Dilepton from Passage of Jets Through Spherical Expanding QGP

We calculate the large mass dileptons production from the jet-dilepton conversion in spherical expanding quark-gluon plasma at Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) energies. The jet-dilepton production exceeds the thermal and Drell-Yan dilepton production in the large mass region of 4.5 GeV< M< 5.5 GeV and 7 GeV< M< 9 GeV in central Pb+Pb collisions at √s_NN=2.76 TeV and 5.5 TeV, respectively. We present the solution of (1+3)-dimensional fluid hydrodynamics with spherical symmetry. We find that the transverse flow of the QGP leads to a rapid cooling of the fire ball and suppression of the jet-dilepton conversion. The suppression is also evident at intermediate and large mass at LHC energies. The energy loss of the jet-dilepton conversion is concerned.     

Large mass dilepton production from jet-dilepton conversion in the quark-gluon plasma

We calculate the production of large mass dileptons from the passage of jets passing through the quark-gluon plasma. Using the relativistic kinetic theory, we rigorously derive the production rate for the jet-dilepton conversion in the hot medium. The jet-dilepton conversion is compared with the thermal dilepton emission and the Drell-Yan process. The contribution of the jet-dilepton conversion is not prominent for all values of the invariant mass M, and the Drell-Yan process is found to dominate over the thermal dilepton emission and the jet-dilepton conversion for M>2.5 GeV at RHIC. The jet-dilepton conversion is the dominant source of large mass dileptons in the range of 4 GeV<M<10 GeV at LHC.     

Particle multiplicities in lead-lead collisions at the CERN large hadron collider from nonlinear evolution with running coupling corrections

We present predictions for the pseudorapidity density of charged particles produced in central Pb-Pb collisions at the LHC. Particle production in such collisions is calculated in the framework of k(t) factorization. The nuclear unintegrated gluon distributions at LHC energies are determined from numerical solutions of the Balitsky-Kovchegov equation including recently calculated running coupling corrections. The initial conditions for the evolution are fixed by fitting Relativistic Heavy Ion Collider data at collision energies square root[sNN]=130 and 200 GeV per nucleon. We obtain dNch(Pb-Pb)/deta(square root[sNN]=5.5 TeV)/eta=0 approximately 1290-1480.     

Probing small parton densities in ultraperipheral A A and pA collisions at the CERN large Hadron Collider

We calculate photoproduction rates for several hard processes in ultraperipheral proton-lead and lead-lead collisions at the CERN Large Hadron Collider (LHC) with square root of sNN = 8.8 and 5.5 TeV, respectively, which could be triggered in the large LHC detectors. We use ATLAS as an example. The lead ion is treated as a source of (coherently produced) photons with energies and intensities greater than those of equivalent ep collisions at the DESY collider HERA. We find very large rates for both inclusive and diffractive production that will extend the HERA x range by nearly an order of magnitude for similar virtualities. We demonstrate that it is possible to reach the kinematic regime where nonlinear effects are larger than at HERA.     

Searches for Dark Matter via Mono-W Production in Inert Doublet Model at the LHC

The Inert Doublet Model(IDM) is one of the many beyond Standard Model scenarios with an extended scalar sector, which provide a suitable dark matter particle candidate. Dark matter associated visible particle production at high energy colliders provides a unique way to determine the microscopic properties of the dark matter particle. In this paper, we investigate that the mono-W + missing transverse energy production at the Large Hadron Collider(LHC),where W boson decay to a lepton and a neutrino. We perform the analysis for the signal of mono-W production in the IDM and the Standard Model(SM) backgrounds, and the optimized criteria employing suitable cuts are chosen in kinematic variables to maximize signal significance. We also investigate the discovery potential in several benchmark scenarios at the 14 TeV LHC. When the light Z_2 odd scalar higgs of mass is about 65 GeV, charged Higgs is in the mass range from 120 GeV to 250 GeV, it provides the best possibility with a signal significance of about 3σ at an integrated luminosity of about 3000 fb~(-1).     

From RHIC to LHC: a relativistic diffusion approach

We investigate the energy dependence of stopping and hadron production in high‐energy heavy‐ion collisions based on a three‐sources Relativistic Diffusion Model. The transport coefficients are extrapolated from Au + Au and Cu + Cu at RHIC energies ( = 19.6–200 GeV) to Pb + Pb at LHC energies = 5.52 TeV. Rapidity distributions for net protons, and pseudorapidity spectra for produced charged particles in central collisions are compared to data at RHIC energies, and discussed for several extrapolations to LHC energies.     

Strange particle production in relativistic nucleus-nucleus collisions at RHIC and LHC energy regions

PACIAE, a parton and hadron cascade model, is utilized to systematically investigate strange particle production and strangeness enhancement in Au+Au collisions and in Pb+Pb collisions with the √s_NN=200 GeV at the RHIC and 2.76 TeV at the LHC, respectively. The experimental results at different centralities, using data from the STAR collaboration and the ALICE collaboration, are well described by the PACIAE model. This may represent the importance of the parton and hadron rescatterings, as well as the reduction mechanism for strange quark suppression, that are implemented in the PACIAE model.     

Radial profile of bottom quarks in jets in high-energy nuclear collisions

Angular correlations between a heavy quark(HQ) and its tagged jet are potentially new tools to gain insight into the in-medium partonic interactions in relativistic heavy-ion collisions.In this work,we present the first theoretical study on the radial profiles of B mesons in jets in Pb+Pb collisions at the Large Hadron Collider(LHC).The initial production of a bottom quark tagged jet in p+p is computed by SHERPA,which matches the next-toleading order matrix elements with contributions of parton showers,whereas the massive quark traversing the quarkgluon plasma is described by a Monte Carlo model,SHELL,which can simultaneously simulate light and heavy flavor in-medium energy loss within the framework of Langevin evolution.In p+p collisions,we find that at lower p_T~Q the radial profiles of heavy flavors in jets are sensitive to the heavy quark mass.In 0-10% Pb+Pb collisions at S_(NN)~(1/2)=5.02 TeV,we observe an inverse modification pattern of the B meson radial profiles in jets at 4 p_T~Q 20 GeV compared to those of D mesons:the jet quenching effects narrow the jet radial profiles of B mesons in jets while broadening those of D mesons in jets.We find that in A+A collisions,the contribution dissipated from the higher p_T~Q 20 GeV region naturally has a narrower initial distribution and consequently leads to a narrower modification pattern of the radial profile;however the diffusion nature of the heavy flavor in-medium interactions will give rise to a broader modification pattern of the radial profile.These two effects consequently compete and offset with each other,and the b quarks in jets benefit more from the former and suffer less diffusion effect compared to that of c quarks in jets.These findings can be tested in the future experimental measurements at the LHC to gain better understanding of the mass effect of jet quenching.     

Search for top quark FCNC couplings in Z′ models at the LHC and CLIC

The top quark is the heaviest particle to date discovered, with a mass close to the electroweak symmetry breaking scale. It is expected that the top quark would be sensitive to the new physics at the TeV scale. One of the most important aspects of the top quark physics can be the investigation of the possible anomalous couplings. Here, we study the top quark flavor changing neutral current (FCNC) couplings via the extra gauge boson Z′ at the Large Hadron Collider (LHC) and the Compact Linear Collider (CLIC) energies. We calculate the total cross sections for the signal and the corresponding Standard Model (SM) background processes. For an FCNC mixing parameter x=0.2 and the sequential Z′ mass of 1 TeV, we find the single top quark FCNC production cross sections 0.38(1.76) fb at the LHC with $\sqrt{s_{pp}}=7(14)$ TeV, respectively. For the resonance production of sequential Z′ boson and decays to single top quark at the Compact Linear Collider (CLIC) energies, including the initial state radiation and beamstrahlung effects, we find the cross section to be 27.96(0.91) fb at $\sqrt{s_{e^{+}e^{-}}}=1(3)$ TeV, respectively. We make the analysis to investigate the parameter space (mixing-mass) through various Z′ models. It is shown that the results benefit from the flavor tagging.     

Discovering new physics in the decays of black holes

If the scale of quantum gravity is near a TeV, the CERN Large Hadron Collider (LHC) will be producing one black hole (BH) about every second, thus qualifying as a BH factory. With the Hawking temperature of a few hundred GeV, these rapidly evaporating BHs may produce new, undiscovered particles with masses approximately 100 GeV. The probability of producing a heavy particle in the decay depends on its mass only weakly, in contrast with the exponentially suppressed direct production. Furthermore, backgrounds in the BH sample can be made small. Using the Higgs boson as an example, we show that it may be found at the LHC on the first day of its operation, even with incomplete detectors.     

Top quark forward-backward asymmetry and same-sign top quark pairs

The top quark forward-backward asymmetry measured at the Tevatron collider shows a large deviation from standard model expectations. Among possible interpretations, a nonuniversal Z' model is of particular interest as it naturally predicts a top quark in the forward region of large rapidity. To reproduce the size of the asymmetry, the couplings of the Z' to standard model quarks must be large, inevitably leading to copious production of same-sign top quark pairs at the energies of the Large Hadron Collider (LHC). We explore the discovery potential for tt and ttj production in early LHC experiments at 7-8 TeV and conclude that if no tt signal is observed with 1 fb?1 of integrated luminosity, then a nonuniversal Z' alone cannot explain the Tevatron forward-backward asymmetry.     

Search for a fourth generation t' Quark in p ̄p collisions at √s = 1.96 TeV

We present a search for pair production of a fourth generation t' quark and its antiparticle, followed by their decays to a W boson and a jet, based on an integrated luminosity of 5.3 fb(-1) of proton-antiproton collisions at √s = 1.96 TeV collected by the D0 Collaboration at the Fermilab Tevatron Collider. We set upper limits on the t' ?t' production cross section that exclude at the 95% C.L. a t' quark that decays exclusively to W+jet with a mass below 285 GeV. We observe a small excess in the μ+jets channel which reduces the mass range excluded compared to the expected limit of 320 GeV in the absence of a signal.     

LHC capabilities for quarkonium

The measurement of the charmonium and bottomonium resonances in nucleus-nucleus collisions provides crucial information on high-density QCD matter. First, the suppression of quarkonia production is generally agreed to be one of the most direct probes of quark-gluon plasma formation. The observation of anomalous J/ψ suppression at the CERN-SPS and at RHIC is well established but the clarification of some important remaining questions requires equivalent studies of the ϒ family, will be possible at the LHC. Second, the production of heavy-quarks proceeds mainly via gluon-gluon fusion processes and, as such, is sensitive to saturation of the gluon density at low-x in the nucleus. Measured departures from the expected vacuum quarkonia cross-sections in Pb+Pb collisions at the LHC will thus provide valuable information not only on the thermodynamical state of the produced partonic medium, but also on the initial-state modifications of the nuclear parton distribution functions. The capabilities of the LHC detectors (ALICE, ATLAS and CMS) to study quarkonia production in Pb+Pb collisions at 5.5 TeV per nucleon pair are discussed.     

Signatures of gravitational fixed points at the Large Hadron Collider

We study quantum-gravitational signatures at the CERN Large Hadron Collider (LHC) in the context of theories with extra spatial dimensions and a low fundamental Planck scale in the TeV range. Implications of a gravitational fixed point at high energies are worked out using Wilson's renormalization group. We find that relevant cross sections involving virtual gravitons become finite. Based on gravitational lepton pair production we conclude that the LHC is sensitive to a fundamental Planck scale of up to 6 TeV.     

Charmonium production in fixed-target experiments with SPS and LHC beams at CERN

The possibility of measuring cross sections for the production of J/ψ mesons in fixed-target experiments with the proton and ion beams of the Large Hadron Collider (LHC) at CERN (Switzerland) is considered. At the present time, measurements of charmonium production in proton-proton collisions at an energy of 7 TeV have begun at LHC. Previously, the production of J/ψ and ψ′ mesons was studied in the NA38, NA50, and NA60 fixed-target experiments with beams of the CERN synchrotron (SPS) and in the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC, Brookhaven National Laboratory, USA). A normal nuclear absorption of J/ψ mesons in proton-nucleus collisions and an enhanced, anomalous, suppression of the production of charmonium states in central collisions of relativistic nuclei were observed. At the present time, there are no theoretical models that could describe the entire body of experimental data. Measurements over a broad interval of proton and ion energies are required. Measurements of charmonium production using LHC beams with fixed targets in the energy range between the SPS and RHIC energies-a beam of 7-TeV protons (√s = 114.6 GeV) and a beam of 2.75-TeV/nucleon lead ions (√s = 71.8 GeV)-will provide an additional possibility for studying the charmonium-production mechanism. Estimates of the geometric acceptance, luminosity, and counting rate for the production of J/ψ mesons are presented.     

How to probe high gluon densities in pp collisions at the Large Hadron Collider

We present a model for hadron production in the proton fragmentation region in pp collisions at the CERN Large Hadron Collider which accounts for the first time for effects of very strong small x gluon fields. Average transverse momenta acquired by the valence quarks exceed 1 GeV/c for central collisions and result in the suppression of leading baryon production and an additional energy flow to smaller rapidities. A strong dependence on the impact parameter will allow one to investigate the propagation of leading partons through gluon fields of a strength comparable to the ones encountered in heavy ion collisions at the LHC and in cosmic-ray-air interactions at highest energies.     

Electromagnetic and hadronic interactions of ultrarelativistic nuclei

Beam nuclei accelerated at the Large Hadron Collider (LHC) at CERN are lost due to interactions with the counter-rotating beam, residual gas, and accelerator elements. Proper modelling of the beam transport and radiation load on accelerator components requires reliable prediction of the yields of nuclear fragments produced in electromagnetic dissociation and hadronic fragmentation of beam nuclei. We investigate electromagnetic and hadronic fragmentation of lead nuclei in collisions with various nuclei and single electrons at the injection and collision energies of the LHC. The consideration is based on the RELDIS and abrasion-ablation models. Since this approach well describes Pb fragmentation data at 30 and 158 A GeV, its validity for Pb nuclei at the LHC collision energy is also expected.     

Jet signals for low mass strings at the large hadron collider

The mass scale M{s} of superstring theory is an arbitrary parameter that can be as low as few TeVs if the Universe contains large extra dimensions. We propose a search for the effects of Regge excitations of fundamental strings at the CERN Large Hadron Collider (LHC), in the process pp-->gamma+jet. The underlying parton process is dominantly the single photon production in gluon fusion, gg-->gammag, with open string states propagating in intermediate channels. If the photon mixes with the gauge boson of the baryon number, which is a common feature of D-brane quivers, the amplitude appears already at the string disk level. It is completely determined by the mixing parameter-and it is otherwise model (compactification) independent. Even for relatively small mixing, 100 fb{-1} of LHC data could probe deviations from standard model physics, at a 5sigma significance, for M{s} as large as 3.3 TeV.     

Charmonium production in proton-proton collisions and in collisions of lead nuclei at CERN and comparison with Brookhaven data

A review of experimental data on charmoniumproduction that were obtained in fixed-target experiments at the SPS synchrotron and in proton-proton collisions and in collisions of lead nuclei in beams of the Large Hadron Collider (LHC) at CERN (Switzerland) is presented. A comparison with data obtained at the Brookhaven National Laboratory (USA) from experiments at the Relativistic Heavy Ion Collider (RHIC) is performed. Measurement of the suppression of J/ψ-meson production as a possible signal of the production of quark-gluon plasmawas proposed back in 1986 by T. Matsui and H. Satz. An anomalous suppression of J/ψ-meson production was discovered by the NA50 Collaboration at SPS (CERN) in central collisions of lead nuclei at the c.m. collision energy of 158 GeV per nucleon. Data obtained at the c.m. energy of 200 GeV per nucleon in the PHENIX experiment at RHIC indicate that, depending on multiplicity, the suppression of J/ψ-meson production at this energy approximately corresponds to the suppression of J/ψ-meson production in collisions of lead nuclei at the SPS accelerator. Theoretical models that take into account the regeneration of J/ψ mesons describe better RHIC experimental data. The measurement of charmonium production in proton-proton collisions and in collisions of lead nuclei in LHC beams revealed the importance of taking into account the regeneration process. At the LHC energies, it is also necessary to take into account the contribution of B-meson decays. Future measurements of charmonium production at the LHC to a higher statistical precision and over an extended energy region would be of importance for obtaining deeper insight into the mechanism of charmonium production and for studying the properties of matter at high energy density and temperature.     

Search for a neutral Higgs boson decaying to a W boson pair in pp collisions at square root of s = 1.96 TeV

We present the results of a search for standard model Higgs boson production with decay to WW*, identified through the leptonic final states e+ e- nu nu,+/-mu -/+nu nu and mu+ mu- nu nu. This search uses 360 pb -1 of data collected from pp collisions at square root of s =1.96 TeV by the upgraded Collider Detector at Fermilab (CDF II). We observe no signal excess and set 95% confidence level upper limits on the production cross section times branching ratio for the Higgs boson to WW* or any new scalar particle with similar decay products. These upper limits range from 5.5 to 3.2 pb for Higgs boson masses between 120 and 200 GeV/c2.