Search results for "Quark"
showing 10 items of 2905 documents
Dark matter searches using accelerometer-based networks
2021
Quantum science and technology 6(3), 034004 (2021). doi:10.1088/2058-9565/abef4f
Fitting strategies to extract the axial charge of the nucleon from lattice QCD
2014
We report on a comparison of several fit methods used for the extraction of the nucleon axial charge gA from lattice QCD with two dynamical flavours of O(a) improved Wilson quarks. We use plateau fits, summed operator insertions (the summation method) and a new “midpoint” method to investigate contributions from excited states that affect the determination of gA. We also present a method to perform correlated fits when the standard estimator for the inverse of the covariance matrix becomes unstable.
Zb(10610) and Zb′(10650) decays in a covariant quark model
2017
We present a calculation of the strong decays of the exotic states ${Z}_{b}(10610)$ and ${Z}_{b}^{\ensuremath{'}}(10650)$ using a covariant quark model. We use a molecular-type four-quark current for the coupling of the ${Z}_{b}(10610)$ and ${Z}_{b}^{\ensuremath{'}}(10650)$ to the constituent heavy and light quarks.
Weak Mixing, CP Violation and Rare Decays
1989
This review summarizes experimental information on weak couplings of quark flavours from weak decays and weak production of heavy flavours and the relation of the observed direct CP violation to a non-trivial phase in the quark mixing matrix. The interest in this field is twofold: on the one side, we can measure precisely the parameters of the standard model in its own framework; on the other side, any inconsistency amongst these measurements or evidence for any process forbidden in the standard model will lead beyond that model.
HIDDEN CHARM MOLECULES IN A FINITE VOLUME
2013
In the present paper we address the interaction of charmed mesons in hidden charm channels in a finite box. We use the interaction from a recent model based on heavy quark spin symmetry that predicts molecules of hidden charm in the infinite volume. The energy levels in the box are generated within this model, and several methods for the analysis of these levels ("inverse problem") are investigated.
EPPS16 – First nuclear PDFs to include LHC data
2017
We present results of our recent EPPS16 global analysis of NLO nuclear parton distribution functions (nPDFs). For the first time, dijet and heavy gauge boson production data from LHC proton–lead collisions have been included in a global fit. Especially, the CMS dijets play an important role in constraining the nuclear effects in gluon distributions. With the inclusion of also neutrino–nucleus deeply-inelastic scattering and pion–nucleus Drell–Yan data and a proper treatment of isospin-corrected data, we were able to free the flavor dependence of the valence and sea quark nuclear modifications for the first time. This gives us less biased, yet larger, flavor by flavor uncertainty estimates. …
Search for Gluino-Mediated Bottom Squark Production inpp¯Collisions ats=1.96 TeV
2009
We report on a search for the supersymmetric partner of the bottom quark produced from gluino decays in data from 2.5 fb{sup -1} of integrated luminosity collected by the Collider Detector at Fermilab at {radical}s = 1.96 TeV. Candidate events are selected requiring two or more jets and large missing transverse energy. At least two of the jets are required to be tagged as originating from a b quark to enhance the sensitivity. The results are in good agreement with the prediction of the standard model processes, giving no evidence for gluino decay to sbottom quarks. This result constrains the gluino-pair-production cross section to be less than 40 fb at 95% credibility level for a gluino mas…
TRANSVERSE MOMENTUM-DEPENDENT PARTON DISTRIBUTIONS FROM LATTICE QCD
2012
Starting from a definition of transverse momentum-dependent parton distributions for semi-inclusive deep inelastic scattering and the Drell-Yan process, given in terms of matrix elements of a quark bilocal operator containing a staple-shaped Wilson connection, a scheme to determine such observables in lattice QCD is developed and explored. Parametrizing the aforementioned matrix elements in terms of invariant amplitudes permits a simple transformation of the problem to a Lorentz frame suited for the lattice calculation. Results for the Sivers and Boer-Mulders transverse momentum shifts are presented, focusing in particular on their dependence on the staple extent and the Collins-Soper evol…
Comment On The Lepton Mixing Matrix
1980
The problem of finding a suitable parametrization for a nontrivial lepton mixing matrix is considered in the framework of the ''sequential'' Weinberg-Salam theory. It is noted that in the case of n lepton generations there are in fact n+1 different theories, corresponding to different numbers m of right-handed neutrino fields present in the Lagrangian. These (n,m) models conserve CP for leptonic couplings naturally only for m=0 or 1 when n > or = 3. These models would seem to be useful as self-consistent approximations for reducing the number of parameters in the experimental analysis of lepton mixing matrices.
Instanton induced quark dynamics and the pentaquark
2004
We analyze the existence of the exotic $\Theta^+$ from the perspective of instanton induced quark dynamics. The 't Hooft interaction gives strong attraction in specific channels of the triquark $ud\bar s$ and diquark $ud$ configurations. In particular it leads to a light $ud\bar s$ triquark cluster, with the mass around $750 {\rm MeV}$, in the I=0, $S=1/2$ and color 3 configuration, and a light $ud$-diquark configuration, with mass $440 {\rm MeV}$, in the I=0, S=0 and color {$\bar{3}$} configuration. If we consider the pentaquark as a bound state of such triquark and diquark configurations in a relative L=1 state we obtain good agreement with the data. The small width of $\Theta^+$ has a na…