TOTEM moving physics ‘forward’ at the LHC When protons meet head on at the LHC, the collisions provide a micro-laboratory to investigate many phenomena, including the protons themselves. This is the physics that the TOTEM (TOTal cross section, Elastic scattering and di!raction dissocia- tion Measurement at the LHC) experiment is especially designed to explore. By making precise measurements on particles that emerge from collisions very close to the direction of the LHC beams — the ‘forward’ direction — TOTEM probes physics that is not easily accessible by other LHC experiments. The initial protons can simply change direction without losing energy, in ‘elastic’ collisions, or they can generate new particles, in ‘inelastic’ collisions. Among a range of studies, TOTEM is mea- suring the total probability, or ‘cross-section’, for proton–proton interactions — in a sense, the overall size that a proton presents as a ‘target’. The experiment is also investigating scattering phenomena analogous to the di!raction of light. TOTEM has detectors on both sides of the interaction region at Point 5, where the CMS experiment is located. In each direction, there are two ‘telescopes’ to track charged particles and two sets of ‘Roman pots’ — movable devices that come particularly close to the beam — containing detectors to track elastically- scattered protons. www.cern.ch Approval as 5thPrototype LHC experiment RomanGEM potchambers testsRoman assembled pots installed forRoman 1st time inpots LHC equipped tunnel at with 220 siliconm detectorsFirst collisionsFirst detected results published on total Installation andInstallation commissioning of silicon of detectors T2 at 220 m Track multiplicities elastic cross-section published 2004 2005 2006 2007 2008 2009 2009 2010 2011 2012 Roman pots Particle telescopes Roman pots are devices named after their shape Two T1 telescopes are located starting from and their original use by physicists from Rome in Edgeless silicon 10.5 m from the interaction point inside the the 1970s at CERN’s "rst proton–proton collider, TOTEM’s silicon detectors are ‘edgeless’ in that endcaps of the CMS magnet. Each is made up the Intersecting Storage Rings. TOTEM has they have an insensitive region close to the of "ve detection planes, based on gas-"lled Roman pot stations at distances of 147-149 m beam of only a few hundredths of a millimetre. cathode-strip chambers. and 215-220 m on either side of the interaction Every detector is divided into 512 strips to Two T2 telescopes are installed external to CMS point. All of the stations have two units, each determine the location of scattered particles at a distance starting from 13.4 m. Each has a consisting of two pots that move vertically and with high precision. cylindrical structure, divided into 10 detection one that moves horizontally. Each pot contains planes that consist of pairs of semi-circular GEM 10 silicon detectors. chambers arranged back-to-back. TOTEM in numbers Little gems Some 100 people from 15 institutes in 7 countries The GEM (gas electron multiplier) chambers use work on the TOTEM experiment. technology invented at CERN, which combines excellent spatial resolution with a high rate- capability and good radiation resistance. CERN CH-1211 Geneva 23 Communication Group, September 2012 CERN-Brochure-2012-004-Eng Photos: CERN Photo Service totem-experiment.web.cern.ch.