ATLAS sensitivity to top quark and W boson polarizationin $t\bar{t}$ events

The inelastic production of mesons in ep collisions has been studied with the ZEUS detector at HERA using an integrated luminosity of . The mesons were identified using the decay channel . The measurements were performed in the kinematic range , , 0.2 < z < 0.9 and , where Q² is the virtuality of the exchanged photon, W is the photon-proton centre-of-mass energy, z is the fraction of the photon energy carried by the meson in the proton rest frame and is the rapidity of the in the laboratory frame. The measured cross sections are compared to theoretical predictions within the non-relativistic QCD framework including colour-singlet and colour-octet contributions, as well as to predictions based on the k_T-factorisation approach. Calculations of the colour-singlet process generally agree with the data, whereas inclusion of colour-octet terms spoils this agreement.Received: 18 May 2005, Revised: 24 June 2005, Published online: 27 July 2005     

A new measurement of $J/\psi$ suppression in Pb-Pb collisions at 158 GeV per nucleon

We present a new measurement of production in Pb-Pb collisions at 158 GeV/nucleon, from the data sample collected in year 2000 by the NA50 Collaboration, under improved experimental conditions with respect to previous years. With the target system placed in vacuum, the setup was better adapted to study, in particular, the most peripheral nuclear collisions with unprecedented accuracy. The analysis of this data sample shows that the cross-sections ratio measured in the most peripheral Pb-Pb interactions is in good agreement with the nuclear absorption pattern extrapolated from the studies of proton-nucleus collisions. Furthermore, this new measurement confirms our previous observation that the cross-sections ratio departs from the normal nuclear absorption pattern for semi-central Pb-Pb collisions and that this ratio persistently decreases up to the most central collisions. Received: 25 August 2004, Revised: 15 December 2004, Published online: 21 January 2005     

Direct fragmentation of quarkonia including Fermi motionusing light-cone wave function

We investigate the effect of Fermi motion on the direct fragmentation of the and states employing a light-cone wave function. Consistent with such a wave function we set up the kinematics of a heavy quark fragmenting into quarkonia such that the Fermi motion of the constituents splits into a longitudinal as well as a transverse direction and thus calculate the fragmentation functions for these states. In the framework of our investigation, we estimate that the fragmentation probabilities of and may increase at least up to 14 percent when including this degree of freedom. Received: 11 May 2004, Revised: 23 April 2005, Published online: 31 May 2005 PACS: 13.87.Fh, 13.85.Ni, 12.38.Bx, 12.39.Hg An erratum to this article is available at .     

New J/\psi suppression data and the comovers interaction model

New data on the suppression both in proton-nucleus and in lead-lead interactions have been presented recently by the NA50 collaboration. We show that these data, together with the final ones on sulfur-uranium interactions, can be described in the framework of the comovers interaction model with a unique set of three parameters: the nuclear absorption cross-section, the comovers interaction cross-section and a single (rescaled) absolute normalization. Expectations for suppression at RHIC are also discussed.Received: 3 April 2003, Published online: 11 July 2003     

Additional J/\Psi suppression from high density effects

At high energies the saturation effects associated to the high parton density should modify the behavior of the observables in proton-nucleus and nucleus-nucleus scattering. In this paper we investigate the saturation effects in the nuclear production and estimate the modifications in the energy dependence of the cross section as well as in the length of the nuclear medium. In particular, we calculate the ratio of to Drell-Yan cross sections and show that it is strongly modified if the high density effects are included. Moreover, our results are compared with the data from the NA50 Collaboration and predictions for the RHIC and LHC kinematic regions are presented. We predict an additional suppression associated to the high density effects.Received: 10 October 2003, Revised: 23 December 2003, Published online: 25 February 2004     

Charmonium production and nuclear absorption in p-A interactions at 450 GeV

The production of and charmonium states in proton-nucleus interactions has been investigated by the NA50 experiment, at the CERN SPS. High statistics data sets were collected with collisions induced by 450 GeV protons incident on Be, Al, Cu, Ag and W targets. The and production cross-sections have been determined for each p-A system and their dependences on the nucleus size have been studied, leading to the so-called normal nuclear absorption. Comparing the two patterns we see that the nuclear absorption is stronger for the than for the . Given the high statistics of the data samples, the (or rapidity) differential cross-sections of the and states have also been studied, for each of the target nuclei.Received: 23 September 2003, Revised: 29 November 2003, Published online: 29 January 2004     

Exclusive photoproduction of a heavy vector meson in QCD

The process of exclusive heavy vector meson photoproduction, , is studied in the framework of QCD factorization. The mass of the produced meson, or , provides a hard scale for the process. We demonstrate that, in the heavy quark limit and at the one-loop order in perturbation theory, the amplitude factorizes in a convolution of a perturbatively calculable hard-scattering amplitude with the generalized parton densities and the non-relativistic QCD matrix element . We evaluate the hard-scattering amplitude at one-loop order and compare the data with theoretical predictions using an available model for generalized parton distributions.Received: 22 January 2004, Published online: 23 March 2004     

Open and hidden charm production in dA collisions at RHIC and LHC

We discuss aspects of open and hidden charm production in deuterium-nucleus collisions at RHIC and LHC energies. We describe calculations of the total cross section and the charm quark transverse momentum distributions. We next explain how shadowing and moderate nuclear absorption can explain the PHENIX d Au/pp ratios and predict the combined effect of shadowing and absorption in 6.2 TeV d + Pb collisions.Arrival of the final proofs: 28 April 2005     

The $\beta$-function in duality-covariant non-commutative $\phi^4$-theory

We compute the one-loop -functions describing the renormalisation of the coupling constant and the frequency parameter for the real four-dimensional duality-covariant non-commutative -model, which is renormalisable to all orders. The contribution from the one-loop four-point function is reduced by the one-loop wavefunction renormalisation, but the -function remains non-negative. Both and vanish at the one-loop level for the duality-invariant model characterised by . Moreover, also vanishes in the limit , which defines the standard non-commutative -quantum field theory. Thus, the limit exists at least at the one-loop level.Received: 19 March 2004, Published online: 5 May 2004     

J/\psi production in Indium-Indium collisions

The study of dilepton production in heavy-ion collisions at the CERN SPS provided some of the most interesting observations done so far in the search for the quark gluon plasma. However, several aspects of the understanding of these measurements need to be clarified. For example, the study of the J/ production in different colliding systems should help to disentangle which is the variable driving the J/ suppression. The NA60 experiment, with a new radiation tolerant Silicon pixel detector, studied Indium-Indium interactions in the year 2003. In this paper, we present the J/ / DY ratio, integrated over all the centralities of the collisions, together with a first study of the J/ transverse momentum and polarization. Arrival of the final proofs: 1 July 2005 PACS: 25.75.Dw, 25.75.Nq, 13.20.Gd     

The rare annihilation decays $\bar{B}^0_{s,d} \to J/\psi\gamma$

We investigate the physics potential of the annihilation decays in the standard model and beyond. In a naive factorization approach, the branching ratios are estimated to be and . In the framework of QCD factorization, we compute the non-factorizable corrections and get , . Future measurements of these decays would be useful for testing the factorization frameworks. The smallness of these decays in the SM makes them sensitive probes of new physics. As an example, we will consider the possible admixture of the (V + A) charge current to the standard (V-A) current. This admixture will give a significant contribution to the decays.Received: 29 August 2003, Revised: 17 January 2004, Published online: 19 March 2004Corresponding author: Y.D. Yang     

Quarkonium production from d + Au to Au + Au collisions

The PHENIX experiment measured J/ production in pp, d + Au and Au + Au reactions at = 200 GeV over a wide range of rapidity and transverse momentum. The nuclear modification factor obtained by comparing the d + Au and pp cross sections as a function of rapidity, is consistent with shadowing of the gluon distribution functions. J/ production in Au + Au collisions was compared to the production in pp collisions and it was found to be inconsistent with models that predict strong enhancement relative to binary collision scaling. Arrival of the final proofs: 29 June 2005 PACS: 25.75-q, 25.75-Dw, ^* Deceased Spokesperson     

An analysis of the time-dependent CP asymmetryin $B \to \pi \pi$ decays in the standard model

Measurements of the time-dependent CP-asymmetry in the decay and its charge conjugate by the BELLE and BABAR collaborations currently yield and , characterizing the direct and mixing-induced CP-asymmetries, respectively. We study the implication of these measurements on the CKM phenomenology taking into account the available information in the quark mixing sector. Our analysis leads to the results that the ratio |P _c /T _c | involving the QCD-penguin and tree amplitudes and the related strong phase difference in the decays are quite substantial. Using the isospin symmetry to constrain |P _c /T _c | and , where parameterizes the penguin-induced contribution, we present a fit of the current data including the measurements of and . Our best-fits yield , , , , and . At 68% C.L., the ranges are , , , and . Currently en vogue dynamical approaches to estimate the hadronic matrix elements in decays do not provide a good fit of the current data.Received: 5 April 2004, Published online: 14 July 2004A.Ya. Parkhomenko: On leave of absence from Department of Theoretical Physics, Yaroslavl State University, Sovietskaya 14, 150000 Yaroslavl, Russia.     

Exclusive semileptonic rare decays $B \to K^{(*)} l^ + l^-$ in a SUSY SO(10) GUT

In the SUSY SO(10) GUT context, we study the exclusive processes . Using the Wilson coefficients of the relevant operators including the new operators which are induced by neutral Higgs boson (NHB) penguins, we evaluate some possible observables associated with these processes like the invariant mass spectrum (IMS), lepton pair forward-backward asymmetry (FBA), lepton polarization asymmetries etc. In this model the contributions from Wilson coefficients , among new contributions, are dominant. Our results show that the NHB effects are sensitive to the FBA, , and of decay, which are expected to be measured in B factories, the deviation of in can reach 0.1 from SM, which could be seen in B factories, and the average of the normal polarization can reach several percent for and it is 0.05 or so for , which could be measured in the future super B factories and provide useful information to probe new physics and discriminate different models.Received: 30 October 2004, Published online: 9 March 2005     

Inelastic $J/\psi$ and $\Upsilon$ hadroproduction

We consider the prompt hadroproduction of and the states caused by the fusion of a symmetric colour-octet state, (gg)_8s , and an additional gluon. The cross sections are calculated in leading-order perturbative QCD. We find a considerable enhancement in comparison with previous perturbative QCD predictions. Indeed, the resulting cross sections are found to be consistent with the values measured at the Tevatron and RHIC, without the need to invoke non-perturbative colour-octet type of contributions.Received: 16 October 2004, Revised: 10 November 2004, Published online: 11 January 2005     

Search for a narrow charmed baryonic state decaying to $D^{\ast \pm} p^\mp$in ep collisions at HERA

A resonance search has been made in the invariant-mass spectrum with the ZEUS detector at HERA using an integrated luminosity of . The decay channels and (and the corresponding antiparticle decays) were used to identify mesons. No resonance structure was observed in the mass spectrum from more than 60 000 reconstructed mesons. The results are not compatible with a report of the H1 Collaboration of a charmed pentaquark, .Received: 14 September 2004, Revised: 29 September 2004, Published online: 9 November 2004     

CP asymmetry in $B \rightarrow \phi K_{S}$ in a general two-Higgs-doublet model with fourth-generation quarks

We discuss the time-dependent CP asymmetry of the decay in an extension of the standard model with both a two Higgs doublet and additional fourth-generation quarks. We show that, although the standard model with a two Higgs doublet and the standard model with fourth-generation quarks alone are not likely to largely change the effective from the decay , the model with both an additional Higgs doublet and fourth-generation quarks can easily account for the possible large negative value of without conflicting with other experimental constraints. In this model, additional large CP violating effects may arise from the flavor-changing Yukawa interactions between neutral Higgs bosons and the heavy fourth-generation down type quark, which can modify the QCD penguin contributions. With the constraints obtained from processes such as and , this model can lead to an effective as large as - 0.4 in the CP asymmetry of .Received: 25 March 2004, Revised: 20 April 2004, Published online: 18 June 2004     

Multiphoton radiation in leptonic <Emphasis Type="Italic">W</Emphasis>-boson decays

We explore CP violation in decay processes in the presence of the anomalous right-handed and couplings. The complex anomalous top coupling can be a source of new CP violation and may lead to a deviation of the observed weak phase in decays, which accounts for the present disagreement of the observed between and decays. Direct CP violation is also predicted. Received: 27 November 2002, Revised: 28 March 2003, Published online: 2 June 2003     

Charmonium suppression by thermal dissociation and percolation

I discuss the charmonium suppression in deconfined medium by thermal dissociation and parton percolation. I point out the differences and show predictions for suppression at different energy and/or for different interacting nuclei.Received: 14 February 2005, Published online: 31 May 2005PACS: 25.75.Nq,12.38.Mh,25.75.-q,24.85. + p     

Strongest gravitational waves from neutrino oscillationsat supernova core bounce

Resonant active-to-active ( ), as well as active-to-sterile ( ) neutrino ( ) oscillations can take place during the core bounce of a supernova collapse. Besides, over this phase, weak magnetism increases the antineutrino ( ) mean free path, and thus its luminosity. Because the oscillation feeds mass-energy into the target species, the large mass-squared difference between the species ( ) implies a huge amount of energy to be given off as gravitational waves ( erg s^-1), due to anisotropic but coherent flow over the oscillation length. This asymmetric -flux is driven by both the spin-magnetic and the universal spin-rotation coupling. The novel contribution of this paper stems from (1) the new computation of the anisotropy parameter -0.01, and (2) the use of the tight constraints from neutrino experiments as SNO and KamLAND, and the cosmic probe WMAP, to compute the gravitational-wave emission during neutrino oscillations in supernovae core collapse and bounce. We show that the mass of the sterile neutrino that can be resonantly produced during the flavor conversions makes it a good candidate for dark matter as suggested by Fuller et al. , Phys. Rev. D 68, 103002 (2003). The new spacetime strain thus estimated is still several orders of magnitude larger than those from diffusion (convection and cooling) or quadrupole moments of neutron star matter. This new feature turns these bursts into the more promising supernova gravitational-wave signals that may be detected by observatories as LIGO, VIRGO, etc., for distances far out to the VIRGO cluster of galaxies.Received: 26 November 2003, Revised: 26 February 2004, Published online: 3 June 2004