NuTeV – charged, neutral currents induced by neutrinos New measurement of Weinberg angle Deduced Weinberg angle “anomalous” Review Explanations for the NuTeV Anomaly CSV + Isospin Dep Nuclear + Strange Solved ? The NuTeV Anomaly: Solved?? Beyond the Standard Model?? “QCD Effects”?? Tim Londergan Nuclear Theory Center, Indiana University Tony Thomas 60 th Birthday CSSM, Adelaide Feb 15-19, 2010 Supported by NSF PHY- 0854805 With W. Bentz, I. Cloet & Tony Thomas
44
Embed
NuTeV – charged, neutral currents induced by neutrinos New measurement of Weinberg angle Deduced Weinberg angle “anomalous” Review Explanations for the.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
NuTeV – charged, neutral currents induced by neutrinosNew measurement of Weinberg angle Deduced Weinberg angle “anomalous” Review Explanations for the NuTeV Anomaly CSV + Isospin Dep Nuclear + Strange Solved ?
The NuTeV Anomaly: Solved?? Beyond the Standard Model?? “QCD Effects”??
Tim Londergan Nuclear Theory Center, Indiana UniversityTony Thomas 60th Birthday CSSM, Adelaide Feb 15-19, 2010
Supported by NSF PHY- 0854805With W. Bentz, I. Cloet & Tony Thomas
Happy Birthday, Tony !
Possible “New Physics” beyond the Standard Model?look at most likely possible new particles; can any remove the NuTeV anomaly?
Normal (“QCD”) Explanations of NuTeV Anomaly? radiative correctionsparton Charge Symmetry Violationstrange quark momentum asymmetry
Decay of charged pi, K produces neutrinos, antineutrinos; Almost pure muon neutrinos; (small νe contamination from Ke3 decay)
Only neutrinos penetrate shielding
The Paschos-Wolfenstein Ratio: Neutrino Total Cross Sections on Isoscalar Target:
The Paschos-Wolfenstein Ratio: Neutrino Total Cross Sections on Isoscalar Target:
Paschos & Wolfenstein ( PR D7, 91 (73)): Independent measurement of Weinberg angle, using ratio of total X-sections for neutrinos, antineutrinos on isoscalar target: PW ratio minimizes sensitivity to PDFs, higher-order corrections
The Paschos-Wolfenstein Ratio:
PW Ratio depends on the following assumptions: • Isoscalar target (N=Z)
• include only light (u, d) quarks
• neglect charm quark mass
• assume isospin symmetry for PDFs
• no nuclear effects (parton shadowing, EMC, ….)
• no contributions outside Standard Model
NuTeV Determination of Weinberg Angle:
• Construct ratios Very precise charged/neutral current ratios: Different cuts, acceptance: don’t construct PW ratio directly
Monte Carlo fits produce a NuTeV value for the Weinberg angle:
The NuTeV result is ~ 3σ above the very precise value (from EW processes at LEP)
“New Physics” explanation for NuTeV?
The problem: extremely precise EW data supports SM! • Mass, width of Z, W• X-sections, branching ratios at Z peak [LEP, SLD]• LR and FB asymmetries in e+e- scattering• new particles must satisfy all these constraints• EW constraints ~ 0.1% level [NuTeV ~ 1.2%] • “new physics” hard to satisfy EW constraints!
NuTeV
Physics Beyond the Standard Model? Attempts to explain NuTeV with “new physics”
• Davidson et al [J High E Phys 2, 37 (’02)] considered various scenarios (oblique corrections, extra Z’s, SUSY loops, leptoquarks) – very difficult to explain NuTeV result
• Kurylov, Ramsey-Musolf, Erler [NP B667, 321 (’03)] detailed analysis of SUSY contributions to NuTeV: SUSY loops cannot explain NuTeV R-parity violating (RPV) contributions in principle could explain NuTeV anomaly in practice, ruled out by other precision EW data
“Beyond the Standard Model:” choose most promising types of particles
adjust can you fit existing data + NuTeV ?
• oblique corrections [high mass scale, couples only to vector bosons]: parameters constrained by EW data – can’t fit NuTeV
• extra Z’ (mixed with Z) – doesn’t fix; strongly constrained by LEP/SLD (also latest muon g-2)
[Davidson etal, J HE Phys 2, 37 (2002)]
“Beyond SM” II: More Attempts to fit NuTeV
• minimal SUSY loops – No – most have wrong sign; others violate existing constraints • Leptoquarks (bosons that couple to leptons & quarks): carefully tuned mass splittings still possible – could be tested at LHC [Davidson etal, J HE Phys 2, 37 (2002)]• Unmixed extra Z’ – might help reduce NuTeV anomaly (fine tuning)
MSSM, light sleptinos, gauginos Leptoquark (solid); extra gauge bosons (red)
Summary, “New Physics” Contributions to NuTeV:
Contributions outside Standard Model?
• Difficult to achieve
• Strong constraints from extremely precise LEP/SLD results
Phenomenology: MRST global fit limits valence CSV -0.8 ≤ κ ≤ +0.65 κ = -0.6 remove 100% of NuTeV anomaly! κ = +0.6 anomaly twice as large!
Theoretical estimates: quark model remove ~ 30% of anomaly “QED splitting” remove ~ 30% (total CSV remove ~60% of anomaly) at current limits, CSV could produce observable effects
(~ 5-6%) (or more?) in certain reactions
Summary, CSV Effects on Weinberg angle
MRST global fit to valence CSV
90% confidence limits:
Strange Quark Contributions to PW Ratio:
PW contribution from strange quarks:
Strange quark normalization: constrained(N has zero net strangeness)
If s quarks carry more momentum than sbar decrease anomaly
Determination of s, sbar quark PDFs: Opposite sign dimuons from neutrinos
• CCFR: charge of faster muon determines neutrino or antineutrino; • most precise way to determine s, sbar PDFs CCFR, NuTeV
s-sbar momentum asymmetry
Analysis of s quark momentum asymmetry
Most recent fit of s quark distributions. NuTeV: [Mason etal, PRL 99, 192001 (07)]
s-(x) > 0, x > 0.004; best value removes ~ 1/4 of NuTeV anomalys-(x) changes sign at extremely small x value (no theoretical reason)Changeover point can be moved with resulting χ2 increase
Analysis of s quark momentum asymmetry
Most recent fit of s quark distributions. NuTeV: [Mason etal, PRL 99, 192001 (07)]
s-(x) > 0, x > 0.004; best value removes ~ 1/4 of NuTeV anomalys-(x) changes sign at extremely small x value (no theoretical reason)Changeover point can be moved with resulting χ2 increase
Isospin Dependent Nuclear Effects
Isovector-vector exchange (generally attributed to ρ0 exchange) will contribute to the NuTeV exp’t [Cloet, Bentz, Thomas PRL 102, 252301 (09)]
This produces effects very similar to parton CSV, when N ≠ Z(although this nuclear effect respects charge symmetry) Modification of nucleon structure in nuclei
ρ0 exchange produces slight additional attraction for u quarks, slight additional repulsion for d quarks
Isospin Dependent Nuclear Effects
These effects should produce distinctive and measurable modifications of the EMC effect for N ≠ Z nuclei[see Cloet talk]
Isospin Dependent Nuclear Effects
These effects should produce distinctive and measurable modifications of the EMC effect for N ≠ Z nuclei[see Cloet talk]
They will also modify the NuTeV result: for iron we estimate~ 40% reduction of the NuTeV anomaly [Bentz etal, arXiV:0908.3198 (nucl-th)]
Reassessment of NuTeV, Weinberg Angle
NuTeV Result now liesright on theory curve. Inner error bars: statistical Outer errors: total uncertainty
Contributions to NuTeV: CSV ~ 60%Isospin dep ~ 40%s quarks: slight increase in error bars Bentz etal, arXiV:0908.3198
Conclusions:
NuTeV: Measured CC, NC X-sections for on Fe Large (~ 3σ), surprising discrepancy for
“New Physics” – difficult to fit LEP results, NuTeV “most probable new particles” unlikely very delicate “QCD Corrections” to NuTeV measurement??
Conclusions:
NuTeV: Measured CC, NC X-sections for on Fe Large (~ 3σ), surprising discrepancy for
“New Physics” – difficult to fit LEP results, NuTeV “most probable new particles” unlikely very delicate “QCD Corrections” to NuTeV measurement??
•parton CSV best guess removes ~ 60%• could remove full effect [MRST]• strange quark asymmetry ~ 1σ (we assume 0)• isospin-dept nuclear ~ 40%, Cloet etal
Conclusions:
NuTeV: Measured CC, NC X-sections for on Fe Large (~ 3σ), surprising discrepancy for
“New Physics” – difficult to fit LEP results, NuTeV “most probable new particles” unlikely very delicate “QCD Corrections” to NuTeV measurement??
•parton CSV best guess removes ~ 60%• could remove full effect [MRST]• strange quark asymmetry ~ 1σ (we assume 0)• isospin-dept nuclear ~ 40%, Cloet etal
CSV, isospin dep’t nuclear: at present, most plausible explanations for NuTeV anomaly
small additive contrib’ns from strangeness, radiative corrections ??
Tony & Adelaide:
I have had many enjoyable & productive visits to Adelaide
The atmosphere has always been conducive to doing one’s best work How wonderful that Tony & Joan are back again in Adelaide!
Separate Neutral, Charged-Current Events
Charged current: Track through several platesLarge visible energy deposit
Neutral current: Short visible trackLarge missing energy
NuTeV event selection: • Large E in calorimeter • event vertex in fiducial volume
NuTeV Events: • 1.62 million • 351,000
NuTeV Detector: 18 m long, 690-ton steel scintillator; Steel plates interspersed with liq scintillator, drift chambers
NuTeV Determination of Weinberg Angle: • Construct ratios Individual ratios less dependent on overall normalization Very precise charged/neutral current ratios: Different cuts, acceptance: don’t construct PW ratio directly• : depends strongly on Weinberg angle
• : weak dependence on Weinberg angle
These ratios lead to a NuTeV value for the Weinberg angle:
The NuTeV result is ~ 3σ above the very precise value (from EW processes at LEP)
3σ below SM
agree with SM
NuTeV work at LO in QCD (with improvements) and find