Thank You Guido

It is with great sadness that I heard (reading it here first) about the passing away of Guido Altarelli...

Researchers' Night 2015

Last Friday I was invited by the University of Padova to talk about particle physics to the general...

One Dollar On 5.3 TeV

This is just a short post to mention one thing I recently learned from a colleague - the ATLAS...

Statistics Lectures For Physicists In Traunkirchen

The challenge of providing Ph.D. students in Physics with an overview of statistical methods and...

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Tommaso DorigoRSS Feed of this column.

I am an experimental particle physicist working with the CMS experiment at CERN. In my spare time I play chess, abuse the piano, and aim my dobson telescope at faint galaxies.... Read More »

I will be attending next week to a conference in Split (Croatia). The conference is titled "LHC Days", and has the purpose of bringing together experimental physicists working at the main CERN experiments with theorists and experimentalists from all over the world, to discuss the current status and the future perspectives of research in particle physics, focusing of course on the Large Hadron Collider at CERN.
Georges Charpak, a French physicist and 1992 Nobel Prize winner, died yesterday.

Of Polish origin, Charpak gave crucial contributions to experimental physics, in particular for his invention of the multiwire proportional chamber in 1968.

Back then, the signal of passage of charged particles was recorded by bubble chamber images and images triggered by spark chambers - where the charge deposition would create a discharge in a very high electric field.
With the fresh news of the election of Pierluigi Campana as spokesperson of the LHCb experiment, the Italian participation to the LHC experiments at the CERN laboratories is close to a grand slam: three of the four experiments along the ring are led by Italian physicists. Campana joins Guido Tonelli (CMS), Fabiola Gianotti (ATLAS), and Jurgen Schukraft (ALICE).

Italians have consistently led CERN experiments, so the election of Campana is no surprise to most of us: still, it speaks volumes about the professionality of Italians in high-energy physics and the recognition that they are given by their colleagues abroad.
The Large Hadron Collider is increasing gradually the number of proton bunches that circulate in the machine. Yesterday's fill saw 104 colliding proton bunches,  producing the record instantaneous luminosity of 3.5 x 10^31 collisions per square centimeter per second. This is no surprise, of course: luminosity is essentially the product of the number of particles crossing each other per second divided by the cross section of the beams, so if you increase the particles and manage to keep the beam transverse size constant, luminosity must go up.
"At that time, although recognized for the very high quality and reliability of its accelerator engineering, CERN unfortunately did not have a similar reputation in its physics, and it was still recovering from disasters such as the "split A2" affair. CERN always seemed to be second best behind the leading U.S. laboratories, with their vastly more experienced physicists. And during the 1960s it had been repeatedly beaten into the ground, for example, over the discoveries of the Omega- hypheron, the two types of neutrinos, and CP violation in K0 decay. All these things could and should have been found first at CERN, with its far greater technical resources, but the Americans had vastly more experience and know-how."

Donald Perkins
Despite time is a scarce resource for me these days, and my "working time balance" shows deep red, I am presently spending some of it to investigate a very interesting statistical effect of general nature, although specially connected to the issue of discovery thresholds in particle physics.

I am triggered by the recent eported observation of a new particle, which has been claimed at a significance corresponding to the coveted 5 standard deviations after a previous evidence had been extracted from 40% less data at 3.8 standard deviations. The matter has left me slightly dubious about the precision of the latter claim.

Now, before I state the problem, let me explain in short how significance is calculated in these kinds of new particle searches.