A bstract Measurements are reported of the central exclusive production of J/ψ and ψ (2 S ) mesons in pp collisions at a centre-of-mass energy of 13 TeV. Backgrounds are significantly reduced compared to previous measurements made at lower energies through the use of new forward shower counters. The products of the cross-sections and the branching fractions for the decays to dimuons, where both muons are within the pseudorapidity range 2 . 0 < η < 4 . 5, are measured to be $$ \begin{array}{c}\hfill {\sigma}_{J/\psi \to {\mu}^{+}{\mu}^{-}} = 435 \pm 18 \pm 11 \pm 17\ \mathrm{p}\mathrm{b}\hfill \\ {}\hfill {\sigma}_{\psi (2S)\to {\mu}^{+}{\mu}^{-}} = 11.1 \pm 1.1 \pm 0.3 \pm 0.4\ \mathrm{p}\mathrm{b}.\hfill \end{array} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mtable> <mml:mtr> <mml:mtd> <mml:msub> <mml:mi>σ</mml:mi> <mml:mrow> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>−</mml:mo> </mml:msup> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mspace/> <mml:mn>435</mml:mn> <mml:mspace/> <mml:mo>±</mml:mo> <mml:mspace/> <mml:mn>18</mml:mn> <mml:mspace/> <mml:mo>±</mml:mo> <mml:mspace/> <mml:mn>11</mml:mn> <mml:mspace/> <mml:mo>±</mml:mo> <mml:mspace/> <mml:mn>17</mml:mn> <mml:mspace/> <mml:mi>p</mml:mi> <mml:mi>b</mml:mi> </mml:mtd> </mml:mtr> <mml:mtr> <mml:mtd> <mml:msub> <mml:mi>σ</mml:mi> <mml:mrow> <mml:mi>ψ</mml:mi> <mml:mfenced> <mml:mrow> <mml:mn>2</mml:mn> <mml:mi>S</mml:mi> </mml:mrow> </mml:mfenced> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>−</mml:mo> </mml:msup> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mspace/> <mml:mn>11.1</mml:mn> <mml:mspace/> <mml:mo>±</mml:mo> <mml:mspace/> <mml:mn>1.1</mml:mn> <mml:mspace/> <mml:mo>±</mml:mo> <mml:mspace/> <mml:mn>0.3</mml:mn> <mml:mspace/> <mml:mo>±</mml:mo> <mml:mspace/> <mml:mn>0.4</mml:mn> <mml:mspace/> <mml:mi>p</mml:mi> <mml:mi>b</mml:mi> <mml:mtext>.</mml:mtext> </mml:mtd> </mml:mtr> </mml:mtable> </mml:math> The first uncertainties are statistical, the second are systematic, and the third are due to the luminosity determination. The cross-sections are also measured differentially for meson rapidities between 2.0 and 4.5. Good agreement is observed with theoretical predictions. Photoproduction cross-sections are derived and compared to previous experiments, and a deviation from a pure power-law extrapolation of lower energy data is observed.
Tópico:
Particle physics theoretical and experimental studies
