21 research outputs found
Phase II study of ‘high-dose’ celecoxib and metronomic ‘low-dose’ cyclophosphamide and methotrexate in patients with relapsed and refractory lymphoma
Production of Lambda and Sigma^0 hyperons in proton-proton collisions
This paper reports results on simultaneous measurements of the reaction
channels pp -> pK+\Lambda and pp -> pK+\Sigma^0 at excess energies of 204, 239,
and 284 MeV (\Lambda) and 127, 162, and 207 MeV (\Sigma^0). Total and
differential cross sections are given for both reactions. It is concluded from
the measured total cross sections that the high energy limit of the cross
section ratio is almost reached at an excess energy of only about 200 MeV. From
the differential distributions observed in the overall CMS as well as in the
Jackson and helicity frames, a significant contribution of interfering nucleon
resonances to the \Lambda production mechanism is concluded while resonant
\Sigma^0-production seems to be of lesser importance and takes place only
through specific partial waves of the entrance channel. The data also indicate
that kaon exchange plays a minor role in the case of \Lambda- but an important
role for \Sigma^0-production. Thus the peculiar energy dependence of the
\Lambda-to-\Sigma^0 cross section ratio appears in a new light as its
explanation requires more than mere differences between the p\Lambda and the
p\Sigma^0 final state interaction. The data provide a benchmark for theoretical
models already available or yet to come.Comment: 18 pages, 10 figures; accepted by The European Physical Journal A
(EPJ A
Systematic study of the pp -> pp omega reaction
A systematic study of the production of omega-mesons in
proton-proton-collisions was carried out in a kinematically complete experiment
at three excess energies(epsilon= 92, 128, 173MeV). Both protons were detected
using the large-acceptance COSY-TOF spectrometer at an external beam line at
the Cooler Synchrotron COSY at Forschungszentrum J\"ulich. The total cross
section, angular distributions of both omega-mesons and protons were measured
and presented in various reference frames such as the overall CMS, helicity and
Jackson frame. In addition, the orientation of the omega-spin and invariant
mass spectra were determined. We observe omega-production to take place
dominantly in Ss and Sp final states at epsilon = 92, 128 MeV and,
additionally, in Sd at epsilon= 173 MeV. No obvious indication of resonant
omega-production via N^*-resonances was found, as proton angular distributions
are almost isotropic and invariant mass spectra are compatible with phase space
distributions. A dominant role of ^3P_1 and ^1S_0 initial partial waves for
omega-production was concluded from the orientation of the decay plane of the
omega-meson. Although the Jackson angle distributions in the omega-p-Jackson
frame are anisotropic we argue that this is not an indication of a resonance
but rather a kinematical effect reflecting the anisotropy of the omega angular
distribution. The helicity angle distribution in the omega-p-helicity frame
shows an anisotropy which probably reflects effects of the omega angular
momenta in the final state; this observable may be, in addition to the
orientation of the omega decay plane, the most sensitive one to judge the
validity of theoretical descriptions of the production process.Comment: 17 pages, 16 figures, accepted for publication in EPJ
The pK0\Sigma+ final state in proton-proton collisions
This paper reports results from a study of the reaction pp->pK0\Sigma+ at
beam momenta of p_{beam} = 2950, 3059, and 3200 MeV/c (excess energies of
\epsilon= 126, 161, and 206 MeV). Total cross sections were determined for all
energies; a set of differential cross sections (Dalitz plots; invariant mass
spectra of all two-body subsystems; angular distributions of all final state
particles; distributions in helicity and Jackson frames) are presented for
\epsilon= 161 MeV. The total cross sections are proportional to the volume of
available three-body phase-space indicating that the transition matrix element
does not change significantly in this range of excess energies. It is concluded
from the differential data that the reaction proceeds dominantly via the
N(1710)P_{11} and/or N(1720)P_{13} resonance(s); N(1650)S_{11} and
\Delta(1600)P_{33} could also contribute.Comment: 15 pages, 10 figure
Chiral perturbation theory calculation for pn -> dpipi at threshold
We investigate the reaction pn -> dpipi in the framework of Chiral
Perturbation Theory. For the first time a complete calculation of the leading
order contributions is presented. We identify various diagrams that are of
equal importance as compared to those recognized in earlier works. The diagrams
at leading order behave as expected by the power counting. Also for the first
time the nucleon-nucleon interaction in the initial, intermediate and final
state is included consistently and found to be very important. This study
provides a theoretical basis for a controlled evaluation of the non-resonant
contributions in two-pion production reactions in nucleon-nucleon collisions.Comment: 24 pages, 3 figures, 3 table
Influence of N*-resonances on hyperon production in the channel pp->K+ Lambda p at 2.95, 3.20 and 3.30 GeV/c beam momentum
Hyperon production in the threshold region was studied in the reaction pp ->
K+Lp using the time-of-flight spectrometer COSY-TOF. Exclusive data, covering
the full phase-space, were taken at the three different beam momenta of
p_beam=2.95, 3.20 and 3.30 GeV/c, corresponding to excess energies of
epsilon=204, 285 and 316 MeV, respectively. Total cross-sections were deduced
for the three beam momenta to be 23.9+/-0.8 +/-2.0 ub, 28.4+/-1.3 +/-2.2 ub and
35.0+/-1.3 +/-3.0 ub. Differential observables including Dalitz plots were
obtained. The analysis of the Dalitz plots reveals a strong influence of the
N(1650)-resonance at p_beam=2.95 GeV/c, whereas for the higher momenta an
increasing relative contribution of the N(1710)- and/or of the
N(1720)-resonance was observed. In addition, the pL-final-state interaction
turned out to have a significant influence on the Dalitz plot distribution.Comment: accepted for publication at Physics Letters B; some minor text
changes were done; also the scale of the ordinates of figure 9 has been
changed
\pi^0 \pi^0 Production in Proton-Proton Collisions at Tp=1.4 GeV
The reaction pp->pppi0pi0 has been investigated at a beam energy of 1.4 GeV
using the WASA-at-COSY facility. The total cross section is found to be (324 +-
21_systematic +- 58_normalization) mub. In order to to study the production
mechanism, differential kinematical distributions have been evaluated. The
differential distributions indicate that both initial state protons are excited
into intermediate Delta(1232) resonances, each decaying into a proton and a
single pion, thereby producing the pion pair in the final state. No significant
contribution of the Roper resonance N*(1440) via its decay into a proton and
two pions is foundComment: Submitted to PL
Measurement of the _np → dπ0π0 reaction with polarized beam in the region of the d*(2380) resonance
We report on a high-statistics measurement of the most basic double-pionic fusion reaction _np 2192 dπ0π0 over the energy region of the d*(2380) resonance by use of a polarized deuteron beam and observing the double fusion reaction in the quasifree scattering mode. The measurements were performed with the WASA detector setup at COSY. The data reveal substantial analyzing powers and confirm conclusions about the d* resonance obtained from unpolarized measurements. We also confirm the previous unpolarized data obtained under complementary kinematic conditions