a 0 + (980)-resonance production in the reaction pp → dπ + η close to the $$K\bar K$$ threshold

Scalar-isovector K¯ production close to threshold

“…At T p = 2.83 GeV, kaons with p K + = (625 − 1000) MeV/c have been detected in a different part of the SD, consisting of one layer of 6 scintillation counters for TOF-stop ("sidewall counters"). Two multi-wire proportional chambers (MWPCs) positioned between the TOF-start and -stop counters allow one to deduce the ejectile momenta and to suppress background from secondary scattering [21,22].…”

“…The final goal of these investigations is the extraction of the a 0 /f 0 -mixing amplitude, a quantity which is believed to shed light on the nature of these resonances [19,20]. As a first step the reactions pp → dK +K 0 [21] and pp → dπ + η [22] have been measured in parallel at the ANKE spectrometer [23] for T p =2.65 GeV, corresponding to an excess energy of Q=47.4 MeV with respect to the K +K 0 threshold. The data for the strangeness decay channel -which are almost background free -indicate that more than 80% of the kaon pairs are produced in a relative s-wave, corresponding to the a + 0 channel [21].…”

“…The data for the strangeness decay channel -which are almost background free -indicate that more than 80% of the kaon pairs are produced in a relative s-wave, corresponding to the a + 0 channel [21]. On the other hand, the π + η signal sits on top of a strong but smooth background of multi-pion production which, together with the small acceptance of ANKE for this channel, makes the interpretation of the a + 0 signal model-dependent [22]. However, the obtained branching ratio σ(pp→d(K +K 0 ) s−wave )/σ(pp→da + 0 →dπ + η) = 0.029 ± 0.008 stat ± 0.009 sys [22] is in line with values from literature [3].…”

“…On the other hand, the π + η signal sits on top of a strong but smooth background of multi-pion production which, together with the small acceptance of ANKE for this channel, makes the interpretation of the a + 0 signal model-dependent [22]. However, the obtained branching ratio σ(pp→d(K +K 0 ) s−wave )/σ(pp→da + 0 →dπ + η) = 0.029 ± 0.008 stat ± 0.009 sys [22] is in line with values from literature [3].…”