The CMS detector as compared to ATLAS CMS Detector Description –Inner detector and comparison with ATLAS –EM detector and comparison with ATLAS –Calorimetric response and comparison with ATLAS –Muon Spectrometer and comparison with ATLAS –Trigger philosophy of CMS

General view of CMS For an excellent general review, there is a recent publication by D. Froidevaux and P. Sphicas in Annu. Rev. Nucl. Part. Sci

Detail view of the CMS Detector Very nice modularity for installation and MUON access.

First results will come fast Combining the 2 experiments can lead to fast results (2009).

Optimized Tracker Layout double single Central Support Tube removed TOB: Outer Barrel TIB: Inner Barrel TID: Inner Disks TEC: End Caps

ID Status Some Numbers 6,136 Thin wafers 19,632 Thick wafers 6,136 Thin detectors (1 sensor) 9,816 Thick detectors (2 sensors) Thin modules (ss +ds) Thick modules (ss +ds) 10.0 M strips  electronics channels 78,256 APV chips 26 M Bonds 223 m 2 of silicon sensors

Comparing Characteristics(ID) Froidevaux & Sphicas

CMS ECAL

Higgs event into two Photons

Module Assembly Steps 2/3 of the Barrel Modules Have been completed

CMS EM Calorimeter PbWO4 crystals provide an excellent energy resolution. Problem is to keep down constant term and the lack of longitudinal sampling.

CMS Hadron Calorimeter To save critical space in the magnetic volume, all readout fibers are brought to the end-plates

Comparison of Photon Energy Resolution The constant term plays the main role for high energy

Comparison of E(T) resolution CMS can probably benefit from an energy flow algorithm to compensate for the lack of longitudinal sample in the calorimeter as well as the large opening cone of the jets (due to the magnetic field).

CMS MUON Spectrometer Combination of Drift Cells in the barrel with RPC’s Combination of CSC’s with RPC’s in the End- Cap. Two independent triggers up to eta<1.6. Bending power obtained from the solenoid up to eta< <eta<2.4 is mainly dominated by the innermost layers.

CMS MUON System close to completion Both Barrel and End-Cap MUON’s and Hadron calorimeters have been completed in the surface and took cosmic data. First End-Cap sector has been lowered to the IP.

Comparison of the MUON Systems At high rapidity, toroidal field provides better resolution. At low rapidity, high solenoidal field is superior.

Comparison of Trigger Architectures Although the LV-1 trigger is similar for both experiments, the higher level is different, with ATLAS using less BW due to the ROI concept, while CMS using modern network switching technology to perform reduction on full event.

Conclusions Using different and complementary technologies, the two large LHC experiments arrive at similar overall performances. The higher magnetic field has advantages (better P resolution) and disadvantages (lower tracking eff.). The crystal calorimeter has advantages (superior energy resolution) and disadvantages (no longitudinal sampling and hard to keep constant term). The MUON acceptance, although smaller in CMS, benefits from a simpler geometry and uniform magnetic field. At the end, the two experiments will be very competitive and provide good Physics results.