Production of b-quark jets at the large Hadron Collider in the parton-reggeization approach

The inclusive hadroproduction of b-quark jets and $b\bar b$ -quark dijets at the Large Hadron Collider is considered by using the hypothesis of gluon Reggeization in t-channel exchanges at high energies. Experimental data obtained by the ATLAS Collaboration are described well within all of the presented kinematical regions for single b-quark jets and $b\bar b$ -quark dijets without resort to any free parameters.     

Production and correlations of <Emphasis Type="Italic">b</Emphasis> quarks at the LHC energies

Processes leading to b-quark production at the LHC energies are simulated by using the Pythia generator. For proton-proton interactions at 7 and 14 TeV, the cross sections for b-quark production are evaluated for three mechanisms that are taken into account in the Pythia generator. These are quark-pair production, the excitation of sea quarks, and gluon splitting. Correlations of azimuthal angles of b-quark emission and properties of accompanying particles in events induced by the various mechanisms of b-quark production are calculated. The results are compared with data from the CDF experiment.     

QCD effects and b-tagging at LEP I

We analyze the impact of using b-tagged samples in studying non-Abelian effects due to QCD in e ⁺ e ^? → 4jet events at ${sqrt s=M_{Z^0}}$, using angular variable analyses and comparisons with e ⁺ e ^? → 3jetγ events. We find that QCD effects are largely enhanced in b-quark samples with respect to ‘unflavoured’ ones, where energy-ordering is used to distinguish between gluon and quark jets. We show that the b-quark mass influences the angular distributions significantly and should not be neglected.     

QCD effects andb-tagging at LEP I

We analyze the impact of usingb-tagged samples in studying non-Abelian effects due to QCD ine ⁺ e ^? → 4jet events at √s=M _z ⁰, using angular variable analyses and comparisons withe ⁺ e ^? → 3jetγ events. We find that QCD effects are largely enhanced inb-quark samples with respect to ‘unflavoured’ ones, where energy-ordering is used to distinguish between gluon and quark jets. We show that theb-quark mass influences the angular distributions significantly and should not be neglected.     

b-Jet asymmetries inZ decays

The forward-backward asymmetry ofb-quark jets inZ decays can be exploited to determine sin²θ _W very accurately. Electroweak and QCD corrections are analysed in detail.     

Three-loop running of the strong coupling constant and the mass of the <Emphasis Type="Italic">b</Emphasis>-quark in the supersymmetric QCD

Supersymmetric extension of the QCD (SQCD) is considered and the scale dependence of some important parameters, i.e. strong coupling α _s and b-quark running mass m _b , is studied with the help of threeloop renormalization group equations. Five-flavour QCD is considered as a low-energy effective theory of SQCD and two-loop decoupling (threshold) effects are taken into account. Variations in running α _s and m _b at the GUT scale μ_GUT = 10¹⁶ GeV due to uncertainties in the initial experimental data and the ambiguities in the decoupling scale are analyzed for a particular point of the parameter space. Comparison with known results is given.     

Determination of the b -quark mass and nonperturbative parameters in semileptonic B -meson decays at BABAR⋆

Knowing the mass of the b -quark is essential to the study of the structure and decays of B -mesons as well as to future tests of the Higgs mechanism of mass generation. We present recent preliminary measurements of the b -quark mass and related nonperturbative parameters from moments of kinematic distributions in charmed and charmless semileptonic B -meson decays. Their determination from charmless semileptonic B -meson decays is the first measurement in this mode. The data were collected by the BABAR detector at the PEP-II asymmetric-energy e ⁺ e ^- -collider at the Stanford Linear Accelerator Center at a center-of-mass energy of 10.58GeV. Original article based on material presented at HADRON 2007.     

Magnetic moments ofb-quark baryons in broken SU(5) symmetry

The magnetic moments ofb-quark baryons within the framework of five quark models are derived. Also the transition magnetic moments of variousb-quark baryons are calculated.     

P and CP violation in<Emphasis Type="Italic">B</Emphasis> physics

While the Kobayashi-Maskawa single phase origin of CP violation passed its first crucial precision test inB → J/ψK s, the chirality of weakb-quark couplings has not yet been carefully tested. We discuss recent proposals for studying the chiral and CP-violating structures of these couplings in radiative and hadronicB decays.     

Electromagnetic Mass Differences of Strange,Charm, b-Quark and t-Quark Mesons

We estimate the electro-magnetic mass differences of strange, charm b- and t-quark meson isodoublets in a parametrized potential model including the gluonic hyperfine splitting term explicitly. The numerical results of the mass differences for strange, charm and b-quark mesons agree well with the available experimental values. We predict the electromagnetic mass differences of t-quark mesons: .     

Strangephilic Higgs bosons in the MSSM

We suggest a new CPX-derived scenario for the search for strangephilic MSSM Higgs bosons at the Tevatron and the LHC, in which all neutral and charged Higgs bosons decay predominantly into pairs of strange quarks and into a strange and a charm quark, respectively. The proposed scenario is realized within a particular region of the MSSM parameter space and requires large values of tan?β, where threshold radiative corrections are significant to render the effective strange-quark Yukawa coupling dominant. Experimental searches for neutral Higgs bosons based on the identification of b-quark jets or τ leptons may miss a strangephilic Higgs boson and its existence could be inferred indirectly by searching for hadronically decaying charged Higgs bosons. Potential strategies and experimental challenges to search for strangephilic Higgs bosons at the Tevatron and the LHC are discussed.     

Effect of upsilon poles on the analyticity constraints for heavy meson form factors

We derive optimal bounds on the Isgur-Wise function, taking into account the information about the measured masses of the upsilon poles present in the heavy meson elastic form factor. In the largeb-quark mass limit, when the poles move towards the threshold, our results approach the bounds originally derived by de Rafael and Taron.     

An upper bound for thet-quark mass from duality and unitarity

We attempt to predict the mass of thet-quark from the approach based on duality and unitarity, employing the values of known Regge slopes and vector meson masses. Thet-quark mass is shown to be bounded approximately by 65 GeV, using the maximum possible value for the γ slope. This upper bound is sensitive, however, to the γ slope, and hence it will be considerably reduced if the reliable value is obtained. The importance to find the χ _b state ((bb)³ P ₂) is emphasized. The χ _b mass is also predicted to be less than 9.89 GeV.     

Moments of the heavy-quark parton distribution function from QCD sum rules

The moments of the heavy-quark parton distribution functions in a heavy pseudoscalar meson are calculated from QCD sum rules. Expanding these sum rules in the inverse heavy-quark mass we obtain the heavy-mass limits of the moments. Comparison with the finite-mass results reveals that while the heavy-mass expansion works reasonably well for the b quark, one has to take into account terms of higher order than (1/m _c )² for the c quark. This result can provide a quantitative assessment of c- and b-quark fragmentation models based on the heavy-quark mass limit. The text was submitted by the authors in English.     

Transversity distribution and polarized fragmentation function from semi-inclusive pion electroproduction

A method is discussed to determine the hitherto unknown u-quark transversity distribution from a planned HERMES measurement of a single target-spin asymmetry in semi-inclusive pion electroproduction off a transversely polarized target. Assuming u-quark dominance, the measurement yields the shapes of the transversity distribution and of the ratio , of polarized and unpolarized u-quark fragmentation functions. The unknown relative normalization can be obtained by identifying the transversity distribution with the well-known helicity distribution at large x and small . The systematic uncertainty of the method is dominated by the assumption of u-quark dominance. Received: 18 June 2000 / Revised version: 20 November 2000 / Published online: 5 February 2001     

Heavy hybrid stars from multi-quark interactions

We explore the possibility of obtaining heavy hybrid stars within the framework of the two flavor Nambu-Jona-Lasinio model that includes 8-quark interactions in the scalar and in the vector channel. The main impact of the 8-quark scalar channel is to reduce the onset of quark matter, while the 8-quark vector channel acts to stiffen the equation of state at high densities. Within the parameter space where the 4-quark vector channel is small, and the 8-quark vector channel sizeable, stable stars with masses of 2 M _⊙ and above are found to hold quark matter in their cores.

     

Top-quark <Emphasis Type="Italic">p</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript>-spectra at CMS and flavor independence of <Emphasis Type="Italic">z</Emphasis>-scaling

We present new results of analysis of top-quark differential cross sections obtained by the CMS Collaboration in pp collisions in the framework of the z-scaling approach. The spectra are measured over a wide range of collision energy \(\sqrt s = 7,8,13TeV\) and transverse momentum p _T = 30?500 GeV/c of top-quark using leptonic and jet decay modes. Flavor independence of the scaling function ψ(z) is verified in the new kinematic range. The results of analysis of the top-quark spectra obtained at the LHC are compared with similar spectra measured in \(\overline p p\) collisions at the Tevatron energy \(\sqrt s = 1.96TeV\). A tendency to saturation of ψ(z) for the process at low z and a power-law behavior of ψ(z) at high z is observed. The measurements of high-p _T is observed. The measurements of highspectra of the top-quark production at highest LHC energy is of interest for verification of self-similarity of particle production, understanding flavor origin and search for new physics symmetries with top-quark probe.