Decay Branching Ratios Research Articles

Decays of B, B_s and B_c to D-wave heavy\u2013light mesons

We study the weak decays of bar{B}_{(s)} and B_c into D-wave heavy–light mesons, including J^P=2^- (D_{(s)2},D'_{(s)2},B_{(s)2}, B'_{(s)2}) and 3^- (D^*_{(s)3}, B^*_{(s)3}) states. The weak decay hadronic matrix elements are obtained based on the instantaneous Bethe–Salpeter method. The branching ratios for the bar{B} decays are mathcal {B}[bar{B}rightarrow D_{2}e{bar{nu }}_e] = 1.1^{-0.3}_{+0.3} times 10^{-3}, mathcal {B}[bar{B}rightarrow D'_2e{bar{nu }}_e]=4.1^{-0.8}_{+0.9} times 10^{-4}, and mathcal {B}[bar{B}rightarrow D^*_3e{bar{nu }}_e]=1.0^{-0.2}_{+0.2} times 10^{-3}, respectively. For the semi-electronic decays of bar{B}_s to D_{s2}, D'_{s2}, and D^*_{s3}, the corresponding branching ratios are 1.7^{-0.5}_{+0.5}times 10^{-3}, 5.2^{-1.5}_{+1.6}times 10^{-4}, and 1.5^{-0.4}_{+0.4}times 10^{-3}, respectively. The branching ratios of the semi-electronic decays of B_c to D-wave D mesons are in the order of 10^{-5}. We also obtained the forward–backward asymmetry, angular spectra, and lepton momentum spectra. In particular the distribution of decay widths for the 2^- states D_2 and D'_2 varying along with mixing angle are presented.

Kaon Flavour Physics Strikes Back

In this short presentation I emphasize the increased importance of kaon flavour physics in the search for new physics (NP) that we should witness in the rest of this decade and in the next decade. The main actors will be the branching ratios for the rare decays and , to be measured by NA62 and KOTO, and their correlations with the ratio ε′/ε on which recently progress by lattice QCD and large N dual QCD approach has been made implying a new flavour anomaly. Further correlations of , and ε′/ε with εK, ΔMK, KL → μ+ μ− and will help us to identify indirectly possible NP at short distance scales. This talk summarizes the present highlights of this facinating field including some results from concrete NP scenarios.

Next-to-leading order prediction for the decay mu to ekern0.22em left({e}^{+}{e}^{-}right);nu kern0.2em overline{nu}

We present the differential decay rates and the branching ratios of the muon decay with internal conversion, mu to ekern0.22em left({e}^{+}{e}^{-}right);nu kern0.2em overline{nu} , in the Standard Model at next-to-leading order (NLO) in the on-shell scheme. This rare decay mode of the muon is among the main sources of background to the search for μ → eee decay. We found that in the phase space region where the neutrino energies are small, and the three-electron momenta have a similar signature as in the μ → eee decay, the NLO corrections decrease the leading-order prediction by about 10 − 20% depending on the applied cut.

The Kaon identification system of the NA62 experiment

The main goal of the NA62 experiment at the CERN SPS is to measure the branching ratio of the ultra-rare decay with 10% accuracy. This can be achieved by detecting about 100 Standard Model events with 10% background in 2 - 3 years of data taking. NA62 is exposed to a 750 MHz high-energy unseparated charged hadron beam, with a 6% kaons component, and uses kaon decay-in-flight technique. Precise timing matching of the incident kaon and of the downstream charged track is essential to reject accidental coincidences when working in such a high rate environment. This is achieved by the kaon tagging system KTAG, which identifies kaons with an efficiency higher than 95% and provides precise time information with a resolution better than 100 ps. KTAG re-uses the Cherenkov radiator and optics of a CEDAR, a ring-focusing Cherenkov detector designed for MHz beam intensity in the 1970s. To reach the required performance, KTAG is equipped with new photon detectors, electronics readout, mechanics, cooling and safety systems.

Prospects for exotics and LFV at NA62

The NA62 experiment at the CERN SPS is designed to measure the branching ratio of the ultra-rare decay with 10% precision. For this purpose the experiment aims to collect of the order of 100 events which would require at least 1013K+ decays in the fiducial volume of the detector. The large sample of K+ decays that will be available at NA62 allows the experiment to carry out a rich program for rare and forbidden K+ and π0 decays, including lepton flavour and/or number violating modes, sterile neutrinos, exotic particles (e.g. Dark Photons). NA62’s potential for such searches in K+ and π0 decays is discussed, with initial sensitivity estimates. In addition, plans for continuing the experiment after 2021 (Long Shutdown 2) are presented, including in particular the possibility to operate in a beam-dump mode for exploring various Dark Matter scenarios.

Measurement of with NA48/2 at CERN

The exclusive branching ratio of the radiative decay is measured using data collected by the NA48/2 experiment at CERN in 2003-2004. The measurement is performed in the phase-space region of the mass of the electron-positron pair, . This is the most accurate measurement of the exclusive . The result, is compatible with the theoretical value, 8.51 × 10−8, calculated using the Chiral Perturbation Theory framework at next-to-leading order.

Rare four-leptonic B-decays with light leptons in the final state in the Standard Model

We present predictions for the four-leptonic decays of B−-mesons with three light charged leptons and one neutrino in the final states. We obtain the branching ratio for decay at the level 1.3 × 10−7 taking into account the photon emission from the u- and b- valence quarks of B− –meson and the Bremsstrahlung. The contribution of the virtual photon was calculated using the Vector Meson Dominance model (VMD). As a next step we present prediction for branching ratio of the decay and the estimation for .

Coupled channels approach to photo-meson production on the nucleon

The coupled channels Lagrangian approach of the Giessen model (GiM) for meson production on the nucleon is discussed and applied to a selected set of meson production channels on the nucleon, ranging from πN → πN and γ N → π N , eta-production and associated strangeness production to 2π N channels in the resonance energy region. We present an updated coupled-channel analysis of eta-meson production including all recent photoproduction data on the proton. The dip structure observed in the differential cross sections at c.m. energies W=1.68 GeV is explained by destructive interference between the S 11 (1535) and S 11 (1560) states, not confirming the postulated sharp state. Kaon production on the nucleon is investigated in K Λ and K Σ exit channels. The approach to 2π N production has been significantly improved by using the isobar approximation with σN and π Δ1232 intermediate states. Three-body unitarity is maintained up to interference between the isobar subchannels. We obtain R σ N (1440)=27+4 -9 % and R π Δ (1440)=12+5 -3 % for the for the σ N and π Δ1232 decay branching ratios of N *(1440) respectively. The extracted π N inelasticities and reaction amplitudes are consistent with the results of other groups.

FCNC decays of standard model fermions into a dark photon

We analyze a new class of FCNC processes, the $f \to f^{\prime} \, \bar{\gamma}$ decays of a fermion $f$ into a lighter (same-charge) fermion $f^{\prime}$ plus a {\it massless} neutral vector boson, a {\it dark photon} $\bar{\gamma}$. A massless dark photon does not interact at tree level with observable fields, and the $f \!\to\! f^{\prime} \, \bar{\gamma}$ decay presents a characteristic signature where the final fermion $f^{\prime}$ is balanced by a {\it massless invisible} system. Models recently proposed to explain the exponential spread in the standard-model Yukawa couplings can indeed foresee an extra unbroken {\it dark} $U(1)$ gauge group, and the possibility to couple on-shell dark photons to standard-model fermions via one-loop magnetic-dipole kind of FCNC interactions. The latter are suppressed by the characteristic scale related to the mass of heavy messengers, connecting the standard model particles to the dark sector. We compute the corresponding decay rates for the top, bottom, and charm decays ($t\to c\, \bar{\gamma},u\, \bar{\gamma}$, $\;b\to s\, \bar{\gamma},d\, \bar{\gamma}$, and $c\to u \bar{\gamma}$), and for the charged-lepton decays ($\tau \to \mu\, \bar{\gamma}, e\, \bar{\gamma}$, and $\mu \to e \bar{\gamma}$) in terms of model parameters. We find that large branching ratios for both quark and lepton decays are allowed in case the messenger masses are in the discovery range of the LHC. Implications of these new decay channels at present and future collider experiments are briefly discussed.

Search for massive neutrinos in π + → e + ν e ${\pi }^{+}{\rightarrow }e^{+}{\nu }_{e}$ decay

The PIENU experiment aims to measure the branching ratio of the charged pion decay with precision of < 0.1 %. This measurement is much sensitive to search for massive neutrinos coupled to electrons in ${\pi }^{+}{\rightarrow }e^{+}{\nu }_{e}$ decay. The initial analysis was completed and the upper limit on the neutrino mixing parameter |U e i |2 in the neutrino mass range of 0 to 55 MeV/c 2 was improved by a factor of 1.5, and the sensitivity for the mass range of 68 to 129 MeV/c 2 was improve by a factor of up to 4.

Direct measurement of low-energyNe22(p,γ)Na23resonances

The $^{22}$Ne(p,$\gamma$)$^{23}$Na reaction is the most uncertain process in the neon-sodium cycle of hydrogen burning. At temperatures relevant for nucleosynthesis in asymptotic giant branch stars and classical novae, its uncertainty is mainly due to a large number of predicted but hitherto unobserved resonances at low energy. Purpose: A new direct study of low energy $^{22}$Ne(p,$\gamma$)$^{23}$Na resonances has been performed at the Laboratory for Underground Nuclear Astrophysics (LUNA), in the Gran Sasso National Laboratory, Italy. Method: The proton capture on $^{22}$Ne was investigated in direct kinematics, delivering an intense proton beam to a $^{22}$Ne gas target. $\gamma$ rays were detected with two high-purity germanium detectors enclosed in a copper and lead shielding suppressing environmental radioactivity. Results: Three resonances at 156.2 keV ($\omega\gamma$ = (1.48\,$\pm$\,0.10)\,$\cdot$\,10$^{-7}$ eV), 189.5 keV ($\omega\gamma$ = (1.87\,$\pm$\,0.06)\,$\cdot$\,10$^{-6}$ eV) and 259.7 keV ($\omega\gamma$ = (6.89\,$\pm$\,0.16)\,$\cdot$\,10$^{-6}$ eV) proton beam energy, respectively, have been observed for the first time. For the levels at 8943.5, 8975.3, and 9042.4 keV excitation energy corresponding to the new resonances, the $\gamma$-decay branching ratios have been precisely measured. Three additional, tentative resonances at 71, 105 and 215 keV proton beam energy, respectively, were not observed here. For the strengths of these resonances, experimental upper limits have been derived that are significantly more stringent than the upper limits reported in the literature. Conclusions: Based on the present experimental data and also previous literature data, an updated thermonuclear reaction rate is provided in tabular and parametric form. The new reaction rate is significantly higher than previous evaluations at temperatures of 0.08-0.3 GK.

Charged lepton flavor-violating transitions in color octet model

We study charged lepton flavor-violating (LFV) transitions in the color octet model that generates neutrino mass and lepton mixing at one loop. By taking into account neutrino oscillation data and assuming octet particles of TeV scale mass, we examine the feasibility to detect these transitions in current and future experiments. We find that for general values of parameters the branching ratios for LFV decays of the Higgs and $Z$ bosons are far below current and even future experimental bounds. For LFV transitions of the muon, the present bounds can be satisfied generally, while future sensitivities could distinguish between the singlet and triplet color-octet fermions. The triplet case could be ruled out by future $\mu-e$ conversion in nuclei, and for the singlet case the conversion and the decays $\mu\to 3e,~e\gamma$ play complementary roles in excluding relatively low mass regions of the octet particles.

Status of Pion Decay Experiments

The branching ratio of pion decays, , has provided a sensitive test of electron-muon universality in weak interactions. The uncertainty of the Standard Model prediction is at a 0.01% level. Although a recent measurement, Re/μ = (1.2344 ± 0.0023(stat) ± 0.0019(syst)) × 10-4, reduced the experimental uncertainty by a factor of two, there is room for improvement by more than an order of magnitude. The status of two experiments at TRIUMF and PSI as well as related pion decay experiments is presented.

Charged lepton flavor violating processes and scalar leptoquark decay branching ratios in the colored Zee-Babu model

We consider a neutrino mass generating model which employs a scalar leptoquark, $\Delta$, and a scalar diquark, $S$. The new scalars $\Delta$ and $S$ carry the standard model $SU(3)_c\times SU(2)_L\times U(1)_Y$ quantum numbers $(3,1,-1/3)$ and $(6,1,-2/3)$, respectively. The neutrino masses are generated at the two-loop level, as in the Zee-Babu model\cite{Zee-Babu}, and $\Delta/S$ plays the role of the doubly/singly charged scalar in the Zee-Babu model. With a moderate working assumption that the magnitudes of the six Yukawa couplings between $S$ and the down-type quarks are of the same order, strong connections are found between the neutrino masses and the charged lepton flavor violating processes. In particular, we study $Z\rightarrow \overline{l} l'$, and $l\rightarrow l' \gamma$ and find that some portions of the parameter space of this model are within the reach of the planned charged lepton flavor violating experiments. Interesting lower bounds are predicted that $B(Z\rightarrow \overline{l} l')\gtrsim 10^{-16}-10^{-14}(10^{-14})\times(1\mbox{TeV}\cdot m_S/7 m_\Delta^2)^2$ and $B(l\rightarrow l' \gamma)\gtrsim 10^{-17}-10^{-16}(10^{-18}-10^{-16})\times(1 \mbox{TeV}\cdot m_S/7 m_\Delta^2)^2$ for neutrino masses being the normal(inverted) hierarchical pattern. The type of neutrino mass hierarchy could also be determined by measuring the charged lepton flavor violating double ratios. Moreover, definite leptoquark decay branching ratios are predicted when there is no Yukawa interaction between the right-handed fermions and $\Delta$ ( the branching fraction of $\Delta$ to a charged lepton and a quark is 50\%), which could help refine the collider search limit on the scalar leptoquark mass.

Higgs production in association with a top-antitop pair in the Standard Model Effective Field Theory at NLO in QCD

We present the results of the computation of the next-to-leading order QCD corrections to the production cross section of a Higgs boson in association with a top-antitop pair at the LHC, including the three relevant dimension-six operators ($O_{t \varphi }, O_{\varphi G}, O_{tG}$) of the standard model effective field theory. These operators also contribute to the production of Higgs bosons in loop-induced processes at the LHC, such as inclusive Higgs, $Hj$ and $HH$ production, and modify the Higgs decay branching ratios for which we also provide predictions. We perform a detailed study of the cross sections and their uncertainties at the total as well as differential level and of the structure of the effective field theory at NLO including renormalisation group effects. Finally, we show how the combination of information coming from measurements of these production processes will allow to constrain the three operators at the current and future LHC runs. Our results lead to a significant improvement of the accuracy and precision of the deviations expected from higher-dimensional operators in the SM in both the top-quark and the Higgs-boson sectors and provide a necessary ingredient for performing a global EFT fit to the LHC data at NLO accuracy.

Revisiting the exclusion limits from direct chargino-neutralino production at the LHC

We revisit the existing limits on the gaugino masses in various Supersymmetric (SUSY) scenarios derived from Run-I data of the LHC. These limits obtained from the various final states rely heavily on the simplified assumptions regarding the masses, compositions and decay branching ratios of the gauginos. The most promising exclusion limits on the gaugino masses are obtained from trilepton final states while the second lightest neutralino ($\widetilde \chi_2^0$) decaying into the SM-like Higgs and lightest SUSY particle (LSP) results in the weakest bounds. Our aim is to assess the extent of deviation of these exclusion limits in more realistic scenarios. After a brief discussion on the various decay modes of the $\widetilde \chi_2^0$ and the lightest chargino ($\widetilde \chi^{\pm}_1$), we proceed to validate the ATLAS exclusion limits obtained from trilepton, $l\gamma\gamma$ and $lb\bar b$ final states associated with missing energy. We then consider different combinations of the relevant branching ratios to study their impact on the existing bounds. The results are presented alongside the existing exclusion limits to showcase the extent of the obtained deviation. We also observe that the three-body decay modes of $\widetilde \chi_2^0$ and $\widetilde \chi^{\pm}_1$ via off-shell slepton decays resulting in trilepton final states provide bounds that are far more severe in some parts of the available parameter space than that obtained from the usual two-body decay modes of the aforementioned gauginos.

Heavy pseudoscalar twist-3 distribution amplitudes within QCD theory in background fields

In this paper, we study the properties of the twist-3 distribution amplitude (DA) of the heavy pseudo-scalars such as $\eta_c$, $B_c$ and $\eta_b$. New sum rules for the twist-3 DA moments $\left<\xi^n_P\right>_{\rm HP}$ and $\left<\xi^n_\sigma\right>_{\rm HP}$ up to sixth orders and up to dimension-six condensates are deduced under the framework of the background field theory. Based on the sum rules for the twist-3 DA moments, we construct a new model for the two twist-3 DAs of the heavy pseudo-scalar with the help of the Brodsky-Huang-Lepage prescription. Furthermore, we apply them to the $B_c\to\eta_c$ transition form factor ($f^{B_c\to\eta_c}_+(q^2)$) within the light-cone sum rules approach, and the results are comparable with other approaches. It has been found that the twist-3 DAs $\phi^P_{3;\eta_c}$ and $\phi^\sigma_{3;\eta_c}$ are important for a reliable prediction of $f^{B_c\to\eta_c}_+(q^2)$. For example, at the maximum recoil region, we have $f^{B_c\to\eta_c}_+(0) = 0.674 \pm 0.066$, in which those two twist-3 terms provide $\sim33\%$ and $\sim22\%$ contributions. Also we calculate the branching ratio of the semi-leptonic decay $B_c \to\eta_c l\nu$ as $Br(B_c \to\eta_c l\nu) = \left( 9.31^{+2.27}_{-2.01} \right) \times 10^{-3}$.

Single production ofX±5/3andY∓4/3vectorlike quarks at the LHC

Two triplet vector-like quarks (VLQs) with hypercharges of $Y=2/3, -1/3$ and one singlet scalar boson are embedded in the standard model (SM) to resolve the 750 GeV diphoton excess. The constraints on the tree-level Higgs- and $Z$-mediated flavor-changing neutral currents are discussed in detail. Besides the resolution of excess, it is found that the signal strength of diphoton Higgs decay can have a $10\%$ deviation from the SM prediction and that the upper limits of the branching ratios for rare top-quark decays are $BR(t\to c (h, Z)) < (6.8, 0.48) \times 10^{-5}$. We find that the production cross section of a single VLQ by electroweak processes is larger than that of VLQ-pair by QCD processes. To explore the signals of the heavy VLQs at the LHC, we throughly analyze the production of single $X_{\pm 5/3}$ and $Y_{\mp 4/3}$ via $q_i q'_j$ annihilations in $pp$ collisions at $\sqrt{s}=13$ TeV. It is found that the electroweak production cross sections for $d X_{5/3}$, $u Y_{-4/3} $, and $d Y_{4/3} $ channels with $m_X=m_Y=1$ TeV can be $84.3$, $72.3$, and $157.8$ fb, respectively; and the dominant decay modes are $X_{5/3} \to (c,t) W^+$ and $Y_{-4/3} \to (s,b) W^-$. With adopting kinematic cuts, the significance for $pp\to d W^+ t$ channel can be over $5\sigma$.

D → a1, f1 transition form factors and semileptonic decays via 3-point QCD sum rules

By using the 3-point QCD sum rules, we calculate the transition form factors of [Formula: see text] decays into the spin triplet axial vector mesons [Formula: see text], [Formula: see text], [Formula: see text]. In the calculations, we consider the quark contents of each meson in detail. In view of the fact that the isospin of [Formula: see text] is one, we calculate the [Formula: see text] and [Formula: see text] transition form factors separately. In the case of [Formula: see text], [Formula: see text], the mixing between light flavor [Formula: see text] singlet and octet is taken into account. Based on the form factors obtained here, we give predictions for the branching ratios of relevant semileptonic decays, which can be tested in the future experiments.

New class of SO(10) models for flavor

We present a new class of unified models based on SO(10) symmetry which provides insights into the masses and mixings of quarks and leptons, including the neutrinos. The key feature of our proposal is the absence of Higgs boson 10_H belonging to the fundamental representation that is normally employed. Flavor mixing is induced via vector-like fermions in the 16 + 16-bar representation. A variety of scenarios, both supersymmetric and otherwise, are analyzed involving a 126_H along with either a 45_H or a 210_H of Higgs boson employed for symmetry breaking. It is shown that this framework, with only a limited number of parameters, provides an excellent fit to the full fermion spectrum, utilizing either type-I or type-II seesaw mechanism. These flavor models can be potentially tested and distinguished in their predictions for proton decay branching ratios, which are analyzed.