October 29, 2008 8:33 WSPC/139-IJMPA 04234
International Journal of Modern Physics A Vol. 23, No. 25 (2008) 4081–4105 c World Scientific Publishing Company !
LHC’s ATLAS AND CMS DETECTORS∗
, , , MARIA SPIROPULU∗ ‡ and STEINAR STAPNES∗ † §
∗Physics Department, CERN, CH-1211 Geneva, Switzerland and
†Department of Physics, University of Oslo, 0316 Blindern, Oslo, Norway ‡smaria@cern.ch §[email protected]
We describe the design of the ATLAS and CMS detectors as they are being prepared to commence data-taking at CERN’s Large Hadron Collider (LHC). The very high energy proton–proton collisions are meant to dissect matter and space–time itself into its primary elements and generators. The detectors by synthesizing the information from the debris of the collisions are reconstituting the interactions that took place. LHC’s ATLAS and CMS experiments (and not only these) are at the closest point of answering in the lab some of the most puzzling fundamental observations in nature today.
Keywords: LHC; ATLAS and CMS detectors.
1. Introduction The Large Hadron Collider (LHC)1 is the largest and most complex scientific under- taking ever attempted. Its results will determine the future of the full discipline of high energy physics. The LHC will produce 14 TeV proton–proton collisions in the next year and we expect it will discover a new sector of particles/fields associated with electroweak symmetry breaking and dark matter. The two major experimental observations behind this expectation are:
(1) the masses of the W and Z vector bosons; (2) the dark matter in the universe.
These, in concert with the theoretical considerations are corroborative evidence for physics mechanisms that broaden the Standard Model (SM). Both the ATLAS (A large ToroidaL ApparatuS)2,3 and the CMS (Compact Muon Solenoid4–6) experiments are in the stage of commissioning and integration.
∗This paper is also published in Perspectives on LHC Physics, edited by G. Kane and A. Pierce (World Scientific, 2008).
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Fig. 1. This “gold plated” event going through all central detectors — the tracker, the hadronic calorimeter, HCAL (top and bottom), the electromagnetic calorimeter ECAL and the muon Drift Tubes — it was recorded in August 2006 in the CMS assembly hall at Point 5; Run No. 2378, event 123 at a magnetic field of 3.8 T.
Fig. 2. This cosmic muon event recorded with ATLAS is going through all barrel detectors. The tracker (silicon strip and straw tracker), hadronic calorimeter and muon detectors were read out, while the barrel liquid argon calorimeter (been operated in several periods earlier) and pixel system (being cabled) were not read out. The event was recorded in March 2008 at Point 1. October 29, 2008 8:33 WSPC/139-IJMPA 04234
LHC’s ATLAS and CMS Detectors 4083
The experiments have been collecting cosmic data with the major detectors in place already since 2006 (see for example an event display of a cosmic muon observed at the CMS Magnet and Cosmic Test runs in Fig. 1 and a recent one at ATLAS in Fig. 2) and finalizing the analysis of beam tests of most-all detector elements. The experiments are also preparing the strategies for the careful understanding and use of the SM data at 14 TeV.
1.1. LHC : The machine The LHC is built in a circular tunnel 27 km in circumference. The tunnel is buried around 50 to 175 m underground and straddles the Swiss and French borders on the outskirts of Geneva as shown in Fig. 4. It will circulate the first beams in the summer of 2008 and provide first collisions at high energy soon after. The LHC is at the edge of the accelerator based energy frontier as illustrated in the “Livingston plot” shown in Fig. 3. Note that since the 30’s (with the 600 MeV Cockcroft-Walton — not shown here) the effective energy increase is more than 11 orders of magnitude while the effective cost per GeV of a typical accelerator is drastically reduced (see also Ref. 7). In accelerator based high energy physics experiments, the type and number of particles brought into collision and their center-of-mass energy characterize an interaction.
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