Fragmentation production of Ωccc baryons at LHC energies

Within the nonrelativistic quark-diquark model for heavy baryons, the fragmentation functions for the transitions of a c-quark and a doubly charmed vector diquark into an Ω_ccc baryon are calculated in the leading order of perturbative QCD. The cross section for Ω _ccc production in high-energy hadron interactions is estimated. It is assumed that Ω_ccc baryons are formed via the fragmentation of a c quark or a vector (cc) diquark produced in the partonic subprocesses gg → c $\bar c$ , q $\bar q$ → c $\bar c$ , gg → (cc)+ $\bar c$ + $\bar c$ , and q $\bar q$ → (cc)+ $\bar c$ + $\bar c$ .     

e^ + e^ - \to b\bar bW^ + W^ - events at the next linear collider: colour structure of top signal and irreducible backgroundevents at the next linear collider: colour structure of top signal and irreducible background

We examine the colour structure and charged particle yield for both the $t\bar t$ signal and the irreducible background processes contributing to $e^ + e^ - \to b\bar bW^ + W^ - $ production close to the $t\bar t$ threshold. The charged particle multiplicity for the various components of the cross section is computed as a function of several kinematic variables. Our study may have important implications for recently proposed studies of interconnection phenomena in $t\bar t$ production at high-energye ⁺ e ^? colliders.     

Scattering length expansion of the coupled channels\bar pp \to \bar \Lambda \Lambda and\bar \Lambda \Lambda \to \bar \Lambda \Lambda near theΛ production threshold

We fit the scattering lengths in the triplets-,p- andd- waves for the two channels \(\bar pp \to \bar \Lambda \Lambda\) and \(\bar \Lambda \Lambda \to \bar \Lambda \Lambda\) near theΛ production threshold to the differential cross section \(\frac{{d\sigma }}{{d\Omega }}(\bar pp \to \bar \Lambda \Lambda )\) and to the polarization P.     

Production and rescattering of heavy quarks in ultrarelativistic nucleus-nucleus collisions

Contributions of various mechanisms to the heavy-quark-production cross section in ultrarelativistic nucleus-nucleus collisions, including the direct pair production $b\bar b$ and $c\bar c$ as a result of hard primary collisions and pair production in showers induced by hard-produced partons in the initial and final states, are investigated. The sensitivity of the muon pair spectra with large invariant masses (from semileptonic $B\bar B$ decays) and spectra of the secondary J/ψ (from individual B decays) to the multiple scattering and the energy losses of b quarks in dense quark-gluon matter is studied. The formation of such matter is expected in heavy-ion collisions at the LHC.     

Glueball plus pion production in hadron collisions

Using a non-relativistic gluon bound-state model for glueballs (G), we compute the subprocess $q\bar q \to G\pi $ , and we therefrom derive the yield of the overall reaction $p\bar p \to G\pi X$ , assuming the glueball and the pion to be emitted with their transverse momenta large, opposite and approximately equal. Numerical results are presented in the form ofp _T spectra for various glueball candidates and their possible quantum states, assuming those particles to be produced, in the type of reactions here considered, at high-energy $p\bar p$ colliders such as the CERN $Sp\bar pS$ .     

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.     

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.     

Strange and non-strange (Anti-) baryon production at 200 A GeV/c

Rapidity distributions of net hyperons $\left( {\Lambda - \bar \Lambda } \right)$ are compared to distributions of participant protons $\left( {p - \bar p} \right)$ . Strangeness production (mean multiplicities of produced Λ/Σ⁰ hyperons and $\left\langle {K + \bar K} \right\rangle $ in central nucleusnucleus collisions is shown for different collision systems at different energies. An enhanced production of $\bar \Lambda $ compared to $\bar p$ is observed at 200 GeV per nucleon.     

Glueball plus pion production in hadron collisions

Using a non-relativistic gluon bound-state model for glueballs (G), we compute the subprocess $q\bar q \to G\pi $ , and we therefrom derive the yield of the overall reaction $p\bar p \to G\pi X$ , assuming the glueball and the pion to be emitted with their transverse momenta large, opposite and approximately equal. Numerical results are presented in the form ofp _T spectra for various glueball candidates and their possible quantum states, assuming those particles to be produced, in the type of reactions here considered, at high-energy $p\bar p$ colliders such as the CERN $Sp\bar pS$ .     

Λ\bar \Lambda longitudinal polarization: A signature for the formation of a quark-gluon plasma in heavy ion collisions

The high relative abundance ofs \(\bar s\) quarks in the quark-gluon plasma will result in peculiar hadronization ratios whereby the Ξ/Λ ratio should be much higher than in usual processes. As a result the Λ( \(\bar \Lambda\) ) should exhibit a sizeable longitudinal polarization due to their importantΞ( \(\bar \Xi\) ) filiation. Discussing such spin effect, the report starts with the determination of theW spin, a recent and successful application of the helicity formalism.     

Fine and hyperfine structures of heavy quarkonia and perturbative quantum chromodynamics

Spectroscopies of the heavy quarkonia, \(c\bar c\) , \(b\bar b\) and \(t\bar t\) , are analysed with a potential model. Relativistic effects are taken into account and spin dependent interactions are investigated in detail. We propose a flavor independent potential which has a Lorentz vector term determined by the perturbative QCD at short distances and a Lorentz scalar term confining quarks at large distances. It is stressed that the short range attenuation of the vector Coulomb potential has significant effects on the fine and hyperfine structures of the \(c\bar c\) and \(b\bar b\) systems, and also on the \(t\bar t\) level structure. We study the decay property of the \(t\bar t\) system using the calculated wave functions.     

Very high energy nucleus-nucleus collisions and multi-chain model

Inclusive and semi-inclusive production of Λ and \(\bar \Lambda\) inK ⁺ p interactions is studied at an incident momentum of 70 GeV/c. Cross sections and single particle distributions are presented and compared with data at lower energies. Scaling is observed between 32 and 70 GeV/c in the Feynmanx variable in the target and the beam fragmentation regions for Λ and \(\bar \Lambda\) inclusive production respectively. An increase of Λ ( \(\bar \Lambda\) ) production is observed in the beam (target) fragmentation regions, whereas the data at 70 and 32 GeV/c are reasonably close in the central region. The dependence of the Λ( \(\bar \Lambda\) ) polarization as a function ofx is measured and found to be in general agreement with the results at 32 GeV/c. The (Λ \(\bar \Lambda\) ) pair production cross section increases significantly from 32 to 70 GeV/c. The Λ and \(\bar \Lambda\) production associated with an identified proton is also studied.     

TheN\bar N and ππ decay modes of baryonium

A non-relativistic quark model is used to calculate the decay widths of baryonium states to \(N\bar N,N\bar \Delta \) , \(N\bar N,N\bar \Delta \) and \(\Delta \bar \Delta \) . Large widths are found and used to estimate the \(\bar pp\) and \(\bar pn\) elastic cross-sections. The couplings of baryonium states to two identical mesons are also investigated.     

Coupled-Channels Approach and Simple Models in the Theory of Exotic Atom Formation

Atomic collisions of slow negative particles X ^? (μ^?, $\bar p$ , etc.) are considered using coupled channels semiclassical approximation that takes into account 2- and 3-particle channels. Analytical expression for differential elastic cross section is proposed. Differential cross section reveals essential quantum interference effects. Inelastic $\bar p$ –Ne and $\bar p$ –Ar cross sections are considered using model potentials.     

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.     

Diffractive proteon fragmentation in 16, 32, and 110 GeV/cK − p interactions and the diffractive production of heavy quarks(s\bar s,c\bar c)

The inclusive proton diffraction dissociation cross sections in 16, 32, and 110 GeV/cK ^? p interactions are determined from the spike nearx=1 in the inclusive negative particle spectra and are compared to those obtained inK?p interactions using other selection methods at various energies. The same procedure is applied to events containing aV ⁰ in order to obtain the cross section for diffractive \(s\bar s\) production. While the total cross section for proton diffraction is found to be approximately constant in the energy range studied here, proton diffraction yielding an \(s\bar s - pair\) is found to increase significantly. In particular it is almost constant at 85 μb forΛ ⁰ and Σ production but for \(NK\bar K\) it rises from zero at 16 GeV.c to about 200 μb at 110 GeV/c. From the result for \(s\bar s\) diffractive production an estimate for the \(c\bar c\) diffractive production cross section of approximately 1–10 μb at 110 GeV/c is obtained.     

\bar \Lambda Production inK − p interactions at 32 GeV/c

Antilambda production is studied inK ^? p interactions at 32 GeV/c. Both total and differential cross sections are presented. The inclusive \(\bar \Lambda \) production cross section amounts to 109±7 μb. A remarkable energy dependence is observed, σ( \(\bar \Lambda \) ) increasing by a factor of four between 14.3 and 32 GeV/c. Thep _⊥ ² distribution exhibits an exponential fall-off with a slope of 3.3±0.2 (GeV/c)^?2. Most of the \(\bar \Lambda \) 's are emitted in the forward hemisphere. The invariantx distribution increases between 14.3 and 32 GeV/c. Data are presented for \(\bar \Lambda \) production inK ^- p→Λ \(\bar \Lambda \) +X K ^- p→ \(\bar \Lambda \) K ⁿ +X, andK ^- p→ \(\bar \Lambda \) p+X.     

The process\pi ^0 \to \lambda _\gamma \bar \lambda _\gamma as an alternative to\pi ^0 \to v\bar v

The process \(\pi ^0 \to \lambda _\gamma \bar \lambda _\gamma \) is investigated as an alternative to \(\pi ^0 \to v\bar v\) . It is shown that the experimental bound on the branching fraction for missing energy (in the form of \(\lambda _\gamma \bar \lambda _\gamma \) and/or \(v\bar v\) ) may be understood in terms of \(\pi ^0 \to \lambda _\gamma \bar \lambda _\gamma \) for the kinematically allowed photino mass, if the squark mass is >8 GeV.