Hunting effective LSPs at LEP 200

Relatively light sneutrinos, which are experimentally allowed, may significantly affect the currently popular search strategies for supersymmetric particles by decaying dominantly into an invisible channel. In certain cases the second lightest neutralino may also decay invisibly leading to two extra carriers of missing energy — in addition to the lightest supersymmetric particle (LSP) — the effective LSPs (ELSPs). It is shown that these ELSPs are allowed in supergravity models with common scalar and gaugino masses at the unification scale for a sizable region of parameter space and are consistent with all constraints derived so far from SUSY searches. The pair production of right handed sleptons, which can very well be the lightest charged SUSY particles in this scenario, at LEP 200 and their decay signatures are discussed. The signal survives kinematical cuts required to remove the standard model background. Charginos are also pair produced copiously if kinematically accessible; they also decay dominantly into hadronically quiet di-lepton + modes leading to interesting unlike sign dilepton events which are again easily separable from the Standard Model backgrounds at LEP 200 energies.     

Lepton decay channels of egret gluinos at the LHC

Prospects for observing a SUSY-like signal from two gluinos are investigated within a certain region of the mSUGRA parameter space, where the cross section of the two gluino production in pp collisions at the LHC ( = 14 TeV) via gluon-gluon fusion (gg → ) is estimated at a rather high level of 17.3 pb. In this so-called EGRET region, the lightest stable neutralinos can serve as cold dark matter particles and are natural explanations of the excess of diffuse galactic gamma rays observed by the EGRET space apparatus. The -event selection relies on a very clear signature when decay products of each gluino contain one b-anti-b pair, one or two lepton-antilepton pair(s) and a neutralino. Rather high transverse-missing energy, carried away by the two neutralinos, is an essential signature of the events and also allows the relevant Standard Model background to be reduced significantly. In particular, it was found that the clear signatures of the selected processes demonstrate good prospects discovering the EGRET gluinos at the LHC. Furthermore, these signatures allow one to distinguish different mSUGRA parameters m _1/2 inside the EGRET region. The text was submitted by the authors in English.     

Radiative production of the lightest neutralino in e + e − annihilation

The production of the lightest stable neutralino in the process including general mixing of gauginos and Higgsinos is studied. General formulas for the differential cross section are presented. The dependence of the differential cross section on the photon energy spectrum and also the dependence of the total cross section on the beam energies for three different mixing scenarios are illustrated. The text was submitted by the author in English.     

Radioactive Production of the Lightest Neutralino in the Process of <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> Annihilation

The production of the lightest stable neutralino in the reaction with general mixing of the higgsino and gaugino is studied. General formulas for differential cross sections are presented. The dependence of the effective differential cross section on the photon energy spectrum and electron mass is illustrated together with the dependence of the effective total cross section on the beam energy for three different scenarios. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 48–57, June, 2005.     

Neutrino telescopes as a direct probe of supersymmetry breaking

We consider models where the scale of supersymmetry breaking lies between 5 x 10(6) and 5 x 10(8) GeV. In this class of theories, which includes models of mediated supersymmetry breaking, the lightest supersymmetric particle is the gravitino, and the next to lightest is typically a long-lived charged slepton with a lifetime between a microsecond and a second, depending on its mass. We investigate the production of these particles by the diffuse flux of high energy neutrinos colliding with nucleons in the Earth, and the potential for their observation in large ice or water Cerenkov detectors. The small production cross section is partially compensated by the very long range of sleptons. The signal, two well-separated parallel tracks, has very little background. Using the Waxman-Bahcall limit for the neutrino flux results in up to four events a year in km3 experiments.     

QCD Corrections to Squark Production in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> Annihilation in the MSSM with Complex Parameters

We discuss the pair production of scalar quarks in e ⁺ e ⁻ annihilation within the MSSM with complex parameters. We calculate the SUSY-QCD corrections to the cross section and show that the effect of the CP phases of these complex parameters on the cross section can be quite strong in a large region of the MSSM parameter space. This could have important implications for squarks searches and the MSSM parameter determination in future collider experiments. PACS number(s): 14.80. Ly, 12.60. Jv, 13.10. + q, 13.88. +e.     

The role of beam polarization for radiative neutralino production at the ILC

We analyze the impact of electron and positron beam polarization on radiative neutralino production at the international linear collider (ILC). We focus on three different mSUGRA scenarios in turn at the Higgs strahlung threshold, the top pair production threshold, and at 500 GeV. In these scenarios at the corresponding , radiative neutralino production is the only supersymmetric production mechanism that is kinematically allowed. The heavier neutralinos and charginos as well as the sleptons, squarks and gluinos are too heavy to be pair produced. We calculate the signal cross section and also the standard model background from radiative neutrino production. For our scenarios, we obtain significances larger than 10 and signal to background ratios between 2% and 5%, if we have electron beam polarization –0.8 and positron beam polarization –0.3. If we have electron beam polarization of , then the signal is observable with but both the significance and the signal to background ratio are significantly improved for .     

Trilepton+top signal from chargino-neutralino decays of MSSM charged Higgs bosons at the LHC

We perform for the Large Hadron Collider (LHC) a detailed study of charged Higgs boson production via the top-bottom quark associated mode followed by decays into a chargino and a neutralino, with masses and couplings as given by the general minimal supersymmetric standard model (MSSM). We focus our attention on the region of parameter space with and intermediate values of , where identification of via decays into standard model (SM) particles has proven to be ineffective. Modelling the CMS detector, we find that a signature consisting of three hard leptons accompanied by a hadronically reconstructed top quark plus substantial missing transverse energy, which may result from decays, can be made viable over a large variety of initially overwhelming SM and MSSM backgrounds, provided MSSM input parameters are favourable: notably, small and light sleptons are important prerequisites. We quantify these statements by performing a fairly extensive scan of the parameter space, including realistic hadron-level simulations, and delineate some potential discovery regions.Received: 16 April 2003, Revised: 23 June 2003, Published online: 29 August 2003S. Moretti: Formerly at: Theory Division, CERN, 1211 Geneva 23, Switzerland and Institute for Particle Physics Phenomenology, University of Durham, Durham DH1 3LE, UK     

Next-to-leading order QCD predictions for associated production of top squarks and charginos at the CERN LHC

We present the calculations of the complete next-to-leading order (NLO) inclusive total cross sections for the associated production processes in the minimal supersymmetric standard model at the CERN Large Hadron Collider. Our calculations show that the total cross sections for the production for the lighter top squark masses in the region 100 GeV 160 GeV can reach 1 pb in the favorable parameter space allowed by the current precise experiments, and in other cases the total cross sections generally vary from 10 fb to several hundred fb except for both 500 GeV and the production channel. Moreover, we find that the NLO QCD corrections in general enhance the leading order total cross sections significantly, and vastly reduce the dependence of the total cross sections on the renormalization/factorization scale, which leads to increased confidence in predictions based on these results.Received: 2 March 2003, Revised: 28 May 2003, Published online: 11 July 2003     

Probing the Stau－Stau－Higgs Couplings in the MSSM at NLC

In the minimal supersymmetric standard model (MSSM) with CP violating phases, this paper discusses the production of the lJghtest neutral Higgs boson in association with tau sleptons at future high-energy e^ e^- linear colliders. In parameter space of the constrained MSSM, the production cross section of e^ e^→h^0T1 T1^- can be very substantial at high energies. This process would provide a production mechanism for probing couplings of neutral Higgs bosoas to tau sleptons as well as some soft supersymmetric breaking parameters at next linear colliders.     

Probing the Stau-Stau-Higgs Couplings in the MSSM at NLC

In the minimal supersymmetric standard model (MSSM) with CP violating phases, this paper discussesthe production of the lightest neutral Higgs boson in association with tau sleptons at future high-energy e e- linearcolliders. In parameter space of the constrained MSSM, the production cross section of e e- → h0τ1 τ1- can be verysubstantial at high energies. This process would provide a production mechanism for probing couplings of neutral Higgsbosons to tau sleptons as well as some soft supersymmetric breaking parameters at next linear colliders.     

Search for supersymmetric particles in light gravitino scenarios and sleptons NLSP

A search for sleptons, neutralinos, charginos, sgoldstinos and heavy stable charged sleptons in the context of scenarios where the lightest supersymmetric particle is the gravitino, is presented. Data collected during 2000 with the DELPHI detector at centre-of-mass energies from 204 to 208 GeV were analysed and combined with all the data collected from 1995 to 1999 at lower energies. No evidence for the production of sleptons, neutralinos and charginos has been found, therefore new limits on the mass of these supersymmetric particles and on the model parameter space are set. The search for heavy stable charged sleptons also updates the stable sleptons mass limit. The absence of evidence for sgoldstino production allows limits to be set on its mass and on the scale of supersymmetry breaking. Received: 6 November 2002 / Published online: 14 February 2003     

On the LHC observation of gluinos from the Egret-preferred region

Prospects for observation of a SUSY-like signal from two gluinos are investigated within a certain region of the mSUGRA parameter space, where the cross section of the two-gluino production in pp-collisions at the LHC ( = 14 TeV) is estimated at a rather high level of 17.3 pb. In this so-called EGRET-preferred region, the lightest stable neutralinos χ ₁⁰ can serve as cold-dark-matter particles and can naturally explain the excess of diffuse Galactic gamma rays observed by the EGRET space apparatus. The -event selection relies on a clear signature when decay products of each gluino contain one b pair, one or two l pair(s) or one or two light q pair(s), and a neutralino. Rather high transverse missing energy carried away by the two neutralinos is the essential signature of the events using of which allows the relevant Standard Model background to be reduced significantly. Furthermore, distributions of the reconstructed invariant masses of two opposite-charged-lepton or light-jet pairs produced by the χ ₂⁰ → χ ₁⁰ l ⁺ l ⁻ and χ ₂⁰ → χ ₁⁰ q three-body decays have kinematic end points which measure the difference between masses of χ ₂⁰ and χ ₁⁰. In particular, it was found that these signatures of selected processes demonstrate good prospects for discovery of gluinos at the LHC. These signatures allow one to distinguish different mSUGRA parameters m _1/2 within the EGRET-preferred region (at a higher than 6σ confidence level with 300 fb⁻¹ data). The text was submitted by the authors in English.     

Unparticle searches through gamma–gamma scattering

We investigate the effects of unparticles on γγ→γγ scattering for the photon collider mode of the future multi-TeV e⁺e^- linear collider. We show the effects of unparticles on the differential, and total scattering cross sections for different polarization configurations. Considering 1-loop standard model background contributions from the charged fermions and W^± bosons to the cross section, we calculate the upper limits on the unparticle couplings λ₀ to the photons for various values of the scaling dimension d (1<d<2) at = 0.5–5 TeV.     

Neutral-meson production in <Emphasis Type="Italic">pp</Emphasis> collisions at RHIC and QCD test of <Emphasis Type="Italic">z</Emphasis> scaling

New experimental data on inclusive cross section of neutral-vector-meson (ω ⁰, ϕ, K _S ⁰) production in proton-proton collisions at = 200 GeV obtained at RHIC are analyzed in the framework of z scaling. Properties of z-presentation are used to predict hadron yields over a wide range of transverse momentum p _T and collisions energy . The next-to-leading-order perturbative QCD calculations of inclusive cross sections of π ⁰ mesons produced in pp and collisions over a wide range of and p _T are compared with ISR, S pS, RHIC data and predictions of z scaling. The dependence of the spectra in p _T and z presentations for different parton distribution and fragmentation functions is studied. The sensitivity of the obtained results to the choice of the renormalization (μ _R ), initial-state factorization (μ _F ), and final-state factorization (fragmentation) (μ _H ) scales is verified. It is shown that self-similar features of particle production dictated by the z scaling give strong restriction on the asymptotic behavior of the inclusive spectra in high-p _T region. The text was submitted by the author in English.     

Charged Higgs Boson Contribution to \overline{\nu}_{e}-e Scattering from Low to Ultrahigh Energy in Higgs Triplet Model

We study the $\overline{\nu}_{e}-e$ scattering from low to ultrahigh energy in the framework of Higgs Triplet Model (HTM). We add the contribution of charged Higgs boson exchange to the total cross section of the scattering. We obtain the upper bound $h_{ee}/M_{H^{\pm}}\lesssim2.8\times10^{-3}~\mbox{GeV}^{-1}$ in this process from low energy experiment. We show that by using the upper bound obtained, the charged Higgs contribution can give enhancements to the total cross section with respect to the SM prediction up to 5.16 % at E≤10¹⁴ eV and maximum at $s\approx M_{H^{\pm}}^{2}$ and would help to determine the feasibility experiments to discriminate between SM and HTM at current available facilities.     

Hierarchical radiative masses in a supersymmetric three-family model without higgsinos

We study the scalar potential and the mass spectrum of the supersymmetric extension of a three-family model based on the local gauge group , with anomalies canceled among the three families in a non-trivial fashion. In this model the slepton multiplets play the role of the Higgs scalars and no higgsinos are required, with the consequence that the sneutrino, the selectron and six other sleptons play the role of the Goldstone bosons of the theory. By introducing an Abelian anomaly-free discrete symmetry and aligning the vacuum in a convenient way, we get a consistent mass spectrum for the scalars and for the spin 1/2 quarks and charged leptons, where only the top and charm quarks and the tau lepton acquire tree-level masses while the remaining ordinary charged fermions acquire radiative hierarchical masses.Received: 9 August 2004, Revised: 10 March 2005, Published online: 8 June 2005PACS: 12.60.Jv, 12.60.Cn, 12.15.Ff     

Squark Pair Production at Muon Colliders in the MSSM with CP Violation

We study the pair production of scalar quark in a muon collider within the MSSM with CP violation. We show that including the CP phases can strongly affect the cross section of the process: \(\mu^{+}\mu^{-}\rightarrow \tilde{q}_{i}\bar{\tilde{q}}_{j}\). This could have an important impact on the search for squarks and the determination of the MSSM parameters at future colliders.     

Inclusive photoproduction of <Emphasis Type="Italic">D</Emphasis><Superscript>*</Superscript> mesons with massive charm quarks

We have calculated the next-to-leading order cross sections for the inclusive production of D ^* mesons in collisions at HERA in two approaches using massive or massless charm quarks. The usual massive theory for the direct cross section with charm quarks only in the final state was transformed into a massive theory with subtraction by subtracting the mass divergent and additional finite terms calculated earlier in connection with the process . This theory approaches the massless theory with increasing transverse momentum. The difference between the massive and the massless approach with subtraction is studied in detail in those kinematic regions relevant for comparison with experimental data. With these results and including the resolved cross section which is dominated by the part originating from the charm in the photon, we compute the fully inclusive cross section and compare it with preliminary data from the ZEUS collaboration at HERA. We find on average good agreement.Received: 5 October 2004, Published online: 26 November 2004