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G. Pancheri

Publications and source records attributed to G. Pancheri.

At least 73 records · Page 4Linked to original sources
arXiv2002

Scanning of the e+e- to pi+pi- cross--section below 1 GeV by radiative events with untagged photon

We discuss an inclusive approach to the measurement of the e+e- --> pi+ pi- cross--section by the radiative return method without photon tagging. The essential part of this approach is the choice of rules for event selection which provide rejection of events with 3 (or more) pions and decrease the final--state radiation background. The radiative corrections to the initial--state radiation process are computed for DAPhNE conditions, using the quasi--real electron approximation for both, the cross--section and the underlying kinematics. The two cases of restricted and unrestricted pion phase space are considered. Some numerical calculations illustrate our analytical results.

hep-ph↗
arXiv2001

On Factorization, Quark Counting, and Vector Dominance

Using an eikonal structure for the scattering amplitude, Block and Kaidalov have derived factorization theorems for nucleon-nucleon, $γp$ and $γγ$ scattering at high energies, using only some very general assumptions. We present here an analysis giving experimental confirmation for factorization of cross sections, nuclear slope parameters B and $ρ$-values (ratio of real to imaginary portion of forward scattering amplitudes), showing that: i) the three factorization theorems hold, ii) the additive quark model holds to ~1%, and iii) vector dominance holds to better than ~4%.

hep-ph↗
arXiv2001

Dispersive Techniques for $α_s$, $R_{had}$ and Instability of the Perturbative Vacuum

Recent dispersive techniques developed by us are applied to discuss three problems: 1. A long standing discrepan-cy between the measurements of $R(s)$ for $\sqrt{s} = (5÷7.5)GeV$ by Crystal Ball and MARK I has been analyzed and its consequences analyzed for the number of contributing quarks. 2. Noting that the perturbative $α_s$ has the wrong analyticity, analytic models consistent with asymptotic freedom (AF) and confinement have been constructed and applied to discuss $τ$ decay. 3. It is shown that AF leads to a wrong sign for $\im\big(α(s)\big)$ which signals an instability of the perturbative QCD vacuum.

hep-ph↗
arXiv2001

Total Cross Sections

A unified approach to total cross-sections, based on the QCD contribution to the rise with energy, is presented for the processes $pp$, $p{\bar p}$, $γp, γγ, e^+e^- \to hadrons$. For proton processes, a discussion of the role played by soft gluon summation in taming the fast rise due to mini-jets is presented. For photon-photon processes, a comparison with other models indicates the need for precision measurements in both the low and high energy region, likely only with measurements at future Linear Colliders.

hep-ph↗
arXiv2001

$σ^{tot}_{ee γγ}$ at $e^+e^-$ colliders}

In this talk I briefly summarize different models for $σ^{tot}_{2 γ}$ ($e^+e^- \to γγ\to$ hadrons) and contrast model predictions with the data. I will then discuss the capability of the future $e^+e^-$ and $γγ$ colliders to distinguish between various models and end with an outlook for future work.

hep-ph↗
arXiv2001

Total Photonic and Hadronic Cross-sections

We discuss total cross-sections within the context of the QCD calculable mini-jet model, highlighting its successes and failures. In particular we show its description of $γγ\to hadrons$ and compare it with OPAL and L3 data. We extrapolate this result to $γp$ total cross-sections and propose a phenomenological ansätz for virtual photon cross-sections. We point out that the good agreement with data obtained with the Eikonal Minijet Model should not hide the many uncertainties buried in the impact parameter distribution. A model obtained from Soft Gluon Summation is briefly discussed and its application to hadronic cross-sections is shown.

hep-ph↗
arXiv2001

$γγ$ cross-sections and $γγ$ colliders

We summarize the predictions of different models for total $γγ$ cross-sections. The experimentaly observed rise of $σ_{γγ}$ with $\sqrt{s_{γγ}}$, faster than that for $σ_{\bar p p}$, $σ_{γp}$ is in agreement with the predictions of the Eikonalized Minijet Models as opposed to those of the Regge-Pomeron models. We then show that a measurement of $σ_{γγ}$ with an accuracy of $\lessapprox 8-9% (6-7%)$ is necessary to distinguish among different Regge-Pomeron type models (among the different parametrisations of the EMM models) and a precision of $\lessapprox$ 20% is required to distinguish among the predictions of the EMMs and of those models which treat like 'photon like a proton', for the energy range $300 < \sqrt{s_{γγ}} < 500$ GeV. We further show that the difference in model predictions for $σ_{γγ}$ of about a factor 2 at $\sqrt{s_{γγ}} = 700 $ GeV reduces to $\sim$ 30% when folded with bremsstrahlung $γ$ spectra to calculate $σ({e^+e^- \to e^+e^-γγ\to e^+e^-X})$. We point out then the special role that $γγ$ colliders can play in shedding light on this

hep-ph↗
arXiv2000

Hadronic cross-sections in gamma gamma processes and the next linear collider

In this note we address the issue of theoretical estimates of the hadronic cross-sections for \gamgam processes. We compare the predictions of the minijet model with data as well as other models, highlighting the band of uncertainties in the theoretical predictions as well as those in the final values of the $σ(\gamgam \go {\rm hadrons})$ extracted from the data. We find that the rise of $σ_{γγ}^{\rm tot}$ with energy shown in the latest \gamgam data is in tune with the faster rise expected in the Eikonal Minijet Models (EMM). We present an estimate of the accuracy with which this cross-section needs to be measured, in order to distinguish between the different theoretical models which try to `explain ' the rise of total cross-sections with energy. We find that the precision of measurement required to distinguish the EMM type models from the proton-like models, for $300 < \sqrt{s}_{\gamgam} < 500$ GeV, is $\lsim 20 %$, whereas to distinguish between various proton-like models or among the different parametrizations of the EMM, a precision of $\lsim 8-9 %$ or $\lsim 6-7%$ respectively, is required. We also comment briefly on the implications of these predictions for hadronic backgrounds at the next linear collider (NLC) to be run in the \gamgam mode or \eplem mode.

hep-ph↗
arXiv2000

Radiative Corrections to the Hadronic Cross-Section Measurement at DAPHNE

The hadronic invariant mass distribution for the process of electron-positron annihilation into a pair of charged pions accompanied by a photon radiated from the initial state has been studied for the region of DA$Φ$NE energies. The Born cross-section and the electromagnetic radiative corrections to it are calculated for realistic conditions of the KLOE detector. The dependence on the physical parameters which define the event selection is obtained.

hep-ph↗
arXiv2000

Chiral loops and a_0(980) exchange in ϕ->π^0ηγ

The radiative $ϕ\toπ^0ηγ$ decay is discussed emphasizing the effects of the $a_0$(980) scalar resonance which dominates the high values of the $π^0η$ invariant mass spectrum. In its lowest part, the proposed amplitude coincides with the reliable and ChPT-inspired contribution coming from chiral loops. The $a_0$(980) resonance is then incorporated exploiting the complementarity between ChPT and the linear sigma model for this channel. The recently reported experimental invariant mass distribution and branching ratio can be satisfactorily accommodated in our framework. For the latter, a value of $B(ϕ\toπ^0ηγ)$ in the range $(0.75$--$0.95)\times 10^{-4}$ is predicted.

hep-ph↗
arXiv2000

The ratio Phi->K+K-/K0K0bar

The ratio Phi->K+K-/K0K0bar is discussed and its present experimental value is compared with theoretical expectations. A difference larger than two standard deviations is observed. We critically examine a number of mechanisms that could account for this discrepancy, which remains unexplained. Measurements at DAPHNE at the level of the per mille accuracy can clarify whether there exist any anomaly.

hep-ph↗
arXiv2000

Breaking the Barriers - Uniting Accelerator and Cosmic Ray p-p Cross Sections

We make a QCD-inspired parameterization of all accelerator data on forward proton-proton and antiproton-proton scattering amplitudes. Using vector dominance and the additive quark model, we show that the same parameters also fit gamma p and gamma gamma interactions. Using the high energy predictions of our model, along with Glauber theory, we calculate proton-air cross sections at energies near sqrt s approx 30 TeV. The comparisons of p-air cosmic ray measurements with our QCD model predictions provide a strong constraint on the inclusive particle production cross section.

hep-ph↗
arXiv1999

QCD and Total Cross-sections

We discuss models for total cross-sections, show their predictions for photon-photon collisions and compare them with the recent LEP measurements. We show that the extrapolations to high center of mass energies within various models differ by large factors at high energies and discuss the precision required from future measurements at the proposed Linear Collider which would allow to distinguish between them.

hep-ph↗
arXiv1999

Models for Photon-photon Total Cross-sections

We present here a brief overview of recent models describing the photon-photon cross-section into hadrons. We shall show in detail results from the eikonal minijet model, with and without soft gluon summation.

hep-ph↗
arXiv1999

Hadronic Total Cross-sections Through Soft Gluon Summation in Impact Parameter Space

The Bloch-Nordsieck model for the parton distribution of hadrons in impact parameter space, constructed using soft gluon summation, is investigated in detail. Its dependence upon the infrared structure of the strong coupling constant $α_s$ is discussed, both for finite as well as singular, but integrable, $α_s$. The formalism is applied to the prediction of total proton-proton and proton-antiproton cross-sections, where screening, due to soft gluon emission from the initial valence quarks, becomes evident.

hep-ph↗
arXiv1998

Photon-Proton and Photon-Photon Scattering from Nucleon-Nucleon Forward Amplitudes

We show that the data on $γp$ and $γγ$ interactions can be derived from the $pp$ and $\bar p p$ forward scattering amplitudes using vector meson dominance and the additive quark model. The nucleon-nucleon data are parameterized using a model where high energy cross sections rise with energy as a consequence of the increasing numbers of soft partons populating the colliding particles. We present detailed descriptions of the data on the total and elastic cross sections, the ratio of the real to imaginary part of the forward scattering amplitude, and on the slope of the differential cross sections for $pp$, $\bar p p$, $γp$, $γγ$, $γp \to γV$ and $γγ\to V_i V_j$ reactions, where $V= ρ, ω, ϕ$. We make a wide range of predictions for future HERA and LHC experiments and for $γγ$ measurements at LEP.

hep-ph↗
arXiv1998

Eikonalised minijet model analysis of sigma_(gamma gamma)^(inel)

We study the theoretical predictions for the total inelastic $γγ$ cross-sections, with an emphasis on the eikonalised minijet model (EMM). In the context of the EMM, we discuss a new ansatz for the overlap function involving the photons. We discuss the dependence of the EMM predictions on various input parameters as well as predictions for \siggg from a simple extension of the Regge Pomeron Exchange model. We then compare both with the recent LEP data.

hep-ph↗