arXiv subjects

M. Mielke

Publications and source records attributed to M. Mielke.

At least 19 recordsLinked to original sources

arXiv2020

Total and differential cross sections of the $\boldsymbol{dp\to {}^3}\textrm{He}\,\boldsymbolη$ reaction at excess energies between 1 and 15 MeV

New high precision total and differential cross sections are reported for the $dp\to {}^3\textrm{He}\,η$ reaction close to threshold. The measurements were performed using the magnetic spectrometer ANKE, which is an internal fixed target facility at the COSY cooler synchrotron. The data were taken for deuteron beam momenta between $3.14641~\textrm{GeV}/c$ and $3.20416~\textrm{GeV}/c$, which corresponds to the range in excess energy $Q$ for this reaction between $1.14~\textrm{MeV}$ and $15.01~\textrm{MeV}$. The normalization was established through the measurement in parallel of deuteron-proton elastic scattering and this was checked through the study of the $dp\to {}^3\textrm{He}\,π^0$ reaction. The previously indicated possible change of sign of the slope of the differential cross sections near the production threshold, which could be explained by a rapid variation of the $s$- and $p$-wave interference term, is not confirmed by the new data. The energy dependence of the total cross section and the $90^{\circ}$ slope parameter are well explained by describing the final state interaction in terms of a complex Jost function and the results are significant in the discussion of $η$-mesic nuclei. In combination with recently published WASA-at-COSY data [P. Adlarson $et\, al.$, Phys. Lett. B 782, 297 (2018)], a smooth variation of the slope parameter is achieved up to an excess energy of $80.9~\textrm{MeV}$.

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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 $|t| <0.2\;(\textrm{GeV}/c)^2$.

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arXiv2016

Measurement of spin observables in the quasi-free np-> {pp}_s pi- reaction at 353 MeV

The transverse spin correlations A_{x,x} and A_{y,y} have been measured in the pol{d} pol{p} -> p_spec {pp}_s pi- reaction at COSY-ANKE at 353 MeV per nucleon. Here {pp}_s denotes a proton-proton pair with low excitation energy, which is dominantly in the 1S0 state. By measuring three protons in the final state it was possible to extract events where there was a spectator proton p_spec so that the reaction could be interpreted in terms of quasi-free pol{n} pol{p} -> {pp}_s pi-. The proton analyzing power in this reaction was also deduced from this data set by averaging over the polarization of the deuteron beam. The values of A_y^p were shown to be consistent with a refined analysis of our earlier results obtained with a polarized proton incident on a deuterium target. Taking these data in combination with our earlier measurements of the differential cross sections and analyzing powers in the pol{p} p -> {pp}_s pi^0 reaction, a more robust partial wave decomposition was achieved. Three different acceptable solutions were found and the only way of resolving this ambiguity without further theoretical input would be through a measurement of the mixed spin-correlation parameter A_{x,z}.

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arXiv2016

Coherent pion production in proton-deuteron collisions

Values of the proton analysing power in the $pd\to{}^{3}\textrm{He}\,π^0/^{3}\textrm{H}\,π^+$ reactions at 350-360~MeV per nucleon were obtained by using a polarised proton beam incident on a deuterium cluster-jet target and with a polarised deuteron beam incident on a target cell filled with polarised hydrogen. These results have a much larger angular coverage than existing data. First measurements are also presented of the deuteron vector analysing power and the deuteron-proton spin correlations. Data were also obtained on the deuteron-proton spin correlation and proton analysing power at small angles at 600~MeV per nucleon, though the angular coverage at this energy was much more restricted even when using a deuteron beam. By combining the extrapolated values of the spin correlations to the forward or backward directions with published measurements of the deuteron tensor analysing powers, the relative phases between the two non-vanishing amplitudes were evaluated.

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arXiv2015

Toward polarized antiprotons: Machine development for spin-filtering experiments

The paper describes the commissioning of the experimental equipment and the machine studies required for the first spin-filtering experiment with protons at a beam kinetic energy of $49.3\,$MeV in COSY. The implementation of a low-$β$ insertion made it possible to achieve beam lifetimes of $τ_{\rm{b}}=8000\,$s in the presence of a dense polarized hydrogen storage-cell target of areal density $d_{\rm t}=(5.5\pm 0.2)\times 10^{13}\,\mathrm{atoms/cm^{2}}$. The developed techniques can be directly applied to antiproton machines and allow for the determination of the spin-dependent $\bar{p}p$ cross sections via spin filtering.

physics.acc-ph↗

arXiv2015

Analysing powers and spin correlations in deuteron-proton charge exchange at 726 MeV

The charge exchange of vector polarised deuterons on a polarised hydrogen target has been studied in a high statistics experiment at the COSY-ANKE facility at a deuteron beam energy of Td = 726 MeV. By selecting two fast protons at low relative energy E_{pp}, the measured analysing powers and spin correlations are sensitive to interference terms between specific neutron-proton charge-exchange amplitudes at a neutron kinetic energy of Tn ~ 1/2 Td =363 MeV. An impulse approximation calculation, which takes into account corrections due to the angular distribution in the diproton, describes reasonably the dependence of the data on both E_{pp} and the momentum transfer. This lends broad support to the current neutron-proton partial-wave solution that was used in the estimation.

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arXiv2014

Study of the $\vec{p}d \to n\{pp\}_{s}$ charge-exchange reaction using a polarised deuterium target

The vector and tensor analysing powers, $A_y$ and $A_{yy}$, of the $\vec{p}d \to n\{pp\}_{s}$ charge-exchange reaction have been measured at a beam energy of 600 MeV at the COSY-ANKE facility by using an unpolarised proton beam incident on an internal storage cell target filled with polarised deuterium gas. The low energy recoiling protons were measured in a pair of silicon tracking telescopes placed on either side of the target. Putting a cut of 3 MeV on the diproton excitation energy ensured that the two protons were dominantly in the $^{1}S_{0}$ state, here denoted by $\{pp\}_{s}$. The polarisation of the deuterium gas was established through measurements in parallel of proton-deuteron elastic scattering. By analysing events where both protons entered the same telescope, the charge-exchange reaction was measured for momentum transfers $q\geq 160$ MeV/$c$. These data provide a good continuation of the earlier results at $q\leq 140$ MeV/$c$ obtained with a polarised deuteron beam. They are also consistent with impulse approximation predictions with little sign evident for any modifications due to multiple scatterings.

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arXiv2014

Absence of spin dependence in the final state interaction of the d(pol) p --> 3He eta reaction

The deuteron tensor analysing power t_{20} of the d(pol) p --> 3He eta reaction has been measured at the COSY-ANKE facility in small steps in excess energy Q up to Q = 11 MeV. Despite the square of the production amplitude varying by over a factor of five through this range, t_{20} shows little or no energy dependence. This is evidence that the final state interaction causing the energy variation is not influenced by the spin configuration in the entrance channel. The weak angular dependence observed for t_{20} provides useful insight into the amplitude structure near threshold.

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arXiv2014

Isospin effects in the exclusive dp -> 3Heπ+π- reaction

The differential cross section for the exclusive dp -> 3Heπ+π- reaction has been measured with high resolution and large statistics over a large fraction of the backward 3He hemisphere at the excess energy 265 MeV using the COSY-ANKE magnetic spectrometer. Though the well-known ABC enhancement is observed in the π+π- spectrum, the differences detected between the π+3He and π-3He invariant-mass distributions show that there must be some isospin-one ππ production even at relatively low excess energies. The invariant-mass differences are modeled in terms of the sequential decay N*(1440) -> Delta(1232)π -> Nππ.

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arXiv2013

The production of K+K- pairs in proton-proton collisions below the phi meson threshold

The pp -> ppK+K- reaction was measured below the phi threshold at a beam energy of 2.568 GeV using the COSY-ANKE magnetic spectrometer. By assuming that the four-body phase space is distorted only by the product of two-body final state interactions, fits to a variety of one-dimensional distributions permit the evaluation of differential and total cross sections. The shapes of the distributions in the Kp and Kpp invariant masses are reproduced only if the K-p interaction is even stronger than that found at higher energy. The cusp effect in the K+K- distribution at the K0K0bar threshold is much more clear and some evidence is also found for coupling between the K-p and K0bar n channels. However, the energy dependence of the total cross section cannot be reproduced by considering only a simple product of such pair-wise final state interactions.

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arXiv2013

Excitation of the Delta(1232) isobar in deuteron charge exchange on hydrogen at 1.6, 1.8, and 2.3 GeV

The charge-exchange break-up of polarised deuterons pol{d}p -> {pp}n, where the final {pp} diproton system has a very low excitation energy and hence is mainly in the 1S0 state, is a powerful tool to probe the spin-flip terms in the proton-neutron charge-exchange scattering. Recent measurements with the ANKE spectrometer at the COSY storage ring at 1.6, 1.8, and 2.27 GeV have extended these studies into the pion-production regime in order to investigate the mechanism for the excitation of the Delta(1232) isobar in the pol{d}p -> {pp}X reaction. Values of the differential cross section and two deuteron tensor analysing powers, A_{xx} and A_{yy}, have been extracted in terms of the momentum transfer to the diproton or the invariant mass Mx of the unobserved system X. The unpolarised cross section in the high Mx region is well described in a model that includes only direct excitation of the Delta isobar through undistorted one pion exchange. However, the cross section is grossly underestimated for low Mx, even when Delta excitation in the projectile deuteron is included in the calculation. Furthermore, direct Delta production through one pion exchange only reproduces the angular dependence of the difference between the two tensor analysing powers.

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arXiv2012

The neutron-proton charge-exchange amplitudes measured in the dp -> ppn reaction

The unpolarised differential cross section and the two deuteron tensor analysing powers A_{xx} and A_{yy} of the pol{d}p -> (pp)n charge-exchange reaction have been measured with the ANKE spectrometer at the COSY storage ring. Using deuteron beams with energies 1.2, 1.6, 1.8, and 2.27 GeV, data were obtained for small momentum transfers to a (pp) system with low excitation energy. The results at the three lower energies are consistent with impulse approximation predictions based upon the current knowledge of the neutron-proton amplitudes. However, at 2.27GeV, where these amplitudes are far more uncertain, agreement requires a reduction in the overall double-spin-flip contribution, with an especially significant effect in the longitudinal direction. These conclusions are supported by measurements of the deuteron-proton spin-correlation parameters C_{x,x} and C_{y,y} that were carried out in the pol{d}pol{p} -> (pp)n reaction at 1.2 and 2.27GeV. The values obtained for the proton analysing power also suggest the need for a radical re-evaluation of the neutron-proton elastic scattering amplitudes at the higher energy. It is therefore clear that such measurements can provide a valuable addition to the neutron-proton database in the charge-exchange region.

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arXiv2012

New determination of the mass of the eta meson at COSY-ANKE

A value for the mass of the eta meson has been determined at the COSY-ANKE facility through the measurement of a set of deuteron laboratory beam momenta and associated 3He center-of-mass momenta in the d+p -> 3He+X reaction. The eta was then identified by the missing-mass peak and the production threshold determined. The individual beam momenta were fixed with a relative precision of 3 x 10^-5 for values around 3 GeV/c by using a polarized deuteron beam and inducing an artificial depolarizing spin resonance, which occurs at a well-defined frequency. The final-state momenta in the two-body d+p -> 3He+eta reaction were investigated in detail by studying the size of the 3He momentum ellipse with the forward detection system of the ANKE spectrometer. Final alignment of the spectrometer for this high precision experiment was achieved through a comprehensive study of the 3He final-state momenta as a function of the center-of-mass angles, taking advantage of the full geometrical acceptance. The value obtained for the mass, m(eta)=(547.873 +- 0.005(stat) +- 0.027(syst)) MeV/c^2, is consistent and competitive with other recent measurements, in which the meson was detected through its decay products.

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arXiv2011

Differential cross section and analysing power of the quasi-free pn -> {pp}_s pi- reaction at 353 MeV

In order to establish links between p-wave pion production in nucleon-nucleon collisions and low energy three-nucleon scattering, an extensive programme of experiments on pion production is currently underway at COSY-ANKE. The final proton pair is measured at very low excitation energy, leading to an S-wave diproton, denoted here as {pp}_s. By using a deuterium target we have obtained data on the differential cross section and analysing power of the quasi-free pol{p}n -> {pp}_s pi^- reaction at 353 MeV. The spectator proton p_sp was either measured directly in silicon tracking telescopes or reconstructed using the momentum of a detected pi^-. Both observables can be described in terms of s-, p-, and d-wave pion production amplitudes. Taken together with the analogous data on the pol{p}p -> {pp}_s pi^0 reaction, full partial wave decompositions of both processes were carried out.

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arXiv2011

Differential cross section and analysing power of the pp -> {pp\}_s pi0 reaction at 353 MeV

In order to establish links between p-wave pion production in nucleon-nucleon collisions and low energy three-nucleon scattering, an extensive programme of experiments on pion production is currently underway at COSY-ANKE. The final proton pair is detected at very low excitation energy, leading to an S-wave diproton, denoted here as {pp}_s. We now report on measurements of the differential cross section and analysing power of the pol{p}p->{pp}_s pi^0$ reaction at 353 MeV. Both observables can be described in terms of s- and d-wave pion production and, by using the phase information from elastic pp scattering, unique solutions can be obtained for the corresponding amplitudes. This information is vital for the partial wave decomposition of the corresponding pn->{pp}_s pi^- reaction and hence for the extraction of the p-wave terms.

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arXiv2010

Energy dependence of hard bremsstrahlung production in proton-proton collisions in the Delta(1232) region

Hard bremsstrahlung production in proton-proton collisions has been studied with the ANKE spectrometer at COSY-Juelich in the energy range of 353-800 MeV by detecting the final proton pair {pp}_s from the pp -> {pp}_s reaction with very low excitation energy. Differential cross sections were measured at small diproton c.m. angles from 0 to 20 degrees and the average over this angular interval reveals a broad peak at a beam energy around 650 MeV with a FWHM of about 220 MeV, suggesting the influence of Delta(1232)N intermediate states. Comparison with deuteron photodisintegration shows that the cross section for diproton production is up to two orders of magnitude smaller, due largely to differences in the selection rules.

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arXiv2010

High precision beam momentum determination in a synchrotron using a spin resonance method

In order to measure the mass of the eta meson with high accuracy using the d+p -> 3He+eta reaction, the momentum of the circulating deuteron beam in the Cooler Synchrotron COSY of the Forschungszentrum Juelich has to be determined with unprecedented precision. This has been achieved by studying the spin dynamics of the polarized deuteron beam. By depolarizing the beam through the use of an artificially induced spin resonance, it was possible to evaluate its momentum p with a precision of dp/p < 10-4 for a momentum of roughly 3 GeV/c. Different possible sources of error in the application of the spin resonance method are discussed in detail and its possible use during a standard experiment is considered.

physics.acc-ph↗

arXiv2010

The energy dependence of the pp->K+ n Sigma+ reaction close to threshold

The production of the Sigma+ hyperon through the pp->K+nSigma+ reaction has been investigated at four energies close to threshold, 1.826, 1.920, 1.958, and 2.020 GeV. At low energies, correlated K+pi+ pairs can only originate from Sigma+ production so that their measurement allows the total cross section for the reaction to be determined. The results obtained are completely consistent with the values extracted from the study of the K+-proton correlation spectra obtained in the same experiment. These spectra, as well as the inclusive K+ momentum distributions, also provide conservative upper limits on the Sigma+ production rates. The measurements show a Sigma+ production cross section that varies roughly like phase space and, in particular, none of the three experimental approaches used supports the anomalously high near-threshold pp->K+ nSigma+ total cross section previously reported [T. Rozek et al., Phys. Lett. B 643, 251 (2006)].

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