Taming Unphysical Scales for Physical Predictions

30 Mar 2017, 09:55 → 31 Mar 2017, 18:10 Europe/London

Emmanuel College, Cambridge

Workshop on renormalisation and factorisation scale choices for precision predictions of cross sections at the LHC

Rationale:

• Perturbative predictions of any LHC observable depend on factorization and renormalization scales
• Scale choices are important in any kinematics but will be critical for describing still-unexplored regimes like:
  • boosted regime/particle productions at high p_T 
  • production and decay of high mass particles
  • jet physics, especially for jets at large rapidity
• Guessing the right scale for a process is not an easy task
• Is there such a thing as correct scale choice?
  • Or are there only more-or-less smart choices?
  • There are definitely very wrong choices, which lead to an unstable perturbative behavior

Context:

The convening of this meeting has been compelled by a convergence of new LHC-related developments:

• The calculation of almost all major two-to-two processes at NNLO
• NLO calculations now allow detailed access to even the most subtle effects
• Mature LO and NLO merging techniques that have been very successful in bridging various multiplicities
• Resummation at NNLL is turning into a bread-and-butter phenomenology

These new developments would make it possible to quantify the impact of various scale-setting procedures; this was not possible in the past.

Workshop goals:

• To draw attention to the last missing piece in the precision physics puzzle: the choice of unphysical factorisation and renormalisation scales
• Bringing together leading researchers in order to debate ways of setting scales
• Be the first step towards harmonised scale-setting accord across LHC processes and for the benefit of precision LHC phenomenology

Related Workshop:

The Workshop will immediately follow the annual Workshop on Parton Showers and Resummation PSR2017. Both Workshops will be held in the same venue. Participants may wish to take advantage of this opportunity and attend both meetings. More information about PSR2017 is available here: https://indico.cern.ch/e/PSR2017.

Organizers:

• Michal Czakon (RWTH Aachen University)
• Joey Huston (Michigan State University)
• Alexander Mitov (Cambridge University)
• Bryan Webber (Cambridge University)
• Malgorzata Worek (RWTH Aachen University)

Thursday 30 March

Morning Session: Jets + Top Quark

1 Welcome

Speaker: Alexander Mitov (University of Cambridge (GB))

2 Scale choices, uncertainties and correlations for jet observables

Speaker: Bogdan Malaescu (Centre National de la Recherche Scientifique (FR))

ScalesJetObservables_Malaescu.pdf

10:30 Discussion 20'

3 Scales for single jet inclusive production at the LHC through NNLO

Speaker: James Currie

currie_cambridge.pdf

11:15 Discussion 20'

4 Scales for differential top-quark pair production through NNLO

Speaker: Alexander Dimitrov Mitov (CERN)

SCALES-Alexander-Mitov.pdf

SCALES-Alexander-Mitov.pptx

12:00 Discussion 20'

Lunch

Afternoon Session I: H/W/Z + jets

5 Scales for top quark production with a jet including decays and off-shell effects through NLO

Speaker: Malgorzata Maria Worek (Rheinisch-Westfaelische Tech. Hoch. (DE))

cambridge.pdf

14:05 Discussion 20'

6 Lessons from Measurements of W/Z/H+jets production

Speaker: Prof. Joey Huston (Michigan State University (US))

huston_cambridge_scales.pdf

14:55 Discussion 20'

7 Scales for Z/H in association with a jet through NNLO

Speaker: Nigel Glover (Durham University)

cambridge2.pdf

15:40 Discussion 20'

Coffee Break

Afternoon Session II: Alternative methods to scale setting

8 Optimal choice of factorisation scales for the description of jet production at the LHC

Speakers: Alan Martin, Mikhail Ryskin (Petersburg Nuclear Physics Institute), Nigel Glover (Durham University)

Nigel.pdf

16:40 Discussion 10'

9 BLM/PMC scale setting and its applications to collider physics

Speaker: Stanley J. Brodsky (SLAC National Accelerator Laboratory, Stanford University)

sjb Cambridge PMC March 30, 2017 For Webpage.pdf

sjb Cambridge PMC March 30, 2017 For Webpage.pptx

10 BLM/PMC in top-pair production

Speakers: Alexander Mitov (University of Cambridge (GB)), Herschel Chawdhry

FINAL_Herschel_A_Chawdhry_SCALES_workshop_presentation_30th_March_2017.pdf

17:35 Discussion 30'

Reception

Conference dinner

Friday 31 March

Morning Session I: PDF’s and ratios

11 Scale variation and PDF uncertainties

Speaker: Stefano Forte (Università degli Studi e INFN Milano (IT))

scales.pdf

09:20 Discussion 20'

12 Scale variation and scale error determination in ratios

Speaker: Fernando Febres Cordero (University of Freiburg)

Ratios_Cambridge_Mar_2017.pdf

10:00 Discussion 20'

Coffee break

Morning Session II: Ratios, NLO Merging and Resummation

13 Scale-related issues in parton showers

Speaker: Frank Martin Krauss (University of Durham (GB))

Krauss-Scales_Cambridge17.pdf

11:20 Discussion 20'

14 Scale variation for the ratio of W/Z pT's

Speaker: Jonas Lindert

JL_SCALES17.pdf

12:00 Discussion 20'

Lunch

Afternoon Session: Resummation and Parton Showers

15 Scales for merging of jet multiplicities in top, H and W production

Speakers: Stefan Hoche (SLAC National Accelerator Laboratory (US)), Stefan Hoeche (SLAC)

Hoeche_MINLO_17-03.pdf

13:55 Discussion 20'

16 Profile scales in the context of resummed distributions

Speaker: Frank Tackmann (Deutsches Elektronen-Synchrotron (DE))

2017-03-31_profile_scales_FT.pdf

14:35 Discussion 20'

14:55 Coffee break 10'

17 Scales in SCET

Speaker: Matthew Schwartz

Scales-schwartz.pdf

15:30 Discussion 20'

Closing discussions

15:50 Workshop closing discussion 30'