Hyperon production in the threshold region was studied in the reaction pp→K+Λp using the time-of-flight spectrometer COSY-TOF. Exclusive data, covering the full phase-space, were taken at three ...different beam momenta pbeam=2.59, 2.68 and 2.85 GeV/c (corresponding to excess energies of ɛ=85, 115 and 171 MeV). Total cross-sections were deduced to be 7.4±0.5 μb, 8.6±0.6 μb and 16.5±0.4 μb, respectively. Differential observables including Dalitz plots were obtained. From the investigation of the Dalitz plot at pbeam=2.85 GeV/c a dominant contribution of the N∗(1650)-resonance to the reaction mechanism was found. In addition the pΛ-final-state interaction turned out to have a significant influence on the Dalitz plot distribution even 171 MeV above threshold.
Production of antihydrogen Baur, G.; Boero, G.; Brauksiepe, A. ...
Physics letters. B,
02/1996, Letnik:
368, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Results are presented for a measurement for the production of the antihydrogen atom
H
0 ≡
p
e
+
, the simplest atomic bound state of antimatter.
A method has been used by the PS210 collaboration at ...LEAR which assumes that the production of
H
0
is predominantly mediated by the e
+e
−-pair creation via the two-photon mechanism in the antiproton-nucleus interaction. Neutral
H
0
atoms are identified by a unique sequence of characteristics. In principle
H
0
is well suited for investigations of fundamental CPT violation studies under different forces, however, in our investigations we concentrate on the production of this antimatter object, since so far it has never been observed before.
The production of 11 antihydrogen atoms is reported including possibly 2±1 background signals, the observed yield agrees with theoretical predictions.
The energy dependence of the total cross section for the
pp→
pK
+
Λ reaction was measured in the threshold region covering the excess energy range up to 7 MeV.
Existing model calculations describe ...the slope of the measured cross sections well, but are too low by a factor of two to three in rate.
The data were used for a precise determination of the beam momentum of the COSY-synchrotron.
The reaction
pp→
K
+
Λp was measured exclusively at the cooler synchrotron COSY at beam momenta of p
Beam = 2.50
GeV/c and p
Beam = 2.75
GeV/c using the TOF detector. Angular and momentum ...distributions were obtained for the full phase space of the reaction products. Total cross sections were extracted to be (2.7 ± 0.3)
μb and (12.0 ± 0.4)
μb, respectively. The polarization of the
Λ-hyperon was determined as a function of its transversal momentum and was found to be negative for transverse momentum transfers of p
T
≥ 0.3
GeV/c. The results together with existing data are compared with phenomenological parametrizations and model calculations on the basis of meson exchange.
Hyperon production in the threshold region was studied in the reaction pp→K+Λp using the time-of-flight spectrometer COSY-TOF. Exclusive data, covering the full phase-space, were taken at the three ...different beam momenta of pbeam=2.95, 3.20 and 3.30 GeV/c, corresponding to excess energies of ε=204, 285 and 316 MeV, respectively. Total cross-sections were deduced for the three beam momenta to be 23.9±0.8±2.0 μb, 28.4±1.3±2.2 μb and 35.0±1.3±3.0 μb. Differential observables including Dalitz plots were obtained. The analysis of the Dalitz plots reveals a strong influence of the N(1650)-resonance at pbeam=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 pΛ-final-state interaction turned out to have a significant influence on the Dalitz plot distribution.
The two-pion production reaction
pp
→
pp
π
+
π
−
was measured with a polarized proton beam at
T
p
≈ 750 and 800MeV using the short version of the COSY-TOF spectrometer. The implementation of a ...delayed-pulse technique for Quirl and central calorimeter provided positive π
+
identification in addition to the standard particle identification, energy determination as well as time-of-flight and angle measurements. Thus all four-momenta of the emerging particles could be determined with 1–4 overconstraints. Total and differential cross-sections as well as angular distributions of the vector analyzing power have been obtained. They are compared to previous data and theoretical calculations. In contrast to predictions we find significant analyzing-power values up to
A
y
= 0.3. The data taken in the energy region of the excitation of the Roper resonance confirm that its dominant ππ decay channel is
N
*
→
N
σ.
At COSY pp-bremsstrahlung was measured at a beam momentum of 797 MeV/c using an external proton beam. Data were taken with a wide angle spectrometer covering a solid angle of approximately 1 sr. The ...complete data set is presented in a series of c.m. angular distributions as well as a single Dalitz plot. The absence of final state interaction effects is understood as being due to a general insensitivity of the pp
γ reaction to the spin-singlet component of the NN interaction. Coplanar angular distributions (in the laboratory system) are well reproduced by recent model calculations; also good agreement is found with the original TRIUMF data K. Michaelian et al., Phys. Rev. D 41 (1990) 286 when omitting the rescaling factor of 2/3.
Results from PS185 Johansson, T.; Barnes, P.D.; Bassalleck, B. ...
Nuclear physics. A,
08/1999, Letnik:
655, Številka:
1
Journal Article
Recenzirano
The PS185 experiment at LEAR/CERN has studied strangeness production in antiproton-proton collisions. Exclusive final states of antihyperon-hyperon pairs have been measured in order to investigate ...strange-quark production dynamics. A comprehensive data set is available for the
ΛΛ
channel and observables include total and differential cross sections, polarisations and spin correlations. Data from other hyperon channels, such as
Σ
0Λ + c.c.
,
Σ
+Σ
+
and
Σ
−Σ
−
, are also available. The analysis of a spin transfer measurement for the
pp →
ΛΛ
reaction using a polarised proton target is in progress.
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