Search for: All records

The CERN LHC provided proton and heavy ion collisions during its Run 2 operation period from 2015 to 2018. Proton-proton collisions reached a peak instantaneous luminosity of 2.1× 10³⁴cm^-2s^-1, twice the initial design value, at √(s)=13 TeV. The CMS experiment records a subset of the collisions for further processing as part of its online selection of data for physics analyses, using a two-level trigger system: the Level-1 trigger, implemented in custom-designed electronics, and the high-level trigger, a streamlined version of the offline reconstruction software running on a large computer farm. This paper presents the performance of the CMS high-level trigger system during LHC Run 2 for physics objects, such as leptons, jets, and missing transverse momentum, which meet the broad needs of the CMS physics program and the challenge of the evolving LHC and detector conditions. Sophisticated algorithms that were originally used in offline reconstruction were deployed online. Highlights include a machine-learning b tagging algorithm and a reconstruction algorithm for tau leptons that decay hadronically.

 

Abstract The production of Z bosons associated with jets is measured in $$\text {p}\text {p}$$ pp collisions at $$\sqrt{s}=13\,\text {Te}\hspace{-.08em}\text {V} $$ s = 13 Te V with data recorded with the CMS experiment at the LHC corresponding to an integrated luminosity of 36.3 $$\,\text {fb}^{-1}$$ fb - 1 . The multiplicity of jets with transverse momentum $$p_{\textrm{T}} > 30\,\text {Ge}\hspace{-.08em}\text {V} $$ p T > 30 Ge V is measured for different regions of the Z boson’s $$p_{\textrm{T}} (\text {Z })$$ p T ( Z ) , from lower than 10 $$\,\text {Ge}\hspace{-.08em}\text {V}$$ Ge V to higher than 100 $$\,\text {Ge}\hspace{-.08em}\text {V}$$ Ge V . The azimuthal correlation $$\varDelta \phi $$ Δ ϕ between the Z boson and the leading jet, as well as the correlations between the two leading jets are measured in three regions of $$p_{\textrm{T}} (\text {Z })$$ p T ( Z ) . The measurements are compared with several predictions at leading and next-to-leading orders, interfaced with parton showers. Predictions based on transverse-momentum dependent parton distributions and corresponding parton showers give a good description of the measurement in the regions where multiple parton interactions and higher jet multiplicities are not important. The effects of multiple parton interactions are shown to be important to correctly describe the measured spectra in the low $$p_{\textrm{T}} (\text {Z })$$ p T ( Z ) regions. 

Abstract Multijet events at large transverse momentum ( $$p_{\textrm{T}}$$ p T ) are measured at $$\sqrt{s}=13\,\text {TeV} $$ s = 13 TeV using data recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of $$36.3{\,\text {fb}^{-1}} $$ 36.3 fb - 1 . The multiplicity of jets with $$p_{\textrm{T}} >50\,\text {GeV} $$ p T > 50 GeV that are produced in association with a high- $$p_{\textrm{T}}$$ p T dijet system is measured in various ranges of the $$p_{\textrm{T}}$$ p T of the jet with the highest transverse momentum and as a function of the azimuthal angle difference $$\varDelta \phi _{1,2}$$ Δ ϕ 1 , 2 between the two highest $$p_{\textrm{T}}$$ p T jets in the dijet system. The differential production cross sections are measured as a function of the transverse momenta of the four highest $$p_{\textrm{T}}$$ p T jets. The measurements are compared with leading and next-to-leading order matrix element calculations supplemented with simulations of parton shower, hadronization, and multiparton interactions. In addition, the measurements are compared with next-to-leading order matrix element calculations combined with transverse-momentum dependent parton densities and transverse-momentum dependent parton shower.