Probing the medium-induced energy loss of bottom quarks by dimuon production in heavy ion collisions at LHC

The potential of coming experiments on the Large Hadron Collider (LHC) to observe the rescattering and energy loss of heavy quarks in the dense matter created in heavy ion collisions is discussed. We analyze the sensitivity of high-mass pairs from semileptonic decays and secondary 's from single B decays to the medium-induced bottom quark energy loss. Received: 18 December 2000 / Revised version: 17 May 2001 / Published online: 6 July 2001     

Proton–proton interaction in constituent quarks model at LHC energies

In this paper we consider soft processes at LHC energies in the framework of the constituent quark model. We show that this rather naive model is able to describe all available soft process data at lower energies and to predict the behavior of the total cross section, the elastic and diffractive cross sections at LHC energy. It turns out that the “input” pomeron that has been used in this approach has parameters that are close to the so called “hard” pomeron with rather large intercept Δ≈0.12 and small value of the slope α^′ _P≈0.08 GeV^-2. We show that the elastic amplitude has a minimum at impact parameter b=0 and a maximum at b≈2 GeV^-1. Such a behavior is the result of overlapping of the parton clouds that belong to the different quarks in the hadron.     

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.     

Inclusive production at LHC energies

We consider the first LHC data for pp collisions in the framework of Regge theory. The integral cross sections and inclusive densities of secondaries are determined by the Pomeron exchange, and we present the corresponding predictions for them. The first measurements of inclusive densities in the midrapidity region are in agreement with these predictions. The contribution of the baryon-number transfer due to String Junction diffusion in the rapidity space is at the origin of the differences in the inclusive spectra of particle and antiparticle in the central region, and this effect could be significant at LHC energies. We discuss the first data of ALICE and LHCb collaborations on the baryon/antibaryon asymmetry at LHC.     

Single top production associated with a neutral scalar at LHC in topcolor-assisted technicolor

The topcolor-assisted technicolor (TC2) model predicts a number of neutral scalars like the top-pion (π⁰_t) and the top-Higgs (h⁰_t). These scalars have flavor-changing neutral-current (FCNC) top quark couplings, among which the top-charm transition couplings may be sizable. Such FCNC couplings induce single top productions associated with a neutral scalar at the CERN Large Hadron Collider (LHC) through the parton processes cg→t π⁰_t and cg→t h⁰_t. In this paper we examine these productions and find their production rates can exceed the 3σ sensitivity of the LHC in a large part of parameter space. Since in the Standard Model and the minimal supersymmetric model such rare productions have unobservably small production rates at the LHC, these rare processes will serve as a good probe for the TC2 model.     

Single slepton production associated with a top quark at LHC in NLO QCD

Single slepton production in association with a top quark at the CERN Large Hadron Collider (LHC) is one of the important processes in probing the R-parity violation couplings. We calculate the QCD next-to-leading order (NLO) corrections to the $pp \to t\tilde{\ell}^{-}(\bar{t}\tilde{\ell}^{+})+X$ process at the LHC and discuss the impacts of the QCD corrections on kinematic distributions. We investigate the dependence of the leading order (LO) and the NLO QCD corrected integrated cross section on the factorization/renormalization energy scale, slepton, stop-quark and gluino masses. We find that the uncertainty of the LO cross section due to the energy scale is obviously improved by the NLO QCD corrections, and the exclusive jet event selection scheme keeps the convergence of the perturbative series better than the inclusive scheme. The results show that the polarization asymmetry of the top-quark will be reduced by the NLO QCD corrections, and the QCD corrections generally increase with the increment of the $\tilde{t}_{1}$ or $\tilde {g}$ mass value.     

Single top production associated with a neutral scalar at LHC in topcolor-assisted technicolor

The topcolor-assisted technicolor(TC2)model predicts a number of neutral SCalars like the top-pion (π0t)and the top-Higgs(h0t).These scalar8 have flavor-changing neutral-current(FCNC)top quark couphngs,among which the top-charm transition couplings may be sizable.Such FCNC couplings induce single top productions associated with a neutral scalar at the CERN Large Hadron Collider(LHC)through the parton processes cg→tπ0t and cg→th0t.In this paper we examine these productions and find their production rates can exceed the 3σ sensitivity of the LHC in a large part of parameter space.Since in the Standard Model and the minimal supersymmetric model such rare productions have unobservably small production rates at the LHC.these rare processes will serve as a good probe for the TC2 model.     

Multiple charm production at the LHC energy

Cross sections for J/ψ mesons produced in association with open charm and two charmed hadrons from different $c\bar c$ pairs under LHC conditions are predicted theoretically. The respective processes are considered both in single and in double parton interactions. Particular attention is given to kinematical limits of the LHCb detector, and a comparison with the most recent experimental data is performed for them.     

Identification of extra neutral gauge bosons at the LHC using b and t quarks

New neutral gauge bosons (Z' 's) are predicted by many models of physics beyond the standard electroweak theory. It is possible that a Z' will be discovered by the Large Hadron Collider program. The next step would be to measure its properties to identify the underlying theory that gave rise to the Z'. Heavy quarks have the unique property that they can be identified in the final states. In this Letter we demonstrate that measuring Z' decays to b- and t-quark final states can act as an effective means of discriminating between models with extra gauge bosons.     

Higgs signal in chargino-neutralino production at the LHC

We have analyzed the prospect of detecting a Higgs signal in mSUGRA/cMSSM based Supersymmetric (SUSY) model via chargino-neutralino ( ${\tilde{\chi}}^{\pm}_{1}\tilde{\chi}^{0}_{2}In order to generate mass for an abelian spin-1 vector field while preserving gauge invariance we couple it to a symmetric tensor. The derivative coupling includes up to three derivatives. We show that unitarity, causality and absence of Stueckelberg (compensating) fields single out a unique model up to trivial field redefinitions. The model contains one massive and one massless spin-1 particle. It is shown by means of a master action to be dual to the direct sum of a Maxwell plus a Maxwell?CProca theory.     

Standard and SUSY Higgs production at the LHC

Recent theoretical developments concerning Higgs production at the large hadron collider are reviewed, both in the standard model and in the MSSM. Emphasis is put on the inclusive and exclusive cross-sections for gluon fusion, as well as on the associated production with bottom quarks.     

Top-quark pair production near threshold at LHC

The next-to-leading order analysis for the cross section for hadroproduction of top-quark pairs close to threshold is presented. Within the framework of non-relativistic QCD a significant enhancement compared to fixed-order perturbation theory is observed which originates from the characteristic remnant of the 1S peak below production threshold of top-quark pairs. The analysis includes all color-singlet and color-octet configurations of top-quark pairs in S-wave states and, for the dominant configurations, it employs all-order soft-gluon resummation for the hard parton cross section. Numerical results for the Large Hadron Collider at TeV and TeV and also for the Tevatron are presented. The possibility of a top-quark mass measurement from the invariant-mass distribution of top-quark pairs is discussed.