Branching Ratio BR Research Articles

LARGE SU(3) BREAKING EFFECTS AND CP VIOLATION IN B+ DECAYS INTO THREE CHARGED OCTET PSEUDOSCALAR MESONS

The LHCb collaboration has recently reported evidence for nonzero CP asymmetries in B+ decays into π+K+K-, π+π+π-, K+K+K- and K+π+π-. The branching ratios for these decays have also been measured with different values ranging from 5×10-6 to 51×10-6. If flavor SU(3) symmetry is a good symmetry for B decays, in the case that the dominant amplitude is momentum independent it is expected that branching ratios Br and CP violating rate differences [Formula: see text] satisfy, Br (π+π+π-) = 2 Br (π+K+K-), Br (K+K+K-) = 2 Br (K+π+π-) and Δ CP (π+π+π-) = 2Δ CP (π+K+K-) = -Δ CP (K+K+K-) = -2Δ CP (K+π+π-). The experimental data do not exhibit the expected pattern for the branching ratios. The rate differences for B+→π+π+π- and B+→K+ K+ K- satisfy the relation between ΔS = 0 and ΔS = 1 as well, but the other two do not, with the CP asymmetries having different signs than expected. In this paper, we study how to include momentum dependent and also SU(3) breaking effects on these decays to explain experimental data. We find that by including only the lowest order derivative terms, in the SU(3) limit, the decay patterns cannot be explained. Large SU(3) breaking effects are needed to explain the data.

An extra Z′ gauge boson as a source of Higgs particles

Models with extra gauge bosons are well motivated extensions of the standard model (SM) because of their connection with several unification schemes. These models include an extended Higgs sector in order to break the gauge symmetry and generate the required masses. The resulting spectrum of Higgs bosons could be searched for at current and future colliders using SM-like production mechanisms. However, the existence of the new gauge bosons could provide new production mechanisms, which could be used to probe the non-standard properties of Higgs particles. In this paper, we study the 3-body decays of the Z′ associated with a model with an extra U(1)′, which could be used as a source of Higgs bosons. We find that the decays of a Z′ into a Higgs boson and a top–anti-top pair, namely , can reach branching ratios (Br′s) as high as 10−3, which could be detected at future colliders. We also study the production of Higgs bosons in association with the Z vector boson at a linear collider, through the reaction e+e− → Z, Z′ → Z + h, including both the resonant and non-resonant effects.

The inclusive decay [formula omitted] revisited

The inclusive decay rate b→cc¯s is enhanced considerably due to perturbative QCD corrections. We recalculate the dominant part of the NLO–QCD corrections, because they cannot be reconstructed from the literature and we give the full expressions in this paper. Further we include some previously neglected corrections originating from penguin diagrams. Combined with the impressive progress in the accurate determination of input parameters like charm quark mass, bottom quark mass and CKM parameters, this enables us to make a very precise prediction of the corresponding branching ratio Br(b→cc¯s)=(23±2)%. This result is an essential ingredient for a model and even decay channel independent search for new physics effects in B decays.

Search for the CP violating KS → 3π° decay with the KLOE detector

We present a new search for the KS → 3π0 decay performed with the KLOE detector operating at the DAΦNE ϕ-factory. The KS mesons were tagged via registration of KL mesons which crossed the drift chamber without decaying and interacted with the KLOE electromagnetic calorimeter. The KS → 3π0 decay was then searched requiring six prompt photons. To suppress background, originating from fake KS tags and KS → 2π0 decays with additional two spurious clusters, we have performed a discriminant analysis based on kinematical fit, testing of the signal and background hypotheses and exploiting of the differences in kinematics of the KS decays into 2π0 and 3π0. In a sample of about 1.7·109 ϕ → KSKL events we have found no candidates in data and simulated background samples. Normalizing to the number of KS → 2π0 events in the same sample, we have set the upper limit on the KS → 3π0 branching ratio BR(KS → 3π0) < 2.6 · 10−8 at 90% C.L., five times lower than the previous limit. This upper limit can be translated into a limit on the modulus of the η000 parameter amounting to |η000| < 0.0088 at 90% C.L., improving by a factor two the latest direct measurement.

Search for pair production of heavy top-like quarks decaying to a high-[formula omitted]W boson and a b quark in the lepton plus jets final state at [formula omitted] with the ATLAS detector

A search is presented for production of a heavy up-type quark (t′) together with its antiparticle, assuming a significant branching ratio for subsequent decay into a W boson and a b quark. The search is based on 4.7 fb−1 of pp collisions at s=7 TeV recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. Data are analyzed in the lepton+jets final state, characterized by a high-transverse-momentum isolated electron or muon, large missing transverse momentum and at least three jets. The analysis strategy relies on the substantial boost of the W bosons in the t′t¯′ signal when mt′≳400 GeV. No significant excess of events above the Standard Model expectation is observed and the result of the search is interpreted in the context of fourth-generation and vector-like quark models. Under the assumption of a branching ratio BR(t′→Wb)=1, a fourth-generation t′ quark with mass lower than 656 GeV is excluded at 95% confidence level. In addition, in light of the recent discovery of a new boson of mass ∼126 GeV at the LHC, upper limits are derived in the two-dimensional plane of BR(t′→Wb) versus BR(t′→Ht), where H is the Standard Model Higgs boson, for vector-like quarks of various masses.

A search for flavour changing neutral currents in top-quark decays in pp collision data collected with the ATLAS detector at $ \sqrt{s}=7\;TeV $

Abstract A search for flavour changing neutral current (FCNC) processes in top-quark decays by the ATLAS Collaboration is presented. Data collected from pp collisions at the LHC at a centre-of-mass energy of $ \sqrt{s}=7\;TeV $ during 2011, corresponding to an integrated luminosity of 2.1 fb−1, were used. A search was performed for top-quark pair-production events, with one top quark decaying through the t → Zq FCNC (q = u, c) channel, and the other through the Standard Model dominant mode t → W b. Only the decays of the Z boson to charged leptons and leptonic W -boson decays were considered as signal. Consequently, the final-state topology is characterised by the presence of three isolated charged leptons, at least two jets and missing transverse momentum from the undetected neutrino. No evidence for an FCNC signal was found. An upper limit on the t → Zq branching ratio of BR(t → Zq) &lt; 0.73% is set at the 95% confidence level.

The birds and the Bs in RS: the b → sγ penguin in a warped extra dimension

We calculate contributions to the photon and gluon magnetic dipole operators that mediate b -> s gamma and b -> d gamma transitions in the Randall-Sundrum model of a warped extra dimension with anarchic bulk fermions and a brane localized Higgs. Unlike the Standard Model, there are large contributions to the left-handed b quark decays, parameterized by the Wilson coefficient C'_7, due to the pattern of bulk fermion localization, and sizable contributions from the gluonic penguins, C(')_8, through renormalization group mixing. Further, unlike the Randall-Sundrum result for mu -> e gamma, the unprimed Wilson coefficients receive non-negligible contributions from the misalignment of the bulk fermion spectrum with the Standard Model flavor sector. We compare the size of effects and the constraints imposed by the branching ratios Br(B -> X_s gamma) and <Br(B -> X_d gamma)> within the minimal and the custodial model. Within the custodial framework, we study the effect on a number of benchmark observables and find that Br(B -> X_s mu^+ mu^-) and the forward-backward asymmetry in B -> K^* mu^+ mu^- remain close to their Standard Model predictions. On the other hand, there can be large enhancements of the time-dependent CP asymmetry in B -> K^* gamma and the transverse asymmetry A_T^(2).

Search for charged Higgs bosons in e+e- collisions at [Formula: see text

A search is made for charged Higgs bosons predicted by Two-Higgs-Doublet extensions of the Standard Model (2HDM) using electron-positron collision data collected by the OPAL experiment at sqrt{s}=189mbox{--}209 mbox{GeV}, corresponding to an integrated luminosity of approximately 600 pb−1. Charged Higgs bosons are assumed to be pair-produced and to decay into mathrm{q} bar{mathrm{q}}, τντ or AW±. No signal is observed. Model-independent limits on the charged Higgs-boson production cross section are derived by combining these results with previous searches at lower energies. Under the assumption mathrm{BR} (mathrm{H}^{pm} to taunu_{tau}) + mathrm{BR} (mathrm{H}^{pm} to mathrm{q} bar{mathrm{q}}) = 1, motivated by general 2HDM type II models, excluded areas on the [m_{mathrm{H}^{pm}} , mathrm{BR} (mathrm {H}^{pm} to taunu_{tau})] plane are presented and charged Higgs bosons are excluded up to a mass of 76.3 GeV at 95 % confidence level, independent of the branching ratio BR(H±→τντ). A scan of the 2HDM type I model parameter space is performed and limits on the Higgs-boson masses m_{mathrm{H}^{pm}} and mA are presented for different choices of tanβ.

Flavor violating processes with sgoldstino pair production

In supersymmetric extensions of the Standard Model of particle physics (SM), goldstino superpartners --- scalar and pseudoscalar sgoldstinos --- can be light enough for emerging in decays of SM particles. Sgoldstino interaction with SM fields is suppressed by the scale of supersymmetry breaking in the whole theory. Hence, searches for sgoldstinos give an opportunity to probe the underlying mechanism of supersymmetry breaking. Sgoldstino couplings to SM fields are proportional to the supersymmetry breaking parameters --- MSSM soft terms --- and therefore can lead to flavor violating processes in quark and lepton sectors. We consider flavor violating processes involving sgoldstino pair production which are driven by sgoldstino couplings proportional to squark and slepton soft mass terms, \tilde{m^2_{LL}} and \tilde{m^2_{RR}}. We find that present limits on off-diagonal entries in squark and slepton squared mass matrices allow t-, b-, c-quark and \tau-lepton decays at levels available for study with existing data (BaBar, Belle, CLEOc) and in ongoing experiments (LHCb, CMS, ATLAS). In particular, we obtain the following branching ratios Br(t--> c SP)\lesssim 10^{-7}, Br(\tau--> \mu SP) \lesssim 10^{-7}, Br(B_s--> SP) \lesssim 10^{-4}, Br(B--> K^{(*)} SP) \lesssim 10^{-4}, Br(D--> SP) \lesssim 10^{-7} with sgoldstino subsequent decays into kinematically allowed pairs of SM particles \gamma\gamma, e^+e^-, \mu^+\mu^-, etc. Remarkably, the prominent signature of sgoldstino pair production is two muon pairs with pair momenta peaked at sgoldstino masses.

Z′→gggdecay in left-right symmetric models with three and four fermion families

We study the ${Z}^{\ensuremath{'}}\ensuremath{\rightarrow}\overline{q}q,ggg$ decays in the context of a manifest left-right symmetric gauge theory with three and four generations. The ${Z}^{\ensuremath{'}}$ couplings to quarks are fixed essentially by the parameters of the standard model and we obtain $\ensuremath{\Gamma}({Z}^{\ensuremath{'}}\ensuremath{\rightarrow}q\overline{q})\ensuremath{\approx}14\text{ }\text{ }\mathrm{GeV}$ for ${M}_{{Z}^{\ensuremath{'}}}\ensuremath{\approx}1\text{ }\text{ }\mathrm{TeV}$. For the ${Z}^{\ensuremath{'}}\ensuremath{\rightarrow}ggg$ decay and three families we obtain a branching ratio $\mathrm{BR}({Z}^{\ensuremath{'}}\ensuremath{\rightarrow}ggg)=\frac{\ensuremath{\Gamma}({Z}^{\ensuremath{'}}\ensuremath{\rightarrow}ggg)}{\ensuremath{\Gamma}({Z}^{\ensuremath{'}}\ensuremath{\rightarrow}q\overline{q})}=1.2\ensuremath{-}2.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ for ${m}_{{Z}^{\ensuremath{'}}}=700--1500\text{ }\text{ }\mathrm{GeV}$. The fourth generation produces an enhancement in the branching ratio for ${Z}^{\ensuremath{'}}$ masses close to the ${\overline{b}}^{\ensuremath{'}}{b}^{\ensuremath{'}}$ threshold and a dip for ${Z}^{\ensuremath{'}}$ masses close to the ${\overline{t}}^{\ensuremath{'}}{t}^{\ensuremath{'}}$ threshold. Using the values of the fourth-generation quark masses allowed by electroweak precision data, we obtain a branching ratio $\mathrm{BR}({Z}^{\ensuremath{'}}\ensuremath{\rightarrow}ggg)=(1\ensuremath{-}6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ for ${m}_{{Z}^{\ensuremath{'}}}=(700--1500)\text{ }\text{ }\mathrm{GeV}$.

Formula omitted] bremsstrahlung as the dominant annihilation channel for dark matter, revisited

We revisit the calculation of electroweak bremsstrahlung contributions to dark matter annihilation. Dark matter annihilation to leptons is necessarily accompanied by electroweak radiative corrections, in which a W or Z boson is also radiated. Significantly, while many dark matter models feature a helicity suppressed annihilation rate to fermions, bremsstrahlung process can remove this helicity suppression such that the branching ratios Br(ℓνW), Br(ℓ+ℓ−Z), and Br(ν¯νZ) dominate over Br(ℓ+ℓ−) and Br(ν¯ν). We find this is most significant in the limit where the dark matter mass is nearly degenerate with the mass of the boson which mediates the annihilation process. Electroweak bremsstrahlung has important phenomenological consequences both for the magnitude of the total dark matter annihilation cross section and for the character of the astrophysical signals for indirect detection. Given that the W and Z gauge bosons decay dominantly via hadronic channels, it is impossible to produce final state leptons without accompanying protons, antiprotons, and gamma rays.

Determination of the η-transition form factor in the [formula omitted] reaction

The Dalitz decay η→γe+e− has been measured using the combined Crystal Ball and TAPS photon detector setup at the electron accelerator MAMI-C. Compared to the most recent transition form-factor measurement in the e+e− channel, statistics have been improved by one order of magnitude. The e+e− invariant mass distribution shows a deviation from the QED prediction for a point-like particle, which can be described by a form-factor. Using the usual monopole transition form-factor parameterization, F(m2)=(1−m2/Λ2)−1, a value of Λ−2=(1.92±0.35(stat)±0.13(syst)) GeV−2 has been determined. This value is in good agreement with a recent measurement of the η Dalitz decay in the μ+μ− channel and with recent form-factor calculations. An improved value of the branching ratio BR(η→γe+e−)=(6.6±0.4(stat)±0.4(syst))⋅10−3 has been determined.

Calibration and monitoring of the MEG experiment by a proton beam from a Cockcroft–Walton accelerator

The MEG experiment at PSI searches for the decay μ → e γ at a level of ≈ 10 − 13 on the branching ratio BR ( μ → e γ / μ → tot ), well beyond the present experimental limit ( BR ≤ 1.2 × 10 − 11 ) and is sensitive to the predictions of SUSY-GUT theories. To reach this goal the experiment uses one of the most intense continuous surface muon beams available ( ≈ 10 8 μ / s ) and relies on advanced technology (LXe calorimetry, a gradient-field superconducting spectrometer as well as flexible and powerful trigger and acquisition systems). In order to maintain the highest possible energy, time and spatial resolutions for such detector, frequent calibration and monitoring, using a Cockcroft–Walton proton accelerator, are required. The proton beam is brought to the centre of MEG by a special bellows insertion system and travels in a direction opposite to the one of the normal μ ‐ beam . Protons interact with a lithium tetraborate (Li 2B 4O 7) nuclear target and produce one γ (17.6 MeV) from the reaction Li ( p , γ ) 3 7 Be 4 8 or two coincident γ s (11.67 and 4.4 MeV) from the reaction B ( p , γ 1 ) 5 11 C ⁎ 6 12 . The 17.6 MeV γ is used for calibrating and monitoring the LXe calorimeter ( σ E γ / E γ = 3.85 ± 0.15 % at 17.6 MeV) while the coincident 11.67 and 4.4 MeV γ s are used to measure the relative timing of the calorimeter and the spectrometer timing counters ( σ Δ t = 0.450 ± 0.015 ns ).

W/Zbremsstrahlung as the dominant annihilation channel for dark matter

Dark matter annihilation to leptons, $\chi \chi \rightarrow l \bar{l}$, is necessarily accompanied by electroweak radiative corrections, in which a W or Z boson is radiated from a final state particle. Given that the W and Z gauge bosons decay dominantly via hadronic channels, it is thus impossible to produce final state leptons without accompanying protons, antiprotons, and gamma rays. Significantly, while many dark matter models feature a helicity suppressed annihilation rate to fermions, radiating a massive gauge boson from a final state fermion removes this helicity suppression, such that the branching ratios Br(l \nu W), Br(l^+l^- Z), and Br(\nu\nubar Z) dominate over Br(l\bar{l}). W/Z-bremsstrahlung thus allows indirect detection of many WIMP models that would otherwise be helicity-suppressed, or v^2 suppressed. Antiprotons and even anti-deuterons become consequential final state particles. This is an important result for future DM searches. We discuss the implications of W/Z-bremsstrahlung for "leptonic" DM models which aim to fit recent cosmic ray positron and antiproton data.

Lepton flavor violation in complex SUSY seesaw models with nearly tribimaximal mixing

We survey the lepton flavor violation branching ratios Br(mu->e,gamma), Br(tau->mu,gamma), and Br(tau->e,gamma) in mSUGRA for a broad class of lepton mass matrix textures that give nearly tribimaximal lepton mixing. Small neutrino masses are generated by the type-I seesaw mechanism with non-degenerate right-handed neutrino masses. The textures exhibit a hierarchical mass pattern and can be understood from flavor models giving rise to large leptonic mixing. We study the branching ratios for the most general CP-violating forms of the textures. It is demonstrated that the branching ratios can be enhanced by 2-3 orders of magnitude as compared to the CP-conserving case. The branching ratios exhibit, however, a strong dependence on the choice of the phases in the Lagrangian which affects the significance of flavor models. In particular, for general CP-phases, the lepton flavor violating rates appear to be essentially uncorrelated with the possible high- and low-energy lepton mixing parameters, such as the reactor angle.

Fluorescence features of Sm3+ ions in Na2SO4–MO–P2O5 glass system—Influence of modifier oxide

Abstract Na2SO4–P2O5:Sm3+ glasses mixed with three different alkaline earth modifier oxides viz., MgO, CaO and BaO were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature; the Judd–Ofelt theory was successfully applied to characterize these spectra. From this theory, various radiative properties like transition probability A, branching ratio βr, the radiative lifetime τr, for various emission levels in the spectra of these glasses have been determined and reported. An attempt has also been made to throw some light on the relationship between the structural modifications and luminescence efficiencies in the change of scenario for modifying oxides in the glass network.

Influence of Crystallization on the Luminescence Characteristics of Pr3+ Ions in PbO–Sb2O3–B2O3 Glass System

PbO–Sb2O3–B2O3 glasses mixed with different concentrations of Pr2O3 (ranging from 0 to 0.6 mol%) were crystallized. The samples were characterized by X‐ray diffraction (XRD) and transmission electron microscopy techniques. The XRD studies have revealed the presence of Pb5Sb2O8, Pb3(SbO4)2, PbB4O7, β‐PrSbO4, Pr3SbO7, and Pr3Sb5O12 crystalline phases. Optical absorption (in the visible and NIR regions) and fluorescence spectra of these samples have been recorded at room temperature. The Judd–Ofelt theory could successfully be applied to characterize the absorption and luminescence spectra of Pr3+ ions in these samples. From the luminescence spectra, various radiative properties like transition probability A, branching ratio βr, and the radiative lifetime τr for various emission levels originating from the 3P0 level of Pr3+ ion in the glasses glass ceramic samples have been evaluated. The radiative lifetime of the 3P0→3H6 transition is measured and the quantum efficiency has been estimated. The crystallization causes to improve the luminescence efficiency to a large extent. The changes observed in the radiative properties due to crystallization have been discussed in the light of varying co‐ordinations of antimony ions in the glass network.

TENSION BETWEEN SCALAR/PSEUDOSCALAR NEW PHYSICS CONTRIBUTION TO Bs → μ+μ- AND B → Kμ+μ-

New physics in the form of scalar/pseudoscalar operators cannot lower the semileptonic branching ratio Br (B → K μ+μ-) below its standard model value. In addition, we show that the upper bound on the leptonic branching ratio Br (Bs → μ+μ-) sets a strong constraint on the maximum value of Br (B → K μ+μ-) in models with multiple Higgs doublets: with the current bound, Br (B → K μ+μ-) cannot exceed the standard model prediction by more than 2.5%. The conclusions hold true even if the new physics couplings are complex. However, these constraints can be used to restrict new physics couplings only if the theoretical and experimental errors in Br (B → K μ+μ-) are reduced to a few per cent. The constraints become relaxed in a general class of models with scalar/pesudoscalar operators.

Study ofBc→KKdecay with perturbative QCD approach

In the framework of the perturbative QCD approach, we study the charmless pure weak annihilation Bc->KK decay and find that the branching ratio BR(Bc->KK) O(10^-7). This prediction is so tiny that the Bc->KK decay might be unmeasurable at the Large Hadron Collider.

A limit for the [formula omitted] decay from the MEG experiment

A search for the decay μ + → e + γ , performed at PSI and based on data from the initial three months of operation of the MEG experiment, yields an upper limit on the branching ratio of BR ( μ + → e + γ ) ⩽ 2.8 × 10 − 11 (90% C.L.). This corresponds to the measurement of positrons and photons from ∼ 10 14 stopped μ + -decays by means of a superconducting positron spectrometer and a 900 litre liquid xenon photon detector.