Branching Fraction Br Research Articles

Form factors of Λb0→Λc(2595)+ within light-cone QCD sum rules

In this work, we calculated the form factors of the weak decay process Λb0→Λc(2595)+, where the final charm baryon represents an excited state with spin-parity 12-. Utilizing the light-cone QCD sum rules approach, we incorporated the contributions of the lowest two charm baryon states: the ground state Λc with JP=12+ and the excited state Λc(2595)+ with JP=12- in the hadronic representation of the Λb→Λc(2595)+ transition correlation function. This approach allows us to extract the form factors of the Λb0→Λc(2595)+ from Λb0→Λc+ transition. During the light-cone QCD sum rules procedure, we employed the light-cone distribution amplitudes (LCDAs) of the Λb baryon. Furthermore, by combining these form factors with the helicity amplitudes of the bottom baryon transition matrix elements, we calculated the differential decay widths for the processes Λb0→Λc(2595)+ℓ-ν¯ℓ and provided the optimal choice of the interpolating current for Λc in this process. Additionally, within the lifetime of Λb0, we obtained the absolute branching fractions for the semileptonic decays Λb0→Λc(2595)+ℓ-ν¯ℓ. With the branching fractions of Λb0→Λc(2595)+ℓ-ν¯ℓ calculated in this work, we also determined the parameter R(Λc(2595)+) which tests the lepton flavor universality. This parameter is defined as the ratio of branching fractions Br(Λb0→Λc(2595)+τ-ν¯τ) and Br(Λb0→Λc(2595)+μ-ν¯μ). Our results provide a valuable theoretical test for these decay channels and offer insights into the LCDAs of bottom baryons, paving the way for further in-depth investigations.

Light new physics in B→K(*)νν¯ ?

The study of the rare decays B→K(*)νν¯ offers a window into the dynamics operating at the electroweak scale, allowing studies of the Standard Model and searches for heavy new physics. However, the analysis of these decays is also potentially sensitive to the on shell production of new light bosons X through the process B→K(*)X. In particular, Belle II has recently measured B+→K+νν¯, finding a 2.8σ excess under the assumption of heavy new physics. Since this excess is rather localized in the kaon energy, a fit that includes the decay mode B+→K+X to the kinematic distributions prefers mX≈2 GeV with branching fraction Br[B→KX]=(8.8±2.5)×10−6 and a significance of ≈3.6σ. However, no excess was found in the measurements of B→K(*)νν¯, and a global analysis of the Belle II and data leads to Br[B→KX]=(5.1±2.1)×10−6 with a reduced significance of ≈2.4σ. We then study various simplified dark-flavored models and present a possible UV completion based on a gauged B3−L3 symmetry, highlighting the discovery potential of dedicated searches for B→K(*)X at Belle II. Published by the American Physical Society 2024

Branching fraction of the decay B+ → π+τ+τ− and lepton flavor universality test via the ratio Rπ(τ/μ)

Among (semi)leptonic rare B-decays induced by the b→d flavor changing neutral current, the decay B+→π+μ+μ− is the only one observed so far experimentally. Related decays involving the e+e− and τ+τ− pairs are the targets for the ongoing experiments at the LHC, in particular LHCb, and Belle II. The muonic and electronic semileptonic decays have almost identical branching fractions in the Standard Model (SM). However, the tauonic decay B+→π+τ+τ− differs from the other two due to the higher reaction threshold which lies slightly below the ψ(2S)-resonance. We present calculations of the ditauon (τ+τ−) invariant-mass distribution and the branching fraction Br(B+→π+τ+τ−) in the SM based on the Effective Electroweak Hamiltonian approach, taking into account also the so-called long-distance contributions. The largest theoretical uncertainty in the short-distance part of the decay rates is due to the B→π form factors, which we quantify using three popular parametrizations. The long-distance contribution can be minimized by a cut on the ditauon mass mτ+τ−>Mψ(2S). Once available, the branching fractions in the tauonic and muonic (and electronic) modes provide stringent test of the lepton flavor universality in the b→d transitions. We illustrate this by calculating the ratio Rπ(τ/μ)≡Br(B+→π+τ+τ−)/Br(B+→π+μ+μ−) in the SM for the total and binned ratios of the branching fractions.

Measurements of the Absolute Branching Fractions of [formula omitted

A study of the two body decays B±→Xcc‾K±, where Xcc‾ refers to one charmonium state, is reported by the BaBar experiment using a data sample of 424 fb−1. The absolute determination of many branching fractions for these decays are significantly improved compared to previous BaBar measurements. Evidence is found at 3 σ level for the decay B+→X(3872)K+. The absolute branching fraction BR(B+→X(3872)K+)=(2.1±0.6(stat)±0.3(syst))⋅10−4 is measured for the first time. From this, it follows that the branching fraction BR(X(3872)→J/ψπ+π−) is equal to (4.1±1.3)%, supporting the hypothesis of a molecular component for this resonance.

Study of Rare Mesonic Decays Involving Di-Neutrinos in Their Final State

We have studied phenomenological implication of R-parity violating (Rp) Minimal Supersymmetric Model (MSSM) via analyses of pure leptonic (M→νν¯) and semileptonic decays of pseudoscalar mesons (M→Xνν¯). These analyses involve comparison between theoretical predictions made by Rp MSSM and the Standard Model (SM) with the experimental results like branching fractions (Br) of the said process. We have found, in general, that Rp contribution dominates over the SM contribution, i.e., by a factor of 10 for the pure leptonic decays of KL,S and by 102 and 104 in case of Bs and Bd, respectively. Furthermore, the limits obtained on Rp Yukawa couplings (λαkβ′λαkγ′⁎) by using Br (M→Xνν¯) are used to calculate Br (M→νν¯). This demonstrates the role of Rp MSSM as a viable model for the study of new physics contribution in rare decays at places like Super B factories, KOTO (J-PARC) and NA62 at CERN.

New measurements on physics of B-hadrons in ATLAS experiment

Recent results on B-hadron physics in ATLAS are reviewed. A new measurement of CP-violating parameters in B s → J/ψφ decay is performed on full Run 1 statistics. Branching fraction BR(B s → μ+μ−) = (0.9 −0.8 +1.1 )×10−9 is measured, below the Standard Model (SM) prediction.

Measurement of the running of the fine structure constant and γγ physics at KLOE-2

A measurement of the effective QED coupling constant αQED(s) in the time-like region 600–975 MeV by using the Initial State Radiation process e+e−→μ+μ−γ will be presented. It represents the first measurement of the running of αQED in this energy region. Our results show more than 5 σ significance on the hadronic contribution to the running of α(s), which is the strongest direct evidence ever achieved both in time- and space-like regions by a single experiment. By using the dipion cross section previously measured at KLOE, the Real and Imaginary part of the shift Δα has been extracted. By fitting the ReΔα, the product of the Branching Fraction BR(ω→e+e−)BR(ω→μ+μ−) has been measured. Status and prospects in γγ physics at KLOE-2 experiment will be also presented.

Measurement of the inclusive electron spectrum from B meson decays and determination of |Vub|

Based on the full BaBar data sample of 466.5 million BBbar pairs, we present measurements of the electron spectrum from semileptonic B meson decays. We fit the inclusive electron spectrum to distinguish Cabibbo-Kobayashi-Maskawa (CKM) suppressed B -> Xu e nu decays from the CKM-favored B -> Xc e nu decays, and from various other backgrounds, and determine the total semileptonic branching fraction BR(B -> X e nu) = (10.34 +- 0.04_stat +- 0.26_syst)%, averaged over B+- and B0 mesons. We determine the spectrum and branching fraction for charmless B -> Xu e nu decays and extract the CKM element |Vub|, by relying on four different QCD calculations based on the heavy quark expansion. While experimentally, the electron momentum region above 2.1GeV/c is favored, because the background is relatively low, the uncertainties for the theoretical predictions are largest in the region near the kinematic endpoint. Detailed studies to assess the impact of these four predictions on the measurements of the electron spectrum, the branching fraction, and the extraction of the CKM matrix element |Vub| are presented, with the lower limit on the electron momentum varied from 0.8GeV/c to the kinematic endpoint. We determine |Vub| using each of these different calculations and find, |Vub| = (3.794 +- 0.107_exp +0.292-0.219_SF +0.078-0.068_theory)*10^{-3} (De Fazio and Neubert), (4.563 +- 0.126_exp +0.230-0.208_SF +0.162-0.163_theory)*10^{-3} (Bosh, Lange, Neubert, and Paz), (3.959 +- 0.104_exp +0.164-0.154_SF +0.042-0.079_theory)*10^{-3} (Gambino, Giordano, Ossola, and Uraltsev), (3.848 +- 0.108_exp +0.084-0.070_theory)*10^{-3} (dressed gluon exponentiation), where the stated uncertainties refer to the experimental uncertainties of the partial branching fraction measurement, the shape function parameters, and the theoretical calculations.

Search for narrow scalar X → γγ in the mass range 65–600 GeV with the ATLAS detector

A search for scalar narrow resonance X decaying into two photons in the mass range 65-600 GeV is performed using 20 fb-1 of pp collision data collected with the ATLAS detector at s=8 TeV at the Large Hadron Collider. The signal associated to the diphoton decay of the Higgs boson with a mass of 125.9 GeV is treated as a background. No significant evidence for an additional signal is observed. The result is presented as a model-independent limit on the production cross-section times the branching fraction BR (X→γγ), in a fiducial volume where the reconstruction efficiency is independent of the event topology. The upper limits set extend over a considerably wider mass range than the limits previously set by the ATLAS and CMS collaborations.

Leptoquark induced rare decay amplitudesh→τ∓μ±andτ→μγ

Rare decay modes of the newly discovered standard-model-like Higgs boson $h$ may test the flavor changing couplings in the leptoquark sector through the process $h \to \tau^\mp\mu^\pm$. Motived by the recently reported excess in LHC data from the CMS detector, we found that a predicted branching fraction Br($h \to \tau^\mp\mu^\pm$) at the level of 1\% is possible even though the coupling parameters are subjected to the stringent constraint from the null observation of $\tau\to\mu\gamma$, where the destructive cancellation among amplitudes is achievable by fine tuning.

Bilinear $$R$$ R parity violation at the ILC: neutrino physics at colliders

Supersymmetry (SUSY) with bilinearly broken \(R\) parity (bRPV) offers an attractive possibility to explain the origin of neutrino masses and mixings. In such scenarios, the study of neutralino decays at colliders gives access to neutrino sector parameters. The ILC offers a very clean environment to study the neutralino properties as well as its subsequent decays, which typically involve a \(W\) or \(Z\) boson and a lepton. This study is based on ILC beam parameters according to the Technical Design Report for a center of mass energy of \(500~\hbox {GeV}\). A full detector simulation of the International Large Detector (ILD) has been performed for all Standard Model backgrounds and for neutralino pair production within a simplified model. The bRPV parameters are fixed according to current neutrino data. In this scenario, the \(\tilde{\chi }^0_1\) mass can be reconstructed with an uncertainty of \(\delta m^{{\mathrm {fit}}}_{\widetilde{\chi }^{0}_{1}}=(40\text {(stat.)} \oplus 50\text {(syst.)})~\hbox {MeV}\) for an integrated luminosity of \(500\,\hbox {fb}^{-1}\) from direct \(\tilde{\chi }^0_1\) pair production, thus, to a large extent independently of the rest of the SUSY spectrum. The achievable precision on the atmospheric neutrino mixing angle \(\sin ^2 \theta _{23}\) from measuring the neutralino branching fractions BR(\(\tilde{\chi }_1^0\rightarrow W\mu \)) and BR(\(\tilde{\chi }_1^0\rightarrow W \tau \)) at the ILC is in the same range than current uncertainties from neutrino experiments. Thus, the ILC could have the opportunity to unveil the mechanism of neutrino mass generation.

Invisible decay of muonium: Tests of the standard model and searches for new physics

In the Standard Model there are several canonical examples of pure leptonic processes involving the muon, the electron and the corresponding neutrinos which are connected by the crossing symmetry: i) the decay of muon, ii) the inverse muon decay, and iii) the annihilation of a muon and an electron into two neutrinos. Although the first two reactions have been observed and measured since long ago, the third process, resulting in the invisible final state, has never been experimentally tested. It may go either directly, or, at low energies, via the annihilation of a muon and an electron from an atomic bound state, called muonium (M=\mu^+e^-). The M\to \nu_\mu \nu_e decay is expected to be a very rare process, with the branching fraction predicted to be Br(M\to \nu_\mu\nu_e) = 6.6 10^{-12} with respect to the ordinary muon decay rate. Using the reported experimental results on precision measurements of the positive muon lifetime by the MuLan Collaboration, we set the first limit Br(M \to invisible) < 5.7 10^{-6}, while still leaving a big gap of about six orders of magnitude between this bound and the predictions. To improve substantially the limit, we proposed to perform an experiment dedicated to the sensitive search for the M\to invisible decay. A feasibility study of the experimental setup shows that the sensitivity of the search for this decay mode in branching fraction Br(M\to invisible) at the level of 10^{-12} could be achieved. If the proposed search results in a substantially higher branching fraction than predicted, say Br(M \to invisible) < 10^{-10}, this would unambiguously indicate the presence of new physics. We point out that such a possibility may occur due the muonium-mirror muonium conversion in the mirror matter model. A result in agreement with the Standard Model prediction would be a clean check of the pure leptonic bound state annihilation.

Search for resonances decaying toηcπ+π−in two-photon interactions

We report a study of the process gamma gamma -> X -> eta_c pi+ pi-, where X stands for one of the resonances chi_{c2}(1P), eta_c(2S), X(3872), X(3915), or chi_{c2}(2P). The analysis is performed with a data sample of 473.9 fb^{-1} collected with the BaBar detector at the PEP-II asymmetric-energy electron-positron collider. We do not observe a significant signal for any channel, and calculate 90% confidence-level upper limits on the products of branching fractions and two-photon widths Gamma(X -> gamma gamma)BR(X -> eta_c pi+ pi-): 15.7 eV for chi_{c2}(1P), 133 eV for eta_c(2S), 11.1 eV for X(3872) (assuming it to be a spin-2 state), 16 eV for X(3915) (assuming it to be a spin-2 state), and 19 eV for chi_{c2}(2P). We also report upper limits on the ratios of branching fractions BR(eta_c(2S) -> eta_c pi+ pi-)/BR(eta_c(2S)-> K_S^0 K+ pi-) < 10.0 and BR(chi_{c2}(1P) -> eta_c pi+ pi-)/BR(chi_{c2}(1P)-> K_S^0 K+ pi-) <32.9 at the 90% confidence level.

Measurement of the ratio of branching fractionsB(B0→K*0γ)/B(Bs0→ϕγ)

The ratio of branching fractions of the radiative B decays B0 -> K*0 gamma and Bs0 -> phi gamma has been measured using 0.37 fb-1 of pp collisions at a centre of mass energy of sqrt(s) = 7 TeV, collected by the LHCb experiment. The value obtained is BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) = 1.12 +/- 0.08 ^{+0.06}_{-0.04} ^{+0.09}_{-0.08}, where the first uncertainty is statistical, the second systematic and the third is associated to the ratio of fragmentation fractions fs/fd. Using the world average for BR(B0 -> K*0 gamma) = (4.33 +/- 0.15) x 10^{-5}, the branching fraction BR(Bs0 -> phi gamma) is measured to be (3.9 +/- 0.5) x 10^{-5}, which is the most precise measurement to date.

Search for the decay [formula omitted] with the ATLAS detector

A blind analysis searching for the decay Bs0→μ+μ− has been performed using proton–proton collisions at a centre-of-mass energy of 7 TeV recorded with the ATLAS detector at the LHC. With an integrated luminosity of 2.4 fb−1 no excess of events over the background expectation is found and an upper limit is set on the branching fraction BR(Bs0→μ+μ−)<2.2(1.9)×10−8 at 95% (90%) confidence level.

Bs Semileptonic Decays to Ds and Ds* in Bethe–Salpeter Method

Using the relativistic Bethe–Salpeter method, the electron energy spectrum and the semileptonic decay widths of Bs0 → Ds−ℓ+νℓ and Bs0 → Ds*−ℓ+νℓ are calculated. We obtain a large branching fraction Br(Bs → Dseνe) = (2.85 ± 0.35)% and Br(Bs → Ds*eνe) = (7.09 ± 0.88)%, which can be easily detected in future experiments.

Search for Invisible Decays of theΥ(1S)

We search for invisible decays of the Upsilon(1S) meson using a sample of 91.4 x 10^{6} Upsilon(3S) mesons collected at the BaBar/PEP-II B-factory. We select events containing the decay Upsilon(3S) -> pi+ pi- Upsilon(1S) and search for evidence of an undetectable Upsilon(1S) decay recoiling against the dipion system. We set an upper limit on the branching fraction BR(Upsilon(1S) -> invisible) < 3.0 x 10^{-4} at the 90% confidence level.

- 0 Mixing as a Possible Origin of the Hypothetical Isospin Non-Conservation in the X(3872) -&gt; + -J/ Decay

The ratio of branching fractions Br(X(3872) --> gamma J/psi)/ Br(X(3872) --> pi^+ pi^- J/psi) is studied by assuming that the X(3872) --> pi^+ pi^- J/psi decay proceeds through the rho^0 meson pole which is caused by the omega-rho^0 mixing. As the result, it is seen that the calculated ratio is compatible with the measured values of the ratio when X(3872) is an axial-vector tetra-quark state, while it would be much larger than the measurements when it is a charmonium. Therefore, the existing data on the ratio seem to favor the tetra-quark interpretation of X(3872) over the charmonium, although a small mixing of the charmonium is not excluded.

Dalitz analysis ofB→Kπ+ψ′decays and theZ(4430)+

From a Dalitz plot analysis of B --> K pi psi' decays, we find a signal for Z(4430)+ --> pi+ psi' with a mass M= (4443(+15-12)(+19-13))MeV/c^2, width Gamma= (107(+86-43)(+74-56))MeV, product branching fraction BR(B0 --> K- Z(4430)+) x BR(Z(4430)+ --> pi+ psi')= (3.2(+1.8-0.9)(+5.3-1.6)) x 10^{-5}, and significance of 6.4sigma that agrees with previous Belle measurements based on the same data sample. In addition, we determine the branching fraction BR(B^0 --> K*(892)^0 psi')= (5.52(+0.35-0.32)(+0.53-0.58)) x 10^{-4} and the fraction of K*(892)^0 mesons that are longitudinally polarized f_L= 44.8(+4.0-2.7)(+4.0-5.3)%. These results are obtained from a 605fb^{-1} data sample that contains 657 million B-anti-B pairs collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy e+e- collider.

Evidence forB+→K¯*0K*+

We present measurements of the branching fraction and fraction of longitudinal polarization for the decay B+ -> K*0bar K*+ with a sample of 467 +/- 5 million BBbar pairs collected with the BaBar detector at the PEP-II asymmetric-energy e+e- collider at the SLAC National Accelerator Laboratory. We obtain the branching fraction Br(B+ -> K*0bar K*+) = (1.2 +/- 0.5 +/- 0.1) x 10^{-6} with a significance of 3.7 standard deviations including systematic uncertainties. We measure the fraction of longitudinal polarization f_L = 0.75+0.16-0.26 +/- 0.03. The first error quoted is statistical and the second is systematic.