Low mass neutralino dark matter in mSUGRA and more general models in the light of LHC data

The b\tau j \etslash signal at the ongoing LHC experiments is simulated with Pythia in the mSUGRA and other models of SUSY breaking. Special attention is given on the compatibility of this signature with the low mass neutralino dark matter (LMNDM) scenario consistent with WMAP data. In the mSUGRA model the above signal as well as the LMNDM scenario are strongly disfavoured due to the constraints from the on going SUSY searches at the LHC. This tension, however, originates from the model dependent correlations among the parameters in the strong and electroweak sectors of mSUGRA. That there is no serious conflict between the LMNDM scenario and the LHC data is demonstrated by constructing generic phenomenological models such that the strong sector is unconstrained or mildly constrained by the existing LHC data and parameters in the electroweak sector, unrelated to the strong sector,yield DM relic density consistent with the WMAP data. The proposed models, fairly insensitive to the conventional SUSY searches in the jets + \etslash and other channels, yield observable signal in the suggested channel for \lum \gsim 1 \ifb of data. They are also consistent with the LMNDM scenario and can be tested by the direct dark matter search experiments in the near future. Some of these models can be realized by non-universal scalar and gaugino masses at the GUT scale.Comment: 33 pages, 2 figures, analyses updated for 1 fb^{-1} of LHC data and presented in a new section, some new references have been added, published in Phys. Rev.

Scenery from the Top: Study of the Third Generation Squarks at CERN LHC

In the minimal supersymmetric standard model (MSSM) properties of the third generation sfermions are important from the viewpoint of discriminating the SUSY breaking models and in the determination of the Higgs boson mass. If gluinos are copiously produced at CERN LHC, gluino decays into tb through stop and sbottom can be studied using hadronic decays of the top quark. The kinematical endpoint of the gluino decays can be evaluated using a W sideband method to estimate combinatorial backgrounds. This implies that fundamental parameters related to the third generation squarks can be reliably measured. The top-quark polarization dependence in the decay process may also be extracted by looking at the b jet distribution near the kinematical endpoint.Comment: 4 pages in PRL format, 4 Postscript figures, uses revtex

Measurement of the Superparticle Mass Spectrum in the Long-Lived Stau Scenario at the LHC

In supersymmetric scenarios with a long-lived stau, the LHC experiments provide us with a great environment for precise mass measurements of superparticles. We study a case in which the mass differences between the lightest stau and other sleptons are about 10 GeV or larger, so that the decay products of heavier sleptons are hard enough to be detected. We demonstrate that the masses of neutralinos, sleptons, and squarks can be measured with a good accuracy.Comment: 20 pages, 6 figure

SUSY Parameter Analysis at TeV and Planck Scales

Coherent analyses at future LHC and LC experiments can be used to explore the breaking mechanism of supersymmetry and to reconstruct the fundamental theory at high energies, in particular at the grand unification scale. This will be exemplified for minimal supergravity.Comment: 7 pages, 3 figures, uses espcrc2.sty (included), Proceedings, Loops and Legs 2004, Zinnowitz on Usedo

Mixed Higgsino Dark Matter from a Reduced SU(3) Gaugino Mass: Consequences for Dark Matter and Collider Searches

In gravity-mediated SUSY breaking models with non-universal gaugino masses, lowering the SU(3) gaugino mass |M_3| leads to a reduction in the squark and gluino masses. Lower third generation squark masses, in turn, diminish the effect of a large top quark Yukawa coupling in the running of the higgs mass parameter m_{H_u}^2, leading to a reduction in the magnitude of the superpotential mu parameter (relative to M_1 and M_2). A low | mu | parameter gives rise to mixed higgsino dark matter (MHDM), which can efficiently annihilate in the early universe to give a dark matter relic density in accord with WMAP measurements. We explore the phenomenology of the low |M_3| scenario, and find for the case of MHDM increased rates for direct and indirect detection of neutralino dark matter relative to the mSUGRA model. The sparticle mass spectrum is characterized by relatively light gluinos, frequently with m(gl)<<m(sq). If scalar masses are large, then gluinos can be very light, with gl->Z_i+g loop decays dominating the gluino branching fraction. Top squarks can be much lighter than sbottom and first/second generation squarks. The presence of low mass higgsino-like charginos and neutralinos is expected at the CERN LHC. The small m(Z2)-m(Z1) mass gap should give rise to a visible opposite-sign/same flavor dilepton mass edge. At a TeV scale linear e^+e^- collider, the region of MHDM will mean that the entire spectrum of charginos and neutralinos are amongst the lightest sparticles, and are most likely to be produced at observable rates, allowing for a complete reconstruction of the gaugino-higgsino sector.Comment: 35 pages, including 26 EPS figure

Slepton mass-splittings as a signal of LFV at the LHC

Precise measurements of slepton mass-splittings might represent a powerful tool to probe supersymmetric (SUSY) lepton flavour violation (LFV) at the LHC. We point out that mass-splittings of the first two generations of sleptons are especially sensitive to LFV effects involving $\tau-\mu$ transitions. If these mass-splittings are LFV induced, high-energy LFV processes like the neutralino decay {\nt}_2\to\nt_1\tau^{\pm}\mu^{\mp} as well as low-energy LFV processes like $\tau\to\mu\gamma$ are unavoidable. We show that precise slepton mass-splitting measurements and LFV processes both at the high- and low-energy scales are highly complementary in the attempt to (partially) reconstruct the flavour sector of the SUSY model at work. The present study represents another proof of the synergy and interplay existing between the LHC, i.e. the {\em high-energy frontier}, and high-precision low-energy experiments, i.e. the {\em high-intensity frontier}.Comment: 11 pages, 5 figures. v2: added discussion on backgrounds, added references, version to be published on JHE

Measurement of SUSY masses via cascade decays for SPS 1a

If R-parity conserving supersymmetry exists below the TeV-scale, new particles will be produced and decay in cascades at the LHC. The lightest supersymmetric particle will escape the detectors, thereby complicating the full reconstruction of the decay chains. In this paper we expand on existing methods for determining the masses of the particles in the cascade from endpoints of kinematical distributions. We perform scans in the mSUGRA parameter space to delimit the region where this method is applicable. From the examination of theoretical distributions for a wide selection of mass scenarios it is found that caution must be exerted when equating the theoretical endpoints with the experimentally obtainable ones. We provide analytic formulae for the masses in terms of the endpoints most readily available. Complications due to the composite nature of the endpoint expressions are discussed in relation to the detailed analysis of two points on the SPS 1a line. Finally we demonstrate how a Linear Collider measurement can improve dramatically on the precision of the masses obtained