DIS Parity at 12 GeV P. A. Souder

  12. Phenomenological Parton CSV PDFs MRST Phenomenological PDFs include CSV for 1st time: Martin, Roberts, Stirling, Thorne (03): Choose restricted form for parton CSV: 90% conf limit (κ) [f(x): 0 integral; matches to valence at small, large x] Best fit: κ = -0.2, large uncertainty ! Best fit remarkably similar to model CSV predictions Bag model ADEL MRST The QCD of DIS Parity at 12 GeV P. A. Souder

  13. Prediction (2004) Blue curve: Gluck, Jimenez-Delgado, Reya +Thomas and Londergan The QCD of DIS Parity at 12 GeV P. A. Souder

  14. Higher Twist Coefficients in parity conserving (Di) and nonconserving (Ci) Scattering Evolves according To DGLAP equations Higher Twist is what is left over Higher Twist is any Q2-dependent deviation From the SM prediction (Does not Evolve) The QCD of DIS Parity at 12 GeV P. A. Souder

  15. Going from LO to NNNLO Greatly Reducesthe Extracted Higher Twist Coefficients F2(x,Q2)=F2(x)(1+D(x)/Q2) Q2=(W2-M2)/(1/x-1) Q2min=Q2(W=2) MRST, PLB582, 222 (04) If D(x)~C(x), Parity might show higher twist At high x without needing QCD evolution. The QCD of DIS Parity at 12 GeV P. A. Souder

  16. Interpretation of Higher Twist  • APV sensitive to diquarks: ratio of weak to electromagnetic charge depends on amount of coherence • Do diquarks have twice the x of single quarks? • If Spin 0 diquarks dominate, likely only 1/Q4 effects • On the other hand, some higher twist effects may cancel in ratio, so APV may have little dependence on Q2. Observing a clean higher twist operator has recently become very interesting. The QCD of DIS Parity at 12 GeV P. A. Souder

  17. What is going on at high x? • Real higher twist • Slow convergence of NnLO analysis • Limited Q2 range The QCD of DIS Parity at 12 GeV P. A. Souder

  18. Looking beyond the parton description PV Deep Ineslastic eD (J Lab 12 GeV) ~0.4% Different PDF fits E=11 GeV q=12.50 Probing Higher Twist with PV Sacco, Ramsey-Mulolf preliminary Effect is small at x~0.2 The QCD of DIS Parity at 12 GeV P. A. Souder

  19. APV in DIS on 1H + small corrections • Allows d/u measurement on a single proton! • Vector quark current! (electron is axial-vector) • Determine that higher twist is under control • Determine standard model agreement at low x • Obtain high precision at high x The QCD of DIS Parity at 12 GeV P. A. Souder

  20. Uncertainties in d/u at High x, and the Errors we Would Like to Achieve with PV Measurements Deuteron analysis has nuclear corrections APV for the proton has no such corrections Must simultaneously constrain higher twist effects The challenge is to get statistical and systematic errors ~ 2% The QCD of DIS Parity at 12 GeV P. A. Souder

  21. Complete PV DIS Program (Including 12 GeV) • Hydrogen and Deuterium targets • Better than 2% errors for each point • It is unlikely that any effects are larger than 5-10% • x-range 0.25-0.75 • W2 well over 4 GeV2 • Q2 range a factor of 2 for each x point • (Except x~0.75) • Moderate running times • With HMS/SHMS: integrates all of this physics • With larger solid angle apparatus: higher twist, CSV, d/u… The QCD of DIS Parity at 12 GeV P. A. Souder

  22. Scorecard The QCD of DIS Parity at 12 GeV P. A. Souder

  23. Theoretical Issues The QCD of DIS Parity at 12 GeV P. A. Souder

  24. Theory Error Budget to Interpret ±1% Data `Theory dirt’ includes unknown and uninteresting effects b(x)/a(x)~13% 0.3<f(y)<0.8 a(x) Theory dirt must be <0.5% Observe hadronic physics effects>3% Background for electroweak studies b(x) Theory dirt must be <3% Set new limits on the small C2’s The QCD of DIS Parity at 12 GeV P. A. Souder

  25. Phenomenology and R The QCD of DIS Parity at 12 GeV P. A. Souder

  26. Most QCD cancels in a(x) Assumptions: 1: CVC (Charge Symmetry) 2: Quarks contribute incoherently (Higher Twist) Goal of program is to test these assumptions. R=σL/σT cancels Charge Symmetry 1: Strange quarks (absent at large x) 2: up≠dn (Our main interest) The QCD of DIS Parity at 12 GeV P. A. Souder

  27. Higher Twist without the QPM Bjorken, PRD 18, 3239 (78) Wolfenstein, NPB146, 477 (78) Zero in QPM The QCD of DIS Parity at 12 GeV P. A. Souder

  28. Axial hadronic current 2 Methods: 1: Use data only: a: σγZA≈F3ν and use neutrino data b: σγ from electromagnetic data 2: Use QPM and make corrections: a: Sea quarks are absent at high x b: R from electromagnetic data c: Ignore higher twist Should be good to ~3%, which is ample Is higher twist a big problem at the highest a values? The QCD of DIS Parity at 12 GeV P. A. Souder

  29. Neutrino data on xF3 from NuTeV, CCFR, CDHSW Nice data set! But it is shown on a log plot. What does it look like on a linear scale? The QCD of DIS Parity at 12 GeV P. A. Souder

  30. Compare ν F3 to global parton fitson a linear scale Note vertical scale Useful at x~0.5 Problems at x~0.7 15% 0.45 0.55 40% 0.65 0.75 The QCD of DIS Parity at 12 GeV P. A. Souder

  31. Parton Distribution Functions Sea quarks that contribute to a(x) and s quarks that contribute to a(x) vanish rapidly for x>0.5 CAUTION: PDF’s use as input 40 years of precise data plus ‘reasonable’ guesses. One must distinguish which features are data and which features are guesses. The QCD of DIS Parity at 12 GeV P. A. Souder

  32. μ- p p μ+ How do we know that antiquarks are negligible at large x? Drell-Yan production of muon pairs The small quantity is directly observed. No subtractions are needed, as is the case for F3 data. When xF=0, x1=x2=x, and M=x2s. Hence x for both the quark and anti-quark are known. The cross section drops rapidly with x Clean data exist with x~0.6 and Mμμ2>10 Smith et al., PRL 46, 1607(81) The QCD of DIS Parity at 12 GeV P. A. Souder

  33. Data on R vs x R is ~20%; →10% in f(y) →1% in f(y)b(x) Large x bins The QCD of DIS Parity at 12 GeV P. A. Souder

  34. A clean example of Higher Twist data Angular dependence of Drell-Yan production Clean signature for HT: wrong cosθ dependence (Shows up at high xπ) HT is absent for most of the kinematic range Figure from Heinrich et al., PRD 44, 1909 (91) The QCD of DIS Parity at 12 GeV P. A. Souder

  35. Apparatus Needed for PVDIS The QCD of DIS Parity at 12 GeV P. A. Souder

  36. Need high rates at high x • For the first time: sufficient rates to make precision PV DIS measurements • solid angle > 200 msr • Resolution<2% • Count at 100 kHz • online pion rejection of 102 Large Angle Large Acceptance: Concept • CW 90 µA at 11 GeV • 40-60 cm liquid H2 and D2 targets • Luminosity > 1038/cm2/s JLab Upgrade Need magnet to block γ’s and low energy π’s The QCD of DIS Parity at 12 GeV P. A. Souder

  37. B points out of page Large Acceptance: Solenoid vs Toroid Problem: shield detector from line of sight photons Solenoid takes advantage of the small beam spot requires less bending With solenoid, detectors can be far from target. Small beam spot gives excellent resolution The QCD of DIS Parity at 12 GeV P. A. Souder

  38. Plan View of the Spectrometer Price~$10M Is the physics worth the money? CDF or BaBar Solenoid? The QCD of DIS Parity at 12 GeV P. A. Souder

  39. Kinematic acceptance Large angles required for large x W>2 Good resolution needed to maintain integrity of the bins θ>35o Θ<20o The QCD of DIS Parity at 12 GeV P. A. Souder

  40. 1% Resolution needed for clean bins The QCD of DIS Parity at 12 GeV P. A. Souder

  41. Projected errors, 60 days, deuterium 11 GeV 8.8 GeV The QCD of DIS Parity at 12 GeV P. A. Souder

  42. Projected errors, 60 days, proton • Physics • d/u • Higher twist The QCD of DIS Parity at 12 GeV P. A. Souder

  43. Additional Physics Topics The QCD of DIS Parity at 12 GeV P. A. Souder

  44. EMC effect in Parity Violation ? This study might be done with 8.5 GeV beam, 50 μa beam Cross section data from J. Gomez et.al. PRD 49 (1994) 4348 The QCD of DIS Parity at 12 GeV P. A. Souder

  45. Other Users of the Spectrometer Workshop last Monday • A1n • SDIS • Charm from H A1n A1n→1 as x→1?? (Show that result is independent of W, Q2) 0 These programs are a significant source of motivation for the proposed spectrometer 0 x 1 The QCD of DIS Parity at 12 GeV P. A. Souder

  46. Summary and Outlook • Parity-Violating DIS can probe exciting new physics at high x • One can start now (at 6 GeV) • Do 2 low Q2 points (P-05-007, X. Zheng contact) • Q2 ~ 1.1 and 1.9 GeV2 • A short run to probe TeV physics in PV DIS off 2H: LOI for Hall C • The bulk of the program requires a dedicated spectrometer/detector • CSV can be probed at high x • Higher twist can be controlled or exploited • Additional physics topics could be addressed by the dedicated spectrometer • A1n • SDIS The QCD of DIS Parity at 12 GeV P. A. Souder

  47. Fractional effects of CSV Prediction by MRST, hep-ph/041104 The QCD of DIS Parity at 12 GeV P. A. Souder

  48. Geometry for a Solenoidal Spectrometer The QCD of DIS Parity at 12 GeV P. A. Souder

  49. Resolution of Spectrometer The QCD of DIS Parity at 12 GeV P. A. Souder

  50. Rates as a function of kinematic bin The QCD of DIS Parity at 12 GeV P. A. Souder

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