Sneutrino Mass Measurements at e+e- Linear Colliders

It is generally accepted that experiments at an e+e- linear colliders will be able to extract the masses of the selectron as well as the associated sneutrinos with a precision of ~ 1% by determining the kinematic end points of the energy spectrum of daughter electrons produced in their two body decays to a lighter neutralino or chargino. Recently, it has been suggested that by studying the energy dependence of the cross section near the production threshold, this precision can be improved by an order of magnitude, assuming an integrated luminosity of 100 fb^-1. It is further suggested that these threshold scans also allow the masses of even the heavier second and third generation sleptons and sneutrinos to be determined to better than 0.5%. We re-examine the prospects for determining sneutrino masses. We find that the cross sections for the second and third generation sneutrinos are too small for a threshold scan to be useful. An additional complication arises because the cross section for sneutrino pair to decay into any visible final state(s) necessarily depends on an unknown branching fraction, so that the overall normalization in unknown. This reduces the precision with which the sneutrino mass can be extracted. We propose a different strategy to optimize the extraction of m(\tilde{\nu}_\mu) and m(\tilde{\nu}_\tau) via the energy dependence of the cross section. We find that even with an integrated luminosity of 500 fb^-1, these can be determined with a precision no better than several percent at the 90% CL. We also examine the measurement of m(\tilde{\nu}_e) and show that it can be extracted with a precision of about 0.5% (0.2%) with an integrated luminosity of 120 fb^-1 (500 fb^-1).Comment: RevTex, 46 pages, 15 eps figure

A Detailed Analysis of One-loop Neutrino Masses from the Generic Supersymmetric Standard Model

In the generic supersymmetric standard model which had no global symmetry enforced by hand, lepton number violation is a natural consequence. Supersymmetry, hence, can be considered the source of experimentally demanded beyond standard model properties for the neutrinos. With an efficient formulation of the model, we perform a comprehensive detailed analysis of all one-loop contributions to neutrino masses.Comment: 27 pages Revtex, no figur

Gluino Decay as a Probe of High Scale Supersymmetry Breaking

A supersymmetric standard model with heavier scalar supersymmetric particles has many attractive features. If the scalar mass scale is O(10 - 10^4) TeV, the standard model like Higgs boson with mass around 125 GeV, which is strongly favored by the LHC experiment, can be realized. However, in this scenario the scalar particles are too heavy to be produced at the LHC. In addition, if the scalar mass is much less than O(10^4) TeV, the lifetime of the gluino is too short to be measured. Therefore, it is hard to probe the scalar particles at a collider. However, a detailed study of the gluino decay reveals that two body decay of the gluino carries important information on the scalar scale. In this paper, we propose a test of this scenario by measuring the decay pattern of the gluino at the LHC.Comment: 29 pages, 9 figures; version published in JHE

The neutralino projector formalism for complex SUSY parameters

We present a new formalism describing the neutralino physics in the context of the minimal supersymmetric model (MSSM), where CP violation induced by complex $M_1$ and $\mu$ parameters is allowed. The formalism is based on the construction of neutralino projectors, and can be directly generalized to non-minimal SUSY models involving any number of neutralinos. It extends a previous work applied to the real SUSY parameter case. In MSSM, the method allows to describe all physical observables related to a specific neutralino, in terms of its CP eigenphase and three complex numbers called its "reduced projector elements". As the experimental knowledge on the neutralino-chargino sectors will be being accumulated, the problem of extracting the various SUSY parameters will arise. Motivated by this, we consider various scenarios concerning the quantities that could be first measured. Analytical disentangled expressions determining the related SUSY parameters from them, are then derived, which also emphasize the efficiency of the formalism.Comment: Version accepted in Phys. Rev. D. e-mail: [email protected]

CP violation in chargino decays in the MSSM

In the minimal supersymmetric standard model (MSSM) with complex parameters, supersymmetric loop effects can lead to \emph{CP} violation. We calculate the rate asymmetries of decays of charginos into the lightest neutralino and a $W$ boson on the basis of the most important loop contributions in the third generation squark sectors. It turns out that the \emph{CP} violating asymmetries can be a few per cent in typical regions of the parameter space of the MSSM. These processes would provide very promising channels for probing \emph{CP} violation in the MSSM at future high-energy colliders.Comment: 15 pages, 5 figures, LaTeX2

Neutralino Decays at the CERN LHC

We study the distribution of lepton pairs from the second lightest neutralino decay \tchi^0_2\to\tchi^0_1 l^+l^-. This decay mode is important to measure the mass difference between \tchi^0_2 and the lightest neutralino \tchi^0_1, which helps to determine the parameters of the minimal supersymmetric standard model at the CERN LHC. We found that the decay distribution strongly depends on the values of underlying MSSM parameters. For some extreme cases, the amplitude near the end point of the lepton invariant mass distribution can be suppressed so strongly that one needs the information of the whole m_{ll} distribution to extract m_{\tchi^0_2}-m_{\tchi^0_1}. On the other hand, if systematic errors on the acceptance can be controlled, this distribution can be used to constrain slepton masses and the Z\tchi^0_2\tchi^0_1 coupling. Measurements of the velocity distribution of \tchi^0_2 from samples near the end point of the m_{ll} distribution, and of the asymmetry of the p_T of leptons, would be useful to reduce the systematic errors.Comment: 23 pages, latex2e, 9 figures, minor change, accepted to PR

Pair Production of the Lightest Chargino via Gluon-Gluon Collisions

The production of the lightest chargino pair from gluon-gluon fusion is studied in the minimal supersymmetric model(MSSM) at proton-proton colliders. We find that with the chosen parameters, the production rate of the subprocess can be over 2.7 femto barn when the chargino is higgsino-like, and the corresponding total cross section in proton-proton collider can reach 56 femto barn at the LHC in the CP-conserving MSSM. It shows that this loop mediated subprocess can be competitive with the standard Drell-Yan subprocess in proton-proton colliders, especially at the LHC. Furthermore, our calculation shows it would be possible to extract information about some CP-violating phase parameters, if we collected enough chargino pair events.Comment: 39 pages, LaTex, 8 figure