# Measurement of $\psi(2S)$ polarisation in $pp$ collisions at $\sqrt{s}=7$ TeV

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## Abstract

The polarisation of prompt $\psi(2S)$ mesons is measured by performing an angular analysis of $\psi(2S)\rightarrow \mu^{+} \mu^{-}$ decays using proton-proton collision data, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected by the LHCb detector at a centre-of-mass energy of 7 TeV. The polarisation is measured in bins of transverse momentum $p_\mathrm{T}$ and rapidity $y$ in the kinematic region $3.5<p_\mathrm{T}<15$ GeV$/c$ and $2.0<y<4.5$, and is compared to theoretical models. No significant polarisation is observed.

 Invariant mass distribution of $\psi {(2S)}$ candidates in the kinematic region $5< p_{\rm T} <7 {\mathrm{ Ge V /}c}$ and $2.5 ## Tables and captions  Sources of systematic uncertainties on the polarisation parameter$\lambda_\theta$in the helicity and Collins-Soper frames. For each type of uncertainty, the average and the range over all$\psi {(2S)}$kinematic bins are shown. Table_1.pdf [26 KiB] HiDef png [98 KiB] Thumbnail [46 KiB] tex code Measured prompt$\psi {(2S)}$polarisation parameters$\lambda_\theta$,$\lambda_{\theta\phi}$,$\lambda_{\phi}$and$\lambda_{\mathrm{inv}}$in bins of$p_{\rm T}$and$y$in the helicity frame. The first uncertainty is statistical and the is second systematic. Table_2.pdf [43 KiB] HiDef png [220 KiB] Thumbnail [94 KiB] tex code Measured prompt$\psi {(2S)}$polarisation parameters$\lambda_\theta$,$\lambda_{\theta\phi}$,$\lambda_{\phi}$and$\lambda_{\mathrm{inv}}$in bins of$p_{\rm T}$and$y\$ in the Collins-Soper frame. The first uncertainty is statistical and the second is systematic. Table_3.pdf [43 KiB] HiDef png [221 KiB] Thumbnail [94 KiB] tex code

Created on 20 August 2019.Citation count from INSPIRE on 20 August 2019.