Measurements of the \(\chi\)\(_c\) and \(\chi\)\(_b\) quarkonium states in \(\rho\)\(\rho\) collisions with the ATLAS experiment

Chisholm , Andrew Stephen (2014). Measurements of the \(\chi\)\(_c\) and \(\chi\)\(_b\) quarkonium states in \(\rho\)\(\rho\) collisions with the ATLAS experiment. University of Birmingham. Ph.D.

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Abstract

The chi_b bottomonium states are observed through the reconstruction of the radiative decays chi_b(nP)→Upsilon(1S) gamma using 4.4/fb of pp collision data collected at sqrt(s) = 7 TeV with the ATLAS experiment. The production of the chi_b(1P) and chi_b(2P) bottomonium states is observed in addition to a candidate for a new bottomonium state, consistent with theoretical expectations for the chi_b(3P) states. The production-averaged mass barycentre for the chi_b(3P) candidate is measured to be 10541\(\pm\)11 (stat.) \(\pm\) 30 (syst.) MeV. The consequences of this discovery for our understanding of bottomonium production phenomenology in hadronic collisions is reviewed. The production of the chi_c1 and chi_c2 charmonium states has been measured in sqrt(s) = 7 TeV pp collisions with the ATLAS experiment using a data sample representing an integrated luminosity of 4.5/fb. The prompt and non-prompt production cross sections for the chi_c1 and chi_c2 states are measured within the region | y(J/psi)| < 0.75. These measurements suggest that 24-28% of prompt J/psi are produced in feed-down from radiative chi_c1 and chi_c2 decays. The production of the chi_c2 state, relative to the chi_c1 state, is measured for both prompt and non-prompt production processes. This collection of measurements is compared to a number of theoretical predictions for chi_cJ production at the LHC. The branching fraction B(B\(\pm\)→chi_c1 K\(\pm\)) = (4.9\(_pm\)\(\pm\) (stat.) \(\pm\)0.6 (syst.))x 10^-4 is also measured with the same dataset and chi_c event selection.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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