Nov 23, 2011
Targeting the proton
It is great that TOTEM is able to see the dip in proton–proton collisions at 7 TeV at the LHC, after it was seen only at the ISR with a maximum energy of 60 GeV, and also to see that the dip moves towards smaller |t| (CERN Courier October 2011 p7). This was indeed what was expected from various models. I find the comments on the failure of the models to reproduce the data a little severe, since Bourrely-Soffer-Wu and Petrov predict the dip at the right place, but are off by less than a factor of 2 from the data.
However the main reason for writing is that I see that only 5 lines of a column are devoted to the results obtained by the pp colliders, at CERN and at Fermilab in a 3-page article. It is true that TOTEM (and soon other experiments) has taken a big step, but we must remember that pp experiments also made a big step at the time, already showing that the proton becomes "larger". They also showed that the proton becomes darker. The UA4/2 experiment, using a measurement of the real part of the scattering amplitude made a fit that favours a log s2 dependence for the high-energy cross-section. They predict at 7 TeV, σtotal = 92+/–3 mb. We shall see soon if this is confirmed by present experiments.
To end I would like to say that we are in an exciting period where, while the Higgs appears and disappears, tremendous progress is made by all groups, TOTEM, CMS, ATLAS, ATLAS-ALFA on elastic and inelastic proton-proton scattering The forthcoming "Blois" meeting in Vietnam, at the end of the year, should be extremely exciting.
André Martin, CERN.