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 Z 0 pole matter effects in ν oscillations are sensitive to only flavor non- diagonal couplings Some outstanding puzzles in neutrino physics –~3σ NuTeV result σ(νq→νq)/σ(νq→μq ’ ) –~2σ deficit in “N ν ” LEP measurement of Γ(Z 0 →νν) –To date, only ~5% precision on σ(νe→νe) 21 February 2011 NuTeV Revisited, K. McFarland 2

3. 1984 Walter Mondale asks “where’s the beef”? KSM takes driver’s education FNAL-E744 (CCFRW) takes data 1993 William Jefferson Clinton becomes President KSM plays minor role in production of his first offspring, who today wants to take driver’s ed NuTeV Experiment proposed to recycle CCFR detector with a new beamline 1996 William Jefferson Clinton invites an intern back to see his cigar collection KSM analyzes E744 (and E770) data to measure NC/CC NuTeV takes first beam 1997 Father of one of KSM’s pothead buddies from college with cartoon last name finds himself looking blue dress DNA NuTeV data taking complete 2001 Men with box cutters kill thousands. US begins self-destructive response KSM presents NuTeV results “A departure from prediction” at Fermilab Wine and Cheese 2002 Last “Saddam [yes]” election MINERvA and T2K proposed (leaving to later immitation “Saddam [yes]” style elections) “The NuTeV-a result-a, she ees-a sheet-a” – Quote from Theorist, whose last name begins with one of “DGLAP”

4. 21 February 2011 NuTeV Revisited, K. McFarland 4 Measure NC/CC ratio to extract ratio of weak couplings –ratio is experimentally and theoretically robust –largest uncertainty: suppression of charm production in CC (m c ) –can extract sin 2  W. NuTeV measurement often quoted this way. With neutrino and anti-neutrino beams, can form NuTeV Measurement Technique Charged-Current (CC) Neutral-Current (NC)

5. 21 February 2011 NuTeV Revisited, K. McFarland 5 Beam identifies neutral currents as or    in mode 3     in  mode 4     Beam only has  electron neutrinos  Important background for NC events since no final state muon NuTeV Sign-Selected Beamline Dipoles make sign selection - Set   type - Remove e from K L (Bkgnd in previous exps.)

6. 21 February 2011 NuTeV Revisited, K. McFarland 6 Paschos-Wolfenstein à la NuTeV NuTeV result: –Statistics dominate uncertainty EWK fit (LEPEWWG 2001): –0.2227  0.00037, a 3  discrepancy NuTeV fit for sin 2 θ W and m c given external constraint from strange sea analysis. (More later)

7. QCD Symmetry Violations What symmetry violations can affect the result? 1. u≠d in target (neutron excess) 2. asymmetric heavy seas

8. 21 February 2011 NuTeV Revisited, K. McFarland 8 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 of first two effects, can calculate them for R -

9. Asymmetric Strange Sea 1. Why it might be so 2. How it is measured at NuTeV This is what drives us to update the NuTeV measurement This is what drives us to update the NuTeV measurement

10. 21 February 2011 NuTeV Revisited, K. McFarland 10 A Very Strange Asymmetry 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) Brodsky and Ma, Phys. Let. B392 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 sin 2 θ W Why might one think that the strange and anti-strange seas would be different? G.P. Zeller et al., Phys.Rev.D65:111103,2002)

11. 21 February 2011 NuTeV Revisited, K. McFarland 11 How Does NuTeV Measure This?  ± from semi-leptonic charm decay Fits to NuTeV and CCFR  and  dimuon data can measure the strange and antistrange seas separately –NuTeV separate and   beams important for reliable separation of s and  s

12. 21 February 2011 NuTeV Revisited, K. McFarland 12 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 value towards standard model and increase uncertainties –at NLO, with CTEQ6 as base PDF courtesy heroic efforts of D. Mason, P. Spentzouris

13. NuTeV Update 1. Effects incorporated –Numerical Estimations 2. To do

14. 21 February 2011 NuTeV Revisited, K. McFarland 14 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 ν e 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

15. 21 February 2011 NuTeV Revisited, K. McFarland 15 Changes in Prediction of R ν published: updated: RνRνRνRν R νbar Source σ pub σ new Δ σ pub σ new Δ m top n/an/a+0.00001n/an/a-0.00015 d/u0.000040.00013+0.000000.000040.00018+0.00000 νeνeνeνe0.000280.00029+0.000780.000620.00062+0.00085 Strange PDFs 0.000230.00036-0.000380.000520.00078+0.00029 NLO QED 00.00013n/a00.00061n/a NLO QCD 00.00004n/a00.00043n/a

16. 21 February 2011 NuTeV Revisited, K. McFarland 16 NuTeV 99% Conf. Prediction Graphical Shifts in R ν d/u νeνe m top Strange Sea, S - /S + =0.09

17. 21 February 2011 NuTeV Revisited, K. McFarland 17 NuTeV 99% Conf. Prediction Directions of Effects not Considered (length of arrows are arbitrary) mcmc Shadowing (VMD) Valence Isospin Violation

18. 21 February 2011 NuTeV Revisited, K. McFarland 18 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”…

19. 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 21 February 2011 NuTeV Revisited, K. McFarland 19