arXiv subjects

B. Lorentz

Publications and source records attributed to B. Lorentz.

At least 37 records · Page 2Linked to original sources

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.

hep-ex↗

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.

nucl-ex↗

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.

nucl-ex↗

arXiv2019

Feasibility Study for an EDM Storage Ring

This project exploits charged particles confined as a storage ring beam (proton, deuteron, possibly $^3$He) to search for an intrinsic electric dipole moment (EDM, $\vec d$) aligned along the particle spin axis. Statistical sensitivities can approach $10^{-29}$~e$\cdot$cm. The challenge will be to reduce systematic errors to similar levels. The ring will be adjusted to preserve the spin polarization, initially parallel to the particle velocity, for times in excess of 15 minutes. Large radial electric fields, acting through the EDM, will rotate the polarization ($\vec d \times\vec E$). The slow rise in the vertical polarization component, detected through scattering from a target, signals the EDM. The project strategy is outlined. It foresees a step-wise plan, starting with ongoing COSY activities that demonstrate technical feasibility. Achievements to date include reduced polarization measurement errors, long horizontal-plane polarization lifetimes, and control of the polarization direction through feedback from the scattering measurements. The project continues with a proof-of-capability measurement (precursor experiment; first direct deuteron EDM measurement), an intermediate prototype ring (proof-of-principle; demonstrator for key technologies), and finally the high precision electric-field storage ring.

physics.acc-ph↗

arXiv2018

Resonance-like coherent production of a pion pair in the reaction $pd \rightarrow pdππ$ in the GeV region

The reaction $p + d \rightarrow p + d + X$ was studied at 0.8-2.0 GeV proton beam energies with the ANKE magnetic spectrometer at the COSY synchrotron storage ring. The proton-deuteron pairs emerging with high momenta, 0.6-1.8 GeV/$c$, were detected at small angles with respect to the proton beam. Distribution over the reaction missing mass $M_x$ reveals a local enhancement near the threshold of the pion pair production specific for the so-called ABC effect. The enhancement has a structure of a narrow bump placed above a smooth continuum. The invariant mass of the $dππ$ system in this enhancement region exhibits a resonance-like peak at $M_{dππ} \approx 2.36$ GeV/$c^2$ with the width $Γ\approx 0.10$ GeV/$c^2$. A possible interpretation of these features is discussed.

nucl-ex↗

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.

nucl-ex↗

arXiv2018

Measurement of the analyzing powers in pd elastic and pn quasi-elastic scattering at small angles

The analyzing powers in proton-deuteron elastic and proton-neutron quasi-elastic scattering have been measured at small angles using a polarized proton beam at the COSY storage ring incident on an unpolarized deuterium target. The data were taken at 796MeV and five higher energies from 1600MeV to 2400MeV. The analyzing power in pd elastic scattering was studied by detecting the low energy recoil deuteron in telescopes placed symmetrically in the COSY plane to the left and right of the beam whereas for pn quasi-elastic scattering a low energy proton was registered in one of the telescopes in coincidence with a fast scattered proton measured in the ANKE magnetic spectrometer. Though the experiment explores new domains, the results are consistent with the limited published information.

nucl-ex↗

arXiv2018

An Isotensor Dibaryon in the $pp \to ppπ^+π^-$ Reaction?

Exclusive measurements of the quasi-free $pp \to ppπ^+π^-$ 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.

nucl-ex↗

arXiv2018

Experimental and theoretical study of deuteron-proton elastic scattering for proton kinetic energies between $T_p = 882.2\;\textrm{MeV}$ and $T_p = 918.3\;\textrm{MeV}$

New precise unpolarised differential cross sections of deuteron-proton elastic scattering have been measured at 16 different deuteron beam momenta between $p_d = 3120.17\;\textrm{MeV}/c$ and $p_d =3204.16\;\textrm{MeV}/c$ at the COoler SYnchrotron COSY of the Forschungszentrum Jülich. The data, which were taken using the magnetic spectrometer ANKE, cover the equivalent range in proton kinetic energies from $T_p = 882.2\;\textrm{MeV}$ to $T_p = 918.3\;\textrm{MeV}$. The experimental results are analysed theoretically using the Glauber diffraction model with accurate nucleon-nucleon input. The theoretical cross section at $T_p = 900\;\textrm{MeV}$ agrees very well with the experimental one at low momentum transfers $|t| <0.2\;(\textrm{GeV}/c)^2$.

nucl-ex↗

arXiv2018

Backward single-pion production in the $\boldsymbol{pd\rightarrow {}^3\textrm{He}\,π^0}$ reaction with WASA-at-COSY

New data on the production of single neutral pions in the $pd\rightarrow{}^3\textrm{He}\,π^0$ 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.

nucl-ex↗

arXiv2018

Deuteron analysing powers in deuteron-proton elastic scattering at 1.2 and 2.27 GeV

The vector and tensor analysing powers in deuteron-proton elastic scattering have been measured in the forward hemisphere at deuteron kinetic energies of 1.2 GeV and 2.27 GeV using the ANKE spectrometer at the COSY storage ring. The results are compared with other experimental data and with predictions made within the framework of Glauber multiple scattering theory.

nucl-ex↗

arXiv2018

Phase Measurement for Driven Spin Oscillations in a Storage Ring

This paper reports the first simultaneous measurement of the horizontal and vertical components of the polarization vector in a storage ring under the influence of a radio frequency (rf) solenoid. The experiments were performed at the Cooler Synchrotron COSY in Jülich using a vector polarized, bunched $0.97\,\textrm{GeV/c}$ deuteron beam. Using the new spin feedback system, we set the initial phase difference between the solenoid field and the precession of the polarization vector to a predefined value. The feedback system was then switched off, allowing the phase difference to change over time, and the solenoid was switched on to rotate the polarization vector. We observed an oscillation of the vertical polarization component and the phase difference. The oscillations can be described using an analytical model. The results of this experiment also apply to other rf devices with horizontal magnetic fields, such as Wien filters. The precise manipulation of particle spins in storage rings is a prerequisite for measuring the electric dipole moment (EDM) of charged particles.

physics.acc-ph↗

arXiv2018

Importance of d-wave contributions in the charge symmetry breaking reaction $dd \to {}^4\text{He}π^0$

This letter reports a first quantitative analysis of the contribution of higher partial waves in the charge symmetry breaking reaction $dd \to {}^4\text{He}π^0$ using the WASA-at-COSY detector setup at an excess energy of $Q = 60$ MeV. The determined differential cross section can be parametrized as $\text{d}σ/\text{d}Ω= a + b\cos^{2}θ^*$, where $θ^*$ is the production angle of the pion in the center-of-mass coordinate system, and the results for the parameters are $a = \left(1.55 \pm 0.46 (\text{stat}) ^{+0.32}_{-0.8} (\text{syst}) \right)$ 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 $Δ$ isobar to the $dd \to {}^4\text{He}π^0$ reaction and is, therefore, crucial for a quantitative understanding of quark mass effects in nuclear production reactions.

nucl-ex↗

arXiv2018

Search for $C$ violation in the decay $η\rightarrowπ^0+e^++e^-$ with WASA-at-COSY

We report on the investigation of the rare decay $η\rightarrowπ^0+\text{e}^++\text{e}^-$ 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 Jülich, Germany. In total $3\times10^7$ events of the reaction $\text{p}+\text{d}\rightarrow{^3\text{He}}+η$ have been recorded at an excess energy of $Q = 59.8\,\textrm{MeV}$. Based on this data set the $C$ parity violating decay $η\rightarrowπ^0+γ^*\rightarrowπ^0+\textrm{e}^++\textrm{e}^-$ via a single-photon intermediate state has been searched for, resulting in new upper limits of $Γ\left(η\rightarrowπ^0+\textrm{e}^++\textrm{e}^-\right)/ Γ\left(η\rightarrowπ^++π^-+π^0\right) < 3.28\times10^{-5}$ and $Γ\left(η\rightarrowπ^0+\textrm{e}^++\textrm{e}^-\right)/ Γ\left(η\rightarrow\textrm{all}\right) < 7.5\times10^{-6}\ (\textrm{CL} = 90\,\%)$, respectively.

hep-ex↗

arXiv2018

Total and differential cross sections of $η$-production in proton-deuteron fusion for excess energies between $Q_η=13\;\text{MeV}$ and $Q_η=81\;\text{MeV}$

New data on both total and differential cross sections of the production of $η$ mesons in proton-deuteron fusion to ${}^3\text{He}\,η$ in the excess energy region $13.6\;\text{MeV}\leq Q_η\leq 80.9\;\text{MeV}$ 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 $p_p = 1.60\;\text{GeV}/c$ and $p_p = 1.74\;\text{GeV}/c$. While significant structure of the total cross section is observed in the energy region $20\;\text{MeV}\lesssim Q_η\lesssim 60\;\text{MeV}$, a previously reported sharp variation around $Q_η\approx 50\;\text{MeV}$ 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.

nucl-ex↗

arXiv2017

Spin dependence of η meson production in proton-proton collisions close to threshold

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} ppη 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 η meson.

nucl-ex↗

arXiv2017

The connection between zero chromaticity and long in-plane polarization lifetime in a magnetic storage ring

In this paper, we demonstrate the connection between a magnetic storage ring with additional sextupole fields set so that the x and y chromaticities vanish and the maximizing of the lifetime of in-plane polarization (IPP) for a 0.97-GeV/c deuteron beam. The IPP magnitude was measured by continuously monitoring the down-up scattering asymmetry (sensitive to sideways polarization) in an in-beam, carbon-target polarimeter and unfolding the precession of the IPP due to the magnetic anomaly of the deuteron. The optimum operating conditions for a long IPP lifetime were made by scanning the field of the storage ring sextupole magnet families while observing the rate of IPP loss during storage of the beam. The beam was bunched and electron cooled. The IPP losses appear to arise from the change of the orbit circumference, and consequently the particle speed and spin tune, due to the transverse betatron oscillations of individual particles in the beam. The effects of these changes are canceled by an appropriate sextupole field setting.

physics.acc-ph↗

arXiv2017

Phase locking the spin precession in a storage ring

This letter reports the successful use of feedback from a spin polarization measurement to the revolution frequency of a 0.97 GeV/$c$ bunched and polarized deuteron beam in the Cooler Synchrotron (COSY) storage ring in order to control both the precession rate ($\approx 121$ kHz) and the phase of the horizontal polarization component. Real time synchronization with a radio frequency (rf) solenoid made possible the rotation of the polarization out of the horizontal plane, yielding a demonstration of the feedback method to manipulate the polarization. In particular, the rotation rate shows a sinusoidal function of the horizontal polarization phase (relative to the rf solenoid), which was controlled to within a one standard deviation range of $σ= 0.21$ rad. The minimum possible adjustment was 3.7 mHz out of a revolution frequency of 753 kHz, which changes the precession rate by 26 mrad/s. Such a capability meets a requirement for the use of storage rings to look for an intrinsic electric dipole moment of charged particles.

physics.acc-ph↗