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Implications of NuTeV Standard Model Test

Implications of NuTeV Standard Model Test. NuTeV – charged, neutral currents induced by neutrinos New measurement of Weinberg angle Possible “New Physics” Beyond Standard Model? Normal (“QCD”) Explanations of NuTeV Anomaly? radiative corrections parton Charge Symmetry Violation

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Implications of NuTeV Standard Model Test

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  1. Implications of NuTeV Standard Model Test • NuTeV – charged, neutral currents induced by neutrinos • New measurement of Weinberg angle • Possible “New Physics” Beyond Standard Model? • Normal (“QCD”) Explanations of NuTeV Anomaly? • radiative corrections • parton Charge Symmetry Violation • strange quark momentum asymmetry • nuclear, shadowing corrections Beyond the Standard Model?? “QCD Effects”?? Tim Londergan Nuclear Theory Center, Indiana University PAVI06 Milos, Greece May 16-20, 2006 Supported by NSF PHY- 0244822 In collaboration with Tony Thomas (Adelaide/JLab)

  2. The NuTeV Experiment: charged, neutral currents from neutrino DIS 800 GeV p at FNAL produce pi, K from interactions in BeO target; Decay of charged pi, K produces neutrinos, antineutrinos; Almost pure muon neutrinos; (small νe contamination from Ke3 decay) Only neutrinos penetrate shielding • Dipoles select sign of charged meson: • Determine nu/nubar type NuTeV: Rochester/Columbia/FNAL/Cincinnati/Kansas State/Northwestern/ Oregon/Pittsburgh neutrino collaboration G. Zeller etal, PRL 88, 091802 (02); PR D65, 111103 (02)

  3. SeparateNeutral, Charged-Current Events NuTeV Detector: 18 m long, 690-ton steel scintillator; Steel plates interspersed with liq scintillator, drift chambers Charged current: Track through several plates Large visible energy deposit Neutral current: Short visible track Large missing energy • NuTeV Events: • 1.62 million n • 351,000 • NuTeV event selection: • Large E in calorimeter • event vertex in fiducial volume

  4. The Paschos-Wolfenstein Ratio: Neutrino Total Cross Sections on Isoscalar Target: Paschos & Wolfenstein ( PR D7, 91 (73)): Independent measurement of Weinberg angle, using ratio of total X-sections for neutrinos, antineutrinos on isoscalar target: PW ratio minimizes sensitivity to PDFs, higher-order corrections

  5. 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 contributions outside Standard Model

  6. NuTeV Determination of Weinberg Angle: • Construct ratios • Individual ratios less dependent on overall normalization • Very precise charged/neutral current ratios: • Different cuts, acceptance: don’t construct PW ratio directly • : depends strongly on Weinberg angle • : weak dependence on Weinberg angle 3σ below SM agree with SM These ratios lead to a NuTeV value for the Weinberg angle: The NuTeV result is ~ 3 σ above very precise value (from EW processes at LEP)

  7. NuTeV Result: 3σ Discrepancy from LEP value NuTeV work at LO in QCD (with improvements) and find s2w(NuTeV)=0.2276±0.0013stat ±0.0006syst ±0.0006th -0.00003(Mt/GeV-175)+0.00032 lnMH/100GeV where s2w=1-M2w/M2z (on-shell) Global fit:s2w= 0.2229 ±0.0004 ~2.8σ discrepancy SM Nuclear effects and ν oscillation explanations very unlikely Corresponds to 1.2% decrease in gL2; This is large compared to precision of EW measurements!

  8. Low Q2 (~10-4 GeV2) atomic PV exp’t in Cs [PRL 82, 2484 (99)] Moller scatt exp’t (E158) at SLAC; Q2~ 0.026 GeV2 [PRL 95, 081601 (05)] NuTeV exp’t, Q2 ~ 20 GeV2 [PRL 88, 091802 (02)] LEP, e+ e- at Z pole, Q2 = MZ2 Qweak, pol e-p at JLab (proposed), “Running” of Weinberg Angle Effective Weinberg angle depends on Q2 Warning: gauge and process dependent parameter E158: Q dependence of Weinberg angle confirmed at 6σ level NuTeV: discrepancy of ~3σ with SM prediction [Czarnecki-Marciano, PRD53, 1066 (96)] Qweak

  9. “New Physics” explanation for NuTeV? • The problem: extremely precise • EW data confirms SM! • Mass, width of Z, W • X-sections, branching ratios • at Z peak [LEP, SLD] • LR and FB asymmetries in e+e- • scattering • new particles must satisfy all • these constraints • EW constraints ~ 0.1% level • [NuTeV ~ 1.2%] • new particles have heavy masses •  Q2 dependence must be slow • “new physics” hard to satisfy • EW constraints! NuTeV

  10. “Designer Particles” I:delicately adjust to fit all existing data • oblique corrections [high mass • scale, couples only to vector • bosons]: parameters constrained • by EW data – can’t fit NuTeV • extra Z’ (unmixed) – possible; • runs into trouble with • latest muon g-2

  11. “Designer Particles” II: More Attempts to fit NuTeV • minimal SUSY loops – No – most have wrong sign; others violate • existing constraints • Leptoquarks (bosons that couple to leptons & quarks): models with • very carefully tuned mass splittings still possible – could be tested at • Tevatron, LHC [Davidson, Gambino etal, J High E Phys 2, 37 (2002)] MSSM, light sleptinos, gauginos Leptoquark (solid); extra gauge bosons (red)

  12. EW Radiative Corrections • EM radiative corrections, process specific to NuTeV, are large • Bremsstrahlung from final state lepton in CC significant correction. • Not present in NC (promotes CC events to higher y so they pass energy cut) • {dRn, dRn, dsin2qW} ≈ {+.0074,+.0109,-.0030} • New calculation of this effect (Diener, Dittmaier, Hollik PR D69, 073005 (04) ) • not yet implemented in analysis • Corrections likely larger than NuTeV estimate D. Yu. Bardin and V. A. Dokuchaeva, JINR-E2-86-260, (1986)

  13. Isospin Violating Corrections to PW Ratio: Changes in PW ratio from isospin violating PDFs: PW Correction  valence parton charge symmetry violation (CSV) parton charge symmetry: CS: (rotation of 180o about “2” axis in isospin space) • We know the origins of parton CSV: • quark mass difference: • Electromagnetic contributions: most important EM effect: n-p mass difference

  14. CSV Contribution to NuTeV Result: Sather: Analytic Quark Model Approximation for Valence Parton CSV. Leads to analytic results (model-dependent) PW Ratio CSV Corr’n using Sather: Rodionov: Sather: CTEQ4LQ: 40% decrease in anomaly! NuTeV: Don’t evaluate PW Ratio! CSV Contrib’n to NuTeV result: • Calculate parton CSV at low (quark model) momentum scale • Evolve up to Q2 of NuTeV exp’t (20 GeV2) • Evaluate with NuTeV functional 30% decrease in anomaly

  15. Phenomenological Parton CSV PDFs MRST PDFs from global fits include CSV for 1st time: Martin, Roberts, Stirling, Thorne [Eur Phys J C35, 325 (04)]: Choose restricted form for parton CSV: 90% conf limit (κ) [f(x): 0 integral; matches to valence PDFs at small, large x] Best fit: κ = -0.2, large uncertainty ! Best fit remarkably similar to quark model CSV calculations ADEL (1994) MRST (2004)

  16. “QED Splitting”: a New Source of Isospin Violation MRST, Eur.Phys.J. 39, 155 (05); Glueck, Jimenez-Delgado, Reya, PRL95, 022002 (05) “QED evolution”, quark radiates photon Evolve in Q2 • qualitatively similar to quark model CSV • QED varied while quarks “frozen” • contributes even if mu = md and Mn= Mp • add to quark model CSV term • increase CSV ~ factor 2 • MRST incorporate QED splitting with PDFs • in global fit to high energy data

  17. Summary, CSV Effects on Weinberg angle • Phenomenology: • MRST global fit  limits valence CSV • -0.8 ≤ κ≤ +0.65 κ = -0.6  remove NuTeV anomaly! • κ = +0.6  anomaly twice as large! • Theoretical estimates: • quark model remove ~1/3 anomaly • “QED splitting” remove ~1/3  at current limits, CSV could produce observable effects (~ 5-6%) in certain reactions 90% confidence limits: MRST global fit to valence CSV

  18. Strange Quark Contributions to PW Ratio: Contribution from strange quarks: s-sbar momentum asymmetry Strange quark normalization: constrained (no net strangeness in nucleon) If s quarks carry more momentum than sbar decrease anomaly Determination of s, sbar quark PDFs: Opposite sign dimuons from neutrinos • CCFR: charge of faster muon determines neutrino or antineutrino; • most precise way to determine s, sbar PDFsCCFR, NuTeV

  19. Analyses of s quark momentum asymmetry • NuTeV: analyzed s, sbar for small x: • Best fit: • Do not enforce normalization condition • NLO treatment of dimuon prod’n • But, from normalization: • If s < sbar for small x, requires s > sbar for large x CTEQ:[Kretzer etal, PRL 93, 041802 (04), Olness etal, Eur Phys J C40, 145 (05)] • Global analysis of parton PDFs  CTEQ6 • Includes CCFR, NuTeV dimuon data • (includes expt’l cuts on dimuons) • Extract “best fit” for s, sbar dist’ns • [enforce s normalization cond’n] • Catani et al. hep-ph/0404240; 0406338 • in NNLO, can generate nonzero momentum asymmetry • find small mom asymmetry < 0 from 3-loop contrib’ns

  20. positive [S-] Results: CTEQ Global fit vs. Bjorken x μ± other • CTEQ: S- > 0, strange asymmetry • decreases NuTeV anomaly; • dimuon data: most sensitive for s PDFs • CTEQ: s contrib’n removes • 0  25% of anomaly -.001 < [S-] < +.004

  21. NuTeV Analysis of s, sbar Quark Dist’n: • Re-analyzed dimuon data: • preliminary analysis [S-] ~ 0 • appears negative • strangeness not conserved? • NLO treatment of dimuon prod’n • NuTeV group: • now using CTEQ PDFs (u,d) • very similar analysis method • acceptance corrections? • fragmentation functions? • charm mass (CTEQ uses HERA data)? Qualitative disagreement between NuTeV/CTEQ, using same data, techniques to extract s, sbar ??

  22. Nuclear Effects ?? NuTeV: All data neutrino DIS on iron Nuclear modification of PDFs: Shadowing EMC Effect Fermi motion …. Miller/Thomas Int J Mod Phys A20, 95 (05): Shadowing effect for NuTeV?? charged leptons: Vector meson dominance nCC events: Miller/Thomas: n shadowing very different from m n NC events: Zo: very small coupling to r  NC shadowing ~ 0 Different shadowing for  account for anomaly?? NuTeV: NO ! • Shadowing low Q2, data much higher Q2 • value very close to SM value (should be quite different in MT scenario) Shadowing: increase NuTeV anomaly?? Nuclear effects in n reactions: Hirai, Kumano, Nagai, PR D71, 113007 (05)

  23. Nuclear Effects (part II) Brodsky, Schmidt, Yang (PR D70, 116003 (04)) Shadowing/Antishadowing ν-A processes • include Pomeron, Odderon, Reggeon effects • obtain both shadowing, antishadowing effects • both constructive, destructive interference • processes modified in different ways Predict greater effect on than Remove ~ 20% of Weinberg angle anomaly Partial contribution along with CSV, s quarks ??

  24. Conclusions: • NuTeV: Measured CC, NC X-sections for on Fe • Large (~ 3σ), surprising discrepancy for • “New Physics” – difficult to fit LEP results, NuTeV “designer particles” unlikely very delicate • “QCD Corrections” to NuTeV measurement?? • radiative corr’ns new calc’n, not in analyses • parton CSV  ~ could remove effect [MRST] • strange quark asymmetry ~ 1-2 σ[CTEQ] • nuclear effects ~ 20%, Brodsky etal (model dependence) NuTeV: no!! • CSV, strangeness at present, most plausible explanations for NuTeV anomaly • small additive contrib’ns from CSV, strangeness, nuclear effects ??

  25. Implications of NuTeV Standard Model Test • NuTeV – charged, neutral currents induced by neutrinos • New measurement of Weinberg angle • Possible “New Physics” Beyond Standard Model? • Normal (“QCD”) Explanations of NuTeV Anomaly? • radiative corrections • parton Charge Symmetry Violation • strange quark momentum asymmetry • nuclear, shadowing corrections Beyond the Standard Model?? “QCD Effects”?? Tim Londergan Nuclear Theory Center, Indiana University PAVI06 Milos, Greece May 16-20, 2006 Supported by NSF PHY- 0244822 In collaboration with Tony Thomas (Adelaide/JLab)

  26. Suppressed sensitive to sin2θw Large radiative corrections, ≈-40% Czarnecki-Marciano,Denner-Pozzorini,Petriello,Ferroglia et al Very low Q2 atomic PV exp’t in Cs JLab: Qweak e-p PV exp’t NuTeV/LEP/ PV MØller/ Qweak E158 at SLAC first measurement of PV in MØller sc. huge luminosity high polarization (~80%) Warning: gauge and process dependent parameter At tree level, APV≈280 10-9 Qweak !!

  27. “QCD Corrections” to the NuTeV Result: ( “Something Old”) Isoscalar Effect (N ≠Z for Fe) Depends only on 2nd moment of light quark valence PDFs (momentum carried by up, down valence quarks) Isoscalar corrrection to PW ratio: NuTeV Isoscalar correction: • NuTeV exp’t doesn’t evaluate PW ratio • Isoscalar correction from Monte Carlo simulation of exp’t • Although NuTeV significant difference from PW corr’n, under control

  28. Qualitative Features of Parton Distributions At low Q2, generate from quark models: “Majority” valence quark: “Minority” valence quark residual (ud) diquark residual (uu) diquark Under CSV n p, residual (ud) diquark residual (dd) diquark [only n-p mass difference] [diquark mass difference] [True for all intermediate states!]

  29. Calculating CSV Corrections to PW Ratio: • Construct models for valence parton distributions • Test how these models behave under CSV transformation: • Predict sign, magnitude of CSV effects in NuTeV exp’t CSV Corrections to PW Ratio: • CSV correction to PW ratio independent of Q2 • Both numerator, denominator involve 2nd moment of valence dist’ns • numerator, denominator evolve identically with Q2 under LO evolution, • Evaluate valence PDFs at low Q2 • Dominated by configurations with 3 valence quarks • Easy to calculate, study behavior

  30. Quantitative Estimates of Parton CSV Quark-model formula for parton PDFs: X = qq; 3q+qbar; 4q+2 qbar. …. Large x: dominated by X=diquark states Sather: study variation with nucleon, quark mass: analytic expression small shift in PDFs, due to quark, nucleon mass. For large x, Sather predicts d > u in both cases. (From normalization, d < u at small x) [work at low Q2 where 3-quark states dominate]

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