Physics

In the 'sometimes what you don't find can be important too' department, a new high-accuracy calibration of the LUX (Large Underground Xenon) dark matter detector's sensitivity to ultra-low energy events strongly confirms the result that it did not find low-mass dark matter particles last summer during its initial run.


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.
Yesterday I visited a high school in Treviso, a small centre in north-west Italy. The students of the last two years participate in a program called "masterclasses" which includes lessons on particle physics and astrophysics and a visit to the department of Physics in Padova, where they will be taught how to distinguish particle decays using real LHC data.

First principles are calculations that rely on established mathematical laws of nature without additional assumptions or special models.

But when it comes to the early universe, what are those first principles? We're talking really ab initio - "from the beginning" - as in from the beginning of time onward.  

In the beginning, the cosmos experienced rapid inflation, electrons and protons floated free from each other, the universe transitioned from complete darkness to light, and enormous stars formed and exploded to start a cascade of events leading to our present-day universe.


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.