A Quantum Diaries Survivor

Readers familiar with this blog know that I am a die-hard skeptic on the issue of physics beyond the Standard Model. However, today I am wearing my fluctuation-enthusiast hat, and I will be trying to argue in favor of the possible signal of new physics that is coming out of the Tevatron data. Please do not get confused: everything is still in order. Maybe.

Detailed balance is a simple and powerful rule to describe the dynamics of two-state systems.If you know the probability of a transition from a state A to the other state B of a physical system (in some appropriate time unit), and you also know the probability of the reverse reaction , then you automatically know what is equilibrium condition for N bodies distributed in the two states: .

Besides the usual share of random readers who google something and get directed here by mere chance (to be read: by the sheer amount of valuable information I have posted here), this blog is read by an interesting mix of particle physicists, students, experts in other fields of Physics, and Science amateurs -plus a small number of science reporters looking for news.Of course I love each and every one of my faithful readers like good teachers love their pupils, but among the varied crowd, the readers which I am most happy to host here are students and amateurs, because they provide me with true motivation for spending my time writing popularization articles. Without them, many of my posts would lose their meaning.

One year ago, a paper by a distinguished group of theorists announced first evidence of new physics from measurements of the properties of B_s mesons performed at the Tevatron by the CDF and DZERO experiments. They had combined all the available information, obtaining a result which disagreed with the Standard Model (SM) prediction by more than three standard deviations.

A new paper on the ArXiV caught my attention this evening for several reasons. First of all, because two of its five authors (J.Ellis, J.R.Espinosa, G.F.Giudice, A.Hoecker, and A.Riotto) are (or have been) my colleagues in Padova University; second, because the title is quite catchy; third, because indeed the results it presents are valuable food for thought.

In this two-parts article I wish to describe in some detail, but still at an elementary level, the characteristics of one of the most important probes of the physics of subnuclear collisions at today's particle physics experiments: jets of hadrons originated from energetic bottom quarks, or more familiarly, b-jets. By posting a dedicated article on b-jets, I hope I will be able to describe in more detail elsewhere other physics topics, such as Higgs boson decays or top quark signatures, without being hampered by having to introduce the phenomenology and detection of b-jets from scratch every time.

As silly as it may look, I am going to start this post by publishing for the third time in a row the same figure. That is because I want to keep the promise I made earlier that I would explain in terms as simple as possible (although not simpler) the details hidden behind the coloured curves and functions pictured there. I will also take this chance to come down a little from the level of technicality of the recent posts: after all, this blog is supposedly for everybody, and not just for Ph.D. students and recipients.

Yesterday I posted a short article whose main purpose was to show a figure I had received from Sven Heinemeyer, a phenomenologist who specializes in the study of Minimal Supersymmetric extensions of the Standard Model (MSSM).Besides predicting a mirror copy of Standard Model (SM) particles, MSSM models are characterized by containing not just one, but five distinct Higgs bosons; over much of the space of possible parameters of these theories, one of the five Higgs bosons is quite similar to the one and only SM Higgs, so that one can discuss the SM Higgs and the lightest neutral scalar of the MSSM together without generating confusion.

...waiting for a piece I will post tomorrow, to stimulate your curiosity -and allow me to travel from Venice to Patras by ship, with no internet connection.The subject is not only the Higgs mass, but the top quark mass. Which top mass ? The "pole" mass -the real part of the pole in the perturbative top-quark propagator. Have I lost you ? Ok, do not worry -definitions are for theorists. Let us just say that the top quark, being a complicated coloured object which thus cannot live free of the influence of strong interactions,is measurable at a hadron collider like the Tevatron only within uncertainties of the order of a constant called "Lambda QCD", which is of the order of 200 MeV.

A new public document has been made available on the CMS public web page yesterday morning. It reports on a study of the reach of the CMS detector, with data collectable in 2010, for a signal of large extra dimensions, using the very distinctive signature of a high-energy jet recoiling against -well, recoiling against nothing; or better, something which left our world and entered into another dimension of space.

The Arxiv is an online repository of scientific papers in physics, astronomy, maths, cosmology, computer science, and a few other topics, where papers due to be published on scientific journals are submitted by the authors, and become quickly accessible for free to anybody before the peer-review process ran by the journals is over and they get printed there.

Patrick Draper is a graduate student in physics at the University of Chicago and Argonne National Lab. He is a native of Illinois and lives in Hyde Park, Chicago with his wife Karen and parrot Felix, to whom he is grateful for their love, patience, and correcting his sign errors. He is a supporter of the international effort to put a muon collider on Mars, and is waiting for NASA to return his phone calls.I asked Patrick to write here about his studies on the discovery reach for a MSSM Higgs boson after I saw his paper on the arxiv a month ago, and am now glad I did. Enjoy!