First Record of Reversed Symmetry in Etropus cyclosquamus and Second Record in Citharichthys spilopterus (Bothidae, Pisces) in the Gulf of Mexico, with a Plausible Genetic Explanation for Reversal

The discovery of the first instance of reversed eye symmetry in the shelf flounder, Etropus cyclosquamus, and the second instance in the bay whiff, Citharichthys spilopterus, are reported. Two reversed bay whiffs and three reversed shelf flounders were collected in the Gulf of Mexico. Four of these specimens were taken from the vicinity of Fort Walton Beach, Okaloosa County, in northern Florida, and one was taken from Higgs Beach in Key West, Monroe County, Fl. The collection of these fish is reported because of the infrequent occurrence of reversed eye symmetry in flatfishes in the Gulf of Mexico. The fish serve as the first record of eye symmetry reversal in E. cyclosquamus and the second record for C. spilopterus in the Gulf of Mexico. This is the second record of reversal for the genus Etropus and the third record for Citharichthys in the western Atlantic Ocean. The putative causes of symmetry reversal in pleuronectiform fish are briefly examined. A plausible genetic explanation for reversal is proposed. The explanation attempts to reconcile the environmental causality of eye symmetry with the accepted genetic model of Brown and Wolpert

The Threespine Bass, Synagrops trispinosus (Perciformes; Acropomatidae), an Addition to the Fish Fauna of the Gulf of Mexico

We present the first documented record of Synagrops trispinosus in the Gulf of Mexico. This record represents a moderate extension to the known southern Caribbean distribution; it is nevertheless a new addition to the ichthyofauna of U.S. coastal waters

Study of the doubly charmed tetraquark T+cc

Quantum chromodynamics, the theory of the strong force, describes interactions of coloured quarks and gluons and the formation of hadronic matter. Conventional hadronic matter consists of baryons and mesons made of three quarks and quark-antiquark pairs, respectively. Particles with an alternative quark content are known as exotic states. Here a study is reported of an exotic narrow state in the D0D0π+ mass spectrum just below the D*+D0 mass threshold produced in proton-proton collisions collected with the LHCb detector at the Large Hadron Collider. The state is consistent with the ground isoscalar T+cc tetraquark with a quark content of ccu⎯⎯⎯d⎯⎯⎯ and spin-parity quantum numbers JP = 1+. Study of the DD mass spectra disfavours interpretation of the resonance as the isovector state. The decay structure via intermediate off-shell D*+ mesons is consistent with the observed D0π+ mass distribution. To analyse the mass of the resonance and its coupling to the D*D system, a dedicated model is developed under the assumption of an isoscalar axial-vector T+cc state decaying to the D*D channel. Using this model, resonance parameters including the pole position, scattering length, effective range and compositeness are determined to reveal important information about the nature of the T+cc state. In addition, an unexpected dependence of the production rate on track multiplicity is observed

First Record of Reversed Symmetry in Etropus cyclosquamus and Second Record in Citharichthys spilopterus (Bothidae, Pisces) in the Gulf of Mexico, with a Plausible Genetic Explanation for Reversal

The discovery of the first instance of reversed eye symmetry in the shelf flounder, Etropus cyclosquamus, and the second instance in the bay whiff, Citharichthys spilopterus, are reported. Two reversed bay whiffs and three reversed shelf flounders were collected in the Gulf of Mexico. Four of these specimens were taken from the vicinity of Fort Walton Beach, Okaloosa County, in northern Florida, and one was taken from Higgs Beach in Key West, Monroe County, Fl. The collection of these fish is reported because of the infrequent occurrence of reversed eye symmetry in flatfishes in the Gulf of Mexico. The fish serve as the first record of eye symmetry reversal in E. cyclosquamus and the second record for C. spilopterus in the Gulf of Mexico. This is the second record of reversal for the genus Etropus and the third record for Citharichthys in the western Atlantic Ocean. The putative causes of symmetry reversal in pleuronectiform fish are briefly examined. A plausible genetic explanation for reversal is proposed. The explanation attempts to reconcile the environmental causality of eye symmetry with the accepted genetic model of Brown and Wolpert

Search for Bc+→π+μ+μ−B_c^+\to\pi^+\mu^+\mu^- decays and measurement of the branching fraction ratio B(Bc+→ψ(2S)π+)/B(Bc+→J/ψπ+){\cal B}(B_c^+\to\psi(2S)\pi^+)/{\cal B}(B_c^+\to J/\psi \pi^+)

International audienceThe first search for nonresonant $B_c^+\to\pi^+\mu^+\mu^-$ decays is reported. The analysis uses proton-proton collision data collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 fb$^{-1}$. No evidence for an excess of signal events over background is observed and an upper limit is set on the branching fraction ratio ${\cal B}(B_c^+\to\pi^+\mu^+\mu^-)/{\cal B}(B_c^+\to J/\psi \pi^+) < 2.1\times 10^{-4}$ at $90\%$ confidence level. Additionally, an updated measurement of the ratio of the $B_c^+\to\psi(2S)\pi^+$ and $B_c^+\to J/\psi \pi^+$ branching fractions is reported. The ratio ${\cal B}(B_c^+\to\psi(2S)\pi^+)/{\cal B}(B_c^+\to J/\psi \pi^+)$ is measured to be $0.254\pm 0.018 \pm 0.003 \pm 0.005$, where the first uncertainty is statistical, the second systematic, and the third is due to the uncertainties on the branching fractions of the leptonic $J/\psi$ and $\psi(2S)$ decays. This measurement is the most precise to date and is consistent with previous LHCb results

Helium identification with LHCb

International audienceThe identification of helium nuclei at LHCb is achieved using a method based on measurements of ionisation losses in the silicon sensors and timing measurements in the Outer Tracker drift tubes. The background from photon conversions is reduced using the RICH detectors and an isolation requirement. The method is developed using $pp$ collision data at $\sqrt{s}=13\,{\rm TeV}$ recorded by the LHCb experiment in the years 2016 to 2018, corresponding to an integrated luminosity of $5.5\,{\rm fb}^{-1}$. A total of around $10^5$ helium and antihelium candidates are identified with negligible background contamination. The helium identification efficiency is estimated to be approximately $50\%$ with a corresponding background rejection rate of up to $\mathcal O(10^{12})$. These results demonstrate the feasibility of a rich programme of measurements of QCD and astrophysics interest involving light nuclei

Enhanced production of Λb0\Lambda_{b}^{0} baryons in high-multiplicity pppp collisions at s=13\sqrt{s} = 13 TeV

International audienceThe production rate of $\Lambda_{b}^{0}$ baryons relative to $B^{0}$ mesons in $pp$ collisions at a center-of-mass energy $\sqrt{s} = 13$ TeV is measured by the LHCb experiment. The ratio of $\Lambda_{b}^{0}$ to $B^{0}$ production cross-sections shows a significant dependence on both the transverse momentum and the measured charged-particle multiplicity. At low multiplicity, the ratio measured at LHCb is consistent with the value measured in $e^{+}e^{-}$ collisions, and increases by a factor of $\sim2$ with increasing multiplicity. At relatively low transverse momentum, the ratio of $\Lambda_{b}^{0}$ to $B^{0}$ cross-sections is higher than what is measured in $e^{+}e^{-}$ collisions, but converges with the $e^{+}e^{-}$ ratio as the momentum increases. These results imply that the evolution of heavy $b$ quarks into final-state hadrons is influenced by the density of the hadronic environment produced in the collision. Comparisons with a statistical hadronization model and implications for the mechanisms enforcing quark confinement are discussed

Charge-dependent curvature-bias corrections using a pseudomass method

International audienceMomentum measurements for very high momentum charged particles, such as muons from electroweak vector boson decays, are particularly susceptible to charge-dependent curvature biases that arise from misalignments of tracking detectors. Low momentum charged particles used in alignment procedures have limited sensitivity to coherent displacements of such detectors, and therefore are unable to fully constrain these misalignments to the precision necessary for studies of electroweak physics. Additional approaches are therefore required to understand and correct for these effects. In this paper the curvature biases present at the LHCb detector are studied using the pseudomass method in proton-proton collision data recorded at centre of mass energy $\sqrt{s}=13$ TeV during 2016, 2017 and 2018. The biases are determined using $Z\to\mu^+\mu^-$ decays in intervals defined by the data-taking period, magnet polarity and muon direction. Correcting for these biases, which are typically at the $10^{-4}$ GeV$^{-1}$ level, improves the $Z\to\mu^+\mu^-$ mass resolution by roughly 20% and eliminates several pathological trends in the kinematic-dependence of the mean dimuon invariant mass

Enhanced production of Λb0\Lambda_{b}^{0} baryons in high-multiplicity pppp collisions at s=13\sqrt{s} = 13 TeV

International audienceThe production rate of $\Lambda_{b}^{0}$ baryons relative to $B^{0}$ mesons in $pp$ collisions at a center-of-mass energy $\sqrt{s} = 13$ TeV is measured by the LHCb experiment. The ratio of $\Lambda_{b}^{0}$ to $B^{0}$ production cross-sections shows a significant dependence on both the transverse momentum and the measured charged-particle multiplicity. At low multiplicity, the ratio measured at LHCb is consistent with the value measured in $e^{+}e^{-}$ collisions, and increases by a factor of $\sim2$ with increasing multiplicity. At relatively low transverse momentum, the ratio of $\Lambda_{b}^{0}$ to $B^{0}$ cross-sections is higher than what is measured in $e^{+}e^{-}$ collisions, but converges with the $e^{+}e^{-}$ ratio as the momentum increases. These results imply that the evolution of heavy $b$ quarks into final-state hadrons is influenced by the density of the hadronic environment produced in the collision. Comparisons with a statistical hadronization model and implications for the mechanisms enforcing quark confinement are discussed