CERN Accelerating science

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: : : An event display of a cosmic ray muon crossing CMS: \subref{fig:all} the full detector and \subref{fig:zoom} a detail of the central region. ECAL hits are in magenta, HCAL hits in blue, tracker and muon hits in green. The views represent a section of CMS in a plane perpendicular to the beam direction, the $x$ axis pointing to the centre of the LHC ring and the $y$axis pointing vertically upwards.

: scale=0.39, angle=0

: scale=0.39, angle=0 : : \subref{fig:spectraMu} Momentum spectrum of the muons passing the selections; \subref{fig:spectraEcal} spectrum of the reconstructed energy in the lower ECAL hemisphere. Alogarithmic binning is used.

: scale=0.39, angle=0

: scale=0.39, angle=0 : : Measured distributions of $\Delta E / \Delta x$ in ECAL; \subref{fig:dEodxLow} for muon momenta below 10~GeV/$c$; \subref{fig:dEodxHigh} for muon momenta above 300~GeV/$c$; the fraction of events with $\Delta E/\Delta x > 10$~MeV\,g$^{-1}$\,cm$^2$ is $1.3\times10^{-3}$ and $8\times10^{-2}$ in \subref{fig:dEodxLow} and\subref{fig:dEodxHigh} respectively.

Dependence of the raw $\langle {\rm d}E/{\rm d}x \rangle$ on the angle $\alpha$ between the muon direction and the crystal axis, for muon momentum between 5 and 10~GeV/$c$. Vertical bars representstatistical errors.

: scale=0.45, angle=0

: scale=0.45, angle=0 : : \subref{fig:dEodx} Muon stopping power measured in PbWO$_4$ (dots) as a function of muon momentum compared to expectations \cite{ANP_Tables} (continuous black line). The expected contributions from collision and radiative processes are plotted as well (red dotted line and blue dashed line respectively). \subref{fig:residuals} Ratio of the measured and the expected values of the muon stopping power, as a function of muon momentum. As discussed in the text, in both figures, the shaded grey area indicates the expected 68\,\% probability central interval, while the continuous cyan curves delimit the minimum interval containing 68\,\% of the expected results. ``Experimental errors'' are not shown for reasonsdiscussed in the text.