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Register a new userOn the Production of an Isotensor Dibaryon in the $pp to pppi^+pi^-$ Reaction
على إنتاج الديباريون الإزوتنسور في تفاعل $pp إلى pppi^+pi^-
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تم إجراء قياسات حصرية لإجراء التفاعل الحرة التقريبية $pp$ إلى $pppi^+pi^-$ باستخدام تصادمات $pd$ عند $T_p$ = 1.2 GeV باستخدام إعداد WASA في COSY. تم الحصول على إجمالي الخطوط الضريبية والتفاضلية الخطوط الضريبية التي تغطي المنطقة الطاقية $T_p = 1.08 - 1.36$ GeV ($sqrt s$ = 2.35 - 2.46 GeV)، والتي تشمل مناطق إثارة $N^*(1440)$ و$Delta(1232)Delta(1232)$. وقد أخذت الحسابات التي تصف هذه الإثارات بواسطة تبادل الميزون الطوقي فأخذت بعيدا عن الخطوط الضريبية التفاضلية التجريبية وفشلت في التنبؤ بشكل كبير بإجمالي الخطوط الضريبية المقاسة. ويمكن للريزونانس الثنائي الذري الذي يحتوي على $I(J^P) = 2(1^+)$ المنتج مع بيون أن يتغلب على هذه العيوب. وقد تنبأ بهذا الريزونانس دايسون وزونج وأكثر حديثا ما حسبته غال وغارسيلازو.
Exclusive measurements of the quasi-free $pp to pppi^+pi^-$ reaction have been performed by means of $pd$ collisions at $T_p$ = 1.2 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region $T_p = 1.08 - 1.36$ GeV ($sqrt s$ = 2.35 - 2.46 GeV), which includes the regions of $N^*(1440)$ and $Delta(1232)Delta(1232)$ resonance excitations. Calculations describing these excitations by $t$-channel meson exchange are at variance with experimental differential cross sections and underpredict substantially the measured total cross section. An isotensor $Delta N$ dibaryon resonance with $I(J^P) = 2(1^+)$ produced associatedly with a pion is able to overcome these deficiencies. Such a dibaryon was predicted by Dyson and Xuong and more recently calculated by Gal and Garcilazo.
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Exclusive measurements of the quasi-free $pp to pppi^+pi^-$ reaction have been carried out at WASA@COSY by means of $pd$ collisions at $T_p$ = 1.2 GeV. Total and differential cross sections have been extracted covering the energy region $T_p = 1.08 - 1.36$ GeV, which is the region of $N^*(1440)$ and $Delta(1232)Delta(1232)$ resonance excitations. Calculations describing these excitations by $t$-channel meson exchange are at variance with the measured differential cross sections and underpredict substantially the experimental total cross section. An isotensor $Delta N$ dibaryon resonance with $I(J^P) = 2(1^+)$ produced associatedly with a pion is able to overcome these deficiencies.
The cross section for prompt neutral and charged three pion production in pp interactions was measured at excess energies in the range 160 - 217 MeV. That comprises the first measurement of the pp->pp pi0pi0pi0 reaction and the comparison with the pp->pp pi+pi-pi0 reaction, in a very direct way. The experiment was performed above the eta meson production threshold and the cross section normalization was obtained from a concurrent measurement of the reaction pp->pp eta with the eta decaying into 3 pions. Since the same final states are selected, the measurement has a low systematical error. The measured cross section ratio sigma(pp->pp pi+pi-pi0)/sigma(pp->pp pi0pi0pi0) is compared to predictions of dominance of different isobars in the intermediate state.
Coherent double neutral-pion photoproduction on the deuteron, $gamma{d}${$to$}$pi^0pi^0{d}$, has been experimentally studied at incident photon energies ranging from 0.75 to 1.15 GeV. The total cross section as a function of the $gamma{d}$ center-of-mass energy shows resonance-like behavior, which peaks at approximately 2.47 and 2.63 GeV. The measured angular distribution of deuteron emission is rather flat, which cannot be reproduced by the kinematics of quasi-free $pi^0pi^0$ production with deuteron coalescence. In $pi^0d $ invariant-mass distributions, a clear peak is observed at $2.14{pm}0.01$ GeV$/c^2$ with a width of $0.09{pm}0.01$ GeV$/c^2$. The spin-parity of this state is restricted to $1^+$, $2^+$ or $3^-$ from the angular distributions of the two $pi^0$s. The present work shows strong evidence for the existence of an isovector dibaryon resonance with a mass of 2.14 GeV$/c^2$. The $2^+$ assignment is consistent with the theoretically predicted ${cal{D}}_{12}$ state, and also with the energy dependence of the $pi{d}$ partial-wave amplitude $^3!P_2$ for the $pi^{pm}d${$to$}$pi^{pm}d$ and $pi^+d${$to$}${pp}$ reactions.
Measurements of the $pp to pK^+Lambda$ reaction at $T_p$ = 2.28 GeV have been carried out at COSY-TOF. In addition to the $Lambda p$ FSI and $N^*$ resonance excitation effects a pronounced narrow structure is observed in the Dalitz plot and in its projection on the $pLambda$-invariant mass. The structure appears at the $pp to $N$K^+Sigma$ threshold and is interpreted as $Sigma$N cusp effect. The observed width of 20 MeV/$c^2$ is substantially broader than anticipated from previous inclusive measurements. Angular distributions of this cusp structure are shown to be dissimilar to those in the residual $pK^+Lambda$ channel, but similar to those observed in the $pK^+Sigma^0$ channel.
Data accumulated recently for the exclusive measurement of the $ppto pppi^+pi^-$ reaction at a beam energy of 0.793 GeV using the COSY-TOF spectrometer have been analyzed with respect to possible events from the $pp to nnpi^+pi^+$ reaction channel. The latter is expected to be the only $pipi$ production channel, which contains no major contributions from resonance excitation close to threshold and hence should be a good testing ground for chiral dynamics in the $pipi$ production process. No single event has been found, which meets all conditions for being a candidate for the $pp to nn pi^+pi^+$ reaction. This gives an upper limit for the cross section of 0.16 $mu$b (90% C.L.), which is more than an order of magnitude smaller than the cross sections of the other two-pion production channels at the same incident energy.
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