1Electroweak Measurements at NuTeV:

Are Neutrinos Different?

Mike Shaevitz

Columbia Universityfor the NuTeV Collaboration

• Introduction to Electroweak Measurements

• NuTeV Experiment and Technique

• Experimental and Theoretical Simulation

• Data Sample and Checks

• Electroweak Fits

• Interpretations and Summary

2Electroweak Theory

• Standard Model– Charged Current mediated by W with (V-A)

Neutral Current mediated by Z0 with couplings below – One parameter to measure!

• Weak / electromagnetic mixing parameter sin2W (Related to weak/EM coupling ratio g’=g tanW)

Z Couplings gL gR

e , 0

e , sin

W sin

W

u , c , t sin

W sin

W

d , s , b sin

W sin

W

• Neutrinos are special in SM– Only have left-handed weak interactions

W and Z boson exchange

WZ

W

WF

W

M

MM

gG

ge

cos

,8

2

,sin

2

2

3History of EW Measurements

• Discovery of the Weak Neutral Current (1973 CERN)

• First Generation EW Experiments (late 1970’s)

– Precision at the 10% level

– Tested basic structure of SM MW,MZ

GargamelleHPWF CIT-F

CCFR, CDHS, CHARM, CHARM IIUA1 , UA2 , Petra , Tristan , APV, SLAC eD

NuTeV, D0, CDF, LEP1 SLDLEPII, APV , SLAC-E158

Gargamelle

• Second Generation EW Experiments (late 1980’s)

–Discovery of W,Z boson in 1982-83–Precision at the 1-5% level–Radiative corrections become important–First limits on the Mtop

• Current Generation Experiments– Precision below 1% level– Discovery of the top quark– Constrain MHiggs

Predict light Higgs boson (and possibly SUSY) – Use consistency to search for new physics !

4

5Current Era of Precision EW Measurements

• Precision parameters define the SM:

– EM 45ppb (200ppm@MZ)

– GGeV-2 10ppm

– MZ 23ppm

• Comparisons test the SM and probe for new physics – LEP/SLD (e+e-), CDF/D0 (p-pbar), N , HERA (ep) , APV

• Radiative corrections are large and sensitive to Mtop and MHiggs

– MHiggs constrained in SM to be less than196 GeV at 95%CL

6Are There Cracks?

• All data suggest a light Higgs except AFBb

• Global fit has large =23/15 (9%)– AFB

b is off about 3

• inv also off by – N

gRb too low

Higgs Mass ConstraintLeptons Quarks

Other anomalies: - g-2 at BNL (2.6)

- Atomic Parity Violation (0 – 2.2)

- |Vud| (2.3 – 3.0)

7From Bruce Knuteson’s Columbia Colloquium

Precision Electroweak measurementsPrecision Electroweak measurementsX

Added tohis list

8NuTeV Adds Another Arena

• Precision comparable to collider measurements of MW

• Sensitive to different new physics– Different radiative corrections

• Measurement off the Z pole

– Exchange is not guaranteed to be a Z

• Measures neutrino neutral current coupling– LEP 1 invisible line width is only

other precise measurement

• Sensitive to light quark (u,d) couplings– Overlap with APV, Tevatron Z production

• Tests universality of EW theory over large range of momentum scales

9

• For an isoscalar target composed of u,d quarks:

• NC/CC ratio easiest to measure experimentally but ...– Need to correct for non-isoscalar target, radiative corrections, heavy quark effects, higher twists– Many SF dependencies and systematic uncertainties cancel– Major theoretical uncertainty mc Suppress CC wrt NC

Neutrino EW Measurement Technique

Wemweak QJCoupling 2)3( sin)3(weakJCoupling

Charged-Current(CC)

Neutral-Current(NC)

22422

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10Charm Mass Effects

• CC is suppressed due to final state c-quark Need to know s-quark sea and mc

– Modeled with leading-order slow-rescaling

– Measured by NuTeV/CCFR using dimuon events (NcX X) (NuTeV: M. Goncharov et al., Phys. Rev. D64: 112006,2001 and CCFR: A.O. Bazarko et al., Z.Phys.C65:189-198,1995)

Charged-Current Production Neutral-Current of Charm

M

mQM

Q cx 22

222

11Before NuTEV

• N experiments had hit a brick wall in precision Due to systematic uncertainties (i.e. mc ....)

GeVM

M

M

W

Z

WshellonW

19.014.80

0036.02277.01sin2

22

(All experiments corrected to NuTeV/CCFR mc and to large Mtop > MW )

12NuTeV’s Technique

• R manifestly insensitive to sea quarks– Charm and strange sea error negligible– Charm production small since only enters from dV quarks only which is Cabbibo

suppressed and at high-x

• But R requires separate andbeams NuTeV SSQT (Sign-selected Quad Train)

Cross section differences remove sea quark contributions Reduce uncertainties from charm production and sea

oncontributi No 0

contribute Only 0

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13

• Beam is almost pure or in mode 3 in mode 4

• Beam only has electron neutrinos Important background for

isolating true NC event

NuTeV Sign-Selected Beamline

Dipoles make sign selection - Set type - Remove e from Klong (Bkgnd in previous exps.)

14NuTeV Lab E Neutrino Detector

– 168 Fe plates (3m3m 5.1cm)

– 84 liquid scintillation counters• Trigger the detector• Measure:

Visible energy interaction point Event length

– 42 drift chambers• Localize transverse vertex

– Solid Fe magnet• Measures

momentum/charge

• PT = 2.4 GeV for P/P

690 ton target

Target / CalorimeterToroid Spectrometer

Continuous Test Beamsimultaneous with runs- Hadron, muon, electron beams- Map toroid and calorimeter response

15NuTeV Detector

Picture from 1998 - Detector is now dismantled

16

NuTeV Collaboration

Cincinnati1, Columbia2, Fermilab3, Kansas State4, Northwestern5, Oregon6, Pittsburgh7, Rochester8

(Co-spokepersons: B.Bernstein, M.Shaevitz)

K. S. McFarland

17Neutral Current / Charged CurrentEvent Separation

• Separate NC and CC events statistically based on the “event length”defined in terms of # counters traversed

modes) and both in ratio this(measure

Candidates CC

Candidates NC

eventsLONG

events SHORTexp

cut

cut

LL

LLR

18

• Events selections:–Require Hadronic Energy, EHad > 20 GeV–Require Event Vertex with fiducial volume

• Data with these cuts: 1.62million events 351 thousand events

target - calorimeter toroid spectrometer

Ehad (GeV)

Eve

nts

Dat

a/M

C

Eve

nts

Ehad (GeV)

Dat

a/M

C

NuTeV Data Sample

19Determine Rexp: The Short to Long Ratio:

Short (NC) Events Long (CC) Events Rexp=Short/Long

Neutrino 457K 1167K 0.3916

Antineutrino 101K 250K 0.4050

NC

CC

Cuts:- Ehad > 20 GeV- Fiducial Vol.

Event Length DistributionNeutrinos

Event Length DistributionAntineutrinos

20From Rexp to R

• Cross Section Model– LO pdfs for Iron (CCFR)– Radiative corrections– Isoscalar corrections– Heavy quark corrections

– RLong

– Higher twist corrections

• Detector Response– CC NC cross-talk– Beam contamination– Muon simulation– Calibrations– Event vertex effects

• Neutrino Flux– and e flux

Need detailed Monte Carlo to relate Rexp to R and sin2W

Analysis goal is use data directly to set and check the Monte Carlo simulation

21Monte Carlo also Corrects for NC/CC Confusion

A few CC events look like NC events

• Short CC’s(20% , 10%)– muon exits, range out

at high y

• Short e CC’s (5%)

– e N e X

• Cosmic Rays (Correction) (0.9%/4.7%)

• Long NC’s (0.7%)

– punch-through effects

A few NC events look like CC events

22Key Elements of Monte Carlo

• Parton Distribution Model– Needed to correct for details of the PDF model– Needed to model cross over from short CC events

• Neutrino fluxes– – Electron neutrino CC events always look short

• Shower Length Modeling– Needed to correct for short events that look long

• Detector response vs energy, position, and time– Test beam running throughout experiment crucial

Top Five Largest Corrections

modes running twoin the ,,, ee

Source expR expR Comments

Short CC Background -0.068 -0.026 Check mediumlength events

Electron Neutrinos -0.021 -0.024 Direct check fromdata

EM Radiative Correction +0.0074 +0.0109 Well understood

Heavy mc -0.0052 -0.0117 R technique

Cosmic-ray Background -0.0036 -0.019 Direct from data

Compare to statistical error

23

• PDFs extracted from CCFR data exploiting symmetries:– Isospin symmetry: up=dn , dp=uu , and strange = anti-strange

• Data-driven: uncertainties come from measurements

• LO quark-parton model tuned to agree with data:– Heavy quark production suppression and strange sea

(CCFR/NuTeV NX data)– RL , F2 higher twist (from fits to SLAC, BCDMS)– d/u constraints from NMC, NUSEA(E866) data– Charm sea from EMC F2

cc

This “tuning” of model is crucial for the analysis

),( and ),(

:needs sections-cross /for modelquark CC and NC22 QxqQxq

Neutrino xsec vs y at 190 GeV Antineutrino xsec vs y at 190 GeV

CC

FR D

ata

Use Enhanced LO Cross-Section

24

• Use beam Monte Carlo simulation tuned to match the observed spectrum

–Tuning needed to correct for uncertainties in SSQT alignment and particle production at primary target

–Simulation is very good but needs small tweaks at the level for E , EK , K/ E

vent

sE

vent

s

NuTeV Neutrino Flux

25 Charged-Current Control Sample

• Medium length events (L>30 cntrs) check modeling and simulation of Short charged-currents sample

–Similar kinematics and hadronic energy distribution to short CC events

–

• Good agreement between data and MC for the medium length events.

20 50 100 180 20 50 100 180 EHad (GeV)

26

• Approximately 5% of short events are e CC events (It would take a 20% mistake in e to move NuTeV value to SM)

– Main e source is K decay (93% / 70%)

– Others include KL,’s (4%/18%) reduced by SSQT and Charm (2%/9%)

– Main uncertainty is K

e3 branching ratio (known to 1.4%) !!

• But also have direct e measurement techniques.

98%1.7%

98%1.6%

NuTeV Electron Neutrino Flux

27Direct Measurments of e Flux

1. CC (wrong-sign) events in antineutrino running constrain charm and KL production

2. Shower shape analysis can statistically pick out events (EGeV)

3. e from very short events (EGeV)–Precise measurement of e in tail region of flux–Observe more e than predicted above 180 GeV,and a smaller excess in beam–Conclude that we should require Ehad < 180 GeV

)(0.041.01

)(03.005.1:/

e

eMCmeas NN

NuTeV preliminaryresult did not havethis cutshifts sin2W by +0.002

20 50 100 180 20 50 100 180 EHad (GeV)

DataMC

28

dof

dof

Verify systematic uncertainties with data to Monte Carlo comparisons as a function of exp. variables.

• Longitudinal Vertex: checks detector uniformity

Rexp Stability Tests vs. Experimental Parameters

Note: Shift from zero is because NuTeV result differs from Standard Model

29

• Rexp vs. length cut: Check NC CC separation syst.– “16,17,18” Lcut is default: tighten loosen selection

• Rexp vs. radial bin: Check corrections for e and short CC which change with radius.

Stability Tests (cont’d)

Yellow band is stat error

30

Short Events(NC Cand.) vs Ehad

Long Events(CC Cand.) vs Ehad

Distributions vs. Ehad

31Stability Test: Rexp vs EHad

• Short/Long Ratio vs EHad checks stability of final measurement over full kinematic region

–Checks almost everything: backgrounds, flux, detector modeling, cross section model, .....

exp exp

20 50 100 180 20 50 100 180 EHad (GeV)

20 50 100 180 20 50 100 180 EHad (GeV)

32Fit for sin2W

)1(sin

9

5sin

2

1)(

)(4220)(

)()(

CC

CC

WW

CC

NCR

) (i.e. ssystematic sin

small sin

large sin

exp2

exp

2

exp

2

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cW

WW

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tsmeasuremendimuon from 14.038.1input Also and sin

:parameters two to and offit usSimultaneo2

expexp

c

cW

mm

RR

This combined fit is equivalent to using R in reducing systematic uncertainty

.)(06.0.)(09.032.1

.)(0009.0.)(0013.02277.0sin

)(2

syststatm

syststat

:Result

c

shellonW

(From NuTeV and CCFR)

33Uncertainties in Measurement

• sin2W error statistically dominated R technique

• R uncertainty dominated by theory model

34NuTeV Technique Gives Reduced Uncertainties

4 better

6 better

35

0016.02277.0.)(0009.0.)(0013.02277.0sin )(2

syststatshellon

W

agreementGoodSMR

differenceSMR

)4066.0:(0027.04050.0

3)3950.0:(0013.03916.0

exp

exp

• NuTeV result:– Error is statistics dominated– Is 2.3 more precise than previous N experiments

where sin2W = 0.2277 and syst. dominated

• Standard model fit (LEPEWWG): 0.2227 0.00037 A 3 discrepancy ...........

The Result

Phys.Rev.Lett. 88,91802 (2002)

36Result from Fit to R and R

agreementGoodSMdifferenceSMRR

)4066.0:(3)3950.0:(0027.04050.00013.03916.0 expexp

:tsmeasuremen and Separating

)0.1 :(SM .)(0032.0.)(0026.09884.0 fit) paramete-(1strength coupling / CC toNC theof in termsOr

20

syststat

agreementSMdifferenceSMgg RL

)0301.0:( 6.2)3042.0:(0011.00308.0 00137.030005.0

:couplings handed-right andleft of In terms 22

Discrepancy is left-handed coupling to u and d quarks

Discrepancy is neutrinos not antineutrinos

NC coupling is too small

37

Comparison to Other EW Measurements

Each electroweak measurement also indicates a range of Higgs masses

MW = 80.136 0.084 GeV

from

QCD and electroweak radiative corrections are small

Precision comparable to collider measurements but value is smaller

2

2)(2 1sin

Z

WshellonW M

M

38SM Global Fit with NuTeV sin2W

• Without NuTeV: – 2/dof = 19.6/14,

probability of 14%

• With NuTeV: – 2/dof = 28.8/15,

probability of 1.7%

• Upper mHiggs limit only weakens slightly

NuTeV

39Possible Interpretations

• Changes in Standard Model Fits– Change PDF sets– Change MHiggs

• “Old Physics” Interpretations: QCD– Violations of “isospin” symmetry– Strange vs anti-strange quark asymmetry– Shadowing and other nuclear effects

• Are ’s Different?– Special couplings to new particles– Mixing and Oscillation Effects

• “New Physics” Interpretations– New Z’ or lepto-quark exchanges– New particle loop corrections– Mixtures of new physics

40Standard Model Fits to Quark Couplings

• Difficult to explain discrepancy with SM using:– Parton distributions or LO vs NLO or– Electroweak radiative corrections: heavy mHiggs

and 22 eff

ReffL gg

agreementSMgdifferenceSMg

RR

R

L

)0301.0:(0011.00310.06.2)3042.0:(0014.03005.0

: and fit toparameter Two

2

2expexp

Example variationswith LO/NLO PDF Sets(no NLO mc effects)

(S.Davidson et al. hep-ph/0112302)

WRRR

WWLLL

dug

dug

N

4952222

4952

212222

sin

sinsin

:are couplings thetarget,isoscalar an For

41Symmetry Violating QCD Effects

• Paschos-Wolfenstein Relation 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

• Violations of these symmetries can arise from1. A 2Z due to neutron excess (corrected for in NuTeV)

2. Isospin violating PDF’s, up(x) dn(x)(Sather; Rodinov, Thomas and Londergan; Cao and Signal)

– Changes d/u of target mean NC coupling

3. Asymmetric heavy-quark sea, s(x) = s (x) (Signal and Thomas; Burkhardt and Warr; Brodsky and Ma)

– Strange sea doesn’t cancel in R

4. Mechanisms for different shadowing in NC/CC– Effects RR directly

Bottom Line: R technique is very robust

42Detailed Examination of Symmetry Violation Effects

New Publication:

On the Effects of Asymmetric Strange Seas and Isospin-Violating Parton Distribution Functions on sin2W Measured in the NuTeV Experiment. (G.P. Zeller et al., Phys.Rev.D65:111103,2002; hep-ex/0203004)

• Parameterize the shifts from various asymmetries for the NuTeV sin2W analysis technique

1

0

2 );();(sin dxeffectxeffectxFW

F(x

;eff

ect)

difference SM vsNuTeV eexplain th could

038.0

18.0fraction momentumquark Valence

ssccudduxdx

duxdxnval

pval

nval

pval

pval

pval

43Quantitative Results:Isopin Symmetry Violation

• Isospin symmetry violation: up dn and dp un

– Full “Bag Model” calculation: (Thomas et al., MPL A9 1799)

sin2W = 0.0001• Violation is x dependent; opposite sign at large and small x• Largest contribution from md – mu ~ 4 MeV and then mdd – muu mass

differences.

– “Meson Cloud Model”: (Cao et al., PhysRev C62 015203)

sin2W = +0.0002

– What is needed to explain the NuTeV data?

– Can global PDF fits accommodate a large enough isospin violation to explain NuTeV? CTEQ

44Quantitative Results:Strange vs. Anti-strange asymmetry

• Non-perturbative QCD effects can generate a strange vs. anti-strange momentum asymmetry

– Fits to NuTeV and CCFR and dimuon data can measure this asymmetry: sc X

– NuTeV separate and beams important for reliable separation of s ands distributions

(NuTeV: M. Goncharov et al.and CCFR: A.O. Bazarko et al.)

45Preliminary NLO Analysis of NuTeV Dimuon Data(Dave Mason et al.(NuTeV Collab.), ICHEP02 Proceedings)

s = s

s (black) s (blue)

46Nuclear Effects

• Use NuTeV CC data to fit parton distributions? Need to worry about nuclear effects that could be

different for W and Z exchange?

• Most nuclear effects are only large at small Q2 and would effect W and Z the same

– EMC effect – Nuclear shadowing – Vector meson dominance (VMD)

• VMD could be different for W and Z exchange (Miller and Thomas, hep-ex/0204007)

– No evidence for predicted 1/Q2 dependence in the NuTeV kinematic region x > 0.01 (NMC)

– NuTeV sees no effect with increasing the Ehad cut.

– Low-x phenomena like VMD effects mainly sea quarks and the effect is canceled in R-

• Would increase both Rand R

• To explain deviation from SM would require a very large Rshift and make the discrepancy with SM 4.5

These nuclear effects will change Rand R more than R- Making their deviation with the SM much more significant Hard to explain NuTeV discrepancy with nuclear effects

GeV 16

GeV 252

22 Q

47

LEP 1 measures Z lineshape and partial decay widths to infer the “number of neutrinos”

Neutrino oscillations (Giunti et al. hep-ph/0202152) es oscillation make real e background subtraction smaller

(Requires high m2 and ~20% mixing; will be addressed by MiniBooNE) NuTeV measures e flux from shower shape analysis hard to allow such large mixing

Are ’s Different?

.)(0032.0.)(0026.09884.0

coupling / in the change a asfit result NuTeV 20 syststat

vv

low 9.1)0028.09947.0(3)(

)(3 exp

Z

ZN

SM

48“New Physics” Interpretations

• Z’, LQ, ... exchange–NuTeV needs LL enhancedrelative to LR coupling

• Gauge boson interactions–Allow generic couplings–Example: Extra Z’ boson

• Mixing with E(6) Z’• Z’=Zcos + Zcos • LEP/SLC mix<10-3

• Hard to accommodate entire NuTeV discrepancy.–Global fits somewhat better with E(6) Z’ included

Example: Erler and Langacker: SM 7.5 mZ’=600 GeV, mixing ~10-3,

–“Almost sequential” Z’ with opposite coupling• NuTeV would want mZ’ ~1.2 TeV• CDF/D0 Limits: mZ’ > 700 GeV

(Cho et al., Nucl.Phys.B531, 65.; Zeppenfeld and Cheung, hep-ph/9810277; Langacker et al., Rev.Mod.Phys.64,87; Davidson et al., hep-ph/0112302 .)

(S.Davidson et al. hep-ph/0112302)

49New Physics Radiative Corrections:S,T,U Formalism

• Radiative corrections– 1) Vertex corrections

– 2) Box corrections

– 3) Vacuum polarization or oblique (propagator) corrections• Use S,T,U formalism

to parameterize these type of corrections

• S and T only, = 11.3 / 3 df cannot explain neutrino results

Vertex and box corrections suppressed orwould make fermions heavy - May be different for b-quarks which are related to heavy top mass

NuTeV

LEP Z NuTeV

W. Loinaz, et al. (hep-ph/0210193)

50Recent Summary of Possible InterpretationsS.Davidson, S.Forte,P.Gambino,N.Rius,A.Strumia (hep-ph/0112302)

• QCD effects:– Small asymmetry in momentum carried by strange vs antistrange quarks

CCFR/NuTeV dimuons limits– Small isospin violation in PDFs expected to be small

• Propagator and coupling corrections to SM gauge bosons:– Small compared to effect– Hard to change only Z

• MSSM:– Loop corrections wrong sign and small compared to NuTeV

• Contact Interactions:– Left-handed quark-quark-lepton-lepton vertices, LLqq , with strength

of the weak interaction Look Tevatron Run II

• Leptoquarks:– SU(2)L triplet with non-degenerate masses can fit NuTeV

and evade decay constraints

• Extra U(1) vector bosons (“Designer Z”) :– An unmixed Z’ with B-3L symmetry can explain NuTeV– Mass: 600 < MZ’< 5000 GeV or 1 < MZ’ < 10 GeV

51

“The NuTeV Anomaly, Neutrino Mixing and a Heavy Higgs”W. Loinaz, N. Okamura, T. Takeuchi, and L. Wijewardhana (hep-ph/0210193)

• Suppression of the Z coupling occur naturally in models which mix the neutrinos with heavy gauge singlet states

– i.e. L = coslight + sinheavy Z reduced by cos2

– Models would then reduce:• sin2NuTeV by

• Z invisible width by

– But this changes GF extracted from -decay by and messes up dozens of Z-pole agreements

• Can fix this if GF is compensated by a shift in the parameter (T) allowed with “new physics”

• Fits to Z-pole and NuTeV data of “new physics” (S and T parameters) plus this Z Need heavy Higgs (T < 0) with an mixing)

Apparent NC couplingto the Z is too small Reduced coupling due to neutrino mixing

LEP Z

52W. Loinaz et al. Model Cont’d:

Trying to Fit It All Together

• Including S, T, and Mixing () Good fit with = 1.2 / 2 df

Best T<0 “new physics” is big Mhiggs

• But this fit contradicts MW-boson so need

(Note: MW off ~1.5 with SM MHiggs= 85 GeV and off > 2 with MHiggs= 115 GeV)

• Conclusion: Everything fits with– Mixed neutrinos: – Heavy Higgs: Mhiggs GeV

– New physics (U-parameter type) New heavy bound states???

53Lose-Lose vs. Win-Win(M. Chanowitz, Phys.Rev.D66:073002,2002 - hep-ph/0207123)

• MHiggs prediction from the SM are only valid if SM is valid which doesn’t seem to be the case

– Global fit to all data give poor confidence level of CL = 1%

• From NuTeV and AbFB vs the leptonic measures

– Global fit removing NuTeV and AbFB gives good

confidence level of CL = 65% • But this fit give an MhHggs= 43 GeV which has a CL

of 3.5% to be consistent with the LEP MHiggs>114 GeV

Lose - Lose

• The SM is disfavored and need new physics whether one includes NuTeV and Ab

FB or not.

– If NuTeV and AbFB are correct, then need new

physics to explain their 3 discrepancies.

– If NuTeV and AbFB are due to systematic

uncertainties, then need new physics to explain why MHiggs is so low

Win - Win

NuTeV + AhadFBAlep+ MW

54Future Measurements

• Unfortunately, the high-energy neutrino beam at Fermilab has been terminated Need to rely on other experiments for progress

• Upcoming new measurements:– Low Q2 measurements:

(New physics could shift NuTeV/APV different from Z-pole LEP/SLD)

• SLAC E-158 Pol. electron-electron scattering

• JLab QWEAK Pol. elastic ep

(But these test e’s and not ’s)• Other measurements need theory input

(g-2, APV, |Vud|)

– High energy measurements:• Fermilab Tevatron CDF/D0 Run 2 and

LHC searches for Z’ and leptoquarks

– Neutrino mixing and oscillations?

(Plot from J.Erler and P.Langacker)

Tevatron(D0,CDF) LHC(Atlas,CMS)

Future

55Summary• NuTeV measurement has the precision to be important for SM electroweak test

Many experimental checks and the R technique is robust with respect to systematic uncertainties

• For NuTeV the SM predicts but we measure

sin2W(on-shell) (stat.)(syst.)

(Previous neutrino measurements gave 0.2277

• In comparison to the Standard Model

The NuTeV data prefers lower effective left-handed quark couplings

Or neutral current coupling that is ~1.1% smaller than expected

• The discrepancy with the Standard Model could be related to:

Quark model uncertainties but unlikely or only partially

and / or

Possibly new physics that is associated with neutrinos and interactions with left-handed quarks or neutrino mixing/oscillations

Jan/Feb 2002 CERN Courier article:“Is the latest NuTeV result a blip or another neutrino surprise? Only time will tell.”

Concluding remark from Tatsu Takeuchi at Fermilab Wine-n-Cheese last Friday: “The Standard Model is finally showing cracks and water is starting to rush into the Titanic.”