Strangeness%20Asymmetry%20of%20the%20Nucleon%20and%20other%20QCD%20Aspects%20of%20the%20NuTeV%20Anomaly

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Strangeness Asymmetry of the Nucleon and other
QCD Aspects of the NuTeV Anomaly
Strangeness Asymmetry of the Nucleon and other SM
Aspects of the NuTeV Anomaly

• Stefan Kretzer
• Brookhaven National Laboratory RIKEN-BNL

• Collaboration with
• M.-H. Reno
• CTEQ F. Olness, J. Pumplin, D. Stump, and
  W.-K. Tung, et al.

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• Based on
• The parton structure of the Nucleon and
  Precison Measurement of the Weinberg Angle in
  Neutrino ScatteringBNL-NT-03-16
  RBRC-328hep-ph/0312322 with F. Olness, D.
  Stump, J. Pumplin, M.H. Reno, and W.-K. Tung
• Neutrino Dimuon Production and the Strangeness
  Asymmetry of the Nucleon BNL-NT-03-17
  RBRC-329hep-ph/0312323 with CTEQ
• Target Mass Corrections to Electroweak
  Structure Functions and Perturbative Neutrino
  Cross SectionsPRD 69, 034002 (2004)with M.H.
  Reno

• Comprehensive Review Article
• Old and New Physics Interpretation of the NuTeV
  AnomalyJHEP 020237 (2002)S. Davidson, S.
  Forte, P. Gambino, N. Rius, and A. Strumia

• Additional Related Work
• T. Londergan A.W. Thomas, MRST, K. McFarland
  S. Moch, B. Dobrescu R.K. Ellis, K. Diener S.
  Dittmaier W. Hollik, S. Kumano, J. Qiu I.
  Vitev, F.G. Cao A.I. Signal, S. Brodsky B.
  Ma, S.A. Kulagin,

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NuTeV Anomaly
Atomic Parity Violation
SM fit Talk by S. Roth
SLAC E158Parity Violation in Møller Scattering
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The NuTeV Anomaly
The NuTeV measurement
PRL 88, (2002)
It was inspired by, and is related (but not
identical) to, the Paschos-Wolfenstein (1973)
Ratio
(isoscalar target, )
SM explanation(s) or Signal for New Physics?
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Long Event ' Charged Current Event Short Event '
Neutral Current Event
' ?
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Theorists Observables

• Paschos-Wolfenstein
• Parton model
• Isoscalar target

• technical (standard) effects
• EW radiative corrections
• Non-isoscalarity (Fe)
• NLO QCD and masses
• physical (new) effects
• Higher twist
• Nuclear effects (A' 56)

• Cross section ratios

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The Paschos Wolfenstein a la NuTeV claim The
correlations in a simultaneous fit to are
essentially the same as in .
Is based on a LO MC model?
Has to await an experimental reanalysis (NLO QCD,
electroweak corrections, )
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Model-independency

• Model cross sections provide model parameters.
• Theory cross sections provide theory parameters.

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Technical (standard) Effects (NLO QCD
electroweak , very briefly)
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M.H. Reno, SK (2003)

• Target mass corrections to ew structure
  functions along the OPE (Georgi Politzer)
  approachO(MN2n/Q2n)
• NLO DGLAP

twist ?2

• NLOO(?s) corrections for light and charm
  quarks
• O(mc2n/Q2n)

• ? scaling _at_ NLO

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• Digested results on standard QCD corrections
• NLO, TMC, and m? corrections ( PDF
  uncertainties)
• shift by an amount that is of the
  order of the experimental accuracy for
  (lt1).
• shift by an amount that is
  negligible compared to the experimental error
  attributed to (lt1).
• Seeming discrepancies with analytic NLO
  estimates by Bogdan Dobrescu and Keith Ellis
  (hep-ph/0310154) have been understood.
• These results do not permit reliable conclusions
  on the signficance of the anomaly None of the
  above Rs is actually measured. Only NuTeV can
  come to a definitive answer.
• The results do indicate that the corrections
  have to be considered in an experimental
  reanalysis.

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Electroweak Corrections
In the NuTeV measurement of the Weinberg angle in
neutrino DIS electroweak corrections have been
applied according to
Recently, these corrections have been reevaluated
in Diener Dittmaier Hollik hep-ph/0310364.DDH
analyze only , not .
An investigation of electroweak corrections is
limited by the same constraints as the
investigation of NLO QCD corrections that the
theory observables do not really match with the
NuTeV Monte Carlo fit.
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Digested results on electroweak corrections
Different q ! q ? factorization schemes DDHBD
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Physical (new) results on the NuTeV
anomaly and on parton structure
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Corrections to R- for the moment

• Lets neglect cuts / exp. Issues ideal
  Paschos-Wolfenstein relation and look for big
  effects that are unaffected by O(30) detector
  effect corrections
• Lets neglect evolution / scale dependence
• Lets neglect NLO corrections
• Lets assume the target material (mostly Fe) is
  isoscalar and that isospin is exact
• Lets assume mc0
• Let me focus on the quark / antiquark asymmetry
  for strange sea quarks

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Then
is not protected by any symmetry
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Phys. Lett. B381 (1996)
Theoretical expectationsS. Brodsky B.-Q. Ma
(1996)p ! ? K fluctuation
More recent resultsF.G. Cao A.I. Signal
(2003)A.W. Thomas W. Melnitchouk F.M.
Steffens (2000) And phenomenology fromV.
Barone C. Pascaud F. Zomer (2000)
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What do we know about ?

• Before any data, two things
• (exact
  sum rule )oscillation)
• 
  (positivity)

• For more information, we have to ask data
• dimuon production
  (CCFR, NuTeV, )
• further (weak) constraints
• s g ! c W- background to sign-selected W
  production (W charge asymmetry) at the Tevatron

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Reminder
S- is not a local operator. (Higher, uneven
moments are.)
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CTEQ Global Analysis

• Same ingredients as CTEQ6 analysis
• Add CCFR-NuTeV dimuon data
• Allow a non-symmetric strangeness sector

Parametrization of the Strangeness sector (at
some QQ0)
Where x0 is to be determined by the condition
s-0. Sum rule and positivity are then
satisfied.
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Charged Current neutrinoproduction of charm
T. GottschalkM. Gluck, E. Reya, SKAivazis,
Collins, Olness, Tung
W

c
g
s
LO
NLO

• Data from CCFR/NuTeV (see D. Masons talk)
  determine the strange sea within a CTEQ global
  analysis.
• NLO corrections are not yet included in current
  CTEQ analysis (to meet the LO acceptance
  correction model).
• NLO corrections become sizable at high energy
  (HERA) but are well behaved for fixed target
  scattering (CCFR/NuTeV).

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CC charm LO/NLO stability
PDF hard scattering
NLO T. Gottschalk M. Gluck, E. Reya,
SK ACOT
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CC charm LO/NLO stability
PDF hard scattering fragmentation
NLO M. Gluck, E. Reya, SK
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Differential production cross section and
acceptance
D. Mason, F. Olness, SK
Acceptance vs. rapidity
d ?
z
rapidity
Acceptance vs. z
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The results on the last 3 slides suggest that the
perturbative NLO effects will be small compared
to the non-perturbative uncertainties in S-.
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Typical fit results Vs. Bjorken x
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Lagrangian multiplier results for S-
NuTeV/CCFR data
Other (less) sensitive data
Rule of thumb The 3 ? anomaly corresponds
to S- 100 ' 0.5
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• Further uncertainties
• LO NLO PDF analysis
• charm mass
• charm fragmentation and decay
• Are considered in our estimate for the range of
  S- (! conclusions).
• The general features of the LM parabola stay the
  same, the minimum wanders within a range that is
  consistent with the width of the ?2 vs. S-
  parabola.

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Future prospects for S-?

• W and associated charm (jet)productionconceiva
  ble _at_ Tevatron, RHIC, LHCBut statistics
  (efficiency driven)and high scale are unlikely
  to permitto access a small asymmetry.
• CC charm _at_ HERA ditto
• LatticeThe moment S- itself does not
  correspond to a local operator.Higher, uneven
  moments (n3,5,)can be related to local
  operators and could presumably clarify the sign
  of the x! 1 behaviour, though not the magnitude
  of S-.
• Semi-Inclusive DIS (eRHIC)?

g
c
W
s
Baur, Halzen, Keller, Mangano, Riesselmann
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Martin, Roberts, Stirling, Thorne
MRST analysis of isospin violations uvn(x)dvp(x)
? f(x)with s01 dx f(x)0 finds ? f(x) lt 3-10
(8 x)
Best fit value of ? removes half of the
discrepancy with the SM. Within a permissible
variation of ?2MRST -0.007 lt ? sin ?W lt 0.007the
full 3 ? are covered.
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Main conclusions of the CTEQ strangeness analysis

• However, the strong interplay between the
  existing experimental constraints and the global
  theoretical constraints, particularly the sum
  rule, places quite robust limits on acceptable
  values of the strangeness asymmetry momentum
  integral S-.

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Implication on the NuTeV anomaly

• We estimate that -0.001 lt S- lt 0.004. A sizable
  negative S- is disfavored by both dimuon and
  other inclusive data.

We have done a NLO calculation of the
Paschos-Wolfenstein relation, using the new CTEQ
PDFs. According to this calculation, a value of
S- lt 0.0017 (central value) can reduce the
NuTeV anomaly from a 3 s effect to 1.5 s a value
of S- 0.003 0.004 would then reduce it to
within 1 s. The actual effect on the NuTeV
measurement must await re-analysis by the
experimental group, correcting current flaws,
extending to NLO, as well as taking into account
global constraints. The variation of S-
underestimates the full uncertainties (isospin,
higher twist, ). Again, a definitive answer will
have to come from NuTeV. The bounds of current
uncertainty studies suggest that the dimuon data,
the Weinberg angle measurement and other global
data sets used in QCD parton structure analysis
can all be consistent with the SM.
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• Status (theory) of the NuTeV anomaly
• The cross section ratios that are
  closely related to the NuTeV extraction of the
  Weinberg angle have been thoroughly reevaluated
  by many authors under several SM corrections
• pQCD corrections (NLO masses)
• electroweak corrections
• nucleon parton structure uncertainties
• The exact impact of the corrections on the
  extraction of sin2 ?W cannot be quantified in
  theory because of the involved Monte Carlo /
  detector effects in modeling long and short
  events in the NuTeV experiment. The closely
  related theoretical observables receive
  corrections that are of the order of the assigned
  experimental errors or bigger. Partonic
  uncertainties (strangeness asymmetry, ) do even
  survive in the ideal Paschos-Wolfenstein ratio.
• These effects have, so far, not been assigned a
  systematic error in the NuTeV value of sin2 ?W.
  Claims that they cancel in the NuTeV (LO Monte
  Carlo) analysis procedure are a posteriori and
  have not been substantiated by an analysis that
  takes them into account ab initio. The
  corresponding programs are available from the
  authors. Before a careful re-assessment of all
  theoretical uncertainties (pQCD non-pQCD
  electroweak) the 3 ? discrepancy with the SM
  cannot be taken at face value.

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• An afterthought on S(emi)I(inclusive)DIS
• Current fragmentation into strange hadronsis
  challenging for all the non-strange background
  fragmentation channels. A good knowledge of the
  corresponding FFs would be required.
• An asymmetry between strange and anti-strange
  target fragmentation / fracture products might be
  more promising? Energy conservation

x

z
1
M
(1-x)
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Backup Slides
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Paschos-Wolfenstein à la NuTeV
K. McFarland _at_ Win03

• NuTeV result
• Statistics dominate uncertainty
• Standard model fit (LEPEWWG)
• 0.2227 ? 0.00037, a 3s discrepancy

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Quality of fit to the neutrino dimuon data
x ' 0.02 -- 0.3 Q2/GeV2 ' 2. -- 50.(Data
points are color-coded according to x for each
x, they are ordered in y.)
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5 representative fits obtained using LM method
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The Lagrange Multiplier Method in Global Analysis
S-
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