Physics

The job of experimental particle physicist is strongly correlated with worldwide travel. Paid for and self-inflicted, sure. But not exactly always pleasant, nor to exotic destinations. In fact, experimental facilities are usually located in notably un-fancy places. The Chicago suburbs, country at the border of Switzerland and France, a mine underground in a God-forgotten place, not to mention the South Pole. One learns to take it as part of the package. Sure, conferences are sometimes located in more interesting places, but this is a rather rare occurrence. I attend a conference a year,…

NASA's Fermi Gamma-ray Space Telescope, launched June 2008, has certainly started its career with a (big) bang, discovering a new class of pulsars and watching flaring jets in galaxies billions of light-years away. Now it's going after another cosmic mystery; high-energy particles in cosmic rays. Cosmic rays are hyperfast electrons, positrons, and atomic nuclei moving at nearly the speed of light. Astronomers believe that the highest-energy cosmic rays arise from exotic places within our galaxy, such as the wreckage of exploded stars.  Fermi's Large Area Telescope (LAT) is highly…

Triggered by a preprint appeared three days ago on the ArXiV -a fundamental resource for particle physicists willing to stay in touch with the latest developments of the theory and new experimental results-  this morning I was gearing up to write a post with a careful, didactical discussion of why we believe that the subnuclear world includes three generations of quarks and three generations of leptons, what is the evidence for this peculiar fact, and what would a fourth generation of matter imply for e.g. searches of the Higgs boson. Unfortunately, my memory is still good enough to let…

2008 was a horrible year for the Large Hadron Collider. Just nine days after an extremely successful, highly publicized start-up on September 10th, when hundreds of reporters gathered at CERN to follow the protons as they ventured sector by sector to manage a full turn of the 27 km ring, a stupidly crafted electrical connection failed in sector 3-4 of the machine. This brought above criticality a superconducting solenoid, vaporized six tons of liquid helium, and damaged 53 expensive magnets in the sector with a powerful blast. From a public-relation point of view, amassing a huge firing…

These are hard times for evil guys like me, who are always willing to speculate wildly on particle physics results -only to secretly chuckle at the ripples their extrapolations make, knowing for a fact that the Standard Model is as solid as it has ever been. Suggestive new results which offer themselves as the first hint of a breakdown of the Standard Model are indeed quite rare nowadays. In a famous post which originated a $1000 bet (taken up in part by Prof. Gordon Watts and in part by Prof. Jacques Distler), no less than 32 months ago I was writing in my old blog: What do we have to show…

A comment in the thread under my recent post on the greedy bump bias stimulates me to provide here idiot-proof instructions on how to study the effect by yourself, if you wish to spend your time this way. In fact, if I provide you with a simple piece of code plus some fairly immediate instructions on how to set up ROOT in your own PC, I bet you can be up and checking biases in five minutes. Want to try ? Let's see. Go to the ROOT home page. Give a look at the main page, and then go to the section where you can download the recommended version of the program. Scroll down that page until…

The idea that far distant particles can somehow 'talk' to each other led Einstein to call it 'spooky action at a distance'. Having confirmed its existence, scientists today are learning how to use this 'spooky action' as a helpful tool. Now a team of physicists at the University of Bristol and Imperial College London have harnessed this phenomenon to shed light on another unusual and previously difficult aspect of quantum physics - that of distinguishing between two similar quantum devices. In the everyday world any process can be considered as a black box device with an input and an output;…

Here is the concluding part (for the first part see here) of a discussion of a few subtleties involved in the extraction of small new particle signals hiding within large backgrounds. This is a quite common problem arising in data analysis at particle physics experiments, but it is not restricted to that field. Quite on the contrary: narrow Gaussian signals are commonplace in many experimental sciences, and their identification and measurement is thus an issue of common interest. I have to warn you, dear readers: many of you will find the discussion below quite boring. If you have no interest…

I stumbled on this amazing set of videos: physics legend Hans Bethe giving lectures on theoretical physics to his retirement community neighbors. It's not as crazy as it sounds - a running joke around Ithaca (where I grew up and where Bethe's university, Cornell, is located) is that one of the top physics departments in the US is at the Kendal retirement community in Ithaca. In spite of the miserable weather, a large number of Cornell professors choose to retire there. Few people can lecture coherently on quantum theory at age 93 (Bethe's age when he gave these lectures in 1999). Hans Bethe…

If you have recently given a close enough look at the search results that the CDF and DZERO experiments have been producing at a regular pace on the Higgs boson - every six months, that is: for summer and winter conferences - and your exposure to particle physics results is not broad enough, you might have gotten a biased perception of how searches for new particles are performed nowadays. Indeed, all recent Tevatron searches for the Higgs feature a combination of heavy weaponry: quite advanced statistical methods which include multi-variate likelihoods, neural network classifiers, boosted…