arXiv subjects
Publications and source records attributed to J. Kenichi Mizukoshi.
We address the complementarity of the CERN Large Hadron Collider and an $e^+ e^-$ Linear Collider in determining SUSY model parameters for a particular SO(10) SUSY GUT case study.
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(\tildeν_μ) and m(\tildeν_τ) 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(\tildeν_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).
There are many models with non-universal soft SUSY breaking sfermion mass parameters at the grand unification scale. Even in the mSUGRA model scalar mass unification might occur at a scale closer to M_Planck, and renormalization effects would cause a mass splitting at M_GUT. We identify an experimentally measurable quantity Delta that correlates strongly with delta m^2 = m^2_{selectron_R}(M_GUT) - m^2_{selectron_L}(M_GUT), and which can be measured at electron-positron colliders provided both selectrons and the chargino are kinematically accessible. We show that if these sparticle masses can be measured with a precision of 1% at a 500 GeV linear collider, the resulting precision in the determination of Delta may allow experiments to distinguish between scalar mass unification at the GUT scale from the corresponding unification at Q ~ M_Planck. Experimental determination of Delta would also provide a distinction between the mSUGRA model and the recently proposed gaugino-mediation model. Moreover, a measurement of Delta (or a related quantity Delta') would allow for a direct determination of delta m^2.
We performed an analysis on the detection of a long-lived slepton at a linear collider with $\sqrt{s}=500$ GeV. In GMSB models a long-lived NLSP is predicted for large value of the supersymmetry breaking scale $\sqrt{F}$. Furthermore in a large portion of the parameter space this particle is a stau. Such heavy charged particles will leave a track in the tracking volume and hit the muonic detector. In order to disentangle this signal from the muon background, we explore kinematics and particle identification tools: time of flight device, dE/dX and Cerenkov devices. We show that a linear collider will be able to detect long-lived staus with masses up to the kinematical limit of the machine. We also present our estimation of the sensitivity to the stau lifetime.
In a supersymmetric model, the presence of a right handed neutrino with a large Yukawa coupling $f_ν$ would affect slepton masses via its contribution to the renormalization group evolution between the grand unification and weak scales. Assuming a hierarchichal pattern of neutrino masses, these effects are large for only the third generation of sleptons. We construct mass combinations to isolate the effect of $f_ν$ from mass corrections already expected from tau Yukawa couplings. We then analyze the size of these effects, assuming that the Super-Kamiokande data constrain 0.033 eV $\alt m_{ν_τ} \alt 0.1$ eV and that neutrino masses arise via a see-saw mechanism. We also explore whether these effects might be detectable in experiments at future $e^+e^-$ linear colliders. We find that $m_{\tnu_τ}$ needs to be measured with a precision of about 2-3% to measure the effect of $f_ν$ if the neutrino and top Yukawa couplings unify at the grand unification scale. In a simple case study, we find a precision of only 6-10% might be attainable after several years of operation. If the neutrino Yukawa coupling is larger, or in more complicated models of neutrino masses, a determination of $\ttau_1$ and $\tnu_τ$ masses might provide a signal of a Yukawa interaction of neutrinos.