Friday, 13 November 2015

KIAS-CFHEP Workshop Liveblog: Day Five Session Four

We come to the final session of the conference, which has only a single talk scheduled.  (Plus final thanks I'm sure.)

4:00 pm: Collider Phenomenology, hypotheses and measurements, Michael Spannowsky

Several approaches that we can take right now: SUSY, composite Higgs, effective operators.  Whatever we choose, modern analyses use simplified models.

The whole community is emotionally effected by the lack of naturalness promised by our data!  Plus, perhaps we have oversold what can be learned from the Higgs boson.  We essentially found it in the bin but it tells us nothing about the underlying physics.

The interpretation of any measurement is model-dependent.  Interpretation requires communication between different scales.  Increasing model complexity also means increasing model flexibility.  Our study of the Higgs physics at Run 1 has mostly used the very simple κ framework, modelling the Higgs couplings with a simple rescaling of the SM value.

There has also been a (somewhat long-running) struggle to come to a suitable unified language/basis for Higgs EFT.  Different bases, how many operators, validity of measurements and theory.  Even if flavour-blind, over 59 operators.  Though many are constrained by EW physics.  Focusing on operators relative to new Higgs physics gives us 8 operators.

Important that kinematic distributions set the validity of the EFT themselves.  Deviations set limits on Wilson coefficients.  Other observations more or less bound NP scale Λ.  This lets us properly understand where the constraints lie in the EFT parameter space.

However, LHC probes varying scales but generally low compared to Λ.  Need to renormalise from Λ to measurement scale, which is complicated due to the different scales measured.  Compare flavour physics, where typically there is only a single scale, e.g. the B meson mass.  Importantly get both running and mixing of Wilson coefficients with scale.  For example, can have T parameter at high scale but not at low scale.  Some efforts to place limits already.  Some of these constraints are in region where EFT is dubious, at least as simply presented.

Simplified models another approach.  Suitable for approaches with relatively light new particles.  Examples include singlet (Higgs portal), 2HDM variants, and triplet models (Georgi-Machacek).  Constraints from direct searches already push to alignment or decoupling limits.  Georgi-Machacek interesting as no decoupling limit, so can be truly excluded at LHC.

Dark matter searches involved similar question: EFT or simplified model.

Interpretation of results depends on language used.  Example: CMS width measurement, which uses on-shell and off-shell measurements of cross sections.  Claim to give model-independent bound on the width.  But only actually works for κ framework or EFT.  Simplified models can contribute on-shell only (e.g. Higgs portal) or new light scalars can cancel the on-shell enhancement.  In full UV models, the Higgs width is not a free parameter, so the constraint is not of general use.

Also, LEP measurements in same way give much stronger bounds than the LHC can ever do.

Matrix element method as tool for jet substructure, in contrast to previous use as hypothesis testing tool.  Computational challenges all over the place.  Parton shower with Sudakov factors and splitting functions.  Idea seems to be to calculate a library of these for signals and backgrounds.  Improves on tagging efficiency by factor of 2 to 4.  Relatively insensitive to pile up.  Application: discrimination of dijets, ditops and ditop resonances.

Summary: optimising data analysis and interpretations must be a primary goal at the LHC.  There is always a trade off between generality and precision.

Why stable to pile up? Using smaller jets.  Pile up goes like R squared, so this makes things much better.  Also, inbuilt pruning procedure to assign subjets to ISR/FSR.

KIAS-CFHEP Workshop Liveblog: Day Five Session Three

Our third session of the day is another plenary, three talks with titles that don't make the connection immediately obvious.

KIAS-CFHEP Workshop Liveblog: Day Five Session Two

The last day of the conference, and the day after the banquet.  As seems to be traditional, I overslept and missed the first session.  Oh well.  I missed two ILC talks that would probably have been interesting, but so be it.

Thursday, 12 November 2015

KIAS-CFHEP Workshop Liveblog: Day Four Session Four

For the final parallel session of the conference, I've decided to stay on the top floor for what is another flavour session.

Judicial Bigotry

Utah judge orders child taken away from adoptive parents because they are lesbian:
Utah state child welfare officials on Wednesday were wrangling with a ruling by a juvenile court judge who ordered a baby to be taken from lesbian foster parents and instead placed with a heterosexual couple, saying it was for the child’s wellbeing.
Sumner, from the child welfare agency, said she could not speak to specifics of the case but confirmed that the couple’s account of the ruling was accurate — the judge’s decision was based on the couple being lesbians. The agency was not aware of any other issues with their performance as foster parents.
Contrast that with the legal position of the Americal Psychological Association, from 2010:
There Is No Scientific Basis For Concluding That Gay And Lesbian Parents Are Any Less Fit Or Capable Than Heterosexual Parents, Or That Their Children Are Any Less Psychologically Healthy And Well Adjusted
(That's from the table of contents.) Or a literature review for the Australian Psychological Society from 2007:
The research indicates that parenting practices and children’s outcomes in families parented by lesbian and gay parents are likely to be at least as favourable as those in families of heterosexual parents, despite the reality that considerable legal discrimination and inequity remain significant challenges for these families.
(That's from the conclusion.)  In short, this judge acted not based on data but on the basis of his own homophobia.  Hardly surprising, but still outrageous.

[Edited to add reference for APA legal brief.]

KIAS-CFHEP Workshop Liveblog: Day Four Session Two

We have what I presume are two talks on the theory of flavour (the second one is another TBA talk).

KIAS-CFHEP Workshop Liveblog: Day Four Session One

So yesterday was interesting, the first time I've explored any of Seoul.  Won't be the last time, I'm sure.  Today we have sessions on flavour physics before lunch, and the second parallel session of the conference in the afternoon.  The flavour section is itself split into experiment first, then theory.

Wednesday, 11 November 2015

KIAS-CFHEP Workshop Liveblog: Day Three Session Two

We return for the final session of this short day with two talks marked as 'TBA'.

KIAS-CFHEP Workshop Liveblog: Day Three Session One

Our third day, which is a half-day so we can explore Seoul after lunch, is given the vague title "Astro-interplay And other topics".

Tuesday, 10 November 2015

KIAS-CFHEP Workshop Liveblog: Day Two Session Four

The final session of the day is, as promised, more SUSY aligned.  We also have a challenging six talks.

KIAS-CFHEP Workshop Liveblog: Day Two Session Three

This is the first of two afternoons of parallel sessions.  I've decided to stay on the fifth floor, and attend the session on composite Higgs followed by supersymmetry.

KIAS-CFHEP Workshop Liveblog: Day Two Session Two

We continue after coffee.

KIAS-CFHEP Workshop Liveblog: Day Two Session One

We had a very nice reception last night, together with cheese—good cheese—which is not common here in Korea.  Today we have morning plenary talks on Cosmology, followed by the first parallel sessions after lunch.

Monday, 9 November 2015

KIAS-CFHEP Workshop Liveblog: Day One Session Four

The final session of the day is also the most intense plenary session, with four talks.

KIAS-CFHEP Workship Liveblog: Day One Session Three

We return after lunch for more plenary talks (only two days this week have parallel sessions).  Our focus has moved to theory.

KIAS-CFHEP Workshop Liveblog: Day One Session Two

We return from the coffee break to finish the LHC experimental talks, followed by a discussion of Higgs theory.

KIAS-CFHEP Workshop Liveblog: Day One Session One

I've been in Korea less than three months and already I'm at my second conference here.  There's another one the first week of December that I could go too, to, though I probably won't; I need some time to do my own research.  This one gave me an excuse for my first visit to Seoul, though I haven't seen much of the city yet.

The full title of this conference is the KIAS-CFHEP Workshop and the 5th KIAS Workshop on Particle Physics and Cosmology, which is a bit too long for a title of this post.  We start, as is conventional, with experimental talks.

Monday, 2 November 2015

Dark Matter Interactions and Galaxy Structures

Another thing I rather fell behind on with my move to Korea is my academic reading.  So I only recently got around to a short and interesting paper from August on interacting dark matter (DM).1  This is one of those papers that takes a shockingly simple idea, the kind that you look at afterwards and wonder why you didn't think about it.  But it should make it easier to address a long-standing and fairly perplexing puzzle in dark matter physics.