Higgs ... Numerology?

The Christmas season is generally a quiet time in terms of new research papers.  The reason's pretty obvious; with so many people taking time off, anything you put out won't be read as much.  And that's assuming you haven't dashed off somewhere yourself.  Still, things don't drop to a complete halt, and you get odd little papers like this one on the Higgs decay.

New LEP Paper

Twelve years ago, LEP -- the Large Electron-Positron collider -- finished taking data.  That's so long ago I was still an undergraduate, YouTube and Facebook didn't exist and even Google was relatively unknown.  So I was quite surprised to see a new paper on the arXiv from the LEP collaborations.

Some thoughts on the Nobel Prize

One of the dangers of working in a scientific field is becoming short-sighted, and thinking that it is automatically the most important area of research.  That is something I think many of us in the particle physics community have been guilty of with regards to the Nobel Prize in Physics this year.  The discovery of a Higgs-like particle at the LHC has been of great significance to us.  It justifies the construction of the LHC, meets the predictions of almost fifty years and opens new doorways to future physics.  For most of us, the only question was how the Nobel committee would resolve the problem of too many candidates; do you award it to the experimental collaborations?  Who among them?  What about the theorists; it's now properly recognised that in addition to Peter Higgs, several other people offered essential insights to the theoretical framework of the "Higgs mechanism".

Of course, the committee resolved this issue by giving the prize to a different field of physics, quantum optics.

Fingerprinting the Higgs

This blog post title stolen from Christophe Grojean and his collaborators.

With Thursday's mammoth Angband post finally finished, I figure it might be a good time to talk about physics instead.  And what better thing to talk about than what the theory community has been up to in the last three and a half weeks?  Yes, as expected there have been an abundance of Higgs-related papers of varying quality since the discovery announcement back on the 4th.  Thankfully, since many of them tread over similar ground I can cover multiple papers at once!

A Few More Thoughts on the Higgs

It's been almost a week since ATLAS and CMS announced their discoveries.  Even within the field, not much has changed.  What has is mostly a perspective; we have a Higgs, probably, so it becomes an input to our models instead of an output.  There have been a lot of new papers on the arXiv, especially this week, but the biggest splurge came with the hints last December.  So far I haven't seen anything really notable, though I'll admit I'm a bit behind on my reading.

What do we know about the discovery?  It looks very much like a we would expect.  The nice thing about the Standard Model is that when it comes to the Higgs, it is highly predictive.  All the relevant couplings relevant were known long ago; only the mass and the Higgs self-coupling were not predicted.  Now that we know the mass, we also know the latter value too, but this cannot be measured at the LHC.  When we compare those predictions to the data, everything more or less agrees.  Only the Higgs decay to two photons is not within the error bars, but the difference is still small.  The most interesting hint is that the decay to W bosons is small, but the Higgs-W coupling is also relevant for Higgs production, and the evidence there is consistent.  Of course, the fact that the differences are small won't and hasn't stopped people writing papers!

Discovery

So.  The LHC has found something.

Watching the webcast now, CMS claims 5 sigma combining the diphoton and ZZ channels.  It looks very compelling.

Of course, there's some way to go to confirm that what's seen is actually the Higgs.  But all the different decay channels seem to match up as expected, within the errors.  It looks very Standard Model like.

Update: Nothing in ditau.  That might be interesting.

Update 2:  ATLAS comes in with 5 sigma excesses in the same channels, at the same points.  That's pretty much unequivocal.

The biggest thing missing is Higgs to WW.  Neither experiment saw much of an excess there, and that's the key to proving the new state is the Higgs, in that it is responsible for giving mass to the W and Z bosons.  Then, a longer period of measuring the fermionic branching ratios, and maybe the total width in the diphoton and ZZ channels.

Still, I think we can safely predict Nobels for the collaborations and/or Peter Higgs this year.

The Tevatron Higgs Announcement

The Tevatron today announced stronger evidence for the Higgs from its own searches.  There had been rumours that such an announcement would be made before the LHC likely claims discovery on Wednesday.

The Tevatron results are not enough, by the standards of the particle physics community, to claim discovery.  They are not even enough to claim "evidence", a lower standard where people tend to start getting excited.  But the results are very interesting and useful, even so.  A big part of this is because the Tevatron search channels are different to the ones currently used by the LHC.

The Good and Bad Side of Finding the Higgs

In a previous post, I commented

Of course, in some respects it would be more interesting if those hints are wrong and there is no Standard Model Higgs ...

I thought I'd expand on this a bit.  You see, the LHC is a multi-billion dollar, multi-national enterprise.  Finding the Higgs would justify the whole endeavour, and should ensure funding for the next round of experiments, be it a linear collider, muon accelerator or whatever.  So why would I want there to be no Higgs?

Higgs Discovery on the Horizon?

A CERN press release confirms what I think most people in the field expected:

CERN will hold a scientific seminar at 9:00CEST on 4 July to deliver the latest update in the search for the Higgs boson. At this seminar, coming on the eve of this year’s major particle physics conference, ICHEP, in Melbourne, the ATLAS and CMS experiments will deliver the preliminary results of their 2012 data analysis.

 If the hints of a Higgs that were seen in last year's data are true, it is likely that this seminar will serve to announce that fact.  This would be the first discovery of a new fundamental particle since the top quark in 1995, and would essentially justify the LHC.  Exciting times!  Of course, in some respects it would be more interesting if those hints are wrong and there is no Standard Model Higgs ...

Brought to You by the Letter S

Ah, Supersymmetry.  I've been meaning to talk about Supersymmetry, or SUSY for short, for some time.  I was obviously setting things up in this post from almost a month ago, back when I was in England, but I've been planning this post for longer than that.  SUSY is the most popular theoretical framework for new particle physics, and as much as I'd like it not to be true, I need to worry about it all the same.¹

The Hierarchy Problem

I've got several drafts in progress, but none of them look like getting finished soon and I wanted to get something substantial out today.  So I thought I'd talk briefly about an important concept in theoretical particle physics, the hierarchy problem.

In Which I Ramble About The Higgs

It's an exciting time to be a particle physicist.

One of the main reasons, and the focus of this post, is related to the one remaining undiscovered particle of the Standard Model---the Higgs.  The Standard Model of particle physics essentially came together during the seventies, making it older than me, and it has passed almost all experimental tests since then.[1]  In particular, it predicted the existence of several particles that have since been discovered, including the W and Z bosons and the top quark.  But the key to the model, what in many ways defines it, is the Higgs; and this particle will either be found or ruled out by the end of the year.  Indeed, the ATLAS and CMS experiments at the Large Hadron Collider both reported possible hints of the Higgs last December.