Search

The high-precision kaonic neon X-ray transitions measurement performed by the SIDDHARTA-2 collaboration at the DA$\Phi$NE collider is reported. Both the X-ray energies and yields for high-n transitions were measured, demonstrating the feasibility of sub-eV Xray spectroscopy for kaonic atoms using low-Z gaseous targets. The measurement provides valuable insights into the de-excitation processes in kaonic atoms, providing new input data for the refinement of the corresponding theoretical models, and a framework for testing Quantum Electrodynamics in strange exotic atoms., Comment: 9 pages, 3 figures, 1 table

The SIDDHARTA-2 collaboration aims to measure for the first time the shift and width induced on the $1s$ level of kaonic deuterium by the strong interaction. In the preliminary phase to the experiment, a test run using a Helium-4 target was performed to optimize the performance of the full experimental apparatus. This preliminary study highlighted the possibility to measure transition lines coming from intermediate mass kaonic atoms, such as kaonic carbon and kaonic aluminum. In order to measure transitions where strong interaction is manifesting at higher energies, out of the energy range of the SIDDHARTA-2 apparatus, the collaboration is testing a new detector system which exploits a novel compound semiconductor, the Cadmium Zinc Telluride. Tests are now running at DA$\Phi$NE to study the performance of this detector, exploring the possibility to build a dedicated setup., Comment: 10 pages, 3 figures, eQCD conference

The SIDDHARTA-2 collaboration built a new cadmium-zinc-telluride (CZT, CdZnTe)-based X-ray detection system, used for the first time in the DA$\Phi$NE electron-positron collider at INFN-LNF. The aim of this work is to show that these detectors present optimal long- and short-term linearity and stability to perform precise spectroscopic measurements in a collider environment. The spectra used as references for calibration are reported, and the results about the linearity and stability studies are presented. It is also discussed and showed what is the proper function to describe all the effects that alter the Gaussian shape in semiconductors, particularly evident in the CZT case. Good residuals and resolutions were obtained for all the calibrations. In a test run with the source and the collider beam on, it was demonstrated that the calibrations made with beam off are optimal also when the beam is on, and the actual systematics in a physics run were estimated. These promising results show the potentialities of this detector in the high rate environment of a particle collider, and pave the way for the use of CZT detectors in kaonic atoms researches and in accelerators, with applications for particle and nuclear physics., Comment: 15 pages, 9 figures, 3 tables

An HPGe detector equipped with a transistor reset preamplifier and readout with a CAEN DT5781 fast pulse digitizer was employed in the measurement of X-rays from kaonic lead at the DA$\Phi$NE $e^+e^-$ collider at the Laboratori Nazionali di Frascati of INFN. A thin scintillator in front of a lead target was used to select kaons impinging on it and to form the trigger for the HPGe detector. We present the results of the kaonic lead feasibility measurement, where we show that the resolution of the HPGe detector in regular beam conditions remains the same as that without the beam and that a satisfactory background reduction can be achieved. This measurement serves as a test bed for future dedicated kaonic X-rays measurements for the more precise determination of the charged kaon mass., Comment: 14 pages, 7 figures

In this paper we present the results of a new kaonic helium-4 measurement with a 1.37 g/l gaseous target by the SIDDHARTA-2 experiment at the DA{\Phi}NE collider. We measured, for the first time, the energies and yields of three transitions belonging to the Mseries. Moreover, we improved by a factor about three, the statistical precision of the 2p level energy shift and width induced by the strong interaction, obtaining the most precise measurement for gaseous kaonic helium, and measured the yield of the L{\alpha} transition at the employed density, providing a new experimental input to investigate the density dependence of kaonic atoms transitions yield., Comment: 12 pages, 5 figures, 3 tables

The SIDDHARTA-2 collaboration at the INFN Laboratories of Frascati (LNF) aims to perform groundbreaking measurements on kaonic atoms. In parallel and beyond the ongoing kaonic deuterium, presently running on the DA$\Phi$NE collider at LNF, we plan to install additional detectors to perform further kaonic atoms' studies, taking advantage of the unique low energy and low momentum spread $K^-$ beam delivered by the at-rest decay of the $\phi$ meson. CdZnTe devices are ideal for detecting transitions toward both the upper and lower levels of intermediate-mass kaonic atoms, like kaonic carbon and aluminium, which have an important impact on the strangeness sector of nuclear physics. We present the results obtained in a set of preliminary tests conducted on DA$\Phi$NE, in view of measurements foreseen in 2024, with the twofold aim to tune the timing window required to reject the extremely high electromagnetic background, and to quantify the readout electronics saturation effect due to the high rate, when placed close to the Interaction Region (IR). In the first test we used commercial devices and electronics, while for the second one both were customized at the IMEM-CNR of Parma and the University of Palermo. The results confirmed the possibility of finding and matching a proper timing window where to identify the signal events and proved better performances, in terms of energy resolution, of the custom system. In both cases, strong saturation effects were confirmed, accounting for a loss of almost 90\% of the events, which will be overcome by a dedicated shielding structure foreseen for the final experimental setup.

The SIDDHARTA-2 experiment installed at the DA$\mathrm{\Phi}$NE collider of INFN-LNF performed, for the first time, measurements of high-n transitions in intermediate mass kaonic atoms during the data taking campaigns of 2021 and 2022. Kaonic carbon, oxygen, nitrogen and aluminium transitions, which occur in the setup materials, were measured by using the kaons stopped in the gaseous helium target cell with aluminium frames and Kapton walls, and are reported in this paper. These new kaonic atoms measurements add valuable input to the kaonic atoms transitions data base, which is used as a reference for theories and models of the low-energy strong interaction between antikaon and nuclei. Moreover, these results pave the way for future dedicated kaonic atoms measurements through the whole periodic table and to a new era for the antikaon-nuclei studies at low energy., Comment: 8 pages, 7 figures

We present the tests performed by the SIDDHARTA-2 collaboration at the DA{\Phi}NE collider with a quasi-hemispherical CdZnTe detector. The very good room-temperature energy resolution and efficiency in a wide energy range show that this detector technology is ideal for studying radiative transitions in intermediate and heavy-mass kaonic atoms. The CdZnTe detector was installed for the first time in an accelerator environment to perform tests on the background rejection capabilities, which were achieved by exploiting the SIDDHARTA-2 Luminosity Monitor. A spectrum with an $^{241}Am$ source has been acquired, with beams circulating in the main rings, and peak resolutions of 6% at 60 keV and of 2.2% at 511 keV have been achieved. The background suppression factor, which turned out to be of the order of $\simeq10^{5-6}$, opens the possibility to plan for future kaonic atom measurements with CdZnTe detectors.

The SIDDHARTA-2 experiment at the DA$\Phi$NE collider aims to perform precision measurements of kaonic atoms X-ray spectroscopy for the investigation of the antikaon-nucleon strong interaction. To achieve this goal, novel large-area Silicon Drift Detectors (SDDs) have been developed. These devices have special geometry, field configuration and readout electronics that ensure excellent performance in terms of linearity and stability. The paper presents preliminary results for the linearity determination and stability monitoring of the SDDs system during the measurement of kaonic deuterium carried out in the summer of 2022.

In this paper, we present the first tests performed after the full installation of the SIDDHARTA-2 experimental apparatus on the Interaction Region of the DA{\Phi}NE collider at the INFN National Laboratories of Frascati. Before starting the first measurement of the kaonic deuterium 2p{\rightarrow}1s transition, accurate evaluation of the background rejection. mainly achieved with the Kaon Trigger system, was required. This run, performed in the period 04-26/05/2022 with a 4 He gaseous target, confirmed the 10^5 rejection factor obtained with a reduced version of the setup and different machine conditions in 2021. This important outcome motivated the filling of the target cell with deuterium and the starting of the measurement campaign of the kaonic deuterium 2p{\rightarrow}1s transition.

The excitation function for the $pd\rightarrow$ $d p \pi^{0}$ reaction has been measured by WASA-at-COSY experiment with the aim of searching for $^{3}\hspace{-0.03cm}\mbox{He}$-$\eta$ mesic nuclei. The measurement in the vicinity of $\eta$ meson production was performed using a ramped proton beam. The data analysis and interpretation was carried out with the assumption that the $\eta$-mesic Helium decays via the formation of an intermediate N$^{*}$(1535) resonance. No direct signal of the $\eta$-mesic nucleus is observed in the excitation function. We determine a new improved upper limit for the total cross section for the bound state production and decay in the $pd\rightarrow$ $(^{3}\hspace{-0.03cm}\mbox{He}$-$\eta)_{bound} \rightarrow$ $d p \pi^{0}$ process. It varies between 13 nb to 24 nb for the bound state with width in the range $\Gamma \in (5,50)$ MeV.

Differential cross section for the 1H(d,pp)n breakup reaction at deuteron beam energy of 340 MeV has been measured with the use of WASA detector at COSY-Juelich. The set of proton-proton coincidences registered at Forward Detector has been analysed on dense grid of kinematic variables, giving in total around 5600 data points. The cross section data are compared to theoretical predictions based on the state-of-the-art nucleon-nucleon potentials, combined with three-nucleon force, Coulomb interaction or carried out in a relativistic regime.

We report on the experimental search for the bound state of an $\eta$ meson and $^{3}\hspace{-0.03cm}\mbox{He}$ nucleus performed using the WASA-at-COSY detector setup. In order to search for the $\eta$-mesic nucleus decay, the $pd\rightarrow$ $^{3}\hspace{-0.03cm}\mbox{He} 2\gamma$ and $pd\rightarrow$ $^{3}\hspace{-0.03cm}\mbox{He} 6\gamma$ channels have been analysed. These reactions manifest the direct decay of $\eta$ meson bound in $^{3}\hspace{-0.03cm}\mbox{He}$ nucleus. This non-mesonic decay channel has been considered for the first time. When taking into account only statistical errors, the obtained excitation functions reveal a slight indication for a possible bound state signal corresponding to an $^3$He-$\eta$ nucleus width $\Gamma$ above 20 MeV and binding energy $B_s$ between 0 and 15 MeV. However, the determined cross sections are consistent with zero in the range of the systematic uncertainty. Therefore, as final result we estimate only the upper limit for the cross section of the $\eta$-mesic $^{3}\hspace{-0.03cm}\mbox{He}$ nucleus formation followed by the $\eta$ meson decay which varies between $2$ nb and $15$ nb depending on possible bound state parameters., Comment: Article accepted to be published in PLB

New data on the production of single neutral pions in the $pd\rightarrow{}^3\textrm{He}\,\pi^0$ reaction are presented. For fifteen proton beam momenta between $p_p=1.60\;\textrm{GeV}/c$ and $p_p=1.74\;\textrm{GeV}/c$, differential cross sections are determined over a large fraction of the backward hemisphere. Since the only previous systematic measurements of single-pion production at these energies were made in collinear kinematics, the present work constitutes a significant extension of the current knowledge on this reaction. Even this far above the production threshold, significant changes are found in the behaviour of the angular distributions over small intervals in beam momentum., Comment: 9 pages, 5 figures, 3 tables submitted to EPJA

Exclusive measurements of the quasi-free $pp \to pp\pi^+\pi^-$ reaction have been performed by means of $pd$ collisions at $T_p$ = 1.2 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region $T_p = 1.08 - 1.36$ GeV ($\sqrt s$ = 2.35 - 2.46 GeV), which includes the regions of $N^*(1440)$ and $\Delta(1232)\Delta(1232)$ resonance excitations. Calculations describing these excitations by $t$-channel meson exchange are at variance with experimental differential cross sections and underpredict substantially the measured total cross section. An isotensor $\Delta N$ dibaryon resonance with $I(J^P) = 2(1^+)$ produced associatedly with a pion is able to overcome these deficiencies. Such a dibaryon was predicted by Dyson and Xuong and more recently calculated by Gal and Garcilazo.

Exclusive measurements of the quasi-free $pp \to pp\pi^+\pi^-$ reaction have been carried out at WASA@COSY by means of $pd$ collisions at $T_p$ = 1.2 GeV. Total and differential cross sections have been extracted covering the energy region $T_p = 1.08 - 1.36$ GeV, which is the region of $N^*(1440)$ and $\Delta(1232)\Delta(1232)$ resonance excitations. Calculations describing these excitations by $t$-channel meson exchange are at variance with the measured differential cross sections and underpredict substantially the experimental total cross section. An isotensor $\Delta N$ dibaryon resonance with $I(J^P) = 2(1^+)$ produced associatedly with a pion is able to overcome these deficiencies., Comment: arXiv admin note: substantial text overlap with arXiv:1803.03192

We report on the investigation of the rare decay $\eta\rightarrow\pi^0+\text{e}^++\text{e}^-$ which is of interest to study both $C$ violation in the electromagnetic interaction and to search for contributions from physics beyond the Standard Model, since the allowed decay via a two-photon intermediate state is strongly suppressed. The experiment has been performed using the WASA-at-COSY installation, located at the COSY accelerator of the Forschungszentrum J\"ulich, Germany. In total $3\times10^7$ events of the reaction $\text{p}+\text{d}\rightarrow{^3\text{He}}+\eta$ have been recorded at an excess energy of $Q = 59.8\,\textrm{MeV}$. Based on this data set the $C$ parity violating decay $\eta\rightarrow\pi^0+\gamma^*\rightarrow\pi^0+\textrm{e}^++\textrm{e}^-$ via a single-photon intermediate state has been searched for, resulting in new upper limits of $\Gamma\left(\eta\rightarrow\pi^0+\textrm{e}^++\textrm{e}^-\right)/ \Gamma\left(\eta\rightarrow\pi^++\pi^-+\pi^0\right) < 3.28\times10^{-5}$ and $\Gamma\left(\eta\rightarrow\pi^0+\textrm{e}^++\textrm{e}^-\right)/ \Gamma\left(\eta\rightarrow\textrm{all}\right) < 7.5\times10^{-6}\ (\textrm{CL} = 90\,\%)$, respectively., Comment: 7 pages, 8 figures, submitted to PLB

New data on both total and differential cross sections of the production of $\eta$ mesons in proton-deuteron fusion to ${}^3\text{He}\,\eta$ in the excess energy region $13.6\;\text{MeV}\leq Q_\eta \leq 80.9\;\text{MeV}$ are presented. These data have been obtained with the WASA-at-COSY detector setup located at the Forschungszentrum J\"ulich, using a proton beam at 15 different beam momenta between $p_p = 1.60\;\text{GeV}/c$ and $p_p = 1.74\;\text{GeV}/c$. While significant structure of the total cross section is observed in the energy region $20\;\text{MeV}\lesssim Q_\eta \lesssim 60\;\text{MeV}$, a previously reported sharp variation around $Q_\eta\approx 50\;\text{MeV}$ cannot be confirmed. Angular distributions show the typical forward-peaking that was reported elsewhere. For the first time, it is possible to study the development of these angular distributions with rising excess energy over a large interval., Comment: 8 pages, 7 figures, preprint submitted to Physics Letters B

In this report one of the methods used for the luminosity determination for the experiment performed by WASA Collaboration to search for 3He-eta mesic nuclei is presented. The method is based on the analysis of pd -> 3He eta process.

Taking advantage of the high acceptance and axial symmetry of the WASA-at-COSY detector, and the high degree of the polarized proton beam of COSY, the reaction pp{\to} pp{\eta} has been measured close to threshold to explore the analyzing power Ay. The angular distribution of Ay is determined with the precision improved by more than one order of magnitude with respect to previous results allowing a first accurate comparison with theoretical predictions. The determined analyzing power is consistent with zero for an excess energy of Q = 15 MeV signaling s wave production with no evidence for higher partial waves. At Q = 72 MeV the data reveals strong interference of P s and P p partial waves and cancellation of (P p) and Ss*Sd contributions. These results rule out the presently available theoretical predictions for the production mechanism of the {\eta} meson., Comment: Accepted for publication in Phys. Rev. Lett

This letter reports a first quantitative analysis of the contribution of higher partial waves in the charge symmetry breaking reaction $dd \to {}^4\text{He}\pi^0$ using the WASA-at-COSY detector setup at an excess energy of $Q = 60$ MeV. The determined differential cross section can be parametrized as $\text{d}\sigma/\text{d}\Omega = a + b\cos^{2}\theta^*$, where $\theta^*$ is the production angle of the pion in the center-of-mass coordinate system, and the results for the parameters are $a = \left(1.55 \pm 0.46 (\text{stat}) ^{+0.32}_{-0.8} (\text{syst}) \right)$ pb/sr and $b = \left(13.1 \pm 2.1 (\text{stat}) ^{+1.0}_{-2.7} (\text{syst})\right)$ pb/sr. The data are compatible with vanishing p-waves and a sizable d-wave contribution. This finding should strongly constrain the contribution of the $\Delta$ isobar to the $dd \to {}^4\text{He}\pi^0$ reaction and is, therefore, crucial for a quantitative understanding of quark mass effects in nuclear production reactions., Comment: 5 figures

Exclusive measurements of the quasi-free $pn \to pp\pi^-$ and $pp \to pp\pi^0$ reactions have been performed by means of $pd$ collisions at $T_p$ = 1.2 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region $T_p = 0.95 - 1.3$ GeV ($\sqrt s$ = 2.3 - 2.46 GeV), which includes the regions of $\Delta(1232)$, $N^*(1440)$ and $d^*(2380)$ resonance excitations. From these measurements the isoscalar single-pion production has been extracted, for which data existed so far only below $T_p$ = 1 GeV. We observe a substantial increase of this cross section above 1 GeV, which can be related to the Roper resonance $N^*(1440)$, the strength of which shows up isolated from the $\Delta$ resonance in the isoscalar $(N\pi)_{I=0}$ invariant-mass spectrum. No evidence for a decay of the dibaryon resonance $d^*(2380)$ into the isoscalar $(NN\pi)_{I=0}$ channel is found. An upper limit of 90 $\mu$b (90 $\%$ C.L.) corresponding to a branching ratio of 5 $\%$ has been deduced., Comment: erratum: the upper limit for the branching ratio of the decay $d^*(2380) \to (NN\pi)_{I=0}$ is a factor of two smaller than given in the previous version of this article

We report on the status of the search for eta-mesic nuclei and the studies of the interaction of the eta meson with nucleons. Recently we have completed the analysis of the new WASA-at-COSY data on the production of the eta meson with polarized proton beam. New results on the analyzing power for the pp->ppeta reaction with more than an order of magnitude improved precision shed a new light on the production mechanism of the eta meson in nucleon-nucleon collisions. Also, the latest results of the search for eta-mesic nuclei are discussed., Comment: 4 pages, presented at 14th International Workshop on Meson Production, Properties and Interaction KRAK\'OW, POLAND (MESON 2016), accepted for publication in EPJ

The search for 4He-eta bound states was performed with the WASA-at-COSY facility via the measurement of the excitation function for the dd->3He n pi0 and dd->3He p pi- processes. The beam momentum was varied continuously between 2.127 GeV/c and 2.422 GeV/c, corresponding to the excess energy for the dd->4He eta reaction ranging from Q=-70 MeV to Q=30 MeV. The luminosity was determined based on the dd->3He n reaction and quasi-free proton-proton scattering via dd->pp n_spectator n_spectator reactions. The excitation functions determined independently for the measured reactions do not reveal a structure which could be interpreted as a narrow mesic nucleus. Therefore, the upper limits of the total cross sections for the bound state production and decay in dd->(4He-eta)_bound->3He n pi0 and dd->(4He-eta)_bound->3He p pi- processes were determined taking into account the isospin relation between both the channels considered. The results of the analysis depend on the assumptions of the N* momentum distribution in the anticipated mesic-4He. Assuming as in the previous works, that this is identical with the distribution of nucleons bound with 20 MeV in 4He, we determined that (for the mesic bound state width in the range from 5 MeV to 50 MeV) the upper limits at 90% confidence level are about 3 nb and about 6 nb for npi0 and ppi- channels, respectively. However, based on the recent theoretical findings of the N*(1535) momentum distribution in the N*-3He nucleus bound by 3.6 MeV, we find that the WASA-at-COSY detector acceptance decreases and hence the corresponding upper limits are 5 nb and 10 nb for npi0 and ppi- channels respectively., Comment: This article will be submitted to JHEP

Using the production reactions $pd\to {}^3\mbox{He}\,\omega$ and $pp\to pp\omega$, the Dalitz plot distribution for the $\omega \to \pi^+ \pi^- \pi^0$ decay is studied with the WASA detector at COSY, based on a combined data sample of $ (4.408\pm 0.042) \times 10^4$ events. The Dalitz plot density is parametrised by a product of the $P$-wave phase space and a polynomial expansion in the normalised polar Dalitz plot variables $Z$ and $\phi$. For the first time, a deviation from pure $P$-wave phase space is observed with a significance of $4.1\sigma$. The deviation is parametrised by a linear term $1+2\alpha Z$, with $\alpha$ determined to be $+0.147\pm0.036$, consistent with the expectations of $\rho$-meson-type final-state interactions of the $P$-wave pion pairs., Comment: 8 pages, 7 figures

Various theoretical calculations based on QCD or hadronic interactions predict that in addition to the recently observed dibaryon resonance $d^*(2380)$ with $I(J^P) = 0(3^+)$ there should also exist a dibaryon resonance with mirrored quantum numbers $I(J^P) = 3(0^+)$. We report here on a search for such a $NN$-decoupled state in data on the $pp \to pp\pi^+\pi^+\pi^-\pi^-$ reaction. Since no clear-cut evidence has been found, we give upper limits for the production cross section of such a resonance in the mass range 2280 - 2500 MeV.