arXiv subjects
Publications and source records attributed to G. Pancheri.
Scattering and formation experiments can be performed not only with particle beams, but also, as of old, with particle sources. DA\PhiNE at the c.m. energy of the ϕis a relatively clean source of low-momentum charged and neutral kaons. As such, it can allow experiments unthinkable of at conventional kaon beams. This talk is dedicated to a presentation both of this viewpoint and of the physics that could be learned in this way.
An impact parameter representation for soft gluon radiation is applied to obtain both the initial decrease of the total cross-section ($σ_{tot}$) for proton-proton collisions as well as the later rise of $σ_{tot}$ with energy for both $pp$ and $p\bar{p}$. The non-perturbative soft part of the eikonal includes only limited low energy gluon emission and leads to the initial decrease in the proton-proton cross- section. On the other hand, the rapid rise in the hard, perturbative jet part of the eikonal is tamed into the experimentally observed mild increase by soft gluon radiation whose maximum energy rises slowly with energy.
In this paper we consider the possibility to test the FSR model in the reaction $e^+e^-\toπ^+π^-γ$ at DA$Φ$NE. We propose to consider the low $Q^2$ region ($Q^2$ is the invariant mass squared of the di-pion system) to study the different models describing $gamma^*\toπ^+π^-γ$ interaction. As illustration we compare the scalar QED and Resonance Perturbation Theory prediction for the $e^+e^-\toπ^+π^-γ$ cross section. We also consider the contribution coming from the $ϕ$ direct decay ($ϕ\toπ^+π^-γ$). We find the low $Q^2$ region is sensitive to FSR models.
This report summarizes a study of the physics potential of the CLIC e+e- linear collider operating at centre-of-mass energies from 1 TeV to 5 TeV with luminosity of the order of 10^35 cm^-2 s^-1. First, the CLIC collider complex is surveyed, with emphasis on aspects related to its physics capabilities, particularly the luminosity and energy, and also possible polarization, γγand e-e- collisions. The next CLIC Test facility, CTF3, and its R&D programme are also reviewed. We then discuss aspects of experimentation at CLIC, including backgrounds and experimental conditions, and present a conceptual detector design used in the physics analyses, most of which use the nominal CLIC centre-of-mass energy of 3 TeV. CLIC contributions to Higgs physics could include completing the profile of a light Higgs boson by measuring rare decays and reconstructing the Higgs potential, or discovering one or more heavy Higgs bosons, or probing CP violation in the Higgs sector. Turning to physics beyond the Standard Model, CLIC might be able to complete the supersymmetric spectrum and make more precise measurements of sparticles detected previously at the LHC or a lower-energy linear e+e- collider: γγcollisions and polarization would be particularly useful for these tasks. CLIC would also have unique capabilities for probing other possible extensions of the Standard Model, such as theories with extra dimensions or new vector resonances, new contact interactions and models with strong WW scattering at high energies. In all the scenarios we have studied, CLIC would provide significant fundamental physics information beyond that available from the LHC and a lower-energy linear e+e- collider, as a result of its unique combination of high energy and experimental precision.
We discuss the need to compare total cross-section measurements at LHC and HERA with each other and with available models in order to obtain a more precise prediction of the total hadronic cross-section at the future Linear Collider, thus leading to a better estimate of the hadronic background.
The process of $e^+e^-$ annihilation into a $π^+π^-$ pair with radiation of a photon is considered. The amplitude of the reaction $e^+e^-\toπ^+π^-γ$ consists of the model independent initial-state radiation (ISR) and model-dependent final-state radiation (FSR). The general structure of the FSR tensor is constructed from Lorentz covariance, gauge invariance and discrete symmetries in terms of the three invariant functions. To calculate these functions we apply Chiral Perturbation Theory (ChPT) with vector and axial-vector mesons. The contribution of $e^+e^-\toπ^+π^-γ$ process to the muon anomalous magnetic moment is evaluated, and results are compared with the dominant contribution in the framework of a hybrid model, consisting of VMD and point-like scalar eletrodynamics. The developed approach allows us also to calculate the $π^+π^-$ charge asymmetry.
The physics underlying the fall and eventual rise in various total cross-sections at high energies has been investigated over a decade using a model based on the Bloch-Nordsieck resummation in QCD. Here a brief review of our latest results is presented and comparison made with experimental data on $pp$, $γproton$ and $γγ$ total cross-sections.
A sum rule is derived for elastic scattering of hadrons at high energies which is in good agreement with experimental data on $p\bar{p}$ available upto the maximum energy $\sqrt{s} = 2 TeV$. Physically, our sum rule reflects the way unitarity correlates and limits how large the elastic amplitude can be as a function of energy to how fast it decreases as a function of the momentum transfer. The universality of our result is justified through our earlier result on equipartition of quark and glue momenta obtained from the virial theorem for massless quarks and the Wilson conjecture
The process of $e^+ e^-$ annihilation into $π^+ π^-$ pair with radiation of the photon is considered. The amplitude of the reaction $e^+ e^- \to π^+ π^- γ$ consists of the model independent initial-state radiation (ISR) and model dependent final-state radiation (FSR). The general structure of the FSR tensor is constructed from Lorentz covariance, gauge invariance and discrete symmetries in terms of the three invariant functions. To calculate these functions we apply Chiral Perturbation Theory (ChPT) with vector and axial-vector mesons. The contribution of $e^+ e^- \to π^+ π^- γ$ process to the muon anomalous magnetic moment is evaluated, and results are compared with the dominant contribution in framework of a hybrid model, consisting of VMD and point-like scalar electrodynamics. The developed approach allows us also to calculate the $π^+ π^-$ charge asymmetry.
Similarly to the electromagnetic pseudoscalar-meson transition form factors one can define also strange-quark vector current pseudoscalar-meson transition form factors, contributing only to a behaviour of the isoscalar parts of the previous ones. Their explicit form is found by constructing unitary and analytic models of the strange pseudoscalar-meson transition form factors dependent only on $ω$ and $ϕ$ coupling constant ratios as a free parameters. Numerical values of these ratios are then determined from the corresponding pseudoscalar-meson transition form factors by employing the $ω$-$ϕ$ mixing and a special assumption on the coupling of the quark components of vector-meson wave functions to flavour component of currents under consideration.
Present-day experimental and phenomenological situation about pseudoscalar ($π^0$, $η$, $η'$) meson transition form factors is briefly reviewed. Necessity of more sophisticated behaviours in time-like region of these form factors is emphasized. Four-resonance unitary and analytic model of the pseudoscalar meson transition form factors is constructed, which describes well all existing experimental information.
We discuss present predictions for the total $γγ$ and $γp $ cross-sections, highlighting why predictions differ. We present results from the Eikonal Minijet Model and improved predictions based on soft gluon resummation.
In this note we address the issue of measurability of the hadronic cross-sections at a future photon collider as well as for the two-photon processes at a future high energy linear $e^+e^-$ collider. We extend, to higher energy, our previous estimates of the accuracy with which the \gamgam\ cross-section needs to be measured, in order to distinguish between different theoretical models of energy dependence of the total cross-sections. We show that the necessary precision to discriminate among these models is indeed possible at future linear colliders in the Photon Collider option. Further we note that even in the $e^+e^-$ option a measurement of the hadron production cross-section via \gamgam processes, with an accuracy necessary to allow discrimination between different theoretical models, should be possible. We also comment briefly on the implications of these predictions for hadronic backgrounds at the future TeV energy $e^+e^-$ collider CLIC.
In this talk we present an update of model predictions for the $γγ$ total cross-section in the TeV region. The update includes preliminary results for $γγ$ cross-sections using the Bloch-Nordsieck model for the overlap function of the partons in the transverse space, use of the CJLK parametrisation of the photonic parton densities that has recently become available and extension to the higher $γγ$ energies relevant to the planned CLIC collider.
The complementarity between Chiral Perturbation Theory and the Linear Sigma Model is exploited to study $π^0π^0$ production in $ϕ$ radiative decays, where the effects of the $f_0(980)$ scalar resonance, and those of its more controversial $σ(500)$ partner, should become manifest via the $ϕ\to K^+ K^- (γ)\toπ^0π^0γ$ decay chain. The recently reported data on $ϕ\toπ^0π^0γ$ coming from the VEPP-2M $e^+ e^-$ collider in Novosibirsk and the DA$Φ$NE $ϕ$-factory in Frascati can be reasonably described in our approach, which we propose as a promising first step towards more detailed analyses. The $f_0(980)$ contribution, which appears as a moderately narrow peak at the high part of the dipion mass spectrum, can be interpreted as the isoscalar member of the scalar nonet with a large $f_0 K\bar{K}$ coupling and an $f_0ππ$ coupling suppressed by almost ideal $σ$-$f_0$ mixing. Indeed, the mixing angle in the flavour basis is found to be $ϕ_{S}\approx -6^\circ$, if the $f_0$-propagator is approximated by a simple Breit-Wigner, or $ϕ_{S}\approx -9^\circ$, if an improved two-channel analysis is performed. The $σ(500)$ resonance, which is then strongly coupled to pion pairs, yields a tiny contribution because, in our approach, its coupling to kaon pairs is proportional to $m^2_σ-m^2_K$ and thus quite small.
The forward elastic scattering of light on light, {\em i.e.,} the reaction $γ+γ\to γ+γ$ in the forward direction, is analyzed utilizing real analytic amplitudes. We calculate $ρ_{γγ}$, the ratio of the real to the imaginary portion of the forward scattering amplitude, by fitting the total $γγ$ cross section data in the high energy region $5 GeV \le \sqrt s \le 130 $ GeV, assuming a cross section that rises asymptotically as $\ln^2 s$. We then compare $ρ_{γγ}$ to $ρ_{nn}$, the ratio of the even portions of the $pp$ and $\pbar p$ forward scattering amplitudes, as well as to $ρ_{γp}$, the $ρ$ value for Compton scattering. Within errors, we find that the three $ρ$-values in the c.m.s. energy region $5 GeV \le \sqrt s \le 130$ GeV are the same, as predicted by a factorization theorem of Block and Kadailov.
We discuss the high energy behaviour of total cross-sections for protons and photons, in a QCD based framework with particular emphasis on the role played by soft gluons
We examine the energy dependence of total cross-sections for photon processes and discuss the QCD contribution to the rising behaviour