Isgur-Wise functions from the MIT bag model

The Isgur-Wise functions for the ground state to ground state semileptonic decays involvingb→c transitions are calculated from the (modified) MIT bag model. It is checked that the results for the decays \(\bar B \to Dl\bar v\) and \(\bar B \to D^* l\bar v\) agree well with experiment. Predictions for the decays \(\Lambda _b \to \Lambda _c l\bar v,\bar B_s \to D_s^* l\bar v\) and \(\bar B_s \to D_s^* l\bar v\) are given and discussed.     

QCD calculation ofB \to \pi l\bar v_l and the matrix element |V bu|

Using QCD sum rules for a two-point function involving beauty vector currents, together with current algebra-PCAC sum rules, we estimate the hadronic matrix element in \(B \to \pi l\bar v_l \) . We find \(\Gamma \left( {\bar {\rm B}^0 \to \pi ^ + l\bar v_l } \right) = \left( {1.45 \pm 0.59} \right) \times 10^{13} \left| {V_{bu} } \right|^2 s^{ - 1} \) . As a byproduct, the vector current contribution to the decay \(B \to \rho l\bar v_l \) is also estimated.     

Quark-diagram estimates ofCP violation in two-body baryonicB_d^0 - \bar B_d^0 decays

CP violation in partial-decay-rate asymmetries are examined for some two-body baryonic decays of \(B_d^0 - \bar B_d^0 \) system. We discuss two feasible experimental circumstances: the symmetrice ⁺ e ^? collisions (i) on theZ ⁰ resonance to produce incoherent \(B_d^0 \bar B_d^0 \) states, and (ii) just above the ?(4S) resonance to produceC=even \(B_d^0 \bar B_d^0 \) states. Using the quark-diagram scheme, we estimate the branching ratios of those decays, and the numbers ofb \(\bar b\) pairs needed for testing theCP-violating effects for 3σ signature. We find that the promising channels may beB _d ⁰ , \(\bar B_d^0 \to p\bar p\) , \(\Delta ^ + \bar \Delta ^ - \) , \(p\bar \Delta ^ - \) , \(\Delta ^ + \bar p\) , \(n\bar n\) , \(\Delta ^0 \bar \Delta ^0 \) , \(n\bar \Delta ^0 \) , \(\Delta ^0 \bar n\) , \(\Sigma _c^ + \bar \Sigma _c^ - \) , \(\Lambda _c^ + \bar \Lambda _c^ - \) , \(\Sigma _c^ + \bar \Lambda _c^ - \) , \(\Lambda _c^ + \bar \Sigma _c^ - \) , \(\Sigma _c^0 \bar \Sigma _c^0 \) , \(\Xi _c^0 \bar \Xi _c^0 \) , which should be interesting for experimental observation.     

W-production viaZ-decay

We calculate the decay rate for the processZ Boson→W Boson+fermion+antifermion. The result is applied to compute the decay rates for \(Z \to W^ + + l + \bar v_l \) ,l=e, μ or τ andZ→W ⁺+anything in the Weinberg-Salam model. At the present experimental value of sin² θ _w=0.23 the branching ratios for the above processes are \(\Gamma (Z \to W^ + l\bar v_l )/\Gamma (Z \to all) \simeq 9 \times 10^{ - 9} \) and Γ(Z→W ⁺+anything)/Γ(Z→all)?8×10^?8.     

Comparison of strange antibaryon and strange meson production inK + p interactions at 32 GeV/c

New experimental results are presented on inclusive production properties of \(\bar \Sigma ^{ * + } \) (1385) and \(\bar \Sigma ^{ * + } \) (1385) inK ⁺ p interactions at 32 GeV/c. The analysis is based on significantly larger statistics than previously available. A comparison is also made of invariantx-distributions ofK ⁰/ \(\bar K^0 \) , \(\bar \Lambda \) and \(\bar \Xi ^ + \) and of \(\bar \Sigma ^{ * \pm } \) (1385) andK ^*+(892). These spectra exhibit regularities expected from the quark-recombination picture when it is assumed that the strange mesons and antibaryons are produced off the strange \(\bar s\) -valence-quark in the incidentK ⁺ meson. Transverse momentum distributions are also presented forK ^*+(892) and \(\bar \Sigma ^{ * \pm } \) (1385) and found to be very similar. The results on strange antibaryon average multiplicities disagree strongly with a recent version of the additive quark model.     

Perturbative QCD coherence ine + e − annihilation

We study the pattern of soft parton radiation in the hard annihilation processes \(e^ + e^ - \to q\bar q\gamma \) and \(e^ + e^ - \to q\bar qg\) by explicit evaluation of the cross sections for \(e^ + e^ - \to q\bar q\gamma g\) and \(e^ + e^ - \to q\bar qgg + q\bar qq\bar q\) taken care of correct normalization. We find the coherence effects as observed experimentally and discuss why these effects are not present in the usual models based onO(α _s ² ) perturbation theory with subsequent independent fragmentation.     

Multi-quark structure ofU(3.1)

We interpret the recently observedU(3.1) mesons with the \(\Lambda \bar p\) + pions decays as the bound state of \(\Lambda ,\bar p\) andX ₀(1480). TheX ₀(1480) is a mesonium with \(Q^2 \bar Q^2 \) structures observed in γγ reactions and \(\bar pn\) annihilations. With this interpretation, we can understand its decay modes. Furthermore, we predict the ratio of \(\sigma (\Lambda \bar p\pi ^ + \pi ^ - )/\sigma (\Lambda \bar p\pi ^ + \pi ^ + )\) to be ?3.1 for centrally produced events and that the width of \(U^ - (\Lambda \bar p\pi ^ + \pi ^ - )\) to be greater than that of \(U^ + (\Lambda \bar p\pi ^ + \pi ^ + )\) . Both predictions seem to be in reasonable accord with the available data. We call for the detection of the \(\Lambda \bar p\pi ^ - \pi ^ - \) mode to verify the present interpretation.     

Prospects of technicolor-signatures in hadronic collisions

Within the context of the Dimopoulos' one family model, we consider possible technicolor signatures in hadronic reactions at high energies. For the single-production of light color-singlet states (P ⁰,P ³,P ^±) in \(p\bar p\) annihilation, we find the Compton-scattering processgc→P ⁰ c most promising. In case of PGB-pair-production, the reaction in \(p\bar p \to P^ + P^ - \) via the subprocess \(q\bar q\xrightarrow{{\gamma ,Z^0 }}P^ + P^ - \) , as well as the production of heavy color-triplets (P ₃) via \(p\bar p \to P_3 \bar P_3 \) via \(q\bar q\) andgg-fusion at Tevatron-energies, appear to be best suited for detecting these objects.     

Baryon pairs production ine + e − annihilation at\sqrt s = 2.4 GeV

Search for baryon pairs production ine ⁺ e ^? annihilation at \(\sqrt s = 2386 MeV\) is reported. The data relate to a luminosity of 161 nb^?1 collected by the DM2 experiment at DCI, the Orsay colliding ring. First measurements of directe ⁺ e ^? annihilation into \(\Lambda \bar \Lambda \) and ofe ⁺ e ^?→ \(p\bar p\) at this energy are presented. First observation of a goode ⁺ e ^?→ \(n\bar n\) candidate is reported and upper limits are given fore ⁺ e ^?→ \(n\bar n, \Lambda \bar \sum ^0 + c.c.\) and \(\Sigma ^0 \bar \Sigma ^0 \) .     

Charm production in fixed target experiments

Prompt lepton production in proton beam dump experiments has been critically analysed within the general frame work of \(A_c \bar D\) and \(D\bar D\) production and their subsequent semileptonic decays. Realistic decay modes based on recent experiments are used. We have investigated the effect of using differentx dependences for the charm particles obtained either from simple quark counting rules or as inferred from strange particle production data. The \(D\bar D\) production is assumed to have a linearA dependence and for the \(A_c \bar D\) process bothA ¹ andA ^2/3 dependence is used. We show that by a simultaneous fit to the energy and angular distributions of prompt leptons in all the experiments the ratio of \(A_c \bar D\) to \(D\bar D\) production cross section can be determined. A comparison of this fit with these experimental distributions indicates that thex dependences based on strange particle data are strongly favoured. AnA ^2/3 dependence for \(A_c \bar D\) production, which corresponds to a quasi-diffractive process, is favoured although within existing errorsA ¹ dependence cannot be ruled out. Putting together the cross section results from our analysis with other results at similar energies (p _1ab ～400GeV/c) the production cross sections ( \(A_c \bar D\) ) and ( \(D\bar D\) ) are estimated to be ～25 and ～20 μb/nucleon respectively leading to a total inclusive charm cross section of ～90 μb/nucleon.     

Mixings and CP violations of theB^0 - \bar B^0 system in the four-generation model

We study the mixings and CP violations in the \(B^0 - \bar B^0 \) system together with the \(K^0 - \bar K^0 \) one in the four-generation model, taking into account the ARGUS data for the \(B_d^0 - \bar B_d^0 \) mixing. We take typical six cases of the mixing hierarchy and search for the allowed regions of three phases in the 4×4KM matrix. The CP violating parameter ? _K in the \(K^0 - \bar K^0 \) system gives a severe constraint for the phases, and the smaller mixing than that in the three-generation model is predicted for the \(B_s^0 - \bar B_s^0 \) system. The asymmetry parameters for the two-body non-leptonic decays of theB ⁰ and \(\bar B^0 \) mesons are also predicted.     

Continuum mixing and coupled channel effects inc\bar c andb\bar b quarkonium

We apply the unitarized quark model to heavy \(c\bar c\) and \(b\bar b\) quarkonium and study mass shifts and mixings induced by hadronic coupled channel effects. In particular, we study the two-meson continuum mixing in the quarkonium wave functions. It is found that the continuum component is 2–20% in the \(c\bar c\) and \(b\bar b\) states, measured as the squared sum of two-meson amplitudes \((D\bar D,D\bar D^ * + cc,D^ * \bar D^ * ,F\bar F,F\bar F^ * + cc,F^ * \bar F^ * for c\bar c)\) . It is the largest for states near or above the first threshold. These continuum mixings reduce the predicted radiative widths by 5–30%. The mass shifts of theP andF wave \(q\bar q\) states are similar to those ofS andD wave states previously studied. The computed resonance mixing matrices are explicitly given, enabling future calculations of relativistic effects, QCD effects, etc., to include also the coupled channel effects.     

Neutrino-pair bremsstrahlung and the number of lepton generations

Neutrino pair creation in bremsstrahlung processes of the type \(l \to l{\text{ }}v{\text{ }}\bar v\) contains vital information on the number of lepton generations, and is catalyzed by the coherent nuclear Coulomb effect or other forms of intense fields. Of particular interest is the ratio \(R_{v\bar v} = \sigma [1\mathop \to \limits_A l(v\bar v)]/\sigma [1\mathop \to \limits_A l'(v\bar v)]\) (wherel, l′ are distinct charged leptons). It is sensitive to the number of neurino types and their couplings in the same way that the ratio \(R_{q\bar q} = \sigma [e^ + e^ - \to {\text{hadrons}}]/\sigma [e^ + e^ - \to \mu ^ + \mu ^ - ]\) is to those of quarks. In the Weinberg-Salam model withN lepton generations, the ratio \(R_{v\bar v}\) is approximately given by \([(N + 4) + 4(1 - 4\sin ^2 \theta _W )]/8\) .     

p¯p Annihilation into two mesons in the quark rearrangement model and the quark annihilation model

The relativistic³ P ₀ model is applied to the \(p\bar p\) annihilation into twoS-wave mesons. We calculate the branching ratios of the \(p\bar p\) annihilation at rest into two mesons in the quark rearrangement model and in the quark annihilation model. In the annihilation model, we project the intermediate \(cq\bar q\) state to eigenstates ofSU (4) with the relative angular momentum of \(cq\bar q\) equals orp. In the rearrangement model, no annihilation occurs from theS-wave \(p\bar p\) and certain branching ratios conflict with the experimental data. Detailed comparison with the experiment needs inclusion ofP-wave mesons in the final state, nevertheless we find that the annihilation model gives qualitatively better results than the rearrangement model. The effect of initial state interaction through \(N\bar \Delta \pm \Delta \bar {\rm N}\) or \(\Delta \bar \Delta \) channels is discussed.     

The semileptonic decaysB→Mτν as a probe of hadron dynamics

We show how data on \(\bar B \to M\tau \bar v\) can be used to probe models for the hadronic form-factors which describe the \(\bar B \to M\) transition, whereM isD,D ^* etc. Extra form-factors contribute to \(\bar B \to M\tau \bar v\) , as compared to \(\bar B \to Me\bar v\) , and these may be studied by observing the polarisation of the outgoing τ. Model predictions for the decay rate and the τ polarisation are presented.     

Effective potential for local composite operators and the problem of factorization of multi-field condensates

A new formulation of effective potential for local composite operators is given. The two-fermion condensate \(\langle \bar \Psi \Psi \rangle \) and four-fermion condensate \(\langle \bar \Psi \Psi \bar \Psi \Psi \rangle \) are calculated simultaneously in the Gross-Neveu model up to next-to-the-leading order in 1/N expansion. It is shown that factorization \(\langle \bar \Psi \Psi \bar \Psi \Psi \rangle = C_1 \langle \bar \Psi \Psi \rangle ^2 \) holds only in theN→∞ limit and the non-factorized part of \(\langle \bar \Psi \Psi \bar \Psi \Psi \rangle \) contributed by the order-1/N terms is comparable to \(C_1 \langle \bar \Psi \Psi \rangle ^2 \) when takingN=3.     

Gaugino-Higgsino mixing in selectron and sneutrino pair production

We study \(e^ + e^ - \to \tilde e^ + \tilde e^ - \) together with \(\tilde e^ \pm \) decay emphasizing the importance of neutralino mixing in thet-channel at energies above theZ ⁰ resonance. This illustrated in three different mixing scenarios. Formulae for \(e^ + e^ - \to \bar \tilde v_e \tilde v_e \) are also given.     

Coherence ofu\bar u andd\bar d final states: Possible influence onZ 0 decay width ande + e − annihilation cross section

The decay width of theZ ⁰ associated with its coupling tou andd quarks is usually expressed as the incoherent sum of the widths into \(u\bar u\) and \(d\bar d\) final states, \(\Gamma (u\bar u) + \Gamma (d\bar d)\) . We examine a specific correction to this estimate arising from the coherence of the \(u\bar u\) and \(d\bar d\) systems, dictated by isospin symmetry. The decay width is written in the alternative form Γ(G=+1)+Γ(G=?1), which recognises that final hadronic states can be classified according to even and odd G-parity. Assuming that states withG=+1(?1) evolve from configurations containing even (odd) numbers ofG=?1 systems, and considering various multiplicity distributions for such systems, small corrections are obtained relative to the conventional estimate. A similar analysis applied to the cross section for \(e^ + e^ - \to u\bar u, d\bar d\) yields small energy-dependent corrections to the parameter R.     

Open beauty production in high energy π−-tungsten interactions

We present a study of \(B\bar B\) meson pair production inπ ^? interactions at 140, 194 and 286 GeV incident pion energy. At 286 GeV, where we have the best statistics, we find a model-dependent \(B\bar B\) production cross-section \(\sigma _{BB} = 14_{ - 6}^{ + 7} nb/nucleon\) .