A Quantum Diaries Survivor

I have written enough today about the topic of Higgs boson searches at the LHC by discussing the new ATLAS limits (see previous post), but I feel that, before going to bed, I need to point out the new results on the same topic by CMS, the competitor experiment. As you know, I work in CMS and I have to be twice as cautious when I write about the results of my own experiment, because some of my colleagues have uncovered nerves when it comes to blogs. However, the little I'll say here tonight should cause no discomfort to anybody.

Much awaited, the results of searches for the Higgs boson at the Large Hadron Collider have been released by the ATLAS collaboration, and are being shown at the Lepton-Photon conference in Mumbay, India. I will provide here just the main results, with little commentary - I wish to let the cake cool down a bit before discussing the subject in detail, examining the various inputs.

In my latest instantiation of the "Guess the plot" series I offered a clipped part of a graph showing branching fractions of the Higgs boson. One of the readers made a comment which I was proud to read, since it showed that interested readers of this blog with no specialized education in particle physics can get to know quite a lot about the matter. I answered there more extensively than I do on average, and then I thought that the answer could be of some use to others to whom the thread had fallen out of the horizon. So I am recycling it here.

Like it or not, the Tevatron is going to shut down for good next month. This machine has provided us with tremendous new investigation power in the high-energy frontier of particle physics, and has led the research of hadronic collisions for over two decades. But all good things come to an end.

For this instance of my "Guess the plot" series I wish to go back to the basics. So I picked a graph which allows me to illustrate a general concept, something about particle physics (but we could say physics in general, and actually extending to other exact sciences) which is a source of endless awe for me: the fact that some functions exist, in the infinite-dimensional space of all real functions of a real variable, which describe some specific feature of our world.

Apologizing with those of you who feel they have had too little particle physics this week, I am reporting today after a longish pause on a new search performed by the CMS experiment, one which has some interesting features, at least to me.

Do you remember the dijet mass bump found by CDF in W plus jets events ? That signal, whose significance exceeded four standard deviations, had everybody around go crazy for a while.

As a 20-year-long (ok well, 19) member of the CDF collaboration, I am very proud of this wonderful experiments' accomplishments in all areas of high-energy physics, from exotic searches to Higgs searches, from top quark measurements to b-physics measurements, and what not. CDF is a landmark in experimental physics, and the longest-lasting physics experiment ever. But it is not foulproof - nobody is in this wild world of statistical flukes and impossible-to-unearth systematic effects.

While experimentalists gathered in Grenoble present the latest results on High-Energy Physics searches and measurements, phenomenologists like Sven Heinemeyer are working 24/7 to update the picture of the breathing space left for Supersymmetry, in the light of the most recent searches.You of course do not need to be reminded that Supersymmetry is not a theory but a framework, within which a host of possible manifestations of subnuclear physics are configurable based on the value of 120-or-so free parameters. Because of that, if one wants to discuss in detail what are the most likely versions of SUSY left on the table, and what is the value of the most representative and critical theory parameters, one needs more than paper and pencil.

In the last few days I described in some detail (here and here) the six searches for the Standard Model Higgs boson just produced by CMS, the experiment at the CERN Large Hadron Collider to which I proudly belong.

In my short summary of analyses recently published by CMS, yesterday I left out one which had not yet been released. It is the search for the "golden channel" of Higgs decay, the one which motivated the construction of detectors with large acceptance to energetic leptons: the decay to two Z bosons, with a subsequent decay of the Z's to two charged leptons each.

An orgy of new results has started. Let me just show a few of them concerning Higgs searches in CMS - I am on vacation after all, and I have little time left to comment these interesting new papers and plots after all the sunbathing and restaurants.Let us start with the Higgs search in the diphoton decay mode by CMS (paper here). With 1.09 inverse femtobarns of data, CMS has a pretty good reach even to this very rare decay mode of the Higgs boson. Let me remind you that only a handful every thousand Higgs particles decay into two photons, in the most favourable circumstances.