B-meson Decay Research Articles

CP-violating polarization asymmetry in charmless two-body decays of beauty baryons

Several baryons containing a heavy b-quark, the b-baryons, have been discovered. The charmless two-body decays of b-baryons can provide a new platform for CP violating studies in a similar way as charmless two-body decays of B-meson. In b-baryon decays there are new CP violating observable related to baryon polarization. We show that in the flavor $SU(3)$ limit there exist relations involve different combinations of the decay amplitudes compared with those in CP violating rate asymmetry. These new relations therefore provide interesting tests for the mechanism of CP in the standard model (SM) and flavor $SU(3)$ symmetry. Future data from LHCb can test these relations.

Updated Next-to-Next-to-Leading-Order QCD Predictions for the Weak Radiative B-Meson Decays.

Weak radiative decays of the B mesons belong to the most important flavor changing processes that provide constraints on physics at the TeV scale. In the derivation of such constraints, accurate standard model predictions for the inclusive branching ratios play a crucial role. In the current Letter we present an update of these predictions, incorporating all our results for the O(α_{s}^{2}) and lower-order perturbative corrections that have been calculated after 2006. New estimates of nonperturbative effects are taken into account, too. For the CP- and isospin-averaged branching ratios, we find B_{sγ}=(3.36±0.23)×10^{-4} and B_{dγ}=(1.73_{-0.22}^{+0.12})×10^{-5}, for E_{γ}>1.6 GeV. Both results remain in agreement with the current experimental averages. Normalizing their sum to the inclusive semileptonic branching ratio, we obtain R_{γ}≡(B_{sγ}+B_{dγ})/B_{cℓν}=(3.31±0.22)×10^{-3}. A new bound from B_{sγ} on the charged Higgs boson mass in the two-Higgs-doublet-model II reads M_{H^{±}}>480 GeV at 95% C.L.

B -meson decay constants from 2+1 -flavor lattice QCD with domain-wall light quarks and relativistic heavy quarks

We calculate the B-meson decay constants f_B, f_Bs, and their ratio in unquenched lattice QCD using domain-wall light quarks and relativistic b-quarks. We use gauge-field ensembles generated by the RBC and UKQCD collaborations using the domain-wall fermion action and Iwasaki gauge action with three flavors of light dynamical quarks. We analyze data at two lattice spacings of a ~ 0.11, 0.086 fm with unitary pion masses as light as M_pi ~ 290 MeV; this enables us to control the extrapolation to the physical light-quark masses and continuum. For the b-quarks we use the anisotropic clover action with the relativistic heavy-quark interpretation, such that discretization errors from the heavy-quark action are of the same size as from the light-quark sector. We renormalize the lattice heavy-light axial-vector current using a mostly nonperturbative method in which we compute the bulk of the matching factor nonperturbatively, with a small correction, that is close to unity, in lattice perturbation theory. We also improve the lattice heavy-light current through O(alpha_s a). We extrapolate our results to the physical light-quark masses and continuum using SU(2) heavy-meson chiral perturbation theory, and provide a complete systematic error budget. We obtain f_B0 = 199.5(12.6) MeV, f_B+ = 195.6(14.9) MeV, f_Bs = 235.4(12.2) MeV, f_Bs/f_B0 = 1.197(50), and f_Bs/f_B+ = 1.223(71), where the errors are statistical and total systematic added in quadrature. These results are in good agreement with other published results and provide an important independent cross check of other three-flavor determinations of $B$-meson decay constants using staggered light quarks.

Semileptonic B decays at Belle

Recent results from the Belle experiment on semileptonic decays of B-mesons are reviewed, including their effect on the determination of the CKM matrix elements |Vcb| and |Vub|.

A combined fit on the annihilation corrections in [formula omitted] decays within QCDF

Motivated by the possible large annihilation contributions implied by recent CDF and LHCb measurements on nonleptonic annihilation B-meson decays, and the refined experimental measurements on hadronic B-meson decays, we study the strength of annihilation contributions within QCD factorization (QCDF) in this paper. With the available measurements of two-body Bu,d,s→ππ,πK,KK decays, a comprehensive fit on the phenomenological parameters XAi,f (or ρAi,f and ϕAi,f) which are used to parameterize the endpoint singularity in annihilation amplitudes is performed with the statistical χ2 approach. It is found that (1) flavor symmetry breaking effects are hardly to be distinguished between XA,si and XA,di due to the large experimental errors and theoretical uncertainties, where XA,si and XA,di are related to the nonfactorization annihilation contributions in Bs and Bu,d decay, respectively. So XA,si≃XA,di is a good approximation by now. (2) In principle, parameter XAf which is related to the factorization annihilation contributions and independent of the initial state can be regarded as the same variable for Bu,d,s decays. (3) Numerically, two solutions are found, one is (ρAi,ϕAi[°])=(2.98−0.86+1.12,−105−24+34) and (ρAf,ϕAf[°])=(1.18−0.23+0.20,−40−8+11), the other is (ρAi,ϕAi[°])=(2.97−0.90+1.19,−105−24+32) and (ρAf,ϕAf[°])=(2.80−0.21+0.25,165−3+4). Obviously, nonfactorization annihilation parameter XAi is generally unequal to factorization annihilation parameter XAf, which differs from the traditional treatment. With the fitted parameters, all results for observables of Bu,d,s→ππ,πK,KK decays are in good agreement with experimental data.

A comprehensive analysis of hadronic b → s transitions in a family non-universal Z′ model

Motivated by the latest improved measurements of B-meson decays, we make a comprehensive analysis of the impact of a family non-universal boson on mixing and two-body hadronic B-meson decays, all being characterized by the quark-level transition. Explicitly 22 decay modes and the related 52 observables are considered, and some interesting correlations between them are also carefully examined. Firstly, the allowed oases of coupling parameters and are extracted from mixing. Then, in the ‘SM limit’ (i.e., no new types of -induced four-quark operators arise compared to the SM case), we study the effects on , and decays. It is found that a new weak phase is crucial for resolving the observed ‘ CP puzzle’ and the allowed cases of the other coupling parameters are also strongly restricted. Moreover, the effects on , and decays, being induced by the same quark-level transitions, are also investigated. In particular, it is found that the decay , once measured, would play a key role in revealing the observed ‘ CP puzzle’ and probing possible new physics hints. Finally, to check the non-universality of couplings to light-quark pairs, we have studied the decays in detail and found that the left-handed coupling is different from the one, which is due to the large reported by the BaBar Collaboration.

Decay constants of B-mesons from non-perturbative HQET with two light dynamical quarks

We present a computation of B-meson decay constants from lattice QCD simulations within the framework of Heavy Quark Effective Theory for the b-quark. The next-to-leading order corrections in the HQET expansion are included non-perturbatively. Based on Nf=2 gauge field ensembles, covering three lattice spacings a≈(0.08–0.05) fm and pion masses down to 190 MeV, a variational method for extracting hadronic matrix elements is used to keep systematic errors under control. In addition we perform a careful autocorrelation analysis in the extrapolation to the continuum and to the physical pion mass limits. Our final results read fB=186(13) MeV, fBs=224(14) MeV and fBs/fB=1.203(65). A comparison with other results in the literature does not reveal a dependence on the number of dynamical quarks, and effects from truncating HQET appear to be negligible.

Searching for the origin of CP violation in Cabibbo-suppressed D-meson decays

The recent evidence of large direct CP violation in D0 decay at LHCb suggests that such CP studies may become an important avenue for understanding CP. In this paper, we make several suggestions to try to clarify the role of new physics in these results. We propose that the enhancement needed in the Standard Model to attribute the observed CP violation in D to two pseudoscalar modes may not operate for inclusive final states where asymmetries will likely approximate the quark level expectation. Experimentally testing this principle requires a search for CP asymmetries in final states containing K and K-bar with a total energy of less than M_D. We also propose that CP asymmetries may be enhanced in modes where the tree is color suppressed. In particular, the final state rho0 rho0 is of special interest; similarly Ds-> rho0 K+ and rho0 K*+ likewise appear interesting. We discuss how isospin symmetry yields observables sensitive to certain classes of new physics and suppressed in the Standard Model. Some modes considered in this context are D-> pi pi, rho pi, rho rho as well as Ds-> K* pi. We also consider how such analysis may eventually be supplemented by information about the weak phases in D0 decay. In order to obtain this information experimentally, we consider various methods for preparing an initial state which is a quantum mechanical mixture of D0 and D0-bar. This may be done through the use of natural D0 D0-bar oscillations; observing D0-mesons which arise from Bd or Bs mesons which themselves are oscillating or from quantum correlations in D0 pairs which arise from either psi" decay or B-meson decay. Observing CP violation in the magnitudes of decay amplitudes should be within the capability of experiments in the near future however obtaining the weak phases through the methods we discuss will likely require future generations of machines.

Full 1-loop calculation of BR([formula omitted]) in models beyond the MSSM with SARAH and SPheno

We present the possibility of calculating the quark flavor changing neutral current decays Bs0→ℓℓ̄ and Bd0→ℓℓ̄ for a large variety of supersymmetric models. For this purpose, the complete one-loop calculation has been implemented in a generic form in the Mathematica package SARAH. This information is used by SARAH to generate Fortran source code for SPheno for a numerical evaluation of these processes in a given model. We comment also on the possibility to use this setup for non-supersymmetric models. Program summaryProgram title: SARAHCatalogue identifier: AEIB_v2_1Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEIB_v2_1.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 467777No. of bytes in distributed program, including test data, etc.: 3927691Distribution format: tar.gzProgramming language: Mathematica, Fortran.Computer: All computers which can run Mathematica and SPheno.Operating system: Linux, MacOS.Classification: 11.1, 11.6.Catalogue identifier of previous version: AEIB_v2_0Journal reference of previous version: Comput. Phys. Comm. 184 (2013) 1792Does the new version supercede the previous version?: Yes, the new version includes all known features of previous versions but provides also the new features mentioned below.Nature of problem:Models beyond the SM can have new contributions to the decays of neutral B-mesons. For a precise prediction of the corresponding branching ratios a full 1-loop calculation including all possible wave, penguin and box diagrams is necessary. This usually requires a big effort and public codes for these calculations so far only support a few selected models.Solution method:The implementation of a new model in SARAH is easy and straightforward. In addition, SARAH is already delivered with many different supersymmetric and a few non-supersymmetric models. As a first step, SARAH derives the analytical expressions for masses, interactions and renormalization group equations for the given model. Furthermore, SARAH checks for all possible tree- and 1-loop diagrams which can contribute to the B-meson decays into two leptons. This information is exported to Fortran source code which can afterwards be compiled with SPheno. This generates a fully functional spectrum generator: besides the mass spectrum, sparticle and Higgs decays the new SPheno modules also calculate precision observables like the B-meson decays based on the parameters chosen by the user.Reasons for new version:The possible decays of neutral B-mesons into two leptons are constraining models beyond the Standard Model. SARAH allows, in the new version, the production of SPheno source code to calculate those decays at full 1-loop for a large variety of models.Summary of revisions:Full 1-loop calculation of Bs,d0→ℓℓ̄ for any model which can be implemented in SARAH.Restrictions:SARAH can only calculate the renormalization group equations for a supersymmetric model. Hence, for a non-supersymmetric model it is not possible to calculate the running parameters which enter the calculation. These have to be provided by the user as input. In addition, the effects of chiral resummation as well as next-to-leading order QCD corrections known for the MSSM are not included.Unusual features:This is the first public tool which allows a full 1-loop calculation of B-meson decays in more complicated models than the minimal or next-to-minimal supersymmetric standard model. Any new contribution in a renormalizable model stemming from an extended matter content or gauge sector is taken into account.Running time:Measured CPU time for the evaluation of the MSSM using a Lenovo Thinkpad X220 with i7 processor (2.53 GHz). Calculating the complete Lagrangian: 9 s. Calculating all vertices: 51 s. Output of the UFO model files: 49 s.

Light inflaton after LHC8 and WMAP9 results

We update the allowed parameter space of the simple chaotic inflationary model with quartic potential and light inflaton [Bezrukov,Gorbunov'2009] taking into account recent results from cosmology (CMB observations from SPT, ACT and WMAP) and from particle physics (LHC hints of the SM Higgs boson). The non-minimal (yet small) coupling to gravity of the inflaton becomes essential to fit the observational data. The inflaton has mass above 300 MeV and can be searched for at B-factories in B-meson two-body decays to kaon and inflaton. The inflaton lifetime depends on the model parameters, resulting in various inflaton signatures: either a missing energy, or a displaced vertex from the B-meson decay position, or a resonance in the Dalitz plot of a three particle decay. We also discuss the implementation of the inflaton model to the nuMSM, where the inflaton can be responsible for production of the dark matter sterile neutrino in the early Universe.

Nonperturbative tuning of an improved relativistic heavy-quark action with application to bottom spectroscopy

We calculate the masses of bottom mesons using an improved relativistic action for the b-quarks and the RBC/UKQCD Iwasaki gauge configurations with 2+1 flavors of dynamical domain-wall light quarks. We analyze configurations with two lattice spacings: a^{-1} = 1.729 GeV (a ~ 0.11 fm) and a^{-1} = 2.281 GeV (a ~ 0.086 fm). We use an anisotropic, clover-improved Wilson action for the b-quark, and tune the three parameters of the action nonperturbatively such that they reproduce the experimental values of the B_s and B_s* heavy-light meson states. The masses and mass-splittings of the low-lying bottomonium states (such as the eta_b and Upsilon) can then be computed with no additional inputs, and comparison between these predictions and experiment provides a test of the validity of our method. We obtain bottomonium masses with total uncertainties of ~0.5-0.6% and fine-structure splittings with uncertainties of ~35-45%; for all cases we find good agreement with experiment. The parameters of the relativistic heavy-quark action tuned for b-quarks presented in this work can be used for precise calculations of weak matrix elements such as B-meson decay constants and mixing parameters with lattice discretization errors that are of the same size as in light pseudoscalar meson quantities. This general method can also be used for charmed meson masses and matrix elements if the parameters of the heavy-quark action are appropriately tuned.

Revisiting the Γ(K→eν)/Γ(K→μν) ratio in supersymmetric unified models

It has been pointed out that supersymmetric extensions of the Standard Model can induce significant changes to the theoretical prediction of the ratio Γ(K→eν)/Γ(K→μν)≡R K , through lepton flavour violating couplings. In this work we carry out a full computation of all one-loop corrections to the relevant νlH + vertex, and discuss the new contributions to R K arising in the context of different constrained (minimal supergravity-inspired) models which succeed in accounting for neutrino data, further considering the possibility of accommodating a near-future observation of a μ→eγ transition. We also re-evaluate the prospects for R K in the framework of unconstrained supersymmetric models. In all cases, we address the question of whether it is possible to saturate the current experimental sensitivity on R K while in agreement with the recent limits on B-meson decay observables (in particular BR(B s →μ + μ −) and BR(B u →τν)), as well as BR(τ→eγ) and available collider constraints. Our findings reveal that in view of the recent bounds, and even when enhanced by effective sources of flavour violation in the right-handed $\tilde{e}-\tilde{\tau}$ sector, constrained supersymmetric (seesaw) models typically provide excessively small contributions to R K . Larger contributions can be found in more general settings, where the charged Higgs mass can be effectively lowered, and even further enhanced in the unconstrained MSSM. However, our analysis clearly shows that even in this last case SUSY contributions to R K are still unable to saturate the current experimental bounds on this observable, especially due to a strong tension with the B u →τν bound.

Search for theZ1(4050)+andZ2(4250)+states inB¯0→χc1K−π+andB+→χc1KS0π+

We search for the Z1(4050)+ and Z2(4250)+ states, reported by the Belle Collaboration, decaying to χc1π+ in the decays B¯0→χc1K−π+ and B+→χc1KS0π+ where χc1→J/ψγ. The data were collected with the BABAR detector at the SLAC PEP-II asymmetric-energy e+e− collider operating at center-of-mass energy 10.58 GeV, and correspond to an integrated luminosity of 429 fb−1. In this analysis, we model the background-subtracted, efficiency-corrected χc1π+ mass distribution using the Kπ mass distribution and the corresponding normalized Kπ Legendre-polynomial moments, and then test the need for the inclusion of resonant structures in the description of the χc1π+ mass distribution. No evidence is found for the Z1(4050)+ and Z2(4250)+ resonances, and 90% confidence level upper limits on the branching fractions are reported for the corresponding B-meson decay modes.5 MoreReceived 25 November 2011DOI:https://doi.org/10.1103/PhysRevD.85.052003© 2012 American Physical Society

B-meson semi-inclusive decay to2−+charmonium in nonrelativistic QCD andX(3872)

The semi-inclusive B-meson decay into spin-singlet D-wave $2^{-+}$ charmonium, $B\to \eta_{c2}+X$, is studied in nonrelativistic QCD (NRQCD). Both color-singlet and color-octet contributions are calculated at next-to-leading order (NLO) in the strong coupling constant $\alpha_s$. The non-perturbative long-distance matrix elements are evaluated using operator evolution equations. It is found that the color-singlet $^1D_2$ contribution is tiny, while the color-octet channels make dominant contributions. The estimated branching ratio $B(B\to \eta_{c2}+X)$ is about $0.41\,\times10^{-4}$ in the Naive Dimensional Regularization (NDR) scheme and $1.24\,\times10^{-4}$ in the t'Hooft-Veltman (HV) scheme, with renormalization scale $\mu=m_b=4.8$\,GeV. The scheme-sensitivity of these numerical results is due to cancelation between ${}^1S_0^{[8]}$ and ${}^1P_1^{[8]}$ contributions. The $\mu$-dependence curves of NLO branching ratios in both schemes are also shown, with $\mu$ varying from $\frac{m_b}{2}$ to $2m_b$ and the NRQCD factorization or renormalization scale $\mu_{\Lambda}$ taken to be $2m_c$. Comparison of the estimated branching ratio of $B\to \eta_{c2}+X$ with the observed branching ratio of $B \to X(3872)+K$ may lead to the conclusion that X(3872) is unlikely to be the $2^{-+}$ charmonium state $\eta_{c2}$.

CP violation studies at Belle

CP-violation in the Standard Model (SM) is described by a single parameter and the pattern of possible CP-violating phenomena is thus extremely constrained. The Belle experiment at the KEK laboratory in Tsukuba (Japan) is testing if this pattern actually occurs by analyzing a sample of about 770 million B-meson decays. CP-violation observed at Belle is consistent with the Cabibbo-Kobayashi-Maskawa (CKM) mechanism, the theory of CP-violation within the SM. We briefly describe how the unitarity triangle allows to probe the CKM theory and review recent measurements of its angles and sides, namely determinations of the CKM angles ϕ 1 and ϕ 3, and the CKM magnitudes |V cb | and |V ub |.

Nuclear suppression of : From RHIC to the LHC

A parameter-free calculation for J/Psi suppression in pA collisions, based on the dipole description, is confronted with the new data from the PHENIX experiment. Achieving good agreement, we employed this model predicting the contribution of initial state interactions (ISI) to J/Psi suppression in AA collisions. Such a transition from pA to AA is not straightforward, since involves specific effects of double color filtering and boosting of the saturation scale. Relying on this refined ISI contribution, we updated the previous analysis of RHIC data on J/Psi production in Cu-Cu and Au-Au collisions at \sqrt{s}=200 GeV, and determined the transport coefficient of the created dense medium at q_0=0.6 GeV^2/fm. Nuclear effects for J/Psi production at the LHC are predicted using the transport coefficient q_0=0.8 GeV^2/fm, extracted from data on suppression of high-p_T hadrons in central lead-lead collisions at \sqrt{s}=2.76 TeV. Our analysis covers only direct J/Psi production, while data may also include the feed-down from decay of heavier states and B-mesons.

First performance results for the LHCb Silicon Tracker

The LHCb detector is a single arm forward spectrometer designed to study the decays of B-mesons in proton-proton collisions at the Large Hadron Collider (LHC). The LHCb Silicon Tracker (ST) is a silicon micro-strip detector with a sensitive area of 12 m 2 and a total of 272 thousand readout channels. The detector, which was fully installed by early summer 2008, currently has more than 99% of channels fully functioning. We present the results of calibration and performance studies of the ST using data collected by the experiment during LHC proton-proton collisions in late 2009 and spring 2010.

A Comparative Study of fB within QCD Sum Rules with Two Typical Correlators up to Next-to-Leading Order

The B-meson decay constant fB is an important component for studying the B-meson decays, which can be studied through QCD sum rules. We make a detailed discussion on fB from two sum rules up to next-to-leading order, i.e. sum rules I and II, which are derived from the conventional correlator and the correlator with chiral currents respectively. It is found that these two sum rules are consistent with each other. The sum rules II involves less non-perturbative condensates as that of sum rules I, and in principle, it can be more accurate if we know the dimension-four gluon condensate well. It is found that fB decreases with the increment of mb, and to compare with the Belle experimental data on fB, both sum rules I and II prefer smaller pole b-quark mass, mb = 4.68 ± 0.07 GeV. By varying all the input parameters within their reasonable regions and by adding all the uncertainties in quadrature, we obtain fB = 172+23−25 MeV for sum rules I and fB = 214+26−34 MeV for sum rules II.

Search for Non-Standard Model Physics in Rare Decays at the Tevatron

In this proceeding we report the most recent results from the CDF and DØ collaborations on the rare decays of b-mesons. The presented results show a new DØ limit for B ( B s 0 → μ + μ − ) that represent the best single measurement on this mode so far, an update of the B ( B s 0 → ϕ ϕ ) with, for the first time, an angular analysis on the final state, a new measurement of the B ( B 0 → K ⋆ 0 μ + μ − ) and B ( B + → K + μ + μ − ) with an interesting measurement on the forward-backward asymmetry for those channels and the first observation of the B ( B s 0 → ϕ μ + μ − ) .

Measurement ofCPviolating asymmetries inB0→K+K−KS0decays with a time-dependent Dalitz approach

We report a measurement of CP violating asymmetries in B0(B¯0)→K+K−KS0 decays with a time-dependent Dalitz approach. This analysis is based on a data sample of 657×106 BB¯ pairs accumulated at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. As the result of an unbinned maximum likelihood fit to the selected candidates, the mixing-induced and direct CP violation parameters ϕ1eff and ACP are obtained for B0→ϕ(1020)KS0, B0→f0(980)KS0, and other B0→K+K−KS0 decays. We find four solutions that describe the data. There are ϕ1eff(B0→ϕ(1020)KS0)=(32.2±9.0±2.6±1.4)°;ϕ1eff(B0→ϕ(1020)KS0)=(26.2±8.8±2.7±1.2)°;ϕ1eff(B0→ϕ(1020)KS0)=(27.3±8.6±2.8±1.3)°;andϕ1eff(B0→ϕ(1020)KS0)=(24.3±8.0±2.9±5.2)°. The values for the CP violating phase in B0→ϕ(1020)KS0 are similar, but other properties of the Dalitz plot are quite different for the four solutions. These four solutions have consistent ϕ1eff values for all three B-meson decay channels and none of them deviates significantly from the values measured in B→(cc¯)K0 decays with the currently available statistics. In addition, we find no significant direct CP violation.Received 22 July 2010DOI:https://doi.org/10.1103/PhysRevD.82.073011© 2010 The American Physical Society