arXiv subjects

P. Ciambrone

Publications and source records attributed to P. Ciambrone.

At least 37 records · Page 2Linked to original sources

arXiv2017

The active muon shield in the SHiP experiment

The SHiP experiment is designed to search for very weakly interacting particles beyond the Standard Model which are produced in a 400 GeV/c proton beam dump at the CERN SPS. An essential task for the experiment is to keep the Standard Model background level to less than 0.1 event after $2\times 10^{20}$ protons on target. In the beam dump, around $10^{11}$ muons will be produced per second. The muon rate in the spectrometer has to be reduced by at least four orders of magnitude to avoid muon-induced combinatorial background. A novel active muon shield is used to magnetically deflect the muons out of the acceptance of the spectrometer. This paper describes the basic principle of such a shield, its optimization and its performance.

physics.ins-det↗

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

A facility to Search for Hidden Particles (SHiP) at the CERN SPS

A new general purpose fixed target facility is proposed at the CERN SPS accelerator which is aimed at exploring the domain of hidden particles and make measurements with tau neutrinos. Hidden particles are predicted by a large number of models beyond the Standard Model. The high intensity of the SPS 400~GeV beam allows probing a wide variety of models containing light long-lived exotic particles with masses below ${\cal O}$(10)~GeV/c$^2$, including very weakly interacting low-energy SUSY states. The experimental programme of the proposed facility is capable of being extended in the future, e.g. to include direct searches for Dark Matter and Lepton Flavour Violation.

physics.ins-det↗

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↗

arXiv2015

Commissioning of the new taggers of the KLOE-2 experiment

In order to fully reconstruct the gamma gamma processes (e+e- -> e+e- gamma gamma) in the energy region of the phi meson production, new detectors along the DAFNE beam line have been installed in order to detect the scattered e+e-.

physics.ins-det↗

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

Performance of the Muon Identification at LHCb

The performance of the muon identification in LHCb is extracted from data using muons and hadrons produced in J/ψ->μμ, Λ->pπand D^{\star}->πD0(Kπ) decays. The muon identification procedure is based on the pattern of hits in the muon chambers. A momentum dependent binary requirement is used to reduce the probability of hadrons to be misidentified as muons to the level of 1%, keeping the muon efficiency in the range of 95-98%. As further refinement, a likelihood is built for the muon and non-muon hypotheses. Adding a requirement on this likelihood that provides a total muon efficiency at the level of 93%, the hadron misidentification rates are below 0.6%.

physics.ins-det↗

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

Precision measurement of $σ(e^+e^-\rightarrowπ^+π^-γ)/σ(e^+e^-\rightarrow μ^+μ^-γ)$ and determination of the $π^+π^-$ contribution to the muon anomaly with the KLOE detector

We have measured the ratio $σ(e^+e^-\rightarrowπ^+π^-γ)/σ(e^+e^-\rightarrow μ^+μ^-γ)$, with the KLOE detector at DA$Φ$NE for a total integrated luminosity of $\sim$ 240 pb$^{-1}$. From this ratio we obtain the cross section $σ(e^+e^-\rightarrowπ^+π^-)$. From the cross section we determine the pion form factor $|F_π|^2$ and the two-pion contribution to the muon anomaly $a_μ$ for $0.592<M_{ππ}<0.975$ GeV, $Δ^{ππ} a_μ$= $({\rm 385.1\pm1.1_{stat}\pm2.7_{sys+theo}})\times10^{-10}$. This result confirms the current discrepancy between the Standard Model calculation and the experimental measurement of the muon anomaly.

hep-ex↗

arXiv2013

Performance of the LHCb muon system

The performance of the LHCb Muon system and its stability across the full 2010 data taking with LHC running at ps = 7 TeV energy is studied. The optimization of the detector setting and the time calibration performed with the first collisions delivered by LHC is described. Particle rates, measured for the wide range of luminosities and beam operation conditions experienced during the run, are compared with the values expected from simulation. The space and time alignment of the detectors, chamber efficiency, time resolution and cluster size are evaluated. The detector performance is found to be as expected from specifications or better. Notably the overall efficiency is well above the design requirements

physics.ins-det↗