Ital Qq Research Articles

Probing color-singlet exchange in Z+2-jet events at the CERN LHC.

The purely electroweak process {ital qq}{r_arrow}{ital qqZ} (via {ital t}-channel {gamma}/{ital Z} or {ital W} exchange) provides a copious and fairly clean source of color-singlet exchange events in {ital pp} collisions at the CERN LHC. A judicious choice of phase-space region allows the suppression of QCD backgrounds to the level of the signal. The color-singlet-exchange signal can be distinguished from QCD backgrounds by the radiation patterns of additional minijets in individual events. A rapidity-gap trigger at the minijet level enhances substantially the signal versus the background. Analogous features of weak-boson scattering events make {ital Z}+2-jet events at the CERN LHC an ideal laboratory for investigation of the soft-jet activity expected in weak-boson scattering events. {copyright} {ital 1996 The American Physical Society.}

Heavy Higgs boson production in association with three jets at hadron supercolliders.

We consider the real emission QCD correction to heavy Higgs boson production via weak boson fusion in high energy pp collisions. The O(${\mathrm{\ensuremath{\alpha}}}_{\mathit{s}}$) corrections are determined for the complete electroweak qq\ensuremath{\rightarrow}${\mathit{qqW}}^{+}$${\mathit{W}}^{\mathrm{\ensuremath{-}}}$ process. The presence of a third parton in the final state affects the formation of rapidity gaps only slightly. In particular, soft emission into the gap region is severely suppressed. Also, we investigate how the additional hard emission affects forward-jet-tagging and central-jet-vetoing efficiencies in the search for H\ensuremath{\rightarrow}${\mathit{W}}^{+}$${\mathit{W}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\mathit{l}}^{+}$\ensuremath{\nu}${\mathit{l}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\nu}\ifmmode\bar\else\textasciimacron\fi{} decays.

Possibility of new dibaryons containing heavy flavors.

In a recent paper we have shown that the possibility of including heavy flavor in the dibaryon sector can lead to some new favored configurations (relative to the baryon-baryon threshold). In this study we extend our previous work by a systematic study of all the physical [ital Qq][sup 5] systems in a simple chromomagnetic model. In the first part we assume that the [ital q] quarks belong to the fundamental irrep of SU(3)[sub [ital F]] and that the [ital Q] quark has infinite mass. These assumptions are subsequently relaxed by introducing two mass parameters [delta] and [eta]. Once these symmetries are broken we gain access in our model to a large number of new dibaryons containing heavy flavor. Some of them could be stable against decay via strong interactions, and we indicate the most favorable cases.

Strangeness production in hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions in the dual parton model.

[Lambda], [bar [Lambda]], and [ital K][sub [ital S]][sup 0] production is studied in a Monte Carlo dual parton model for hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions with an SU(3) symmetric sea for chain formation (chain ends) but strangeness suppression in the chain fragmentation process. Additionally, ([ital qq])-([ital [bar q]] [ital [bar q]]) production from the sea was introduced into the chain formation process with the same probability as for the [ital q][r arrow][ital qq] branching within the chain decay process. With these assumptions, multiplicity ratios and Feynman-[ital x] distributions for strange particles in [ital h]-[ital h] and multiplicity ratios in heavy ion collisions are reasonably well reproduced.

Two-body decays of charm mesons and the role of exotic mesons.

Two-body decays of charm mesons (except for decays into the final states involving [eta] or [eta][prime]) are studied from a perspective in which dynamical contributions of hadrons are explicitly taken into account. All the observed values of branching ratios for the two-body decays of charm mesons are reproduced well. In particular, a solution to the well-known puzzle, [Gamma]([ital D][sup 0][r arrow][ital K][sup +][ital K[minus]])/[Gamma]([ital D][sup 0][r arrow][pi][sup +][pi][sup [minus]])[congruent]2--3, is presented. Contributions of exotic ([ital QQ])([ital [bar Q][bar Q]]) mesons can explain the large violation of the charm counterpart of the [vert bar][Delta][ital I][vert bar]=1/2 rule in consistency with the small violation of the [vert bar][Delta][ital I][vert bar]=1/2 rule in the [ital K][r arrow][pi][pi] decays.

KK-bar molecules.

We have extended and improved our previous studies of the {ital qq{bar q}}{ital {bar q}} system, paying special attention to the {ital K{bar K}} channels. The new results clarify and reinforce the {ital K{bar K}} molecule interpretation of the {ital S}{sup *} and {delta}. Effective meson-meson potentials extracted from the {ital qq{bar q}}{ital {bar q}} system and couplings to {ital q{bar q}} scalar mesons lead to coupled-channel amplitudes which closely resemble those observed in both the {ital S}{sup *} and {delta} channels. We also show that the {ital K{bar K}} molecules have properties consisent with experimental results on the production of the {ital S}{sup *} and {delta} and of low-mass {ital K{bar K}} pairs.