Searcharxiv⌕ Search

arXiv subjects

R. Di Salvo

Publications and source records attributed to R. Di Salvo.

At least 37 records · Page 2Linked to original sources
arXiv2014

Study of Dalitz decay phi -> eta e+e- with KLOE detector

We have studied the vector to pseudoscalar conversion decay phi -> eta e+e-, with eta -> pi0pi0pi0, with the KLOE detector at DAPHNE. The data set of 1.7 fb-1 of e+e- collisions at sqrt(s)~Mphi contains a clear conversion decay signal of ~31,000 events from which we measured a value of BR(phi -> eta e+e-)=(1.075+-0.007+-0.038)x10-4. The same sample is used to determine the transition form factor by a fit to the e+e- invariant mass spectrum, obtaining b(phi eta) =(1.17 +- 0.10 + 0.07) GeV-2, that improves by a factor of five the precision of the previous measurement and is in good agreement with VMD expectations.

hep-ex↗
arXiv2014

Search for light vector boson production in $e^+e^- \rightarrow μ^+ μ^- γ$ interactions with the KLOE experiment

We have searched for a light vector boson $U$, the possible carrier of a "dark force", with the KLOE detector at the DA$Φ$NE \epm\ collider, motivated by astrophysical evidence for the presence of dark matter in the universe. Using \epm\ collisions collected with an integrated luminosity of $239.3$~pb$^{-1}$, we look for a dimuon mass peak in the reaction \epm\to$μ^+ μ^-$\gam, corresponding to the decay $U\toμ^+μ^-$. We find no evidence for a $U$ vector boson signal. We set a 90\% CL upper limit for the mixing parameter squared between the photon and the $U$ boson of 1.6$\times$10$^{-5}$ to 8.6$\times$10$^{-7}$ for the mass region $520<m_{\rm U}<980$ MeV.

hep-ex↗
arXiv2014

Test of CPT and Lorentz symmetry in entangled neutral kaons with the KLOE experiment

Neutral kaon pairs produced in phi decays in anti-symmetric entangled state can be exploited to search for violation of CPT symmetry and Lorentz invariance. We present an analysis of the CP-violating process phi->K_S K_L->pi+pi-pi+pi- based on 1.7 fb-1 of data collected by the KLOE experiment at the Frascati phi-factory DAFNE. The data are used to perform a measurement of the CPT-violating parameters Delta_amu for neutral kaons in the contest of the Standard Model Extension framework. The parameters measured in the reference frame of the fixed stars are: Delta_ao = (-6.0 +- 7.7_{stat} +- 3.1_{syst}) x 10^{-18} GeV Delta_ax = ( 0.9 +- 1.5_{stat} +- 0.6_{syst}) x 10^{-18} GeV Delta_ay = (-2.0 +- 1.5_{stat} +- 0.5_{syst}) x 10^{-18} GeV Delta_az = ( 3.1 +- 1.7_{stat} +- 0.5_{syst}) x 10^{-18} GeV These are presently the most precise measurements in the quark sector of the Standard Model Extension.

hep-ex↗
arXiv2013

Measurement of the Σ beam asymmetry for the ω photo-production off the proton and the neutron at GRAAL

We report on new measurements of the beam asymmetry for ω photo-production on proton and neutron in Hydrogen and Deuterium targets from the GRAAL collaboration. The beam asymmetry values are extracted from the reaction threshold (E_γ = 1.1 GeV in the free nucleon kinematics) up to 1.5 GeV of incoming photon energy. For the first time both the radiative and the three-pion decay channels are simultaneously investigated on the free proton. Results from the two decay channels are in agreement and provide important constraints for the determination of resonant state contributions to the ω production mechanism. First experimental results on the deuteron allow the extraction of the Σ beam asymmetry on quasi-free nucleons. Comparison of the results for free and quasi-free kinematics on the proton shows a generally reasonable agreement, similar to the findings in pseudo-scalar meson photo-production reactions. For the first time measurements on quasi-free neutrons are available, showing that both the strength and the angular distributions of the beam asymmetry are sensibly different from the results on the proton target.

nucl-ex↗
arXiv2013

Recent results on hadron physics at KLOE

One of the basic motivations of the KLOE and KLOE-2 collaborations is the test of fundamental symmetries and the search for phenomena beyond the Standard Model via the hadronic and leptonic decays of ground-state mesons and via their production in the fusion of virtual gamma quanta exchanged between colliding electrons and positrons. This contribution includes brief description of results of recent analysis of the KLOE data aimed at (i) the search for the dark matter boson, (ii) determination of the hadronic and light-by-light contributions to the g-2 muon anomaly and (iii) tests of QCD anomalies.

hep-ex↗
arXiv2013

A new limit on the CP violating decay KS -> 3pi0 with the KLOE experiment

We have carried out a new direct search for the CP violating decay KS -> 3pi0 with 1.7 fb^-1 of e+e- collisions collected by the KLOE detector at the phi-factory DAFNE. We have searched for this decay in a sample of about 5.9 x 10^8 KS KL events tagging the KS by means of the KL interaction in the calorimeter and requiring six prompt photons. With respect to our previous search, the analysis has been improved by increasing of a factor four the tagged sample and by a more effective background rejection of fake KS tags and spurious clusters. We find no candidates in data and simulated background samples, while we expect 0.12 standard model events. Normalizing to the number of KS -> 2pi0 events in the same sample, we set the upper limit on BR(KS -> 3pi0 < 2.6 x 10^-8 at 90% C.L., five times lower than the previous limit. We also set the upper limit on the eta_000 parameter, |eta_000 | < 0.0088 at 90% C.L., improving by a factor two the latest direct measurement.

hep-ex↗
arXiv2013

Limit on the production of a light vector gauge boson in phi meson decays with the KLOE detector

We present a new limit on the production of a light dark-force mediator with the KLOE detector at DAPHNE. This boson, called U, has been searched for in the decay phi --> eta U, U --> e+ e-, analyzing the decay eta --> pi0 pi0 pi0 in a data sample of 1.7 fb-1. No structures are observed in the e+e- invariant mass distribution over the background. This search is combined with a previous result obtained from the decay eta --> pi+ pi- pi0, increasing the sensitivity. We set an upper limit at 90% C.L. on the ratio between the U boson coupling constant and the fine structure constant of alpha'/alpha < 1.7x10^-5 for 30<M_U<400 MeV and alpha'/alpha < 8x10^-6 for the sub-region 50<M_U<210 MeV. This result assumes the Vector Meson Dominance expectations for the phietagamma^* transition form factor. The dependence of this limit on the transition form factor has also been studied.

hep-ex↗
arXiv2012

Measurement of η meson production in γγ interactions and Γ(η-->γγ) with the KLOE detector

We present a measurement of η meson production in photon-photon interactions produced by electron-positron beams colliding with \sqrt{s}=1 GeV. The measurement is done with the KLOE detector at the ϕ-factory DAΦNE with an integrated luminosity of 0.24 fb^{-1}. The e^+e^- --> e^+e^-η cross section is measured without detecting the outgoing electron and positron, selecting the decays η-->π^+π^-π^0 and η-->π^0π^0π^0. The most relevant background is due to e^+e^- --> ηγ when the monochromatic photon escapes detection. The cross section for this process is measured as σ(e^+e^- -->ηγ) = (856 \pm 8_{stat} \pm 16_{syst}) pb. The combined result for the e^+e^- -->e^+e^-η cross section is σ(e^+e^- -->e^+e^-η) = (32.72 \pm 1.27_{stat} \pm 0.70_{syst}) pb. From this we derive the partial width Γ(η-->γγ) = (520 \pm 20_{stat} \pm 13_{syst}) eV. This is in agreement with the world average and is the most precise measurement to date.

hep-ex↗
arXiv2012

Measurement of Γ(η-> π^+π^-γ)/Γ(η-> π^+π^-π^0) with the KLOE Detector

The ratio R_η=Γ(η-> π^+π^-γ)/Γ(η-> π^+π^-π^0) has been measured by analyzing 22 million ϕ\to ηγdecays collected by the KLOE experiment at DA\PhiNE, corresponding to an integrated luminosity of 558 pb^{-1}. The η\to π^+π^-γproceeds both via the ρresonant contribution, and possibly a non-resonant direct term, connected to the box anomaly. Our result, R_η= 0.1856\pm 0.0005_{stat} \pm 0.0028_{syst}, points out a sizable contribution of the direct term to the total width. The di-pion invariant mass for the η-> π^+π^-γdecay could be described in a model-independent approach in terms of a single free parameter, α. The determined value of the parameter αis α= (1.32 \pm 0.08_{stat} +0.10/-0.09_{syst}\pm 0.02_{theo}) GeV^{-2}

hep-ex↗
arXiv2012

Virtual Compton Scattering and the Generalized Polarizabilities of the Proton at Q^2=0.92 and 1.76 GeV^2

Virtual Compton Scattering (VCS) on the proton has been studied at Jefferson Lab using the exclusive photon electroproduction reaction (e p --> e p gamma). This paper gives a detailed account of the analysis which has led to the determination of the structure functions P_LL-P_TT/epsilon and P_LT, and the electric and magnetic generalized polarizabilities (GPs) alpha_E(Q^2) and beta_M(Q^2) at values of the four-momentum transfer squared Q^2= 0.92 and 1.76 GeV^2. These data, together with the results of VCS experiments at lower momenta, help building a coherent picture of the electric and magnetic GPs of the proton over the full measured Q^2-range, and point to their non-trivial behavior.

nucl-ex↗
arXiv2010

Proposal for taking data with the KLOE-2 detector at the DA$Φ$NE collider upgraded in energy

This document reviews the physics program of the KLOE-2 detector at DA$Φ$NE upgraded in energy and provides a simple solution to run the collider above the $ϕ$-peak (up to 2, possibly 2.5 GeV). It is shown how a precise measurement of the multihadronic cross section in the energy region up to 2 (possibly 2.5) GeV would have a major impact on the tests of the Standard Model through a precise determination of the anomalous magnetic moment of the muon and the effective fine-structure constant at the $M_Z$ scale. With a luminosity of about $10^{32}$cm$^{-2}$s$^{-1}$, DA$Φ$NE upgraded in energy can perform a scan in the region from 1 to 2.5 GeV in one year by collecting an integrated luminosity of 20 pb$^{-1}$ (corresponding to a few days of data taking) for single point, assuming an energy step of 25 MeV. A few years of data taking in this region would provide important tests of QCD and effective theories by $γγ$ physics with open thresholds for pseudo-scalar (like the $η'$), scalar ($f_0,f'_0$, etc...) and axial-vector ($a_1$, etc...) mesons; vector-mesons spectroscopy and baryon form factors; tests of CVC and searches for exotics. In the final part of the document a technical solution for the energy upgrade of DA$Φ$NE is proposed.

hep-ex↗
arXiv2010

Limits on light-speed anisotropies from Compton scattering of high-energy electrons

The possibility of anisotropies in the speed of light relative to the limiting speed of electrons is considered. The absence of sidereal variations in the energy of Compton-edge photons at the ESRF's GRAAL facility constrains such anisotropies representing the first non-threshold collision-kinematics study of Lorentz violation. When interpreted within the minimal Standard-Model Extension, this result yields the two-sided limit of 1.6 x 10^{-14} at 95% confidence level on a combination of the parity-violating photon and electron coefficients kappa_{o+} and c. This new constraint provides an improvement over previous bounds by one order of magnitude.

hep-ex↗
arXiv2010

A new limit on the light speed isotropy from the GRAAL experiment at the ESRF

When the electrons stored in the ring of the European Synchrotron Radiation Facility (ESRF, Grenoble) scatter on a laser beam (Compton scattering in flight) the lower energy of the scattered electron spectra, the Compton Edge (CE), is given by the two body photon-electron relativistic kinematics and depends on the velocity of light. A precision measurement of the position of this CE as a function of the daily variations of the direction of the electron beam in an absolute reference frame provides a one-way test of Relativistic Kinematics and the isotropy of the velocity of light. The results of GRAAL-ESRF measurements improve the previously existing one-way limits, thus showing the efficiency of this method and the interest of further studies in this direction.

physics.acc-ph↗
arXiv2008

Measurements of polarized photo-pion production on longitudinally polarized HD and Implications for Convergence of the GDH Integral

We report new measurements of inclusive pion production from frozen-spin HD for polarized photon beams covering the Delta(1232) resonance. These provide data simultaneously on both H and D with nearly complete angular distributions of the spin-difference cross sections entering the Gerasimov-Drell-Hearn (GDH) sum rule. Recent results from Mainz and Bonn exceed the GDH prediction for the proton by 22 microbarns, suggesting as yet unmeasured high-energy components. Our pi0 data reveal a different angular dependence than assumed in Mainz analyses and integrate to a value that is 18 microbarns lower, suggesting a more rapid convergence. Our results for deuterium are somewhat lower than published data, considerably more precise and generally lower than available calculations.

hep-ex↗
arXiv2008

Lowering the Light Speed Isotropy Limit: European Synchrotron Radiation Facility Measurements

The measurement of the Compton edge of the scattered electrons in GRAAL facility in European Synchrotron Radiation Facility (ESRF) in Grenoble with respect to the Cosmic Microwave Background dipole reveals up to 10 sigma variations larger than the statistical errors. We now show that the variations are not due to the frequency variations of the accelerator. The nature of Compton edge variations remains unclear, thus outlining the imperative of dedicated studies of light speed anisotropy.

astro-ph↗
arXiv2007

Measurement of eta photoproduction on the proton from threshold to 1500 MeV

Beam asymmetry and differential cross section for the reaction gamma+p->eta+p were measured from production threshold to 1500 MeV photon laboratory energy. The two dominant neutral decay modes of the eta meson, eta->2g and eta->3pi0, were analyzed. The full set of measurements is in good agreement with previously published results. Our data were compared with three models. They all fit satisfactorily the results but their respective resonance contributions are quite different. The possible photoexcitation of a narrow state N(1670) was investigated and no evidence was found.

nucl-ex↗
arXiv2006

Monte Carlo simulation of virtual Compton scattering below pion threshold

This paper describes the Monte Carlo simulation developed specifically for the VCS experiments below pion threshold that have been performed at MAMI and JLab. This simulation generates events according to the (Bethe-Heitler + Born) cross section behaviour and takes into account all relevant resolution-deteriorating effects. It determines the `effective' solid angle for the various experimental settings which are used for the precise determination of photon electroproduction absolute cross section.

physics.data-an↗