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The NuTeV Anomaly: Solved??

NuTeV – charged, neutral currents induced by neutrinos New measurement of Weinberg angle Deduced Weinberg angle “anomalous” Review Explanations for the NuTeV Anomaly CSV + Isospin Dep Nuclear + Strange  Solved ?. The NuTeV Anomaly: Solved??.

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The NuTeV Anomaly: Solved??

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  1. NuTeV – charged, neutral currents induced by neutrinos New measurement of Weinberg angle Deduced Weinberg angle “anomalous” Review Explanations for the NuTeV Anomaly CSV + Isospin Dep Nuclear + Strange  Solved? The NuTeV Anomaly: Solved?? Beyond the Standard Model?? “QCD Effects”?? Tim Londergan Nuclear Theory Center, Indiana University Tony Thomas 60th Birthday CSSM, Adelaide Feb 15-19, 2010 Supported by NSF PHY- 0854805 With W. Bentz, I. Cloet & Tony Thomas

  2. Happy Birthday, Tony !

  3. Possible “New Physics” beyond the Standard Model? • look at most likely possible new particles; • can any remove the NuTeV anomaly? • Normal (“QCD”) Explanations of NuTeV Anomaly? • radiative corrections • parton Charge Symmetry Violation • strange quark momentum asymmetry • nuclear shadowing corrections • isospin dependent nuclear corrections • Which explanation(s) seem most plausible ? • Are they capable of removing NuTeV anomaly? The NuTeV Anomaly Weinberg angle 3σ below standard model result How to Interpret this?

  4. The Weinberg Angle Erler & Langacker (2008): 5 current expt’s Weinberg angle “runs” in Q2 as a result of loop corrections

  5. The Weinberg Angle Erler & Langacker (2008): 5 current expt’s CS APV, PRL82 2484 (‘99) E158 Moller,PRL95 081601 (‘05) NuTeV,PRL88 091802 (‘02) LEP,SLC: e+e- Z poleP Rep 427 257 (06) e chg asymm Tevatron: PRL 101 211801 (‘08) Weinberg angle “runs” in Q2 as a result of loop corrections

  6. The Weinberg Angle Erler & Langacker (2008): 5 current expt’s CS APV, PRL82 2484 (‘99) E158 Moller,PRL95 081601 (‘05) NuTeV,PRL88 091802 (‘02) LEP,SLC: e+e- Z poleP Rep 427 257 (06) e chg asymm Tevatron: PRL 101 211801 (‘08) Weinberg angle “runs” in Q2 as a result of loop corrections 2 Planned Experiments (red): (estimated error bars) Qweak (ep Jlab) e-D PVDIS at Jlab

  7. The NuTeV Experiment: charged, neutral currents from neutrino DIS 800 GeV p at FNAL produce pi, K from interactions in BeO target; NuTeV: Rochester/Columbia/FNAL/Cincinnati/Kansas State/Northwestern/ Oregon/Pittsburgh neutrino collaboration G. Zeller etal, PRL 88, 091802 (02); PR D65, 111103 (02)

  8. 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)

  9. The Paschos-Wolfenstein Ratio: Neutrino Total Cross Sections on Isoscalar Target:

  10. 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

  11. The Paschos-Wolfenstein Ratio: • PW Ratio depends on the following assumptions: • Isoscalar target (N=Z) • include only light (u, d) quarks • neglect charm quark mass • assume isospin symmetry for PDFs • no nuclear effects (parton shadowing, EMC, ….) • no contributions outside Standard Model

  12. NuTeV Determination of Weinberg Angle: • Construct ratios • Very precise charged/neutral current ratios: • Different cuts, acceptance: don’t construct PW ratio directly Monte Carlo fits produce a NuTeV value for the Weinberg angle: The NuTeV result is ~ 3σ above the very precise value (from EW processes at LEP)

  13. “New Physics” explanation for NuTeV? • The problem: extremely precise • EW data supports 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 physics” hard to satisfy • EW constraints! NuTeV

  14. Physics Beyond the Standard Model?Attempts to explain NuTeV with “new physics” • Davidson et al [J High E Phys 2, 37 (’02)] • considered various scenarios (oblique corrections, extra Z’s, SUSY loops, leptoquarks) – very difficult to explain NuTeV result • Kurylov, Ramsey-Musolf, Erler [NP B667, 321 (’03)] • detailed analysis of SUSY contributions to NuTeV: • SUSY loops cannot explain NuTeV • R-parity violating (RPV) contributions  • in principle could explain NuTeV anomaly • in practice, ruled out by other precision EW data

  15. “Beyond the Standard Model:”choose most promising types of particles adjust  can you fit existing data + NuTeV ? • oblique corrections [high mass • scale, couples only to vector • bosons]: parameters constrained • by EW data – can’t fit NuTeV • extra Z’ (mixed with Z) – • doesn’t fix; strongly constrained • by LEP/SLD (also latest muon • g-2) [Davidson etal, J HE Phys2, 37 (2002)]

  16. “Beyond SM” 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): carefully • tuned mass splittings still possible – could be tested at • LHC [Davidson etal, J HE Phys 2, 37 (2002)] • Unmixed extra Z’ – might help reduce NuTeV anomaly (fine tuning) MSSM, light sleptinos, gauginos Leptoquark (solid); extra gauge bosons (red)

  17. Summary, “New Physics” Contributions to NuTeV: Contributions outside Standard Model? • Difficult to achieve • Strong constraints from extremely precise LEP/SLD results • Requires low-mass particles, propertiesconstrained

  18. “QCD Contributions” to NuTeV: Most Likely effects within Standard Model • Radiative Corrections? • Partonic charge symmetry violation • Strange quark momentum asymmetry • Nuclear modification of parton distributions

  19. Isospin Violation and the NuTeV Experiment Isospin violation in PDFs will contribute to NuTeV exp’t PW Correction valence parton charge symmetry violation (CSV) parton charge symmetry: CS: (rotation of 180o about “2” axis in isospin space) NuTeV: very weak dependence on sea quark CSV, dominated by valence CSV • Origins of parton CSV; convenient to ascribe to  • quark mass difference: • Electromagnetic contributions: most important EM effect: n-p mass difference

  20. Isospin Violating Corrections to PW Ratio: Changes in PW ratio from isospin violating PDFs: Isospin violating PW Correction  depends completely on valence CSV momentum difference (2nd moment of valence CSV PDFs) Quark models suggest  These quantities may be reasonably model-independent Londergan & Thomas, PR D67, 111901 (’03)

  21. CSV Contribution to NuTeV Result: PW Ratio CSV Corr’n (analytic approximation): Rodionov: Sather: CTEQ4LQ: 40% decrease in anomaly!

  22. CSV Contribution to NuTeV Result: PW Ratio CSV Corr’n (analytic approximation): 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

  23. “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 include in DGLAP evolution in Q2

  24. “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 include in DGLAP evolution in Q2 • correct to lowest order in αQED • QED varied while QCD force “fixed” • contributes even if mu = md and Mn= Mp • evolve from mqto Q(mq  Q0 and Q0  Q) • for mq2 < q2 < Q02 , Glueck “freeze” quark PDFs

  25. CSV Effects from “QED Splitting”: MRST, Eur.Phys.J. 39, 155 (05); Glueck etal, PRL95, 022002 (05) Glueck valence results: Quark model • add to quark model CSV term • increase CSV ~ factor 2 QED

  26. Phenomenological Parton CSV PDFs MRST PDFs  global fits including CSV: Martin, Roberts, Stirling, Thorne [Eur Phys J C35, 325 (04)]: 90% conf limit (κ) Best fit: κ = -0.2 (90% confidence level -0.8 ≤ κ ≤ +0.65) MRST (2004)

  27. Phenomenological Parton CSV PDFs MRST PDFs  global fits including CSV: Martin, Roberts, Stirling, Thorne [Eur Phys J C35, 325 (04)]: 90% conf limit (κ) Best fit: κ = -0.2 (90% confidence level -0.8 ≤ κ ≤ +0.65) ADEL (1994) MRST (2004) Best fit remarkably similar to quark model CSV calculations

  28. Summary, CSV Effects on Weinberg angle • Phenomenology: • MRST global fit  limits valence CSV • -0.8 ≤ κ≤ +0.65 κ = -0.6  remove 100% of NuTeV anomaly! • κ = +0.6  anomaly twice as large! • Theoretical estimates: • quark model remove ~ 30% of anomaly • “QED splitting” remove ~ 30% • (total CSV  remove ~60% of anomaly)  at current limits, CSV could produce observable effects (~ 5-6%) (or more?) in certain reactions 90% confidence limits: MRST global fit to valence CSV

  29. Strange Quark Contributions to PW Ratio: PW contribution from strange quarks: s-sbar momentum asymmetry Strange quark normalization: constrained (N has zero net strangeness) 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

  30. Analysis of s quark momentum asymmetry Most recent fit of s quark distributions. NuTeV:[Mason etal, PRL 99, 192001 (07)] s-(x) > 0, x > 0.004; best value removes ~ 1/4 of NuTeV anomaly s-(x) changes sign at extremely small x value (no theoretical reason) Changeover point can be moved with resulting χ2increase

  31. Analysis of s quark momentum asymmetry Most recent fit of s quark distributions. NuTeV:[Mason etal, PRL 99, 192001 (07)] s-(x) > 0, x > 0.004; best value removes ~ 1/4 of NuTeV anomaly s-(x) changes sign at extremely small x value (no theoretical reason) Changeover point can be moved with resulting χ2increase

  32. Isospin Dependent Nuclear Effects Isovector-vector exchange (generally attributed to ρ0 exchange) will contribute to the NuTeV exp’t [Cloet, Bentz, Thomas PRL 102, 252301 (09)] ρ0 exchange produces slight additional attraction for u quarks, slight additional repulsion for d quarks This produces effects very similar to parton CSV, when N ≠ Z (although this nuclear effect respects charge symmetry) Modification of nucleon structure in nuclei

  33. Isospin Dependent Nuclear Effects These effects should produce distinctive and measurable modifications of the EMC effect for N ≠ Z nuclei [see Cloet talk]

  34. Isospin Dependent Nuclear Effects These effects should produce distinctive and measurable modifications of the EMC effect for N ≠ Z nuclei [see Cloet talk] They will also modify the NuTeV result: for iron we estimate ~ 40% reduction of the NuTeV anomaly [Bentz etal, arXiV:0908.3198 (nucl-th)]

  35. Reassessment of NuTeV, Weinberg Angle NuTeV Result now lies right on theory curve. Inner error bars: statistical Outer errors: total uncertainty Contributions to NuTeV: CSV ~ 60% Isospin dep ~ 40% s quarks: slight increase in error bars Bentz etal, arXiV:0908.3198

  36. Conclusions: • NuTeV: Measured CC, NC X-sections for on Fe Large (~ 3σ), surprising discrepancy for • “New Physics” – difficult to fit LEP results, NuTeV “most probable new particles” unlikely very delicate • “QCD Corrections” to NuTeV measurement??

  37. Conclusions: • NuTeV: Measured CC, NC X-sections for on Fe Large (~ 3σ), surprising discrepancy for • “New Physics” – difficult to fit LEP results, NuTeV “most probable new particles” unlikely very delicate • “QCD Corrections” to NuTeV measurement?? • parton CSV  best guess removes ~ 60% • could remove full effect [MRST] • strange quark asymmetry ~ 1σ (we assume 0) • isospin-dept nuclear ~ 40%, Cloet etal

  38. Conclusions: • NuTeV: Measured CC, NC X-sections for on Fe Large (~ 3σ), surprising discrepancy for • “New Physics” – difficult to fit LEP results, NuTeV “most probable new particles” unlikely very delicate • “QCD Corrections” to NuTeV measurement?? • parton CSV  best guess removes ~ 60% • could remove full effect [MRST] • strange quark asymmetry ~ 1σ (we assume 0) • isospin-dept nuclear ~ 40%, Cloet etal • CSV, isospin dep’t nuclear: at present, most plausible explanations for NuTeV anomaly • small additive contrib’ns from strangeness, radiative corrections ??

  39. Tony & Adelaide: • I have had many enjoyable & productive visits to Adelaide • The atmosphere has always been conducive to doing one’s best work • How wonderful that Tony & Joan are back again in Adelaide!

  40. 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

  41. 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 ~ 3σ above the very precise value (from EW processes at LEP)

  42. 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 Corresponds to 1.2% decrease in gL2; This is large compared to precision of EW measurements!

  43. 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) ) • NuTeV data currently under re-analysis • Corrections likely larger than NuTeV estimate D. Yu. Bardin and V. A. Dokuchaeva, JINR-E2-86-260, (1986)

  44. Models for CSV in Valence PDFs Construct quark models that reproduce qualitative features of PDFs Examine their behavior under charge symmetry operations Sather: Analytic Quark Model Approximation for Valence Parton CSV. 2nd moment analytic result ( model-independent) Quark models  predict sign, magnitude for 2nd moment of valence parton CSV

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