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Exclusive dimuon production in ultraperipheral Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV with ATLAS

The ATLAS collaboration
CERN-EP-2020-138, 2020.

Abstract
Exclusive dimuon production in ultraperipheral collisions (UPC), resulting from photon-photon interactions in the strong electromagnetic fields of colliding high-energy lead nuclei, $\mathrm{PbPb}(\gamma\gamma) \rightarrow \mu^+\mu^- (\mathrm{Pb}^{(\star)}\mathrm{Pb}^{(\star)} )$, is studied using $\mathcal{L}_{\mathrm{int}} = 0.48$ nb$^{-1}$ of $\sqrt{s_\mathrm{NN}}=5.02$ TeV lead-lead collision data at the LHC with the ATLAS detector. Dimuon pairs are measured in the fiducial region $p_{\mathrm{T}\mu} > 4$ GeV, $|\eta_{\mu}| < 2.4$, invariant mass $m_{\mu\mu} > 10$ GeV, and $p_{\mathrm{T,\mu\mu}} < 2$ GeV. The primary background from single-dissociative processes is extracted from the data using a template fitting technique. Differential cross sections are presented as a function of $m_{\mu\mu}$, absolute pair rapidity ($|y_{\mu\mu}|$), scattering angle in the dimuon rest frame ($|\cos \vartheta^{\star}_{\mu\mu}|$) and the colliding photon energies. The total cross section of the UPC $\gamma \gamma \rightarrow \mu^{+}\mu^{-}$ process in the fiducial volume is measured to be $\sigma_{\mathrm{fid}}^{\mu\mu} = 34.1 \! \pm \! 0.3 \mathrm{(stat.)} \! \pm \! 0.7 \mathrm{(syst.)}$ $\mu\mathrm{b}$. Generally good agreement is found with calculations from STARlight, which incorporate the leading-order Breit-Wheeler process with no final-state effects, albeit differences between the measurements and theoretical expectations are observed. In particular, the measured cross sections at larger $|y_{\mu\mu}|$ are found to be about 10-20% larger in data than in the calculations, suggesting the presence of larger fluxes of photons in the initial state. Modification of the dimuon cross sections in the presence of forward and/or backward neutron production is also studied and is found to be associated with a harder incoming photon spectrum, consistent with expectations.

  • Differential cross section for mass in 10 < |m_mumu| < 20 GeV

    Data from arXiv:2011.12211 Figure 6a

    10.17182/hepdata.104407.v1/t1

    Differential UPC dimuon cross sections shown as a function of $|y_{\mu\mu}|$ in the interval $10 < |m_{\mu\mu}| < 20$ GeV.

  • Differential cross section for mass in 20 < |m_mumu| < 40 GeV

    Data from arXiv:2011.12211 Figure 6b

    10.17182/hepdata.104407.v1/t2

    Differential UPC dimuon cross sections shown as a function of $|y_{\mu\mu}|$ in the interval $20 < |m_{\mu\mu}| < 40$ GeV.

  • Differential cross section for mass in 40 < |m_mumu| < 80 GeV

    Data from arXiv:2011.12211 Figure 6c

    10.17182/hepdata.104407.v1/t3

    Differential UPC dimuon cross sections shown as a function of $|y_{\mu\mu}|$ in the interval $40 < |m_{\mu\mu}| < 80$ GeV.

  • Data/STARlight ratio in 10 < |m_mumu| < 20 GeV

    Data from arXiv:2011.12211 Figure 6d

    10.17182/hepdata.104407.v1/t4

    Ratio of differential UPC dimuon cross sections from data and STARlight shown as a function of $|y_{\mu\mu}|$ in the interval...

  • Data/STARlight ratio in 20 < |m_mumu| < 40 GeV

    Data from arXiv:2011.12211 Figure 6e

    10.17182/hepdata.104407.v1/t5

    Ratio of differential UPC dimuon cross sections from data and STARlight shown as a function of $|y_{\mu\mu}|$ in the interval...

  • Data/STARlight ratio in 40 < |m_mumu| < 80 GeV

    Data from arXiv:2011.12211 Figure 6f

    10.17182/hepdata.104407.v1/t6

    Ratio of differential UPC dimuon cross sections from data and STARlight 2.0 shown as a function of $|y_{\mu\mu}|$ in the...

  • Differential cross section for mass in 0 < |y_mumu| < 0.8

    Data from arXiv:2011.12211 Figure 7a

    10.17182/hepdata.104407.v1/t7

    Differential UPC dimuon cross sections shown as a function of $|m_{\mu\mu}|$ in the interval $0 < |y_{\mu\mu}| < 0.8$.

  • Differential cross section for mass in 0.8 < |y_mumu| < 1.6

    Data from arXiv:2011.12211 Figure 7b

    10.17182/hepdata.104407.v1/t8

    Differential UPC dimuon cross sections shown as a function of $|m_{\mu\mu}|$ in the interval $0.8 < |y_{\mu\mu}| < 1.6$.

  • Differential cross section for mass in 1.6 < |y_mumu| < 2.4

    Data from arXiv:2011.12211 Figure 7c

    10.17182/hepdata.104407.v1/t9

    Differential UPC dimuon cross sections shown as a function of $|m_{\mu\mu}|$ in the interval $1.6 < |y_{\mu\mu}| < 2.4$.

  • Data/STARlight ratio in 0 < |y_mumu| < 0.8

    Data from arXiv:2011.12211 Figure 7d

    10.17182/hepdata.104407.v1/t10

    Ratio of differential UPC dimuon cross sections from data and STARlight shown as a function of $|m_{\mu\mu}|$ in the interval...

  • Data/STARlight ratio in 0.8 < |y_mumu| < 1.6

    Data from arXiv:2011.12211 Figure 7e

    10.17182/hepdata.104407.v1/t11

    Ratio of differential UPC dimuon cross sections from data and STARlight shown as a function of $|m_{\mu\mu}|$ in the interval...

  • Data/STARlight ratio in 1.6 < |y_mumu| < 2.4

    Data from arXiv:2011.12211 Figure 7f

    10.17182/hepdata.104407.v1/t12

    Ratio of differential UPC dimuon cross sections from data and STARlight 2.0 shown as a function of $|m_{\mu\mu}|$ in the...

  • Diff. cross section for |cos(theta*)| in 10 < |m_mumu| < 20 GeV

    Data from arXiv:2011.12211 Figure 8a

    10.17182/hepdata.104407.v1/t13

    Differential UPC dimuon cross sections shown as a function of $|\cos\theta^{\star}_{\mu\mu}|$ in the interval $10 < |m_{\mu\mu}| < 20$ GeV.

  • Diff. cross section for |cos(theta*)| in 20 < |m_mumu| < 40 GeV

    Data from arXiv:2011.12211 Figure 8b

    10.17182/hepdata.104407.v1/t14

    Differential UPC dimuon cross sections shown as a function of $|\cos\theta^{\star}_{\mu\mu}|$ in the interval $20 < |m_{\mu\mu}| < 40$ GeV.

  • Diff. cross section for |cos(theta*)| in 40 < |m_mumu| < 80 GeV

    Data from arXiv:2011.12211 Figure 8c

    10.17182/hepdata.104407.v1/t15

    Differential UPC dimuon cross sections shown as a function of $|\cos\theta^{\star}_{\mu\mu}|$ in the interval $40 < |m_{\mu\mu}| < 80$ GeV.

  • Data/STARlight ratio for |cos(theta*)| in 10 < |m_mumu| < 20 GeV

    Data from arXiv:2011.12211 Figure 8d

    10.17182/hepdata.104407.v1/t16

    Ratio of differential UPC dimuon cross sections from data and STARlight shown as a function of $|\cos\theta^{\star}_{\mu\mu}|$ in the interval...

  • Data/STARlight ratio for |cos(theta*)| in 20 < |m_mumu| < 40 GeV

    Data from arXiv:2011.12211 Figure 8e

    10.17182/hepdata.104407.v1/t17

    Ratio of differential UPC dimuon cross sections from data and STARlight shown as a function of $|\cos\theta^{\star}_{\mu\mu}|$ in the interval...

  • Data/STARlight ratio for |cos(theta*)| in 40 < |m_mumu| < 80 GeV

    Data from arXiv:2011.12211 Figure 8f

    10.17182/hepdata.104407.v1/t18

    Ratio of differential UPC dimuon cross sections from data and STARlight 2.0 shown as a function of $|\cos\theta^{\star}_{\mu\mu}|$ in the...

  • Diff. xsect for |cos(theta*)| in 10<|m_mumu|<20 GeV, |y|<0.8

    Data from arXiv:2011.12211 Figure 9a

    10.17182/hepdata.104407.v1/t19

    Differential UPC dimuon cross sections shown as a function of $|\cos\theta^{\star}_{\mu\mu}|$ in the interval $10 < |m_{\mu\mu}| < 20$ GeV...

  • Diff. xsect for |cos(theta*)| in 20<|m_mumu|<40 GeV, |y|<0.8

    Data from arXiv:2011.12211 Figure 9b

    10.17182/hepdata.104407.v1/t20

    Differential UPC dimuon cross sections shown as a function of $|\cos\theta^{\star}_{\mu\mu}|$ in the interval $20 < |m_{\mu\mu}| < 40$ GeV...

  • Diff. xsect for |cos(theta*)| in 40<|m_mumu|<80 GeV, |y|<0.8

    Data from arXiv:2011.12211 Figure 9c

    10.17182/hepdata.104407.v1/t21

    Differential UPC dimuon cross sections shown as a function of $|\cos\theta^{\star}_{\mu\mu}|$ in the interval $40 < |m_{\mu\mu}| < 80$ GeV...

  • Data/SL ratio for |cos(theta*)| in 10<|m_mumu|<20 GeV, |y|<0.8

    Data from arXiv:2011.12211 Figure 7d

    10.17182/hepdata.104407.v1/t22

    Ratio of differential UPC dimuon cross sections from data and STARlight shown as a function of $|\cos\theta^{\star}_{\mu\mu}|$ in the interval...

  • Data/SL ratio for |cos(theta*)| in 20<|m_mumu|<40 GeV, |y|<0.8

    Data from arXiv:2011.12211 Figure 9e

    10.17182/hepdata.104407.v1/t23

    Ratio of differential UPC dimuon xsects from data and STARlight shown as a function of $|\cos\theta^{\star}_{\mu\mu}|$ in the interval $20...

  • Data/SL ratio for |cos(theta*)| in 40<|m_mumu|<80 GeV, |y|<0.8

    Data from arXiv:2011.12211 Figure 9f

    10.17182/hepdata.104407.v1/t24

    Ratio of differential UPC dimuon cross sections from data and STARlight 2.0 shown as a function of $|\cos\theta^{\star}_{\mu\mu}|$ in the...

  • Differential cross section as a function of k_max

    Data from arXiv:2011.12211 Figure 10a

    10.17182/hepdata.104407.v1/t25

    Differential cross section as a function of k_max

  • Data/STARlight ratios as a function of k_max

    Data from arXiv:2011.12211 Figure 10b

    10.17182/hepdata.104407.v1/t26

    Ratio of data/STARlight for differential cross sections as a function of k_max

  • Differential cross section as a function of k_min

    Data from arXiv:2011.12211 Figure 10a

    10.17182/hepdata.104407.v1/t27

    Differential cross section as a function of k_min

  • Data/STARlight ratios as a function of k_mi

    Data from arXiv:2011.12211 Figure 10b

    10.17182/hepdata.104407.v1/t28

    Ratio of data/STARlight for differential cross sections as a function of k_min

  • Differential cross sections in alpha (acoplanarity)

    Data from arXiv:2011.12211 Figure 12a

    10.17182/hepdata.104407.v1/t29

    Differential cross sections in $\alpha$ (acoplanarity) integrated over the full fiducial volume

  • Xn0n fractions vs. $m_{\mu\mu}$ for $0<|y_{\mu\mu}|<0.8$

    Data from arXiv:2011.12211 Figure 11d

    10.17182/hepdata.104407.v1/t30

    Fraction of Xn0n events as a function of $m_{\mu\mu}$ for $0<|y_{\mu\mu}|<0.8$

  • Xn0n fractions vs. $y_{\mu\mu}$ for $10<|m_{\mu\mu}|<20$ GeV

    Data from arXiv:2011.12211 Figure 11a

    10.17182/hepdata.104407.v1/t31

    Fraction of Xn0n events as a function of $y_{\mu\mu}$ for $10<|m_{\mu\mu}|<20$ GeV

  • Xn0n fractions vs. $m_{\mu\mu}$ for $0.8<|y_{\mu\mu}|<1.6$

    Data from arXiv:2011.12211 Figure 11e

    10.17182/hepdata.104407.v1/t32

    Fraction of Xn0n events as a function of $m_{\mu\mu}$ for $0.8<|y_{\mu\mu}|<1.6$

  • Xn0n fractions vs. $y_{\mu\mu}$ for $20<|m_{\mu\mu}|<40$ GeV

    Data from arXiv:2011.12211 Figure 11b

    10.17182/hepdata.104407.v1/t33

    Fraction of Xn0n events as a function of $y_{\mu\mu}$ for $20<|m_{\mu\mu}|<40$ GeV

  • Xn0n fractions vs. $m_{\mu\mu}$ for $1.6<|y_{\mu\mu}|<2.4$

    Data from arXiv:2011.12211 Figure 11f

    10.17182/hepdata.104407.v1/t34

    Fraction of Xn0n events as a function of $m_{\mu\mu}$ for $1.6<|y_{\mu\mu}|<2.4$

  • Xn0n fractions vs. $y_{\mu\mu}$ for $40<|m_{\mu\mu}|<80$ GeV

    Data from arXiv:2011.12211 Figure 11c

    10.17182/hepdata.104407.v1/t35

    Fraction of Xn0n events as a function of $y_{\mu\mu}$ for $40<|m_{\mu\mu}|<80$ GeV

  • XnXn fractions vs. $m_{\mu\mu}$ for $0<|y_{\mu\mu}|<0.8$

    Data from arXiv:2011.12211 Figure 11d

    10.17182/hepdata.104407.v1/t36

    Fraction of XnXn events as a function of $m_{\mu\mu}$ for $0<|y_{\mu\mu}|<0.8$

  • XnXn fractions vs. $y_{\mu\mu}$ for $10<|m_{\mu\mu}|<20$ GeV

    Data from arXiv:2011.12211 Figure 11a

    10.17182/hepdata.104407.v1/t37

    Fraction of XnXn events as a function of $y_{\mu\mu}$ for $10<|m_{\mu\mu}|<20$ GeV

  • XnXn fractions vs. $m_{\mu\mu}$ for $0.8<|y_{\mu\mu}|<1.6$

    Data from arXiv:2011.12211 Figure 11e

    10.17182/hepdata.104407.v1/t38

    Fraction of XnXn events as a function of $m_{\mu\mu}$ for $0.8<|y_{\mu\mu}|<1.6$

  • XnXn fractions vs. $y_{\mu\mu}$ for $20<|m_{\mu\mu}|<40$ GeV

    Data from arXiv:2011.12211 Figure 11b

    10.17182/hepdata.104407.v1/t39

    Fraction of XnXn events as a function of $y_{\mu\mu}$ for $20<|m_{\mu\mu}|<40$ GeV

  • XnXn fractions vs. $m_{\mu\mu}$ for $1.6<|y_{\mu\mu}|<2.4$

    Data from arXiv:2011.12211 Figure 11f

    10.17182/hepdata.104407.v1/t40

    Fraction of XnXn events as a function of $m_{\mu\mu}$ for $1.6<|y_{\mu\mu}|<2.4$

  • XnXn fractions vs. $y_{\mu\mu}$ for $40<|m_{\mu\mu}|<80$ GeV

    Data from arXiv:2011.12211 Figure 11c

    10.17182/hepdata.104407.v1/t41

    Fraction of XnXn events as a function of $y_{\mu\mu}$ for $40<|m_{\mu\mu}|<80$ GeV

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