Scattering at NuTeV. Kevin McFarland University of Rochester for the NuTeV Collaboration. Neutrinos and Implications for New Physics 11 October 2002

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1 sin 2 W from Neutrino Scattering at NuTeV Kevin McFarland University of Rochester for the NuTeV Collaboration Neutrinos and Implications for New Physics 11 October 2002 Outline 1. Why Study Electroweak Physics with Neutrinos? 2. The NuTeV Experiment ffl Key Elements of the Analysis ffl NuTeV s Surprising Results ffl Interpretation 3. Global Context and Conclusions

2 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 2 The Role of NuTeV Neutrino scattering played a key historical role in electroweak unification ffl Discovery of Neutral Current (Gargamelle, FNAL-E1A) ffl First determimation of high-energy parameter in EW theory sin 2 W ο 0:2 ) M W ο 0:9 M Z... but why continue to study when we make copious on-shell W and Z bosons at colliders? Z ffl Testing in a wide range of processes and momentum scales ensures universality of the electroweak theory 2 Momentum Transfer (GeV ) Atomic Parity Violation SLAC e-d NuTeV ffl NuTeV is sensitive to different processes On-shell W and Z bosons,! Measurement is off the Z pole (contributions besides Z?),! Measure neutral current neutrino couplings? LEP I invisible line width is only other precise measurement

3 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 3 Methodology µ W Coupling / I (3) weak Coupling / Z I weak (3) Q em sin 2 W Isoscalar target composed of only u,d uarks at tree level: Llewellyn Smith Relation: R () = ff() NC ff () CC = ρ sin2 W sin4 W 0 B CC ff () + ff() CC CC 11 ffl R, R easy to measure experimentally ffl Cross-section ratios reduce effects of,! Experimental systematics, flux,! Parton distribution functions (PDFs) ffl To extract sin 2 W from the measured ratio:,! isovector target (2Z 6= A),! heavy uark seas (and kinematic suppression),! radiative corrections, higher twist, R L

4 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 4 Heavy Quark Effects µ W Z s,d c µ s,d s,d ffl Suppression of CC cross section for interactions with massive charm uark in final state ffl Model: leading-order slow-rescaling (x! ο = Q2 +m 2 c 2M ) ffl Parameters measured by NuTeV/CCFR in dimuon events (M. Goncharov et al., Phys. Rev. D64, (2001)) ffl Limits precision of previous N measurements... sin 2 on shell W 1 M 2 W 2 = 0:2277 ± 0:0031 M Z ) M W = 80:14 ± 0:16 GeV

5 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 5 NuTeV s Approach Large charm production errors ) need techniue insensitive to sea Paschos-Wolfenstein Relation: R = ff NC ffnc ffcc ffcc = ρ 2 µ sin2 A W = R rr 1 r _ µ+ W+ W- s, (d V + ds ) c s, ds c TeVatron 800 GeV protons ffl R is manifestly insensitive to sea uarks,! Charm and strange sea errors are negligible... (Most of charm from s(x) scattering),! Massive charm production enters from d V uarks only... (Cabbibo suppressed and at high x) ffl Separate, beams ) NuTeV SSQT SSQT Sign NuTeV Decay Pipe Selected Shielding Quadrupole Train Wrong Sign π,κ DUMPED Protons, K L DUMPED Right Sign π,κ ACCEPTED NuTeV

6 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 6 Neutral Current/Charged Current Event Separation Event Length µ W 690 Ton Calorimeter Muon Toroid Event Length Z Separate by simple length cut SHORT events L LONG» Lcut events = L > Lcut NC candidates = CC candidates in and beams (1.62 and 0.35 million events) R exp =

7 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 7 Summary of Corrections to Rexp Corrections Applied to Data Effect ffirexp ffirexp Control Cosmic Ray Background y Beam μ Background y Vertex Efficiency y Effects in Monte Carlo that relate R ( ) to R ( ) exp Effect ffirexp ffirexp Control Short CC Background y, p nu nubar Electron Neutrinos , p Long NC y, p Counter Noise y Heavy m c y, R L y, EM Radiative Correction Weak Radiative Correction d/u y Higher Twist y Recall: R exp and R exp measured to a precision of and , respectively Key to coping techniues y: Determined from data p : Checked with data : Independent Simulation : R techniue

8 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 8 μ Charged-Current Background ffl High y charged-current is background to NC sample ffl ( ) NC & CC uark model cross-section,! R L term added to F 2, xf 3 to describe g! ffl PDFs extracted from CCFR ff CC ffl Other data determines s(x), d=u, R L, higher twist, F cc 2 ffl Data-driven: uncertainties come from measurements ffl Check by looking at long exit CC events which start in the detector center and stop before toroid

9 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 9 Electron Neutrinos Approximately 5% of all short events are e CC. ) It would take a 20% mistake in e to move sin 2 W to SM value ffl Excess of e over e in beam is due to K + e3 decay,! Vast majority of e / e in / beams,! K L and charm decay, which make both e and e, are small ffl K ± e3 decay is very well understood,! K ± production... is constrained by μ and μ flux,! Use predicted flux (few % shifts from production data), except high energy tail (E > 180 GeV direct measurement) ffl Have (less precise) direct measurements of e and e,! N meas =N pred : 1:05 ± 0:03 ( e ), 1:01 ± 0:04 ( e ) (80 <E < 180 GeV)

10 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 10 Stability of Rexp (cont d) ffl R vs. length cut: Checks NC $ CC separation 16,17,18 L cut is default: tighten$loosen selection ffl R vs. radial bin : Checks electron neutrino and short CC events More NC background near edge NuTeV Target, 60"x60" "Radial" Bins

11 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 11 Stability of Rexp (cont d) R exp vs. E had : Checks stability of final measurement over full kinematic range Checks almost everything - backgrounds, flux, detector modeling, cross section model,... (Green band is ±1ff systematic uncertainty)

12 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 12 The Result sin 2 (on shell) W = 0:2277 ± 0:0013 (stat) ± 0:0009 (syst) 0 1 M top (175 2 GeV ) 2 A + 0:00032 ln (50 GeV ) 2 MHiggs 150 GeV ffl In good agreement with previous N: sin 2 W = ± ffl Standard Model fit (LEPEWWG): 0:2227 ± 0:00037 SOURCE OF UNCERTAINTY ffisin 2 W ffir ffir exp exp Data Statistics Monte Carlo Statistics TOTAL STATISTICS e ; e Flux Interaction Vertex Shower Length Model Counter Efficiency, Noise, Size Energy Measurement TOTAL EXPERIMENTAL Charm Production, s(x) R L ff =ff Higher Twist Radiative Corrections Charm Sea Non-Isoscalar Target TOTAL MODEL TOTAL UNCERTAINTY In the end, why is NuTeV so much more precise than CCFR? ffl R method makes charm production error small ffl Few K L because of beam ) e greatly reduced

13 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 13 Comparison to Direct M W sin 2 (on shell) W 1 M W 2 M Z 2 Given the precise measurement of the Z mass from LEP can express NuTeV sin 2 W as an euivalent M W / / / / / / / / / * : Preliminary CDF D0 ALEPH* DELPHI* L3* OPAL* Direct World Average Indirect World Average (LEP1/SLD/APV/m t ) (LEPEWWG) NuTeV Mw (GeV) ffl In standard electroweak theory, NuTeV precision is comparable to a single direct measurement of M W ffl More inconsistent with direct M W than other data

14 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 14 Quark Couplings: (g eff L (g eff R )2 )2 and 2 parameter fit to R, R : R = g 2 L + rg2 R R = g 2 L + 1 r g2 R g 2 L u 2 L + d2 L g 2 R u2 R + d2 R NuTeV measures: (g eff L )2 = 0:3001 ± 0:0014 (g eff R )2 = 0:0308 ± 0:0011 ρ corr = 0:02 ffl Assuming predicted coupling, (g eff L )2 appears low

15 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 15 Interpretations ffl Symmetry violations in QCD ffl New Interactions ffl Neutral current coupling of Z?? sin 2 W (N)

16 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 16 Symmetry Violating QCD Effects Paschos-Wolfenstein, R = 1 2 sin2 W ffl Assumes total u and d momenta eual in target ffl Assumes sea momentum symmetry, s = s and c = c ffl Assumes nuclear effects common in W /Z exchange Violations of these symmetries can arise from 1. A 6= 2Z, e.g., high Z neutron excess (CORRECTED) ffl Changes d/u of target ) mean NC coupling ffl Large correction, ο :008, known precisely from material survey, chemical assay of target 2. Isospin violating PDFs, e.g., u p (x) 6= d n (x) ffl Changes d/u of target ) mean NC coupling (Sather; Rodinov, Thomas and Londergan; Cao and Signal) 3. Asymmetric heavy seas, e.g., s(x) 6= s(x) ffl Strange sea doesn t cancel in R (Signal and Thomas; Burkhardt and Warr; Brodsky and Ma) 4. Nuclear Effects Different for NC/CC ffl Changes R, R directly ffl Shadowing region (low x), EMC region (high x) (Thomas and Miller; Schmitt et al; Kumano)

17 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 17 Symmetry Violation in the Nucleon Strange-Antistrange Sea Asymmetry ffl If S S ο +0:0020, =) ffisin 2 W = 0:0026 (m c = 0) (S. Davidson et al.,hep-ph/ ) ffl Significant overestime of effect on sin 2 W ffl But NuTeV dimuon data measures s, s separately in cross-section model used in sin 2 W measurement S S = 0:0027 ± 0:0013 =) ffisin 2 W ο +0:0020 ± 0:0009 Then sin 2 W = 0:2297 ± 0:0019 (3:7ff above SM) Isospin symmetry violations ffl Small nucleon isospin is established; m n 6= m p ffl LARGE isospin violation needed to explain NuTeV, Bag model Thomas et al., Mod. Phys. LettȦ9, Z,! ffisin 2 (on shell) W = 0:0001,! ο 0:0004 shifts at high, low x cancel [d p (x) u n (x)]= Z [d p (x) +u n (x)] ο 5% Meson Cloud model Cao & Signal, Phys. Rev. C62, ,! ffisin 2 (on shell) W = +0:0002 ffl Are models trustworthy? Can global fits accomodate large isospin violation to explain NuTeV?

18 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 18 Process-Dependent Nuclear Effects ffl Nuclear effects on PDFs are large ffl NuTeV analysis uses only PDFs on iron F 2 (X) / F 2 (D) NMC Ca/D SLAC E87 Fe/D 0.8 SLAC E139 Fe/D E665 Ca/D 0.8 Parameterization Error in parameterization x ffl Why believe these effects are process independent? ffl Models: e.g., Pomeron description of high Q 2 shadowing,! NMC High Q 2 data shows predicted log Q 2 behavior ffl F CC 2 =F `2 supports picture ffl No independent test of NC

19 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 19 Process-Dependent Nuclear Effects (continued) ffl VMD predicts nuclear shadowing different for W, Z (G. Miller and A. Thomas, hep-ex/ ),! No evidence for predicted 1=Q 2 behavior in NuTeV kinematic region x > 0:01 (NMC),! Effect would increase R, R,! Low x ) effect cancels in R Interesting idea, but... inconsistent with NuTeV

20 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 20 New Tree Level Physics? ffl Natural interpretation of result??? ffl Z 0, LQ, etc. ffl Must enhance LL not LR coupling ffl E(6) Z 0 accounts for NuTeV?,! Contact terms shift LR coupling,! Mixing (here )toz severely limited by LEP/SLD (Z 0 Z χ cosfi + Z ψ sin fi) (Cho et al., Nucl. Phys. B531, 65. Zeppenfeld and Cheung, hep-ph/ Langacker et al., Rev. Mod. Phys ) ffl Almost seuential Z 0 with opposite coupling to,! NuTeV preferred mass range: 1:2 +0:3,! CDF/D0 limits: M Z 0 SM > 0:2 TeV ο 700 GeV. LEP II? ffl Contact interaction with LL coupling,! Λ LL = 4:5 ± 1 TeV,! Consistent with other ` data? (Barger,Cheung,Hagiwara,Zeppenfeld),! Depends on:? Lepton RH couplings? How seriously one takes 2 3ff discrepancies in this data ( CKM unitarity, e + e!, APV?)

21 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 21 Neutral Current Interactions ffl LEP I measures Z lineshape and decay partial widths to infer the number of neutrinos,! Their result is N = 3 exp(z!) = 3 (0:9947 ± 0:0028) SM (Z!),! LEP I direct partial width (fl) ) N = 3 (1:00 ± 0:02) ffl ( ) μ e! ( ) μ e scattering (CHARM II et al.),! PDG fit: g 2 V + g2 A = 0:259 ± 0:014, cf.0:258 predicted ffl NuTeV can fit for a deviation in & NC rate,! ρ 2 0 = 0:9884 ± 0:0026(stat) ± 0:0032(syst) / / / / CHARM II et al. LEP I Direct LEP I Lineshape NuTeV Neutrino NC Rate/Prediction ffl In this interpretation, NuTeV confirms and strengthens LEP I indications of weaker neutrino neutral current,! NB: This is not a uniue or model-independent interpretation!,! Theoretically awkward to accomodate without changing W` vertex as well? Latter is possible? (T. Takeuchi, hep-ph/ )

22 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 22 Global EW Fit (LEPEWWG) Measurement Pull (O meas O fit )/σ meas α (5) had (m Z ) ± m Z [GeV] ± Γ Z [GeV] ± σ 0 had [nb] ± R l ± A 0,l fb ± A l (P τ ) ± R b ± R c ± A 0,b fb ± A 0,c fb ± A b ± A c ± A l (SLD) ± sin 2 θ lept eff (Q fb ) ± m W [GeV] ± Γ W [GeV] ± m t [GeV] ± sin 2 θ W (N) ± Q W (Cs) ± ffl A 0;b FB problem persists (ß 2:6ff) ffl Without NuTeV: χ 2 =dof = 19:6=14 (14% probability) ffl With NuTeV: χ 2 =dof = 28:8=15 (1:7% probability) ffl Choices are made in selecting data, e.g., # M W combined from e + e, pp " Q W data massaged post hoc " W but not G F from P jv u j 2

23 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 23 The Higgs Mass ( Chanowitz, Phys.Rev.Lett. 87 (2001) , in preparation ) ffl A lep : χ 2 /dof=1:7=2 ( Z, M W consistent) Higgs in LEP 2 range ffl A had +NuTeV: χ 2 /dof=3:9=3 ffl A 0;b FB dominates A had m H dependence,! m H resolving power of NuTeV is less ffl Chanowitz Lose-lose theorem:,! Removing data that drives high χ 2 would drive Higgs mass further into LEP 2 excluded region

24 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 24 The Higgs Mass (cont d) Confidence Level of Fit Euiv. ff Fit CL(χ 2 ) CL(m H ) Product Significance W/o NuTeV, A had W/o NuTeV W/o A had W/ All (M. Chanowitz, in preparation) ffl Can we fix consistency of data?,! Z 0 models (Erler and Langacker, Phys.Rev.Lett.84 (2000) 212),! Beautiful mirrors (Choudhury, Tait, Wagner PRD65 (2002) ) ffl Is this really worth worrying about? 6 4 theory uncertainty α (5) had = ± ± % probable χ 2 χ Excluded Preliminary m H [GeV] ffl Provocative? Sure... ffl But it is a fair comparison of two hypotheses: 2. m Higgs < 200 GeV χ 2 Median /15 dof 1% probable 10% probable 1. Electroweak standard model describes all data

25 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 25 Conclusions Surprise! ffl NuTeV measures R, R to precisely determine sin 2 W,! The SM predicts 0:2227 ± 0:0003, but we measure: sin 2 (on shell) W = 0:2277 ± 0:0013(stat) ± 0:0009(syst),! NuTeV consistent with earlier N data,! Neutral-current couplings of neutrinos suspect? ffl Global Electroweak fit is now uite unhealthy,! A 0;b FB also discrepant,! Other concerns at Z pole: M W, inv?,! Off-pole: e + e!?, CKM Unitarity? Atomic parity violation? ffl Without a smoking gun for new physics...,! Interpretation remains a Rorschach test? A complicated conseuence of mundane physics?? Or might experimental results be pointing to TeV scale physics?

26 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 26 BACKUP: Neutron Beta Decay PERKEO II (Heidelberg-ILL- GSI-Mainz) If G F is universal, 3-generation unitarity :0ff away from expectation!

27 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV 27 BACKUP: Higgs Mass Range of LEPEWWG Variables Γ Z [GeV] σ 0 had [nb] R 0 l A 0,l fb A l (P τ ) R 0 b R 0 c A 0,b fb A 0,c fb A b A c A l (SLD) sin 2 θ lept eff (Q fb ) m W [GeV] Γ W [GeV] sin 2 θ W (N) Q W (Cs) M H [GeV]

28 Kevin McFarland, sin 2 W from Neutrino Scattering at NuTeV A Contents 1. sin 2 W from Neutrino Scattering at NuTeV The Role of NuTeV Methodology Heavy Quark Effects NuTeV s Approach Neutral Current/Charged Current Event Separation Summary of Corrections to R exp μ Charged-Current Background Electron Neutrinos Stability of R exp (cont d) Stability of R exp (cont d) The Result Comparison to Direct M W Quark Couplings: (g eff L )2 and (g eff R ) Interpretations Symmetry Violating QCD Effects Symmetry Violation in the Nucleon Process-Dependent Nuclear Effects Process-Dependent Nuclear Effects (continued) New Tree Level Physics? Neutral Current Interactions Global EW Fit (LEPEWWG) The Higgs Mass The Higgs Mass (cont d) Conclusions BACKUP: Neutron Beta Decay BACKUP: Higgs Mass Range of LEPEWWG Variables