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Past, Present and the Future of Precision sin 2 q W Measurements

Explore the evolution of sin2qW measurements from past to present and future advancements, including experimental techniques, event separation, and analyzing results. Learn about the significance of sin2qW in the electroweak sector of the Standard Model and its implications for understanding physics beyond the SM.

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Past, Present and the Future of Precision sin 2 q W Measurements

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  1. Past, Present and the Future of Precision sin2qW Measurements • Introduction • Past measurements • Current Improvement • Measurement at a Neutrino Factory • Conclusions Jae Yu (for NuTeV Collaboration) University of Texas at Arlington NuFact’03, June 9, 2003 Columbia University, New York

  2. NuTeV Collaboration T. Adams4, A. Alton4, S. Avvakumov7, L.de Babaro5, P. de Babaro7, R.H. Bernstein3, A. Bodek7, T. Bolton4, S. Boyd8, J. Brau6, D. Buchholz5, H. Budd7, L. Bugel3, J. Conrad2, R.B. Drucker6, B.T.Fleming3, J.A.Formaggio2, R. Frey6, J. Goldman4, M. Goncharov4, D.A. Harris3, R.A. Johnson1, J.H.Kim2, S.Kutsoliotas9, M.J. Lamm3, W. Marsh3, D. Mason6, J. McDornald8, K.S.McFarland7, C. McNulty2, Voica Radescu8, W.K. Sakumoto7, H. Schellman5, M.H. Shaevitz2, P. Spentzouris3, E.G.Stern2, M. Vakili1, A. Vaitaitis2, U.K. Yang7, J. Yu3*, G.P. Zeller2, and E.D. Zimmerman2# • University of Cincinnati, Cincinnati, OH45221, USA • Columbia University, New York, NY 10027 • Fermi National Accelerator Laboratory, Batavia, IL 60510 • Kansas State University, Manhattan, KS 66506 • Northwestern University, Evanston, IL 60208 • University of Oregon, Eugene, OR 97403 • University of Rochester, Rochester, NY 14627 • University of Pittsburgh, Pittsburgh, PA 15260 • Bucknell University, Lewisburg, PA 17837 • *:Current affiliation at the University of Texas at Arlington • #:Current affiliation at the University of Colorado, Boulder J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  3. sin2qW and n-N scattering • In the electroweak sector of the Standard Model, it is not known a priori what the mixture of electrically neutral electomagnetic and weak mediator is This fractional mixture is given by the mixing angle • Within the on-shell renormalization scheme, sin2qW is: • Provides independent measurement of MW & information to pin down MHiggs • Comparable size of uncertainty to direct measurements • Measures light quark couplings  Sensitive to other types (anomalous) of couplings • In other words, sensitive to physics beyond SM  New vector bosons, compositeness,n-oscillations, etc J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  4. How did we measure? • Cross section ratios between NC and CC proportional to sin2qW • Llewellyn Smith Formula: Some corrections are needed to extract sin2qW from measured ratios (radiative corrections, heavy quark effects, isovector target corrections, HT, RL) J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  5. Previous Experiment • Conventional neutrino beam from p/k decays • Focus all signs of p/k for neutrinos and antineutrinos • Both ` nm , nm in the beam (NC events are mixed) • Very small cross section  Heavy neutrino target • ne are the killers (CC events look the same as NC events) J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  6. Event Length y-view Charged Current Events Nothing is coming in!!! m x-view m y-view Neutral Current Events Nothing is coming in!!! Nothing is going out!!! x-view How Do We Separate Events? J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  7. Event Length • Define an Experimental Length variable • Distinguishes CC from NC experimentally in statistical manner Compare experimentally measured ratio to theoretical prediction of Rn J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  8. Past Experimental Results • Significant correlated error from CC production of charm quark (mc) modeled by slow rescaling, in addition to ne error J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  9. The NuTeV Experiment • Suggestion by Paschos-Wolfenstein by separating n and`n beams: • Reduce charm CC production error by subtracting sea quark contributions • Only valence u, d, and s contribute while sea quark contributions cancel out • Massive quark production through Cabbio suppressed dv quarks only • Smarter beamline • Separate n and`n beam • Removes all neutral secondaries to eliminate ne content J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  10. Events and EHad After Event Selection Events passing cuts: 1.62M n & 350k `n (<En>~100GeV) J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  11. Mode Nshort Nlong Rn=Nshort/NLong 457k 1167k 101k 250k NuTeV Event Length Distributions Energy Dependent Length cut implemented to improve statistics and reduce systematic uncertainties. Good Data-MC agreement in the cut region J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  12. Event Contamination and Backgrounds • SHORT nmCC’s (20% n, 10% `n) • m exit and rangeout • SHORT ne CC’s (5%) • neNeX • Cosmic Rays (0.9%) • LONGnmNC’s (0.7%) • hadron shower • punch-through effects • Hardm Brem(0.2%) • Deep m events J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  13. Other Systematic Effects Sources of experimental uncertainties kept small, through modeling using n and TB data J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  14. MC to Relate Rnexp to Rn and sin2qW • Parton Distribution Model (<Q2> ~ 25 GeV2 for nm, 16 GeV2 for `nm) • Correct for details of PDF model  Used CCFR data for PDF • Model cross over from short nm CC events • Neutrino Fluxes • nm,ne,`nm,`ne in the two running modes • ne CC events always look short • Shower length modeling • Correct for short events that look long • Detector response vs energy, position, and time • Continuous testbeam running minimizes systematics J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  15. sin2qW Fit to Rnexp and R`nexp • Thanks to the separate beam Measure Rn’s separately • Use MC to simultaneously fit and to sin2qW and mc, and sin2qW and r • Rn Sensitive to sin2qW while R`nisn’t, so Rnis used to extract sin2qW and R`nto control systematics • Single parameter fit, using SM values for EW parameters (r0=1) • Two parameter fit for sin2qW and r0yields Syst. Error dominated since we cannot take advantage of sea quark cancellation J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  16. Dominant uncertainty NuTeV sin2qWUncertainties Source of Uncertainty d sin2qW Statistical 0.00135 ne flux 0.00039 Event Vertex 0.00030 Length (Other effects) 0.00027 (23) 1-Loop Electroweak Radiative Corrections based on Bardin, DokuchaevaJINR-E2-86-2 60 (1986) Total Experimental Systematics 0.00063 CC Charm production, sea quarks 0.00047 RL 0.00032 0.00022 Higher Twist 0.00014 RadiativeCorrection 0.00011 Non-isoscalar target 0.00005 Total Physics Model Systmatics 0.00064 Total Uncertainty 0.00162 DMW (GeV/c2) 0.08 J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  17. }Dominant error }Beamline worked! }Technique worked! Past vs Present Uncertainty Comparisons J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  18. The Present (NuTeV) sin2qW Comparable precision but value smaller than other measurements Confidence level in upper Mhiggs limit weakens slightly. J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  19. Model Independent Analysis • Performed the fit to quark couplings (and gL andgR) • For isoscalar target, the nN couplings are • From two parameter fit to and (SM: 0.3042 -2.6s deviation) (SM: 0.0301  Agreement) Difficult to explain the disagreement with SM by: Parton Distribution Function or LO vs NLO or Electroweak Radiative Correction: large MHiggs J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  20. What is the discrepancy due to (Old Physics)? • R- technique is sensitive to q vs`q differences and NLO effect • Difference in valence quark and anti-quark momentum fraction • Isospin symmetry assumption might not be entirely correct • Expect violation about 1%  NuTeV reduces this effect by using the ratio of n and `ncross sections  Reducing dependence by a factor of 3 • s vs`s quark asymmetry • s and`s needs to be the same but the momentum could differ if +30% asymmetry • NuTeV LO di-m measurement shows Ds=s -`s ~-0.0027 • NuTeV NLO analysis show no-asymmetry (D. Mason, et al., ICHEP02 proceedings) • NLO and PDF effects • PDF, mc, Higher Twist effect, etc, are small changes • Heavy vs light target PDF effect (Kovalenko et al., hep-ph/0207158) • Using PDF from light target on Iron target could make up the difference  NuTeV result uses PDF extracted from CCFR (the same target) J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  21. What other explanations (New Physics)? • Heavy non-SM vector boson exchange: Z’, LQ, etc • LL coupling enhanced than LR needed for NuTeV • Propagator and coupling corrections • Small compared to the effect • MSSM : Loop corrections wrong sign and small for the effect • Gauge boson interactions • Allow generic couplings  Extra Z’ bosons??? • LEP and SLAC results says < 10-3 • Many other attempts in progress but so far nothing seems to explain the NuTeV results • Lepto-quarks • Contact interactions with LL coupling (NuTeV wants mZ’~1.2TeV, CDF/D0: mZ’>700GeV) • Almost sequential Z’ with opposite coupling to n Langacker et al, Rev. Mod. Phys. 64 87; Cho et al., Nucl. Phys. B531, 65; Zppenfeld and Cheung, hep-ph/9810277; Davidson et al., hep-ph/0112302 J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  22. NLO Upgrade of sin2qW Analysis • To address concerns within the community • Don’t expect to see large effects • LO x-sec model describe CC x-sec data well • Gambino, et al., (hep-ph/0112302) shown little NLO PDF effect to R- • s level shifts to R- small (Davidson, hep-ph/0112302 & Kulagin, hep-ph/0301045) • To calculate O(as) pQCD corrections to the differential X-sec for n,`n DIS • NuTeV (Zeller & McFarland) is collaborating with Theorists • FNAL Theory group: K. Ellis, B. Dobrescu, W. Gigele • DESY: Seven-Olaf Moch • others • Approach based on Altarellu, Ellis & Martinelli, NP B143, 521 (1978) • X-sec’s written in terms of xF1, F2, xF3 • pQCD corrections affect 2xF1-F2=FL & xF3-F2 • FL effect taken into account via RL • Need as correction of xF3-F2, because as2 is small (Zijlstra, PLB297, 377, 1992) • Calculations and Implementation of the correction in progress J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  23. sin2qW Measurement at a NuFact • Neutrinos come from m decays • Good understanding of the beam content and flux • Better collimated than conventional beam • Large neutrino flux (105~106 higher than the current) But… • Always two neutrinos simultaneously in the given beam ( `ne+nm or `nm+ne) • Traditional heavy target detector will not work • Will screw up NC counting due to ne CC events • Need light target detectors  Can afford to do this • Might need new techniques for NC to CC ratio • Can’t distinguish ne vs nm induced NC events J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  24. 1m P-ID & Momentum Hadronic Energy m-ID and Momentum A Light Target sin2qW Detector at a NuFact • ne and nm from muon decays are in the beam at all times • Must use light target (D2) detectors J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  25. Source of Uncertainty d sin2qW Statistical 1.35x10-32.13x10-4 ne flux 3.9x10-40 Event Vertex 3.0x10-4 3.0x10-6 Energy Measurements 1.80x10-4 9.00x10-5 Total Experimental Systematics 6.30x10-49.00x10-5 CC Charm production, sea quarks 4.70x10-4 2.40x10-4 Higher Twist 1.40x10-4 1.40x10-4 Non-isoscalar target correction 5.00x10-5 0 (D2 target) 2.20x10-4 1.50x10-4 Radiative Correction 1.10x10-4 1.10x10-4 RL 3.20x10-4 9.00x10-5 Total Physics Model Systmatics 6.40x10-44.6x10-4 Total Uncertainty 1.62x10-35.15x10-4 DMW (GeV/c2) 0.080.025 Expectation at a NuFact Using a 1m thick D2 target, one can obtain about 20M nm CC events per yearWith the help of good p-id, the stat doubles  Length related uncertainties become irrelevant J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  26. Experimental and Theoretical Issues Experimental Issues • Must be able to reverse beam polarity and measure current well • Detector must be light weight • Must be able to distinguish primary e, m, and p • Need to control overall p-ID efficiency to be better than 10-3 • High electron detection efficiency • Good EM and Hadronic shower ID • Good charged particle momentum measurement • Good vertex measurement w/ triggering capability at the target Theoretical Issues • Better measured charm CC x-sec • Need to understand radiative correction better • Better understanding of higher twist effects J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

  27. Conclusions • NuTeV has improved sin2qW • NuTeV result deviates from SM prediction by about +3s (PRL 88, 091802, 2002) • Interpretations of this result implicates lower left-hand coupling (-2.6s) but good agreement in right-hand coupling with SM • NuTeV discrepancy has generated a lot of interest in the community • Still could be a large statistical fluctuation (5s has happened before) • No single one can explain the discrepancy • NuTeV working on NLO analysis of sin2qW • A Neutrino factory can provide a dramatic improvement in sin2qW • Large neutrino flux (both ne and nm) • Significant improvement in uncertainties (DMW<25MeV) • Light target detector with p-id would be necessary • Theoretical improvement will help further improving the measurement J. Yu: Past, Present and Future of Precision sin2qW Measurements, NuFact’03

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