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First measurement of quarkonium polarization in nuclear collisions at the LHC

The ALICE collaboration
Phys.Lett.B 815 (2021) 136146, 2021.

Abstract (data abstract)
The polarization of inclusive J/$\psi$ and $\Upsilon(1{\rm S})$ produced in Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}=5.02$ TeV at the LHC is measured with the ALICE detector. The study is carried out by reconstructing the quarkonium through its decay to muon pairs in the rapidity region $2.5<y<4$ and measuring the polar and azimuthal angular distributions of the muons. The polarization parameters $\lambda_{\theta}$, $\lambda_{\phi}$ and $\lambda_{\theta\phi}$ are measured in the helicity and Collins-Soper reference frames, in the transverse momentum interval $2<p_{\rm T}<10$ GeV/$c$ and $p_{\rm T}<15$ GeV/$c$ for the J/$\psi$ and $\Upsilon(1{\rm S})$, respectively. The polarization parameters for the J/$\psi$ are found to be compatible with zero, with a maximum deviation at low $p_{\rm T}$ of about $2\sigma$, for both reference frames and over the whole $p_{\rm T}$ range. The values are compared with the corresponding results obtained for pp collisions at $\sqrt{s}=7$ and 8 TeV in a similar kinematic region by the ALICE and LHCb experiments. Although with much larger uncertainties, the polarization parameters for $\Upsilon(1{\rm S})$ production in Pb-Pb collisions are also consistent with zero.

  • Table 1

    Data from Figure 3

    10.17182/hepdata.102403.v1/t1

    J/$\psi$ polarization parameters, measured for Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV, in the helicity and Collins-Soper reference frames in the...

  • Table 2

    Data from Figure 3

    10.17182/hepdata.102403.v1/t2

    J/$\psi$ polarization parameters, measured for Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV, in the helicity and Collins-Soper reference frames in the...

  • Table 3

    Data from Figure 3

    10.17182/hepdata.102403.v1/t3

    J/$\psi$ polarization parameters, measured for Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV, in the helicity and Collins-Soper reference frames in the...

  • Table 4

    Data from Figure 3

    10.17182/hepdata.102403.v1/t4

    J/$\psi$ polarization parameters, measured for Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV, in the helicity and Collins-Soper reference frames in the...

  • Table 5

    Data from Figure 3

    10.17182/hepdata.102403.v1/t5

    J/$\psi$ polarization parameters, measured for Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV, in the helicity and Collins-Soper reference frames in the...

  • Table 6

    Data from Figure 3

    10.17182/hepdata.102403.v1/t6

    J/$\psi$ polarization parameters, measured for Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV, in the helicity and Collins-Soper reference frames in the...

  • Table 7

    No Figure

    10.17182/hepdata.102403.v1/t7

    $\Upsilon(1{\rm S})$ polarization parameters in the helicity and Collins-Soper reference frames measured in Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV in...

  • Table 8

    No Figure

    10.17182/hepdata.102403.v1/t8

    $\Upsilon(1{\rm S})$ polarization parameters in the helicity and Collins-Soper reference frames measured in Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV in...

  • Table 9

    No Figure

    10.17182/hepdata.102403.v1/t9

    $\Upsilon(1{\rm S})$ polarization parameters in the helicity and Collins-Soper reference frames measured in Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV in...

  • Table 10

    No Figure

    10.17182/hepdata.102403.v1/t10

    $\Upsilon(1{\rm S})$ polarization parameters in the helicity and Collins-Soper reference frames measured in Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV in...

  • Table 11

    No Figure

    10.17182/hepdata.102403.v1/t11

    $\Upsilon(1{\rm S})$ polarization parameters in the helicity and Collins-Soper reference frames measured in Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV in...

  • Table 12

    No Figure

    10.17182/hepdata.102403.v1/t12

    $\Upsilon(1{\rm S})$ polarization parameters in the helicity and Collins-Soper reference frames measured in Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV in...

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