Precision Measurement of sin2qW from NuTeVJae Yu (for NuTeV Collaboration)University of Texas at ArlingtonSSI 2002, Aug. 14, 2002IntroductionPast measurementsCurrent ImprovementsWhats so new about the results?Conclusions

NuTeV CollaborationT. Adams4, A. Alton4, S. Avvakumov7, L.de Babaro5, P. de Babaro7, R.H. Bernstein3, A. Bodek7, T. Bolton4, J. Brau6, D. Buchholz5, H. Budd7, L. Bugel3, J. Conrad2, R.B. Drucker6, B.T.Fleming2, 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. Shaevitz2,3, P. Spentzouris3, E.G.Stern2, M. Vakili1, A. Vaitaitis2, U.K. Yang7, J. Yu3*, G.P. Zeller5, and E.D. Zimmerman2University of Cincinnati, Cincinnati, OH45221, USAColumbia 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 University of Texas at Arlington

Electroweak ThreoryStandard Model unifies Weak and EM to SU(2)xU(1) gauge theory Weak neutral current interactionMeasured physical parameters related to mixing parameters for the couplings

Neutrinos in this picture are unique because they only interact through left-handed weak interactions Probe weak sector onlyLess complication in some measurements, such as proton structure

sin2qW and n-N scatteringIn 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 angleWithin the on-shell renormalization scheme, sin2qW is:

Provides independent measurement of MW & information to pin down MHiggsComparable size of uncertainty to direct measurementsMeasures 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

How do we measure?Cross section ratios between NC and CC proportional to sin2qWLlewellyn Smith Formula:Some corrections are needed to extract sin2qW from measured ratios (radiative corrections, heavy quark effects, isovector target corrections, HT, RL)

Previous ExperimentConventional neutrino beam from p/k decays Focus all signs of p/k for neutrinos and antineutrinosOnly nm in the beam (NC events are mixed)Very small cross section Heavy neutrino targetne are the killers (CC events look the same as NC events)

Charged Current EventsNeutral Current EventsHow Do We Separate Events?

Event LengthDefine an Experimental Length variable Distinguishes CC from NC experimentally in statistical mannerCompare experimentally measured ratio

to theoretical prediction of Rn

Past Experimental ResultsSignificant correlated error from CC production of charm quark (mc) modeled by slow rescaling, in addition to ne error

The NuTeV ExperimentSuggestion by Paschos-Wolfenstein formula by separating n and`n beams:

Reduce charm CC production error by subtracting sea quark contributionsOnly valence u, d, and s contributes while sea quark contributions cancel outMassive quark production through Cabbio suppressed dv quarks onlySmarter beamline Removes all neutral secondaries to eliminate ne content

The NuTeV DetectorCalorimeter168 FE plates & 690tons84 Liquid Scintillator42 Drift chambers interspersedSolid Iron ToroidMeasures Muon momentumDp/p~10%Continuous test beam for in-situ calibration

The NuTeV DetectorA picture from 1998. The detector has been dismantled to make room for other experiments, such as D

NuTeV Event SelectionEhad > 20GeVTo ensure vertex finding efficiencyTo reduce cosmic ray contaminationXvert and Yvert within the central 2/3Full hadronic shower and muon containmentFurther reduce ne contaminationLongitudinal vertex, Zvert, cutTo ensure neutrino induced interactionBetter discriminate CC and NC

Events and Flux After SelectionRemaining number of events: 1.62M n & 350k `n

NuTeV Event Length DistributionsEnergy Dependent Length cut implemented to improve statistics and reduce systematic uncertainties.Good Data-MC agreement in the cut region

Event Contamination and BackgroundsSHORT nm CCs (20% n, 10% `n)m exit and rangeoutSHORT ne CCs (5%) neNeXCosmic Rays (0.9%)LONG nm NCs (0.7%)hadron shower punch-through effectsHard m Brem(0.2%)Deep m events

Other Detector EffectsSources of experimental uncertainties kept small, through modeling using n and TB data

EffectSize(dsin2qW)ToolsZvert0.001/inchm+m- eventsXvert & Yvert0.001MCCounter Noise0.00035TB msCounter Efficiency0.0002n eventsCounter active area0.0025/inchn CC, TBHadron shower length0.0015/cntrTB ps and ksEnergy scale0.001/1%TBMuon Energy Deposit0.004n CC

Measurements of ne FluxNeutrino events in anti-neutrino running constraint charm and KL induced production (Ke3) in the medium energy range (80

MC to Relate Rnexp to Rn and sin2qWParton Distribution ModelCorrect for details of PDF model Used CCFR data for PDFModel cross over from short nm CC events

Neutrino Fluxesnm,ne,`nm,`ne in the two running modesne CC events always look shortShower length modelingCorrect for short events that look longDetector response vs energy, position, and timeContinuous testbeam running minimizes systematics

Rnexp Stability CheckCrucial to verify the Rnexp comparison to MC is consistent under changes in cuts and event variablesLongitudinal vertex Detector uniformityLength cut Check CC to NC cross overTransverse vertex NC background at the detector edgeVisible energy (EHad)Checks detector energy scale and other factors Green bands represent 1s uncertainty.

sin2qW Fit to Rnexp and R`nexpThanks to the separate beam Measure Rns separatelyUse MC to simultaneously fit and to sin2qW and mc, and sin2qW and r

Rn Sensitive to sin2qW while R`n isnt, so Rn is used to extract sin2qW and R`n to control systematicsSingle parameter fit, using SM values for EW parameters (r0=1)Two parameter fit for sin2qW and r0 yieldsSyst. Error dominated since we cannot take advantage of sea quark cancellation

NuTeV sin2qW Uncertainties1-Loop Electroweak Radiative Corrections based on Bardin, Dokuchaeva JINR-E2-86-2 60 (1986)Dominant uncertainty

NuTeV vs CCFR Uncertainty Comparisons

The NuTeV sin2qWComparable precision but value smaller than other measurements

SM Global Fits with NuTeV ResultWithout NuTeVc2/dof=20.5/14: P=11.4%With NuTeVc2/dof=29.7/15: P=1.3%Confidence level in upper Mhiggs limit weakens slightly.

Tree-level Parameters: r0 and sin2qW(on-shell)Either sin2qW(on-shell) or r0 could agree with SM but both agreeing simultaneously is unlikely

Model Independent AnalysisPerformed the fit to quark couplings (and gL and gR)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

What is the discrepancy due to (Old Physics)?R- technique is sensitive to q vs`q differences and NLO effectDifference in valence quark and anti-quark momentum fraction Isospin spin symmetry assumption might not be entirely correctExpect violation about 1% NuTeV reduces this effect by using the ratio of n and `n cross sections Reducing dependence by a factor of 3s vs`s quark asymmetrys and `s needs to be the same but the momentum could differA value of Ds=s -`s ~+0.002 could shift sin2qW by -0.0026, explaining the discrepancy (S. Davison, et. al., hep-ph/0112302)NuTeV di-m measurement shows that Ds

What other explanations (New Physics)?Heavy non-SM vector boson exchange: Z, LQ, etcLL coupling enhanced than LR needed for NuTeVPropagator and coupling correctionsSmall compared to the effectMSSM : Loop corrections wrong sign and small for the effectGauge boson interactionsAllow generic couplings Extra Z bosons???LEP and SLAC results says < 10-3Many other attempts in progress but so far nothing seems to explain the NuTeV results Lepto-quarksContact interactions with LL coupling (NuTeV wants mZ~1.2TeV, CDF/D0: mZ>700GeV)Almost sequential Z with opposite coupling to nLangacker 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

Future???Muon storage ring can generate 106 times higher flux and well understood, high purity neutrino beam significant reduction in statistical uncertainty But ne and nm from muon decays are in the beam at all times Deadly for traditional heavy target detectors

ConclusionsNuTeV has measured 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 SMNuTeV discrepancy has generated a lot of interest in the communityStill could be a large statistical fluctuation (5s has happened before) Yet, many interpretations are being generated:Some could explain partially but not allAsymmetric s-quark seaAdditional mediator, extra U(1) vector bosons, etcNo single one can explain the discrepancy it still is a puzzleCould this be a signature of new physics? No other current experiment is equipped to redo this measurementMuon storage ring seems to provide a promising future