Experimentelle Untersuchungen zur Hyperon-Produktion im Proton-Proton-Stoß
Experimentelle Untersuchungen zur Hyperon-Produktion im Proton-Proton-Stoß
The associated strangeness production in the reaction pp $\rightarrow$ pK$^{+}\Lambda$ has beeninvestigated exclusively at two energies above threshold (excess energies $\epsilon_{p}$K$\Lambda$ =85 MeV and 115 MeV) using the time-of-flight spectrometer COSY-TOF. Due tothe delayed weak decay of the h...
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Personal Name(s): | Hesselbarth, Daniel (Corresponding author) |
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Contributing Institute: |
Publikationen vor 2000; PRE-2000; Retrocat |
Imprint: |
Jülich
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
2001
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Physical Description: |
II, 108 p. |
Document Type: |
Report Book |
Research Program: |
Addenda |
Series Title: |
Berichte des Forschungszentrums Jülich
3849 |
Link: |
OpenAccess OpenAccess |
Publikationsportal JuSER |
The associated strangeness production in the reaction pp $\rightarrow$ pK$^{+}\Lambda$ has beeninvestigated exclusively at two energies above threshold (excess energies $\epsilon_{p}$K$\Lambda$ =85 MeV and 115 MeV) using the time-of-flight spectrometer COSY-TOF. Due tothe delayed weak decay of the hyperon ($\Lambda \rightarrow$ p$\pi^{-}$-) the reaction exhibits a verydistinct signature allowing for a nearly background free event sample. Using thelarge phase space acceptance of the TOF spectrometer, all four charged particlesin the output channel are measured. The $\Lambda$-direction vector is reconstructed fromthe coordinates of the primary and secondary vertex, so that the final eventsample is kinematically complete.During the offline analysis first a geometrical reconstruction is performed,where charged tracks are searched for using the detector hits. The tracks foundare fitted geometrically to a system of four tracks, which represents the completetopological description of an event of the type pp $\rightarrow$ pK$^{+}$($\Lambda \rightarrow$ p$\pi^{-}$). lt consists oftwo two-particle subsystems with a common vertex each, representing the primarypair (p,K$^{+}$) and the $\Lambda$-decay pair (p,$\pi^{-}$). Subsequently, each geometrical solutionis undergoing a kinematical fit leading to physically consistent results. MonteCarlo simulations have helped in developing analysis algorithms and have beenused to perform acceptance corrections.As the energies and momenta of all particles are known, any conceivable absoluteor differential observable of the reaction as well as angular correlationscan be extracted. The total cross section of the reaction pp $\rightarrow$ pK$^{+} \Lambda$ has beendetermined to be $\sigma_{tot}$ = 7.4 $\pm$ 0.5 $\mu$b and $\sigma_{tot}$ = 8.6 $\pm$ 0.6 $\mu$b for the excess energiesof 85 MeV and 115 MeV, respectively. Additionally, angular distributions of theprimary particles and invariant mass spectra of the two-particle subsystems arepresented.An observable, which so far has not been shown for this channel is the angulardistribution of the ejectile plane relative to the beam direction. lt is definedby the center-of-mass momenta of the three ejectile particles in pp $\rightarrow$ pK$^{+} \Lambda$. Inthe case of $\Lambda$-production it shows a distinct deviation from phase space behaviour,indicating that the CMS ejectile plane preferrably lies in the beam-targetdirection.The counting rates have been normalized to a simultaneous measurementof pp $\rightarrow$ d$\pi^{+}$. The angular distribution agrees very nicely with the literature,proving that the analysis of the reaction is possible with high statistics and lowbackground using COSY-TOF. |