Measurement of the $\chi_b(3P)$ mass and of the relative rate of $\chi_{b1}(1P)$ and $\chi_{b2}(1P)$ production

TL;DR

This paper reports precise measurements of the $$ meson production rates and the mass of the $(3P)$ state in proton-proton collisions at the LHCb detector, advancing understanding of bottomonium states.

Contribution

The study provides the first precise measurement of the $(3P)$ mass and the relative production rates of $(1P)$ and $(2P)$ states in a new kinematic range.

Findings

Measured the $(3P)$ mass as 10515.7 MeV/c^2 with uncertainties.

Determined the relative prompt production rate of $(1P)$ and $(2P)$ as a function of transverse momentum.

Provided the first detailed measurement of $$ meson production in the specified energy and rapidity range.

Abstract

The production of $\chi_b$ mesons in proton-proton collisions is studied using a data sample collected by the LHCb detector, at centre-of-mass energies of $\sqrt{s}=7$ and $8$ TeV and corresponding to an integrated luminosity of 3.0 fb$^{-1}$. The $\chi_b$ mesons are identified through their decays to $\Upsilon(1S)\gamma$ and $\Upsilon(2S)\gamma$ using photons that converted to $e^+e^-$ pairs in the detector. The relative prompt production rate of $\chi_{b1}(1P)$ and $\chi_{b2}(1P)$ mesons is measured as a function of the $\Upsilon(1S)$ transverse momentum in the $\chi_b$ rapidity range $2.0<y<4.5$. A precise measurement of the $\chi_b(3P)$ mass is also performed. Assuming a mass splitting between the $\chi_{b1}(3P)$ and the $\chi_{b2}(3P)$ states of 10.5 MeV/$c^2$, the measured mass of the $\chi_{b1}(3P)$ meson is $ m(\chi_{b1}(3P))= 10515.7^{+2.2}_{-3.9}(stat) ^{+1.5}_{-2.1}(syst) MeV/c^2.$