Heavy SUSY Higgs bosons at e + e − linear colliders

The production mechanisms and decay modes of the heavy neutral and charged Higgs bosons in the Minimal Supersymmetric Standard Model are investigated at future e ⁺ e ^? colliders in the TeV energy regime. We generate supersymmetric particle spectra by requiring the MSSM Higgs potential to produce correct radiative electroweak symmetry breaking, and we assume a common scalar mass m₀, gaugino mass m_1/2 and trilinear coupling A, as well as gauge and Yukawa coupling unification at the Grand Unification scale. Particular emphasis is put on the low tan β solution in this scenario where decays of the Higgs bosons to Standard Model particles compete with decays to supersymmetric charginos/neutralinos as well as sfermions. In the high tan β case, the supersymmetric spectrum is either too heavy or the supersymmetric decay modes are suppressed, since the Higgs bosons decay almost exclusively into b and τ pairs. The main production mechanisms for the heavy Higgs particles are the associated AH production and H ⁺H^? pair production with cross sections of the order of a few fb.     

Heavy Dirac and Majorana neutrino production ine + e − collisions

The production of heavy Dirac and Majorana neutrinos ine ⁺ e ^? collisions is investigated. The heavy Dirac and/or Majorana neutrinos can be produced in charged and neutral current processes $(e^ + e^ - \to N_1 \bar N_2 )$ . The production of a single heavy neutrino is possible if it mixes with the light neutrino species. The production of heavy neutrinos in Higgs channels is also studied, since in some specific models the Yukawa couplings could be large enough to make the production of heavy neutrinos through Higgs boson exchanges sufficiently large for detection. The most general left-right symmetric model with possibly complexV orA couplings is used in the analytic calculations of the production cross sections, but the numerical examples are given using simplified left-right symmetric model. The interference terms between different production channels have been studied in great detail and in some cases the interference terms are found to be non-negligible in wide range of production spectrum. The pair production cross section is larger in the Dirac case than it is in the Majorana case, but the single heavy Majorana neutrino production cross section is roughly twice as large as that of a Dirac neutrino.     

Spin dependent fragmentation functions for heavy flavor baryons and single heavy hyperon polarization

Spin dependent fragmentation functions for heavy flavor quarks to fragment into heavy baryons are carculated in a quark-diquark model. The production of intermediate spin 1/2 and 3/2 excited states is explicity included. Λ _b , Λ_c and Ξ _c production rate and polarization at LEP energies are calculated and, where possible, compared with experiment. A different approach, also relying on a heavy quark-diquark model, is proposed for the small momentum transfer inclusive production of polarized heavy flavor hyperons. The predicted Λ_c polarization is roughly in agreement with experiment.     

Quantum chromodynamics results from HERA and JLAB

Recent QCD results from electron?Cproton interactions at HERA and JLAB are presented. Inclusive cross-section measurements as well as studies of the hadronic final state like jet production or the production of heavy quarks are discussed. The results are compared with perturbative QCD predictions and their impact on the determination of the parton density functions of the proton as well as of the strong coupling ?? _s is discussed.     

New physics at 1 TeV?

If decays of a heavy particle S are responsible for the diphoton excess with invariant mass 750 GeV observed at the 13 TeV LHC run, it can be easily accommodated in the Standard Model. Two scenarios are considered: production in gluon fusion through a loop of heavy isosinglet quark(s) and production in photon fusion through a loop of heavy isosinglet leptons. In the second case, many heavy leptons are needed or/and they should have large electric charges in order to reproduce experimental data on σ_{pp → SX} · Br(S → γγ).     

Heavy quarks and squarks fromW-gluon fusion

We discussWg-fusion as a source heavy quark and squark pairs at very high energy hadron colliders. EffectiveW approximation is used to calculate the cross-sections analytically in the forward scattering configuration; good agreement is obtained with exact numerical calculations.W-gluon fusion is found to be not nearly as important a production mechanism of heavy squarks as it is of heavy quarks. This is especially true when the mass-splitting within theSU(2) _L doublet is small.     

Producing heavy quark flavors in hadronic collisions—' A test of quantum chromodynamics

It is suggested, within the framework of QDC, that the production of heavy quark flavors in hardronic reactions proceeds via the materialization of a highly virtual gluon into a heavy quark-antiquark pair. Several phenomenological applications are discussed. In particular the charm production cross section at 400 GeV/c proton-nucleus collisions is calculated to be ? 120 nb/nucleon. Anti-proton-nucleon scattering is found to be especially suited for Ψ(J) and charm production, and provides an important and interesting test for the proposed production mechanism.     

Enhancement of heavy quarkonium production in hadron collisions at finite temperature

We estimate how the masses and wave functions of heavy quarkonium mesons change with temperature below the deconfining temperatureT _c . To do so we use simple, theoretically motivated parametrizations of the way the heavy quark potential and quark masses vary with temperature. The effect of these changes on the production of charmonium and bottonium in hadron-hadron collisions is estimated using a standard phenomenological model. We find, for example, that forT close toT _c enhancements by as much as a factor of 3 are possible for charmonium and bottonium highp _T production at SPS energies \(\sqrt s\) =20 GeV. Thep _T and energy dependence of this enhancement is non-trivial. We discuss the relevance of our results for the interpretation of recentJ/ψ data from heavy ion collisions.     

Entropy, baryon asymmetry and dark matter from heavy neutrino decays

The origin of the hot phase of the early universe remains so far an unsolved puzzle. A viable option is entropy production through the decays of heavy Majorana neutrinos whose lifetimes determine the initial temperature. We show that baryogenesis and the production of dark matter are natural by-products of this mechanism. As is well known, the cosmological baryon asymmetry can be accounted for by leptogenesis for characteristic neutrino mass parameters. We find that thermal gravitino production then automatically yields the observed amount of dark matter, for the gravitino as the lightest superparticle and typical gluino masses. As an example, we consider the production of heavy Majorana neutrinos in the course of tachyonic preheating associated with spontaneous B−L breaking. A quantitative analysis leads to constraints on the superparticle masses in terms of neutrino masses: For a light neutrino mass of ¹⁰−5 eV the gravitino mass can be as small as 200 MeV, whereas a lower neutrino mass bound of 0.01 eV implies a lower bound of 9 GeV on the gravitino mass. The measurement of a light neutrino mass of 0.1 eV would rule out heavy neutrino decays as the origin of entropy, visible and dark matter.     

Heavy quarks at RHIC and LHC within a partonic transport model

Production and space-time evolution of heavy quarks in central and non-central heavy-ion collisions at RHIC and LHC are studied with the partonic transport model Boltzmann Approach of MultiParton Scatterings (BAMPS). In addition to the initially created heavy quarks in hard parton scatterings during nucleon-nucleon collisions, secondary heavy quark production in the quark-gluon plasma is investigated and the sensitivity on various parameters is estimated. In BAMPS heavy quarks scatter with particles of the medium via elastic collisions, whose cross section is calculated with the running coupling and a more precise implementation of Debye screening. In this framework, we compute the elliptic flow and nuclear modification factor of heavy quarks and compare it to the experimental data.     

An effective approach to same sign top pair production at the LHC and the forward-backward asymmetry at the Tevatron

We study the phenomenology of same sign top pair production at the LHC in a model-independent way. The complete set of dimension six operators involving two top (or anti-top) quarks is introduced and the connection with all possible t- or s-channel heavy particle exchanges is established. Only in the former case, same and opposite sign top pair production can be related. We find that while current Tevatron data disfavor t-channel models, other production mechanisms are viable and can be tested at the LHC.     

Dynamically generated parton distributions for high energy collisions

The parton distributions of the nucleon are evaluated dynamically using the assumption that at some low resolution scale the nucleon consists entirely of valence quarks. A simple parametrization of the resulting gluon distribution is presented, forx? 10^?5 up toQ ²?10⁶ GeV². This gluon distribution is predicted dicted to be much steeper and larger in the very smallx region (x<10^?2) than usually assumed. Applications to deep inelastic scaling violations and heavy quark (c, b, t) contribution are discussed and presented as well as hadronic heavy quark production at SSC/LHC energies. For example, the \(b\bar b\) production rate at 40 TeV is predicted to be about an order of magnitude larger than that estimated with other gluon distributions so far.     

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^?1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.     

Quarkonium production at the CERNp \bar p collider

Calculations on the production and decays of heavy flavour bound states have recently been implemented in the EUROJET Monte Carlo program for hadronic interactions. The matrix elements that describe the production of heavy quarkonia inp \(\bar p\) interactions are based on fixed order perturbative QCD in combination with the nonrelativistic quarkonium model. The decays of the bound states are a compilation of experimental data and theoretical models. We present a detailed study onJψ and Γ production at the CERNp \(\bar p\) collider and compare our results with data recently obtained by the UA1 experiment.     

Thermal hadron production in high energy heavy ion collisions

We provide a method to test if hadrons produced in high energy heavy ion collisions were emitted at freeze-out from an equilibrium hadron gas. Our considerations are based on an ideal gas at fixed temperatureT _f , baryon number densityn _B , and vanishing total strangeness. The constituents of this gas are all hadron resonances up to a mass of 2 GeV; they are taken to decay according to the experimentally observed branching ratios. The ratios of the various resulting hadron production rates are tabulated as functions ofT _f andn _B . These tables can be used for the equilibration analysis of any heavy ion data; we illustrate this for some specific cases.     

Investigation of the dynamics of gluon distributions in the production of heavy quarks and quarkonia at the LEP2 collider

The inclusive production of heavy quarks and quarkonia in photon-photon collisions at the LEP2 collider is considered within the semihard (k _T-factorization) QCD approach. The dependence of the total and differential cross sections for the production of heavy (c and b) quarks and D* and J/ψ mesons on the choice of unintegrated gluon distribution is studied. The transition of a $c\bar c$ charmed pair to observed J/ψ mesons is described on the basis of the color-singlet model. The results of the calculations are compared with currently available experimental data obtained by the L3, OPAL, ALEPH, and DELPHI Collaborations. It is shown that the polarization properties of J/ψ mesons at the LEP2 collider are sensitive to the behavior of unintegrated gluon distributions. This means that experimental investigations of the polarization properties of quarkonia in photon-photon collisions may provide a direct test of the dynamics of gluon distributions in the photon.     

Forward-backward asymmetry of hadroproduced heavy quarks in QCD

It has been argued that higher order 2→3 O(α_s³ QCD processes play an important role in the hadroproduction of heavy quarks. We propose forward-backward or charge conjugation asymmetry as a distinctive signature of the higher-order QCS production mechanism. We analyse the physical origin of the asymmetries and show that observed forward-backward asymmetries for the heavy quark or decay lepton are 5% or less for realistic experimental conditions. Observation of asymmetries in excess of our calculated values would signal the production of heavy quarks via unconventional mechanisms.     

Trimuon final states in lepton-hadron scattering: Model-independent study of the production mechanism

It is pointed out the trimuon events due to conventional pair creation can be distinguished from heavy lepton and heavy quark production by model-independent spinparity selection rules. Asymmetries and (angular) moment integrals are defined which give a quantitative measure of the contributions due to the “new” sources. The same analysis can be applied to muon-pair production in hadronic collisions to determine the size of charm-particle (and other new flavor) production there.     

Neutral strange particle production in charged current νA-interactions in the energy range 3≦E ν≦30 GeV

For charged current neutrino nucleus interactions at energies below 30 GeV, resulting from an experiment with the freon filled bubble chamber SKAT,K ⁰ and Λ production is investigated. An estimation of the total strange and charm production cross section is made.K ⁰ and Λ production rates are given in dependence on different inclusive variables. The production properties forK ⁰′s and Λ′s are discussed in terms of the Quark-Parton-Model. Comparisons with other ν-experiments at higher energies are performed.