The Sources of b-Quarks at the Tevatron and their Correlations

The leading-log order QCD hard scattering Monte-Carlo models of HERWIG, ISAJET, and PYTHIA are used to study the sources of b-quarks at the Tevatron. The reactions responsible for producing b and bbar quarks are separated into three categories; flavor creation, flavor excitation, and parton-shower/fragmentation. Flavor creation corresponds to the production of a b-bbar pair by gluon fusion or by annihilation of light quarks, while flavor excitation corresponds to a b or bbar quark being knocked out of the initial-state by a gluon or a light quark or antiquark. The third source occurs when a b-bbar pair is produced within a parton shower or during the fragmentation process of a gluon or a light quark or antiquark (includes gluon splitting). The QCD Monte-Carlo models indicate that all three sources of b-quarks are important at the Tevatron and when combined they qualitatively describe the inclusive cross-section data. Correlations between the b and bbar quark are very different for the three sources and can be used to isolate the individual contributions.Comment: RevTex4, 14 pages, 20 figures, submitted to Phys. Rev.

Modeling the jet quenching, thermal resonance production and hydrodynamical flow in relativistic heavy ion collisions

The event topology in relativistic heavy ion collisions is determined by various multi-particle production mechanisms. The simultaneous model treatment of different collective nuclear effects at high energies (such as a hard multi-parton fragmentation in hot QCD-matter, thermal resonance production, hydrodynamical flows, etc.) is actual but rather complicated task. We discuss the simulation of the above effects by means of Monte-Carlo model HYDJET++.Comment: Talk given at Workshop "Hot Quarks 2010" (La Londe Les Maures, France, June 21-26, 2010); 4 pages including 2 figures as EPS-files; prepared using LaTeX package for publication in Journal of Physics: Conference Serie

A Positive-Weight Next-to-Leading-Order Monte Carlo for Z Pair Hadroproduction

We present a first application of a previously published method for the computation of QCD processes that is accurate at next-to-leading order, and that can be interfaced consistently to standard shower Monte Carlo programs. We have considered Z pair production in hadron-hadron collisions, a process whose complexity is sufficient to test the general applicability of the method. We have interfaced our result to the HERWIG and PYTHIA shower Monte Carlo programs. Previous work on next-to-leading order corrections in a shower Monte Carlo (the MC@NLO program) may involve the generation of events with negative weights, that are avoided with the present method. We have compared our results with those obtained with MC@NLO, and found remarkable consistency. Our method can also be used as a standalone, alternative implementation of QCD corrections, with the advantage of positivity, improved convergence, and next-to-leading logarithmic accuracy in the region of small transverse momentum of the radiated parton.Comment: 33 pages, 10 figure

Reconstructing Sparticle Mass Spectra using Hadronic Decays

Most sparticle decay cascades envisaged at the Large Hadron Collider (LHC) involve hadronic decays of intermediate particles. We use state-of-the art techniques based on the \kt jet algorithm to reconstruct the resulting hadronic final states for simulated LHC events in a number of benchmark supersymmetric scenarios. In particular, we show that a general method of selecting preferentially boosted massive particles such as W, Z or Higgs bosons decaying to jets, using sub-jets found by the \kt algorithm, suppresses QCD backgrounds and thereby enhances the observability of signals that would otherwise be indistinct. Consequently, measurements of the supersymmetric mass spectrum at the per-cent level can be obtained from cascades including the hadronic decays of such massive intermediate bosons.Comment: 1+29 pages, 12 figure

Gamma Rays from Clusters and Groups of Galaxies: Cosmic Rays versus Dark Matter

Clusters of galaxies have not yet been detected at gamma-ray frequencies; however, the recently launched Fermi Gamma-ray Space Telescope, formerly known as GLAST, could provide the first detections in the near future. Clusters are expected to emit gamma rays as a result of (1) a population of high-energy primary and re-accelerated secondary cosmic rays (CR) fueled by structure formation and merger shocks, active galactic nuclei and supernovae, and (2) particle dark matter (DM) annihilation. In this paper, we ask the question of whether the Fermi telescope will be able to discriminate between the two emission processes. We present data-driven predictions for a large X-ray flux limited sample of galaxy clusters and groups. We point out that the gamma ray signals from CR and DM can be comparable. In particular, we find that poor clusters and groups are the systems predicted to have the highest DM to CR emission at gamma-ray energies. Based on detailed Fermi simulations, we study observational handles that might enable us to distinguish the two emission mechanisms, including the gamma-ray spectra, the spatial distribution of the signal and the associated multi-wavelength emissions. We also propose optimal hardness ratios, which will help to understand the nature of the gamma-ray emission. Our study indicates that gamma rays from DM annihilation with a high particle mass can be distinguished from a CR spectrum even for fairly faint sources. Discriminating a CR spectrum from a light DM particle will be instead much more difficult, and will require long observations and/or a bright source. While the gamma-ray emission from our simulated clusters is extended, determining the spatial distribution with Fermi will be a challenging task requiring an optimal control of the backgrounds.Comment: revised to match resubmitted version, 35 pages, 16 figures: results unchanged, some discussion added and unnecessary text and figures remove

Fourth Generation Pseudoscalar Quarkonium Production and Observability at Hadron Colliders

The pseudoscalar quarkonium state, eta_4 1^S_0, formed by the Standard Model (SM) fourth generation quarks, is the best candidate among the fourth generation quarkonia to be produced at the LHC and VLHC. The production of this J^{PC} = 0^{-+} resonance is discussed and the background processes are studied to obtain the integrated luminosity limits for the discovery, depending on its mass.Comment: 13 pages, 4 figures, 5 table

Same Sign WW Scattering Process as a Probe of Higgs Boson in pp Collision at s\sqrt{s} = 10 TeV

WW scattering is an important process to study electroweak symmetry breaking in the Standard Model at the LHC, in which the Higgs mechanism or other new physics processes must intervene to preserve the unitarity of the process below 1 TeV. This channel is expected to be one of the most sensitive to determine whether the Higgs boson exists. In this paper, the final state with two same sign Ws is studied, with a simulated sample corresponding to the integrated luminosity of 60 fb$^{-1}$ in pp collision at $\sqrt{s}=$10 TeV. Two observables, the invariant mass of $\mu\mu$ from W decays and the azimuthal angle difference between the two $\mu$s, are utilized to distinguish the Higgs boson existence scenario from the Higgs boson absence scenario. A good signal significance for the two cases can be achieved. If we define the separation power of the analysis as the distance, in the log-likelihood plane, of pseudo-experiments outcomes in the two cases, with the total statistics expected from the ATLAS and CMS experiments at the nominal centre-of-mass energy of 14 TeV, the separation power will be at the level of 4 $\sigma$.Comment: 5 pages, 4 figures, 3 table

SANC integrator in the progress: QCD and EW contributions

Modules and packages for the one-loop calculations at partonic level represent the first level of SANC output computer product. The next level represents Monte Carlo integrator mcsanc, realizing fully differential hadron level calculations (convolution with PDF) for the HEP processes at LHC. In this paper we describe the implementation into the framework mcsanc first set of processes: DY NC, DY CC, ff->HW(Z) and single top production. Both EW and QCD NLO corrections are taken into account. A comparison of SANC results with those existing in the world literature is given

Generic User Process Interface for Event Generators

Generic Fortran common blocks are presented for use by High Energy Physics event generators for the transfer of event configurations from parton level generators to showering and hadronization event generators.Comment: Physics at TeV Colliders II Workshop, Les Houches, France, May 2001 14 pages, 6 figure

Charm-quark fragmentation with an effective coupling constant

We use a recently proposed non-perturbative model, based on an effective strong coupling constant and free from tunable parameters, to study c-flavoured hadron production in e+e- annihilation. Charm-quark production is described in the framework of perturbative fragmentation functions, with NLO coefficient functions, NLL non-singlet DGLAP evolution and NNLL large-x resummation. We model hadronization effects by means of the effective coupling constant in the NNLO approximation and compare our results with experimental data taken at the Z0 pole and at the Upsilon(4S) resonance. We find that, within the experimental and theoretical uncertainties, our model is able to give a reasonable description of D*+-meson spectra from ALEPH for x<1-Lambda/m_c. More serious discrepancies are instead present when comparing with D and D^* data from BELLE and CLEO in x-space. Within the errors, our model is nonetheless capable of reproducing the first ten Mellin moments of all considered data sets. However, the fairly large theoretical uncertainties call for a full NNLO/NNLL analysis.Comment: 26 pages, 10 figures. Analysis in Mellin space and few references adde