6 pages, 3 figures, contribution to proceedings of 40th International Conference on High Energy physics (ICHEP2020), July 28 - August 6, 2020, Prague, Czech Republic (virtual meeting)
Recent measurements based on jet production in high energy pp collisions at the CERN LHC with the CMS detector are reported. Specifically, the measurement of the inclusive jet production cross section as a function of the anti-$k_t$ distance parameter $R$ divided by the jet cross section at $R = 0.4$, is discussed. The cross section ratio is sensitive to various perturbative and non-perturbative treatments of the jet formation process in quantum chromodynamics (QCD). In the second study, the regimes of validity of the parton shower and matrix element approaches are tested on multijet events in pp collisions at $\sqrt{s} = 8$ and $13$ TeV. Special attention is given to the second and third leading $p_\text{T}$ jets and their momenta and rapidity-azimuth correlations. Finally, studies of dijet production where the two leading $p_T$ jets are separated by a large pseudorapidity interval void of charged particles is presented. This signature is expected from hard color singlet exchange (two-gluon exchange in perturbative QCD). The latter can be treated with perturbative QCD techniques based on the Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution equations.
The latest CMS jet measurements in p-p collisions at sqrt(s) = 7 TeV, sensitive to small-x QCD physics, are discussed. These include inclusive forward jet and simultaneous forward-central jet production, as well as production ratios and azimuthal angle decorrelations of jets widely separated in rapidity.
Recent measurements performed by the ATLAS and CMS collaborations on the Run 2 dataset are testing QCD with unprecedented precision. The wealth of data, an ever-improving experimental understanding of jets and photons, and novel measurements of jet substructure enable an improved understanding.
A brief summary of recent measurements of QCD jet production at the LHC, featuring results from ATLAS and CMS, is given. Results for heavy flavours are also shown.
We use public data from the CMS experiment to study the 2-prong substructure of jets. The CMS Open Data is based on 31.8/pb of 7 TeV proton-proton collisions recorded at the Large Hadron Collider in 2010, yielding a sample of 768,687 events containing a high-quality central jet with transverse momentum larger than 85 GeV. Using CMS's particle flow reconstruction algorithm to obtain jet constituents, we extract the 2-prong substructure of the leading jet using soft drop declustering. We find good agreement between results obtained from the CMS Open Data and those obtained from parton shower gen…
We explore the metric space of jets using public collider data from the CMS experiment. Starting from 2.3/fb of 7 TeV proton-proton collisions collected at the Large Hadron Collider in 2011, we isolate a sample of 1,690,984 central jets with transverse momentum above 375 GeV. To validate the performance of the CMS detector in reconstructing the energy flow of jets, we compare the CMS Open Data to corresponding simulated data samples for a variety of jet kinematic and substructure observables. Even without detector unfolding, we find very good agreement for track-based observables after using c…
A measurement of inclusive jet and dijet production cross sections is presented. Data from large hadron collider (LHC) proton-proton collisions at $\sqrt{s}=$ 7 TeV, corresponding to $4.67 fb^{-1}$ of integrated luminosity, have been collected with the compact muon solenoid (CMS) detector. Jets are reconstructed with the anti-$k_T$ clustering algorithm with size parameter $R=0.7$, extending to rapidity $|y|=2.5$, transverse momentum $p_{T}=$ 2 TeV, and dijet invariant mass $M_{JJ}=$ 5 TeV. The measured cross sections are corrected for detector effects and compared to perturbative QCD predictio…
We present predictions for the inclusive production of charm jets in proton-proton collisions at 2.76 and 5.02 TeV. The charm-quark is considered massless. In this scheme we find that the ratio of the next-to-leading order to the leading order cross section (K factor) is almost equal to one depending essentially on the choice of the renormalization and factorization scale. Adding non-pertubative corrections obtained from Pythia Monte Carlo calculations lead to reasonable agreement with experimental c-jet cross sections obtained by the CMS collaboration.
We perform a detailed comparison of next-to-next-to-leading order (NNLO) QCD predictions for the W+jet and Z+jet processes with 7 TeV experimental data from ATLAS and CMS. We observe excellent agreement between theory and data for most studied observables, which span several orders of magnitude in both cross section and energy. For some observables, such as the $H_T$ distribution, the NNLO QCD corrections are essential for resolving existing discrepancies between theory and data.
The underlying event is an important part of high-energy collision events. In the event generators, the underlying event is tuned by fits to collision data. Usually, the underlying event observables are affected by the existence of extra jets and it is difficult to find a part of the phase space which is dominated by the underlying event. In this paper, we suggest to veto the jets in the considered region to disentangle these effects. The idea is verified to work on CMS Open Data. To our knowledge, it is the first time that such ideas are tested on real collision data.
A reanalysis is presented on the CMS result on a search for a W' boson that couples to the top and down quarks. The model is motivated by the Tevatron results on the forward-backward asymmetry of ttbar pair production. In the evaluation of the theoretical cross section of pp -> ttbar + j, the interference effect between the SM and W' amplitudes is shown to be important, though it is ignored in the CMS analysis. The lower mass bound on the W' boson is relaxed from 840 GeV to 740 GeV at the 95% C.L. due to the interference effect. The bound is also compared to the top forward-backward asymmetry.
We present measurements of multi-jet event properties, performed using proton-proton collisions data recorded by the CMS experiment. The jet charge and jet mass distributions are considered in addition to a measurement of the azimuthal angular correlations in 2- and 3-jet events. The measurements are compared to predictions including higher orders matched to parton shower and hadronization, together with predictions from semi-analytical calculations beyond next-to-leading logarithmic accuracy.
The jet reconstruction and jet energy calibration strategies adopted by the CMS and ATLAS experiments are presented. Jet measurements that can be done with early data to confront QCD at the highest transverse momentum scale and search for new physics are described.
We describe recent results from CMS and TOTEM on hard diffraction, diffractive jets and jet gap jet events. We also give the first sensitivities and limits on quartic anomalous couplings and axion-like particles at high mass using the LHC as a $γγ$ collider. The predicted sensitivities with 300 fb$^{-1}$ are better by two or three orders of magnitude compared to the more standard methods at the LHC without measuring intact protons after collision
We present angular correlations in multi-jet events at highest center-of-mass energies and compare the measurements to theoretical predictions including higher order parton radiation and coherence effects.
The performance of jet finding using only charged tracks in CMS has been investigated. Different jet algorithms have been applied to QCD di-jet events, to hadronic tt multi-jet events and on Z+jets events. Results using jets made with tracks only or calorimeter towers are compared for energy response, angular resolution and jet matching to the leading partons. The jet reconstruction performance in the presence of pile-up interactions is presented for the Z+jets sample.
The production of jets at the Large Hadron Collider (LHC) at TeV centre-of-mass energy is summarized, including results from both the ATLAS and CMS detectors. Current jet performance is described, followed by inclusive jet and multi-jet measurements in various final state configurations. Finally some results on heavy flavour and jet substructure are presented.
The splitting function is a universal property of quantum chromodynamics (QCD) which describes how energy is shared between partons. Despite its ubiquitous appearance in many QCD calculations, the splitting function cannot be measured directly since it always appears multiplied by a collinear singularity factor. Recently, however, a new jet substructure observable was introduced which asymptotes to the splitting function for sufficiently high jet energies. This provides a way to expose the splitting function through jet substructure measurements at the Large Hadron Collider. In this letter, we…
The most recent results on searches in lepton plus jet final states motivated by different models beyond the standard model are presented, using pp collision data collected by the ATLAS and CMS detectors during Run I and Run II at the CERN LHC. Leptoquarks and heavy Majorana neutrinos that arise in the left-right model are looked for in the final states with two leptons and two jets (ll + jj; l = e; mu; tau ). Heavy Majorana neutrinos are further investigated by relying on a composite-fermion scenario, considering two leptons and one large-radius jet (ll + J; l = e, mu), and in the context of …
The CMS experiment makes use of a large variety of algorithms to identify the origin of particle jets measured in the detector. Through the study of jet substructure properties, jets originating from quarks, gluons, W/Z/Higgs bosons, top quarks and pileup interactions are identified and categorized. We present new techniques based on machine learning approaches developed for the analysis of the data collected during the LHC Run 2 that significantly surpass the performances of classical taggers.
Many physics analyses at the LHC are looking into processes where the signal jets are originating from quarks, while jets in the background are more gluon enriched. Based on observables sensitive to fundamental differences in the fragmentation properties of gluons and quarks, a likelihood discriminant is constructed to distinguish between jets originating from quarks and gluons. The performance of the tagger is evaluated using Z+jets and dijet events produced in proton-proton collisions at a centre-of-mass energy of 8 TeV, recorded by the CMS experiment at the LHC.
The most recent results of Standard Model physics using 8 and 13 TeV proton-proton collision data recorded by the CMS detector during the LHC Runs I and II are reviewed. This overview includes studies of several results of vector boson production in association with jets. The outlined results are compared to the corresponding theoretical predictions and no significant deviation is observed.
Preliminary results on a variety of jet analyses are presented using pp collision data collected by the CMS experiment at $\sqrt{s}$=7 TeV. We report on measurements of the inclusive jet cross sections, the ratio of the inclusive three-jet over two-jet cross sections, the hadronic event shapes, the jet structure and the dijet azimuthal decorrelations. The data distributions are compared with the predictions of Monte Carlo event generators and with perturbative QCD calculations.
LHC $t\bar{t}$ data have the potential to provide constraints on the gluon distribution, especially at high $x$, with both ATLAS and CMS performing differential measurements. Recently, CMS has measured double-differential $t\bar{t}$ distributions at 8 TeV. In this paper we examine the impact of this data set on the gluon distribution. To that end we develop novel, double-differential NNLO predictions for that data. No significant impact is found when the CMS data is added to the CT14HERA2 global PDF fit, due to the larger impact of the inclusive jet data from both the Tevatron and the LHC. If …
Measurements of Vector Boson production in association with jets are presented, using p-p collision data at sqrt{s} = 7 TeV. The measurements presented include Z + jets azimuthal correlations, event shapes, vector boson + jets differential cross section measurements, hard double-parton scattering using W + jets events and electroweak Z + forward - backward jet production.
We present a study of jet production in association with W and Z bosons in proton-proton collisions at a centre-of-mass energy of 7 TeV using the full 2010 data set collected by CMS corresponding to an integrated luminosity of (35.9 +/- 1.4) inverse picobarn. We report the measurement of ratios s(V + >= n jets)/s(V) and s(V + >= n jets)/s(V + >= (n - 1) jets), where V represents either a W or a Z, s stands for the cross section and n stands for the number of jets.
The flavor dependence of jet quenching is a powerful handle to discriminate between models of parton energy loss in heavy-ion collisions. We demonstrate the capacity of CMS to identify jets initiated by bottom quarks using displaced vertices reconstructed in the silicon tracking system. The b-jet to inclusive jet ratio is measured in PbPb collisions and compared to pp collisions and simulations at the same center-of-mass energy.
We report on the status and history of the CMS commissioning, together with selected results from cosmic-ray muon data. The second part focuses on strategies for optimizing the reconstruction of jets, missing transverse energy and photons for early standard model measurements at ATLAS and CMS with the first collision data from the Large Hadron Collider at CERN.
We present measurements of the forward (3 < |eta| < 5) energy flow in minimum bias events and in events with either hard jets or W and Z bosons produced at central rapidities together with first measurements of the inclusive forward jet cross section and central forward jet correlations. Results are compared to MC models with different parameter tunes for the description of the underlying event.
We present measurements of the inclusive jet production at centre-of-mass energies of 8 and 13 TeV, and of multijets at 8 TeV. These measurements allow to constrain PDFs and the strong coupling constant. Two measurements of the azimuthal correlations at 8 and 13 TeV are also presented, testing higher order QCD calculations.
The study of the associated production of vector bosons and jets constitutes an excellent environment to check numerous QCD predictions. Total and differential cross sections of vector bosons produced in association with jets have been studied in pp collisions using CMS data. Differential distributions as a function of a broad range of kinematical observables are measured and compared with theoretical predictions. In this talk, studies of associated production of vector bosons with inclusive jets and with jets originating from heavy-flavour quarks will be summarized.
We report on the current simulation studies regarding the reconstruction of Jets and Missing Transverse Energy (MET) with the CMS detector at the CERN proton-proton LHC accelerator. The performance of various jet algorithms is compared, when using calorimeter energy deposits as inputs to the algorithm. The plan for obtaining jet energy corrections is outlined and data-driven correction methods are described. Finally, the performance of MET reconstruction is summarized.
Measurements of jet energy scale (JES) and resolution (JER) are presented, based on the legacy reconstruction of 13 TeV proton-proton collision data collected by the CMS experiment during the LHC Run 2 period from 2016-2018. Precision measurement of JES is of the utmost importance for the vast majority of physics measurements and searches at CMS. The high pileup, a harsh radiation environment, and time-dependent variations in detector response and calibration, all make precision JES measurement a challenging task. We present in-situ derivations of JES and JER based on CMS Run 2 data, as well a…
The normalised differential top quark-antiquark production cross section is measured as a function of the jet multiplicity. Using a procedure to associate jets to decay products of the top quarks, the differential cross section of the ttbar production is determined as a function of the additional jet multiplicity. The fraction of events with no additional jets is measured as a function of the threshold required for the transverse momentum of the additional jet. The measurements are compared with predictions from perturbative quantum chromodynamics and no significant deviations are observed.
Jet studies provide an experimental method to explore the features of energy loss in the strongly interacting quark-gluon plasma. Recent jet results from 2.76 TeV PbPb and pp collisions measured with the CMS detector are presented. Jets in the most head-on (central) PbPb collisions are quenched in comparison to pp, and the jets fragment in different ways in the two systems. Measurements from pPb collisions at 5.02 TeV show that the jet and charged particle suppression seen in central PbPb measurements are not due to initial state nuclear effects.
Copious production of very energetic jets is expected at the LHC due to the large increase in collision energy. Jet reconstruction at these high center of mass energies will provide crucial leverage to map out the QCD evolution of parton energy loss and a unique insight into the nature of the hot QCD matter. This article presents jet reconstruction techniques and the preliminary jet results in p+p collisions at $\sqrt{s}=7$ TeV collected by the CMS experiment at the LHC. Jet reconstruction prospects for the heavy ion collisions are also discussed.
Forward (di)jet measurements are a useful tool to constrain the Parton Distribution Functions (PDFs) at low values of parton momentum fraction x, and to study the possible onset of BFKL or gluon saturation QCD evolutions in the proton. We present studies of jet reconstruction capabilities in the CMS Hadron Forward (HF) calorimeter (3<|eta|<5). The expected sensitivity of the inclusive forward jet p_T spectrum to the proton PDF, as well as the azimuthal decorrelation of Mueller-Navelet jets with a large rapidity separation are presented for p-p collisions at sqrt{s} = 14 TeV.
Measurements of inclusive jet and dijet production cross sections are presented. Data from LHC proton-proton collisions at sqrt(s) = 7 TeV, corresponding to 5.0 inverse femtobarns of integrated luminosity, have been collected with the CMS detector. Jets are reconstructed up to rapidity 2.5, transverse momentum 2 TeV, and dijet invariant mass 5 TeV, using the anti-kt clustering algorithm with distance parameter R = 0.7. The measured cross sections are corrected for detector effects and compared to perturbative QCD predictions at next-to-leading order, using five sets of parton distribution func…
This document is dedicated to recent results on the measurements of a vector boson production associated with jets (V+jets) using CMS detector experiment, with a central proton-proton (pp) collision energy of respectively 8 TeV (RunI) and 13 TeV (RunII). The vector boson can be a W boson, Z boson, or photon(γ). The jets are of any flavor, as well as the ones containing heavy flavor quarks, such as bottom(b) quarks. The inclusive cross sections of V+jets processes and differential cross sections as a function of various kinematic observables are presented and compared to several theoretical pre…
The cross section for production of Z bosons with two associated b-jets, and Z decaying to leptons, can be measured at the LHC with about 100 pb-1 of data. We use simulated data to study possible strategies for an early measurement of this process with the CMS detector. The rate and kinematic properties of this final state needs to be well understood because it constitutes a large fraction of the total backgrounds to several of the Higgs discovery channels at the LHC.
We report on the recent CMS measurements of soft hadron-hadron production, including the measurements of inclusive single- and double-diffractive cross sections, as well as the measurement of pseudorapidity distributions, and of the leading charged particle and leading jet cross sections. We present the cross sections for low-pT forward jets production, and production of dijets with large rapidity separation (central-forward, and forward-backward jets). Studies of double parton scattering using four-jet and W+2-jet events, and the cross sections for Drell-Yan with associated jet production are…
The increase of the centre-of-mass energy of the Large Hadron Collider (LHC) to 13 TeV has opened up a new energy regime. Final states including high-momentum multi-jet signatures often dominate beyond standard model phenomena, in particular decay products of new heavy particles. While the potential di-photon resonance currently receives a lot of attention, multi-jet final states pose strong constraints on what physics model an observation could actually be described with. In this presentation, the latest results of the ATLAS and CMS collaborations in high transverse momentum multi-jet final s…
The observation of the electroweak production of a Z boson with two jets in pp collisions at $\sqrt{s} = 8$ TeV with the CMS experiment at the CERN LHC is presented, based on a data sample with an integrated luminosity of 19.7 fb$^{-1}$. The cross section measurement, combining the muon and electron channels, is in agreement with the theoretical expectations. Radiation patterns of selected Z plus two jets events, and the hadronic activity in the rapidity interval between the jets are also measured. These results are of substantial importance in the more general study of vector boson fusion pro…
Dijets in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV are studied with the CMS detector at the LHC. It is shown that the fragmentation functions of jets into charged particle tracks with transverse momenta pT > 4 GeV/c in PbPb collisions are similar to those in pp collisions, for both the leading and subleading jets. In addition, study of high statistics PbPb data acquired in 2011 shows that the quenching phenomenon exists up to highest jet pT values in excess of 300 GeV/c.
We report on cross section measurements for inclusive forward jet production and for the simultaneous production of a forward and a central jet in sqrt{s} = 7 TeV pp-collisions. Data collected in 2010, corresponding to an integrated luminosity of 3.14 pb^{-1}, is used for the measurements. Jets in the transverse momentum range pT = 35 - 140 GeV/c are reconstructed with the anti-kT (R = 0.5) algorithm. The extended coverage of large pseudo-rapidities is provided by the Hadronic Forward calorimeter (3.2 < η< 4.7), while central jets are limited to η< 2.8, covered by the main detector components.…
Results by the CMS Collaboration on forward physics, diffraction, and physics in the small-$x$ limit of quantum chromodynamics (QCD), are presented. In particular, results on azimuthal angle decorrelations between two jets in events where two outermost jets are separated by a large rapidity interval are discussed. In addition, results based on the production of two jets separated by a large rapidity gap (interval void of radiation) are presented. These dijet production processes are expected to be sensitive to Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution effects. We highlight results on incl…
The identification of jets originating from b quarks is crucial both for the searches for new physics and for the measurement of standard model processes. The Compact Muon Solenoid (CMS) collaboration at the Large Hadron Collider (LHC) has developed a variety of algorithms to select b-quark jets based on variables such as the impact parameter of charged particle tracks, properties of reconstructed secondary vertices from heavy hadron decays, and the presence or absence of a lepton in the jet, or combinations thereof. Performance measurements of these b-jet identification algorithms are present…
CMS will use dijets to search for physics beyond the standard model during early LHC running. The inclusive jet cross section as a function of jet transverse momentum, with 10 inverse picobarns of integrated luminosity, is sensitive to contact interactions beyond the reach of the Tevatron. The dijet mass distribution will be used to search for dijet resonances coming from new particles, for example an excited quark. Additional sensitivity to the existence of contact interactions or dijet resonances can be obtained by comparing dijet rates in two distinct pseudorapidity regions.
The top quark mass is measured using $35.9~\mathrm{fb}^{-1}$ of LHC proton-proton collision data collected with the CMS detector at $\sqrt{s}=13~\mathrm{TeV}$ in 2016. The measurement uses the $\mathrm{t}\overline{\mathrm{t}}$ all-jets final state, which comprises a total of six jets. A kinematic fit is performed to reconstruct the decay of the $\mathrm{t}\overline{\mathrm{t}}$ system and suppress QCD multijet background. By means of the ideogram method, the top quark mass is determined, simultaneously constraining an additional jet energy scale factor ($\text{JSF}$). The result of $172.34\pm0…
By applying the Error PDF Updating Method, we analyze the impact of the absolute and normalized single differential cross-sections for top-quark pair production data from the ATLAS and CMS experiments at the Large Hadron Collider, at a centre-of-mass energy of $\sqrt{s}= 8$ TeV, on the CT14HERA2 PDFs. We find that the top quark pair single differential distributions provide minor constraints on the CT14HERA2 gluon PDF when the nominal CT14HERA2 inclusive jet production data are included in the fit. Larger constraints on the gluon distribution are present when the jet data are removed (CT14HERA…
We report on our NLL BFKL studies of Mueller-Navelet jets. We first perform a complete NLL BFKL analysis supplemented by a BLM renormalization scale fixing procedure, which is successfully compared with recent CMS data. Second, we argue for the need of a measurement of an asymmetric jet configuration in order to perform a valuable comparison with fixed order approaches. Third, we predict that the energy-momentum violation is rather tiny in the NLL BFKL approach, for an asymmetric jet configuration. Finally, we argue that the double parton scattering contribution is negligible in the kinematics…
The production of a strongly interacting medium in heavy-ion collisions is identified through suppression of high transverse momentum jets leading to an effect known as jet quenching. Detailed measurements of nuclear modification factors and energy flow of the aforementioned quenched jets are performed with the CMS detector. These new results extend previous measurements to large angles with respect to the quenched jets and increase reach in the transverse momentum range. High statistics pp, pPb and PbPb data taken in 2011-13 are used in the following analysis. A new data-driven method to esti…
We report on potential for measurement of W and Z boson production, as well as the production in association with jets. Of particular interest are jet multiplicity and $P_{\rm T}$ distributions. The 10 to $100 {\rm pb}^{-1}$ datasets expected in the startup year of operation of LHC are likely to already provide information beyond the reach of the Tevatron collider both in jet multiplicity and $P_{\rm T}$ range. We are especially interested in understanding the ratios of W+jets to Z+jets distributions by comparing them to next-to-leading order Monte Carlo generators, as these processes present …
Production of electroweak bosons, heavy quarks and jets in proton-proton collisions probe different aspects of QCD and are sensitive to the details of proton structure, expressed by parton distribution functions (PDFs). Precise measurements of cross sections of these processes are used by the CMS experiment to demonstrate the impact of the LHC data on the PDFs and their precision. The measurements of muon charge asymmetry in W-boson production at a center-of-mass of 7 and 8 TeV is used to improve the constraints on the valence-quark distributions, while the associated production of W-boson and…
