arXiv subjects

F. Piccinini

Publications and source records attributed to F. Piccinini.

At least 91 records · Page 5Linked to original sources

arXiv2005

Four Quark Interpretation of Y(4260)

We propose that the Y(4260) particle recently announced by BaBar is the first orbital excitation of a diquark-antidiquark state ([cs][cbar sbar]). Using parameters recently determined to describe the X(3872) and X(3940) we show that the Y mass is compatible with the orbital excitation picture. A crucial prediction is that Y(4260) should decay predominantly in D_s D_sbar. The Y(4260) should also be seen in B non-leptonic decays in association with one kaon. We consider the full nonet of related four-quark states and their predicted properties. Finally, we comment on a possible narrow resonance in the same channel.

hep-ph↗

arXiv2005

Higgs boson self-couplings at the LHC as a probe of extended Higgs sectors

A study of two-Higgs-doublet models (2HDM) in the decoupling limit reveals the existence of parameter configurations with a large triple-Higgs self-coupling as the only low-energy trace of the departure from a Standard Model (SM) Higgs sector. This observation encourages attempts to search for double Higgs production at the Large Hadron Collider (LHC) even in mass regions which have been shown to be very hard to probe in the context of SM-like Higgs self-couplings. In this document we consider the case of an Intermediate Mass Higgs (IMH) boson, with 120 GeV <= M_H <= 140 GeV, produced in pairs via vector-vector fusion, Higgs-strahlung and associate production with heavy-quarks and decaying into b anti-b pairs. After a detailed signal-to-background analysis, we confirm that the observation of a Higgs-pair signal is very challenging in the framework of the SM, even at the LHC with upgraded luminosity. In contrast, we verify that the sensitivity is sufficient to detect departures from the SM which would escape detection in the measurements of the single-Higgs production channels.

hep-ph↗

arXiv2005

J/Psi strong couplings to the vector mesons

We present a study of the cross sections J/Psi X --> D^(*) \bar D^(*) (X = rho, Phi) based on the calculation of the effective tri- and four-linear couplings J/Psi (X) D^(*) \bar D^(*) within a constituent quark model. In particular, the details of the calculation of the four-linear couplings J/Psi X D^(*)\bar D^(*) are given. The results obtained have been used in a recent analysis of J/Psi absorption by the hot hadron gas formed in peripheral heavy-ion collisions at SPS energies.

nucl-th↗

arXiv2005

Four-Quark Mesons

The features of a model interpreting the light scalar mesons as diquark-antidiquark bound states and the consequences of its natural extension to include heavy quarks are briefly reviewed.

hep-ph↗

arXiv2004

Diquark-Antidiquarks with Hidden or Open Charm and the Nature of X(3872)

Heavy-light diquarks can be the building blocks of a rich spectrum of states which can accommodate some of the newly observed charmonium-like resonances not fitting a pure c-cbar assignment. We examine this possibility for hidden and open charm diquark-antidiquark states deducing spectra from constituent quark masses and spin-spin interactions. Taking the X(3872) as input we predict the existence of a 2++ state that can be associated to the X(3940) observed by Belle and re-examine the state claimed by SELEX, X(2632). The possible assignment of the previously discovered states D_s(2317) and D_s(2457) is discussed. We predict X(3872) to be made of two components with a mass difference related to (m_u-m_d) and discuss the production of X(3872) and of its charged partner X^(+-) in the weak decays of B^(+,0).

hep-ph↗

arXiv2004

Beyond the Standard Model Higgs Boson self-couplings at the LHC

A study of two-Higgs-doublet models (2HDM) in the decoupling limit reveals the existence of parameter configurations with a large triple-Higgs self-coupling as the only low-energy trace of a departure from a Standard Model (SM) Higgs sector. This observation encourages attempts to search for double Higgs production at the Large Hadron Collider (LHC) and its luminosity upgrade (SLHC) even in mass regions which have been shown to be very hard to probe in the context of SM-like Higgs self-couplings. In a scenario where only an Intermediate Mass Higgs (IMH) boson, with 120 GeV <= m_h <= 140 GeV, is discovered at the LHC, with measured couplings to fermions and gauge bosons compatible with their SM values, we show that Higgs-pair production (with each Higgs state decaying in two b bbar pairs) through Weak Boson Fusion (WBF) could open a window on physics beyond the SM in the Higgs sector.

hep-ph↗

arXiv2004

A new look at scalar mesons

Light scalar mesons are found to fit rather well a diquark-antidiquark description. The resulting nonet obeys mass formulae which respect, to a good extent, the OZI rule. OZI allowed strong decays are reasonably reproduced by a single amplitude describing the switch of a qbar-q pair, which transforms the state into two colourless pseudoscalar mesons. Predicted heavy states with one or more quarks replaced by charm or beauty are briefly described; they should give rise to narrow states with exotic quantum numbers.

hep-ph↗

arXiv2004

J/psi Absorption in Heavy Ion Collisions II

Using the methods introduced in a previous paper, we consider the dissociation of J/psi by the lowest-lying pseudoscalar and vector mesons in the hadronic fireball formed in heavy ion collisions, assumed to be a hadron gas at temperature T. Absorption by nuclear matter is accounted for as well. We compare with the S-U and Pb-Pb data presented by the NA50 Collaboration. From data at low centrality we find T=160-180 MeV, close to the predicted temperature of the transition to quark-gluon plasma and to the temperatures measured by hadron abundances. We extrapolate to higher centralities with the approximation of scaling the energy density of the fireball with the average baryon density per unit transverse area. Using the energy-temperature relation of the hadron gas made by the same pseudoscalar and vector mesons, the fall off of J/psi production shown by the NA50 data, can be marginally reproduced only for the highest temperature, T=180 MeV. If we use the energy-temperature relation of a Hagedorn gas with limiting temperature T_H=173 MeV, predictions fall short from reproducing the data. These results suggest that a different mechanism is responsible for the J/psi suppression at large centralities, which could very well be the formation of quark-gluon plasma.

hep-ph↗

arXiv2004

Is the anomalous decay ratio of D_{sJ}(2632) due to isospin breaking?

Quark pair annihilation into gluons is suppressed at large momenta due to the asymptotic freedom. As a consequence, mass eigenvalues of heavy states should be almost diagonal with respect to up and down quark masses, thereby breaking isospin. We suggest the particle observed by the SELEX Collaboration, D_{sJ}(2632) to be to a good extent a [cd][dbar sbar] state, which would explain why its D^0 K^+ mode is anomalously suppressed with respect to D_s eta. Predictions for the rates of the yet unobserved modes D_s pi^0 and D^+ K^0 are given.

hep-ph↗

arXiv2004

J/psi Absorption in Heavy Ion Collisions

We present a new calculation of the pi-J/psi dissociation cross sections within the Constituent Quark-Meson Model recently introduced. To discuss the absorption of J/psi in heavy-ion collisions, we assume the J/psi to be produced inside a thermalized pion gas, as discussed by Bjorken, and introduce the corrections due to absorption by nuclear matter as well. We fit the absorption length of the J/psi to the data obtained at the CERN SPS by the NA50 Collaboration for Pb-Pb collisions. Collisions of lower centrality allow us to determine the temperature and the energy density of the pion gas. For both these quantities we find values close to those indicated by lattice gauge calculations for the transition to a quark-gluon plasma. A simple extrapolation to more central collisions, which takes into account the increase of the energy deposited due to the increased nucleon flux, fails to reproduce the break in J/psi absorption indicated by NA50, thus lending support to the idea that an unconfined quark-gluon phase may have been produced. This conclusion could be sharpened by analysing in a similar way, as a function of centrality, other observables such as strange particle production.

hep-ph↗

arXiv2003

The BABAYAGA event generator

The program BABAYAGA is an event generator for QED processes at flavour factories, mainly intended for luminosity measurement of e+ e- colliders in the center of mass range 1-10 GeV. Recently, the pi+ pi- channel has been added as well. The relevant (photonic) radiative corrections are simulated by means of a Parton Shower in QED. The theoretical precision of the approach is estimated and some phenomenological results are discussed.

hep-ph↗

arXiv2003

ALPGEN, a generator for hard multiparton processes in hadronic collisions

This paper presents a new event generator, ALPGEN, dedicated to the study of multiparton hard processes in hadronic collisions. The code performs, at the leading order in QCD and EW interactions, the calculation of the exact matrix elements for a large set of parton-level processes of interest in the study of the Tevatron and LHC data. The current version of the code describes the following final states: (W -> ffbar') QQbar+ N jets (Q being a heavy quark, and f=l,q), with N<=4; (Z/gamma* -> f fbar)+QQbar+Njets (f=l,nu), with N<=4; (W -> ffbar') + charm + N jets (f=l,q), N<= 5; (W -> f fbar') + N jets (f=l,q) and (Z/gamma* -> f fbar)+ N jets (f=l,nu), with N<=6; nW+mZ+lH+N jets, with n+m+l+N<=8 and N<=3 including all 2-fermion decay modes of W and Z bosons, with spin correlations; Q Qbar+N jets (N<=6) with t -> b f fbar' decays and relative spin correlations included if Q=t; Q Qbar Q' Qbar'+N jets, with Q and Q' heavy quarks (possibly equal) and N<=4; H Q Qbar+N jets (N<=4) with t -> b f fbar' decays and relative spin correlations included if Q=t; N jets, with N<=6. Parton-level events are generated, providing full information on their colour and flavour structure, enabling the evolution of the partons into fully hadronised final states.

hep-ph↗

arXiv2003

Prospects for Higgs properties determination at the LHC

The strategies recently developed to study Higgs boson properties at the LHC are reviewed. It is shown how to obtain model-independent determinations of couplings to fermions and gauge bosons by exploiting different production and decay channels. We consider in some detail the case of Weak Boson Fusion Higgs production with H --> b \bar b as well as the prospects for the determination of the Higgs self-coupling at the SLHC.

hep-ph↗

arXiv2003

b-bbar final states in Higgs production via weak boson fusion at the LHC

We present a study of the Higgs production at the LHC via Weak Boson Fusion, with the Higgs boson decaying into a b-quark pair. A detailed partonic LO calculation of all the potential backgrounds is performed. We conclude that this channel for Higgs production can be extracted from the backgrounds, and present our estimates of the accuracy in the determination of the Hbb Yukawa coupling.

hep-ph↗

arXiv2002

Prospects for Higgs search at the LHC

The present status of theoretical calculations for signal and background processes relevant to the Higgs boson search at the LHC is reviewed, with special emphasis on recent developments. The issue of Higgs properties determination at the LHC is addressed.

hep-ph↗

arXiv2002

A note on the baryonic B-->Lambdabar p eta' decay

In this short note we examine the exclusive three-body B --> Lambdabar p eta' decay using a simple pole model involving a scalar intermediate resonance state. Our aim is to test the recently formulated hypothesis that charmless baryonic B decays could occur mainly in association with eta' or gamma.

hep-ph↗

arXiv2001

Theoretical developments on Quartic Gauge Boson Couplings at LEP

The search for quartic anomalous gauge couplings (QAGC) at LEP requires appropriate predictions for the radiative processes e+ e- \to ν\barνγγ, e+ e- \to q\bar{q}γγand e+ e- \to 4 fermions+γ. The current knowledge on dimension-six operators giving rise to QAGC is briefly reviewed, together with their implementation in event generators. The accuracy of calculations based on real approximations (used up to now for the LEP experimental analysis) is examined by comparing them with the available exact matrix element calculations.

hep-ph↗

arXiv2001

Radiative four-fermion processes at LEP2

The production of four fermions plus a visible photon in electron-positron collisions is analyzed, with particular emphasis on the LEP2 energy range. The study is based on the calculation of exact matrix elements, including the effect of fermion masses. In the light of the present measurements performed at LEP, triple and quartic anomalous gauge couplings are taken into account. Due to the presence of a visible photon in the final state, particular attention is paid to the treatment of higher-order QED corrections. Explicit results for integrated cross sections and differential distributions are shown and commented. The features of the Monte Carlo program WRAP, used to perform the calculation and available for experimental analysis, are described.

hep-ph↗