Measuring quark polarizations at ATLAS and CMS

Abstract

Being able to measure the polarization of quarks produced in various processes at the LHC would be of fundamental significance. Measuring the polarizations of quarks produced in new physics processes, once discovered, can provide crucial information about the new physics Lagrangian. In a series of recent papers, we have investigated how quark polarization measurements can be done in practice. The polarizations of heavy quarks (b and c) are expected to be largely preserved in the lightest baryons they hadronize into, the Lambda_b and Lambda_c, respectively. Furthermore, it is known experimentally that s-quark polarization is preserved as well, in Lambda baryons. We study how ATLAS and CMS can measure polarizations of b, c and s quarks using certain decays of these baryons. We propose to use the Standard Model ttbar and Wc samples to calibrate these measurements. We estimate that the Run 2 dataset will suffice for measuring the quark polarizations in these Standard Model samples with precisions of order 10%. We also propose various additional measurements for the near and far future that would help characterize the polarization transfer from the quarks to the baryons.

6 pages, proceedings of LFC17: Old and New Strong Interactions from LHC to Future Colliders, Trento, September 11-15, 2017

References in corpus (5)

• Measurement of the parity-violating asymmetry parameter alpha_b and the helicity amplitudes for the decay Lambda_b->J/psi+Lambda with the ATLAS detector
• Measurements of top quark spin observables in $t\bar{t}$ events using dilepton final states in $\sqrt{s}=8$ TeV $pp$ collisions with the ATLAS detector
• Production cross sections of hyperons and charmed baryons from $e^{+}{e}^{-}$ annihilation near $\sqrt{s}=10.52$~GeV
• Measurement of the ${\Lambda }_b$ polarization and angular parameters in ${\Lambda }_b\to J/\psi \Lambda$ decays from pp collisions at $\sqrt{s}=$ 7 and 8 TeV
• Probing the $Wtb$ vertex structure in $t$-channel single-top-quark production and decay in $pp$ collisions at $\sqrt{\mathrm{s}}=8$ TeV with the ATLAS detector