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Authors
Masato Yamanaka
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We consider the case that $mu$-$e$ conversion signal is discovered but other charged lepton flavor violating (cLFV) processes will never be found. In such a case, we need other approaches to confirm the $mu$-$e$ conversion and its underlying physics without conventional cLFV searches. We study R-parity violating (RPV) SUSY models as a benchmark. We briefly review that our interesting case is realized in RPV SUSY models with reasonable settings according to current theoretical/experimental status. We focus on the exotic collider signatures at the LHC ($pp to mu^- e^+$ and $pp to jj$) as the other approaches. We show the correlations between the branching ratio of $mu$-$e$ conversion process and cross sections of these processes. It is first time that the correlations are graphically shown. We exhibit the RPV parameter dependence of the branching ratio and the cross sections, and discuss the feasibility to determine the parameters.
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We study radiative gravitino decay within the framework of R-violating supersymmetry. For trilinear R-violating couplings that involve the third generation of fermions, or for light gravitinos, we find that the radiative loop-decay $tilde{G} to gamma u$ dominates over the tree-level ones for a wide set of parameters. We calculate the gravitino decay width and study its implications for cosmology and collider physics. Slow-decaying gravitinos are good dark matter candidates, for a range of parameters that would also predict observable R-violating signatures in colliders. In general the branching ratios are very dependent on the relative hierarchies of R-violating operators, and may provide relevant information on the flavour structure of the underlying fundamental theory.
We consider the supersymmetric extension of the Standard Model with neutrino Yukawa interactions and R-parity violation. We found that R-parity breaking term lambda u H_u H_d leads to an additional F-type contribution to the Higgs scalar potential, and thus to the masses of supersymmetric Higgs bosons. The most interesting consequence is the modification of the tree-level expression for the lightest neutral supersymmetric Higgs boson mass. It appears that due to this contribution the bound on the lightest Higgs mass may be shifted upwards, thus slightly opening the part of the model parameter space excluded by non-observation of the light Higgs boson at LEP in the framework of the Minimal Supersymmetric Standard Model.
We study the production of $(t+bar{t}) tilde{g}$ at the hadron colliders in an R-parity ($R_{p}$) violating supersymmetric model. This process provides us with information not only about $R_{p}$ violation, but may also help us in detecting the supersymmetry itself. It is possible to detect an $R_{p}$ violating signal (with single gluino production) at the future hadron colliders, such as Fermilab Tevatron Run II or CERN Large Hadron Collider (LHC), if the parameters in the supersymmetric $rlap/ R_{p}$ interactions are not too small, e.g. for $m_{tilde{g}}=1$ TeV, $lambda^{}=0.1$, still hundreds of events are produced at LHC with luminosity $30 fb^{-1}$. Even if we could not detect a signal of $ rlap/R_{p}$ in the experiment, we get stringent constraints on the heavy flavour $rlap/R_{p}$ couplings. In addition to the minimal supersymmetric standard model we have also considered some models with a heavy gluino as the lightest supersymmetric particle.
Using $1.06times10^8$ $psi(3686)$ events recorded in $e^{+}e^{-}$ collisions at $sqrt{s}=$ 3.686 GeV with the BESIII at the BEPCII collider, we present searches for C-parity violation in $J/psi to gammagamma$ and $ gamma phi$ decays via $psi(3686) to J/psi pi^+pi^-$. No significant signals are observed in either channel. Upper limits on the branching fractions are set to be $mathcal{B}(J/psi to gammagamma) < 2.7 times 10^{-7}$ and $mathcal{B}(J/psi to gammaphi) < 1.4 times 10^{-6}$ at the 90% confidence level. The former is one order of magnitude more stringent than the previous upper limit, and the latter represents the first limit on this decay channel.
We studied the feasibility of an experiment searching for sub-millicharged particles ($chi$s) using 30 GeV proton fixed-target collisions at J-PARC. The detector is composed of two layers of stacked scintillator bars and PMTs and is proposed to be installed 280 m from the target. The main background is a random coincidence between two layers due to dark counts in PMTs, which can be reduced to a negligible level using the timing of the proton beam. With $N_textrm{POT}=10^{22}$ which corresponds to running the experiment for three years, the experiment provides sensitivity to $chi$s with the charge down to $5times10^{-5}$ in $m_chi<0.2$ $textrm{GeV}/textrm{c}^2$ and $8times10^{-4}$ in $m_chi<1.6$ $textrm{GeV}/textrm{c}^2$. This is the regime largely uncovered by the previous experiments. We also explored a few detector designs to achieve an optimal sensitivity to $chi$s. The photoelectron yield is the main driver, but the sensitivity does not have a strong dependence on the detector configuration in the sub-millicharge regime.
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