CP violation in \Lambda_b \to p \pi^- decay

Using the next-to-leading order QCD corrected effective Hamiltonian, scale and scheme independent Wilson coefficients, we have estimated the branching ratio and CP violating asymmetries for the decay mode in the Standard Model using the framework of generalized factorization. The effects of nonfactorizable contributions are taken into account by treating the effective no. of colors as a free parameter. The form factors are evaluated in the nonrelativistic quark model. The estimated branching ratio is found to be which lies below the current experimental upper limit and the CP violating asymmetries are and . Received: 15 February 2000 / Published online: 8 June 2000     

Two-jet production inp\bar p collisions

The production of two quark/gluon jets in \(p\bar p\) collisions is analyzed. We determine the cross section dependence on the transverse momentum, the rapidities, and on the two-jet invariant mass, and we evaluate the sensitivity of the results on the theoretical input assumptions and the experimental cuts. We extrapolate these results into the TeV energy region.     

Inclusive particle production inp\bar p collisions

We calculate the inclusive production of charged hadrons in collisions at the next-to-leading order in the QCD improved parton model using a new set of fragmentation functions for charged pions and kaons. We predict transverse-momentum distributions and compare them with experimental data from the CERN Collider and the Fermilab Tevatron.     

Thermal hadron production in pp and p\bar p collisions

It is shown that the hadron production in high energy pp and $p\bar p$ collisions, calculated by assuming that particles originate in hadron gas fireballs at thermal and partial chemical equilibrium, agrees very well with the data. The temperature of the hadron gas fireballs, determined by fitting hadron abundances, does not seem to depend on the centre of mass energy, having a nearly constant value of about 170 MeV. This value is in agreement with that obtained in e⁺e^?collisions and supports a universal hadronization mechanism in all kinds of reactions consisting in a parton-hadron transition at critical values of temperature and pressure.     

Antibaryon\left( {\bar p,\bar \Lambda } \right) production in relativistic nuclear collisions

The relativistic meson field theory is used to study the effects of the in-medium interaction on the predicted antibaryon abundancy in hot hadronic matter. It is demonstrated that subtreshold production of antiprotons in high energy heavy ion collisions at E_lab =1–2 GeV/nucleon is enhanced by 2–3 orders of magnitude as compared to a standard fireball model estimate. Furthermore, we show that after the inclusion of interactions the anti-hyperon yields, e.g. \(\bar \Lambda \) /π ^? are enhanced by about a factor ten. Predicted yields are in excess of the data measured by the NA35 and WA85 collaborations at CERN. The annihilation of antibaryons in surrounding matter at the final stage of the reaction may essentially reduce their abundancy.     

Benchmark cross sections forp \bar p collisions at 1.8 TeV

High-energyp \(\bar p\) collisions provide many quantitative tests of the standard model. Of particular interest are “hard scattering” processes, which test not only standard model matrix elements and higher order perturbative corrections, but also the distributions of quarks and gluons in the colliding hadrons. We present detailed comparisons of data from the CERNSp \(\bar p\) S collider with theory, incorporating up-to-date parton distributions derived from recent deep inelastic scattering data. Encouraged by the excellent agreement between data and theory at \(\sqrt s \) =630GeV, we present a complete set of “benchmark” predictions for the FNALp \(\bar p\) collider at \(\sqrt s \) =1.8TeV.     

CP violation in decays Z \rightarrow 4 jets

We analyse CP-violating effects in Z 4 jet decays, assuming the presence of CP-violating effective $ and couplings. We discuss the influence of these couplings on the decay width. Furthermore, we propose various strategies of a direct search for such CP-violating couplings by using different CP-odd observables. The present data of LEP 1 should give significant information on the couplings. Received: 1 February 1999 / Published online: 30 June 1999     

Soft and hard interactions in p \bar p collisions at \sqrt s = 1800 and 630 GeV

We present a study of p $\bar p$ collisions at $\sqrt s = 1800$ and 630 GeV collected using a minimum bias trigger by the CDF experiment in which the data set is divided into two classes corresponding to “soft” and “hard” interactions. For each subsample, the analysis includes measurements of the multiplicity, transverse momentum (p _T ) spectrum, and the average p _T and event-by-event p _T dispersion as a function of multiplicity. A comparison of results shows distinct differences in the behavior of the two samples as a function of the center-of-mass (CM) energy. We find evidence that the properties of the soft sample are invariant as a function of CM energy.     

Cross sections and mean charges of jets inp\bar p collisions

Two jet reactions at collider energies within the frame of QCD are studied. Cross sections and mean charges are shown for both cases when one or two jets are observed. Scaling violations are introduced by means of the Altarelli-Parisi equation for a completely asymmetric sea. The effects due to scaling violation, gluon distribution and gluons in the final state are computed.     

Heavy-quark production in p $$\bar p$$ collisions and unintegrated gluon distributions

The inclusive production of heavy (c and b) quarks in high-energy p\(\bar p\) collisions are considered within the semihard approach in QCD. The dependence of the cross section for heavy-quark production, σ(p_T>p _T ^min ), on unintegrated gluon distributions is studied. The results of this consideration are compared with experimental data obtained by the D0 and CDF Collaborations at Tevatron.     

Higher-order QCD corrections to inclusive particle production inp\bar p collisions

Inclusive single-particle production cross sections have been calculated including higher-order QCD corrections. Transverse-momentum and rapidity distributions are presented and the scale dependence is studied. The results are compared with experimental data from the CERN Collider and the Fermilab Tevatron.Supported by the Bundesministerium für Forschung und Technologie, 05 5HH 91P(8), Bonn, Germany     

Studies in\bar p p annihilation

Evidence is presented that \(\bar p\) p annihilation proceeds via the formation of two jets, with average transverse momentum of the order of the nucleon mass. The implications of this behaviour is linked to the measured cross sections and multiplicities, and explanations for it have been sought in the underlying gluon and quark constituents of the \(\bar p\) p system. The confrontation of the suggested constituent mechanisms and experimental data lead to the concept that charm meson production may play a significant role in the \(\bar p\) p experiments at the highest available energies.     

Studying(\bar cs) spectroscopy in\bar vN collisions

Charmed strange meson neutrinoproduction is investigated. TheD _s ^? (1970) antineutrino production rate is measured. Two higher \((\bar cs)\) states are seen in the decay channels γD _s ^* (2110) andD ^*K, respectively.     

C-odd exchange in high energypp andp \bar p elastic diffraction

Following the arguments of QCD, a proposed model takes into account the significant difference ofpp andp \(\bar p\) elasticd σ/dt discovered at the ISR. An expression forC-odd exchange is discussed and comparison with data is made. Starting from the ISR energies, the model is shown to describe well the data in a wide range of transverse momenta 0≦?t≦10 (GeV/c)² (including the Coulomb-nuclear interference region). Several peculiar predictions of the model will be testable in the TeV energy range and beyond.     

CP nonconservation ine^ + e^ - \to t\bar tg

CP violation effects in $e^ + e^ - \to t\bar tg$ are examined. CP-odd,T _N -odd andT _N -even observables can both be used to extract information on the real and imaginary parts of Feynman amplitudes. The two Higgs doublet model with CP violating phase from neutral Higgs exchange is used to illustrate possible effects. In this particular model the expected luminosity of the future colliders seems to fall short by about one order of magnitude to detect such asymmetries.     

Isospin amplitudes and CP violation in (B \to K \pi) decays

We present a simple isospin invariant parametrization for decay amplitudes which consistently includes CP violation and (quasi-elastic) hadronic final state interactions. We find that the observed decays do not lead to a significant bound on the angle of the unitarity triangle. On the other hand, we claim that a sizeable CP violation asymmetry in rates is by no means excluded. Received: 9 June 1998 / Published online: 8 September 1998