Large Hadron Collider back in Action!

Tuesday 24 November 2009 – Physicists at RHUL are excited about the restart of the operation of the largest scientific experiment in the world. After one year of intensive repairs, tests and improvements, following a serious electrical problem one year ago the Large Hadron Collider (the huge particle smasher in CERN - the European Laboratory for Particle Physics - Geneva) is back in action. Last Friday night saw the injection of the first proton beams into the 27-km long underground ring in 2009. The engineers running the accelerator worked tirelessly through the weekend and on Monday afternoon were able to circulate two counter-rotating proton beams and make them collide. The first proton-proton collisions in the LHC were recorded by the massive ATLAS particle detector in the early afternoon.

Computer display of the result of one of the first proton-proton collisions recorded at the LHC, by the ATLAS experiment. A cut-away sideways view of the cylindrical detector (46m length, 25m diameter) is shown on the left, with the protons entering the detector horizontally from the left and from the right and colliding at the centre. Several particles produced in the collision can be seen flying outwards from the central collision point. An end-on view of the central part of the ATLAS detector is displayed on the top right. (Image available directly from ATLAS website.)

The CMS experiment, the other large particle detector installed in the LHC ring, also recorded proton-proton collisions later on the same day.

The initial collisions were produced at a comparatively low energy (about half of the energy of the record-holding proton-antiproton collisions at the “TeVatron” collider in Chicago, US). In the next few weeks it is expected that the LHC operators will be increasing the collision energy to a value in excess of the competing US collider. Over the next two years it is planned that the energy of the collisions at the LHC will be increased further, in a few steps, to reach the ultimate goal of collisions at the design energy of 14 million million electron-Volts (about 15 times higher energy than the initial collisions produced this week at the LHC).

This week's initial collisions at the LHC mark the start of the data-taking era of the ATLAS and CMS experiments. After more than a decade of laborious construction of the experimental apparatus, the particle detectors will be starting on a long journey of exploration – recording billions of collisions every year – to unveil some of the remaining mysteries in Particle Physics. Physicists will be sifting through the LHC data to search for evidence of rare processes, such as collisions containing the much-sought Higgs particle (which is believed to explain the origin of mass of all fundamental particles) or other more exotic theoretically-predicted particles, still to be observed experimentally.

Dr Pedro Teixeira-Dias, leader of the ATLAS group at RHUL said “This is all very exciting. This week's successes at the LHC mark the start of a journey into new physics territory and is expected to lead to some major new scientific discoveries.”

ATLAS is an international collaboration of approximately 170 groups from Universities and research laboratories from all over the world. The RHUL Centre for Particle Physics is one of the founding groups of the ATLAS experiment, and currently has a group of about 20 physicists (Trash.PhD students, Postdocs, Academic staff) and one Electronics Engineer participating in the experiment.

Physicists in the RHUL ATLAS group will be analysing the collisions collected by ATLAS with a view to search for the existence of the Higgs particle and the Graviton (the quantum of the gravitational force) and study in detail the properties of the top-quark (the heaviest fundamental particle known to date, which will be copiously produced in LHC collisions).

“This is great for the whole particle physics group. Our experimentalists, theorists, and accelerator scientists are all working hard at the LHC frontier; this is the first step of a very exciting journey” said Prof. Grahame Blair, leader of the Centre for Particle Physics at RHUL.

The RHUL Centre for Particle Physics is a group of about 40 physicists carrying out a research programme in the related areas of collider physics, accelerator science (as part of the RHUL-Oxford John Adams Institute) and theoretical particle physics.

-- PedroTeixeiraDias - 25 Nov 2009