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On Rating Universities

In a world where we live hostages of advertisement, where our email addresses and phone numbers...

Goodbye Peter Higgs, And Thanks For The Boson

Peter Higgs passed away yesterday, at the age of 94. The scottish physicist, a winner of the 2013...

Significance Of Counting Experiments With Background Uncertainty

In the course of Statistics for Data Analysis I give every spring to PhD students in Physics I...

The Analogy: A Powerful Instrument For Physics Outreach

About a month ago I was contacted by a colleague who invited me to write a piece on the topic of...

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Tommaso DorigoRSS Feed of this column.

Tommaso Dorigo is an experimental particle physicist, who works for the INFN at the University of Padova, and collaborates with the CMS and the SWGO experiments. He is the president of the Read More »

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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.
I devote only a short piece today to the topic of the week -or the month- in particle physics: as many of you already know, yesterday the CMS collaboration has made public the results of their analysis of two-particle correlations, which evidences an effect never seen before in hadronic collisions, and which has been saluted very emphatically by the press around the world.

The Analysis In Ten Lines