arXiv subjects

P. De Simone

Publications and source records attributed to P. De Simone.

At least 19 recordsLinked to original sources

arXiv2026

Performance of the LHCb muon detector in Run 3

In Run 3 of the LHC, the instantaneous luminosity at the LHCb interaction point has been increased by a factor of five, from $4\times 10^{32}\rm{cm}^{-2}\rm{s}^{-1}$ to $2\times 10^{33}\rm{cm}^{-2}\rm{s}^{-1}$. Several hardware interventions, including a complete overhaul of the readout electronics, have been carried out on the muon detector. The muon identification algorithms in the software trigger were improved with the aim of ensuring Run 2 performance under a higher particle rate. The operation and calibration of the upgraded muon detector are presented. The muon detection efficiency and muon identification performance are evaluated on data calibration samples collected during the year 2024. A muon identification efficiency above 90\% with sub-percent hadron misidentification probability is achieved by exploiting the pattern of hits in the muon detector.

hep-ex↗

arXiv2025

Measurement of $\eta\to\pi^{0}\gamma\gamma$ branching fraction with the KLOE detector

We present a measurement of the radiative decay $\eta\to\pi^0\gamma\gamma$ using 82 million $\eta$ mesons produced in $e^+e^-\to\phi\to\eta\gamma$ process at the Frascati $\phi$-factory DA$\Phi$NE. From the data analysis $1246\pm133$ signal events are observed. By normalising the signal to the well-known $\eta\to3\pi^0$ decay the branching fraction ${\cal B}(\eta\to\pi^0\gamma\gamma)$ is measured to be $(0.98\pm 0.11_\text{stat}\pm 0.14_\text{syst})\times10^{-4}$. This result agrees with a preliminary KLOE measurement, but is twice smaller than the present world average. Results for $d\Gamma(\eta\to\pi^0\gamma\gamma)/dM^2(\gamma\gamma)$ are also presented and compared with latest theory predictions.

hep-ex↗

arXiv2022

Direct tests of T, CP, CPT symmetries in transitions of neutral K mesons with the KLOE experiment

Tests of the T, CP and CPT symmetries in the neutral kaon system are performed by the direct comparison of the probabilities of a kaon transition process to its symmetry-conjugate. The exchange of in and out states required for a genuine test involving an anti-unitary transformation implied by time-reversal is implemented exploiting the entanglement of $K^0\bar{K}{}^0$ pairs produced at a $\phi$-factory. A data sample collected by the KLOE experiment at DA$\Phi$NE corresponding to an integrated luminosity of about 1.7 fb$^{-1}$ is analysed to study the $\Delta$t distributions of the $\phi\to K_{S}K_{L}\to \pi^+\pi^- \: \pi^{\pm}e^{\mp}\nu$ and $\phi\to K_{S}K_{L}\to \pi^{\pm}e^{\mp}\nu \: 3\pi^0$ processes, with $\Delta$t the difference of the kaon decay times. A comparison of the measured $\Delta$t distributions in the asymptotic region $\Delta t \gg \tau_{S}$ allows to test for the first time T and CPT symmetries in kaon transitions with a precision of few percent, and to observe CP violation with this novel method.

hep-ex↗

arXiv2022

Measurement of the $K_S \to \pi e \nu$ branching fraction with the KLOE experiment

The branching fraction for the decay $K_S \to \pi e \nu$ has been measured with a sample of 300 million $K_S$ mesons produced in $\phi \to K_L K_S$ decays recorded by the KLOE experiment at the DA$\Phi$NE $e^+e^-$ collider. Signal decays are selected by a boosted decision tree built with kinematic variables and time-of-flight measurements. Data control samples of $K_L \to \pi e \nu$ decays are used to evaluate signal selection efficiencies. A fit to the reconstructed electron mass distribution finds 49647$\pm$316 signal events. Normalising to the $K_S \to \pi^+\pi^-$ decay events the result for the branching fraction is $\mathcal{B}(K_S \to \pi e \nu) = (7.211 \pm 0.046_{\rm stat} \pm 0.052_{\rm syst}) \times10^{-4}$. The combination with our previous measurement gives $\mathcal{B}(K_S \to \pi e \nu) = (7.153 \pm 0.037_{\rm stat} \pm 0.043_{\rm syst}) \times10^{-4}$. From this value we derive $f_+(0)|V_{us}| = 0.2170 \pm 0.009$.

hep-ex↗

arXiv2021

Precision tests of Quantum Mechanics and CPT symmetry with entangled neutral kaons at KLOE

The quantum interference between the decays of entangled neutral kaons is studied in the process $\phi\rightarrow K_S K_L \rightarrow\pi^+\pi^-\pi^+\pi^-$, which exhibits the characteristic Einstein--Podolsky--Rosen correlations that prevent both kaons to decay into $\pi^+\pi^-$ at the same time. This constitutes a very powerful tool for testing at the utmost precision the quantum coherence of the entangled kaon pair state, and to search for tiny decoherence and CPT violation effects, which may be justified in a quantum gravity framework. The analysed data sample was collected with the KLOE detector at DA$\Phi$NE, the Frascati $\phi$-factory, and corresponds to an integrated luminosity of about 1.7 fb$^{-1}$, i.e. to about $1.7 \times 10^9$ $\phi\rightarrow K_S K_L$ decays produced. From the fit of the observed $\Delta t$ distribution, being $\Delta t$ the difference of the kaon decay times, the decoherence and CPT violation parameters of various phenomenological models are measured with a largely improved accuracy with respect to previous analyses. The results are consistent with no deviation from quantum mechanics and CPT symmetry, while for some parameters the precision reaches the interesting level at which -- in the most optimistic scenarios -- quantum gravity effects might show up. They provide the most stringent limits up to date on the considered models.

hep-ex↗

arXiv2021

Long-term Operation of the Multi-Wire-Proportional-Chambers of the LHCb Muon System

The muon detector of LHCb, which comprises 1368 multi-wire-proportional-chambers (MWPC) for a total area of 435 m2, is the largest instrument of its kind exposed to such a high-radiation environment. In nine years of operation, from 2010 until 2018, we did not observe appreciable signs of ageing of the detector in terms of reduced performance. However, during such a long period, many chamber gas gaps suffered from HV trips. Most of the trips were due to Malter-like effects, characterised by the appearance of local self-sustained high currents, presumably originating from impurities induced during chamber production. Very effective, though long, recovery procedures were implemented with a HV training of the gaps in situ while taking data. The training allowed most of the affected chambers to be returned to their full functionality and the muon detector efficiency to be kept close to 100%. The possibility of making the recovery faster and even more effective by adding a small percentage of oxygen in the gas mixture has been studied and successfully tested.

physics.ins-det↗

arXiv2021

Upper limit on the $η\toπ^{+}π^{-}$ branching fraction with the KLOE experiment

Based on an integrated luminosity of 1.61 fb$^{-1}$ $e^+e^-$ collision data collected with the KLOE detector at DA$Φ$NE, the Frascati $ϕ$-factory, a search for the $P$- and $CP$-violating decay $η\toπ^{+}π^{-}$ has been performed. Radiative $ϕ\toηγ$ decay is exploited to access the $η$ mesons. No signal is observed in the $π^{+}π^{-}$ invariant mass spectrum, and the upper limit on the branching fraction at 90\% confidence level is determined to be ${\mathcal B}(η\toπ^{+}π^{-})<4.9\times10^{-6}$, which is approximately three times smaller than the previous KLOE result. From the combination of these two measurements we get ${\mathcal B}(η\toπ^{+}π^{-}) < 4.4\times10^{-6}$ at 90\% confidence level.

hep-ex↗

arXiv2020

Measurement of the branching fraction for the decay $K_S \to πμν$ with the KLOE detector

Based on a sample of 300 million $K_S$ mesons produced in $ϕ\to K_L K_S$ decays recorded by the KLOE experiment at the DA$Φ$NE $e^+e^-$ collider we have measured the branching fraction for the decay $K_S \to πμν$. The $K_S$ mesons are identified by the interaction of $K_L$ mesons in the detector. The $K_S \to πμν$ decays are selected by a boosted decision tree built with kinematic variables and by a time-of-flight measurement. Signal efficiencies are evaluated with data control samples of $K_L \to πμν$ decays. A fit to the reconstructed muon mass distribution finds $7223 \pm 180$ signal events. Normalising to the $K_S \to π^+ π^-$ decay events the result for the branching fraction is $\mathcal{B}(K_S \to πμν) = (4.56 \pm 0.11_{\rm stat} \pm 0.17_{\rm syst})\times10^{-4}$.

hep-ex↗

arXiv2018

Measurement of the charge asymmetry for the $K_S \rightarrow πe ν$ decay and test of CPT symmetry with the KLOE detector

Using 1.63 fb$^{-1}$ of integrated luminosity collected by the KLOE experiment about $7\times 10^4$ $K_S \rightarrow π^{\pm}e^{\mp}ν$ decays have been reconstructed. The measured value of the charge asymmetry for this decay is $A_S = (-4.9 \pm 5.7_{stat} \pm 2.6_{syst}) \times 10^{-3}$, which is almost twice more precise than the previous KLOE result. The combination of these two measurements gives $A_S = (-3.8 \pm 5.0_{stat} \pm 2.6_{syst}) \times 10^{-3}$ and, together with the asymmetry of the $K_L$ semileptonic decay, provides significant tests of the CPT symmetry. The obtained results are in agreement with CPT invariance.

hep-ex↗

arXiv2018

Combined limit on the production of a light gauge boson decaying into $μ^+μ^-$ and $π^+π^-$

We searched for the $μ^+μ^-$ decay of a light vector gauge boson, also known as dark photon, in the $e^+ e^- \to μ^+ μ^- γ_{\rm ISR}$ process by means of the Initial State Radiation (ISR) method. We used 1.93~fb$^{-1}$ of data collected by the KLOE experiment at the DA$Φ$NE $ϕ$-factory. No structures have been observed over the irreducible $μ^+ μ^-$ background. A 90\% CL limit on the ratio $\varepsilon^2=α^{\prime}/α$ between the dark coupling constant and the fine structure constant of $ 3\times 10^{-6}-2\times 10^{-7}$ has been set in the dark photon mass region between 519 MeV and 973 MeV. This new limit has been combined with the published result obtained investigating the hypothesis of the dark photon decaying into hadrons in $e^+ e^- \to π^+ π^- γ_{\rm ISR}$ events. The combined 90\% CL limit increases the sensitivity especially in the $ρ-ω$ interference region and excludes $\varepsilon^2$ greater than $(13-2)\times 10^{-7}$. For dark photon masses greater than 600 MeV the combined limit is lower than 8~$\times\, 10^{-7}$ resulting more stringent than present constraints from other experiments.

hep-ex↗

arXiv2018

Combination of KLOE $σ\big(e^+e^-\rightarrowπ^+π^-γ(γ)\big)$ measurements and determination of $a_μ^{π^+π^-}$ in the energy range $0.10 < s < 0.95$ GeV$^2$

The three precision measurements of the cross section $σ\big(e^+e^-\rightarrowπ^+π^-γ(γ)\big)$ using initial state radiation by the KLOE collaboration provide an important input for the prediction of the hadronic contribution to the anomalous magnetic moment of the muon. These measurements are correlated for both statistical and systematic uncertainties and, therefore, the simultaneous use of these measurements requires covariance matrices that fully describe the correlations. We present the construction of these covariance matrices and use them to determine a combined KLOE measurement for $σ\big(e^+e^-\rightarrowπ^+π^-γ(γ)\big)$. We find, from this combination, a two-pion contribution to the muon magnetic anomaly in the energy range $0.10 < s < 0.95$ GeV$^2$ of $a_μ^{π^+π^-} = (489.8 \pm 1.7_{\rm stat} \pm 4.8_{\rm sys} ) \times 10^{-10}$.

hep-ex↗

arXiv2017

Measurement of the running of the fine structure constant below 1 GeV with the KLOE Detector

We have measured the running of the effective QED coupling constant $α(s)$ in the time-like region $0.6<\sqrt s< 0.975$ GeV with the KLOE detector at DA$Φ$NE using the Initial State Radiation process $e^+e^-\toμ^+ μ^-γ$. It represents the first measurement of the running of $α(s)$ in this energy region. Our results show a more than 5$σ$ significance of the hadronic contribution to the running of $α(s)$, which is the strongest direct evidence both in time- and space-like regions achieved in a single measurement. By using the $e^+e^-\toπ^+π^-$ cross section measured by KLOE, the real and imaginary part of the shift $Δα(s)$ has been extracted. By a fit of the real part of $Δα(s)$ and assuming the lepton universality the branching ratio $BR(ω\toμ^+μ^-) = (6.6\pm1.4_{stat}\pm1.7_{syst})\cdot 10^{-5} $ has been determined.

hep-ex↗

arXiv2016

Measurement of the $ϕ\to π^0 e^+e^-$ transition form factor with the KLOE detector

A measurement of the vector to pseudoscalar conversion decay $ϕ\to π^0 e^+e^-$ with the KLOE experiment is presented. A sample of $\sim 9500$ signal events was selected from a data set of 1.7 fb$^{-1}$ of $e^+e^-$ collisions at $\sqrt{s} \sim m_ϕ$ collected at the DA$Φ$NE $e^+e^-$ collider. These events were used to obtain the first measurement of the transition form factor $| F_{ϕπ^0}(q^2) |$ and a new measurement of the branching ratio of the decay: $\rm{BR}\,(ϕ\to π^0 e^+e^-) = (\,1.35 \pm 0.05^{\,\,+0.05}_{\,\,-0.10}\,) \times 10 ^{-5}$. The result improves significantly on previous measurements and is in agreement with theoretical predictions.

hep-ex↗

arXiv2016

Measurement of the front-end dead-time of the LHCb muon detector and evaluation of its contribution to the muon detection inefficiency

A method is described which allows to deduce the dead-time of the front-end electronics of the LHCb muon detector from a series of measurements performed at different luminosities at a bunch-crossing rate of 20 MHz. The measured values of the dead-time range from 70 ns to 100 ns. These results allow to estimate the performance of the muon detector at the future bunch-crossing rate of 40 MHz and at higher luminosity.

physics.ins-det↗

arXiv2016

Limit on the production of a new vector boson in $\mathrm{e^+ e^-}\rightarrow {\rm U}γ$, U$\rightarrow π^+π^-$ with the KLOE experiment

The recent interest in a light gauge boson in the framework of an extra U(1) symmetry motivates searches in the mass range below 1 GeV. We present a search for such a particle, the dark photon, in ${\rm e^+ e^-}\rightarrow {\rm U}γ$, U$\rightarrow π^+π^-$ based on 28 million $\mathrm{e^+ e^-} \rightarrow π^+ π^-γ$ events collected at DA$Φ$NE by the KLOE experiment. The $π^+ π^-$ production by initial-state radiation compensates for a loss of sensitivity of previous KLOE ${\rm U} \rightarrow \mathrm{e^+ e^-}$, $μ^+μ^-$ searches due to the small branching ratios in the $ρ-ω$ resonance region. We found no evidence for a signal and set a limit at 90\% CL on the mixing strength between the photon and the dark photon, $\varepsilon^2$, in the U mass range between $527$ and $987$~MeV. Above 700 MeV this new limit is more stringent than previous ones.

hep-ex↗

arXiv2016

Precision measurement of the $η\toπ^+π^-π^0$ Dalitz plot distribution with the KLOE detector

Using $1.6$ fb$^{-1}$ of $e^+ e^-\toϕ\toηγ$ data collected with the KLOE detector at DA$Φ$NE, the Dalitz plot distribution for the $η\to π^+ π^- π^0$ decay is studied with the world's largest sample of $\sim 4.7 \cdot 10^6$ events. The Dalitz plot density is parametrized as a polynomial expansion up to cubic terms in the normalized dimensionless variables $X$ and $Y$. The experiment is sensitive to all charge conjugation conserving terms of the expansion, including a $gX^2Y$ term. The statistical uncertainty of all parameters is improved by a factor two with respect to earlier measurements.

hep-ex↗

arXiv2015

Limit on the production of a low-mass vector boson in $\mathrm{e}^{+}\mathrm{e}^{-} \to \mathrm{U}γ$, $\mathrm{U} \to \mathrm{e}^{+}\mathrm{e}^{-}$ with the KLOE experiment

The existence of a new force beyond the Standard Model is compelling because it could explain several striking astrophysical observations which fail standard interpretations. We searched for the light vector mediator of this dark force, the $\mathrm{U}$ boson, with the KLOE detector at the DA$Φ$NE $\mathrm{e}^{+}\mathrm{e}^{-}$ collider. Using an integrated luminosity of 1.54 fb$^{-1}$, we studied the process $\mathrm{e}^{+}\mathrm{e}^{-} \to \mathrm{U}γ$, with $\mathrm{U} \to \mathrm{e}^{+}\mathrm{e}^{-}$, using radiative-return to search for a resonant peak in the dielectron invariant-mass distribution. We did not find evidence for a signal, and set a 90\%~CL upper limit on the mixing strength between the Standard Model photon and the dark photon, $\varepsilon^2$, at $10^{-6}$--$10^{-4}$ in the 5--520~MeV/c$^2$ mass range.

hep-ex↗

arXiv2015

Search for dark Higgsstrahlung in e+ e- -> mu+ mu- and missing energy events with the KLOE experiment

We searched for evidence of a Higgsstrahlung process in a secluded sector, leading to a final state with a dark photon U and a dark Higgs boson h', with the KLOE detector at DAFNE. We investigated the case of h' lighter than U, with U decaying into a muon pair and h' producing a missing energy signature. We found no evidence of the process and set upper limits to its parameters in the range 2m_mu<m_U<1000 MeV, m_h'<m_U.

hep-ex↗