{"id":184,"date":"2011-07-20T17:48:42","date_gmt":"2011-07-20T08:48:42","guid":{"rendered":"http:\/\/hepsv.sci.osaka-cu.ac.jp\/?p=184"},"modified":"2024-06-21T12:14:14","modified_gmt":"2024-06-21T03:14:14","slug":"observation_of_xib0","status":"publish","type":"post","link":"https:\/\/hepsv.sci.osaka-cu.ac.jp\/en\/ocuhep-news\/observation_of_xib0\/","title":{"rendered":"Observation of \u039eb<\/i><\/sub>0<\/sup><\/span> Baryon"},"content":{"rendered":"

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\"Xib_0_fit\"<\/a>

Figure 5 : Plot of a gausisan fit of the invariant mass distribution of \u039eb<\/i><\/sub>0<\/sup> in Figure 4.<\/p><\/div><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

So far, in the CDF experiment in which the Osaka City University High Energy Physics Laboratory participates, we have reported the discovery of new baryons containing b<\/em> quarks: \u03a3b<\/i><\/sub>\u00b1<\/sup>, \u03a3b<\/i><\/sub>*\u00b1<\/sup><\/span> (High Energy Physics Laboratory News, October 26, 2006<\/a>), and \u039eb<\/i><\/sub>\u2212<\/sup><\/span> (High Energy Physics Laboratory News, June 18, 2007<\/a>). We are pleased to announce the discovery of a new particle, \u039eb<\/i><\/sub>0<\/sup><\/span>. The \u039eb<\/i><\/sub>0<\/sup><\/span> is a baryon with a spin of 1\/2 and an internal structure composed of the quarks (u<\/em>, s<\/em>, b<\/em>). Unlike the previously discovered \u039eb<\/i><\/sub>\u2212<\/sup><\/span>, it contains a u<\/em> quark instead of a d<\/em> quark. Figure 1 classifies spin 1\/2 baryons composed of u<\/em>, d<\/em>, s<\/em>, and b<\/em> quarks based on the number of b<\/em> quarks. The \u039eb<\/i><\/sub>0<\/sup><\/span> falls into the category with one b<\/em> quark. Incidentally, baryons containing two b<\/em> quarks have not yet been discovered.<\/p>\n

The data analysis for this discovery was conducted with a statistical amount corresponding to 4.2 fb\u22121<\/sup> of proton-antiproton collisions at a center-of-mass energy of 1.96 TeV. The \u039eb<\/i><\/sub>0<\/sup><\/span> was identified by reconstructing the decay \u039eb<\/i><\/sub>0<\/sup> \u2192 \u039ec<\/i><\/sub>+<\/sup>\u03c0<\/i>\u2212<\/sup>, \u039ec<\/i><\/sub>+<\/sup> \u2192 \u039e\u2212<\/sup>\u03c0<\/i>+<\/sup>\u03c0<\/i>+<\/sup><\/span>. The \u039e\u2212<\/sup><\/span> further decays into \u039b\u03c0<\/i>\u2212<\/sup><\/span>, and the \u039b<\/span> decays into p<\/i>\u03c0<\/i>\u2212<\/sup><\/span>. Unlike the previous discovery of \u039eb<\/i><\/sub>\u2212<\/sup><\/span>, where the final state included a \u03bc<\/i>+<\/sup>\u03bc<\/i>\u2212<\/sup><\/span> pair from J\/\u03c8<\/i><\/span>, serving as a marker for the reaction, the final state of the \u039eb<\/i><\/sub>0<\/sup><\/span> consists entirely of pions or protons, making it difficult to identify without clear markers. However, thanks to the high-performance silicon vertex detector (SVX), we achieved our goal. Figure 2 shows the decay mode of the \u039eb<\/i><\/sub>0<\/sup><\/span> and the particle detection in the SVX.<\/p>\n

Figure 3 shows the invariant mass distribution reconstructed from \u039e\u2212<\/sup><\/span> and two \u03c0<\/i>+<\/sup><\/span>. A clear peak of \u039ec<\/i><\/sub>\u2212<\/sup><\/span> can be seen at 2.47 GeV\/c<\/em>2<\/sup>. Figure 4 shows the results obtained by reconstructing \u039ec<\/i><\/sub>+<\/sup><\/span> and \u03c0<\/i>\u2212<\/sup><\/span>, with a significant peak observed near 5.8 GeV\/c<\/em>2<\/sup>. Based on the peak width of \u039ec<\/i><\/sub>\u2212<\/sup><\/span> in Figure 3, the mass precision of \u039eb<\/i><\/sub>0<\/sup><\/span> is estimated to be 20 MeV\/c<\/em>2<\/sup>. Fitting the peak in Figure 4 using this value results in Figure 5, yielding a \u039eb<\/i><\/sub>0<\/sup><\/span> signal count of 25.3 +5.6<\/sup>\u22125.4<\/sub>. Statistically processing this data, the probability of the same peak arising from statistical fluctuations in the background events is calculated to be 3.6\u00d710\u221212<\/sup>, corresponding to 6.8\u03c3. This indicates that the discovery of \u039eb<\/i><\/sub>0<\/sup><\/span> is almost certain. The mass of \u039eb<\/i><\/sub>0<\/sup><\/span> has been measured as:<\/p>\n

m<\/em>(\u039eb<\/i><\/sub>0<\/sup><\/span>) = 5787.8\u00b15.0(stat)\u00b11.3(syst) MeV\/c2 <\/sup>.<\/span><\/p>\n

In the CDF experiment, we currently have about twice the amount of data used in this analysis, so there may be further discoveries of new particles in future analyses.<\/p>\n