Jet production and αs measurements at CMS Georgios Mavromanolakis University of Cyprus On behalf of the CMS Collaboration ICHEP 2014: 37th International Conference on High Energy Physics, 2-9 Jul 2014, Valencia, Spain

G. Mavromanolakis, Univ. of Cyprus Outline Introduction Jet Energy Scale and Resolution Selected Results Inclusive jet cross sections Dijet cross sections Measurements of the strong coupling constant Hadronic event shapes (see Poster by R. Gupta) Multijet production (see Poster by D. Roy) Low-pT and forward jet measurements at CMS (see Poster by S. Cerci) Summary - Conclusions G. Mavromanolakis, Univ. of Cyprus

G. Mavromanolakis, Univ. of Cyprus Introduction QCD measurements are of great importance in order to: Test pQCD in a new energy regime, in a totally unexplored kinematic region Provide constraints on PDFs, measure strong coupling constant, study initial and final state radiation and parton showering effects Tune Monte-Carlo generators in order to better describe the data Measure and understand the main background to most new physics searches, or get a chance to have a first glimpse of something new and unexpected G. Mavromanolakis, Univ. of Cyprus

Data Collection The measurements shown in this talk are from the 7 TeV and 8 TeV running period All results shown can be found at: https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResults G. Mavromanolakis, Univ. of Cyprus

Jet Energy Scale and Resolution Plot courtesy of K. Rabbertz CMS DP-2012-006 CMS DP-2013-033 Now at the 1% level! JINST 6 (2011) P11002 G. Mavromanolakis, Univ. of Cyprus

G. Mavromanolakis, Univ. of Cyprus Theoretical Tools Non-perturbative corrections for multi-parton interaction and hadronization Parton showering effects (POWHEG) Perturbative QCD calculations @ NLO NLOJet++/JETPHOX fastNLO PDFs Matrix Element Parton level Particle level Detector level Parton Showering PDFs Parton distribution functions (PDF) CT10 MSTW2008 NNPDF2.1 HERAPDF1.5 ABKM09, ABKM11 LO QCD Monte-Carlo generators PYTHIA6, PYTHIA8 HERWIG++ ALPGEN MADGRAPH G. Mavromanolakis, Univ. of Cyprus

Inclusive Jet Cross Sections at 7 and 8 TeV CMS-PAS-SMP-12-012 CMS-PAS-FSQ-12-031 Phys. Rev. D 87 (2013) 112002 Good description of pQCD@NLO G. Mavromanolakis, Univ. of Cyprus

Inclusive Jet Cross Sections: 7 TeV The experimental uncertainties are comparable to the theoretical ones Some PDFs describe the data better than others These measurements are useful for PDF tuning and for constraining PDFs (see more on E. Lipka’s talk), as well as for determining the strong coupling constant G. Mavromanolakis, Univ. of Cyprus

Inclusive Jet Cross Sections: 8 TeV CMS PAS SMP-12-012 Experimental uncertainties comparable to the theoretical ones Some PDFs describe the data better than others These measurements are useful for PDF tuning and for constraining PDFs, as well as for measuring the strong coupling constant (imminent) G. Mavromanolakis, Univ. of Cyprus

Dijet Cross Sections: 8 TeV CMS-PAS-SMP-14-002 Good description of pQCD@NLO G. Mavromanolakis, Univ. of Cyprus

Dijet Cross Sections: 8 TeV Experimental uncertainties comparable to the theoretical ones. Electroweak corrections included (new) Some PDFs describe the data better than others These measurements useful for PDF tuning and for constraining PDFs G. Mavromanolakis, Univ. of Cyprus

Hadronic Event Shapes at 7 TeV CMS-PAS-SMP-12-022 Central Transverse Thrust Sensitive to the modeling of two-jet and multijet topologies. For a perfectly balanced two jet event it is zero, while in isotropic multi-jet events it is (1-2/π). Jet Broadenings Insensitive to the contribution of the underlying event and hadronization. Sensitive to color coherence effects. Jet Masses Q is the scalar sum of the momenta of all the constituents in jets. The same behavior and dependence as jet broadenings but more sensitive to (initial state) forward radiation. Jet Resolution Estimates the relative strength of the pT of the third jet with respect to the other two jets. Zero for two-jet events, a non-zero value indicates the presence of hard parton emission and is sensitive to parton showering modelling. G. Mavromanolakis, Univ. of Cyprus

Hadronic Event Shapes at 7 TeV Central thrust : all generators show an overall agreement with data to within 10%. Variables sensitive to longitudinal energy flow in the event show a larger disagreement between data and theory. Modeling of color connection between soft scatters and beam remnants, ISR, and FSR are the major sources of the discrepancies between the data and various QCD generators. G. Mavromanolakis, Univ. of Cyprus

G. Mavromanolakis, Univ. of Cyprus Multijets at 7 TeV CMS-PAS-QCD-11-006 Ratio of energy of leading jet to total Kinematic and angular distributions in inclusive multijet final states are a natural probe of QCD and its inner dynamics Comparisons made between data and predictions of leading order calculations and parton shower generators Models with only leading order calculations for dijet production cannot provide a satisfactory description of all multijet distributions G. Mavromanolakis, Univ. of Cyprus

The strong coupling constant : αS C.Quigg Fundamental QCD quantity Least known of the three coupling constants Running of αS sensitive to new physics! G. Mavromanolakis, Univ. of Cyprus

Three to two jet ratio and αS Eur.Phys.J. C73 (2013) 2604 Many systematic uncertainties cancel out in the ratio The ratio is sensitive to the strong coupling constant One of the first and very precise measurement at the TeV scale G. Mavromanolakis, Univ. of Cyprus 16

G. Mavromanolakis, Univ. of Cyprus Three jet mass and αS CMS-PAS-SMP-12-027 First measurement at 1.4 TeV G. Mavromanolakis, Univ. of Cyprus 17

Inclusive jet cross sections and αS CMS-PAS-SMP-12-028 Inclusive jet cross section shows sensitivity to the strong coupling constant Complementary independent measurement of this fundamental quantity G. Mavromanolakis, Univ. of Cyprus 18

G. Mavromanolakis, Univ. of Cyprus Summary - Conclusions Using jets precision QCD measurements have been performed that are being used for testing new physics models, constraining and tuning PDFs, extracting the strong coupling constant and its running, and providing useful information for various aspects of the theoretical modeling (FSR, ISR, color coherence, MPI, hadronization, etc) There are a few more important measurements to come, while there is intense preparation and anticipation for the exciting 13 TeV running! G. Mavromanolakis, Univ. of Cyprus

BACKUP

Non-Perturbative Corrections Non-Perturbative corrections are derived and applied to NLO calculation to account for : Multi-parton interactions (MPI) Hadronization effects (HAD) Used POWHEG interfaced with PYTHIA and HERWIG++ to define an envelope the mean of which is the NP correction, and half of its spread is the systematic uncertainty. G. Mavromanolakis, Univ. of Cyprus 21

G. Mavromanolakis, Univ. of Cyprus CMS Experiment Solenoid 3.8 T Pixels σ/pT~ 1.5∙10-4pT(GeV)⊕0.005 Hadronic Calorimeter σE/E ≈ 120%/√E(GeV) ⊕ 6.9% Electromagnetic Calorimeter σE/E ≈ 2.9%/√E(GeV) ⊕ 0.5%⊕0.13GeV/E Muon Spectrometer σpT/pT ≈ 1% for low pT muons σpT/pT ≈ 5% for 1 TeV muons G. Mavromanolakis, Univ. of Cyprus

G. Mavromanolakis, Univ. of Cyprus Jet Reconstruction Anti-kt clustering algorithm : with a cone R = 0.5 and 0.7 for CMS, which is infrared and collinear safe, geometrically well defined, and tends to cluster around the hard energy deposits Calorimeter Jets : Clustering of Calorimeter Towers composed of ECAL and HCAL energy deposits Particle Flow Jets (CMS) : Clustering of Particle Flow candidates constructed combining information from all sub-detector systems G. Mavromanolakis, Univ. of Cyprus

Inclusive Jet Cross Sections : 7 TeV CMS 5 fb-1 results submitted to PRD, full error correlation matrices will be available Some PDFs describe the data better than others : these measurements useful for PDF tuning and for constraining PDFs G. Mavromanolakis, Univ. of Cyprus

Dijet Cross Sections : 7 TeV Some PDFs describe the data better than others : these measurements useful for PDF tuning and for constraining PDFs G. Mavromanolakis, Univ. of Cyprus

G. Mavromanolakis, Univ. of Cyprus Jet Calibration Dijet asymmetry Photon+Jet Balance G. Mavromanolakis, Univ. of Cyprus

G. Mavromanolakis, Univ. of Cyprus Jet Mass CMS New Massive (SM or new physics) particles can be produced with significant Lorentz boosts => decaying into quarks the masses of the evolved jets can be used to discriminate them from lighter objects generated by QCD. For large boosts decay products emitted as collimated groupings into small sections of the detector => resulting particles can be clustered into a single jet. Jet “grooming” techniques are designed to separate jets from the decay of heavy boosted particles from quark/gluon initiated jets with large mass. G. Mavromanolakis, Univ. of Cyprus