Measurement of J/ψ polarization in pp collisions at $\sqrt{s}=7\ \mathrm{TeV}$

Abstract

An angular analysis of the decay J/ψ→μ+μ− is performed to measure the polarization of prompt J/ψ mesons produced in pp collisions at . The dataset corresponds to an integrated luminosity of 0.37 fb−1 collected with the LHCb detector. The measurement is presented as a function of transverse momentum, pT, and rapidity, y, of the J/ψ meson, in the kinematic region 2<pT<15 GeV/c and 2.0<y<4.5.

Angular decay coefficients of J/ψ mesons at forward rapidity from p+p collisions at sAdare1, Aidala2, Ajitanand3 et al. 2017Phys. Rev. DSelf Cite4270View full textAdd to dashboardCite

“…At the Large Hadron Collider (LHC), the LHCb experiment [32] reported similar, although smaller values of λ θ with similar trend in transverse momentum at forward rapidity. λ θ measured by the ALICE experiment [33] at forward rapidity is consistent with no polarization, although, within experimental uncertainty, it can be said to be similar to the LHCb result.…”

Measurement of the Y(nS) polarizations in pp collisions at s = 7 $$ \sqrt{s}=7 $$ and 8 TeV

“…(1.1), following the approach of refs. [23,24]. The projections of the two-dimensional (cos θ, φ) angular distribution in the HX frame are shown in figure 2 for data accumulated at √ s = 7 TeV in the kinematic region 6 < p Υ T < 8 GeV/c, 2.2 < y Υ < 3.0.…”

“…Calculations based on the colour-singlet model [6][7][8] show good agreement [9][10][11][12][13][14] with the experimental data [15][16][17][18][19][20][21][22] for production cross-sections and the shapes of the transverse momentum spectra. However, this approach fails to describe the spin-alignment (usually labelled as polarization) of S-wave charmonium states [23,24]. Leading-order colour-singlet calculations predict a transverse polarization for the S-wave -1 -…”

Measurements of the X c and X b Quarkonium States in pp Collisions with the ATLAS Experiment

“…In general, all of the prompt charmonium production cross sections measured at the LHC are well described by NRQCD predictions (with LDMEs extracted from Tevatron data). The ALICE, CMS and LHCb experiments have all measured the polarisation of promptly produced J/ψ [83][84][85]. All of the experiments measure only a weak polarisation, consistent with zero in some regions of phase space.…”

“…In the case of the cross section ratios, the combination of the χ c1 and χ c2 polarisation scenarios that gives rise to the maximum variation in the cross section ratios is chosen; J = 1 helicity ±1 combined with J = 2 helicity ±2 gives rise to the upper limit, while J = 1 helicity 0 combined with J = 2 helicity 0 gives rise to the lower limit. The envelope for the measurement of R χ c is calculated assuming overall unpolarised production for prompt J/ψ, motivated by the measurements of ALICE, CMS and LHCb [83][84][85].…”