Bs Mesons Research Articles

Measurement of the [formula omitted] decay properties and search for the B0 → μ+μ− decay in proton-proton collisions at [formula omitted

Measurements are presented of the Bs0→μ+μ− branching fraction and effective lifetime, as well as results of a search for the B0→μ+μ− decay in proton-proton collisions at s=13TeV at the LHC. The analysis is based on data collected with the CMS detector in 2016–2018 corresponding to an integrated luminosity of 140fb−1. The branching fraction of the Bs0→μ+μ− decay and the effective Bs0 meson lifetime are the most precise single measurements to date. No evidence for the B0→μ+μ− decay has been found. All results are found to be consistent with the standard model predictions and previous measurements.

Beauty production in heavy–ion collisions with ALICE at the LHC

In this contribution, the measurement of the centrality dependence of the nuclear modification factor (RAA) of non-prompt D0 meson in Pb-Pb collisions at √SNN = 5.02 TeV is presented. This measurement provides important constraints to the in-medium mass dependence of energy loss and hadroniza-tion of the beauty quark. In addition, the first measurements of non-prompt Ds+ meson production in central and semi-central Pb-Pb collisions at √SNN = 5.02 TeV are discussed. The non-prompt Ds+ meson measurements provide further information on the production and hadronization of Bs0 mesons. Finally, the first measurement of non-prompt D-meson elliptic flow in Pb-Pb collisions at √SNN = 5.02 TeV is shown. This measurement can help to investigate the degree of thermalization of beauty quarks in the hot and dense QCD medium.

Observation of B[formula omitted] mesons and measurement of the B[formula omitted]/B+ yield ratio in PbPb collisions at TeV

The Bs0 and B+ production yields are measured in PbPb collisions at a center-of-mass energy per nucleon pair of 5.02 TeV. The data sample, collected with the CMS detector at the LHC, corresponds to an integrated luminosity of 1.7 nb−1. The mesons are reconstructed in the exclusive decay channels B→s0J/ψ(μ+μ−)ϕ(K+K−) and B→+J/ψ(μ+μ−)K+, in the transverse momentum range 7–50GeV/c and absolute rapidity 0–2.4. The Bs0 meson is observed with a statistical significance in excess of five standard deviations for the first time in nucleus-nucleus collisions. The measurements are performed as functions of the transverse momentum of the B mesons and of the PbPb collision centrality. The ratio of production yields of Bs0 and B+ is measured and compared to theoretical models that include quark recombination effects.

The Bs0 meson decaying into τe mediated by Z′ gauge bosons

We calculate bounds for the branching ratio of the [Formula: see text] decay, for the first time, in the context of flavor changing neutral currents mediated by a [Formula: see text] gauge boson, which can arise from five extended models. In this sense, by using experimental measurements on the [Formula: see text] decay and the [Formula: see text] process, we look for constraints of the [Formula: see text] coupling, where the more restrictive bound is offered by the last one. On the other hand, by employing the experimental restriction on the [Formula: see text] decay, the strength of the [Formula: see text] coupling is estimated. Our analysis is based on the more recent experimental results on searches for the [Formula: see text] gauge boson in ATLAS and CMS detectors. In addition, we revisited the [Formula: see text] meson decays by using different approaches not previously reported. The strengths of the [Formula: see text] and [Formula: see text] couplings were estimated by employing experimental restrictions on the [Formula: see text] decay and the [Formula: see text] conversion rate, respectively. Thus, we predict the following upper bounds: [Formula: see text], [Formula: see text] and [Formula: see text].

The B-meson decays to charmonuim-like states at LHCb

The recent measurements of the B+ → J/ψπ+π+K+ and B0s → J/ψπ+π+K+K− decays are reported, including the most precise measurements of the properties of the χc1(3872) and ψ2(3823) states in B+ decays and the observation of a new exotic state X(3740) in the B0s meson decays.

Measurement of [formula omitted] meson production in pp and PbPb collisions at [formula omitted] TeV

The production cross sections of Bs0 mesons and charge conjugates are measured in proton-proton (pp) and PbPb collisions via the exclusive decay channel Bs0→J/ψϕ→μ+μ−K+K− at a center-of-mass energy of 5.02 TeV per nucleon pair and within the rapidity range |y|<2.4 using the CMS detector at the LHC. The pp measurement is performed as a function of transverse momentum (pT) of the Bs0 mesons in the range of 7 to 50 GeV/c and is compared to the predictions of perturbative QCD calculations. The Bs0 production yield in PbPb collisions is measured in two pT intervals, 7 to 15 and 15 to 50 GeV/c, and compared to the yield in pp collisions in the same kinematic region. The nuclear modification factor (RAA) is found to be 1.5±0.6(stat)±0.5(syst) for 7–15 GeV/c, and 0.87±0.30(stat)±0.17(syst) for 15–50 GeV/c, respectively. Within current uncertainties, the Bs0 results are consistent with models of strangeness enhancement, and suppression by parton energy loss, as observed for the B+ mesons.

Study of the rare decays of Bs0 and B0 mesons into muon pairs using data collected during 2015 and 2016 with the ATLAS detector

A study of the decays Bs0 → μ+μ− and B0 → μ+μ− has been performed using 26.3 fb−1 of 13 TeV LHC proton-proton collision data collected with the ATLAS detector in 2015 and 2016. Since the detector resolution in μ+μ− invariant mass is comparable to the Bs0-B0 mass difference, a single fit determines the signal yields for both decay modes. This results in a measurement of the branching fraction mathrm{mathcal{B}}left({B}_s^0to {mu}^{+}{mu}^{-}right)=left({3.2}_{-1.0}^{+1.1}right)times {10}^{-9} and an upper limit mathrm{mathcal{B}}left({B}^0to {mu}^{+}{mu}^{-}right)<4.3times {10}^{-10} at 95% confidence level. The result is combined with the Run 1 ATLAS result, yielding mathrm{mathcal{B}}left({B}_s^0to {mu}^{+}{mu}^{-}right)=left({2.8}_{-0.7}^{+0.8}right)times {10}^{-9} and mathrm{mathcal{B}}left({B}^0to {mu}^{+}{mu}^{-}right)<2.1times {10}^{-10} at 95% confidence level. The combined result is consistent with the Standard Model prediction within 2.4 standard deviations in the mathrm{mathcal{B}}left({B}^0to {mu}^{+}{mu}^{-}right)-mathrm{mathcal{B}}left({B}_s^0to {mu}^{+}{mu}^{-}right) plane.

Using time-dependent indirect CP asymmetries to measure T and CPT violation in B0–[formula omitted] mixing

Quantum field theory, which is the basis for all of particle physics, requires that all processes respect CPT invariance. It is therefore of paramount importance to test the validity of CPT conservation. In this Letter, we show that the time-dependent, indirect CP asymmetries involving B decays to a CP eigenstate contain enough information to measure T and CPT violation in B0–B¯0 mixing, in addition to the standard CP-violating weak phases. Entangled B0B¯0 states are not required (so that this analysis can be carried out at LHCb, as well as at the B factories), penguin pollution need not be neglected, and the measurements can be made using Bd0 or Bs0 mesons.

Results on b hadron properties in CMS

The lifetime is among the fundamental properties of particles and is one of the important observables in heavy hadrons allowing to test the theoretical tools describing their physics. This report presents lifetime measurements of B0, B0s, Λ0b and B+c hadrons performed on data, corresponding to 19.7 fb-1, collected by the CMS experiment at the LHC at a center-of-mass energy of √s = 8 TeV. The B0 lifetime is measured to be 453:0± 1:6 (stat) ± 1:5 (syst) μm in J/ψK0S and 457:8 ± 2:7 (stat) ± 2:7 (syst) μm in J/ψK*(892)0. The B0s meson lifetime is measured in two decay modes with differing contributions from the heavy and light eigenstates, resulting in two different measured lifetimes: 504:3 ± 10:5 (stat) ±3:7 (syst) μm in J/ψπ+π- and 443:9±2:0 (stat) ±1:2 (syst) μm in J/ψϕ(1020) respectively. The lifetime of the Λ0b hadron is found to be 443:1±8:2 (stat) ±2:7 (syst) μm. The B+c lifetime is measured with respect to the B+ lifetime and is found to be 162:3 ± 8:2 (stat) ± 4:7 (syst) ± 0:1 (τB+) μm.

Spectroscopy, decay properties and Regge trajectories of the B and Bs mesons**A. K. Rai acknowledges the financial support extended by the Department of Science of Technology, India under SERB fast track scheme SR/FTP /PS-152/2012

A Gaussian wave function is used for detailed study of the mass spectra of the B and BS mesons using a Cornell potential incorporated with a \U0001d4aa(1/m) correction in the potential energy term and expansion of the kinetic energy term up to \U0001d4aa(p10) for relativistic correction of the Hamiltonian. The predicted excited states for the B and Bs mesons are in very good agreement with results obtained by experiment. We assign B2(5747) and Bs2(5840) as the 13P2 state, B1(5721) and Bs1(5830) as the 1P1 state, B0(5732) as the 13P0 state, Bs1(5850) as the state and B(5970) as the 23S1 state. We investigate the Regge trajectories in the (J,M2) and (nr,M2) planes with their corresponding parameters. The branching ratios for leptonic and radiative-leptonic decays are estimated for the B and BS mesons. Our results are in good agreement with experimental observations as well as outcomes of other theoretical models.

Rare and semi-rare decays at ATLAS

The measurements of the rare B0-meson decay processes performed by the ATLAS experiment at the LHC are reviewed. Particular attention is given to the measurement of the branching ratios of the Bs0 and B0d meson decays into a pair of muons with the full Run 1 dataset corresponding to an integrated luminosity of 25 fb-1.

CP violation in the Bs0 system

Experimental and theoretical studies of CP violation in the B0s system are reviewed. Updated predictions for the mixing parameters of the B0s mesons expected in the standard model (SM) are given, namely, the mass difference ΔMSMs=18.3±2.7 ps−1, the decay rate difference ΔΓSMs=0.085±0.015 ps−1, and the flavor-specific CP asymmetry as,SMfs=(2.22±0.27)×10−5 and the equivalent quantities in the B0 sector. Current experimental values of ΔMs and ΔΓs agree with remarkable precision with theoretical expectations. This agreement supports the applicability of theoretical tools such as the heavy quark expansion to these decays. CP-violating studies in the B0s system provide essential information to test the SM expectations and to unveil a possible contribution of the new physics (NP). NP effects on ΔMs of the order of 15% are still possible. The CP phase ϕs due to CP violation in interference of decays and mixing can accommodate effects of the order of O(100%). The semileptonic CP asymmetry assl due to CP violation in mixing could still be a factor of 130 larger than its robust SM expectation and thus provides a very clean observable for NP searches. Theoretical improvements that are necessary to make full use of the experimental precision are discussed.

Bs lifetime measurement in the CP-odd channel B0s → J/Ψ f0 (980) by the DO experiment

The lifetime measurement of the B0s meson in the decay channel B0s → J/Ψ f0 (980) is reported, which is a CP-odd state. Using 10.4 fb-1 of data collected with the D0 detector in Run II of the Tevatron, the lifetime of the CP-odd component of the B0s meson is measured to be τ(B0s) = 1.70 ± 0.14 (stat) ± 0.05 (syst) ps.

A new algorithm for identifying the flavour of B0s mesons at LHCb

A new algorithm for the determination of the initial flavour of B0s mesons is presented. The algorithm is based on two neural networks and exploits the b hadron production mechanism at a hadron collider. The first network is trained to select charged kaons produced in association with the B0s meson. The second network combines the kaon charges to assign the B0s flavour and estimates the probability of a wrong assignment. The algorithm is calibrated using data corresponding to an integrated luminosity of 3 fb−1 collected by the LHCb experiment in proton-proton collisions at 7 and 8 TeV centre-of-mass energies. The calibration is performed in two ways: by resolving the B0s–B̄0s flavour oscillations in B0s → D−sπ+ decays, and by analysing flavour-specific B*s2(5840)0 → B+K− decays. The tagging power measured in B0s → D−sπ+ decays is found to be (1.80 ± 0.19 (stat) ± 0.18 (syst))%, which is an improvement of about 50% compared to a similar algorithm previously used in the LHCb experiment.

On the pair correlations of neutral K, D, B and BS mesons with close momenta produced in inclusive multiparticle processes

The phenomenological structure of inclusive cross-sections of the production of two neutral K mesons in collisions of hadrons and nuclei is investigated taking into account the strangeness conservation in strong and electromagnetic interactions. Relations describing the dependenceof the correlations of two short-lived and two long-lived neutral kaons KS∘KS∘,KL∘KL∘ and the correlations of “mixed” pairs KS∘KL∘ at small relative momenta upon the space-time parameters of the generation region of K∘ and K¯∘ mesons have been obtained. It is shown that under the strangeness conservation the correlation functions of the pairs KS∘KS∘ and KL∘KL∘, produced in the same inclusive process, coincide, and the difference between the correlation functions of the pairs KS∘KS∘ and KS∘KL∘ is conditioned exclusively by the production of the pairs of non-identical neutral kaons K∘K¯∘. Analogous correlations for the pairs of neutral heavy mesons D∘,B∘ and BS∘, generated in multiple processes with the charm (beauty) conservation, are analyzed, and differences from the case of neutral K mesons are discussed.

B-meson production at Tevatron and the LHC in the Regge limit of quantum chromodynamics

We study the inclusive hadroproduction of B0, B+, and Bs0 mesons in the leading order in the parton Reggeization approach. We have described B-meson transverse momentumdistributionsmeasured in the central region of rapidity by the CDF Collaboration at Fermilab Tevatron and CMS Collaboration at LHC within uncertainties and without free parameters, applying Kimber–Martin–Ryskin unintegrated gluon distribution function in a proton.

Study of B Meson Production in p+Pb Collisions at √[S(NN)]=5.02 TeV Using Exclusive Hadronic Decays.

The production cross sections of the B^{+}, B^{0}, and B_{s}^{0} mesons, and of their charge conjugates, are measured via exclusive hadronic decays in p+Pb collisions at the center-of-mass energy sqrt[s_{NN}]=5.02 TeV with the CMS detector at the CERN LHC. The data set used for this analysis corresponds to an integrated luminosity of 34.6 nb^{-1}. The production cross sections are measured in the transverse momentum range between 10 and 60 GeV/c. No significant modification is observed compared to proton-proton perturbative QCD calculations scaled by the number of incoherent nucleon-nucleon collisions. These results provide a baseline for the study of in-medium b quark energy loss in Pb+Pb collisions.

B0(s) → μ+μ- combination at the LHC

The combined analysis of the B0s and B0 meson decays into two muons based on the full CMS and LHCb datasets is presented. The simultaneous fit to the datasets yields the most precise measurement of the branching fractions to date with a total uncertainty of about 23% for the B0s meson and 38% for the B0 decay into two muons. The measured branching fractions are compatible with the Standard Model predictions within 1.2σ and 2.2σ for the B0s and B0 signals, respectively. The statistical significance for the B0s signal is 6.2σ and 3.2σ for the B0 signal. This results in the first observation of B0s meson decays into two muons and the first evidence for the B0 sister decay.

Final state interaction phases obtained by data from CP asymmetries

Evidence of physics beyond the Standard Model (SM) of particle physics might be revealed through CP violation. Experimental results from BaBar, Belle, and most recently from LHCb are very interesting in this respect. It is important to calculate various CP violation parameters within the SM. In this Letter, the final state interaction (FSI) phases with the CKM matrix are calculated using the recent experimental results from LHCb on CP violation in B0 and Bs0 meson decays. To obtain the allowed regions of the FSI phases, a simplified form of the Jarlskog determinant of the CKM matrix is used and the CP phase delta close to the maximal value of pi/2 is found. Then, the asymmetry data on B0 and Bs0 from LHCb is used to explore graphically the allowed regions of the FSI phases.

Measurement of the [formula omitted] and [formula omitted] production asymmetries in pp collisions at [formula omitted

The B¯0–B0 and B¯s0–Bs0 production asymmetries, AP(B0) and AP(Bs0), are measured by means of a time-dependent analysis of B0→J/ψK⁎0, B0→D−π+ and Bs0→Ds−π+ decays, using a data sample corresponding to an integrated luminosity of 1.0 fb−1, collected by LHCb in pp collisions at a centre-of-mass energy of 7 TeV. The measurements are performed as a function of transverse momentum and pseudorapidity of the B0 and Bs0 mesons within the LHCb acceptance. The production asymmetries, integrated over pT and η in the range 4<pT<30 GeV/c and 2.5<η<4.5, are determined to be AP(B0)=(−0.35±0.76±0.28)% and AP(Bs0)=(1.09±2.61±0.66)%, where the first uncertainties are statistical and the second systematic.