arXiv subjects

M. Wolke

Publications and source records attributed to M. Wolke.

At least 19 recordsLinked to original sources

arXiv2025

Three-Nucleon Dynamics in the dp breakup collisions at 190 MeV/nucleon using the WASA detector at COSY-J\"{u}lich

The differential cross section for the $^{1}$H$(d,pp)n$ breakup reaction at deuteron beam energy of 380 MeV has been determined with high precision for 189 angular configurations of outgoing protons in the region of forward laboratory angles. The cross section data were compared to theoretical predictions based on the state-of-the-art nucleon-nucleon potentials, combined with a three-nucleon force, the Coulomb interaction or carried out in a relativistic approach. In the region of the lowest differential cross section, the discrepancy between the data and the theoretical predictions is observed, also in the case of relativistic calculations.

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arXiv2025

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

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

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arXiv2023

The HIBEAM Instrument at the European Spallation Source

The European Spallation Source (ESS) will be the world's brightest neutron source and will open a new intensity frontier in particle physics. The HIBEAM collaboration aims to exploit the unique potential of the ESS with a dedicated ESS instrument for particle physics which offers world-leading capability in a number of areas. The HIBEAM program includes the first search in thirty years for free neutrons converting to antineutrons and searches for sterile neutrons, ultralight axion dark matter and nonzero neutron electric charge. This paper outlines the capabilities, design, infrastructure, and scientific potential of the HIBEAM program, including its dedicated beamline, neutron optical system, magnetic shielding and control, and detectors for neutrons and antineutrons. Additionally, we discuss the long-term scientific exploitation of HIBEAM, which may include measurements of the neutron electric dipole moment and precision studies of neutron decays.

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arXiv2023

HighNESS Conceptual Design Report: Volume I

The European Spallation Source, currently under construction in Lund, Sweden, is a multidisciplinary international laboratory. Once completed to full specifications, it will operate the world's most powerful pulsed neutron source. Supported by a 3 million Euro Research and Innovation Action within the EU Horizon 2020 program, a design study (HighNESS) has been completed to develop a second neutron source located below the spallation target. Compared to the first source, designed for high cold and thermal brightness, the new source has been optimized to deliver higher intensity, and a shift to longer wavelengths in the spectral regions of cold (CN, 2--20\,\AA), very cold (VCN, 10--120\,\AA), and ultracold (UCN, ${>}\,{500}$\,\AA) neutrons. The second source comprises a large liquid deuterium moderator designed to produce CN and support secondary VCN and UCN sources. Various options have been explored in the proposed designs, aiming for world-leading performance in neutronics. These designs will enable the development of several new instrument concepts and facilitate the implementation of a high-sensitivity neutron-antineutron oscillation experiment (NNBAR). This document serves as the Conceptual Design Report for the HighNESS project, representing its final deliverable.

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arXiv2023

Measurement of the $K_S \to πe ν$ branching fraction with the KLOE experiment

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

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arXiv2022

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

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

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arXiv2022

The Development of the NNBAR Experiment

The NNBAR experiment for the European Spallation Source will search for free neutrons converting to antineutrons with a sensitivity improvement of three orders of magnitude compared to the last such search. This paper describes progress towards a conceptual design report for NNBAR. The design of a moderator, neutron reflector, beamline, shielding and annihilation detector is reported. The simulations used form part of a model which will be used for optimisation of the experiment design and quantification of its sensitivity.

physics.ins-det↗

arXiv2022

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

The quantum interference between the decays of entangled neutral kaons is studied in the process $ϕ\rightarrow K_S K_L \rightarrowπ^+π^-π^+π^-$, 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 violation effects, which may be justified in a quantum gravity framework. The analysed data sample was collected with the KLOE detector at DA$Φ$NE, the Frascati $ϕ$-factory, and corresponds to an integrated luminosity of about 1.7 fb$^{-1}$, i.e. to about $1.7 \times 10^9$ $ϕ\rightarrow K_S K_L$ decays produced. From the fit of the observed $Δt$ distribution, being $Δt$ the difference of the kaon decay times, the decoherence and CPT violation parameters of various phenomenological models are measured with a largely improved accuracy with respect to previous analyses. The results are consistent with no deviation from quantum mechanics and CPT symmetry, while for some parameters the precision reaches the interesting level at which -- in the most optimistic scenarios -- quantum gravity effects might show up. They provide the most stringent limits up to date on the considered models.

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arXiv2021

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

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

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arXiv2020

Search for the $η$ mesic $^3$He in the $pd\rightarrow d p π^{0}$ reaction with the WASA-at-COSY facility

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

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arXiv2020

Isoscalar Single-Pion Production in the Region of Roper and $d^*(2380)$ Resonances

Exclusive measurements of the quasi-free $pn \to ppπ^-$ and $pp \to ppπ^0$ 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 $Δ(1232)$, $N^*(1440)$ 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 $Δ$ resonance in the isoscalar $(Nπ)_{I=0}$ invariant-mass spectrum. No evidence for a decay of the dibaryon resonance $d^*(2380)$ into the isoscalar $(NNπ)_{I=0}$ channel is found. An upper limit of 90 $μ$b (90 $\%$ C.L.) corresponding to a branching ratio of 5 $\%$ has been deduced.

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arXiv2020

Differential Cross Sections for Neutron-Proton Scattering in the Region of the $d^*(2380)$ Dibaryon Resonance

Differential cross sections have been extracted from exclusive and kinematically complete high-statistics measurements of quasifree polarized $\vec{n}p$ scattering performed in the energy region of the $d^*(2380)$ dibaryon resonance covering the the range of beam energies $T_n$ = 0.98 - 1.29 GeV ($\sqrt s$ = 2.32 - 2.44 GeV). The experiment was carried out with the WASA-at-COSY setup having a polarized deuteron beam impinged on the hydrogen pellet target and utilizing the quasifree process $dp \to np + p_{spectator}$. That way the $np$ differential cross section $σ(Θ)$ was measured over a large angular range. The obtained angular distributions complement the corresponding analyzing power $A_y(Θ)$ measurements published previously. A SAID partial-wave analysis incorporating the new data strengthens the finding of a resonance pole in the coupled $^3D_3 - ^3G_3$ waves.

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arXiv2020

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

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

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arXiv2020

Search for eta mesic 3He with the WASA-at-COSY facility in the pd-> 3He 2gamma and pd-> 3He 6gamma reactions

We report on the experimental search for the bound state of an $η$ meson and $^{3}\hspace{-0.03cm}\mbox{He}$ nucleus performed using the WASA-at-COSY detector setup. In order to search for the $η$-mesic nucleus decay, the $pd\rightarrow$ $^{3}\hspace{-0.03cm}\mbox{He} 2γ$ and $pd\rightarrow$ $^{3}\hspace{-0.03cm}\mbox{He} 6γ$ channels have been analysed. These reactions manifest the direct decay of $η$ 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-$η$ nucleus width $Γ$ 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 $η$-mesic $^{3}\hspace{-0.03cm}\mbox{He}$ nucleus formation followed by the $η$ meson decay which varies between $2$ nb and $15$ nb depending on possible bound state parameters.

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arXiv2019

Study of Three-Nucleon Dynamics in the dp breakup collisions using the WASA detector

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.

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arXiv2018

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

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

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arXiv2018

On the Production of an Isotensor Dibaryon in the $pp \to ppπ^+π^-$ Reaction

Exclusive measurements of the quasi-free $pp \to ppπ^+π^-$ 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 $Δ(1232)Δ(1232)$ 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 $ΔN$ 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.

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arXiv2018

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

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

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