arXiv subjects

A. Khoukaz

Publications and source records attributed to A. Khoukaz.

At least 91 records · Page 5Linked to original sources

arXiv2010

Measurement of the invariant mass distributions for the pp -> ppeta' reaction at excess energy of Q = 16.4 MeV

The proton-proton and proton-eta' invariant mass distributions have been determined for the pp -> ppeta' reaction at an excess energy of Q = 16.4 MeV. The measurement was carried out using the COSY-11 detector setup and the proton beam of the cooler synchrotron COSY. The shapes of the determined invariant mass distributions are similar to those of the pp -> ppeta reaction and reveal an enhancement for large relative proton-proton momenta. This result, together with the fact that the proton-eta interaction is much stronger that the proton-eta' interaction, excludes the hypothesis that the observed enhancement is caused by the interaction between the proton and the meson.

nucl-ex↗

arXiv2009

Invariant mass distributions for the pp to p p eta reaction at Q=10 MeV

Proton-proton and proton-eta invariant mass distributions and the total cross section for the pp to pp eta reaction have been determined near the threshold at an excess energy of Q=10 MeV. The experiment has been conducted using the COSY-11 detector setup and the cooler synchrotron COSY. The determined invariant mass spectra reveal significant enhancements in the region of low proton-proton relative momenta, similarly as observed previously at higher excess energies of Q=15.5 MeV and Q= 40MeV.

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arXiv2009

Generalized Dalitz Plot analysis of the near threshold pp-->ppK+K- reaction in view of the K+K- final state interaction

The excitation function for the $pp\to ppK^+K^-$ reaction revealed a significant enhancement close to threshold which may plausibly be assigned to the influence of the $pK^-$ and $K^+K^-$ final state interactions. In an improved reanalysis of COSY-11 data for the $pp\to ppK^+K^-$ reaction at excess energies of Q = 10 MeV and 28 MeV including the proton-K- interaction the enhancement is confirmed. Invariant mass distributions for the two- and three-particle subsystems allow to test at low excess energies the ansatz and parameters for the description of the interaction in the ppK+K- system as derived from the COSY-ANKE data. Finally, based for the first time on the low energy K+K- invariant mass distributions and the generalized Dalitz plot analysis, we estimate the scattering length for the K+K- interaction to be |Re(a_K^+K^-)| = 0.5 + 4.0 -0.5 fm and Im(a_K^+K^-) = 3.0 +- 3.0 fm.

hep-ph↗

arXiv2009

Precision study of the d+p->3He+eta reaction for excess energies between 20 and 60 MeV

The differential and total cross sections for the d+p->3He+eta reaction have been measured at COSY-ANKE at excess energies of 19.5, 39.4, and 59.4 MeV over the full angular range. The results are in line with trends apparent from the detailed near-threshold studies and also agree with those from CELSIUS, though the present data have higher precision. While at 19.5 MeV the results can be described in terms of s- and p-wave production, by 59.4 MeV higher partial waves are required. Including the 19.5 MeV point together with the near-threshold data in a global s- and p-wave fit gives a poorer overall description of the data though the position of the pole in the 3He scattering amplitude, corresponding to the quasi-bound or virtual state, is hardly changed.

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arXiv2009

Measurement of the isospin-filtering dd -> 4He K+ K- reaction at Q=39 MeV

The total cross section for the dd -> 4He K+ K- reaction has been measured at a beam momentum of 3.7 GeV/c, corresponding to an excess energy of 39 MeV, which is the maximum possible at the Cooler Synchrotron COSY-Jülich. A deuterium cluster-jet target and the ANKE forward magnetic spectrometer, placed inside the storage ring, have been employed in this investigation. We find a total cross section of sigma(tot) < 14 pb, which brings into question the viability of investigating the dd -> 4He a0(980) reaction as a means of studying isospin violation.

nucl-ex↗

arXiv2009

Search for the 3He-eta bound state at COSY-11

We have measured excitation function for dp -> ppp_pi- reaction near the eta production threshold. We observe an enhancement of the counting rate above the threshold which can originate from the production of the eta meson in the reaction dp -> 3He eta and its subsequent absorption on neutron in the 3He nucleus leading to creation of the p_pi- pair.

nucl-ex↗

arXiv2009

Polarizing a stored proton beam by spin flip?

We discuss polarizing a proton beam in a storage ring, either by selective removal or by spin flip of the stored ions. Prompted by recent, conflicting calculations, we have carried out a measurement of the spin flip cross section in low-energy electron-proton scattering. The experiment uses the cooling electron beam at COSY as an electron target. The measured cross sections are too small for making spin flip a viable tool in polarizing a stored beam. This invalidates a recent proposal to use co-moving polarized positrons to polarize a stored antiproton beam.

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arXiv2009

Observation of an ABC effect in proton-proton collisions

The cross section for inclusive multipion production in the pp->ppX reaction was measured at COSY-ANKE at four beam energies, 0.8, 1.1, 1.4, and 2.0 GeV, for low excitation energy in the final pp system, such that the diproton quasi-particle is in the 1S0 state. At the three higher energies the missing mass Mx spectra show a strong enhancement at low Mx, corresponding to an ABC effect that moves steadily to larger values as the energy is increased. Despite the missing-mass structure looking very different at 0.8 GeV, the variation with Mx and beam energy are consistent with two-pion production being mediated through the excitation of two Delta(1232) isobars, coupled to S-- and D-- states of the initial pp system.

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arXiv2008

Neutron-proton charge-exchange amplitudes at 585 MeV

The differential cross section and deuteron analysing powers of the dp -> {pp}n charge-exchange reaction have been measured with the ANKE spectrometer at the COSY storage ring. Using a deuteron beam of energy 1170 MeV, data were obtained for small momentum transfers to a {pp} system with low excitation energy. A good quantitative understanding of all the measured observables is provided by the impulse approximation using known neutron-proton amplitudes. The proof of principle achieved here for the method suggests that measurements at higher energies will provide useful information in regions where the existing np database is far less reliable.

nucl-ex↗

arXiv2008

Isospin dependence of the eta prime meson production in nucleon-nucleon collisions

A comparison of the close-to-threshold total cross section for the eta prime production in pp --> pp eta prime and pn --> pn eta prime reactions constitutes a tool to investigate the eta prime meson structure and the reaction mechanism in the channels of isospin I=0 and I=1 and may provide insight into the flavour-singlet (perhaps also into gluonium) content of the eta prime meson. In this contribution we present preliminary results of measurement of the quasi-free production of the eta prime meson in the proton-neutron collisions conducted using the COSY-11 facility.

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arXiv2008

Near threshold production of the eta meson via the quasi-free pn --> pn eta reaction

Total cross sections for the quasi-free pn --> pn eta reaction in the range from the kinematical threshold up to 20 MeV excess energy have been determined. At threshold they exceed corresponding cross sections for the pp --> pp eta reaction by a factor of about three in contrast to the factor of six established for higher excess energies. To large extent, the observed decrease of the ratio sigma(pn --> pn eta)/sigma(pp --> pp eta) towards threshold may be assigned to the different energy dependence of the proton-proton and proton-neutron final state interactions. The experiment has been conducted using a proton beam of the cooler synchrotron COSY and a cluster jet deuteron target. The proton-neutron reactions were tagged by the spectator proton whose momentum was measured for each event. Protons and neutron outgoing from the pn --> pn eta reaction have been registered by means of the COSY-11 facility, an apparatus dedicated for threshold meson production.

hep-ex↗

arXiv2008

Near threshold production of the pseudoscalar mesons at the COSY-11 facility

We summarise measurements of the COSY-11 collaboration concerning the excitation functions of the near threshold pseudoscalar meson production in the proton-proton interaction. The results are discussed in the context of the meson-nucleon and hyperon-nucleon interactions. We conclude that the $η$-proton interaction is significantly stronger than the eta'-proton interaction. Similarly, we found that the hyperon Lambda interacts with the nucleon considerably stronger than the hyperon Sigma, and that the interaction of (K-)-proton is much stronger than this of the (K+)-proton.

nucl-ex↗

arXiv2008

Dynamics of the near threshold eta meson production in proton-proton interaction

We present the results of measurements of the analysing power for the p(pol)p --> pp eta reaction at the excess energies of Q=10 and 36 MeV, and interpret these results within the framework of the meson exchange models. The determined values of the analysing power at both excess energies are consistent with zero implying that the eta meson is produced predominantly in s-wave.

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arXiv2008

Study of the hadronic production of kaon pairs below the threshold for the phi meson

The near threshold production of K+K- pairs in proton-proton collisions has been investigated at the cooler synchrotron COSY below and above the threshold for the $ϕ$ meson using the COSY-11 and ANKE facilities, respectively. The excitation function determined for the pp-->ppK+K- reaction revealed a statistically significant enhancement close to the threshold which may plausibly be assigned to the influence of the K-p interaction. In addition, observed consistently by both groups, a strong enhancement at low values of the ratio of the K-p to K+p invariant mass distributions shows that the proton interacts much stronger with K- than with K+. In this report we focus on the measurements performed by the COSY-11 collaboration. We explain the experimental method used and present main results of completed analyses as well as a new qualitative elaboration of the ppK+K- events population on the Goldhaber plot. We conclude with the observation that event densities increase at the region where the influence from the K+K- interaction is expected.

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arXiv2008

Observation of inverse diproton photodisintegration at intermediate energies

The reaction pp->{pp}_sγ, where {pp}_s is a proton pair with an excitation energy E_{pp}<3 MeV, has been observed with the ANKE spectrometer at COSY-Juelich for proton beam energies of T_p=0.353, 0.500, and 0.550 GeV. This is equivalent to photodisintegration of a free 1S_0 diproton for photon energies Eγ~ T_p/2. The differential cross sections measured for c.m. angles 0 deg.<θ_{pp}<20 deg. exhibit a steep increase with angle that is compatible with E1 and E2 multipole contributions. The ratio of the measured cross sections to those of np->dγis on the 10^{-3}-10^{-2} level. The increase of the pp->{pp}_sγcross section with T_p might reflect the influence of the Delta(1232) excitation.

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arXiv2008

The WASA Detector Facility at CELSIUS

The WASA 4pi multidetector system, aimed at investigating light meson production in light ion collisions and eta meson rare decays at the CELSIUS storage ring in Uppsala is presented. A detailed description of the design, together with the anticipated and achieved performance parameters are given.

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arXiv2008

Determination of target thickness and luminosity from beam energy losses

The repeated passage of a coasting ion beam of a storage ring through a thin target induces a shift in the revolution frequency due to the energy loss in the target. Since the frequency shift is proportional to the beam-target overlap, its measurement offers the possibility of determining the target thickness and hence the corresponding luminosity in an experiment. This effect has been investigated with an internal proton beam of energy 2.65 GeV at the COSY-Jülich accelerator using the ANKE spectrometer and a hydrogen cluster-jet target. Possible sources of error, especially those arising from the influence of residual gas in the ring, were carefully studied, resulting in a accuracy of better than 5%. The luminosity determined in this way was used, in conjunction with measurements in the ANKE forward detector, to determine the cross section for elastic proton-proton scattering. The result is compared to published data as well as to the predictions of a phase shift solution. The practicability and the limitations of the energy-loss method are discussed.

physics.acc-ph↗

arXiv2008

Lineshape of the Lambda(1405) Hyperon Measured Through its Sigma0 pion0 Decay

The pp -> p K+ Y0 reaction has been studied for hyperon masses m(Y0)<1540 MeV/c2 at COSY-Juelich by using a 3.65 GeV/c circulating proton beam incident on an internal hydrogen target. Final states comprising two protons, one positively charged kaon and one negatively charged pion have been identified with the ANKE spectrometer. Such configurations are sensitive to the production of the ground state Lambda and Sigma0 hyperons as well as the Sigma0(1385) and Lambda(1405) resonances. Applying invariant- and missing-mass techniques, the two overlapping excited states could be well separated, though with limited statistics. The shape and position of the Lambda(1405) distribution, reconstructed cleanly in the Sigma0 pion0 channel, are similar to those found from other decay modes and there is no obvious mass shift. This finding constitutes a challenging test for models that predict Lambda(1405) to be a two-state resonance.

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