Single Production Channel Research Articles

Phenomenology of flavon fields at the LHC

We study low energy constraints from flavour violating processes, production and decay at the LHC of a scalar field varphi (flavon) associated to the breaking of a non-supersymmetric Abelian family symmetry at the TeV scale. This symmetry is constrained to reproduce fermion masses and mixing, up to O(1) coefficients. The non-supersymmetric gauged U(1) models considered are severely restricted by cancellation of anomalies and LEP bounds on contact interactions, consequently its phenomenology is out of the LHC reach. We therefore introduce an effective U(1) which is not gauged and it is broken explicitly by a CP odd term at the TeV scale. This helps us to explore flavour violating processes, production and decay at the LHC for these kind of light scalars. In this context we first study the constraints on the flavon mass and its vacuum expectation value from low energy flavour changing processes such as \mu -> e\gamma . We find that a flavon of about m_\phi <~ 150 GeV could be experimentally allowed. These kind of flavons could be significantly generated at the LHC via the gluon fusion mechanism and the single top production channel g u -> t \phi. The produced flavons can have characteristic decay modes such as t \bar{c} for m_\phi >~ m_t, and \tau \bar{\mu} for m_\phi <~ m_t, which could be effectively useful to detect flavons.

Quark–hadron duality in the Rein–Sehgal model

The quark–hadron duality in CC and NC neutrino interactions is discussed with the assumptions that single pion production is described accurately by the Rein–Sehgal model and that it allows reconstruction of the inclusive cross section in the resonance region. The duality is measured by means of integrals of structure functions in the Nachtmann variable for Q 2 < 3 GeV 2 . The results depend on the precision with which contributions from single pion production channels in the overall cross sections are known. Several approaches to evaluate them are compared. The duality is predicted to be seen for proton target reactions but to be absent for neutron and isoscalar targets. Two-component duality between resonant and valence quark contributions to structure functions is also investigated.

Simulations from a new neutrino event generator

We construct a new Monte Carlo generator of events for neutrino interactions. The dynamical models for quasi-elastic reactions, $\Delta$ excitation and more inelastic events described by the DIS formalism with the PDFs modified according to recent JLab data are used. We describe in detail single pion production channels, which combine the $\Delta$ excitation and DIS contribution. Many comparisons of the outcome of simulations with experimental data are presented.

The utilization of crisp code in hybrid reactor studies

One of the main applications of the Hybrid Reactors (ADS - Accelerator Driven System) is the incineration of transuranics (TRU) by fast neutrons that emerge from a spallation source in a sub critical reactor waste burner [1, 2]. For this application, an accurate description and prediction of spallation reaction is necessary, including all the characteristics concerning spatial and energetic angular distributions, spallation products and neutron multiplicity. To describe the nuclear reactions at intermediate and high energies, Monte Carlo calculations have been used. The CRISP package considers the intranuclear cascade (INC) that occurs during the spallation process in a realistic time-sequence approach in which all particles inside the nucleus can participate in the cascade and the nuclear density fluctuations are naturally taken into account during the process. The occupation number of each single particle level is considered as a function of time and a more realistic Pauli blocking mechanism can be performed. None of the existing models have effectively used all those features. The evaporation of protons and alpha particles are taken into account making possible the correct prediction of fissilities of actinides and pre-actinides [3]. Another implementation is the NN single-pion production reaction. This reaction is especially relevant if one is interested in neutron or proton multiplicities, since the creation/emission of pions is directly related with the excitation energy of the residual nucleus. We will present some results obtained with the CRISP package for proton-nucleus reaction at intermediate and high energies. This package was obtained by the coupling of the MCMC [4] and MCEF [5] codes, with the introduction of some improvements, such as better Pauli blocking mechanism, which constrains the residual nucleus energetic evolution to the Pauli Principle from the ground-state to the final compound-nucleus formed at the end of the intranuclear cascade process, and introduction of the most relevant resonant excitation and the NN single pion production channel. The results of interest for ADS development are consistent with the experimental data at different proton energies. More detailed calculations are being performed for studying other features of proton-nucleus reactions and with different targets.

On the mechanism of the HCCO + O2reaction: Probing multiple pathways to a single product channel

We explore the mechanism of the HCCO + O2 reaction using time-resolved Fourier transform spectroscopy. Utilizing an isotopically labeled reactant (18O2) and state-selective product detection, we determine the relative flux through different paths on the potential energy surface leading to a single asymptote: H + CO + CO2. In the labeled reaction, the dominant isotopic products are C18O and 16OC18O. Combined with data from the corresponding reaction in natural isotopic abundance, these results show that at least 85% of the reactive flux passes through a four-membered OCCO ring intermediate. An alternative reaction path through an energetically allowed three-membered COO ring intermediate represents less than 15% of the total reactive flux. The average energy deposited in vibration of CO and CO2 is in reasonable agreement with a statistical model using the separate statistical ensembles method.

A modeling study of the stratospheric NOx/NOy and NOx/HNO3 ratios: Single‐ versus dual‐channeled mode of OH, NO2 association

UARS observations bearing upon the NOx/NOy and NOx/HNO3 ratios were revisited within the framework of advances in laboratory studies that were spurred by the findings, around 1999, of considerable model underestimation of the observations. The objective was to study the two models of the OH, NO2 association reaction, one that considers the single HNO3 product channel and the other that considers dual HNO3 and HOONO products channels. Rate coefficients of the OH + HNO3 and the single‐channeled OH + NO2 → HNO3 reactions recommended in JPL00‐3 produce remarkably improved agreement between the modeled and observed NOx/HNO3 and NOx/NOy, compared to the case with the recommendations in JPL‐97. This agrees with the results of other previous studies, such as those using the Photochemistry of Ozone Loss in the Arctic Region in Summer and MkIV data. The consumption of OH, NO2 pair in the lower stratosphere via the three‐body association occurs at almost the same rate (within ±5%) whether the single‐ or the double‐channeled version of that process is used with rate coefficients from JPL00‐3. However, only 70–80% of this consumption yields HNO3 in the dual‐channeled version, compared to 100% in the case of the single‐channeled version. Consequently, the dual‐channeled model of HNO3 formation performs better than the single‐channeled model in predicting NOx/HNO3 and NOx/NOy ratios. At 46.4 mbar, for example, the mean percentage difference between the modeled and the observed NOx/HNO3 equals about −10%, if HOONO is included. The corresponding number is about −19% when HOONO is excluded. Because laboratory experiments on OH, NO2 association that directly detect HOONO isomer are still maturing, further studies are needed. Further studies are also needed to understand the intriguing tendency of the model‐measurement differences to maximize around 20 mbar.

Ion-molecule association in acrylonitrile

The association reactions of the acrylonitrile ion, CH 2CHCN +, and the protonated ion derived from acrylonitrile, CH 2CHCNH + with acrylonitrile (CH 2CHCN) have been examined using ion cyclotron resonance (ICR) and flowing afterglow selected ion flow drift tube (FA/SIFDT) techniques at room temperature. These techniques yield different results for these two systems that can be rationalized by considerations of the lifetime of the collision complex. In the CH 2CHCN +/CH 2CHCN system, the measured reaction rate coefficients are: k ICR = 2.5 × 10 −9 cm 3 s −1 with a single product channel (CH 2CHCNH + + C 3H 2N) and k SIFT = 3.1 × 10 −9 cm 3 s −1 (with a 30% product channel to the adduct C 6H 6N 6 +) The rate coefficient and product distributions in the FA/SIFDT instrument are invariant with pressure in the range 0.25–0.75 Torr. In the CH 2CHCNH +/CH 2CHCN system, the measured rate coefficients are: k ICR = 9.2 × 10 −11 cm 3 s −1 at a CH 2CHCN pressure of 3.0 × 10 −4 Torr and k SIFT = 1.6 × 10 −9 cm 3 s −1, where association is the only product channel observed by each technique. The termolecular process corresponding to this latter association has a measured reaction rate coefficient of k 3 = 1.2 × 10 −23 cm 6 s −1 (for M = CH 2CHCN) and k 3 = 8.1 × 10 −25 cm 6 s −1 (for M = He). Both systems were modelled: A double well potential model involving the formation of loosely bound and tightly bound complexes was required to account for the kinetic behaviour of the CH 2CHCN +/CH 2CHCN system whereas a single-well potential model satisfactorily accounted for the behaviour of the CH 2CHCNH +/CH 2CHCN system.

Much ado about leptoquarks: A comprehensive analysis

We examine the phenomenological implications of a $\ensuremath{\sim}200\mathrm{GeV}$ leptoquark in light of the recent excess of events at DESY HERA. Given the relative predictions of events rates in ${e}^{+}p$ versus ${e}^{\ensuremath{-}}p,$ we demonstrate that classes of leptoquarks may be excluded, including those contained in ${\mathrm{E}}_{6}$ grand unified theory (GUT) models. It is shown that future studies with polarized beams at HERA could reveal the chirality of the leptoquark fermionic coupling and that given sufficient luminosity in each ${e}_{L,R}^{\ifmmode\pm\else\textpm\fi{}}$ channel the leptoquark quantum numbers could be determined. The implications of 200--220 GeV leptoquarks at the Fermilab Tevatron are examined. While present Tevatron data most likely exclude vector leptoquarks and leptogluons in this mass region, it does allow for scalar leptoquarks. We find that while leptoquarks have little influence on Drell-Yan production, further studies at the Main Injector may be possible in the single production channel provided the Yukawa couplings are sufficiently large. We investigate precision electroweak measurements as well as the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}q\overline{q}$ at CERN LEP II and find they provide no further restrictions on these leptoquark models. We then ascertain that cross section and polarization asymmetry measurements at the Next Linear Collider (NLC) provide the only direct mechanism to determine the leptoquark's electroweak quantum numbers. The single production of leptoquarks in $\ensuremath{\gamma}e$ collisions by both the back-scattered laser and Weisacker-Williams techniques at the NLC is also discussed. Finally, we demonstrate that we can obtain successful coupling constant unification in models with leptoquarks, both with or without supersymmetry. The supersymmetric case requires the GUT group to be larger than SU(5) such as flipped ${\mathrm{SU}(5)\ifmmode\times\else\texttimes\fi{}\mathrm{U}(1)}_{X}.$

A time-dependent formulation of the scattering matrix for the collinear reaction H + H 2 (υ) » H 2 (υ′) + H

Scattering matrix elements for the collinear reaction H + H 2(υ) » H 2(υ') + H are computed using a new time-dependent method based on the Møller operator formulation of scattering theory. Reaction dynamics are determined by the LSTH potential energy surface where attention is focused on two asymptotic wave packets. One wave packet is prepared in a single reactant channel and propagated forward in time while the other wave packet is prepared in a single product channel and propagated backward in time. The time correlation function between reactant and product wave packets is used to determine the S-matrix element between the corresponding reactant and product channels.

The single top production channel at Tevatron energies

We have analyzed the cross section for single top production at Tevatron energies characterized by a final state of a b b jet pair and a W boson. For a top quark mass of the order of 150 GeV and with suitable cuts introduced in order to reduce the background this channel becomes competitive with the traditional t t pair production. We also discuss as a possible signature the charge asymmetry of the bottom jets with respect to the incoming hadron's directions.

Zinos and scalar muon production at e +e − colliders

Single scalar muon production is examined in detail which results in a final state particularly favourable for detection: two strongly acollinear muons plus large missing energy. Cross sections, missing energy and angular distributions are given. A strong dependence on the zino total width, common to all single production channel, is found.

Charge transfer in N2++H collisions at slow to intermediate velocities.

We have calculated charge-transfer cross sections for collisions of ground-state N/sup 2 +/ ions with atomic hydrogen for barycentric collision energies up to 5.4 keV/amu. The calculations were done using a combination of close-coupled and unitarized distorted-wave techniques after an expansion in NH/sup 2 +/ molecular states. In addition to the entrance channel, we included a single product channel dissociating to N/sup +/(2s2p/sup 3/,/sup 3/D/sup o/)+H/sup +/, both within the /sup 3/Pi symmetry. Our results are in good agreement with recent experimental measurements of state-to-state charge-transfer cross sections except at higher energies, where increasing population of the N/sup +/(2s2p/sup 3/,/sup 3/P/sup o/) level was observed. The charge- transfer excitation process leading to the /sup 3/P/sup o/ N/sup +/ state is not well described by the Landau-Zener approach.

K+pscattering analysis to 2 GeV/c

The ${K}^{+}p$ scattering data up to 2 GeV/c were fitted with a coupled-channel $K$-matrix parametrization in which inelasticity is represented by a single production channel for each partial wave. Several solutions are possible above laboratory kinetic energies about 1 GeV, but all are essentially the same below this energy. All solutions that we have found have a ${P}_{13}$ resonance pole at about total c.m. energy ($1796\ensuremath{-}i101$) MeV. Resonance poles are present in other partial waves but are at considerably higher energies or are considerably farther from the real energy axis. More reliable measurements of polarizations are needed to firmly establish the existence of resonance poles other than the ${P}_{13}$ one. Also, contemporary measurements of the reaction cross sections are needed.

Elastic scattering, pion production, and annihilation into pions in antiproton-proton interactions at 5.7 GeV/c

An extensive investigation of antiproton-proton interactions at 5.7 GeV/c without strange-particle production was carried out using a hydrogen bubble chamber. Cross-sections for different channels are given and discussed. The reliability of the analysis was checked using artificially generated events. The cross-sections for elastic scattering, for all processes involving annihilation, and for all other inelastic processes are respectively σel=(16.3±0.6)mb,σannlbil=(22.5±2.0)mb, σinel=(24.8±2.0)mb. TheN*1:38 is present both in the single and multiple pion production channels. For the reactionOpen image in new window a cross-section of (1.05±0.21) mb was obtained. Cross-sections forN*1238 production in other channels are also given. Some indication of the presence ofI=1/2 isobars was found in the nucleon-pion and the nucleon-two-pion systems. The inelastic nonannihilation reactions were found to be strongly peripheral. The one-pion exchange model including either a form factor or corrections for absorption was applied to the reactionOpen image in new window. Neither version of the model could correctly account for all features of the reaction. The average number of pions in the annihilation was found to be 7.3±0.6. The presence of an asymmetry in the angular distribution of the charged pions was confirmed at this energy; it is due mostly to high-energy pions. The production of ρ and ω mesons was observed in various annihilation channels. Rates of up to 80% for ρ production and up to 15% for ω production were obtained by fitting phase-space and Breit-Wigner curves to the effective-mass distributions of different channels.