Branching Fraction Measurement of B± → χc1π+π−K± and Search for a Narrow Resonance with the Belle Experiment

by Elisabeth Patricia Panzenböck
Doctoral thesis
Date of Examination:2014-12-02
Date of issue:2014-12-09
Advisor:Prof. Dr. Ariane Frey
Referee:Prof. Dr. Ariane Frey
Referee:Prof. Dr. Kenkichi Assoc. Miyabayashi
Persistent Address: http://dx.doi.org/10.53846/goediss-4817

 

 

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Abstract

English

The effective QCD colour potential can be derived by studying quarkonia through spectroscopy to determine their masses. In the charmonium spectrum, which is well understood and precisely measured below the DDbar production threshold, not all predicted states above that threshold have been observed yet and others cannot be assigned to conventional charmonium states. To fathom the nature of the latter so-called exotic or charmonium-like states motivates this thesis. A first observation and measurement of the branching fraction of the four-body B meson decay B± → χc1π+π−K± is presented. In addition, the χc1π+π− invariant mass spectrum is studied in order to search for contributions of any intermediate charmonium(-like) resonance. This study is based on a 772 × 10^6 BBbar pairs data sample produced at a center-of-mass energy of sqrt(s) = 10.58 GeV/c2 corresponding to the Υ(4S) resonance and collected by the Belle detector at the KEKB asymmetric-energy e+e− collider located at KEK, Japan. The signal yield is extracted by an unbinned maximum likelihood fit to the difference-to-beam energy ∆E distribution and the B decay branching fraction is obtained to be B(B+→χc1π+π−K+) = ( 3.89 ± 0.19 (stat) ± 0.20 (syst) ) × 10^−4 . Using the χc1π+π− mass spectrum, an upper limit including both statistical and systematic uncertainties is given for a new decay mode of the exotic X(3872) charmonium-like state, B(B±→X(3872)K±) × B(X(3872)→χc1(1P )π+π−) < 1.4 × 10^−6 @ 90% C.L., as well as a preliminary upper limit for the still undiscovered conventional charmonium χc1(2P) following a mass assumption of 3920 MeV/c2 , B(B±→χc1(2P)K±) × B(χc1(2P)→χc1(1P)π+π−) < 1.1 × 10^−5 @ 90% C.L.. These results favour the hypothesis of X(3872) being an admixture of a D0D∗0 molecule state and a conventional charmonium.
Keywords: Hadron Spectroscopy, X(3872), Chic1(2P), Belle, Exotic Hadrons
 
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