An approach to the study of heavy quarks ine + e − collisions

The production ofb- andt-quarks ine ⁺ e ^? collisions may be appropriately investigated from the observation of like-sign dileptons. We estimate the branching ratios and the average lepton energies in semileptonic decays of heavy particles, taking into account both cascade decays and the mass-mixing of neutral mesons. They are found to be relatively large. Then, we consider the angular distribution and correlations for events wheighted by powers of the lepton energies. These quantities (moments) have a transparent decomposition, where each factor corresponds to a dynamical step in the production of dileptons. Our computations suggest that the study of like-sign dileptons along these lines would provide interesting information on the heavy quark fragmentation and decay.     

Sources of tetramuon production by neutrinos

We evaluate four sources of tetramuon production by neutrinos: (a) heavy quark cascade, (b) heavy lepton cascade, (c) charm production with radiative pair, (d) charm production plus an associated charm pair. Rates relative to ν→μ^? of order (a) 10^?6, (b) 10^?5, (c) 10^?7, (d) 10^?9, can be obtained. Invariant mass and azimuthal correlation distributions in 4μ events are presented. Relative multimuon rates differ strikingly in the models considered.     

Measurement of electron-muon correlations from semi-leptonic D decay in 200 GeV p + p collisions at RHIC-PHENIX

Charm production is a valuable probe of the early stages of a heavy ion collision. Correlated electron-muon pairs are a signature of semi-leptonic D decays, and a measurement of D mesons provides information on charm quark energy loss in the hot medium. The energy loss of heavy quarks is still not fully understood, so it is vital to investigate different decay channels of charm mesons to better understand this process. Measurements of electron-muon pairs suffer less from background than e ⁺ e ⁻ or μ⁺μ⁻ pairs since neither direct lepton production nor resonance decays produce this type of correlated signal. Another advantage is that because electrons are measured in the central arms and muons are measured in the forward region in PHENIX, open charm can be probed in a rapidity region different from previous dilepton measurements. Studying electron-muon pairs in p + p collisions provides an important baseline for the study of these processes in d + Au and Au + Au collisions. The data in this analysis was obtained during the 2006 RHIC run of p + p collisions at 200 GeV. The current status of this analysis will be presented.     

Semileptonic decays of heavy quarks in quantum chromodynamics

We investigate the semileptonic decays of heavy quarks in the leading non-trivial order in quantum chromodynamics. Effects of gluon corrections and the initial quark Fermi motion on the semileptonic rates and decay distributions are calculated. The resulting lepton energy spectrum for the charm semileptonic decay is compared with data to extract the mass of the charm quark. This is combined with the semileptonic branching ratio to predict the charm-quark lifetime. We find the lepton energy spectrum very stable with respect to gluon corrections. Expected spectra from the semileptonic decays of bottom and top quarks are presented. We also study the semileptonic decay process Q → q?v_? + G, involving the emission of a single hard non-collinear gluon. This process should be observable with a branching ratio of a few percent in the decays of top (and heavier) quarks.     

Forward-backward asymmetry in top quark semileptonic decay

The semileptonic decay of the top quark t → bW⁺ → bl⁺ν_l is analyzed in the rest system of the W. The forward-backward asymmetry of the lepton l⁺ with respect to the heavy quark direction is defined and computed. It is argued that this observable will be an ideal tool to study top quark properties at Tevatron and LHC. Higher order QCD corrections are calculated and their structure is elucidated in some detail.     

Review of the top quark mass measurement at the CDF in p \bar p collisions at \sqrt s = 1.96 TeV

Upgraded Tevatron RUN-II luminosity has opened a new chapter in a modern heavy quark studies—a top physics: a dozen level of a Tevatron Run-I top events statistic now is being replaced by hundreds events. This work reviews a mass measurement of the top quark produced at $\sqrt s $ = 1.96 TeV in p $\bar p$ collisions at the Collider Detector at Fermilab (CDF) with the integrated luminosity samples up to 359 pb^?1. The review covers the M(top) measurement using mainly the so-called template methods both in the “lepton + jets” and “dilepton” channels of top quark decay. The CDF top quark mass obtained in the lepton + jets mode is currently the world’s most precise single measurement of this important physical parameter. This work summarizes the essential results of the CDF top quark mass measurement achieved and published for the recent 2003–2005 period.     

A study of B meson oscillations using hadronic Z0 decays containing leptons

An event sample enriched in semileptonic decays of b hadrons is selected using an inclusive lepton selection from approximately 3.0 million hadronic Z⁰ decays collected with the OPAL detector. This sample is used to investigate B meson oscillations by reconstructing a proper decay time for the parent of each lepton, using a jet charge method to estimate the production flavour of this parent, and using the lepton charge to tag the decay flavour. We measure the mass difference between the two B⁰ _d mass eigenstates     

Search for scalar top quark production in p&pmacr; collisions at sqrt

We have searched for direct production of scalar top quarks at the Collider Detector at Fermilab in 88 pb(-1) of p&pmacr; collisions at sqrt[s] = 1.8 TeV. We assume the scalar top quark decays into either a bottom quark and a chargino or a bottom quark, a lepton, and a scalar neutrino. The event signature for both decay scenarios is a lepton, missing transverse energy, and at least two b-quark jets. For a chargino mass of 90 GeV/c(2) and scalar neutrino masses of at least 40 GeV/c(2), we find no evidence for scalar top production and present upper limits on the production cross section in both decay scenarios.     

Jet-like distributions from the weak decay of heavy quarks

We consider the production and weak decay of a pair of heavy quarks (mesons) ine ⁺ e ^? experiments and study their effect on the various jet distributions. The relative magnitudes of the two-quark-jet and three-quark-jet final states, in the decay of a heavy quark are estimated in the framework of an SU(2) _L ×U(1) model. We find that the three quark configuration dominates over the two quark configuration. For the quark jets resulting from the weak decay of the heavy quarks, we calculate the jet distributions in Sphericity, Spherocity and Thrust for the process \(e^ + e^ - \to Q\bar Q \to 6\) quarks. These distributions are compared with the corresponding quantities from the non-perturbative process \(e^ + e^ - \to q\bar q\) and the QCD process \(e^ + e^ - \to q\bar qg\) . We find that the weak decay of heavy quarks is the dominant mechanism for jet broadening ine ⁺ e ^? experiments, in the intermediate energy region relevant for PETRA and PEP.     

Exclusive semileptonic heavy meson decays including lepton mass effects

We discuss the exclusive semi-leptonic (s.l.) bottom meson decaysB→D(D ^*)+l+v where we include non-zero lepton mass effects in the kinematics and dynamics. We develop the general formalism for the non-zero lepton mass case. We then look at how rates, spectra and angular correlations are affected by non-zero lepton masses in the context of a specific spectator quark model. Numerical results are presented for s.l. decays involving thee-, μ- and τ-leptons. We also discuss the s.l. decaysB→π(ρ),D→K(K ^*) and the free quark decay model.     

On the semileptonic decay distributions from the next heavy quark

Motivated by the discovery of λ(9.4), we study the semileptonic decay correlations of the next heavy quark, and their consequences for thee ⁺ e ^? colliding beam and neutrino experiments. A detailed comparison is made with the corresponding correlations from the production and decay of charm and heavy leptons, τ^±. Some tests of the \({\rm B}^0 - \bar {\rm B}^0 \) mixing ( \(B = b\bar q\) withbaQ=?1/3 heavy quark) are suggested fore ⁺ e ^? colliding beam experiments.     

A simple description of the JP = 1+K±π+π− system in the reactions K±p→K±π+π−p

We present the group theoretical analysis of a likely symmetry breaking for the vector-like unified theory based on E₇. The (proton stabilizing) breaking is effected by means of a set of Higgs fields transforming according to the 912, leaving an effective SU₃ × SU₃^c theory. We note that a nilpotent breaking for the quark mass matrix yields the SU₃ limit, as well as a determination of the relative left to right angle in the weak current demanded by the GIM mechanism. No evident correlation between quark and lepton masses emerges. The lepton current contains both doublets and triplets of SU₂^wk. While the quark neutral current is necessarily parity violating, the electron part of the lepton neutral current may be chosen to be purely vectorial. Appropriate phenomenological conclusions are drawn.     

Characteristics of heavy flavour production inep collisions

The production of heavy flavours inep collisions at the HERA energy is studied using a model based on boson-gluon fusion into a heavy quark-antiquark pair followed by gluon emission and string hadronization. Total cross-sections and dependence on basic kinematical variables are given as well as distributions of the most important variables at both the quark and hadron level, e.g. rapidity and transverse momentum. Charm, bottom and top production is compared and signatures for their separation are discussed in terms of decay muons and global event shape properties.     

Trimuons in SU(3) gauge models

We discuss models of weak interactions which can account for the recently observed μ^?μ^?μ⁺ events in v_μ reactions by allowing for the production of a new heavy neutral lepton and a new quark. One model is based on an SU(3) × U(1) gauge theory in shich the left-handed leptons are classified in anti-triplets. The second model catagorizes the leptons in an octet in accord with the more restrictive SU(3) weak gauge theory.     

Calculable observables in quantum chromodynamics: (II). Heavy quark production

It is argued that the color-averaged inclusive cross section dσ/d³p for the production of a heavy quark of given momentum p and given flavor is infrared-singularity free and therefore calculable in perturbative QCD if it is evaluated away from heavy quark thresholds and if the typical reaction energy Q is such that α_s(Q)ln[Q/m(Q)] is small, α_s and m being the strong coupling constant and the heavy quark mass respectively. An interpretation of this cross section is proposed in terms of heavy flavor hadronic production.     

Opposite sign dimuon events produced in narrow band neutrino and antineutrino beams

On the basis of 315 dimuon events of opposite sign for which the nature (and energy) of the incident neutrino is known, and the momenta and hadronic shower energy are measured, we find a) very similar production by neutrinos and antineutrinos, and therefore confirmation of the GIM model for semileptonic weak interactions, b) energy spectra, excitation functions, angular correlations and transverse momentum distributions which are in remarkable agreement with the hypothesis of charm production and decay, c) evidence against models for which the second muon has a heavy lepton as origin, d) evidence against “bottom” quark production by antineutrinos, e) the amount and the structure function for the strange quark-antiquark sea, and f) an approximate branching ratio, of 0.15 for the muonic decay of the semistable charmed meson.     

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.     

Limit on right handed weak coupling parameters from inelastic neutrino interactions

Right handed weak quark currents coupled to the usual left handed weak lepton current would be seen in inclusive antineutrino scattering on nuclei as a contribution at largey with the quark (not antiquark) structure function. We do not see such a term, and can therefore put an upper limit on the relative strengths of such right handed currents: \(\varrho ^2 = \frac{{\sigma _R }}{{\sigma _L }}< 0.009\) , 90% confidence. This measurement puts limits on the mixing angle of left-right symmetric models. In distinction to similar limits derived from muon decay or β decay, our limits are also valid if the right handed neutrino is heavy.     

Evidence for heavy leptons from anomalous μe production in e+e− annihilation

Events of the type $\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{→μ}{}^{\mathrm{\pm }}\text{+e}{}^{\mathrm{?}}\text{+}\text{“nothing”}$ have been observed in the magnetic detector PLUTO at the storage ring DORIS at DESY. The data support the hypothesis of the pair production of heavy leptons, and allow to determine decay parameters. Decay rates into muons and electrons are equal within error, and argue for a new lepton number of the heavy lepton.