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Special issue, XLVI Extraordinary Congress of Polish Physicists, Warsaw, Poland, October 16–18, 2020, Understanding nuclear interactions is the basis for describing nuclear systems, their structure and reac-tions. Studies of reactions in the simplest systems consisting of a few nucleons provide stringent tests for nuclear interaction models. The data collected by our group over the last 30 years are crucial for un-derstanding the few-nucleon system dynamics. Measurements of observables (cross-section, vector and tensor analyzing powers) for the deuteron breakup in collision with a proton/deuteron were conducted at SIN/PSI (Switzerland), KVI (the Netherlands), FZ-Jülich (Germany) and CCB IFJ PAN Kraków (Poland), and provided data covering a wide range of the reaction phase-space. Main conclusions fol-lowing from our research and its current status are presented.

W. Parol, A. Kozela, K. Bodek, A. Deltuva, M. Eslami-Kalantari, J. Golak, N. Kalantar-Nayestanaki, G. Khatri, St. Kistryn, J. Kubo´s, P. Kulessa, A. Magiera, H. Mardanpour, J. G. Messchendorp, I. Mazumdar, R. Skibiński, I. Skwira-Chalot, A. Ramazani-Moghaddam-Arani, D. Rozpędzik, H. Witała, B. Włoch, A. Wrońska, Differential cross sections for the deuteron breakup 1H(d, pp)n reaction were measured for a large set of 243 geometrical configurations at the beam energy of 80 MeV/nucleon. The cross-section data are normalized by the luminosity factor obtained on the basis of a simultaneous measurement of the elastic-scattering channel and the existing cross-section data for this process. The results are compared with the theoretical calculations modeling nuclear interactions with and without taking into account the three-nucleon force (3NF) and the Coulomb interaction. In the validated region of the phase space, both the Coulomb force and 3NF play an important role in providing a good description of the data. There are also regions in which description improvements due to the inclusion of 3NF are insufficient.

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 sections have been extracted from exclusive and kinematically complete high-statistics measurements of quasifree polarized np scattering performed in the energy region of the d*(2380) dibaryon resonance covering the range of beam energies Tn=0.98−1.29 GeV (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→np+pspectator. In this way the np differential cross section σ(Θ) was measured over a large angular range. The obtained angular distributions complement the corresponding analyzing power Ay(Θ) measurements published previously. A SAID partial-wave analysis incorporating the new data strengthens the finding of a resonance pole in the coupled D33-G33 waves.

Pozostali autory: I. Ciepał, K. Bodek, N. Kalantar-Nayestanaki, G. Khatri, St. Kistryn, A. Kozela, J. Kubo´s, P. Kulessa, A. Magiera, J. Messchendorp, I. Mazumdar, W. Parol, R. Ramazani-Sharifabadi, D. Rozpedzik, I. Skwira-Chalot, B. Włoch, A. Wrońska, J. Zejma, Four nucleon scattering at intermediate energies provides unique opportunities to study effects of the two key ingredients of the nuclear dynamics, the nucleon-nucleon P-wave (NNP-wave) and the three-nucleon force (3NF). This is possible only with systematic and precise data, in conjunction with exact theoretical calculations. Using the BINA detector at KVI Groningen, the Netherlands, a rich set of differential cross section of the 2H(d, dp)n breakup reaction at 160 MeV deuteron beam energy has been measured. Besides the three-body breakup, also cross sections of the 2H(d, 3He)n proton transfer reaction have been obtained. The data are compared to the recent calculations for the threecluster breakup.

The~Space Star Anomaly in proton-deuteron breakup cross-section occurs at energies of about 10~MeV. Data for higher energies are sparse. Therefore, a~systematic scan over star configurations in the~range of intermediate energies between 50 and 100 MeV/nucleon is carried out on the~basis of data collected with the~large acceptance BINA detector. The~preliminary cross section results for forward star configurations at 80 MeV/nucleon slightly surpass the~theoretical calculations, but the~systematic uncertainties are still under study. Also, a~new variable describing rotation of star configurations is proposed.

cd autorów: B. Włoch, K. Bodek, I Ciepał, M. Eslami-Kalantari, J. Golak, N. Kalantar-Nayestanaki, G. Khatri, St. Kistryn, A. Kozela, J. Kuboś, P. Kulessa, A. Magiera, H. Mardanpour, J. Messchendorp, I. Mazumdar, W. Parol, A. Ramazani-Moghaddam-Arani, D. Rozpędzik, R. Skibiński, I. Skwira-Chalot, H. Witała, A Wrońska, J. Zejma, Deuteron breakup reactions are basic laboratories for testing nuclear force models. Recent improvements in the data analysis allow for direct identification of neutrons in the BINA detection setup. This opens up the opportunity to study new aspects of few-nucleon system dynamics like charge dependence of nuclear force or Coulomb interaction. In this paper we determine regions along the kinematical curves where differential cross section of deuteron-proton breakup reactions can be measured by the proton-neutron and proton-proton coincidences simultaneously. This is particularly useful for validation of the neutron detection technique.

An experiment to investigate the \(^{1}\)H(d, pp)n breakup reaction using a deuteron beam of 300, 340, 380 and 400 MeV and the WASA detector has been performed at the Cooler Synchrotron COSY-Julich. As a first step the data collected at the beam energy of 340 MeV are analysed, with a focus on the proton-proton coincidences registered in the Forward Detector. The differential cross section is determined for 189 configurations on a dense angular grid defined by the emission angles of the two outgoing protons: two polar angles \(\theta _1\) and \(\theta _2\) (in the range between 5\(^{\circ }\) and 15\(^{\circ }\) with the step size of 2\(^\circ \)) and the relative azimuthal angle \(\varphi _{12}\) (in the range from 20\(^\circ \) to 180\(^\circ \), with the step size of 20\(^\circ \)).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.

Star Anomaly is one of the most intriguing and unsolved discrepancies between theoretical calculations and experimental data observed in the domain of few-nucleon systems at low energies. Previous and upcoming measurements of the breakup reaction with the use of the BINA detector enable systematic studies of the Star configurations at intermediate energies. A dedicated simulation was developed to study feasibility of registering such events with the required accuracy and to support the future data analysis. An additional rotation angle β has been introduced to parametrise the Star configurations. First results concerning the acceptance of certain segments of BINA for registering the Star configurations are presented.

The 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 the WASA detector at COSY-Jülich. The set of proton-proton coincidences registered at the Forward Detector has been analyzed on a 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 a three-nucleon force or the Coulomb interaction or carried out in a relativistic regime.

We report on the search for the rare decay η → π 0 e + e − which is of interest to study C violation in the electromagnetic interaction which would indicate 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 Julich, Germany. In total 3 × 10 7 events of the reaction p d → 3 He η have been recorded at an excess energy of Q = 59.8 MeV . Based on this data set the C parity violating decay η → π 0 γ ⁎ → π 0 e + e − via a single-photon intermediate state has been searched for, resulting in new upper limits of Γ ( η → π 0 e + e − ) / Γ ( η → π + π − π 0 ) 3.28 × 10 − 5 and Γ ( η → π 0 e + e − ) / Γ ( η → all ) 7.5 × 10 − 6 ( CL = 90 % ), respectively.

The search for He 4 - η bound states was performed with the WASA-at-COSY facility via the measurement of the excitation function for the d d → He 3 n π 0 and d d → He 3 p π − processes. The deuteron beam momentum was varied continuously between 2.127 GeV/c and 2.422 GeV/c, corresponding to the excess energy for the d d → He 4 η reaction ranging from Q = − 70 MeV to Q = 30 MeV . The luminosity was determined based on the d d → He 3 n reaction and the quasi-free proton–proton scattering via d d → p p n s p e c t a t o r n s p e c t a t o r 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 d d → ( He 4 - η ) b o u n d → He 3 n π 0 and d d → ( He 4 - η ) b o u n d → He 3 p π − processes were determined taking into account the isospin relation between the both of the considered channels. The results of the analysis depend on the assumptions of the N ⁎ (1535) momentum distribution in the anticipated mesic- He 4 . Assuming, as in the previous works, that this is identical with the distribution of nucleons bound with 20 MeV in He 4 , 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 n π 0 and p π − channels, respectively. However, based on the recent theoretical findings of the N ⁎ (1535) momentum distribution in the N ⁎ - He 3 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 n π 0 and p π − channels respectively.

A set of differential cross section of the three-body $^{2}\mathrm{H}(d,dp)n$ breakup reaction at 160-MeV deuteron beam energy is presented for 147 configurations covering a wide kinematical region around quasifree scattering. The experiment was performed at KVI in Groningen, the Netherlands, using the BINA detector. The cross-section data have been normalized to the $^{2}\mathrm{H}(d,d)^{2}\mathrm{H}$ elastic-scattering cross section. The data are compared to the results of recent single-scattering approximation (SSA) calculations for three-cluster breakup in deuteron-deuteron collisions. This comparison shows that SSA provides the correct order of magnitude of the cross sections. The studied energy is probably too low to meet the SSA assumptions which prevents better accuracy of the description.

A rich set of differential cross section of the three-body $$^{2}$$ H(d,dp)n breakup reaction at 160 MeV deuteron beam energy has been measured over a large range of the available phase space. The experiment was performed at KVI in Groningen, the Netherlands, using the BINA detector. The cross-section data for the breakup reaction have been normalized to the simultaneously measured $$^{2}$$ H(d,d) $$^{2}$$ H elastic scattering cross section. The breakup cross sections obtained for 147 kinematically complete configurations near the quasi-free scattering kinematics are compared to the recent approximate calculations for the three-cluster breakup in deuteron–deuteron collisions. The cross sections for 294 kinematic configurations of the quasi-free scattering regime, for which no theoretical calculations exist, are also presented. Besides the three-body breakup, semi-inclusive energy distributions for the four-body $$^{2}$$ H(d,pp)nn breakup are reported.

The quasifree pp → ppπ+π− reaction has been measured by means of pd collisions at Tp = 1.2 GeV using the WASA detector setup at COSY enabling exclusive and kinematically complete measurements. Total and differential cross sections have been extracted for the energy region Tp = 1.08–1.36 GeV (√s = 2.35–2.46 GeV) covering thus the regions of N∗(1440) and (1232)(1232) resonance excitations. Calculations describing these excitations by t-channel meson exchange as well as isospin relations based on the pp → ppπ0π0 data underpredict substantially the measured total cross section. The calculations are also at variance with specific experimental differential cross sections. An isotensor 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 [Phys. Rev. Lett. 13, 815 (1964)] and more recently calculated by A. Gal and H. Garcilazo [Nucl. Phys. A 928, 73 (2014)].

Differential cross sections of $^{2}$H(d, d)d elastic scattering and proton transfer $^{2}$H(d, $^{3}$He)n reactions at 160 MeV beam energy have been obtained. They have been normalized relative to the existing cross-section data for the $^{2}$H(d, d)d elastic scattering at 180 and 130 MeV, benefiting from the negligible energy dependence of this observable at certain range of the four momentum transfer. The experiment was performed at KVI in Groningen, the Netherlands using the BINA detector. The elastic scattering data are compared to theoretical predictions based on the lowest-order term in the Neumann series expansion for four-nucleon transition operators. The calculations underpredict the data. The data presented in this paper can be used to validate the future theoretical findings.

Various theoretical calculations based on QCD or hadronic interactions predict that in addition to the recently observed dibaryon resonance d⁎(2380) with I(JP)=0(3+) there should also exist a dibaryon resonance with mirrored quantum numbers I(JP)=3(0+). We report here on a search for such a NN-decoupled state in data on the pp→ppπ+π+π−π− 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., This work has been supported by DFG (CL 214/3-1), STFC (ST/L00478X/1) and by the Polish National Science Center through grants Nos. DEC-2013/11/N/ST2/04152 and 2011/03/B/ST2/01847

We report on the experimental search for the bound state of an eta meson and He-3 nucleus performed using the WASA-at-COSY detector setup. In order to search for the eta-mesic nucleus decay, the pd ...

New data on the production of single neutral pions in the $ pd\rightarrow {}^{3}\mathrm{He} \pi^{0}$ reaction are presented. For fifteen proton beam momenta between $ p_{p}=1.60$ GeV/c and $ p_{p}=1.74$ 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.

Exclusive measurements of the quasifree pp→ppπ^{+}π^{-} 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 Δ(1232)Δ(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 ΔN dibaryon resonance with I(J^{P})=2(1^{+}) produced associatedly with a pion is able to overcome these deficiencies.

This letter reports a first quantitative analysis of the contribution of higher partial waves in the charge symmetry breaking reaction dd→4Heπ0 using the WASA-at-COSY detector setup at an excess energy of Q=60MeV. The determined differential cross section can be parametrized as dσ/dΩ=a+bcos2⁡θ⁎, where θ⁎ is the production angle of the pion in the center-of-mass coordinate system, and the results for the parameters are a=(1.55±0.46(stat)+0.32−0.8(syst))pb/sr and b=(13.1±2.1(stat)−2.7+1.0(syst))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 Δ isobar to the dd→4Heπ0 reaction and is, therefore, crucial for a quantitative understanding of quark mass effects in nuclear production reactions.

Exclusive measurements of the quasifree pp→ppπ^{+}π^{-} 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 Δ(1232)Δ(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 ΔN dibaryon resonance with I(J^{P})=2(1^{+}) produced associatedly with a pion is able to overcome these deficiencies.

New data on both total and differential cross sections of the production of η mesons in proton–deuteron fusion to He3η in the excess energy region 13.6MeV≤Qη≤80.9MeV are presented. These data have been obtained with the WASA-at-COSY detector setup located at the Forschungszentrum Jülich, using a proton beam at 15 different beam momenta between pp=1.60GeV/c and pp=1.74GeV/c. While significant structure of the total cross section is observed in the energy region 20MeV≲Qη≲60MeV, a previously reported sharp variation around Qη≈50MeV cannot be confirmed. Angular distributions show the typical forward-peaking that was noted earlier. For the first time, it is possible to study the development of these angular distributions with rising excess energy over a wide interval.

An experiment to investigate the ^{1}H(d,pp)n breakup reaction using a deuteron beam of 300, 340, 380 and 400 MeV and the WASA detector has been performed at the Cooler Synchrotron COSY-Jülich. As a first step, the data collected at the beam energy of 340 MeV are analysed, with a focus on the proton–proton coincidences registered in the Forward Detector. Elastically scattered deuterons are used for precise determination of the luminosity. The main steps of the analysis, including energy calibration, particle identification (PID) and efficiency studies, and their impact on the final accuracy of the result, are discussed.

Proton-deuteron breakup reaction can serve as a tool to test state-of- the-art descriptions of nuclear interactions. At intermediate energies, below the threshold for pion production, comparison of the data with exact theoretical calculations is possible and subtle effects of the dynamics beyond the pairwise nucleon-nucleon interaction, namely the three-nucleon force (3NF), are significant. Beside 3NF, Coulomb interaction or relativistic effects are also important to precisely describe the differential cross section of the breakup reaction. The data analysis and preliminary results of the measurement of proton-induced deuteron breakup at the Cyclotron Center Bronowice, Institute of Nuclear Physics, Polish Academy of Sciences in Krakow are presented.

A set of differential cross-section data of the 1 H(d, pp)n breakup reaction at 130 MeV deuteron beam energy has been measured in the domain of very forward polar angles with the use of the Germanium Wall detector at the Forschungszentrum Julich. The data obtained for over 1000 kinematical points (112 geometries) are compared with the theoretical predictions based on various models of the three-nucleon (3N) dynamics. They comprise: the realistic nucleon-nucleon potentials alone or combined with the three-nucleon force (3NF), the coupled-channel calculations with the explicit treatment of the Δ-isobar excitation and finally, the potentials derived from chiral perturbation theory. In the part of the phase space studied, the Coulomb interaction between protons has a strong impact on the differential cross section of the breakup reaction. The strongest Coulomb effects are found in regions where the relative energy of the two protons is the smallest. In these regions the data are well reproduced exclusively by calculations which include the electromagnetic repulsion between protons. In spite of the dominance of the Coulomb force in the phase space studied, the contribution of 3NF effects is also observed.

A large set of cross-section data for the H-1 (d,pp)n breakup reaction was measured at 130 MeV deuteron beam energy with the Germanium Wall setup covering the range of very forward polar angles. In the investigated part of the phase-space, the dynamics is dominated by the Coulomb force influence. The data are compared with results of theoretical calculations based on the realistic Argonne V18 potential supplemented with the long-range electromagnetic component. The predictions also include the Urbana IX three nucleon force model. The cross-section data reveal seizable Coulomb force effects.

Charge symmetry breaking (CSB) observables are a suitable experimental tool to examine effects induced by quark masses on the nuclear level. Previous high precision data from TRIUMF and IUCF are cu ...

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 article belongs to the Topical Collection "30th anniversary of Few-Body Systems". This work was partially supported by Polish National Science Center from Grant DEC-2012/05/B/ST2/02556 and by the European Commission within the Seventh Framework Programme through IA-ENSAR (Contract No. RII3-CT-2010-262010)., Systems composed of three nucleons have been a subject of precise experimental studies for many years. Recently, the database of observables for the deuteron breakup in collision with protons has been significantly extended at intermediate energies. In this region the comparison with exact theoretical calculations is possible, while the sensitivity to various aspects of the interaction, in particular to the subtle effects of the dynamics beyond the pairwise nucleon–nucleon force, is significant. The Coulomb interaction and relativistic effects show also their influence on the observables of the breakup reaction. All these effects vary with energy and appear with different strength in certain observables and phase-space regions, which calls for systematic investigations of a possibly rich set of observables determined in a wide range of energies. Moreover, a systematic comparison with theoretical predictions performed in coordinates related to the system dynamics in a possibly direct way is of importance. The examples of existing experimental data for the breakup reaction are briefly presented and the amenability of a set of invariant coordinates for that type of analysis is discussed., NCN, European Commission within the Seventh Framework Programme

Thisworkwas partially supported by PolishNational Science Center fromGrant DEC-2012/05/B/ST2/02556 and by the European Commission within the Seventh Framework Programme through IA-ENSAR (Contract No. RII3-CT-2010-262010)., Until recently, all calculations of breakup observables were carried out in a non-relativistic regime. The relativistic treatment of the breakup reaction in 3 N system is quite a new achievement. The detailed study of various aspects of few-nucleon system dynamics in medium energy region, with a particular emphasis on investigation of relativistic effects and their interplay with three nucleon force (3NF) becomes feasible with increasing available energy in the three nucleon system. Therefore an experiment to investigate the 1H(d, pp)n breakup cross section using a deuteron beam of 300, 340, 380 and 400 MeV and the WASA detector has been performed at COSY-Jülich. The almost 4π geometry of the WASA detector gives an unique possibility to study variety of kinematic configurations, which reveal different sensitivity to aspects of dynamics of the three nucleon system. The main steps of the analysis, including energy calibration, PID, normalization and efficiency studies, and their impact on the final accuracy of the result, are discussed., NCN, European Commission within the Seventh Framework Programme through IA-ENSAR

We report on preliminary results of the first measurement of elastic scattering of protons from deuterons and proton induced deuteron breakup at proton beam energy of 108 MeV conducted at new Cyclotron Center Bronowice IFJ PAN in Krakow. The experiment is aimed at precise determination of the differential cross section for extensive set of kinematical configurations in a wide range of angular acceptance. In the first data taking run the average statistical per-point accuracy of about 5% has been reached.

A measurement of the differential cross sections for the proton-deuteron elastic scattering and the deuteron breakup in collision with a proton was carried out at Cyclotron Center Bronowice using the BINA detection system. The very preliminary analysis of the experimental data taken at three proton beam energies: 108, 135 and 160 MeV is presented.

Precise and large sets of cross section, vector $A_{x}, A_{y}$ and tensor$ A_{xx}, A_{xy}, A_{yy}$ analyzing power data for the $^{1}H\left ( d, pp \right )n$ breakup reactions were measured at 100 and 130 MeV deuteron beam energies with the SALAD and BINA detectors at KVI and the Germanium Wall setup at FZ-Jülich. Results are compared with various theoretical approaches which model the three-nucleon system dynamics. The cross section data reveal a sizable three-nucleon force (3NF) and Coulomb force influence. In case of the analyzing powers very low sensitivity to these effects was found and the data are well describe by 2N models only. For $A_{xy}$ at 130 MeV, serious disagreements were observed when 3NF models are included in the calculations.

Experiments devoted to study subtle ingredients of nuclear dynamics were carried out at KVI in Groningen with the use of the $^{1}H\left ( d,pp \right )n$ breakup reaction at the deuteron beam energy of 80 MeV/nucleon. The aim of the work is to determine the breakup cross sections and confront them with the set of modern calculations which model forces acting between nucleons. Elastic scattering process was also measured for the purpose of the cross section normalization. This paper presents preliminary results of the data analysis including geometry cross check, energy calibration, particles identification and sample distributions of the unnormalized breakup cross sections.

The WASA-at-COSY experiment has collected $3\ifmmode\times\else\texttimes\fi{}{10}^{7}$ events with $\ensuremath{\eta}$ mesons produced via the reaction $pd\ensuremath{\rightarrow}^{3}\mathrm{He}\phantom{\rule{0.16em}{0ex}}\ensuremath{\eta}$ at $\mathrm{T}=1.0\phantom{\rule{4pt}{0ex}}\mathrm{GeV}$. Using this data set, we evaluate the branching ratios of the decays $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\gamma}$, $\ensuremath{\eta}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}\ensuremath{\gamma}$, $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{e}^{+}{e}^{\ensuremath{-}}$, and $\ensuremath{\eta}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}{e}^{+}{e}^{\ensuremath{-}}$. The branching ratios are normalized to the $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ decay. In addition an upper limit on a $CP$-violating asymmetry in $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{e}^{+}{e}^{\ensuremath{-}}$ is extracted.

The experiment was performed at CCB IFJ PAN in Kraków with the use of the BINA detector. The experimental program and data analysis of proton-induced deuteron breakup reaction at 108 MeV are presented.