We describe a simple technique for optimizing the extraction of the forward-backward asymmetry (
A
fb
) of Drell-Yan lepton pairs (
e
+
e
−
,
μ
+
μ
−
) produced in
and
pp
collisions at hadron ...colliders. The method employs simple event weights which are functions of the rapidity and |cos
θ
| decay angle of the lepton pair. It yields the best estimate of the acceptance corrected parton level (
) forward backward asymmetry as a function of final state dilepton mass (
M
ℓ
ℓ
). Typically, when compared to the simple count method, the technique reduces the statistical errors by 20% for
, and 40% for
pp
collisions, respectively. The method is equivalent to using the maximum likelihood method, but is much easier to implement. The technique can be used to search for new high mass and large width Z’ bosons which may be best detected through the observation of deviations from the Standard Model expectation for the forward-backward asymmetry. The technique can also be applied in the extraction of the foward-backward asymmetry in the production of top-antitop pairs.
We present a parametrization of the observed enhancement in the transverse electron quasielastic (QE) response function for nucleons bound in carbon as a function of the square of the four momentum ...transfer (Q2) in terms of a correction to the magnetic form factors of bound nucleons. The parametrization should also be applicable to the transverse cross section in neutrino scattering. If the transverse enhancement originates from meson exchange currents (MEC), then it is theoretically expected that any enhancement in the longitudinal or axial contributions is small. We present the predictions of the “Transverse Enhancement” model (which is based on electron scattering data only) for the νμ, \(\bar{\nu}_{\mu}\) differential and total QE cross sections for nucleons bound in carbon. The Q2 dependence of the transverse enhancement is observed to resolve much of the long standing discrepancy in the QE total cross sections and differential distributions between low energy and high energy neutrino experiments on nuclear targets.
We present new parameterizations of vector and axial nucleon form factors. We maintain an excellent descriptions of the form factors at low momentum transfers, where the spatial structure of the ...nucleon is important, and use the Nachtman scaling variable ξ to relate elastic and inelastic form factors and impose quark–hadron duality constraints at high momentum transfers where the quark structure dominates. We use the new vector form factors to re-extract updated values of the axial form factor from neutrino experiments on deuterium. We obtain an updated world average value from ν
μ
d and pion electroproduction experiments of M
A
=1.014± 0.014 GeV/
c
2
. Our parameterizations are useful in modeling neutrino interactions at low energies (e.g. for neutrino oscillations experiments). The predictions for high momentum transfers can be tested in the next generation electron and neutrino scattering experiments.
The uncertainties in parton distribution functions (PDFs) are the dominant source of the systematic uncertainty in precision measurements of electroweak parameters at hadron colliders (e.g.
sin
2
θ
e
...f
f
(
M
Z
)
,
sin
2
θ
W
=
1
-
M
W
2
/
M
Z
2
and the mass of the W boson). We show that measurements of the forward–backward charge asymmetry (
A
F
B
(
M
,
y
)
) of Drell–Yan dilepton events produced at hadron colliders provide a new powerful tool to reduce the PDF uncertainties in these measurements.
Spectral functions that are used in neutrino event, generators to model quasielastic (QE) scattering from nuclear targets include Fermi gas, Local Thomas Fermi gas (LTF), Bodek-Ritchie Fermi gas with ...high momentum tail, and the Benhar-Fantoni two dimensional spectral function. We find that the
ν
dependence of predictions of these spectral functions for the QE differential cross sections (
d
2
σ
/
d
Q
2
d
ν
) are in disagreement with the prediction of the
ψ
′
superscaling function which is extracted from fits to quasielastic electron scattering data on nuclear targets. It is known that spectral functions do not fully describe quasielastic scattering because they only model the initial state. Final state interactions distort the shape of the differential cross section at the peak and increase the cross section at the tails of the distribution. We show that the kinematic distributions predicted by the
ψ
′
superscaling formalism can be well described with a modified
effective spectral function
(ESF). By construction, models using ESF in combination with the transverse enhancement contribution correctly predict electron QE scattering data.
We present a simple method for the extraction of corrections for bias in the measurement of the momentum of muons in hadron collider experiments. Such bias can originate from a variety of sources ...such as detector misalignment, software reconstruction bias, and uncertainties in the magnetic field. The two step method uses the mean
for muons from
Z
→
μμ
decays to determine the momentum scale corrections in bins of charge,
η
and
ϕ
. In the second step, the corrections are tuned by using the average invariant mass
of
Z
→
μμ
events in the same bins of charge
η
and
ϕ
. The forward–backward asymmetry of
Z
/
γ
∗
→
μμ
pairs as a function of
μ
+
μ
−
mass, and the
ϕ
distribution of
Z
bosons in the Collins–Soper frame are used to ascertain that the corrections remove the bias in the momentum measurements for positive versus negatively charged muons. By taking the sum and difference of the momentum scale corrections for positive and negative muons, we isolate additive corrections to
that may originate from misalignments and multiplicative corrections that may originate from mis-modeling of the magnetic field (∫
B
⋅
d
L
). This method has recently been used in the CDF experiment at Fermilab and in the CMS experiment at the Large Hadron Collider at CERN.
We present a parametrization of the observed enhancement in the transverse electron quasielastic (QE) response function for nucleons bound in carbon as a function of the square of the four momentum ...transfer (
Q
2
) in terms of a correction to the magnetic form factors of bound nucleons. The parametrization should also be applicable to the transverse cross section in neutrino scattering. If the transverse enhancement originates from meson exchange currents (MEC), then it is theoretically expected that any enhancement in the longitudinal or axial contributions is small. We present the predictions of the “Transverse Enhancement” model (which is based on electron scattering data only) for the
ν
μ
,
differential and total QE cross sections for nucleons bound in carbon. The
Q
2
dependence of the transverse enhancement is observed to resolve much of the long standing discrepancy in the QE total cross sections and differential distributions between low energy and high energy neutrino experiments on nuclear targets.
We investigate the “low-
ν
” method (developed by the CCFR/NUTEV collaborations) to determine the neutrino flux in a wide band neutrino beam at very low energies, a region of interest to neutrino ...oscillations experiments. Events with low hadronic final state energy
(of 1, 2 and 5 GeV) were used by the MINOS collaboration to determine the neutrino flux in their measurements of neutrino (
ν
μ
) and antineutrino (
) total cross sections. The lowest
ν
μ
energy for which the method was used in MINOS is 3.5 GeV, and the lowest
energy is 6 GeV. At these energies, the cross sections are dominated by inelastic processes. We investigate the application of the method to determine the neutrino flux for
ν
μ
,
energies as low as 0.7 GeV where the cross sections are dominated by quasielastic scattering and
Δ
(1232) resonance production. We find that the method can be extended to low energies by using
values of 0.25 and 0.50 GeV, which are feasible in fully active neutrino detectors such as MINERvA.
Spectral functions do not fully describe quasielastic electron and neutrino scattering from nuclei because they only model the initial state. Final state interactions distort the shape of the ...differential cross section at the peak and increase the cross section at the tails of the distribution. We show that the kinematic distributions predicted by the ψ′ super-scaling formalism can be well described with a modified effective spectral function (ESF). By construction, models using ESF in combination with the transverse enhancement contribution correctly predict electron QE scattering data. Our values for the binding energy parameter Δ are smaller than ϵ¯ extracted within the Fermi gas model from pre 1971 data by Moniz 8, probably because these early cross sections were not corrected for coulomb effects.
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