A Quantum Diaries Survivor

After four months of frenzy by over 1500 teams, the very successful Higgs Challenge launched by the ATLAS collaboration ended yesterday, and the "private leaderboard" with the final standings has been revealed. You can see the top 20 scorers below.

I just read with interest the new paper on the arxiv by my INFN-Padova colleague Massimo Passera and collaborators, titled "Limiting Two-Higgs Doublet Models", and I thought I would explain to you here why I consider it very interesting and what are its conclusions.

One year ago I had the pleasure to spend some time with George Zweig during a conference in Crete (ICNFP 2013). He is a wonderful storyteller and a great chap to hung around with, and I had great fun in the after-dinners on the terrace of the Orthodox Academy of Crete overlooking the Aegean sea, drinking raki and chatting about physics and other subjects.

Among the viable extensions of the standard model, an intriguing class of models involve the concept of a "hidden sector" of new particles only weakly coupled to the standard model one. These particles could be produced in the decay of heavy standard model particles, be invisible, but unstable, and thus soon decay back into standard model bodies, giving funny experimental signatures that our detectors could spot -if we looked for them carefully enough.

Until the second half of the nineties, when the LEP collider started to be upgraded to investigate higher centre-of-mass energies of electron-positron collisions than those until then produced at the Z mass, the Higgs boson was not the main focus of experiments exploring the high-energy frontier. The reason is that the expected cross section of that particle was prohibitively small for the comparatively low luminosities provided by the facilities available at the time. Of course, one could still look for anomalously high-rate production of final states possessing the characteristics of a Higgs boson decay; but those searches had a limited appeal.

Preparing the documents needed for an exam for a career advancement, to a scientist like me, is something like putting order in a messy garage. Leave alone my desk, which is indeed in a horrific messy state - papers stratified and thrown around with absolutely no ordering criterion, mixed with books I forgot I own and important documents I'd rather have reissued rather than searching for them myself. No, I am rather talking about my own scientific production - pubished articles that need to be put in ordered lists, conference talks that I forgot I have given and need to be cited in the curriculum vitae, refereeing work I also long forgot I'd done, internal documents of the collaborations I worked in, students I tutored, courses I gave.

Although now widely accepted as the most natural explanation of the observed features of the universe around us, dark matter remains a highly mysterious entity to this day. There are literally dozens of possible candidates to explain its nature, wide-ranging in size from subnuclear particles all the way to primordial black holes and beyond. To particle physicists, it is of course natural to assume that dark matter IS a particle, which we have not detected yet. We have a hammer, and that looks like a nail.

It is a well-known fact that given the availability of food, we eat far more than what would be healthy for our body. Obesity has become a plague in many countries, and the fact that it correlates very tightly with a decreased life expectancy is not a random chance but the demonstrated result of increased risk of life-threatening conditions connected with excess body fat.Yet we eat, and drink, and eat. We look like self-pleasing monkeys trained to press a button to self-administer a drug. To make matters worse, many of the foods and drinks we consume contain substances purposely added to increase our addiction. So it takes a strong will to control our body weight.

Today the Cornell arxiv features a paper by J. Aguilar Saavedra and F. Jouaquim, titled "A closer look at the possible CMS signal of a new gauge boson". As I read the title I initially felt somewhat lost, as being a CMS member I usually know about the possible new physics signals that my experiment produces, and the fact that we had a possible signal of a new gauge boson had entirely escaped my attention. Hence I downloaded the paper and started reading it, hoping to discover I had discovered something new.

The other day I wrote a post reporting of the lowered expectations of SUSY enthusiasts, who now apparently look forward to seeing 2-sigma effects in the next Run data of the CMS and ATLAS collaborations. That would keep their hope going, apparently.I would have no problem letting them wait for late 2015, when the first inverse femtobarns of 13 TeV collisions will have been given a look at. But another thing happened today which made me change my mind - a colleague noted in the comments thread of that article that the LHC experiments appear to not publish their 2- and 3-sigma excesses when they see them, waiting for more data that "wipes out" the fluctuation. This is a strong (and probably unsupported) claim!

Yesterday I gave a lecture at the 3rd International Conference on New Frontiers in Physics, which is going on in kolympari (Crete). I spoke critically about the five-sigma criterion that is nowadays the accepted standard in particle physics and astrophysics for discovery claims.

My slides, as usual, are quite heavily written, which is a nuisance if you are sitting at the conference trying to follow my speech, but it becomes an asset if you are reading them by yourself post-mortem. You can find them here (pdf) and here (ppt) .

This is just a short update on the saga of the anomalous excess of W-boson-pair production that the ATLAS and CMS collaborations have reported in their 7-TeV and 8-TeV proton-proton collision data. A small bit of information which I was unaware of, and which can be added to the picture.