(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) A global fit to the recent B arrow right K ^sup ^ mu ^sup +^ mu ^sup -^ data shows indications for a large new-physics ...contribution to the Wilson coefficient of the semi-leptonic vector operator. In this article we consider a simple Z ^sup '^-boson model of 3-3-1 type that can accommodate such an effect without violating any other constraint from quark-flavour physics. Implications for yet unobserved decay modes such as B arrow right X ^sub s^ nu ... and longstanding puzzles like B arrow right piK are also discussed. The Z ^sup '^-boson masses required to address the observed anomaly lie in the range of 7 TeV. Such heavy Z ^sup '^ bosons evade the existing bounds from precision data and direct searches, and will remain difficult to discover even at a high-luminosity LHC. The potential of an ILC as well as the next generation of low-energy parity-violation experiments in constraining the Z ^sup '^-boson parameter space is also examined.
The forward LHCb acceptance offers the possibility of measuring the top-quark pair asymmetry in a kinematic region that does not receive overwhelming dilution from the symmetric gluon-fusion channel. ...To investigate this possibility, two leptonic final states are identified, and analysis strategies are proposed for each channel with 14 TeV data. Leading fixed-order predictions are then provided for the relevant leptonic asymmetry variables in each channel. If backgrounds can be experimentally constrained, statistically, a nonzero asymmetry is estimated to be observable beyond 5sigma confidence level with the full LHCb 14 TeV data.
SMEFT at NNLO+PS: Vh production Gauld, Rhorry; Haisch, Ulrich; Schnell, Luc
arXiv (Cornell University),
11/2023
Paper, Journal Article
Open access
In the context of the Standard Model effective field theory (SMEFT) the next-to-next-to-leading (NNLO) QCD corrections to the Higgsstrahlungs (\(Vh\)) processes in hadronic collisions are calculated ...and matched to a parton shower (PS). NNLO+PS precision is achieved for the complete sets of SMEFT operators that describe the interactions between the Higgs and two vector bosons and the couplings of the Higgs, a \(W\) or a \(Z\) boson, and light fermions. A POWHEG-BOX implementation of the computed NNLO SMEFT corrections is provided that allows for a realistic exclusive description of \(Vh\) production at the level of hadronic events. This feature makes it an essential tool for future Higgs characterisation studies by the ATLAS and CMS collaborations. Utilising our new Monte Carlo code the numerical impact of NNLO\(+\)PS corrections on the kinematic distributions in \(pp \to Zh \to \ell^+ \ell^- h\) production is explored, employing well-motivated SMEFT benchmark scenarios.
The LHCb collaboration has recently performed a measurement of the production
rate of inclusive $B$ hadron production ($pp\to BX$) at both 7 and 13~TeV
centre-of-mass (CoM) energies. As part of this ...measurement, the ratio of these
two cross section measurements has been presented differentially in $B$ hadron
pseudorapidity within the range of $\eta_B \in 2.0,5.0$. A large tension
($4\sigma$) is observed for the ratio measurement in the lower pseudorapidity
range of $\eta_B \in 2.0,3.0$, where the data is observed to exceed
theoretical predictions, while consistency is found at larger $\eta_B$ values.
This behaviour is not expected within perturbative QCD, and can only be
achieved by introducing ad-hoc features into the structure of the
non-perturbative gluon PDF within the region of $x\in10^{-3},10^{-4}$.
Specifically, the gluon PDF must grow extremely quickly with decreasing $x$
within this kinematic range, closely followed by a period of decelerated
growth. However, such behaviour is highly disfavoured by global fits to proton
structure. Further studies of the available LHCb $B$ and $D$ hadron cross
section data, available for a range of CoM energies, indicate systematic
tension in the (pseudo)rapidity region of $2.0,2.5$.
The forward LHCb acceptance offers the possibility of measuring the top-quark pair asymmetry in a kinematic region that does not receive overwhelming dilution from the symmetric gluon-fusion channel. ...To investigate this possibility, two leptonic final states are identified, and analysis strategies are proposed for each channel with 14~TeV data. Leading fixed-order predictions are then provided for the relevant leptonic asymmetry variables in each channel. If backgrounds can be experimentally constrained, statistically, a non-zero asymmetry is estimated to be observable beyond 5\(\sigma\) confidence level with the full LHCb 14~TeV data.
Phys. Rev. D 93, 014001 (2016) Predictions are provided for double differential cross sections and
forward-backward ratios of $D^{0}$ production in $p\rm Pb$ (forward) and
$\rm{Pb}$$p$ (backward) ...collisions at 5.02~TeV. The effect of nuclear
corrections on the ratio of differential cross sections ratios is estimated to
be $\simeq$ (10-30)\% in the kinematically accessible region of LHCb, and
interestingly this ratio is approximately flat with respect to $p_T(D^0)$ due
to a compensation of shadowing and anti-shadowing effects arising from the
input nuclear PDFs. In comparison to $J/\psi(\rightarrow\mu^-\mu^+)$
measurements which have already been performed with the available data, the
cross section for $D^{0}(\rightarrow K^-\pi^+)$ production is expected to be
two-orders of magnitude higher.
We extend the recently presented, fully exclusive, next-to-leading-order accurate event generator for the simulation of massless neutral- and charged-current deep inelastic scattering (DIS) to the ...case of incoming neutrinos. The generator can be used to study neutrino-nucleon interactions at (ultra) high energies, and is relevant for a range of fixed-target collider experiments and large-volume neutrino detectors, investigating atmospheric and astrophysical neutrinos. The matching with multi-purpose event generators such as PYTHIA 8 is performed with the POWHEG method, and accounts for parton showering and non-perturbative effects such as hadronization. This makes it possible to investigate higher-order perturbative corrections to realistic observables, such as the distribution of charged particles. To illustrate the capabilities of the code we provide predictions for several differential distributions in fixed-target collisions for neutrino energies up to 1 PeV.
The forward LHCb acceptance opens interesting possibilities of studying
precision Standard Model hard processes in a kinematical region beyond the
reach of ATLAS and CMS. In this paper we perform a ...feasibility study for
cross-section measurements of top quark pairs with the LHCb detector, with an
analysis of signal and background rates for selected final states, and
determine the potential precision achievable at $\sqrt{s} =$ 7 and 14~TeV. We
then study the dependence of theoretical uncertainties on the pseudorapidity
distribution of top quarks produced in pair production at NLO, and observe that
a cross-section measurement at high pseudorapidity has enhanced sensitivity to
probe the high-$x$ gluon PDF as compared to measurements in the central-region.
Based on simulated pseudodata, the impact of a 14~TeV cross-section measurement
on the gluon PDF and charge asymmetry is quantified.
Phys. Rev. Lett. 118, 072001 (2017) The small-$x$ gluon in global fits of parton distributions is affected by
large uncertainties from the lack of direct experimental constraints. In this
work we ...provide a precision determination of the small-$x$ gluon from the
exploitation of forward charm production data provided by LHCb for three
different centre-of-mass (CoM) energies: 5~TeV, 7~TeV and 13~TeV. The LHCb
measurements are included in the PDF fit by means of normalized distributions
and cross-section ratios between data taken at different CoM values, $R_{13/7}$
and $R_{13/5}$. We demonstrate that forward charm production leads to a
reduction of the PDF uncertainties of the gluon down to $x\simeq 10^{-6}$ by up
to an order of magnitude, with implications for high-energy colliders, cosmic
ray physics and neutrino astronomy.
The LHCb collaboration has recently performed a measurement of the production rate of inclusive \(B\) hadron production (\(pp\to BX\)) at both 7 and 13~TeV centre-of-mass (CoM) energies. As part of ...this measurement, the ratio of these two cross section measurements has been presented differentially in \(B\) hadron pseudorapidity within the range of \(\eta_B \in 2.0,5.0\). A large tension (\(4\sigma\)) is observed for the ratio measurement in the lower pseudorapidity range of \(\eta_B \in 2.0,3.0\), where the data is observed to exceed theoretical predictions, while consistency is found at larger \(\eta_B\) values. This behaviour is not expected within perturbative QCD, and can only be achieved by introducing ad-hoc features into the structure of the non-perturbative gluon PDF within the region of \(x\in10^{-3},10^{-4}\). Specifically, the gluon PDF must grow extremely quickly with decreasing \(x\) within this kinematic range, closely followed by a period of decelerated growth. However, such behaviour is highly disfavoured by global fits to proton structure. Further studies of the available LHCb \(B\) and \(D\) hadron cross section data, available for a range of CoM energies, indicate systematic tension in the (pseudo)rapidity region of \(2.0,2.5\).
PDF
