Physics at 13 TeV: TOTEM - a new era of collaboration with CMS

When two protons collide, the simplest thing that can happen is that they emerge with no loss of energy but with a slight change of direction. This is an example of "elastic scattering”. Sometimes they lose some energy instead, a process called central diffraction, one of the diffractive phenomena that the Totem experiment observes in order to study gluon-gluon interactions.


This year, Totem and CMS signed a Memorandum of Understanding for a common upgrade of the forward region (210-220 m from the interaction point) to perform diffractive physics studies on a common ground. “Totem and CMS will coordinate the use of their detectors to measure the total mass created in the collision with unprecedented accuracy,” explains Nicola Turini, Totem Deputy Spokesperson.

In the next run, for the first time, data analysis will be performed in collaboration with CMS and using some common tools. Totem will, however, run alone for special runs dedicated to the measurement of the proton-proton cross section. The particle pile-up remains a significant issue for the experiment, whose specific setup does not allow scientists to reconstruct the collision vertex by looking only at the track geometry, because of the small angles of the incoming protons. “The main idea is to perform vertex matching by looking at the Time of Flight of the particles,” explains Turini. “We are developing timing detectors to be inserted in the roman pots that will allow a complete reconstruction of the leading protons. In this regard, we foresee two possible scenarios: dedicated runs where the beam collision directions are such that the pile-up can be kept to a minimum; or high-luminosity runs for which some new detectors, which are currently under study, will allow us to perform a very accurate pile-up rejection.”

In order to meet the challenges of the new LHC run, the Totem collaboration is working on the development of new detectors, which will improve the performance of the experiment. “Some of these programmes will be carried out in the framework of a common Totem-CMS upgrade,” says Turini. “The merging of the two experiments’ expertise is growing and we will certainly have a very fruitful collaboration.”

Check out more of our Physics at 13 TeV series in "ALICE - scratching under the surface" and "LHCb - a new data-processing strategy". For a theory perspective on the next run, read "Life is Good at 13 TeV".

by Antonella Del Rosso