Narrow Results

Using the effective Lagrangian method, we analyze the corrections to the branching ratio b→sγ from the Higgs sector in the standard model. The numerical result indicates that the corrections from this sector to b→sγ is about -2% as m_h~ 0.5 TeV.

We discuss the corrections from the Kaluza–Klein (KK) modes to the branching ratio of the rare process in extension of the standard model with a universal extra dimension, which was proposed by Appelquist, Cheng and Dobrescu (ACD). Assuming 1/R≫m_W, we sum over the series composed by the KK towers, and get the decoupling result in the limit 1/R→∞. The numerical analysis indicates that the corrections from the KK-excitations to the branching ratio of is about 3.5% as 1/R = 400 GeV.

The Belle collaboration has reported for the inclusive decay . Recently, the LHCb and the CMS collaboration has released the combined limit . The standard model results of the and are found to be within the 1σ of the experimental result. Taking a conservative viewpoint, we use these decays to constrain the braneworld Randall–Sundrum model. The stabilized radion in the Randall–Sundrum model, which is an electro-weak singlet, can cause the flavor changing neutral current (FCNC) b →s transition at the oneloop level. We investigate the possible impact of a stabilized radion on the above two decays and obtain the possible constraints on the radion vev 〈ϕ〉 for an ultra-light radion.

The μνSSM, one of supersymmetric extensions beyond the Standard Model, introduces three singlet right-handed neutrino superfields to solve the μ problem and can generate three tiny Majorana neutrino masses through the seesaw mechanism. In this paper, we investigate the rare decay process in the μνSSM, under a minimal flavor violating assumption for the soft breaking terms. Constrained by the SM-like Higgs with mass around 125 GeV, the numerical results show that the new physics can fit the experimental data for and further constrain the parameter space.

A search for rare decay η′ → 4 π⁰ has been performed with GAMS-4π setup. The new upper limit is BR(η′ → 4 π⁰) < 3.2 ⋅10^-4 at 90% confidence level. The π^- p charge-exchange reaction at 32.5 GeV/c was used as a source of 1.3⋅10⁶η′ mesons. Experiment was carried out at the IHEP U-70 accelerator.

We present an analytic calculation of Branching Ratio (BR) and Charge-Parity (CP) violating asymmetries of the $B_s^0$ meson decays to $D^{+}{D}^{-}$ by calculating the amplitude and the decay width of the process including the chiral loop and gluon condensate to first-order. We find the BR of $B_s^0\to D_s^{+}{D}_s^{-}=(1.8\pm 0.4)\times 10^{-3}$ which is in agreement with other experimental measurements and theoretical predictions. We also calculate the direct CP violation, CP violation in mixing and CP violation due to interference which are $A_{\mathrm{\text{CP}}}^{\mathrm{\text{dir}}}=0.00348\pm 0.00012$, $(A_{\mathrm{\text{CP}}}^{\mathrm{\text{mix}}})=-0.04395\pm 0.00129$ and $(A_{\mathrm{\Delta }\mathrm{\Gamma }})=-0.99903\pm 0.00122$, respectively.

The upcoming upgrades of Large Hadron Collider (LHC) to High Luminosity LHC (HL-LHC) and the proposed Future Circular Collider (FCC-hh) offer an opportunity of observing the Lepton Flavor Violating (LFV) process beyond the Standard Model. Monte Carlo simulation of generating and detecting an LFV process $B^{+}\to K^{+}{\mu }^{-}{\tau }^{+}$ on CMS at LHC (Run-3), HL-LHC, and FCC-hh reference detector (FRD) is performed. This process is favored by the leptoquark models, particularly the three-site Pati–Salam model but disfavored by the gauged $L_{\mu }-L_{\tau }$ model, both of which are introduced to address the $B$ anomalies. We study possible backgrounds with similar final states and use Multi-Variable Analysis (MVA) to discriminate signal events from possible backgrounds. The MVA output is used to estimate Single Event Sensitivity (SES) of this process, yielding encouraging results on CMS at HL-LHC and FRD at FCC-hh with considerable SES values of about $0.0696\pm 0.0010\mathrm{\text{fb}}$ (CMS, LHC Run-3), $0.0070\pm 0.0001\mathrm{\text{fb}}$ (CMS, HL-LHC) and $0.1389\pm 0.0006\mathrm{\text{ab}}$ (FRD, FCC-hh), suggesting it’s promising to probe such process in the future high energy physics experiments and constrain the new physics models more rigorously.

B meson rare decays ( and B → K* γ) are analyzed in the framework of effective field theory of heavy quarks. The semileptonic and penguin type form factors for these decays are calculated by using the light cone sum rules method at the leading order of 1/m_Q expansion. Four exact relations between the two types of form factors are obtained at the leading order of 1/m_Q expansion. In particular, the relations are found to hold for the whole momentum transfer region. We also investigate the validity of the relations resulting from the large energy effective theory based on the general relations obtained in the present approach. The branching ratios of the rare decays are presented and their potential importance for extracting the CKM matrix elements and probing new physics is emphasized.

We present results for measurements of the decays to charmless final states of B⁰ meson to ηK⁰, ηω, with , and of B⁺ to ηρ⁺, η′π⁺. Analyses are based on data taken with the BABAR detector at the PEP-II asymmetric e⁺e^- collider at SLAC. We measure the following branching fractions in units of , , , , and . The charge asymmetries are and . First error is statistical, the second systematic. All results are preliminary.

Electromagnetic radiative penguin decays of the B meson were studied with the BABAR detector at SLAC's PEP-II asymmetric-energy B Factory. Branching fractions and isospin asymmetry of the decay B → K*γ, branching fractions of , and a search for B⁰ → ϕγ are presented. The decay rates may be enhanced by contributions from non-standard model processes.

In this paper, we calculate rare top quark 2-body and 3-body decays in the littlest Higgs Model with T-parity (LHT). We find that the branching ratios of $t\to cX$$(X=g,\gamma ,Z,H)$ and $t\to c{X}_1{X}_2$$(X=g,\gamma ,Z,H,f)$ can be greatly enhanced in the LHT model in the allowed parameter space. The recent measurements of the decay $t\to cg$ can give a strong constraint on the LHT parameters and the decays of $t\to cgg$ and $t\to cb\bar{b}$ can be accessible at the LHC.

Rare and exotic decay modes of the Higgs boson are one kind of interesting decay processes, which can be used as a tool to further test the SM and search for new physics phenomena. In this paper, considering the constraints on the $HZa$ coupling from the relevant LHC data, we calculate the contributions of the light axion-like particle (ALP) with mass less than 200MeV to the rare Higgs decays $H\to \nu \overline{\nu }\gamma$, $H\to {\ell }^{+}{\ell }^{-}\gamma$ and $H\to Z\nu \overline{\nu }$. Our numerical results show that the light ALP can indeed generate significantly contributions to these decay processes. The value of the branching ratio $\mathrm{\text{Br}}(H\to \nu \nu \gamma )$ induced only by ALP is larger than the SM prediction at least one order of magnitude. We expect that our results might be helpful to test the indirect signals of light ALP in near future collider experiments, particularly in future lepton collider experiments.

Rare kaon decays provide unique opportunity to test the Standard Model and probe its possible extensions. The primary goal of the NA62 experiment is the measurement of the decay with a precision of 10% in two years of data taking. The detector setup together with the analysis technique is described.

The Belle II experiment at the SuperKEKB collider is a major upgrade of the KEK “B factory” facility in Tsukuba, Japan. The machine is designed for an instantaneous luminosity of $8\times 10^{35}{\mathrm{\text{cm}}}^{-2}{\mathrm{\text{s}}}^{-1}$, and the experiment is expected to accumulate a data sample of about 50 ab${}^{-1}$. With this amount of data, decays sensitive to physics beyond the Standard Model can be studied with unprecedented precision. One promising set of modes are physics processes with missing energy such as $B^{+}\to {\tau }^{+}\nu$, $B\to D^{(\ast )}\tau \nu$, and $B\to K^{(\ast )}\nu \bar{\nu }$ decays. The $B\to K^{(\ast )}\nu \bar{\nu }$ decay provides one of the cleanest experimental probes of the flavour-changing neutral current process $b\to s\nu \bar{\nu }$, which is sensitive to physics beyond the Standard Model. However, the missing energies of the neutrinos in the final state makes the measurement challenging and requires full reconstruction of the spectator $B$ meson in $e^{+}{e}^{-}\to \mathrm{{\rm Y}}(4S)\to B\bar{B}$ events. This report discusses the expected sensitivities of Belle II for these rare decays.