Measuring c-quark polarization in W +c samples 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 Λ b and Λ c , respectively. Furthermore, it is known experimentally that s-quark polarization is preserved as well, in Λ 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 tt and W c 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.

Rare radiative charm decays within the standard model and beyond

“…Note that the depolarization parameters A and ω 1 are measurable at Atlas, BaBar, Belle, CMS and LHCb [64]. The Λ c polarization itself is measurable at Atlas, CMS and LHCb via pp → t(→ bW + (→ cs))t(→bW − (→ l −ν )) [64] and pp → W − c [65], where P (W − ) c −0.97 [68]. The angular asymmetry is shown in figure 6 for P Λc as expected at the Z, eq.…”

“…Prerequisite for an interpretation of A γ is a measurement of the Λ c polarization, however, irrespective of its precise value, in the SM A γ is expected to be positive at the Z. The branching ratio of Λ c → pγ may be investigated at Belle II [2], the depolarization fraction at the LHC [65], and at the FCC-ee [19] all of this including A γ .…”

Rare radiative charm decays in the standard model and beyond

“…where the parametrization of [17,18,19] is used. The polarization is measurable at future colliders as well as BaBar, Belle and LHC.…”

$O(α_s)$ perturbative and nonperturbative corrections to polarized semileptonic $Λ_b$ decay distributions

“…on e + e − annihilations, the decay of the Z boson to a heavy quark-antiquark pair also shows a significant degree of longitudinal polarization which amount to P b = −0.94 for bottom quarks and P c = −0.68 for charm quarks [16]. In a sequence of papers the possibility to measure the polarization of bottom (and charm) quarks at ATLAS and CMS has been analyzed [17,18,19,20]. The authors come to an affirmative answer, though the quarks are observed only as a jet of hadrons.…”