Analysis of the neutralino system in supersymmetric theories

Charginos [(c)\tilde]± and neutralinos [(c)\tilde]0 in supersymmetric theories can be produced copiously at e+e- colliders and their properties can be measured with high accuracy. Consecutively to the chargino system, in which the SU(2) gaugino parameter M2, the higgsino mass parameter m and tanb can be determined, the remaining fundamental supersymmetry parameter in the gaugino/higgsino sector of the minimal supersymmetric extension of the Standard Model, the U(1) gaugino mass M1, can be analyzed in the neutralino system, including its modulus and its phase in CP-noninvariant theories. The CP properties of the neutralino system are characterized by unitarity quadrangles. Analytical solutions for the neutralino mass eigenvalues and the mixing matrix are presented for CP-noninvariant theories in general. They can be written in compact form for large supersymmetric mass parameters. The closure of the neutralino and chargino systems can be studied by exploiting sum rules for the pair-production processes in e+e- collisions. Thus the picture of the non-colored gaugino and higgsino complex in supersymmetric theories can comprehensively be reconstructed in these experiments

SUSY parameter determination in combined analyses at LHC/LC

We demonstrate how the interplay of a future e+e- LC at its first stage with (s)1/2lesssim500 GeV and of the LHC could lead to a precise determination of the fundamental SUSY parameters in the gaugino/higgsino sector without assuming a specific supersymmetry breaking scheme. We demonstrate this for the benchmark scenario SPS1a, taking into account realistic errors for the masses and cross sections measured at the LC with polarised beams, including errors coming from polarisation measurements, and mass measurements at the LHC. The results clearly demonstrate the complementarity of the LHC and LC, and the benefit from the joint analyses of their data

Combined LHC/ILC analysis of a SUSY scenario with heavy sfermions

We discuss the potential of combined analyses at the Large Hadron Collider and the planned International Linear Collider to explore low-energy supersymmetry in a difficult region of the parameter space characterized by masses of the scalar SUSY particles around 2 TeV. Precision analyses of cross sections for light chargino production and forward--backward asymmetries of decay leptons and hadrons at the ILC, together with mass information on chi^0_2 and squarks from the LHC, allow us to determine the underlying fundamental gaugino/higgsino MSSM parameters and to constrain the masses of the heavy, kinematically inaccessible sparticles. No assumptions on a specific SUSY-breaking mechanism are imposed. For this analysis the complete spin correlations between production and decay processes are taken into account.Comment: new figure added, updated to match the published versio

Identification of extra neutral gauge bosons at the International Linear Collider

Heavy neutral gauge bosons, Z's, are predicted by many theoretical schemes of physics beyond the Standard Model, and intensive searches for their signatures will be performed at present and future high energy colliders. It is quite possible that Z's are heavy enough to lie beyond the discovery reach expected at the CERN Large Hadron Collider LHC, in which case only indirect signatures of Z' exchanges may occur at future colliders, through deviations of the measured cross sections from the Standard Model predictions. We here discuss in this context the foreseeable sensitivity to Z's of fermion-pair production cross sections at an e^+e^- linear collider, especially as regards the potential of distinguishing different Z' models once such deviations are observed. Specifically, we assess the discovery and identification reaches on Z' gauge bosons pertinent to the E_6, LR, ALR and SSM classes of models, that should be attained at the planned International Linear Collider (ILC). With the high experimental accuracies expected at the ILC, the discovery and the identification reaches on the Z' models under consideration could be increased substantially. In particular, the identification among the different models could be achieved for values of Z' masses in the discovery (but beyond the identification) reach of the LHC. An important role in enhancing such reaches is played by the electron (and possibly the positron) longitudinally polarized beams. Also, although the purely leptonic processes are experimentally cleaner, the measurements of c- and b-quark pair production cross sections are found to carry important, and complementary, information on these searches.Comment: 21 page

CP asymmetries in the supersymmetric trilepton signal at the LHC

In the CP-violating Minimal Supersymmetric Standard Model, we study the production of a neutralino-chargino pair at the LHC. For their decays into three leptons, we analyze CP asymmetries which are sensitive to the CP phases of the neutralino and chargino sector. We present analytical formulas for the entire production and decay process, and identify the CP-violating contributions in the spin correlation terms. This allows us to define the optimal CP asymmetries. We present a detailed numerical analysis of the cross sections, branching ratios, and the CP observables. For light neutralinos, charginos, and squarks, the asymmetries can reach several 10%. We estimate the discovery potential for the LHC to observe CP violation in the trilepton channel.Comment: 39 pages, 8 figures, version to appear in EPJC, discussion(s) added, typo in (D.79), (D.118) corrected, new Fig. 7; The European Physical Journal C, Volume 72, Issue 3, 201

Tau-Sleptons and Tau-Sneutrino in the MSSM with Complex Parameters

We present a phenomenological study of tau-sleptons stau_1,2 and tau-sneutrino in the Minimal Supersymmetric Standard Model with complex parameters A_tau, mu and M_1. We analyse production and decays of stau_1,2 and tau-sneutrino at a future e^+ e^- collider. We present numerical predictions for the important decay rates, paying particular attention to their dependence on the complex parameters. The branching ratios of the fermionic decays of stau_1 and tau-sneutrino show a significant phase dependence for tan(beta) < 10. For tan(beta) > 10 the branching ratios for the stau_2 decays into Higgs bosons depend very sensitively on the phases. We show how information on the phase phi(A_tau) and the other fundamental stau parameters can be obtained from measurements of the stau masses, polarized cross sections and bosonic and fermionic decay branching ratios, for small and large tan(beta) values. We estimate the expected errors for these parameters. Given favorable conditions, the error of A_tau is about 10% to 20%, while the errors of the remaining stau parameters are in the range of approximately 1% to 3%. We also show that the induced electric dipole moment of the tau-lepton is well below the current experimental limit.Comment: LaTex, 25 pages, 11 figures (included); v2: extended discussion on error determination, version to appear in Phys.Rev.

Complementarity of the CERN Large Hadron Collider and the e+e−e^+e^- International Linear Collider

The next-generation high-energy facilities, the CERN Large Hadron Collider (LHC) and the prospective $e^+e^-$ International Linear Collider (ILC), are expected to unravel new structures of matter and forces from the electroweak scale to the TeV scale. In this report we review the complementary role of LHC and ILC in drawing a comprehensive and high-precision picture of the mechanism breaking the electroweak symmetries and generating mass, and the unification of forces in the frame of supersymmetry.Comment: 14 pages, 17 figures, to be published in "Supersymmetry on the Eve of the LHC", a special volume of European Physical Journal C, Particles and Fields (EPJC) in memory of Julius Wes

Observation of Polarized Positrons from an Undulator-Based Source

An experiment (E166) at the Stanford Linear Accelerator Center (SLAC) has demonstrated a scheme in which a multi-GeV electron beam passed through a helical undulator to generate multi-MeV, circularly polarized photons which were then converted in a thin target to produce positrons (and electrons) with longitudinal polarization above 80% at 6 MeV. The results are in agreement with Geant4 simulations that include the dominant polarization-dependent interactions of electrons, positrons and photons in matter

Distinguishing between MSSM and NMSSM by combined LHC and ILC analyses

We show that the interplay between the LHC and the e+e- International Linear Collider (ILC) with (s)1/2 = 500 GeV might be crucial for the discrimination between the minimal and next-to-minimal supersymmetric standard model. We present an NMSSM scenario that cannot be distinguished from the MSSM by cross sections and mass measurements if only the light neutralinos and the lightest chargino are kinematically accessible, even if one of the neutralinos has a significant singlino component. Mass predictions for the heavier neutralinos from the ILC analysis and their observation at the LHC lead to a identification of the neutralino mixing character and the underlying supersymmetric model in a combined LHC/ILC analysis. In our numerical example we include errors in the mass measurements and use standard methods of supersymmetric parameter determination