Of Jets • Splitting & Filtering: Unclustering Last Stages (In C/A Algorithm), Throw Away Softer Or More Distant Partner, Recluster with Smaller R

Jet production and properties

Jonathan Butterworth University College London Hadron Collider Physics, Kyoto, 14/11/2012 on behalf of ATLAS, CMS, CDF, D0

14/11/2012 Jon Butterworth, HCP 1 Jet physics at hadron colliders

• High energy hadron colliders are “quark/gluon” colliders • Highest cross-section hard-scattering process is gluon exchange, leading to high transverse momentum quarks or gluons • First probe of physics at the kinematical/ statistical limit • Quarks and gluons radiate a lot, and are confined. What we measure are jets of hadrons.

14/11/2012 Jon Butterworth, HCP 2 Jet physics at hadron colliders

• High energy hadron colliders are “quark/gluon” colliders • Highest cross-section hard-scattering process is gluon exchange, leading to high transverse momentum quarks or gluons • First probe of physics at the kinematical/statistical limit • Quarks and gluons radiate a lot, and are confined. What we measure are jets of hadrons. • Or photons (will only be able to mention briefly)

14/11/2012 Jon Butterworth, HCP 3 Jet production • Sensitive probe of the incoming parton fluxes • Parton densities in the proton

• Cross section depends on coupling αs • Differential cross sections depend upon QCD dynamics • QCD radiation, high order matrix elements, resummation of dominant terms in different kinematic configurations • If SM doesn’t describe what we see, we have new physics

14/11/2012 Jon Butterworth, HCP 4 Jets at the highest scales

• Highest transverse momentum jets; at the TeV scale

• arXiv:1009.5908 (EPJC),arXiv: 1112.6297 (PRD)

14/11/2012 Jon Butterworth, HCP 5 Jets at the highest scales

• Highest transverse momentum jets; at the TeV scale

• arXiv:1009.5908 (EPJC),arXiv: 1112.6297 (PRD) • arXiv:1106.0208 (PRL)

14/11/2012 Jon Butterworth, HCP 6 Jets at the highest scales • Highest transverse momentum jets; at the TeV scale

• arXiv:1009.5908 (EPJC),arXiv: 1112.6297 (PRD) • arXiv:1106.0208 (PRL) • General agreement with NLO QCD calculations (after soft corrections) Signiﬁcant spread in “NLO” predictions. ME/PS matching? MC tune (UE)? PDFs? 14/11/2012 Jon Butterworth, HCP 7 Jets at the highest scales • Highest transverse momentum jets; at the TeV scale

• Highest mass dijet pairs

• arXiv:1009.5908 (EPJC),arXiv: 1112.6297 (PRD) • arXiv:1104.1693 (PLB) • General agreement with NLO QCD calculations (after soft corrections) Signiﬁcant spread in “NLO” predictions. ME/PS matching? MC tune (UE)? PDFs? 14/11/2012 Jon Butterworth, HCP 9 Jets at the highest scales

• Highest mass dijet ATLAS! pairs

• Highest mass dijet pairs

• arXiv:1009.5908 (EPJC),arXiv: 1112.6297 (PRD), ATLAS- CONF-2012-021 • arXiv:1104.1693 (PLB) • Agreement with NLO QCD calculations (fixed order shown, after soft corrections)

14/11/2012 Jon Butterworth, HCP 11 Jets as a probe of the proton

CMS-PAS-QCD-11-004!

14/11/2012 Jon Butterworth, HCP 12 Jets as a probe of the proton

• Use 2.76 TeV CM data to measure cross sections.

ATLAS-CONF-2012-128!

14/11/2012 Jon Butterworth, HCP 13 Jets as a probe of the proton

• Use 2.76 TeV CM data to measure cross sections. • Ratios;

• in xT, many theory uncertainties ~cancel (same x, different Q2)

ATLAS-CONF-2012-128! 14/11/2012 Jon Butterworth, HCP 14 Jets as a probe of the proton

• Use 2.76 TeV CM data to measure cross sections. • Ratios;

• in xT, many theory uncertainties ~cancel (same x, different Q2)

• In pT, jet energy scale ~cancels (dominant experimental uncertainty) ATLAS-CONF-2012-128! 14/11/2012 Jon Butterworth, HCP 15 Jets as a probe of the proton

• Illustrative fit to HERA and ATLAS data • Valence quarks heavily contrained by HERA • High x gluon and sea quarks modified by addition of ATLAS data

ATLAS-CONF-2012-128ç! 14/11/2012 Jon Butterworth, HCP 16 Jets as a probe of the proton

• Illustrative fit to HERA and ATLAS data • Valence quarks heavily contrained by HERA • High x gluon and sea quarks modified by addition of ATLAS data

ATLAS-CONF-2012-128ç! 14/11/2012 Jon Butterworth, HCP 17 Jets as a probe of QCD dynamics • Angular distributions: measure number of neighboring jets above a transverse momentum threshold which accompany a jet, within distance ∆R. • arXiv:1207.4957 (D0 Run II Midpoint Cone algorithm)!

• Compare to NLO QCD; extract αs

14/11/2012 Jon Butterworth, HCP 18 Dijet φ Decorrelation • Study how additional QCD radiation introduces an imbalance between the two highest pT jets Δφ

arXiv:1102.2696 arXiv:1101.5029!

14/11/2012 Jon Butterworth, HCP 19 Dijet φ Decorrelation • Study how additional QCD radiation introduces an imbalance between the two highest pT jets

arXiv:1102.2696 arXiv:1101.5029!

14/11/2012 Jon Butterworth, HCP 20 Dijet φ Decorrelation

arXiv:1102.2696 arXiv:1101.5029!

14/11/2012 Jon Butterworth, HCP 21 Dijets with veto

Select two jet separated by a large rapidity interval

14/11/2012 Jon Butterworth, HCP 22 ATLAS-CONF-2011-038 Dijets with veto

Select two jet separated by a large rapidity interval Selection A: highest pT jets in event

14/11/2012 Jon Butterworth, HCP 23 ATLAS-CONF-2011-038 Dijets with veto

Select two jet separated by a large rapidity interval Selection A: highest pT jets in event Selection B: most forward and backward jets above some cut. Gap fraction = (Number of event with no jets in the gap) (All events) ATLAS-CONF-2011-038 14/11/2012 Jon Butterworth, HCP 24 Dijets with veto

Gap fraction falls with Δy Fairly well described by POWHEG with PYTHIA or HERWIG shower/UE HEJ doing somewhat better at high pT?

arXiv:1107.1641!

14/11/2012 Jon Butterworth, HCP 25 ATLAS-CONF-2011-038 Dijets with veto

However, number of events in gaps not well modelled by HEJ at high pT – much better with NLO + standard parton shower? Under active development… Powerful test of the approximations, and key to understanding “tag” and “veto” jets in e.g. Higgs or Diboson events

arXiv:1107.1641!

14/11/2012 Jon Butterworth, HCP 26 Forward/forward vs central/forward dijets • Herwig variants (angular-order parton showers?) describing shape well. • Problems for Pythia variants arXiv:1202.0704

14/11/2012 Jon Butterworth, HCP 27 Forward/central vs central/central dijets Ratio of “all jet pairs” to “exclusive jet pairs” Disfavours non-DGLAP dynamics?

arXiv:1204.0696

14/11/2012 Jon Butterworth, HCP 28 Three-to-two jet ratio

(D0 Run II Midpoint Cone algorithm) ! arXiv:1209.1140! • Explicit inclusion of higher multiplicity ME arXiv:1106.0647! (+parton show) generally needed for best arXiv:1107.2092! description at low HT

14/11/2012 Jon Butterworth, HCP 29 Three-to-two-jet ratio

! ! CMS QCD 11-003!

14/11/2012 Jon Butterworth, HCP 30 Jets as a probe of QCD dynamics • Bottom &/or charm production introduces another hard (or “semi-hard”) scale. How well is this understood?

arXiv:1210.0441!

14/11/2012 Jon Butterworth, HCP 31 Jets as a probe of QCD dynamics • B jet (and dijet) cross sections compared to NLO QCD See talk by Pavel Reznicek

arXiv:1109.6833 arXiv:1202.4617! 14/11/2012 Jon Butterworth, HCP 32 Jets as a probe of QCD dynamics • B jet (and dijet) cross sections compared to NLO QCD See talk by Pavel Reznicek

arXiv:1109.6833 arXiv:1202.4617! 14/11/2012 Jon Butterworth, HCP 33 Jets as a probe of QCD dynamics • B jet (and dijet) cross sections compared to NLO QCD

arXiv:1109.6833 arXiv:1202.4617! 14/11/2012 Jon Butterworth, HCP 34 Jets as a probe of QCD dynamics

Good agreement with POWHEG, poorer with MC@NLO (seen by both ATLAS & CMS)

arXiv:1109.6833 arXiv:1202.4617! 14/11/2012 Jon Butterworth, HCP 35 Jets as a probe of QCD dynamics • Use properties of displaced decay vertices to distinguish light, c and b jets in dijet events

arXiv:1210.0441!

14/11/2012 Jon Butterworth, HCP 36 A word on Photons • Similar physics, complementary systematics to jet studies • Key background for Higgs

arXiv:1211.1913! 14/11/2012 Jon Butterworth, HCP arXiv:1210.5033! 37 A word on Photons • Similar physics, complementary systematics to jet studies • Key background for Higgs • Diphoton + jet measurements badly needed!

arXiv:1211.1913! 14/11/2012 Jon Butterworth, HCP arXiv:1210.5033! 38 A word on Photons • Similar physics, complementary systematics to jet studies • Key background for Higgs • Diphoton + jet measurements badly needed! • See slide from Ashish Kumar yesterday • γ+jet, γ+c,b-jet results also

available arXiv:1211.1913! 14/11/2012 Jon Butterworth, HCP arXiv:1210.5033! 39 A word on Photons • Similar physics, complementary systematics to jet studies • Key background for Higgs • Diphoton + jet measurements badly needed! • See slide from Ashish Kumar yesterday • γ+jet, γ+c,b-jet results also

available arXiv:1211.1913! 14/11/2012 Jon Butterworth, HCP arXiv:1210.5033! 40 Jet properties • Final stage of jet structure is “soft” non-perturbative QCD.

• Formation of hadrons from gluons, 100 MeV energy scales (ΛQCD) • Vast phase space between quark-gluon scatter (100’s GeV, few TeV) and ΛQCD • Most of jet substructure can be analysed perturbatively • EWSB scale (~100 GeV) lies in this region • Jets may contain objects with EW-scale mass (W,Z,H,t,?)

14/11/2012 Jon Butterworth, HCP 41 Charged-particle content

• How well do we really understand fragmentation

• arXiv:1109.5816

14/11/2012 Jon Butterworth, HCP 42 Jet Shapes

• Study the distribution of energy (pT) around the jet axis

arXiv:1204.3170! arXiv:1101.0070!

14/11/2012 Jon Butterworth, HCP 43 Jet Shapes • Other shapes; width, eccentricity, planar flow…

arXiv:1101.0070!

14/11/2012 Jon Butterworth, HCP 44 Tagging and “Grooming” of jets • Splitting & filtering: Unclustering last stages (in C/A algorithm), throw away softer or more distant partner, recluster with smaller R

• JMB, Davison, Rubin, Salam, PRL 100, 242001 (2008). Kaplan, Rehermann, Schwartz, Tweedie, PRL 101, 142001 (2008). JMB, J Ellis, Raklev, Salam, PRL 103, 241803 (2009). • Variable R parameter

• Krohn, Thaler, Wang, JHEP 0906:059,2009. • “Pruning” or “Trimming”: Remove soft splittings in (re)clustering

• S. Ellis, Vermilion, Walsh, PRD 80, 051501 (2009); Krohn, Thaler, Wang, arXiv: 0912.1342 [hep-ph].

14/11/2012 Jon Butterworth, HCP 45 Tagging and “Grooming” of jets • Distinctive jets shapes (see previous results)

• JMB, Davison, Rubin, Salam, PRL 100, 242001 (2008). Kaplan, Rehermann, Schwartz, Tweedie, PRL 101, 142001 (2008). JMB, J Ellis, Raklev, Salam, PRL 103, 241803 (2009). • N-subjettiness; evaluate how much a jet’s internal structure resemble N subjets.

• Thaler, Van Tilberg, JHEP 1103 (2011)

• kT splitting scale: look for a scale which is not in a “strongly ordered” sequence

• Seymour, Z.Phys. C62 (1994) 127-138 JMB, Cox, Forshaw, PRD 65; 096014 (2002).

14/11/2012 Jon Butterworth, HCP 46 Jet mass • Ungroomed

CMS-PAS-SMP-12-011! 14/11/2012 Jon Butterworth, HCP arXiv:1106.5952! 47 Jet mass • Ungroomed

CMS-PAS-SMP-12-011! 14/11/2012 Jon Butterworth, HCP 48 Jet mass • Ungroomed

CMS-PAS-SMP-12-011! 14/11/2012 Jon Butterworth, HCP 49 Jet mass • Ungroomed Groomed (filtered)

CMS-PAS-SMP-12-011! 14/11/2012 Jon Butterworth, HCP 50 Jet mass • Ungroomed Groomed (filtered)

CMS-PAS-SMP-12-011! 14/11/2012 Jon Butterworth, HCP 51 Jet grooming and subjets

14/11/2012 Jon Butterworth, HCP arXiv:1203.4606! 52 Jet grooming and subjets

• kT scale, N-subjettiness

14/11/2012 Jon Butterworth, HCP arXiv:1203.4606! 53 Summary and Conclusions • Precision QCD, using the understanding (theory and experiment) developing using previous colliders continues to bear fruit at LHC • Impressively precise results, with well-defined and understood jet finders and comparing to state-of-the-art NLO and parton-shower-matched QCD calculations with realistic hadronisation and underlying event • Already constraints on PDFs, and tests of kinematics crucial to understanding physics above the EWSB scale • Jet substructure: key technique for boosted particle measurements, validated in QCD and beginning to live up to its wider potential

14/11/2012 Jon Butterworth, HCP 54 End

14/11/2012 Jon Butterworth, HCP 55