# Pictorial guide to CMS

Sources: CMS Outreach,CMS brochure,CMS Posters
We have 4 main subdetectors in CMS:

1. Tracker
2. Electromagnetic Calorimeter(ECAL)
3. Hadron Calorimeter(HCAL).Part of HCAL can be considered the two forward calorimeters that ensure the covering of the full solid angle.
4. Muon detector

ECAL is known also as Crystal Calorimeter. Also we refer to the Muon detector as Muon chambers because of the way it is built.

In the transverse view we see starting from the center Tracker,Ecal, Hcal, the superconducting coil of the magnet (in black) , Muon. Note the effect of the magnetic field generated from the coil on the muon track.
In this view can be clearly seen how Hcal(the blue detector) has a layer outside the coil:the tailcatcher since it will catch the tail of hadron showers. The outer part has a complex structure:in yellow is the iron slabs in the return yoke, in red the muon chambers distributed in four layers. In grey,just beneath the muon chambers and barely visible, are the RPC chambers.In fact the big Muon chambers are used to measure the exact position of the muon track, the small chambers measure instead the exact time of crossing. This information is used in the trigger.

A first event: note the hits generated in the tracker and in the calorimeters.This event isn't very realistic, since in the reality there will be a huge background present from collisions in the same and in the near bunch crossings. Of course these are simulated Higgs events. These are instead probably true events as seen by Aleph.

Another events. Note the background from minimum bias events in the same bunch crossing. This background is simulated by overlaying many events on the signal event(Pileup) and is different for the different subdetectors.At the luminosity of 1034 there are 17 Pileup events per crossing and crossings from -5 to +3 are to be overlayed for the calorimeter and from -10 to +10 for DT muons!

The LHC accellerator has two bunches of particles crossing each other inside the CMS detector 40,000,000 times each second. Every bunch contains around 1011 protons. In every bunch crossing in the detector, on average 20 collisions occur between two protons from opposite bunches.Because the detector isn't fast enough to "photograph" the single collision, each "event" will contain the superposition of the events from the same bunch crossing plus 9 other nearby bunch crossing for a total of 200 collisions per event in average. This is the pileup.

A huge collaboration!

The main features of CMS detectors are a partition in five wheels of the barrel. Each wheel has 12 wedges in the muon detector. In addition we have two endcaps.The iron yoke is integral part of the Muon detector. CMS has a total of 15 million individual detector channels.Each subdetector uses different detecting techniques.The Tracker has Silicon Microstrips and Pixels, Ecal has Crystals, Hcal has a sandwich of Plastic scintillator and copper, Muon has Drift Tubes in the barrel, Chatode Strips in endcap and Resistive Plate Chambers in both barrel and endcaps.

Since CMS will register only 100 events of the 40,000,000 that we have every second. This reduction is done by the trigger system.

Another event as seen by the tracker. Note the complexity of the tracker layout.

The Tracker is made by three cylinders one inside the other. Note that now the bigger cylinder is built using the same detectors used by the Silicon detector:so the names have changed in Outer and Inner Silicon Detector. Each cylinder has a barrel with a certain number of layers that form the "wall" of the cylinder. The two endcaps are instead composed by many discs .

The Endcap of ECAL:this will include,in addition to crystals also a preshower detector with microstrips.

The Barrel part of ECAL:note the assembly of crystals in "towers" that point to the center of CMS.

This 3D view shows the outer parts of HCAL:these are outside the magnet and are: the "Tailcatcher" in barrel to add enough material to stop all hadrons(inside the coil there is not enough space) and the forward detector(VCAL-Very forward CALorimeter) to completely enclose the space of the collision.

Analysis of Montecarlo event

Objectivity database

How to add your private objects with a private federation

A colorful mess of software packages.Of course for the end user everything will be as easy as using Paw.

Page author Giuseppe Zito: zito@ba.infn.it
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