- Particle Physics in the 2020s
(Invited seminar at LHCb week, Oxford, United Kingdom, September 2019)
- Insights into the logarithmic accuracy of parton showers
(Seminar at the Cavendish Laboratory, University of Cambridge, UK, June 2019)
[abs]
Parton shower algorithms simulate the production of large numbers of
gluons and quarks in high energy collisions. They are essential in
much of collider physics, as a key component of general Monte Carlo
event generators. This talk sets out an approach for assessing the
logarithmic accuracy of parton-shower algorithms based on two broad
criteria: their ability to reproduce the singularity structure of
multi-parton matrix elements, and their ability to reproduce
logarithmic resummation results. The approach is illustrated by
considering properties of two transverse momentum ordered final-state
showers.
- Theoretical path for QCD physics
(Talk at the Open Symposium of the Update of the European Strategy for Particle Physics, Granada, Spain, May 2019)
- LHC and the new Higgs-boson interactions
(Talk at a Saturday Morning of Theoretical Physics, Oxford, UK, May 2019)
[abs]
What the Large Hadron Collider is telling us about the Higgs sector
and its new interactions Over the past two years, CERN's Large Hadron
Collider (LHC) has started to directly probe a qualitatively new class
of interactions, associated with the Higgs boson. These interactions,
called Yukawa interactions, are unlike any other interaction that we
have probed at the quantum level before. In particular, unlike the
electromagnetic, weak and strong forces, they have an interaction
strength that does not come in multiples of some underlying unit
charge. Yukawa interactions are believed to be of fundamental
importance to the world as we know it, hypothesised, for example, to
be responsible for the stability of the proton, and so the universe
and life as we know it.
- Higgs and the new fundamental interactions
(Keynote talk at the Quantum Universe kickoff meeting, Hamburg, Germany, March 2019)
- The Lund jet plane: organising QCD radiation at colliders
(Seminar the University of Birmingham, UK, March 2019)
[abs]
The radiation in collider events, in particular within jets, contains
much information. That radiation is exploited for studies of the Higgs
sector, searches for new physics, understanding vacuum QCD, and
investigating the properties of the quark-gluon plasma. Theorists have
long used so-called Lund diagrams as a tool to help think about the
kinematic regions within jets. A decade of work on devising
observables for studying jets for Higgs and new-physics searches has
recently led to the observation that one can formulate the Lund
diagram as an experimental analysis tool. It provides a physically
powerful representation of any given jet's structure and also
remarkable insight also into features being learnt by AI-based jet
tagging approaches.
- Insights into the logarithmic accuracy of parton showers
(Seminar at Southampton HEP group, UK, February 2019)
- Physics motivations for sub-percent absolute cross sections
(Invited talk at the LHCb UK Annual Meeting 2019, University of Warwick, UK, January 2019)
- Hunting for Terascale physics at the LHC
(Colloquium at the Princeton University Physics Department, Princeton, NJ, USA, December 2010)
[abs]
Over the past year, the Large Hadron Collider at CERN has made
impressive progress, recovering from the 2008 incident, surpassing the
Tevatron as the world's highest energy collider and progressively
increasing the rate of proton-proton collisions that it delivers, so
that it is now starting to explore new territory in the search for
physics at the TeV scale.
This talk will start with a review of the LHC's main goals and the key
milestones of the past twelve months. It will then discuss some
ongoing research aimed at extending the LHC's potential for
discovery. Taking place at the boundary between theory and experiment,
this work concerns searches for new particles that decay to hadrons,
which have in the past been deemed particuarly challenging for the
LHC.
- Giant K-factors
(Joint UMD/Hopkins seminar at the University of Maryland, College Paris, MD, USA, December 2010)
[abs]
It has become evident in the past few years that there are cases
where popular hadron collider observables (HT, etc.) are subject to
"giant" QCD radiative corrections, which are much larger than the
leading-order QCD prediction. In one example from Z+jet production,
supposedly subleading QCD corrections modify the leading-order
prediction by a factor of order 50.
Such giant K-factors usually arise because some new, enhanced
channel opens up in higher orders of perturbation theory. This
understanding can help guide one's choice of experimental
observables, so as to limit the exposure to giant K-factors -- for
example in tails of distributions being used in new-physics
searches. Alternatively, one can supplement existing calculations
for adversely affected observables using a well-motivated procedure
to bring the perturbative QCD predictions back under control.
- Pileup subtraction and rapidity dependence
(Informal talk for the CMS JetMET working group, Geneva, Switzerland, November 2010)
[abs]
This informal talk discusses how the jet-area based pileup subtraction
method can be used to take into account rapidity dependence of the
pileup. Two aspects are considered: the true physical (slowly varying)
rapidity dependence of the pileup, and potential detector-induced
artefacts in small intervals of rapidity.
- Resummation
(Invited talk at QCD in the LHC Era, a meeting in honour of Bryan Webber, Cambridge, UK, September 2010)
- Jet reconstruction with FastJet
(Invited talk at the Jets in Proton-Proton and Heavy-Ion Collisions workshop, Prague, Czech Republic, August 2010)
- Perturbative QCD for the LHC
(Invited plenary talk a ICHEP 2010, Paris, France, July 2010)
- Hadronic jets with substructure: theory review
(Invited talk at Boost 2010, Oxford, UK, June 2010)
- Subtleties of non-perturbative effects in event shapes
(Talk at the Aspen Center for Physics, Aspen, Colorado, USA, June 2010)
[abs]
A discussion of some of the difficulties that arise with analytical
models of non-perturbative effects in event shapes and strong-coupling
fits, examining the impact of the definition of hadron level,
deviations from simple 1/Q dependence in Monte Carlo models and the
dependence of hadronisation on event topology.
- LHC searches: what role for QCD?
(Seminars at the Aspen Center for Physics, Aspen, Colorado, USA, May 2010)
- LHC searches: what role for QCD?
(Colloquium at the Paul Scherrer Institut, Villigen, Switzerland, April 2010)
- Jet clustering tools
(Talk at the MC4LHC readiness workshop, CERN, Geneva, Switzerland, March 2010)
[abs]
A brief overview of current jet clustering methods, the software tools
that implement them and some of the physics considerations in their
use.
- New Jet Methods for High-Multiplicity Environments
(Invited talk at the APS April Meeting, Washington DC, USA, February 2010)
[abs]
Accurate jet reconstruction in high multiplicity environments is
essential to maximize what we learn both in heavy-ion collisions at
RHIC and LHC, and in searches of new (beyond standard model) physics
in high-luminosity LHC proton-proton (pp) running. State of the art
jet-physics methods, developed in parallel for these two environments,
have recently been used by the STAR collaboration for the first ever
measurements of jets in gold-gold collisions. This talk will outline
the theoretical basis of these methods and examine the issues that are
relevant in optimizing their performance, highlighting the different
considerations that should be taken into account when using them for
heavy-ion as opposed to high-luminosity pp collisions.
- Towards Jetography
(Seminar at the C. N. Yang Institute for Theoretical Physics, Stony Brook, USA, February 2010)
- Jets, UE and early LHC data
(Invited talk at LHC@BNL, a joint theory/experiment workshop on early physics at the LHC, Brookhaven National Laboratory, Upton, NY, USA, February 2010)
- LHC searches: what role for QCD?
(Seminar in the High Energy Theory Group, Harvard University, Cambridge (MA), USA, February 2010)
- LHC searches: what role for QCD?
(Seminar at the CCPP, New York University, New York, USA, January 2010)
- Towards jetography
(seminar at the DESY theory group, Hamburg, Germany, November 2008)
[abs]
This talk describes ongoing efforts to develop "jetography". It
illustrates existing jet methods, illustrates the degree to which further
developments can extend their usefulness in LHC searches, discusses
the physics behind these improvements and outlines some of the steps
that still need to be made on the way towards "auto-focus" for jets.
- LHC searches: what role for QCD
(Invited talk at the Forefront of LHC Physics Mini-Symposium, Princeton University, New Jersey, USA, October 2008)
[abs]
This talk considers some of the ways in which QCD might play
a role in searches for new physics at the LHC. It examines the
question of the reliable estimation of backgrounds, as well as that of
how QCD can guide us in designing better tools to extract any new
physics signals from the background.
- LHC searches: what role for QCD
(Informal seminar at Johns Hopkins University, Baltimore, Maryland, USA, October 2008)
- Two lectures on jets
(Lectures at the 2008 CTEQ-MCnet Summer School on QCD Phenomenology and Monte Carlo Event Generators, Debrecen, Hungary, August 2008)
[abs]
These lectures provide an introduction to sequential recombination
and cone-type jet algorithms, including concrete illustrations of
the differences between various cone algorithms. They also discuss
questions related to infrared and collinear safety, and look at
issues and difficulties that arise when trying determine which jet
definitions are "best".
- Jet substructure as a new Higgs search channel at the LHC
(Talk at SUSY08, Seoul, Korea, June 2008)
[abs]
It is widely considered that, for Higgs boson searches at the Large
Hadron Collider, WH and ZH production where the Higgs boson decays to
b anti-b are poor search channels due to large backgrounds. This talk
will show that at high transverse momenta, employing state-of-the-art
jet reconstruction and decomposition techniques, these processes can
be recovered as promising search channels for the standard model Higgs
boson around 120 GeV in mass.
- Jets in QCD, an introduction
(Invited talk at Hard Probes 2008, Illa Da Toxa, Galicia, Spain, June 2008)
[abs]
An introduction to the different kinds of jet algorithms that are in
use, together with a discussion of some issues that are specific to
heavy-ion collisions, including area-based subtraction of underlying
noise.
- Jet Physics at colliders
(Invited plenary talk at the HERA-LHC Workshop, CERN, Geneva, Switzerland, May 2008)
- Jets, our window on partons at the LHC
(Seminar at Turin University, Turin, Italy, May 2008)
[abs]
Jets, collimated bunches of hadrons that result from the
fragmentation of quarks and gluons, will be key observables at
LHC. This talk introduces the issues that are relevant in
hadron-collider jet-physics and reviews recent developments. These
include both technical breakthroughs, finally enabling
hadron-collider jet-finding to be brought up to the standards set
out in the 1990 Snowmass accord, and progress in understanding the
physics of jets, which serves as groundwork for optimising the
practical effectiveness of jet-finding at LHC.
- Jets at LHC: from basics to Higgs hunting
(Seminar at the Cavendish Laboratory, University of Cambridge, UK, May 2008)
[abs]
Jets provide the interface between the theoretical concept of
partons and many experimental hadron-level measurements. Nearly 20
years ago the Snowmass accord set out requirements that jet-finding
should satisfy at hadron colliders. Today these basics are now
finally in place and we can move on to consider the qualitatively
new challenges that will be faced when using jets at the LHC. The
scope for progress will be illustrated with the example of a new
search channel for a low-mass Higgs boson, based on the analysis of
jet substructure.
- Jets at LHC: from basics to Higgs hunting
(Seminar at the CP3, Université Catholique de Louvain, Belgium, May 2008)
[abs]
Jets provide the interface between the theoretical concept of
partons and many experimental hadron-level measurements. Nearly 20
years ago the Snowmass accord set out requirements that jet-finding
should satisfy at hadron colliders. Today these basics are now
finally in place and we can move on to consider the qualitatively
new challenges that will be faced when using jets at the LHC. The
scope for progress will be illustrated with the example of a new
search channel for a low-mass Higgs boson, based on the analysis of
jet substructure.
- Jet algorithms
(Talk for the CMS JetMET working group, CERN, Switzerland, March 2008)
[abs]
An introduction to the behaviour and properties of common jet
algorithms. It discusses infrared and collinear safety issues in
legacy algorithms, with mention of the logic behind the approaches we
have taken to address these issues, and closes with an illustration of
area-based pileup subtraction.
- Theoretical aspects of jet-finding
(Invited talk at the 4th ATLAS hadronic calibration workshop, Tucson (AZ), USA, March 2008)
[abs]
A lecture providing an overview of some of the main issues in
jet-finding, recent progress and an illustration of an advanced
jet-finding application in Higgs searches.
- Jets, our window on partons at the LHC
(Seminar at the LPT, Orsay, Paris, France, January 2008)
[abs]
Jets, collimated bunches of hadrons that result from the fragmentation
of quarks and gluons, will be key observables at LHC. This talk
introduces the issues that are relevant in hadron-collider jet-physics
and reviews recent developments. These include both technical
breakthroughs, finally enabling hadron-collider jet-finding to be
brought up to the standards set out in the 1990 Snowmass accord, and
progress in understanding the physics of jets, which serves as
groundwork for optimising the practical effectiveness of jet-finding
at LHC.
- Matrix combination of BFKL and DGLAP
(Seminar for the BNL theory group, Long Island, USA, December 2007)
[abs]
A progress report (extended version) on a long-term project to put
together DGLAP and the linear regime of BFKL evolution, including
higher order and running-coupling corrections, with emphasis on
developments related to the incorporation of the full matrix (flavour)
structure of the evolution.
- Jets, our window on partons at the LHC
(seminar at the Rutgers High Energy Theory group, New Brunswick (NJ), USA, November 2007)
[abs]
Jets, collimated bunches of hadrons that result from the fragmentation
of quarks and gluons, will be key observables at LHC. This talk
introduces the issues that are relevant in hadron-collider jet-physics
and reviews recent developments. These include both technical
breakthroughs, finally enabling hadron-collider jet-finding to be
brought up to the standards set out in the 1990 Snowmass accord, and
progress in understanding the physics of jets, which serves as
groundwork for optimising the practical effectiveness of jet-finding
at LHC.
- Matrix combination of BFKL and DGLAP
(invited talk at the International Symposium on Multiparticle Dynamics, Berkeley, USA, August 2007)
[abs]
A progress report (short version) on a long-term project to put
together DGLAP and the linear regime of BFKL evolution, including
higher order and running-coupling corrections, with emphasis on
developments related to the incorporation of the full matrix (flavour)
structure of the evolution.
- Recent progress in defining and understanding jets
(invited talk at the International Symposium on Multiparticle Dynamics, Berkeley, USA, August 2007)
[abs]
This talk reviews some of the main developments that have occurred in
jet finding in the past couple of years, including: 1) technical
advances such as fast computational approaches to the kt and
Cambridge/Aachen algorithms, and the complete formulation of a proper
(seedless) cone algorithm; 2) progress in understanding quantitative
behaviour of jet algorithms with respect to underlying event and
hadronisation corrections; 3) work that exploits the better
understanding so as to improve the results from jet algorithms.
- Event shapes for hadron colliders
(seminar at the MPPMU, Munich, Germany, July 2007)
[abs]
Event shapes combine conceptual simplicity with sensitivity to QCD
dynamics over a range of scales and have been the subject of
innumerable studies in e+e- and DIS collisions. This talk examines the
new questions that can be addressed by extending event shapes to
hadron colliders, and presents some concrete examples of how to design
hadron-collider event shapes so as to ensure that they are both
measurable experimentally and calculable theoretically. First results
for resummed distributions are presented based on CAESAR.
- Hopes for LHC jets from a theory perspective
(talk at the Physics at TeV Colliders, Les Houches, France, June 2007)
[abs]
The second of two talks intended to provide an introduction to some of the
current issues in jet physics that could be addressed by the Les
Houches workshop, together with a set of minimal hopes for what might
be a minimum set of requirements for LHC jet-finding.
- Opening talk for jets subgroup of SM handles and candles working group
(plenary talk at the Physics at TeV Colliders, Les Houches, France, June 2007)
[abs]
The second of two talks intended to provide an introduction to some of the
current issues in jet physics that could be addressed by the Les
Houches workshop, together with a set of minimal hopes for what might
be a minimum set of requirements for LHC jet-finding.
- Higher-orders, jets and the interplay between them
(invited talk at the Paris CDF Collaboration Meeting, Paris, France, June 2007)
[abs]
This talks takes a brief look at recent developments in higher-order
QCD calculations for colliders (NLO, NLO with parton showers, NNLO)
and then proceeds to discuss how higher orders are connected with
jets, discussing infrared safety issues, seedless cone definitions,
hadronisation and underlying event in the context of top mass
measurements, and jet flavour.
- Outils de pointe pour la reconstruction QCD aux collisionneurs
(talk (in French) at the Colloque ANR des Jeunes Chercheurs SDU Physique, Orléans, France, April 2007)
[abs]
An overview of current themes in jet physics and of recent
work carried out by the Jussieu group on the subject.
- A practical seedless infrared-safe cone algorithm
(talk given at Rencontres de Moriond: QCD and Hadronic interactions, La Thuile, Italy, March 2007)
[abs]
A brief introduction to the infrared safety issue in the midpoint
(seeded) cone algorithm and an explanation of how to construct an
efficient seedless and infrared-safe cone algorithm, together with an
illustration of its impact for a small choice of physical
observables.
- Characterising non-perturbative effects in jets
(talk at the Ringberg workshop on non-perturbative QCD of jets, Ringberg, Germany, January 2007)
[abs]
This talk examines various non-perturbative contributions to jet
momenta in a hadron-collider context. The main results are that
hadronisation effects scale as 1/R, underlying event and pileup scale
scale as R^{2}, with the same coefficient for all jet
algorithms to first order. Some preliminary results are given also for
higher-order effects.