1 / 19

Revisiting NuTeV -or- What Kevin Did Last Week

Revisiting NuTeV -or- What Kevin Did Last Week. Kevin McFarland Rochester Neutrino Group Meeting 21 February 2011. The Big Picture. Neutrinos are important in electroweak physics there is a glorious history, of course…

isaura
Download Presentation

Revisiting NuTeV -or- What Kevin Did Last Week

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Revisiting NuTeV-or-What Kevin Did Last Week Kevin McFarland Rochester Neutrino Group Meeting 21 February 2011

  2. The Big Picture • Neutrinos are important in electroweak physics • there is a glorious history, of course… • … but precision today in neutrino electroweak couplings lags behind other sectors • neutrino couplings are the most difficult couplings to measure precisely at the Z0 pole • matter effects in ν oscillations are sensitive to only flavor non-diagonal couplings • Some outstanding puzzles in neutrino physics • ~3σNuTeV result σ(νq→νq)/σ(νq→μq’) • ~2σ deficit in “Nν” LEP measurement of Γ(Z0→νν) • To date, only ~5% precision on σ(νe→νe) NuTeV Revisited, K. McFarland

  3. NuTeV Measurement Technique • Measure nNC/CC ratio to extract ratio of weak couplings • ratio is experimentally and theoretically robust • largest uncertainty: suppression of charm production in CC (mc) • can extract sin2qW. NuTeV measurement often quoted this way. • With neutrino and anti-neutrino beams, can form Charged-Current(CC) Neutral-Current(NC) NuTeV Revisited, K. McFarland

  4. Dipoles make sign selection - Set n /n type - Remove ne from KL (Bkgnd in previous exps.) NuTeV Sign-Selected Beamline • Beam identifies neutral currents as n or n(n in n mode 310-4, n in n mode 410-3) • Beam only has ~1.6% electron neutrinos  Important background for NC events since no final state muon NuTeV Revisited, K. McFarland

  5. Paschos-Wolfenstein à la NuTeV NuTeV fit for sin2θWand mc given external constraint from strange sea analysis. (More later) • NuTeV result: • Statistics dominate uncertainty • EWK fit (LEPEWWG 2001): • 0.2227  0.00037, a 3s discrepancy NuTeV Revisited, K. McFarland

  6. QCD SymmetryViolations What symmetry violations can affect the result? u≠d in target (neutron excess) asymmetric heavy seas

  7. Symmetry Violating QCD Effects • Paschos-Wolfenstein R- assumptions: • Assumes total u and d momenta equal in target • Assumes sea momentum symmetry, s =s and c =c • Assumes nuclear effects common in W/Z exchange • To get a rough idea offirst two effects, can calculate them for R- NuTeV Revisited, K. McFarland

  8. Asymmetric Strange Sea Why it might be so How it is measured at NuTeV This is what drives us to update the NuTeV measurement

  9. A Very Strange Asymmetry • Paschos-Wolfenstein relation assumes that strange sea is symmetric, i.e., no “valence” strange distribution • if there were on, this would be a big deal since it is an isovector component of the PDFs(charm sea is heavily suppressed) • ~30% more momentum in strange sea than in half of strange+anti-strange seas would “fix” NuTeV sin2θW • Why might one think that the strange and anti-strange seas would be different? • Perturbative strange sea is (roughly) momentum symmetric… • But “intrinsic” strange sea need not be! • so is a DIS probe of intrinsic strangeness! • Brodsky first suggested it! (though this model at right is excluded by NuTeV data) G.P. Zeller et al., Phys.Rev.D65:111103,2002) Brodsky and Ma, Phys. Let. B392 NuTeV Revisited, K. McFarland

  10. How Does NuTeV Measure This? • m± from semi-leptonic charm decay • Fits to NuTeV and CCFR n and dimuon data can measure the strange and antistrange seas separately • NuTeV separate n and beams important for reliable separation of s ands NuTeV Revisited, K. McFarland

  11. NEW NuTeV NLO Analysis • Have incorporated CTEQ strange “valence” evolution and CTEQ parameterizations • thanks esp. to Amundson, Kretzer, Olness & Tung • NuTeV NLO analysis (Phys.Rev.Lett.99:192001,2007) is near zero, but slightly positive • will shift central valuetowards standard modeland increase uncertainties • at NLO, with CTEQ6 as base PDF courtesy heroic efforts of D. Mason, P. Spentzouris NuTeV Revisited, K. McFarland

  12. NuTeV Update Effects incorporated Numerical Estimations To do

  13. What’s Done? • Three large effects • Estimate for Strange Sea, S-/S+~0.09±0.04 • External K+e3 branching ratio • Brookhaven E-865, famous for “fixing” the unitarity of the first row of the CKM matrix • also improves agreement with our own (less precise) measurement of νe flux • Strong effect on our electron neutrino background • d/u PDF uncertainties • pointed out by Kulagin and Alekhin that these were underestimated in published result • also corrected target neutron excess NuTeV Revisited, K. McFarland

  14. Changes in Prediction of Rν published: updated: NuTeV Revisited, K. McFarland

  15. NuTeV 99% Conf. Prediction Graphical Shifts in Rν mtop d/u νe Strange Sea, S-/S+=0.09 NuTeV Revisited, K. McFarland

  16. NuTeV 99% Conf. Prediction Directions of Effects not Considered(length of arrows are arbitrary) Shadowing (VMD) mc Valence Isospin Violation NuTeV Revisited, K. McFarland

  17. What Are you Working on Now? • Current Work is on Improving Cross-Section Model • LO to NLO QCD cross-section • Higher twist (non-perturbative) effects smaller • Can build on better fits (global!) to two muon data to constrain charm • Base data for cross-section comes from NuTeV (previous analysis used CCFR) • It’s “the gift that keeps on giving”… NuTeV Revisited, K. McFarland

  18. What if We Don’t “Fix” NuTeV? • My money is on the second symmetry violating term, • We may have discovered large (several %) isospin violation in parton distributions NuTeV Revisited, K. McFarland

More Related