TOP2017: Experimental Summary

At the time of the 10th International Workshop on Top Quark Physics (TOP2017), top quark physics is a very dynamic research area. Thanks to the unprecedentedly fast accumulation of high-energy data at the LHC during the ongoing Run~2, statistical starvation is a matter of the past for most of the traditional top-quark analyses, that are now experiencing the luxury of having to worry about how to punch through the "Systematics Wall" and maximize the utility of their data. New processes involving top quarks are being studied for the first time, and the good old pair-production processes are being explored in unusual settings, such as collisions involving heavy ions, or "reference data" collected by the LHC at relatively low centre-of-mass energy. The TOP2017 conference featured 37 talks delivered by experimental physicists, including seven in the "Young Scientists Forum" where young colleagues were given the opportunity to elaborate more deeply than usual on their own work. As it is impossible to do justice to all the experimental results presented at this conference while staying within a reasonable length, this document contains a very biased selection, mostly based on the personal taste of the author.Comment: Proceedings of the 10th International Workshop on Top Quark Physics, Braga, Portugal, September 17-22, 201

Single top-quark production at the Tevatron and the LHC

This paper provides a review of the experimental studies of processes with a single top quark at the Tevatron proton-antiproton collider and the LHC proton-proton collider. Single top-quark production in the t-channel process has been measured at both colliders. The s-channel process has been observed at the Tevatron, and its rate has been also measured at the center-of-mass energy of 8 TeV at the LHC in spite of the comparatively harsher background contamination. LHC data also brought the observation of the associated production of a single top quark with a W boson as well as with a Z boson. The Cabibbo-Kobayashi-Maskawa matrix element |Vtb| is extracted from the single-top-quark production cross sections, and t-channel events are used to measure several properties of the top quark and set constraints on models of physics beyond the Standard Model. Rare final states with a single top quark are searched for, as enhancements in their production rates, if observed, would be clear signs of new physics.Comment: 44 pages, accepted by to Review of Modern Physic

Working Group 5: Physics with Heavy Flavours

This paper summarises a few selected topics discussed during Working Group 5 of the Deep Inelastic Scattering 2017 conference, Physics with Heavy Flavours, related to the study of charm, bottom, and top quark physics. While the programme of this Working Group was structured by thematic areas, this conference was the occasion for intense cross-pollination between traditionally disjoint research lines. The four LHC experiments all contribute to heavy-flavour physics, with some degree of overlap in most areas, while experiments at other accelerators provide vital input in complimentary kinematic regions. Theorists now have the possibility to take inputs from more sources, and experimentalists focus on measurements that maximise utility. The interplay of LHC heavy quark cross-section measurements with DIS expertise is greatly improving PDF precision, leading to much improved models that, amongst other things, better inform the prospects for future colliders.Comment: 14 pages, 11 figures, to appear in the proceedings of 25th International Workshop on Deep Inelastic Scattering and Related Topics (DIS 2017), 3-7 April 2017, University of Birmingham, U

Particle Identification with Energy Loss in the CMS Silicon Strip Tracker

Some complementary methods are proposed for an identification of charged particles based on $dE/dx$ in the silicon microstrip modules of the CMS Tracker. The performance of proton selection is discussed as benchmark, and the impact of the main systematic effects is estimated. Strategies are presented for the validation and calibration of the methods with several categories of data

Fast Simulations of the ATLAS and CMS experiments at LHC

The fast simulation of a high energy physics experiment is a tool used by experimentalists to quickly assess the potentiality of their detectors on a specific analysis or reconstruction tecnique, before imbarking themselves into a more time- and CPU-expensive detailed study with the full simulation. In some cases, it can also be considered the access point for theoreticians wanting to see "how do their model looks like in the real life''. The aim of this contribution is to introduce how fast simulations work in the ATLAS and CMS experiments at LHC, and which are the main differences with respect to a full simulation. A comprehensive comparison of a few results obtained with the full and the fast simulation in CMS is also given, in order to provide an example of application of the two methods

Searching for New Long Lived Particles in Heavy Ion Collisions at the LHC

We show that heavy ion collisions at the LHC provide a promising environment to search for new long lived particles in well-motivated New Physics scenarios. One advantage lies in the possibility to operate the main detectors with looser triggers, which can increase the number of observable events by orders of magnitude if the long lived particles are produced with low transverse momentum. In addition, the absence of pileup in heavy ion collisions can avoid systematic nuisances that will be present in future proton runs, such as the problem of vertex mis-identification. Finally, there are new production mechanisms that are absent or inefficient in proton collisions. We show that the looser triggers alone can make searches in heavy ion data competitive with proton data for the specific example of heavy neutrinos in the Neutrino Minimal Standard Model, produced in the decay of B mesons. Our results suggest that collisions of ions lighter than lead, which are currently under discussion in the heavy ion community, are well-motivated from the viewpoint of searches for New Physics.Comment: Version accepted by Physical Review Letters for publication as a Letter. 6 pages, 3 figure

Heavy baryons as polarimeters at colliders

In new-physics processes that produce b or c jets, a measurement of the initial b or c-quark polarization could provide crucial information about the structure of new physics. In the heavy-quark limit, the b and c-quark polarizations are preserved in the lightest baryons they hadronize into, Lambda_b and Lambda_c, respectively. We revisit the prediction for the polarization retention after the hadronization process and extend it to the case of transverse polarization. We show how ATLAS and CMS can measure the b-quark polarization using semileptonic Lambda_b decays, and the c-quark polarization using Lambda_c+ -> p K- pi+ decays. For calibrating both measurements we suggest to use ttbar samples in which the polarizations can be measured with a precision of order 10% using 100/fb of data in Run 2 of the LHC. LHCb measurements of the transverse polarization in QCD events are motivated as well. An existing LHCb analysis can be significantly improved for this purpose