Paolo Montagna

A theoretical underpinning of the standard model of fundamental particles and interactions is CPT invariance, which requires that the laws of physics be invariant under the combined discrete operations of charge conjugation, parity and time reversal. Antimatter, the existence of which was predicted by Dirac, can be used to test the CPT theorem-experimental investigations involving comparisons of particles with antiparticles are numerous. Cold atoms and anti-atoms, such as hydrogen and antihydrogen, could form the basis of a new precise test, as CPT invariance implies that they must have the same spectrum. Observations of antihydrogen in small quantities and at high energies have been reported at the European Organization for Nuclear Research (CERN) and at Fermilab, but these experiments were not suited to precision comparison measurements. Here we demonstrate the production of antihydrogen atoms at very low energy by mixing trapped antiprotons and positrons in a cryogenic environment. The neutral anti-atoms have been detected directly when they escape the trap and annihilate, producing a characteristic signature in an imaging particle detector.

Production of antihydrogen atoms by mixing antiprotons with a cold, confined, positron plasma depends critically on parameters such as the plasma density and temperature. We discuss nondestructive measurements, based on a novel, real-time analysis of excited, low-order plasma modes, that provide comprehensive characterization of the positron plasma in the ATHENA antihydrogen apparatus. The plasma length, radius, density, and total particle number are obtained. Measurement and control of plasma temperature variations, and the application to antihydrogen production experiments are discussed.

We have developed a new method, based on the ballistic transfer of preaccumulated plasmas, to obtain large and dense positron plasmas in a cryogenic environment. The method involves transferring plasmas emanating from a region with a low magnetic field (0.14 T) and relatively high pressure (${10}^{\ensuremath{-}9}\text{ }\text{ }\mathrm{mbar}$) into a 15 K Penning-Malmberg trap immersed in a 3 T magnetic field with a base pressure better than ${10}^{\ensuremath{-}13}\text{ }\text{ }\mathrm{mbar}$. The achieved positron accumulation rate in the high field cryogenic trap is more than one and a half orders of magnitude higher than the previous most efficient UHV compatible scheme. Subsequent stacking resulted in a plasma containing more than $1.2\ifmmode\times\else\texttimes\fi{}{10}^{9}$ positrons, which is a factor 4 higher than previously reported. Using a rotating wall electric field, plasmas containing about $20\ifmmode\times\else\texttimes\fi{}{10}^{6}$ positrons were compressed to a density of $2.6\ifmmode\times\else\texttimes\fi{}{10}^{10}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$. This is a factor of 6 improvement over earlier measurements.

Antihydrogen is formed when antiprotons are mixed with cold positrons in a nested Penning trap. We present experimental evidence, obtained using our antihydrogen annihilation detector, that the spatial distribution of the emerging antihydrogen atoms is independent of the positron temperature and axially enhanced. This indicates that antihydrogen is formed before the antiprotons are in thermal equilibrium with the positron plasma. This result has important implications for the trapping and spectroscopy of antihydrogen.

The ATHENA apparatus that recently produced and detected the first cold antihydrogen atoms is described. Its main features, which are described herein, are: an external positron accumulator, making it possible to accumulate large numbers of positrons; a separate antiproton catching trap, optimizing the catching, cooling and handling of antiprotons; a unique high resolution antihydrogen annihilation detector, allowing an clear determination that antihydrogen has been produced; an open, modular design making variations in the experimental approach possible and a "nested" Penning trap situated in a cryogenic, 3T magnetic field environment used for the mixing of the antiprotons and positrons.

We show that antihydrogen production is the dominant process when mixing antiprotons and positrons in the ATHENA apparatus, and that the initial production rate exceeds 300 Hz, decaying to 30 Hz within 10 s. A fraction of 65% of all observed annihilations is due to antihydrogen.

The FINUDA experiment collected data to study the production of hypernuclei on different nuclear targets. The hypernucleus formation occurred through the strangeness-exchange reaction $K^-_{stop} + \; ^AZ \rightarrow \; ^A_{\Lambda}Z + \pi^-$. From the analysis of the momentum of the emerging $\pi^-$, binding energies and formation probabilities of $^7_{\Lambda}$Li, $^9_{\Lambda}$Be, $^{13}_{\Lambda}$C and $^{16}_{\Lambda}$O have been measured and are here presented. The behavior of the formation probability as a function of the atomic mass number A is also discussed.

The p̄p total annihilation cross section has been measured, with the Obelix apparatus at LEAR, at ten values of the antiproton incident momentum between 43 and 175 MeV/c. The values of the cross section show that the well known 1p behaviour of the annihilation cross section is drastically modified at very low momenta, which demonstrates the important role of the Coulomb force in low energy p̄p interaction. Moreover, they do not present any explicit resonant behaviour. Finally, when compared to potential model calculations, the data suggest that the percentage of P-wave in p̄p interaction around 50 MeV/c antiproton incident momentum is less than 5%.

We report stopping powers of hydrogen and helium for antiprotons of kinetic energies ranging from about 0.5 keV to 1.1 MeV. The Barkas effect, i.e., a difference in the stopping power for antiprotons and protons of the same energy in the same material, shows up clearly in either of the gases. Moreover, below \ensuremath{\approx}0.5 keV there is indirect evidence for an increase of the antiproton stopping power. This "nuclear" effect, i.e., energy losses in quasimolecular interactions, shows up in fair agreement with theoretical predictions.

The pp total annihilation cross section has been measured at four values of the p̄ incident momentum, between 70 MeV/c and 38 MeV/c, with the Obelix apparatus at LEAR. The new measurements are in agreement with the trend of previous measurements of the pp total annihilation cross section at low energy, performed by the Obelix experiment [A. Bertin et al., Phys. Lett. B 369 (1996) 77; A. Benedettini et al., Nucl. Phys. B (Proc. Suppl.) 56A (1997) 58], as well as with a fit of the latter data based on a low energy expansion of the scattering amplitude [J. Carbonell, K.V. Protasov, A. Zenoni, Phys. Lett. B 397 (1997) 345]. The departure of the annihilation cross section from a smooth behaviour, suggested by a previous measurement of the cross section around 44 MeV/c [A. Bertin et al., Phys. Lett. B 369 (1996) 77], is not confirmed by the new data.

New spectra from the FINUDA experiment of the Non-Mesonic Weak Decay (NMWD) proton kinetic energy for BeΛ9, BΛ11, CΛ12, CΛ13, NΛ15 and OΛ16 are presented and discussed along with the published data on HeΛ5 and LiΛ7. Exploiting the large mass number range and the low energy threshold (15 MeV) for the proton detection of FINUDA, an evaluation of both Final State Interactions (FSI) and the two-nucleon induced NMWD contributions to the decay process has been done. Based on this evaluation, a linear dependence of FSI on the hypernuclear mass number A is found and for the two-nucleon stimulated decay rate the experimental value of Γ2/Γp=0.43±0.25 is determined for the first time. A value for the two-nucleon stimulated decay rate to the total decay rate Γ2/ΓNMWD=0.24±0.10 is also extracted.

The simultaneous measurement of the spatial coordinates and times of p\ifmmode\bar\else\textasciimacron\fi{}s annihilating at rest in a ${\mathrm{H}}_{2}$ target at very low density \ensuremath{\rho} (\ensuremath{\rho}/${\mathrm{\ensuremath{\rho}}}_{0}$${10}^{\mathrm{\ensuremath{-}}2}$, ${\mathrm{\ensuremath{\rho}}}_{0}$ being the STP density) gives the possibility of evaluating the behavior of the p\ifmmode\bar\else\textasciimacron\fi{} stopping power in ${\mathrm{H}}_{2}$ at low energies (below 120 keV). It is different from that of protons (the Barkas effect). Moreover, it is shown that a rise at low-energy values (\ensuremath{\lesssim}1 keV) is needed to agree with experimental data.

We demonstrate three-dimensional imaging of antiprotons in a Penning trap, by reconstructing annihilation vertices from the trajectories of the charged annihilation products. The unique capability of antiparticle imaging has allowed, for the first time, the observation of the spatial distribution of the particle loss in a Penning trap. The radial loss of antiprotons on the trap wall is localized to small spots, strongly breaking the azimuthal symmetry expected for an ideal trap. Our observations have important implications for detection of antihydrogen annihilations.Received 31 July 2003DOI:https://doi.org/10.1103/PhysRevLett.92.065005©2004 American Physical Society

The φπ+/ωπ+ ratio from n¯p annihilations on a liquid hydrogen target, for n¯ momenta between 64 and 297 MeV/c, was measured using the OBELIX spectrometer at LEAR. The ratio R(ϕπ/ωπ)=σ(n¯p→ϕπ+)/σ(n¯p→ωπ+) turned out 0.110±0.015stat±0.006syst. Implications of this result on the OZI rule are discussed.

We demonstrate cooling of 104 antiprotons in a dense, cold plasma of ∼108 positrons, confined in a nested cylindrical Penning trap at about 15 K. The time evolution of the cooling process has been studied in detail, and several distinct types of behavior identified. We propose explanations for these observations and discuss the consequences for antihydrogen production. We contrast these results with observations of interactions between antiprotons and “hot” positrons at about 3000 K, where antihydrogen production is strongly suppressed.

We present evidence showing how antiprotonic hydrogen, the quasistable antiproton (p)-proton bound system, has been synthesized following the interaction of antiprotons with the molecular ion H2+ in a nested Penning trap environment. From a careful analysis of the spatial distributions of antiproton annihilation events, evidence is presented for antiprotonic hydrogen production with sub-eV kinetic energies in states around n=70, and with low angular momenta. The slow antiprotonic hydrogen may be studied using laser spectroscopic techniques.

The results of a measurement of the proton spectra following the non-mesonic weak decay of 5ΛHe, 7ΛLi and 12ΛC are presented and discussed. The experiment was performed at the (e+ e−) collider DAΦNE at Laboratori Nazionale di Frascati of INFN. It is the first measurement for 7ΛLi, and for all the spectra the lower limit on the energy of the protons is 15 MeV, never reached before. All the spectra show a similar shape, namely a peak at around 80 MeV as expected for the free Λp→np weak reaction, with a low energy rise that should be due to final state interactions and/or two-nucleon induced weak processes. The decay spectrum of 5ΛHe is somehow similar to the ones reported by previous measurements and theoretical calculations, but the same does not happen for the 12ΛC one.

The decay of Λ-hypernuclei without π emission, known as Non-Mesonic Weak Decay (NMWD), gives an effective tool to investigate ΔS=1 four-baryon interactions. It was theoretically suggested that the two-nucleon induced mechanism could play a substantial role in reproducing the observed NMWD decay rates and nucleon spectra, but at present no direct evidence of such a mechanism has been obtained. The FINUDA experiment, exploiting the possibility to detect both charged and neutral particles coming from the hypernucleus decay, has allowed us to deduce the relative weight of the two nucleon induced decay rate to the total NMWD rate. The value of Γ2N/ΓNMWD=0.21±0.07stat−0.02sys+0.03sys has been deduced, well consistent with the previous determinations.

The p̄D and p̄4He total annihilation cross sections have been measured with the Obelix apparatus at LEAR at, respectively, three and two values of the p̄ incident momentum between 70 MeV/c and 36 MeV/c. The values of the p̄D annihilation cross section, at such low energies, are in agreement with a surprising result obtained in a recent low statistics measurement of the antiprotonic deuterium Kα X-rays [M. Augsburger et al., Phys. Lett. B 461 (1999) 417] (see following article), concerning the unexpected narrow width of the antiprotonic deuterium 1s level.

The results of the analysis of 3940 (KKπ)ππ events from a sample of 18 millions pp annihilations in the liquid hydrogen target of the OBELIX spectrometer at LEAR (CERN) are presented. The presence of two pseudoscalar states at 1.416±0.002GeV/c2, with width 0.050±0.004GeV/c2, and at 1.46±0.01GeV/c2, with width 0.105±0.015GeV/c2, is established. The lighter mass resonance decays mainly to KKπ, possibly with final state interactions and a small contribution coming from a0π. The higher mass 0−+ state, which is seen for the first time in pp annihilation at rest, decays only to K∗K. Masses, widths and decay modes are in agreement with the analysis of JΨ radiative decay performed by the Mark III Collaboration. From the fit the G-parity was determined to be +1. The dominant three-body decay mode of the lighter pseudoscalar is observed for the first time in this measurement.

New algorithms for the rapid calculation of the Vavilov energy straggling distribution are presented, of accuracy high enough for standard Monte Carlo applications. The average sampling time is about a factor of 6 lower than that obtained with other existing routines in current use.

Antihydrogen can be synthesized by mixing antiprotons and positrons in a Penning trap environment. Here an experiment to stimulate the formation of antihydrogen in the n=11 quantum state by the introduction of light from a CO2 continuous wave laser is described. An overall upper limit of 0.8% with 90% C.L. on the laser-induced enhancement of the recombination has been found. This result strongly suggests that radiative recombination contributes negligibly to the antihydrogen formed in the experimental conditions used by the ATHENA Collaboration.Received 14 July 2006DOI:https://doi.org/10.1103/PhysRevLett.97.213401©2006 American Physical Society

We demonstrate temporally controlled modulation of cold antihydrogen production by periodic RF heating of a positron plasma during antiproton-positron mixing in a Penning trap. Our observations have established a pulsed source of atomic antimatter, with a rise time of about 1 s, and a pulse length ranging from 3 to 100 s. Time-sensitive antihydrogen detection and positron plasma diagnostics, both capabilities of the ATHENA apparatus, allowed detailed studies of the pulsing behavior, which in turn gave information on the dependence of the antihydrogen production process on the positron temperature T. Our data are consistent with power law scaling T−1.1±0.5 for the production rate in the high temperature regime from ∼100 meV up to 1.5 eV. This is not in accord with the behavior accepted for conventional three-body recombination.Received 2 October 2007DOI:https://doi.org/10.1103/PhysRevLett.101.053401©2008 American Physical Society

In view of the High Luminosity LHC, the CMS Muon system will be upgraded to sustain its efficient muon triggering and reconstruction performance. Resistive Plate Chambers (RPC) are dedicated detectors for muon triggering due to their excellent timing resolution. The RPC system will be extended up to 2.4 in pseudorapidity. Before the LHC Long Shutdown 3, new RE3/1 and RE4/1 stations of the forward Muon system will be equipped with improved Resistive Plate Chambers (iRPC) having, compared to the present RPC system, a different design and geometry and 2D strip readout. This advanced iRPC geometry configuration allows the rate capability to improve and hence survive the harsh background conditions during the HL-LHC phase. Several iRPC demonstrator chambers were installed in CMS during the recently completed 2nd Long Shutdown to study the detector behaviour under real LHC conditions. This paper summarizes the iRPC project and its schedule, including the status of the iRPC production sites, details of the chamber quality control procedures and results of the commissioning of the demonstrator chambers.

In view of the High Luminosity upgrade of the CERN LHC, the forward CMS Muon spectrometer will be extended with two new stations of improved Resistive Plate Chambers (iRPC) covering the pseudorapidity range from 1.8 to 2.4. Compared to the present RPC system, the gap thickness is reduced to lower the avalanche charge, and an innovative 2D strip readout geometry is proposed. These improvements will allow iRPC detector to cope with higher background rates. A new Front-End-Board (FEB) is designed to readout iRPC signals with a threshold as low as 30 fC and an integrated Time Digital Converter with a resolution of 30 ps. In addition, the communication bandwidth is significantly increased by using optical fibers. The history, final design, certification, and calibration of this FEB are presented.

Novel data from the $K^{-}_{stop}A$ absorption reaction in light nuclei $^{6,7}$Li and $^{9}$Be are presented. The study aimed at finding $\Lambda t$ correlations. Regardless of $A$, the $\Lambda t$ pairs are preferentially emitted in opposite directions. Reaction modeling predominantly assigns to the $K^-_{stop}A\to\Lambda t(N)A'$ direct reactions the emission of the $\Lambda t$ pairs whose yield is found to range from $10^{-3}$ to $10^{-4}$$/K^-_{stop}$. The experiment was performed with the FINUDA spectrometer at DA$\Phi$NE (LNF).

This Letter is concerned with the study of the Kstop−A→π±Σ∓A′ reaction in p-shell nuclei, i.e., 6,7Li, 9Be, 13C and 16O. The π±Σ∓/Kstop− emission rates are reported as a function of A. These rates are discussed in comparison with previous findings. The ratio π−Σ+/π+Σ− in p-shell nuclei is found to depart largely from that on hydrogen, which provides support for large in-medium effects possibly generated by the sub-threshold Λ(1405). The continuum momentum spectra of prompt pions and free sigmas are also discussed as well as the π±Σ∓ missing mass behavior and the link with the reaction mechanism. The apparatus used for the investigation is the FINUDA spectrometer operating at the DAΦNE ϕ-factory (LNF-INFN, Italy).

Radiomics has emerged as an advanced image processing methodology to define quantitative imaging biomarkers for prognosis and prediction of treatment response and outcome. The development of quantitative imaging biomarkers requires careful analysis to define their accuracy, stability and reproducibility through phantom measurements. Few efforts were devoted to develop realistic anthropomorphic phantoms. In this work, we developed a multimodality image phantom suitable for PET, CT and multiparametric MRI imaging.A tissue-equivalent gel-based mixture was designed and tested for compatibility with different imaging modalities. Calibration measurements allowed to assess gel composition to simulate PET, CT and MRI contrasts of oncological lesions. The characterized gel mixture was used to create realistic synthetic lesions (e.g. lesions with irregular shape and non-uniform image contrast), to be inserted in a standard anthropomorphic phantom. In order to show phantom usefulness, issues related to accuracy, stability and reproducibility of radiomic biomarkers were addressed as proofs-of-concept.The procedure for gel preparation was straightforward and the characterized gel mixture allowed to mime simultaneously oncological lesion contrast in CT, PET and MRI imaging. Proofs-of-concept studies suggested that phantom measurements can be customized for specific clinical situations and radiomic protocols.We developed a strategy to manufacture an anthropomorphic, tissue-equivalent, multimodal phantom to be customized on specific radiomics protocols, for addressing specific methodological issues both in mono and multicentric studies.

The measurement of different reactions of pd annihilation at rest in a gaseous target has been performed using the OBELIX spectrometer at LEAR (CERN). A strong deviation from the OZI-rule prediction was found from the measurement of the ratio R = φπωπ in two regions of proton momenta, P < 200 MeV/c and P > 400 MeV/c: R(φπ−ωπ−) = (133 ± 26) × 10−3 and (113 ± 30) × 10−3, respectively. These values are about 30 times greater than the theoretical prediction. For the first time the excitation of the †-resonance was observed among the final-state products of pd annihilation. The existence of a broad enhancement in the 4π invariant mass at m ≈ 1480 MeV, seen in previous experiments, was confirmed. A ≈ 100 MeV downward shift of the bump position, when the proton momentum increased up to P > 400 MeV/c, was also observed, while the positions of ω, ϱ and f2(1270) did not change with the proton momentum. The following branching ratios were measured: BR(pd → π−φp) = (6.62 ± 0.49) × 10−4, for P < 200 MeV/c; BR(pd → π−φp) = (0.95 ± 0.22) × 10−4, for P > 400 MeV/c; BR(pd → π−ωp) = (49.7 ± 8.9) × 10−4, for P < 200 MeV/c; BR(pd → π−ωp) = (8.38 ± 1.09) × 10−4, for P > 400 MeV/c; BR(pd → 2π−π+p) = (150 ± 6) × 10−4, for P < 200 MeV/c; BR(pd → 2π−π+p) = (16.6 ± 0.9) × 10−4, for P > 400 MeV/c; BR(pd → 3π−2π+p) = (326 ± 12) × 10−4, for P < 200 MeV/c; BR(pd → 3π−2π+p) = (44 ± 7) × 10−4, for P > 400 MeV/c; BR(pd → ΛK+π−) = (0.96 ± 0.19) × 10−4, for P > 400 MeV/c; BR(pd → ΛK+π−π0) = (3.5 ± 0.8) × 10−4, for P > 400 MeV/c; BR(pp → 2π−2π+) = (540 ± 20) × 10−4; BR(pp → 3π−3π+) = (251 ± 21) × 10−4.

The partial wave analysis of the reaction pp → π+π−π0 at rest has been performed for the first time by using high-statistics data sets collected in hydrogen targets at three different densities. The different mixtures of partial waves corresponding to our samples allow a reliable determination of each contribution. This technique is crucial in the identification of the exotic candidate f2(1565) which can be produced by 1S0, 3P1 and 3P2 initial states. The amplitude analysis was performed in the frame of the K-Matrix and P-Vector approach. It requires presence of the exotic candidates f0(1500) and f2(1565) with the following masses and total widths: (1449 ± 20)MeV, (114 ± 30)MeV and (1507 ± 15)MeV, (130 ± 20)MeV respectively. In addition to f0(980), f0(1300) f2(1270) and ϱ(770), a clear evidence of I = 1, JP = 1− signal, which we identify with ϱ(1450), is obtained.

New measurements of the pp total annihilation cross-section at very low momenta (around 50 MeV/c) confirm the previous results obtained by the OBELIX collaboration. The measured values are in general agreement with a scattering length approximation of the annihilation cross-section where the pp scattering lengths are obtained from measurement of the protonium shifts and widths and which accounts for the Coulomb interaction. Partial annihilation cross-sections and annihilation frequencies for some channels have been measured too. The values of the total and partial cross sections at the lowest p momentum show an unexpected behaviour

Abstract A preliminary final state analysis of a sample of n p in-flight annihilations into three and five charged pions is presented. The partial-wave analysis of three-prong data confirms previous interpretations of the Ax ƒ 2 (1520) resonance, from p p annihilations at rest. Concerning five-prong events our analysis favours spin 0 for the already reported ζ (1480) state, but more refined calculations are underway. At high n momenta, the five-prong data show some evidence for a possible spin 2 state at 1640 MeV/c 2 decaying in ρ ° ρ °.

The study of the K±Kmiss0π∓π+π− channel (7016 events), from pp annihilations in a gaseous hydrogen target at NTP, with the OBELIX spectrometer at LEAR (CERN), is presented. A spin-parity analysis provides evidence for two axial vectors, one in the low KKπ mass region, the well established f1(1285), decaying to a0(980)π, the second, the 1++ component of the old puzzling El, the f1(1420), decaying mainly to K∗K, seen for the first time in pp annihilation at rest. The analysis confirms the dominant production of the pseudoscalar η(1405), decaying mainly to (Kπ)SK, and the existence of a second pseudoscalar in the same mass region, the η(1460), decaying mainly to K∗K.

The study of the I=1,JPC=0++ states with the OBELIX detector in the channel p̄p→K±K0Sπ∓ at three different target densities is reported. The data show the evidence for an extra scalar state with mass 1.29±0.01 GeV/c2 and width 0.080±0.005 GeV/c2.

A spin-parity analysis of a sample of p̄p→K+K−π+π−π0 annihilation events taken at rest in gaseous H2 at NTP is reported. The invariant mass spectrum of the K+K−π0 system shows the presence of the E/ι resonance pattern at 1.42 GeV. The analysis of this signal confirms the results obtained by the OBELIX Collaboration in previous works, namely: the existence of two pseudoscalar states at 1.413 ± 0.002 and 1.460±0.012 GeV with widths 0.051 ± 0.004 and 0.120±0.015 GeV, respectively. The p̄p system in the 3P1 wave shows also a signal corresponding to the axial vector f1(1420) decaying to K∗K̄ with mass 1.420±0.003 GeV and width 0.061±0.005 GeV. A study of the incoherent phase space background shows that its origin is mostly due to the reflection of a resonant state in the K+K−π+π− system. The isobar decomposition of this resonant state is mainly f0(1370)(ππ)S, its parameters are: JPC=0++, m=1.670±0.02 GeV and width 0.267±0.036 GeV. This signal can be probably identified with another decay mode of the f0(1710).

An observation of a clear dependence of antihydrogen production on positron plasma shapes is reported.For this purpose a plasma control method has been developed combining the plasma rotating-wall technique with a mode diagnostic system.With the help of real-time and nondestructive observations, the rotating-wall parameters have been optimized.The positron plasma can be manipulated into a wide range of shapes ͑aspect ratio 6.5ഛ ␣ Շ 80͒ and densities ͑1.5ϫ 10 8 ഛ n Շ 7 ϫ 10 9 cm -3 ͒ within a short duration ͑25 s͒ compatible with the ATHENA antihydrogen production cycle.

The antineutron–proton total cross section has been measured in the low momentum range 50–400 MeV/c (below 100 MeV/c for the first time). The measurement was performed at LEAR (CERN) by the OBELIX experiment, thanks to its unique antineutron beam facility. A thick target transmission technique has been used. The measured total cross section shows an anomalous behaviour below 100 MeV/c. A dominance of the isospin I=0 channel over the I=1 one at low energy is clearly deduced.

The results of the spin-parity analysis of pp → 2π+2π− annihilations at very low momentum p (≈ 50 MeV/c) are reported. To describe the data the production of the ϱ, f2, a2 and a1 mesons and the presence of the ππ interaction in S-wave (the σ term) in the final state are necessary. The best fit solution requires also the presence of a ϱ′ state of mass and width M = 1.282 ± 0.037, Γ = 0.236 ± 0.036 GeV/c2 and of a heavy pion π(1300) of mass and width M = 1.275 ± 0.015, Γ = 0.218 ± 0.100 GeV/c2. The measured fraction of the annihilation cross section into 2π+2π− is (7.61 ± 0.35) · 10−2.

A confirming evidence for two pseudoscalar states with masses M1=1405±5, Γ1=50±4 MeV/c2 and M2=1500±10, Γ2=100±20 MeV/c2 is reported. The second pseudoscalar fills the nonet and leaves the first as an outsider supporting the hypothesis for its exotic nature.

The use of low-density hydrogen targets is demonstrated experimentally to be a new way of selecting protonium (pp atom) annihilations with initial angular momentum L = 1. The mean value and the width of the time distributions which occur between protonium formation and annihilation have been measured at room temperature at 8.2, 4.1, 2.1 mbar. They are (110±10; 45±5), (145±15; 82±9) and (210±25;125±9) ns, respectively.

Abstract The p annihilation at rest in a NTP 4He-gas target has been studied by means of the Obelix spectrometer installed at the LEAR accelerator of CERN. Reactions with production of 2π−2π+, 2π−3π+, 2π−2π+p, 2π−π+2p, 2π−3p (with pπ>80 MeV/c and pp>300 MeV/c) have been selected and single- and multinucleon annihilations identified. For the first time some known mesonic and baryonic resonances have been observed in p 4He annihilations and branching ratios are evaluated for a number of reaction channels.

The reaction p̄p→K+K−π0 was analysed for antiproton annihilations at rest at three hydrogen target densities. A strong dependence of the p̄p→φπ0 yield on the quantum numbers of the initial state is observed. The branching ratio of the φπ0 channel from the 3S1 initial state is more than 15 times larger than the one from the 1P1 state. A large apparent violation of the OZI rule for tensor meson production from p̄p-annihilations from the P-waves (1+++2++) is observed: Rexp(f′2π0/f2π0)=(149±20)·10−3, significantly exceeding the OZI-rule prediction R=16·10−3.

Data of antiproton annihilation at rest in a hydrogen gas target at NTP have been collected with the Obelix spectrometer exposed to the beam extracted from the LEAR accelerator of CERN. The reactions pp → φπ0 and pp → φη have been studied. The analysis of the angular distribution of the kaons emitted by the φ decay has shown that the reaction pp → φπ0 occurs essentially from 3S1 states with a production rate RNTP = (2.46 ± 0.23 ± 0.07) × 10−4, while the rate from 1P1 states is compatible with zero. Because of acceptance limitations, 3S1 and 1P1 contributions to the reaction pp → φη could not be resolved and lower and upper limits for the production rate have been measured with the middle value RNTP = (0.87 ± 0.21) × 10−4. Also, for the phase-space K+K−η events the production rate RNTP = (4.67 ± 0.35) × 10−4 has been measured. The φπ0 and φη branching ratios in S- and P-waves (defined in the text) have been estimated in a model dependent way. For the evaluation of the φη rate, a combination of our production rate and of data obtained with a liquid target has been used. The φπ0 production rate, compared to our preliminary value for the ωπ0 production, confirms the strong violation of the OZI rule observed in other experiments. No violation is apparent in the φη production.

The spin-parity analysis of the $\mathrm{n\ifmmode \bar{}\else \={}\fi{}}\stackrel{\ensuremath{\rightarrow}}{p}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ exclusive reaction in flight is presented. The main aim is to study the $({\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})$ invariant mass spectrum in the region around 1500 MeV. The analysis was performed with a Breit-Wigner parametrization for all the resonant states and, for the scalar sector in the mass region below 1.2 GeV, by means of a K-matrix-like treatment. It clearly shows the need for two states, a scalar one ${(0}^{++})$ with mass and width $(1522\ifmmode\pm\else\textpm\fi{}25) \mathrm{MeV}$ and $(108\ifmmode\pm\else\textpm\fi{}33) \mathrm{MeV}$, and a tensorial one ${(2}^{++})$ with mass $(1575\ifmmode\pm\else\textpm\fi{}18) \mathrm{MeV}$ and width $(119\ifmmode\pm\else\textpm\fi{}24) \mathrm{MeV}$, respectively. In addition, the analysis requires the presence of a scalar state at $(1280\ifmmode\pm\else\textpm\fi{}55) \mathrm{MeV}$, $(323\ifmmode\pm\else\textpm\fi{}13) \mathrm{MeV}$ broad, and of a second vectorial one, in addition to the ${\ensuremath{\rho}}^{0}(770)$ signal, with mass and width $(1348\ifmmode\pm\else\textpm\fi{}33) \mathrm{MeV}$ and $(275\ifmmode\pm\else\textpm\fi{}10) \mathrm{MeV}$, respectively.

Data about antiprotons slowing down in gaseous targets at very low energies (E1 keV) show that the stopping power in ${\mathrm{D}}_{2}$ is lower than in ${\mathrm{H}}_{2}$; the right way to explain this behavior seems to be through a nuclear stopping power derived from the classical Rutherford formula. \textcopyright{} 1996 The American Physical Society.

From the study of the annihilation at rest pp → K±Kmiss0π∓π+π− the production rates of the η(1440) → K±KL0π∓ were obtained for three different hydrogen target densities: liquid, gaseous at NTP and at low pressure (5 mbar). The rate values are: fη(1440) (LH) = (6.0±0.5) · 10−4, fη(1440) (NTP) = (2.9±0.4) · 10−4 and fη(1440) (5mbar) = (1.0±0.2) · 10−4. From these results, the density dependence of the annihilation fraction from the 1S0 protonium level can be extracted directly.

The ATHENA experiment at CERN, after producing cold antihydrogen atoms for the first time in 2002, has synthesised protonium atoms in vacuum at very low energies. Protonium, i.e. the antiproton–proton bound system, is of interest for testing fundamental physical theories. In the nested penning trap of the ATHENA apparatus protonium has been produced as result of a chemical reaction between an antiproton and the simplest matter molecule, H2+. The formed protonium atoms have kinetic energies in the range 40–700 meV and are metastable with mean lifetimes of the order of 1 μs. Our result shows that it will be possible to start measurements on protonium at low energy antiproton facilities, such as the AD at CERN or FLAIR at GSI.

The CMS experiment, located at the Large Hadron Collider (LHC) in CERN, has a redundant muon system composed by three different gaseous detector technologies: Cathode Strip Chambers (in the forward regions), Drift Tubes (in the central region), and Resistive Plate Chambers (both its central and forward regions). All three are used for muon reconstruction and triggering. The CMS RPC system confers robustness and redundancy to the muon trigger. The RPC system operation in the challenging background and pileup conditions of the LHC environment is presented. The RPC system provides information to all muon track finders and thus contributing to both muon trigger and reconstruction. The summary of the detector performance results obtained with proton-proton collision at √s = 13 TeV during 2016 and 2017 data taking have been presented. The stability of the system is presented in terms of efficiency and cluster size vs time and increasing instantaneous luminosity. Data-driven predictions about the expected performance during High Luminosity LHC (HL-LHC) stage have been reported.

Abstract A new generation of resistive plate chambers, capable of withstanding high particle fluxes (up to 2000 Hz · cm -2 ) and instrumented with precise timing readout electronics is proposed to equip two of the four high pseudorapidity stations of the CMS muon system. Double-gap RPC detectors, with each gap made of two 1.4 mm High Pressure Laminate electrodes and separated by a gas gap of the same thickness, are proposed. The new layout reduces the amount of the avalanche charge produced by the passage of a charged particle through the detector. This improves the RPC rate capability by reducing the needed time to collect this charge. To keep the RPC efficiency high, a sensitive, low-noise and high time resolution front-end electronics is needed to cope with the lower charge signal of the new RPC. An ASIC called PETIROC that has all these characteristics has been selected to read out the strips of new chambers. Thin (0.6 mm) printed circuit board, 160 cm long, equipped with pickup strips of 0.75 cm average pitch, will be inserted between the two new RPC's gaps. The strips will be read out from both ends, and the arrival time difference of the two ends will be used to determine the hit position along the strip. Results from the improved RPC equipped with the new readout system and exposed to cosmic muons in the high irradiation environment at CERN GIF++ facility are presented in this work.

The stopping power of H, for pS was measured in the p energy interval 1 keV + 120 keV using a low density gas target (ppρ ≈ l0−3 + 10−2 ÷ pρ being the Hz density at STP) with the OBELIX spectrometer at the LEAR of CEBN. Furthermore, the formation of metastable states in the p 4He interaction at rest, having a mean life of the order of 3 μs, was investigated at six target gas pressures (3 atm and 400,250,200,150,50 mbar). The influence of contaminants (like Ha, Ne, Ar, N2 and Xe) on the life of such metastable states was examined at the target gas pressure of 3 atm.

The frequency of the protonium annihilation channel pp → KSKL has been measured at three different target densities: liquid hydrogen (LH), gaseous hydrogen at NTP conditions and gaseous hydrogen at low pressure (5 mbar). The obtained results are: f(pp → KSKL, LH) = (7.8 ± 0.7stat ± 0.3sys) × 10−4, f(pp → KSKL, NTP) = (3.5 ± 0.5stat ± 0.2sys) × 10−4 and f(pp → KSKL, 5 mbar) = (1.0 ± 0.3stat ± 0.1sys) × 10−4. Since the KSKL final stat and be originated only from the 3S1 initial state, these values give direct information on the scaling of the protonium spin-triplet S-wave annihilation probability with the density.

We have investigated an extension of the buffer gas cooling technique to a non-neutral buffer gas. The proposed scheme will allow efficient mass-selective centering of ions confined in a Penning trap in situations where the use of a neutral damping agent is not possible. The present paper reviews the principle of the technique and reports on evidence for sideband cooling of antiprotons in an electron gas, obtained with the ATHENA apparatus at CERN's Antiproton Decelerator facility.

We descrbe how protonium, the quasi-stable antiproton-proton bound system, has been synthesized following the interaction of antiprotons with the molecular ion $ {\rm H}_2^+$ in a nested Penning trap environment. From a careful analysis of the spatial distributions of antiproton annihilation events in the ATHENA experiment, evidence is presented for protonium production with sub-eV kinetic energies in states around n = 70, with low angular momenta. This work provides a new two-body system for studies using laser spectroscopic techniques.

We describe an experiment performed in the ATHENA apparatus in which there is evidence that the antiproton-proton bound state, protonium, has been produced at very low energies in vacuum following the interaction of cold antiprotons with a trapped cloud of molecular hydrogen ions. The latter were confined in a centrifugally separated belt outside a positron plasma used for antihydrogen formation. Studies have been performed at low positron plasma temperatures in which the protonium annihilation signal has been identified along with that from antihydrogen, and we discuss how their contributions can be disentangled. With the positron plasma heated to around 10000 K the ions become distributed in the positrons, and the majority of the annihilation signal can be explained in terms of protonium formation, as antihydrogen creation is heavily suppressed. In this case we compare the observed protonium formation rate with expectations from theory and find reasonable accord, when experimental systematics are taken into account. The effect on the annihilation signals of the passage of an electron current through a pre-loaded positron plasma has been studied in detail, and the results are presented here for the first time.

During 2013 and 2014 (Long Shutdown LS1) the CMS experiment is upgrading the forward region installing a fourth layer of RPC detectors in order to complete and improve the muon system performances in the view of the foreseen high luminosity run of LHC. The new two endcap disks consists of 144 double-gap RPC chambers assembled at three different production sites: CERN, Ghent (Belgium) and BARC (India). The chamber components as well as the final detectors are subjected to full series of tests established in parallel at all the production sites.

The analysis of the first FINUDA paper on the emission of Λp pairs following the K− absorption at rest on 6Li, 7Li, 12C nuclei has been revised by using a much larger data set and an updated analysis techniques. The preliminary results regarding the Be9(Kstop−,Λp)X reaction are discussed.

The Resistive Plate Chambers (RPCs) are employed in the CMS Experiment at the LHC as dedicated trigger system both in the barrel and in the endcap. This article presents results of the radiation background measurements performed with the 2011 and 2012 proton-proton collision data collected by CMS. Emphasis is given to the measurements of the background distribution inside the RPCs. The expected background rates during the future running of the LHC are estimated both from extrapolated measurements and from simulation.

Antinucleon-nucleus annihilations into two-body final states containing only one or no meson are unusual annihilations (Pontecorvo reactions), practically unexplored experimentally, with the exception of the channel p d → π− p, for which only two low-statistics measurements exist. Their physical interest lies in the possibility of exploring small-distance nuclear dynamics, in which an important role can be played by non-nucleonic degrees of freedom. A new measurement of the p d → π− p reaction rate at rest, performed with the OBELIX spectrometer at LEAR, with the best statistics up to now and a careful evaluation of systematic effects is reported, together with a critical analysis of the existing theoretical models. The measured branching ratio, which confirms the previous results, can represent a reference point for the studies in the field.

The results of measuring the ratio R = Y(φπ+π−)Y(ωπ+π−) for antiproton annihilation at rest in a gaseous and a liquid hydrogen target are presented. It was found that the value of this ratio increases with the decrease of the dipion mass, which demonstrates the difference between the φ and ω production mechanisms. An indication of the momentum transfer dependence of the apparent OZI rule violation for the φ production from the 3S1 initial state was found.

This paper reports new experimental results on the annihilation of antiprotons stopped in a4He gas target. The measurement was carried out with the Obelix spectrometer installed at the LEAR machine of CERN. Main results can be summarized as follows, (i) The invariant mass distribution of 2π+2π− produced at rest is similar to those from hydrogen and deuterium targets: the peak seen in recent experiments around 1150 MeV/c2 is absent, (ii) 2π angular correlations are very close to those found for hydrogen. The nuclear structure does not modify remarkably the pion production and emission, (iii) πp and pp angular correlations are strongly peaked close to 180°, in qualitative agreement with INC model predictions, (iv) The pp invariant mass distribution reveals events which may be due to η(ω) absorption; the estimated upper limit for probability of π and ω absorption is about 3 × 10−3. (v) Events having features compatible with two-nucleon annihilations with production of heavy mesonic systems are detected both in the 2π+ 2π− and the 2π−π+ channels. The production rate of the 2π+ 2π− channel is of the order of 5 × 10−3.

The HL-LHC phase is designed to increase by an order of magnitude the amount of data to be collected by the LHC experiments. To achieve this goal in a reasonable time scale the instantaneous luminosity would also increase by an order of magnitude up to 6 · 1034 cm−2s−1. The region of the forward muon spectrometer (|η| > 1.6) is not equipped with RPC stations. The increase of the expected particles flux up to 2 kHz/cm2 (including a safety factor 3) motivates the installation of RPC chambers to guarantee redundancy with the CSC chambers already present. The current CMS RPC technology cannot sustain the expected background level. The new technology that will be chosen should have a high rate capability and provide a good spatial and timing resolution. A new generation of Glass-RPC (GRPC) using low-resistivity glass is proposed to equip at least the two most far away of the four high η muon stations of CMS. First the design of small size prototypes and studies of their performance in high-rate particles flux are presented. Then the proposed designs for large size chambers and their fast-timing electronic readout are examined and preliminary results are provided.

In this article we describe an educational activity on radioactive equilibrium we performed with secondary school students (17–18 years old) in the context of a vocational guidance stage for talented students at the Department of Physics of the University of Pavia. Radioactive equilibrium is investigated experimentally by having students measure the activity of 214Bi from two different samples, obtained using different preparation procedures from an uraniferous rock. Students are guided in understanding the mathematical structure of radioactive equilibrium through a modelling activity in two parts. Before the lab measurements, a dice game, which extends the traditional 'radioactive dice' activity to the case of a chain of two decaying nuclides, is performed by students divided into small groups. At the end of the laboratory work, students design and run a simple spreadsheet simulation modelling the same basic radioactive chain with user defined decay constants. By setting the constants to realistic values corresponding to nuclides of the uranium decay chain, students can deepen their understanding of the meaning of the experimental data, and also explore the difference between cases of non-equilibrium, transient and secular equilibrium.

We report on a systematic study of double-gap and four-gap phenolic resistive plate chambers (RPCs) for the Phase-2 upgrade of the CMS muon system at high η. In the present study, we constructed real-sized double-gap and four-gap RPCs with gap thicknesses of 1.6 and 0.8 mm, respectively, with 2-mm-thick phenolic high-pressure-laminated (HPL) plates. We examined the prototype RPCs with cosmic rays and with 100-GeV muons provided by the SPS H4 beam line at CERN. To examine the rate capability of the prototype RPCs both at Korea University and at the CERN GIF++ facility, the chambers were irradiated with 137Cs sources providing maximum gamma rates of about 1.5 kHz cm−2. For the 1.6-mm-thick double-gap RPCs, we found the relatively high threshold on the produced detector charge was conducive to effectively suppressing the rapid increase of strip cluster sizes of muon hits with high voltage, especially when measuring the narrow-pitch strips. The gamma-induced currents drawn in the four-gap RPC were about one-fourth of those drawn in the double-gap RPC. The rate capabilities of both RPC types, proven through the present testing using gamma-ray sources, far exceeded the maximum rate expected in the new high-η endcap RPCs planned for future phase-II runs of the Large Hadron Collider (LHC).

Results on n̄p annihilation frequencies into π+π0, π+η and K+ Ks final states in the n̄ momentum range between 50 and 400 MeV/c are presented. Information about n̄p annihilation dynamics at low energy have been extracted as well as the first determination of the D-wave contribution to the annihilation in flight below 400 MeV/c. This result is compared with an independent analysis of the n̄p annihilation cross section data.

The annihilation frequencies of 19 p̄p annihilation reactions at rest obtained in different target densities are analysed in order to determine the values of the P-wave annihilation percentage at each target density and the average hadronic branching ratios from P- and S-states. Both the assumptions of linear dependence of the annihilation frequencies on the P-wave annihilation percentage of the protonium state and the approach with the enhancement factors of Batty are considered. Furthermore the cases of incompatible measurements are discussed.

This contribution describes a recent experimental study of the A(Kstop−,π±Σ∓)A′ reaction on light nuclei, Li6,7, Be9, C13 and O16. Final π±Σ∓ pairs arise from π+π−n events. For some nuclei, the π+ momentum spectrum presents peak-strucures in the kinematical interval of formation of Σ-hypernuclear states. The apparatus used for the investigation is the FINUDA spectrometer set at DAΦNE.

The annihilation frequency of the reaction pp → π0π0 has been measured, for the first time by stopping antiprotons in a NTP hydrogen target. The obtained result ƒ(π0π0)NTP = (12.7±0.5±2.0)×10−4 is discussed in the frame of the study of the initial angular momentum of the p̄p system.

The results of a study of the annihilation reactions np → θπ+ and np → ωπ+ are reported; the data were collected by the OBELIX apparatus, with antineutrons annihilating in flight (momenta from ∼ 50 MeV/c to 405 MeV/c). Annihilation frequencies and annihilation cross sections have been deduced, for both channels, as a function of antineutron momentum. From the cross section ratio, a substantial deviation from OZI rule expectations is observed. An ss quark content in the nucleon offers a fairly plausible explanation for such an effect.

Abstract The FINUDA experiment performed a systematic study of both mesonic and non-mesonic weak decay of p - shell Λ-hypernuclei. Recent results on the mesonic decay rates and the non-mesonic decay ratios are illustrated and briefly discussed.

P¯ANDA is a new experiment that will be installed at HESR, the new antiproton storage ring under construction as a part of the FAIR facility at Darmstadt, Germany. This experiment, that will investigate QCD in the charmonium mass regime and other aspects of particle and nuclear physics, will be a fixed target detector with a central spectrometer and a forward one. The central tracker will provide information about decay vertices, momenta and types of charged particles emitted after pp¯ annihilations. The design of the Straw Tube Tracker (STT) together with experimental results of the R&D phase are presented here.

Four double-gap CMS resistive plate chambers are being tested at the CERN Gamma Irradiation Facility to determine the performance and aging effects at the expected conditions of the High Luminosity-Large Hadron Collider. Results up to an integrated charge of 290 millicoulomb/cm2 are reported.

The high pseudo-rapidity region of the CMS muon system is covered by Cathode Strip Chambers (CSC) only and lacks redundant coverage despite the fact that it is a challenging region for muons in terms of backgrounds and momentum resolution. In order to maintain good efficiency for the muon trigger in this region additional RPCs are planned to be installed in the two outermost stations at low angle named RE3/1 and RE4/1. These stations will use RPCs with finer granularity and good timing resolution to mitigate background effects and to increase the redundancy of the system.

Abstract During the upcoming High Luminosity phase of the Large Hadron Collider (HL-LHC), the integrated luminosity of the accelerator will increase to 3000 fb −1 . The expected experimental conditions in that period in terms of background rates, event pileup, and the probable aging of the current detectors present a challenge for all the existing experiments at the LHC, including the Compact Muon Solenoid (CMS) experiment. To ensure a highly performing muon system for this period, several upgrades of the Resistive Plate Chamber (RPC) system of the CMS are currently being implemented. These include the replacement of the readout system for the present system, and the installation of two new RPC stations with improved chamber and front-end electronics designs. The current overall status of this CMS RPC upgrade project is presented.

We report the first measurement of the K+K−, π+π− frequencies for p annihilations at rest in a gaseous H2 target at low pressure (5 mbar). We have obtained: fππ = (4.26±0.11)×10−3, fKK = (0.46±0.03)×10−3. The ratio R = fKK/fππ has also been measured at a pressure of 2 mbar. Comparison with previous measurements shows that fKK decreases monotonically with the target density but its value at 5 mbar is still higher than the value with L X-ray in coincidence.

The results of a search for a possible evidence of a π+π+ resonant state in the n̄p→π+π+π− annihilation reaction with data collected by the OBELIX Experiment are presented. The study has been performed by means of a partial wave analysis in the frame of the isobar model. Production fractions for a possible π+π+ resonance have been evaluated. The observed effects at the π+π+ threshold may be described reasonably well by the contributions of f2(1270), f0(1500), f2(1565) and ρ(1450) states and their interferences, but a meaningful statistical indication for a π+π+ scalar state at about 1400 MeV emerges from the analysis.

The ATHENA experiment at the Antiproton Decelerator facility at CERN aims at testing CPT symmetry with antihydrogen. An overview of the experiment, together with preliminary results of development towards the production of slow antihydrogen are reported.

The π+π−π0, K+K−π0 and K±K0π∓ final states produced by p̄p annihilation at rest at three different hydrogen target densities have been analyzed in the frame of a coupled channel analysis together with ππ and πK scattering data. Here we present the main results which concern masses, widths, ππ and KK partial widths of all the involved resonances (JP=0+,1−,2+), the direct determination of ΓKK/Γππ ratio for f0(1370) and f0(1500) (ΓKK/Γππ=0.91±0.20 and ΓKK/Γππ=0.25±0.03, respectively), the determination of a0(1300) parameters (M=1303±16 MeV; Γ=92±16 MeV) and the observation of two different high mass ρ signals associated to ρ(1450) and ρ(1700) (M=1182±30 MeV; Γ=389±20 MeV and M=1594±20 MeV; Γ=259±20 MeV, respectively).

We measured the in flight annihilation frequencies and cross sections of reactions np → π+π0,π+η and K+KS in the antineutron momentum range between 50 and 400 MeV/c. The annihilation frequencies of these channels from the different allowed initial states were calculated and some information about the np annihilation dynamics were obtained. The first determination of the D-wave contribution in this momentum range was also obtained.

The DAωNE project at the Laboratori Nazionali di Frascati (LNF) is an e+e− collider with electron and positron beams accelerated to 510 MeV by a Linac injector. DAωNE is designed to reach a top luminosity L∼ 1033cm−2s−1, that is, to produce ∼4×103 ω(1020)s−1. The hypernuclear research program at DAωNE relies on low-energy kaons, ∼ 16MeV, being produced by ω-meson decays at rest: ω → K−K+ with a B.R.∼49%. In the initial stage, DAωNE will operate at a L∼ 1032cm−2s−1, however the number of ω produced, and the large geometrical acceptance of the FINUDA detector, ∼ 3sr, will allow a strong hypernuclear physics program to be pursued.

Abstract First results concerning p -p and n -p annihilation cross section and n -p total cross sections at low energies ( 2.25 ≤ E P ≤ 22.76 MeV and 3.4 E n MeV ) obtained by the OBELIX spectrometer are reported. The agreement with the few existing data in this energy range is good; the comparison with some models gives interesting indications on the S and P wave contribution at very low energy and on the range of the elastic interaction.

The proton-antiproton annihilation at rest into the $\phi\eta$ final state was measured for three different target densities: liquid hydrogen, gaseous hydrogen at NTP and at a low pressure of 5 mbar. The yield of this reaction in the liquid hydrogen target is smaller than in the low-pressure gas target. The branching ratios of the $\phi\eta$ channel were calculated on the basis of simultaneous analysis of the three data samples. The branching ratio for annihilation into $\phi\eta$ from the $^3S_1$ protonium state turns out to be about ten times smaller as compared to the one from the $^1P_1$ state.

The ATHENA experiment at CERN produced for the first time in 2002 cold antihydrogen atoms by mixing of antiprotons and a positron plasma. The more relevant results obtained in the last three years are presented and discussed in the light of the antihydrogen formation processes.

A research has been made to look for a signature of the positive-strangeness baryon resonance Θ+(1530), which is expected to decay into pK0. A peak is observed in the pπ+π− invariant mass distribution in antiproton– 4He annihilation reactions at rest with production of two π+π− pairs with invariant mass close to the KS0 mass. The annihilation reactions on 4He can involve two to four nucleons producing an energy blob characterized by high strangeness content. The peak is centred around 1560.0±3.7MeV and its width is very narrow. The statistical significance is 2.7; this value is considered of not sufficient significance to claim support of the Θ+. The data were collected with the Obelix spectrometer at the LEAR machine of CERN.

The FINUDA experiment collected data to study the hypernuclear production on different targets, that is 6Li, 7Li, 9Be, 12C, 13C, D2O, 27Al and 51V. The hypernuclei formation was achieved through the strangeness-exchange reaction Kstop−+AZ→ΛAZ+π−. From the study of the out-coming π−, information about the hypernuclei binding energies and capture rates can be deduced. Such results for the following nuclei 7Li, 9Be, 13C and D2O will be presented.

With the increase of the LHC luminosity foreseen in the coming years, many detectors currently used in the different LHC experiments will be dramatically impacted and some need to be replaced or upgraded. The new ones should be capable to provide time information to reduce the data ambiguity due to the expected high pileup. We propose to equip CMS high |η| muon chambers with pairs of single gap RPC detectors read out by long pickup strips PCB. The precise time measurement (0<15 ps) of the signal induced by particles crossing the detector on both ends of each strip will give an accurate measurement of the position of the incoming particle along the strip. The absolute time measurement, determined by RPC signal (around 1.5 ns) will also reduce the data ambiguity due to the highly expected pileup and help to identify Heavy Stable Charged Particles (HSCP). The development of a specific electronic chain (analog front-end ASIC, time-to-digital converter stage and printed circuit board design) and the corresponding first results on prototype chambers are presented.

The high luminosity expected from the HL-LHC will be a challenge for the CMS detector. The increased rate of particles coming from the collisions and the radioactivity induced in the detector material could cause significant damage and result in a progressive degradation of its performance. Simulation studies are very useful in these scenarios as they allow one to study the radiation environment and the impact on detector performance. Results are presented for CMS RPC stations considering the operating conditions expected at the HL-LHC.

The CMS experiment recorded 177.75 /fb of proton-proton collision data during the RUN-1 and RUN-2 data taking period. Successful data taking at increasing instantaneous luminosities with the evolving detector configuration was a big achievement of the collaboration. The CMS RPC system provided redundant information for the robust muon triggering, reconstruction, and identification. To ensure stable data taking, the CMS RPC collaboration has performed detector operation, calibration, and performance studies. Various software and related tools are developed and maintained accordingly. In this paper, the overall performance of the CMS RPC system and experiences of the data taking during the RUN-2 period are summarised.

New experimental results on pd annihilation at rest into pions plus a high momentum proton in the final state are discussed. The data sample was collected using the OBELIX spectrometer at the LEAR facility (CERN). The annihilation probabilities, or more precisely the yields (Y) via channels pd → 2π−π+π0p and pd → 3π−2π+π0p with proton momenta p > 400 MeV/c have been measured for the first time: Y = (93.2 ± 1.6) × 10−4 and Y = (52.2 ± 1.4) × 10−4, respectively. The signal in the invariant mass distribution of the pπ+ system in the region of the well-known Δ++(1232)-isobar is clearly seen in reactions pd → 2π−π+p, pd → 2π−π+π0p, pd → 3π−2π+p and pd → 3π−2π+π0p. The upper limit on reaction p(Δ−Δ++) → 2π−π+p in the pd annihilation at rest, which could be interpreted as a manifestation of the ΔΔ component of the deuteron, was found to be Y ≤ 6.5 × 10−5 with a 90% confidence level.

The Obelix experiment at CERN collected samples of antiproton annihilations at rest in different gaseous targets, such as hydrogen, deuterium and helium. We analyze a set of the Obelix data using a new technique for measuring, for the first time, the cascade times independent of the capture energy and of the antiproton stopping power. We report on measurements of the cascade times for hydrogen at 3.4, 5.8, 9.8 and 150 mbar and for helium at 8.2, 50 and 150 mbar pressure. An estimate of the antiproton capture energy in hydrogen is also presented.

The annihilation frequency of the reaction $\overline{p}\stackrel{\ensuremath{\rightarrow}}{p}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ at rest in liquid hydrogen has been measured by the Obelix experiment by using different apparatus configurations and trigger conditions. The value obtained is $f({\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0},$ $\mathrm{LH})=(2.8\ifmmode\pm\else\textpm\fi{}{0.1}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{0.4}_{\mathrm{syst}})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}.$ With the same data samples, the ${\ensuremath{\pi}}^{0}\ensuremath{\eta}$ annihilation frequency has been determined to be $f({\ensuremath{\pi}}^{0}\ensuremath{\eta},$ $\mathrm{LH})=(0.9\ifmmode\pm\else\textpm\fi{}{0.2}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{0.1}_{\mathrm{syst}})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}.$ The results are discussed within the frame of the present experimental situation.

The muon spectrometer of the CMS (Compact Muon Solenoid) experiment at the Large Hadron Collider (LHC) is equipped with a redundant system made of Resistive Plate Chambers and Drift Tube in barrel and RPC and Cathode Strip Chamber in endcap region. In this paper, the operations and performance of the RPC system during the first three years of LHC activity will be reported. The stability of RPC performance, such as efficiency, cluster size and noise, will be reported. Finally, the radiation background levels on the RPC system have been measured as a function of the LHC luminosity. Extrapolations to the LHC and High Luminosity LHC conditions are also discussed.

During Run-3, the LHC is preparing to deliver instantaneous luminosity in the range from 5 × 1034 cm−2 s−1 to 7.5 × 1034 cm−2 s−1. To ensure stable data taking, providing redundant information for robust muon triggering, reconstruction and identification, the CMS RPC collaboration has used the opportunity given by the LHC long shutdown 2 (LS2), to perform a series of maintenance and preparation activities for the new data taking period. The overall performance of the RPC system after the LS2 commissioning period and the activities in preparation for future data taking will be presented.

During Run2 the high instantaneous luminosity, up to 2.21034cm−2s−1, lead to a substantial hit rate in the Compact Muon Solenoid experiment’s muon chambers due to multiple background sources to physics processes sought for at LHC. In this article we will describe the analysis method devised to measure and identify the contributions to such background in the Resistive Plate Chambers. Thorough understanding of the background rates provides the base for the upgrade of the muon detectors for the High-Luminosity LHC.

The present Compact Muon Solenoid Resistive Plate Chambers system has been worked efficiently during Run I and Run II of data taking period (Shah et al., 2020) [1]. In the coming years of operation with the High Luminosity LHC (HL-LHC), the expected rate and integrated charge are expected to be about 600 Hz/cm2 and 840 mC/cm2, respectively (including a safety factor of three). Therefore, the HL-LHC phase will be a challenge for the RPC system since the expected operating conditions are much harsher than those for which the detectors have been designed, and could introduce non-recoverable aging effects which can alter the detector properties. A longevity test has been started at the CERN Gamma Irradiation Facility to estimate the impact of HL-LHC conditions on the RPC detector performance in order to determine whether the RPC system will survive the harsher background conditions expected at HL-LHC. The latest results of the irradiation test will be presented.

For the High Luminosity (HL-LHC) upgrade an upgrade of the CMS detector is foreseen. One of the main projects is the development of the improved Resistive Plate Chamber (iRPC) detectors that will be installed in the forward region of CMS. To validate the performance of the new detector gaps with HL-LHC radiation levels, experimental tests have been conducted at the CERN Gamma Irradiation Facility (GIF++). One chamber equipped with electronics is studied and its parameters are monitored as a function of the accumulated charge.