Light Quarks Research Articles

Kinked tracks from Σ+ baryons as a probe of light quark polarizations

Jets initiated by energetic quarks carry in an obvious way approximate information about the original quark energy and momentum. In a less obvious way, they also carry information about the quark polarization. Previous works have shown how the polarization information can be extracted by ATLAS and CMS using events in which the quark hadronizes to an energetic baryon — Λb for b quarks, Λc for c quarks and Λ for s quarks. In this paper we extend these proposals to Σ+ baryons, which can provide sensitivity to polarizations of s and u quarks. We analyze the various aspects of how the kinked track signature of the Σ+→ pπ0 decay can be used for this purpose. We evaluate the feasibility of such measurements in toverline{t} samples.

Light quark and antiquark constraints from new electroweak data

Light quark and antiquark constraints from new electroweak data

Search for excited τ-leptons and leptoquarks in the final state with τ-leptons and jets in pp collisions at sqrt{s} = 13 TeV with the ATLAS detector

A search is reported for excited τ-leptons and leptoquarks in events with two hadronically decaying τ-leptons and two or more jets. The search uses proton-proton (pp) collision data at sqrt{s} = 13 TeV recorded by the ATLAS experiment during the Run 2 of the Large Hadron Collider in 2015–2018. The total integrated luminosity is 139 fb−1. The excited τ-lepton is assumed to be produced and to decay via a four-fermion contact interaction into an ordinary τ-lepton and a quark-antiquark pair. The leptoquarks are assumed to be produced in pairs via the strong interaction, and each leptoquark is assumed to couple to a charm or lighter quark and a τ-lepton. No excess over the background prediction is observed. Excited τ-leptons with masses below 2.8 TeV are excluded at 95% CL in scenarios with the contact interaction scale Λ set to 10 TeV. At the extreme limit of model validity where Λ is set equal to the excited τ-lepton mass, excited τ-leptons with masses below 4.6 TeV are excluded. Leptoquarks with masses below 1.3 TeV are excluded at 95% CL if their branching ratio to a charm quark and a τ-lepton equals 1. The analysis does not exploit flavour-tagging in the signal region.

Universal energy dependence of measured temperatures for baryons produced in heavy-ion collisions

From the data on baryon production in heavy-ion collisions it is shown that a set of measurable functions exist, one for each baryon type, that depend exponentially on transverse momenta up to the maximum values detected for all collision energies ranging from the low end of RHIC BES to the high end of CERN LHC. The implied temperatures satisfy a scaling law in collision energy with a universal exponent for all baryon types which is the novel discovery. A self-similar thermal source is implied. Furthermore, it is shown how the scaling behavior depends on centralities. Those features in the data are related to simple properties of light and strange quarks by use of the recombination model. Prediction of $\phi$ meson production is made and then verified by existing data.

Exclusive semileptonic Bs→Kℓν decays on the lattice

Semileptonic $B_s \to K \ell \nu$ decays provide an alternative $b$-decay channel to determine the CKM matrix element $|V_{ub}|$, and to obtain a $R$-ratio to investigate lepton-flavor-universality violations. Results for the CKM matrix element may also shed light on the discrepancies seen between analyses of inclusive or exclusive decays. We calculate the decay form factors using lattice QCD with domain-wall light quarks and a relativistic $b$-quark. We analyze data at three lattice spacings with unitary pion masses down to $268\,\mathrm{MeV}$. Our numerical results are interpolated/extrapolated to physical quark masses and to the continuum to obtain the vector and scalar form factors $f_+(q^2)$ and $f_0(q^2)$ with full error budgets at $q^2$ values spanning the range accessible in our simulations. We provide a possible explanation of tensions found between results for the form factor from different lattice collaborations. Model- and truncation-independent $z$-parameterization fits following a recently proposed Bayesian-inference approach extend our results to the entire allowed kinematic range. Our results can be combined with experimental measurements of $B_s \to D_s$ and $B_s\to K$ semileptonic decays to determine $|V_{ub}|=3.8(6)\times 10^{-3}$. The error is currently dominated by experiment. We compute differential branching fractions and two types of $R$ ratios, the one commonly used as well as a variant better suited to test lepton-flavor universality.

Nonextensive Boltzmann transport equation: The relaxation time approximation and beyond

We derive approximate iterative analytical solutions of the nonextensive Boltzmann transport equation in the relaxation time approximation. The approximate solutions almost overlap with the exact solution for a considerably wide range of the parameter values found in describing particle spectra originated in high-energy collisions. We also discuss the Landau kinetic approximation of the nonextensive Boltzmann transport equation and the emergence of the nonextensive Fokker–Planck equation, and use it to estimate the drag and diffusion coefficients of highly energetic light quarks passing through a gluonic plasma.

Heavy Quark Diffusion from 2+1 Flavor Lattice QCD with 320MeV Pion Mass.

We present the first calculations of the heavy flavor diffusion coefficient using lattice QCD with light dynamical quarks corresponding to a pion mass of around 320MeV. For temperatures 195 MeV<T<352 MeV, the heavy quark spatial diffusion coefficient is found to be significantly smaller than previous quenched lattice QCD and recent phenomenological estimates. The result implies very fast hydrodynamization of heavy quarks in the quark-gluon plasma created during ultrarelativistic heavy-ion collision experiments.

D -meson semileptonic decays to pseudoscalars from four-flavor lattice QCD

We present lattice-QCD calculations of the hadronic form factors for the semileptonic decays $D\to\pi\ell\nu$, $D\to K\ell\nu$, and $D_s\to K\ell\nu$. Our calculation uses the highly improved staggered quark (HISQ) action for all valence and sea quarks and includes $N_f=2+1+1$ MILC ensembles with lattice spacings ranging from $a\approx0.12$ fm down to $0.042$ fm. At most lattice spacings, an ensemble with physical-mass light quarks is included. The HISQ action allows all the quarks to be treated with the same relativistic light-quark action, allowing for nonperturbative renormalization using partial conservation of the vector current. We combine our results with experimental measurements of the differential decay rates to determine $|V_{cd}|^{D\to\pi}=0.2238(11)^{\rm Expt}(15)^{\rm QCD}(04)^{\rm EW}(02)^{\rm SIB}[22]^{\rm QED}$ and $|V_{cs}|^{D\to K}=0.9589(23)^{\rm Expt}(40)^{\rm QCD}(15)^{\rm EW}(05)^{\rm SIB}[95]^{\rm QED}$ This result for $|V_{cd}|$ is the most precise to date, with a lattice-QCD error that is, for the first time for the semileptonic extraction, at the same level as the experimental error. Using recent measurements from BES III, we also give the first-ever determination of $|V_{cd}|^{D_s\to K}=0.258(15)^{\rm Expt}(01)^{\rm QCD}[03]^{\rm QED}$ from $D_s\to K \ell\nu$. Our results also furnish new Standard Model calculations of the lepton flavor universality ratios $R^{D\to\pi}=0.98671(17)^{\rm QCD}[500]^{\rm QED}$, $R^{D\to K}=0.97606(16)^{\rm QCD}[500]^{\rm QED}$, and $R^{D_s\to K}=0.98099(10)^{\rm QCD}[500]^{\rm QED}$, which are consistent within $2\sigma$ with experimental measurements. Our extractions of $|V_{cd}|$ and $|V_{cs}|$, when combined with a value for $|V_{cb}|$, provide the most precise test of second-row CKM unitarity, finding agreement with unitarity at the level of one standard deviation.

Parton decomposition of nucleon spin and momentum: Gluons from dressed quarks

The lowest two Mellin moments of hadronic Generalized Parton Distributions are explored within a model that allows investigation of the inter-related quark and gluon contributions. For light quarks their dynamical connection is strong due to quark dressing. Our principal focus is the angular momentum J of the nucleon. This work employs and extends dynamical insights obtained from our recent model results for quark and gluon momentum fractions 〈x〉q/g in both pion and nucleon. The employed model is based on the Rainbow-Ladder truncation of the Dyson-Schwinger equations of QCD. The special case of a 1-loop treatment of a single hadronic quark is used to motivate several insights and obtain initial estimates such as the Wilson line correction to the established Landau gauge model (−7% for both Jq and 〈x〉q), and the “binding gluon” contribution to 〈x〉g (≤10%). We obtain the proton J within 1% after inclusion of the pion cloud mechanism to produce the sea. The gluon second Mellin moments of the proton reflect similar dynamics; (〈x〉g, Jg) are (26%, 24%) at model scale, and (40%, 38%) at 2 GeV. We also find that Jtot is shared almost equally between the total orbital and total intrinsic spin contributions.

Study on the weak decay between two heavy baryons {mathcal {B}}_i(frac{1}{2}^+)rightarrow {mathcal {B}}_f(frac{3}{2}^+) in the light-front quark model

In this work, we study the weak decay between two heavy baryons {mathcal {B}}_i(frac{1}{2}^+)rightarrow {mathcal {B}}_f(frac{3}{2}^+) in the light-front quark model where three-quark picture is employed for baryon. We derive general form of transition amplitude of {mathcal {B}}_i(frac{1}{2}^+)rightarrow {mathcal {B}}_f(frac{3}{2}^+), and analyze two specific cases of transitions: the weak decays of single heavy baryon Sigma _{b} rightarrow Sigma _{c}^* and the decays of double-charmed baryon Xi _{cc}rightarrow Sigma _{c}^*(Xi _{c}^*). We compute the hadronic form factors for the transitions and apply them to study the decay widths of the semi-leptonic {mathcal {B}}_i(frac{1}{2}^+)rightarrow {mathcal {B}}_f(frac{3}{2}^+) lbar{nu }_l and non-leptonic {mathcal {B}}_i(frac{1}{2}^+)rightarrow {mathcal {B}}_f(frac{3}{2}^+)M. Previously we studied the transition Sigma _{b} rightarrow Sigma _{c}^* with the quark–diquark picture of baryon in the light-front quark model. Here we revisit this transition with three-quark picture of baryon. At the quark level, the transition Sigma _{b} rightarrow Sigma _{c}^* is induced by the brightarrow c transition.The subsystem of the two unchanged light quarks which possesses definite and same spin in initial and final state can be viewed as a spectator, so the spectator approximation can be applied directly. For the weak decay of doubly charmed baryon Xi _{cc}, a c quark decays to a light quark q_1, so both the initial state cc and final state q_1q_2 (q_1 and the original q_2 in initial state may be the same flavor quarks) which possess definite spin are no longer spectators. A rearrangement of quarks for initial and final states is adopted to isolate the unchanged subsystem cq_2 which can be viewed as the spectator approximately. Future measurements on these channels will constrain the nonperturbative parameter in the wavefunctions and test the model predictions.

Search for effective Lorentz and CPT violation using ZEUS data

Lorentz and CPT symmetry in the quark sector of the Standard Model are studied in the context of an effective field theory using ZEUS e±p data. Symmetry-violating effects can lead to time-dependent oscillations of otherwise time-independent observables, including scattering cross sections. An analysis using five years of inclusive neutral-current deep inelastic scattering events corresponding to an integrated HERA luminosity of 372 pb−1 at s=318 GeV has been performed. No evidence for oscillations in sidereal time has been observed within statistical and systematic uncertainties. Constraints, most for the first time, are placed on 42 coefficients parametrizing dominant CPT-even dimension-four and CPT-odd dimension-five spin-independent modifications to the propagation and interaction of light quarks.5 MoreReceived 4 January 2023Accepted 23 February 2023DOI:https://doi.org/10.1103/PhysRevD.107.092008Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDeep inelastic scatteringEffective field theoryHypothetical particle physics modelsPropertiesLorentz symmetryTechniquesLepton-hadron collidersParticles & Fields

Light quark jet quenching in higher-derivative gravity

We study finite-coupling corrections on the energy loss of light quarks in strongly coupled {mathcal {N}}=4 super Yang–Mills (SYM) plasma. We perform the analysis by computing the stopping distance of an image jet induced by a massless source field, characterized by a massless particle falling along the null geodesic in Einstein gravity with curvature-squared (R^2) corrections. It turns out that the stopping distance in the R^2 theories can be larger or smaller than its SYM counterpart depending on the higher-derivative coefficients. Moreover, we evaluate the stopping distance in the Gauss–Bonnet background and find that increasing lambda _textrm{GB} (a dimensionless parameter in Gauss–Bonnet gravity) leads to a decrease in the stopping distance, thus enhancing the energy loss of light quarks, in agreement with previous findings for the drag force, jet quenching parameter, and the instantaneous energy loss of light quarks using shooting strings.

Proton Structure Functions at Next-to-Leading Order in the Dipole Picture with Massive Quarks.

We predict heavy quark production cross sections in deep inelastic scattering at high energy by applying the color glass condensate effective theory. We demonstrate that, when the calculation is performed consistently at next-to-leading order accuracy with massive quarks, it becomes possible, for the first time in the dipole picture with perturbatively calculated center-of-mass energy evolution, to simultaneously describe both the light and heavy quark production data at small x_{Bj}. Furthermore, we show how the heavy quark cross section data provides additional strong constraints on the extracted nonperturbative initial condition for the small-x_{Bj} evolution equations.

The pentaquark spectrum from Fermi statistics

We study compact hidden charm pentaquarks in the Born–Oppenheimer approximation, previously introduced for tetraquarks, assuming the heavy pair to be in a color octet. We show that Fermi statistics applied to the complex of the three light quarks, also in color octet, requires S-wave pentaquark ground states to consist of three octets of flavour-SU(3)_f, two with spin 1/2 and one with spin 3/2, in line with the observed, strangeness S=0,-1, spectrum. Additional lines corresponding to decays into J/psi +Sigma and J/psi +Xi are predicted. In the language of non-relativistic SU(6), ground state pentaquarks form either a {varvec{56}} or a {varvec{20}} representation, distinguished by presence or absence of pentaquarks decaying in the spin 3/2 decuplet, e.g. in J/psi +Delta ^{++}. Observation of a strangeness S=-2 or isospin I=3/2 pentaquarks would be a clear signature of compact, QCD bound pentaquarks.

Formula omitted] mixing from lattice QCD

In heavy quark limit, the lowest-lying charmed baryons with two light quarks can form an SU(3) triplet and sextet. The Ξc in the SU(3) triplet and Ξc′ in the sextet have the same JPC quantum number and can mix due to the finite charm quark mass and the fact the strange quark is heavier than the up/down quark. We explore the Ξc–Ξc′ mixing by calculating the two-point correlation functions of the Ξc and Ξc′ baryons from lattice QCD. Based on the lattice data, we adopt two independent methods to determine the mixing angle between Ξc and Ξc′. After making the chiral and continuum extrapolation, it is found that the mixing angle θ is 1.2∘±0.1∘, which seems insufficient to account for the large SU(3) symmetry breaking effects found in weak decays of charmed baryons.

Light-front wave functions of vector mesons in an algebraic model

Inspired by the recent development of an algebraic model which provides an adequate and unified description of the internal structure of the lowest-lying pseudoscalar mesons, belonging both to the light quarks sector and to the one of heavy quarks, we perform its first extension to the vector-meson case. The algebraic model describes the meson's structure in terms of the spectral density function that appears in a Nakanishi integral representation of the covariant quark-antiquark bound-state amplitude, i.e., the Bethe-Salpeter amplitude. We compute the leading-twist light-front wave functions of the $\ensuremath{\rho}(770)$, $\ensuremath{\phi}(1020)$, $J/\ensuremath{\psi}$, and $\mathrm{\ensuremath{\Upsilon}}(1S)$ mesons through their connection with the parton distribution amplitudes. Among the results we present, the following are of particular interest: (i) transverse light-front wave functions can be obtained algebraically from the corresponding parton distribution amplitudes, whereas that is not the case for longitudinal light-front wave functions, which requires an intermediate step where a spectral density function must be derived from the particular parton distribution amplitude; (ii) the derived spectral density functions show marked differences between light and heavy vector mesons, the latter being narrower as compared to the former, and these are also nonpositive definite, although the integral over the entire curve is larger than zero as expected; and (iii) the longitudinal and transverse light-front wave functions of vector mesons with light quark content exhibit steep $x$ and ${p}_{\ensuremath{\perp}}^{2}$ dependence, while those of the $J/\ensuremath{\psi}$ and $\mathrm{\ensuremath{\Upsilon}}(1S)$ mesons are characterized by narrow distributions in the $x$ range but, comparatively, much more gradual falloffs with respect to the ${p}_{\ensuremath{\perp}}^{2}$ range depicted.

Off-shell chromomagnetic dipole moments of light quarks in the SM at and beyond the Z gauge boson mass scale

The anomalous chromomagnetic dipole moment, with the gluon off-shell, of the Standard Model (SM) light quarks ([Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text]), at the [Formula: see text] gauge boson mass scale, is computed by using the [Formula: see text] scheme. The numerical results disagree with all the previous predictions reported in the literature and show a discrepancy of up to two orders of magnitude in certain situations.

Towards a Nonperturbative Formulation of the Jet Charge.

The jet charge is an old observable that has proven uniquely useful for discrimination of jets initiated by different flavors of light quarks, for example. In this Letter, we propose an approach to understanding the jet charge by establishing simple, robust assumptions that hold to good approximation nonperturbatively, such as isospin conservation and large particle multiplicity in the jets, forgoing any attempt at a perturbative analysis. From these assumptions, the jet charge distribution with fixed particle multiplicity takes the form of a Gaussian by the central limit theorem and whose mean and variance are related to fractional-power moments of single particle energy distributions. These results make several concrete predictions for the scaling of the jet charge with the multiplicity, explaining many of the results already in the literature, and new results we validate in MonteCarlo simulation.

Spectroscopic Study of $$\pmb {\varOmega _{cc}}$$, $$\pmb {\varOmega _{cb}}$$ and $$\pmb {\varOmega _{bb}}$$ Baryons

In this paper, we presented the mass spectra of the doubly heavy $\Omega$ baryons containing one light (strange) quark and two heavy (charm and bottom) quarks. Our predicted masses can be consider to determine the $J^p$ value for the resonances detected by experimental facilities in future. The masses of ground excited states (1S-6S, 1P-3P, 1D-2D, 1F-2F) are calculated for all possible $J^p$ values, using the Hypercentral Constituent Quark Model (hCQM), by employing screened potential as confining potential with color-Coloumb potential. Regge trajectories are also plotted in $(J, M^2)$ plane for natural and unnatural parities. Doubly heavy Omega states are not declared yet by any experimental facility. We compared our results to the predictions gained from other theoretical approaches, and we found that our predictions are quite close to those of them. Other properties such as magnetic moment (for spin state $\frac{1}{2}$ and $\frac{3}{2}$) and radiative decay width are calculated using the enuerated masses.

Shedding new light on weak annihilation B-meson decays

We identify a novel leading-power contribution to the pure weak annihilation non-leptonic B-meson decay amplitudes, which arises from the hard-collinear gluon exchange between the light quark of the bottom meson and the final-state active partons. This interesting observation is naturally expected to shed new light on deciphering rapidity divergences in the convolution integrals of the soft-collinear factorization formulae. Subsequently we explore an intriguing enhancement mechanism due to the penguin contractions of the current-current operators from the weak effective Hamiltonian, which yields the significant impacts on the CP violating observables.