Measuring quark polarizations at ATLAS and CMS

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.Comment: 6 pages, proceedings of LFC17: Old and New Strong Interactions from LHC to Future Colliders, Trento, September 11-15, 201

Prospects for measuring quark polarization and spin correlations in bbˉb\bar b and ccˉc\bar c samples at the LHC

Polarization and spin correlations have been studied in detail for top quarks at the LHC, but have been explored very little for the other flavors of quarks. In this paper we consider the processes $pp\to q\bar{q}$ with $q = b$, $c$ or $s$. Utilizing the partial preservation of the quark's spin information in baryons in the jet produced by the quark, we examine possible analysis strategies for ATLAS and CMS to measure the quark polarization and spin correlations. We find polarization measurements for the $b$ and $c$ quarks to be feasible, even with the currently available datasets. Spin correlation measurements for $b\bar b$ are possible using the CMS Run 2 parked data, while such measurements for $c\bar c$ will become possible with higher integrated luminosity. For the $s$ quark, we find the measurements to be challenging with the standard triggers. We also provide leading-order QCD predictions for the polarization and spin correlations expected in the $b\bar b$ and $c\bar c$ samples with the cuts envisioned for the above analyses. Apart from establishing experimentally the existence of spin correlations in $b\bar b$ and $c\bar c$ systems produced in $pp$ collisions, the proposed measurements can provide new information on the polarization transfer from quarks to baryons and might even be sensitive to physics beyond the Standard Model.Comment: 50 pages, 5 figure