1. 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

2. 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

3. 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

4. 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:
G. Mavromanolakis, Univ. of Cyprus

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

6. G. Mavromanolakis, Univ. of Cyprus
Theoretical Tools
Non-perturbative corrections for multi-parton interaction and hadronization
Parton showering effects (POWHEG)
Perturbative QCD 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

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

8. 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

9. Inclusive Jet Cross Sections: 8 TeV
CMS PAS SMP
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

10. Dijet Cross Sections: 8 TeV
CMS-PAS-SMP
Good description of
G. Mavromanolakis, Univ. of Cyprus

11. 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

12. Hadronic Event Shapes at 7 TeV
CMS-PAS-SMP
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

13. 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

14. G. Mavromanolakis, Univ. of Cyprus
Multijets at 7 TeV
CMS-PAS-QCD
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

15. 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

16. 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

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

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

19. 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

20. BACKUP

21. 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

22. 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

23. 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

24. 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

25. 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

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

27. 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