A Quantum Diaries Survivor

The Super-CDMS dark-matter search has released two days ago the results from the analysis of nine months of data taking. The experiment has excellent sensitivity to weak interacting massive particles producing inelastic scattering with the Germanium in the detector.The detector is composed of fifteen cylindrical 0.6 kg crystals stacked in groups of three, equipped with ionization and phonon detectors that are capable of measuring the energy of the signals. From that the recoil energy can be derived, and a rough estimate of WIMP candidates mass. The towers are kept at close to absolute zero temperature in the Soudan mine, where backgrounds from cosmic rays and other sources are very small.

Do you remember the CDF Dijet bump at 145 GeV? In 2010, CDF published a paper that showed how the same data sample of W + jet events where they had previously isolated the "single-lepton" WW+WZ signal also presented an intriguing excess of events in the dijet mass distribution, in a region where the background -dominated by QCD radiation produced in association with a W- fell smoothly. That signal generated some controversy within the collaboration, and a lot of interest outside of it. It could be interpreted as some signal of a new technicolor resonance !

The Y(4140) state, a resonance found in decays of the B meson to J/ψ φ K final states, is the protagonist of a long saga. Originally it was obseved by CDF in 4 inverse femtobarns of Run 2 data by Kai Yi, a very active "bump hunter" in the experiment - and I want to add, a successful one! Kai had to withstand a very long review process within the collaboration before the evidence for the new particle could finally be published; and the addition of more data to the analysis, one year afterwards, left many in CDF with the suspect that the particle was maybe there only in the eye of the beholder: the new data did not seem to show a clear hint of the peak seen in the first part.

I believe I am not alone in being fascinated by the ongoing debates about this or that physics experiment being on the verge of destroying the Earth. Microscopic black holes produced by mistake in particle physics experiments sinking down to the center of the Earth and slowly eating us out, small black holes used as "clean" bombs, antimatter weapons, strange-matter bits gradually engulfing everything around. It is quite entertaining and it would be even good for physics outreach if spun the right way, but unfortunately we should not trust too much the sense of humour of our political leaders.

The ATLAS collaboration at the Large Hadron Collider, CERN's 8-TeV proton-proton collider now being recommissioned to run at the close-to-design energy of 13 TeV in 2015, has published a few days ago on the Cornell ArXiv the result of a search for Higgs bosons decaying to Zγ pairs.

A new paper by Davison Soper and Michael Spannowsky has been sent to the Cornell preprint ArXiv last week. It proposes a new technique to reconstruct the decay of heavy particles within hadronic jets, and shows how this can improve the sensitivity to heavy new particles by studying in particular the case of a heavy Z' boson decaying to boosted top quark pairs. I believe the technique is very interesting and I will try to give a few impressions of it here; before I do, let me introduce the topic for outsiders.

On January 25th 1996 the CDF collaboration submitted for publication to Physical Review Letters  the result of their measurement of the rate of jet production as a function of jet transverse energy, performed on 20 inverse picobarns of data collected by the experiment in the 1992-93 run of the Tevatron collider. That measurement deviated at its high-energy tail from predictions of quantum chromodynamics, suggesting that the underlying model -and most likely, the parton distribution functions (PDF) which describe the probability of finding partons with given fractions of their parent momentum- was at fault.

Black holes are all the rage these days, with theorists arguing about firewalls and Hawking's paper being handled by the press in rather improper ways. Meanwhile at the Large Hadron Collider ATLAS and CMS are furthering their searches for microscopic versions of the same objects, which could exist if the energy scale at which quantum gravity effects make themselves felt is orders of magnitude smaller than the place where they ought to be -i.e., at the Planck energy.

I received yesterday a copy of the brand-new book by Ilya Narsky and Frank Porter, "Statistical Analysis Techniques in Particle Physics" (Wiley-vch 2014), and I would like to offer here my impressions and thoughts on the material.

Chapter 10 of the report on the 2013 community summer study held at Snowmass, titled "Communication, Education, and Outreach" is available since Jan 24th in the Cornell ArXiv. It is a 26-pages document describing the importance of outreach activities to foster the development of particle physics, and offering ideas and strategies to improve the communication between scientists and policy makers. This is none other than the problem I have often referred to as the one of "filling the gap" between science and the general media.

Tetraquarks are hypothetical particles made up by four quarks (two quarks and two antiquarks). Unlike mesons (quark-antiquark pairs) and baryons (three-quark or three-antiquark systems), the quarks in a tetraquark are quite loosely bound within their confinement volume by strong interactions, as can be calculated with the help of quantum chromodynamics. Their tendence to separate into two quark-antiquark systems should yield a very short lifetime, making their observation quite difficult. However, some tentative evidence for their existence exists.

In a guest post written three years ago Giorgio Chiarelli told us the story of how the CDF detector saw its first proton-antiproton collisions, during the night of October 13th 1985. It was a very important moment for the history of the collaboration, the start of a data collection campaign that would last over a quarter of a century. Below I wish to tell you the story of one of the worst radiological incidents in the history of the experiment, which happened a few months after those first collisions were recorded.---