Search

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 antiunitary transformation implied by time-reversal is implemented exploiting the entanglement of K0K‾0 pairs produced at a ϕ-factory.A data sample collected by the KLOE experiment at DAΦNE corresponding to an integrated luminosity of about 1.7 fb−1 is analysed to study the Δt distributions of the ϕ→KSKL→π+π−π±e∓ν and ϕ→KSKL→π±e∓ν3π0 processes, with Δt the difference of the kaon decay times. A comparison of the measured Δt distributions in the asymptotic region Δt≫τS 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.

Kaonic atoms are an extremely efficient tool to investigate the strong interaction at the low energy Frontier, since they provide direct access to the K−N interaction at threshold, eliminating the necessity for extrapolation, unlike in the case of scattering experiments. During the 1970s and 1980s, extensive studies were performed on kaonic atoms spanning across a broad spectrum of elements in the periodic table, ranging from lithium to uranium. These measurements provided inputs and constraints for the theoretical description of the antikaon-nuclei interaction potential. Nevertheless, the existing data suffer from significant experimental uncertainties, and numerous measurements have been found to be inconsistent with more recent measurements that utilize advanced detector technology. Furthermore, there remain numerous transitions of kaonic atoms that have yet to be measured. For these reasons, a new era of kaonic atoms studies is mandatory. The DAΦNE electron-positron collider at the INFN Laboratory of Frascati (INFN-LNF) stands out as a unique source of low-energy kaons, having been utilized by Collaborations such as DEAR, SIDDHARTA, and AMADEUS for groundbreaking measurements of kaonic atoms and kaon-nuclei interactions. Presently, the SIDDHARTA-2 experiment is installed at DAΦNE, aiming to perform the first-ever measurement of the 2p → 1s x-ray transition in kaonic deuterium, a crucial step towards determining the isospin-dependent antikaon-nucleon scattering lengths. Based on the experience gained with the SIDDHARTA experiment, which performed the most precise measurement of the kaonic hydrogen 2p → 1s x-ray transition, the SIDDHARTA-2 setup is now fully equipped for the challenging kaonic deuterium measurement. In this paper, we present a comprehensive description of the SIDDHARTA-2 setup and of the first kaonic atoms measurements performed during the commissioning phase of the DAΦNE collider. We also outline a proposal for future measurements of kaonic atoms at DAΦNE beyond SIDDHARTA-2, which is intended to stimulate discussions within the broad scientific community performing research, directly or indirectly, related to this field.

Abstract The ratio R $$ \mathcal{R} $$ = Γ(K S → πeν)/Γ(K S → π + π − ) has been measured with a sample of 300 million K S mesons produced in ϕ → K L K S decays recorded by the KLOE experiment at the DAΦNE e + e − collider. K S → πeν events are selected by a boosted decision tree built with kinematic variables and time-of-flight measurements. Data control samples of K L → πeν decays are used to evaluate signal selection efficiencies. With 49647±316 signal events we measure R $$ \mathcal{R} $$ = (1.0421 ± 0.0066stat ± 0.0075syst) × 10 −3. The combination with our previous measurement gives R $$ \mathcal{R} $$ = (1.0338 ± 0.0054stat ± 0.0064syst) × 10 −3. From this value we derive the branching fraction B $$ \mathcal{B} $$ (K S → πeν) = (7.153 ± 0.037stat ± 0.044syst) × 10 −4 and f +(0)|V us | = 0.2170 ± 0.009.

Abstract The quantum interference between the decays of entangled neutral kaons is studied in the process ϕ → KSKL → π + π − π + π − , which exhibits the characteristic Einstein-Podolsky-Rosen correlations that prevent both kaons to decay into π + π − 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 $$ \mathcal{CPT} $$ violation effects, which may be justified in a quantum gravity framework. The analysed data sample was collected with the KLOE detector at DAΦNE, the Frascati ϕ-factory, and corresponds to an integrated luminosity of about 1.7 fb −1, i.e. to about 1.7 × 109 ϕ → KSKL decays produced. From the fit of the observed ∆t distribution, being ∆t the difference of the kaon decay times, the decoherence and CPT $$ \mathcal{CPT} $$ 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 $$ \mathcal{CPT} $$ 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.

CPT violation could manifest itself in annihilating positronium events, but searching for this effect would require to know the spin of the annihilating system. Here, the authors do this using a positron-emission tomography scanner, finding no violation with a statistical precision of 10−4.

Abstract Based on an integrated luminosity of 1.61 fb −1 e + e − collision data collected with the KLOE detector at DAΦNE, the Frascati ϕ-factory, a search for the P- and CP-violating decay η → π + π − has been performed. Radiative ϕ → ηγ 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 ℬ(η → π + π − ) < 4.9 × 10 −6, which is approximately three times smaller than the previous KLOE result. From the combination of these two measurements we get ℬ(η → π + π − ) < 4.4 × 10 −6 at 90% confidence level.

Abstract Purpose The time-over-threshold (TOT) technique is being used widely due to itsimplications in developing the multi-channel readouts, mainly when fast signal processing is required. Using the TOT technique, as a measure of energy loss instead of charge integration methods, significantly reduces the signal readout costs by combining the time and energy information. Therefore, this approach can potentially be utilized in J-PET tomograph which is built from plastic scintillators characterized by fast light signals. The drawback in adopting this technique lies in the non-linear correlation between input energy loss and TOT of the signal. The main motivation behind this work is to develop the relationship between TOT and energy loss and validate it by the J-PET tomograph setup. Methods The experiment was performed using a 22Na beta emitter source placed in the center of the J-PET tomograph. This isotope produces photons of two different energies: 511 keV photons from the positron annihilation (direct annihilation or through the formation of a para-positronium atom or pick-off process of ortho-positronium atoms) and a 1275 keV prompt photon. This allows the study of the correlation between TOT values and energy loss for energy ranges up to 1000 keV. Since the photon interacts predominantly via Compton scattering inside the plastic scintillator, there is no direct information of the energy deposition. However, using the J-PET geometry, one can measure the scattering angle of the interacting photon. Since the 22Na source emits photons of two different energies, it is necessary to know unambiguously the energy of incident photons and their corresponding scattering angles in order to estimate energy deposition. In summary, this work presents a dedicated algorithm developed to tag photons of different energies and studying their scattering angles to calculate the energy deposition by the interacting photons. Results A new method was elaborated to measure the energy loss by photons interacting with plastic scintillators used in the J-PET tomograph. We find the relationship between the energy loss and TOT is non-linear and can be described by the functions TOT = A0 + A1 * ln(E dep + A2) + A3 * (ln(E dep + A2))2 and TOT = A0 - A1 * A2 E dep $^{E_{dep}}\phantom {\dot {i}\!}$ . In addition, we also introduced a theoretical model to calculate the TOT as a function of energy loss in plastic scintillators. Conclusions A relationship between TOT and energy loss by photons interacting inside the plastic scintillators used in J-PET scanner is established for a deposited energy range of 100–1000 keV.

Abstract Purpose In living organisms, the positron-electron annihilation (occurring during the PET imaging) proceeds in about 30% via creation of a metastable ortho-positronium atom. In the tissue, due to the pick-off and conversion processes, over 98% of ortho-positronia annihilate into two 511 keV photons. In this article, we assess the feasibility for reconstruction of the mean ortho-positronium lifetime image based on annihilations into two photons. The main objectives of this work include the (i) estimation of the sensitivity of the total-body PET scanners for the ortho-positronium mean lifetime imaging using 2γ annihilations and (ii) estimation of the spatial and time resolution of the ortho-positronium image as a function of the coincidence resolving time (CRT) of the scanner. Methods Simulations are conducted assuming that radiopharmaceutical is labeled with 44 S c isotope emitting one positron and one prompt gamma. The image is reconstructed on the basis of triple coincidence events. The ortho-positronium lifetime spectrum is determined for each voxel of the image. Calculations were performed for cases of total-body detectors build of (i) LYSO scintillators as used in the EXPLORER PET and (ii) plastic scintillators as anticipated for the cost-effective total-body J-PET scanner. To assess the spatial and time resolution, the four cases were considered assuming that CRT is equal to 500 ps, 140 ps, 50 ps, and 10 ps. Results The estimated total-body PET sensitivity for the registration and selection of image forming triple coincidences (2γ+γ prompt) is larger by a factor of 13.5 (for LYSO PET) and by factor of 5.2 (for plastic PET) with respect to the sensitivity for the standard 2γ imaging by LYSO PET scanners with AFOV = 20 cm. The spatial resolution of the ortho-positronium image is comparable with the resolution achievable when using TOF-FBP algorithms already for CRT = 50 ps. For the 20-min scan, the resolution better than 20 ps is expected for the mean ortho-positronium lifetime image determination. Conclusions Ortho-positronium mean lifetime imaging based on the annihilations into two photons and prompt gamma is shown to be feasible with the advent of the high sensitivity total-body PET systems and time resolution of the order of tens of picoseconds.

Abstract The determination of low-energy cross sections and branching ratios of the $$\hbox {K}^-$$ K- multi-nucleon absorption processes in $$\Lambda \hbox {p}$$ Λp and $$\Sigma ^0\hbox {p}$$ Σ0p final states performed by the AMADEUS collaboration is presented. Low momentum $$\hbox {K}^-$$ K- ($$p_{\mathrm{K}} \simeq 127\ \hbox {MeV}/\hbox {c}$$ pK≃127MeV/c ) produced at the $$\hbox {DA}\Phi \hbox {NE}$$ DAΦNE collider are impinged on a Carbon target within the KLOE detector and the two and three nucleon absorption processes are disentangled by comparing the experimental data to phenomenological calculations. The $$\Lambda \hbox {p}$$ Λp spectra are interpreted in terms of $$\hbox {K}^{-}$$ K- multi-nucleon absorption processes; the possible contribution of a $$\hbox {K}^{-}\hbox {pp}$$ K-pp bound state is demonstrated to overlap with the two nucleon capture process, its absolute yield thus resulting indistinguishable.

Based on a sample of 300 million KS mesons produced in ϕ→KLKS decays recorded by the KLOE experiment at the DAΦNE e+e− collider we have measured the branching fraction for the decay KS→πμν. The KS mesons are identified by the interaction of KL mesons in the detector. The KS→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 KL→πμν decays. A fit to the reconstructed muon mass distribution finds 7223±180 signal events. Normalising to the KS→π+π− decay events the result for the branching fraction is B(KS→πμν)=(4.56±0.11stat±0.17syst)×10−4. It is the first measurement of this decay mode and the result allows an independent determination of |Vus| and a test of the lepton-flavour universality. Keywords: e+e− collisions, K0 meson, Semileptonic decay

Abstract J-PET is a detector optimized for registration of photons from the electron–positron annihilation via plastic scintillators where photons interact predominantly via Compton scattering. Registration of both primary and scattered photons enables to determinate the linear polarization of the primary photon on the event by event basis with a certain probability. Here we present quantitative results on the feasibility of such polarization measurements of photons from the decay of positronium with the J-PET and explore the physical limitations for the resolution of the polarization determination of 511 keV photons via Compton scattering. For scattering angles of about 82$$^\circ $$ ∘ (where the best contrast for polarization measurement is theoretically predicted) we find that the single event resolution for the determination of the polarization is about 40$$^\circ $$ ∘ (predominantly due to properties of the Compton effect). However, for samples larger than ten thousand events the J-PET is capable of determining relative average polarization of these photons with the precision of about few degrees. The obtained results open new perspectives for studies of various physics phenomena such as quantum entanglement and tests of discrete symmetries in decays of positronium and extend the energy range of polarization measurements by five orders of magnitude beyond the optical wavelength regime.

We searched for the μ+μ− decay of a light vector gauge boson, also known as dark photon, in the e+e−→μ+μ−γISR 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 DAΦNE ϕ-factory. No structures have been observed over the irreducible μ+μ− background. A 90% CL limit on the ratio ε2=α′/α between the dark coupling constant and the fine structure constant of 3×10−6–2×10−7 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−→π+π−γISR events. The combined 90% CL limit increases the sensitivity especially in the ρ–ω interference region and excludes ε2 greater than (13−2)×10−7. For dark photon masses greater than 600 MeV the combined limit is lower than 8 ×10−7 resulting more stringent than present constraints from other experiments. Keywords: e+e− Collisions, Dark forces, Gauge vector boson, Upper limits

Abstract Using 1.63 fb−1 of integrated luminosity collected by the KLOE experiment about 7 × 104 K S → π ± e ∓ ν decays have been reconstructed. The measured value of the charge asymmetry for this decay is A S = (−4.9 ± 5.7stat ± 2.6syst) × 10−3, which is almost twice more precise than the previous KLOE result. The combination of these two measurements gives A S = (−3.8 ± 5.0stat ± 2.6syst) × 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.

We present the analysis of K− absorption processes on He4 leading to Λπ− final states, measured with the KLOE spectrometer at the DAΦNE e+e− collider and extract, for the first time, the modulus of the non-resonant K−n →Λπ− direct production amplitude about 33 MeV below the K‾N threshold. This analysis also allows to disentangle the K− nuclear absorption at-rest from the in-flight capture, for K− momenta of about 120 MeV. The data are interpreted with the help of a phenomenological model, and the modulus of the non-resonant K−n →Λπ− amplitude for K− absorption at-rest is found to be |AK−n→Λπ−|=(0.334±0.018stat−0.058+0.034syst)fm. Keywords: Strong interaction, Strangeness nuclear physics, Antikaon interactions in nuclear matter

Abstract The three precision measurements of the cross section σ(e + e − → π + π −γ(γ)) 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(e + e − → π + π −γ(γ)). We find, from this combination, a two-pion contribution to the muon magnetic anomaly in the energy range 0.10 < s < 0.95 GeV2 of a μ π + π − = 489.8 ± 1.7 stat ± 4.8 s y s × 10 − 10 $$ {a}_{\mu}^{\pi^{+}{\pi}^{-}}=\left(489.8\pm {1.7}_{\mathrm{stat}}\pm {4.8}_{\mathrm{sys}}\right)\times {10}^{-10} $$ . Data vectors and covariance matrices are available at http://www.lnf.infn.it/kloe/ppg/ ppg_2017/ppg_2017.html .

We have measured the running of the effective QED coupling constant α(s) in the time-like region 0.6

We report the measurement of K− absorption processes in the Σ0p final state and the first exclusive measurement of the two nucleon absorption (2NA) with the KLOE detector. The 2NA process without further interactions is found to be 9% of the sum of all other contributing processes, including absorption on three and more nucleons or 2NA followed by final state interactions with the residual nucleons. We also determine the possible contribution of the ppK− bound state to the Σ0p final state. The yield of ppK−/Kstop− is found to be (0.044±0.009stat−0.005+0.004syst)⋅10−2 but its statistical significance based on an F-test is only 1σ.

This article reports on the feasibility of testing of the symmetry under reversal in time in a purely leptonic system constituted by positronium atoms using the J-PET detector. The present state of T symmetry tests is discussed with an emphasis on the scarcely explored sector of leptonic systems. Two possible strategies of searching for manifestations of T violation in nonvanishing angular correlations of final state observables in the decay of metastable triplet states of positronium available with J-PET are proposed and discussed. Results of a pilot measurement with J-PET and assessment of its performance in reconstruction of three-photon decays are shown along with an analysis of its impact on the sensitivity of the detector for the determination of T-violation sensitive observables.

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 U boson, with the KLOE detector at the DAΦNE e+e− collider. Using an integrated luminosity of 1.54 fb−1, we studied the process e+e−→Uγ, with U→e+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, ε2, at 10−6–10−4 in the 5–520 MeV/c2 mass range.

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 DAΦNE. 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 2mμ

We have studied the vector to pseudoscalar conversion decay ϕ→ηe+e−, with η→π0π0π0, with the KLOE detector at DAΦNE. The data set of 1.7 fb−1 of e+e− collisions at s∼Mϕ contains a clear conversion decay signal of ∼31,000 events from which we measured a value of BR(ϕ→ηe+e−)=(1.075±0.007±0.038)×10−4. The same sample is used to determine the transition form factor by a fit to the e+e− invariant mass spectrum, obtaining bϕη=(1.28±0.10−0.08+0.09) GeV−2, that improves by a factor of five the precision of the previous measurement and is in good agreement with VMD expectations. Keywords: e+e− collisions, Conversion decay, Transition form factor

The absolute branching ratio of the K+→π+π−π+(γ) decay, inclusive of final-state radiation, has been measured using ∼17 million tagged K+ mesons collected with the KLOE detector at DAΦNE, the Frascati ϕ-factory. The result is:BR(K+→π+π−π+(γ))=0.05565±0.00031stat±0.00025syst a factor ≃ 5 more precise with respect to the previous result. This work completes the program of precision measurements of the dominant kaon branching ratios at KLOE. Keywords: e+e− experiments, Kaon decays

We have searched for a light vector boson U, the possible carrier of a “dark force”, with the KLOE detector at the DAΦNE e+e− collider, motivated by astrophysical evidence for the presence of dark matter in the Universe. Using e+e− collisions collected with an integrated luminosity of 239.3 pb−1, we look for a dimuon mass peak in the reaction e+e−→μ+μ−γ, corresponding to the decay U→μ+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 1.6×10−5 to 8.6×10−7 for the mass region 520

The excellent quality kaon beam provided by the DAΦNE collider of LNF-INFN (Italy) together with SIDDHARTA/SIDDHARTA-2 new experimental techniques, as very precise and fast-response X-ray detectors, allow to perform unprecedented measurements on light kaonic atoms crucial for a deeper understanding of the low-energy quantum chromodynamics (QCD) in the strangeness sector. In this paper an overview of the main results obtained by the SIDDHARTA collaboration, as well as the future plans related to the SIDDHARTA-2 experiment, are discussed.