Analysis of the differential cross sections for the reaction pp --> ppK+K- in view of the K+K- interaction
Author: Michał Silarski
Supervisor: prof. Paweł Moskal
abstract
Defence year: 2008
Measurements of the pp-->ppK+K- reaction, performed with the experiment COSY-11 at the Cooler Synchrotron COSY, show a significant difference between the obtained excitation function and theoretical expectations including pp-FSI >. The discrepancy may be assigned to the influence of K+K- or K-p interaction. This interaction should manifest itself in the distributions of the differential cross section. This thesis presents an analysis of event distributions as a function of the invariant masses of two particle subsystems. In particular in the analysis two generalizations of the Dalitz plot proposed by Goldhaber and Nyborg are used. The present Investigations are based on the experimental data determined by the COSY-11 collaboration from two measurements at excess energies of Q = 10 MeV and 28 MeV. The experimental distributions are compared to results of Monte Carlo simulations generated with various parameters of the K+K- and K-p interaction. The values of the K+K- scattering length, extracted from two data sets for Q = 10 MeV and 28 MeV amount to: a_K+K- = (11 +- 8) + i(0 +- 6) fm for Q = 10 MeV, and a_K+K- = (0.2 +-0.2) + i(0.0 +- 0.5) fm for Q = 28 MeV, Due to the low statistics, the extracted values have large uncertainties and are consistent with very low values of the real and imaginary part of the scattering length.
Feasibility study of the eta-prime -> pi+pi-pi0 decay using WASA-at-COSY apparatus
Author: Marcin Zieliński
Supervisor: prof. Paweł Moskal
abstract
Defence year: 2008
One of the objectives of the vast physics programme of the recently comissioned WASA-at-COSY facility is the study of fundamental symmetries via the measurements of the eta and eta-prime mesons decays. Especially interesting are isospin violating hadronic precesses of these mesons into 3pi systems driven by the term of QCD Lagrangian which depends on the mass difference of the u and d quarks. When an eta or an eta-prime meson is created in the hadronic reaction signals from such decays may be significantly obscured by the prompt production of pi mesons. In this thesis we present the estimation of the upper limit of the background due to prompt pion production for the eta-prime ->3pi0 and eta-prime->pi+pi-pi decays. Using the data from proton-proton collisions measured by the COSY-11 group we have extracted differential cross sections for the multimeson production with the invariant mass corresponding to the mass of the eta-prime meson. Based on these results and on parametrizations of the total cross sections for the eta-prime meson as well as parametrization of the upper limit for the prompt pi+pi-pi0 production in the collisions of protons we discuss in details the feasibility of a measurement of the eta-prime meson decay into 3pi channels with the WASA-at-COSY facility. Based on the chiral unitary approach the value of the branching ratio BR(eta-prime->pi+pi-pi0) was recently predicted to be about 1%. We show that the WASA-at-COSY has a potential to verify this result empirically.
Symulacje komputerowe reakcji pp->pp eta-prime w celu wyznaczenia szerokości naturalnej mezonu eta-prime z pomiarów wykonanych układem detekcyjnym COSY-11
Author: Eryk Czerwiński
Supervisor: prof. Paweł Moskal
abstract
Defence year: 2006
Symulacja kwazi-swobodnej reakcji nn->d pi- w oddziaływaniu deuteronu z deuteronem
Author: Izabela Drągowska
Supervisor: prof. Paweł Moskal
abstract
Defence year: 2006
Bremsstrahlung radiation in the deuteron - proton collision
Author: Joanna Przerwa
Supervisor: prof. Paweł Moskal
abstract
Defence year: 2004
Despite the fact that Bremsstrahlung radiation has been observed many years ago, it is still the subject of interest of many theoretical and experimental groups. Due to the high sensitivity of the NN --> NNgamma reaction to the nucleon-nucleon potential, Bremsstrahlung radiation is used as a tool to investigate details of the nucleon-nucleon interaction. Such investigations can be performed at the cooler synchrotron COSY in the Research Centre Juelich, by dint of the COSY-11 detection system. For the first time at the COSY--11 experiment signals from gamma - quanta were observed in the time-of-flight distribution of neutral particles measured with the neutral particle detector. In this thesis the results of the identification of Bremsstrahlung radiation emitted via the dp --> dpgamma reaction in data taken with a proton target and a deuteron beam are presented and discussed. The time resolution of the neutral particle detector and its timing calibration are crucial for the identification of the dp --> dpgamma reaction. Therefore, methods of determining the relative timing between individual modules - constituting the neutron detector - and of the general time offset with respect to the other detector components are described. Furthermore the accuracy of the momentum determination of the registered neutron which defines the precision of the event reconstruction was extracted from the data.
Eta and Eta-prime meson production in the quasi-free proton-neutron collisions at the COSY-11 facility
Author: Rafał Czyżykiewicz
Supervisor: prof. Paweł Moskal
abstract
Defence year: 2002
Both, the structure of the eta meson as well as its production mechanism are
still under strong discussion and debate. The most possible hypothesis concerning
the explanation of the almost three times larger mass for this meson observed
experimentally relative to the theoretically calculated mass is a gluonium admixture
to the eta-prime wave function. This gluonium admixture should reflect itself in the
production yield of the eta-prime meson in proton-neutron collisions. Since the production
of eta-prime meson through the gluonium exchange is isospin independent, the ratio
R(eta) = (pn->pn eta)/(pp->pp eta) close to threshold is expected to be R(eta-prime) = 1,
after corrections for initial and final state interactions.
The close to threshold eta-prime production in proton-proton collisions has already
been investigated at the COSY-11 facility. Cross section values in the threshold
region have been measured. However, until now no data have been taken for the
eta-prime meson production in the proton-neutron collision.
In order to investigate the eta-prime production in proton-neutron collisions at the
COSY synchrotron, the COSY-11 facility has been equipped with two new subsystems,
namely the neutron detector and the spectator counter. The optimization
of the topography for these additional detectors, the selection of the most suitable
beam momentum and a discussion for the method of luminosity determination for
the quasi-free pn->pn eta (eta-prime) reactions are presented in this thesis. Rates for the
production of eta and eta-prime mesons in proton-neutron collisions at COSY-11 have been
estimated. For the calculations a special fast program has been written.
Response function of the trigger scintillation detector for the COSY-11 installation
Author: Paweł Moskal
Supervisor: prof. Lucjan Jarczyk
abstract
Defence year: 1993
The aim of this work is to test the response of a scintillation detector to ionizing particles. This counter, consisting of sixteen detection modules, will serve as a trigger of the whole COSY-11 detection system. Thus the time resolution as well as a signal amplitude variation with respect to a hit position is of a special interest. The former because this detector will be used as a start counter for the time of flight measurement, the latter as it will provide energy loss measurements of the registered particles.
The work is divided into two parts. In the first one the main stages of a signal production by scintillation counters are considered. In the second one the first chapter presents measurements of the characteristics
of the photomultiplier, whereas the second one contains a description of the experimental set-ups as well as the method of data evaluation. The final chapter in turn presents the main characteristics of the considered detector.
Near-threshold kaon pair production in proton-proton collisions
Author: Damian Gil
Supervisor: prof. Jerzy Smyrski
abstract
Defence year: 2019
Measurements of the pp -> ppK+K- reaction close to the kinematical threshold allow the studies of the K+K-, pK+ and pK- interactions in the final state. Therefore, these measurements can help to understand the nature of the f0(980) and a0(980) mesons which, according to some theoretical models, are kaonic molecules, and of the Lambda(1405) hyperon which is considered as a pK- bound state.
In the framework of the present work, measurement of the total cross section for the pp -> ppK+K- reaction at incident beam momentum of 3.316 GeV/c, corresponding to the excess energy of only 4.5 MeV, was performed.
The measurement was done at the internal proton beam of the COSY accelerator in Juelich Research Centre in Germany using the COSY-11 detection system. The integrated luminosity, determined using a coincidence measurement of the elastically scattered protons, was 1.52 pb-1. In the absence of ppK+K- events observed in the experiment, an upper limit at 95% level of confidence on the pp -> ppK+K- total cross section of 0.070 nb has been determined.
This limit lies below theoretical calculations taking into account the pp, pK- and K+K- final-state interactions and describing the experimental data available higher above the threshold. This can indicate the influence of the Coulomb interaction which was not
fully included in the theoretical calculations or absorption of kaons due to formation of the K+K- bound state.
Determination of the total width of the eta-prime meson
Author: Eryk Czerwiński
Supervisor: prof. Paweł Moskal
abstract
Defence year: 2009
The aim of this work was to determine the total width of the eta-prime meson. The investigated meson was produced via the pp->ppeta-prime reaction in the collisions of beam protons from COSY synchrotron with protons from a hydrogen cluster target. The COSY-11 detector was used for the measurement of the four-momentum vectors of outgoing protons. The mass of unregistered meson was determined via the missing mass technique, while the total width was directly derived from the mass distributions established at five different beam momenta. Parallel monitoring of the crucial parameters (e.g. size and position of the target stream) and the measurement close-to-threshold permitted to obtain mass resolution of FWHM = 0.33 MeV/c^2.
Based on the sample of more than 2300 reconstructed pp->ppeta-prime events the determined total width of the eta-prime meson amounts to 0.226+-0.017(stat.)+-0.014(syst.) MeV, which is the most precise measurement until now.
Isospin dependence of the eta-prime meson production in collisions of nucleons
Author: Joanna Klaja
Supervisor: prof. Paweł Moskal
abstract
Defence year: 2009
The upper limit of the total cross section for quasi-free pn -> pn eta-prime reaction has been determined in the excess energy range near the kinematic threshold. The measurement has been carried out at the COSY-11 detection setup using a proton beam and a deuteron cluster target. The identification of the eta-prime meson has been performed using the missing mass technique. The energy dependence of the upper limit of the cross section is extracted with a fixed proton beam momentum of p_beam}=3.35GeV/c and exploiting the Fermi momenta of nucleons inside the deuteron. The data cover a range of centre-of-mass excess energies from 0 to 24 MeV. The experimentally determined upper limit of the ratio R(eta-prime)=sigma(pn -> pn eta-prime) sigma(pp -> pp eta-prime), which is smaller than the ratio for the eta meson, excludes the excitation of the S_11(1535) resonance as a dominant production mechanism of the eta-prime meson in nucleon-nucleon collisions. At the same time, the determined upper limits of R(eta-prime) go in the direction of what one would expect in the glue production and production via mesonic currents. For quantitative tests of these mechanisms an order of magnitude larger statistics and a larger energy range would be required. This can be reached with the WASA-at-COSY facility.
Comparative studies of the interaction in the low energy ppeta and ppeta' systems
Author: Paweł Klaja
Supervisor: prof. Paweł Moskal
abstract
Defence year: 2009
The COSY-11 collaboration measured the pp -> ppeta and pp -> ppeta' reactions in order to perform comparative studies of the interactions within the proton-proton-meson system. This thesis presents in detail the analysis of the pp -> ppeta' reaction which was measured at the proton beam momentum of 3.260 GeV/c. The elaboration results in differential distributions of squared invariant proton-proton (s_pp) and proton-eta' (s_peta') masses, as well as in angular distributions and the total cross section at an excess energy of 16.4 MeV. The differential distributions s_pp and s_peta' are compared to theoretical predictions and to the analogous spectra determined for the pp -> ppeta reaction. The comparison of the results for the eta and eta' meson production rather excludes the hypothesis that the enhancement observed in the invariant mass distributions is due to the meson-proton interaction. Further, the shapes of the distributions do not favour any of the postulated theoretical models.
Study of the production mechanism of the eta meson in proton-proton collisions by means of analysing power measurements
Author: Rafał Czyżykiewicz
Supervisor: prof. Paweł Moskal
abstract
Defence year: 2006
The analysing power measurements for the p(pol)p -> pp eta reaction studied in this dissertation are used in the determination of the reaction mechanism of the eta meson production in nucleon-nucleon collisions.
Measurements have been performed in the close-to-threshold energy region at beam momenta of p(beam)=2.010 and 2.085 GeV/c, corresponding to the excess energies of Q = 10 and 36 MeV, respectively. The experiments were realised by means of a cooler synchrotron and storage ring COSY along with a cluster jet target. For registration of the reaction products the COSY-11 facility has been used. The identification of the eta meson has been performed with the missing mass method.
The results for the angular dependence of the analysing power combined with the hitherto determined isospin dependence of the total cross section for the $eta$ meson production in the nucleon-nucleon collisions, reveal a statistically significant indication that the excitation of the nucleon to the S_{11} resonance, the process which intermediates the production of the eta meson, is predominantly due to the exchange of a pi meson between the colliding nucleons.
The determined values of the analysing power at both excess energies are consistent with zero implying that the eta meson is produced predominantly in the s-wave at both excess energies.
Eta-prime meson production in the p p -> p p eta-prime reaction near threshold
Author: Paweł Moskal
Supervisor: prof. Lucjan Jarczyk
abstract
Defence year: 1998
The eta-prime meson belongs to the ground state pseudoscalar meson nonet. According
to the SU(3) classification its quark composition is similar to the structure of
the eta meson. However, due to the small pseudoscalar mixing angle (~15 degrees)
the eta-prime meson is predominantly a flavour singlet state and hence can comprise a
significant amount of gluons. A possible gluon admixture would be reflected in the
production mechanism of the eta-prime meson in the elementary proton-proton reaction,
it would modify an eta-prime-p-p coupling constant which determines the direct production
amplitude, and it would also influence the potential of the proton-eta-prime meson
interaction. These issues make the investigations of the eta-prime meson very interesting.
The total cross section for the production of the eta-prime meson in the pp-->ppeta-prime reaction
has been measured close to the kinematical threshold. The experiment has
been carried out at the cooler synchrotron COSY using the internal proton beam
and the hydrogen cluster target. The ejected charged particles were registered
using the COSY-11 detection system, which allow for an unique identification of
positively charged particles and determination of their four-momentum vectors.
Events with the creation of the eta-prime meson were identified by means of the missing
mass technique. The obtained cross sections for the eta-prime meson production are by about a factor
of fifty smaller that the cross section for the production of the eta meson at the same
center of mass excess energies. Such large difference suggests that these mesons are produced in a rather different way. Comparison of the measured cross section values with calculations based on the
effective Lagrangian approach yields an upper limit for the eta-prime-p-p coupling constant.
The analysis of the energy dependence of the total cross section for the pp-->ppeta-prime reaction suggests that either the primary production amplitude decreases very close to threshold or that the proton-eta-prime interaction is repulsive.
