CMS experiment at LHC
description
Transcript of CMS experiment at LHC
July 2009 1
CMS experiment at LHC
Geoff Hall
Imperial College London
Geoff Hall
July 2009 Geoff Hall2
Large Hadron Collider
Latest CERN accelerator started 2008 26km circumference ring
~100m underground Beams
7 TeV protons or ions, eg Pb
very high intensity 1015 collisions per year
very high rate beams cross @ 40MHz
few “interesting” events ~100 Higgs decays per year
(but a small problem occurred - with a big impact)
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Particle physics in two slides Matter originated in the Big Bang
LHC energies correspond to tiny fraction of a second in the life of the universe
Make up hadronic matter, eg proton (uud) neutron (udd) mesons (q + anti-quark)
Leptons Families - like quarks e- makes atoms with nuclei µ and are like heavy electrons each has a neutrino partner
All quarks and leptons have mass
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Forces hold matter together
Strong nuclearStrong nuclearElectromagneticElectromagnetic
Weak nuclearWeak nuclear
GluonsGluons
QuarksQuarks
Mesons Baryons
Mesons Baryons
NucleiNuclei
PhotonPhoton
AtomsLightChemistryElectronics
AtomsLightChemistryElectronics
Atomselectrons
Atomselectrons
Neutron decayBeta radioactivityNeutrino interactionsSolar burning
Neutron decayBeta radioactivityNeutrino interactionsSolar burning
W & Z BosonsW & Z Bosons
quarksleptons
neutrinos
quarksleptons
neutrinos
Forces are transmitted by fields, also represented by particles (, W, Z, gluon)The “Standard Model” has unified some of the (4) forces of nature … astonishingly successfully
The most significant missing item is mass
It may be explained by a new field (and particle) - Higgs (boson)
Forces are transmitted by fields, also represented by particles (, W, Z, gluon)The “Standard Model” has unified some of the (4) forces of nature … astonishingly successfully
The most significant missing item is mass
It may be explained by a new field (and particle) - Higgs (boson)
July 2009 Geoff Hall5
Experiment by collisions
Colliding beams maximises the energy available to create new particles
uu
d
uu
d
Actually hadron collisions are between their constituent parts…
gluons quarks and the particles they exchange (Z, W,…)
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Experiment design
ppT
pL
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CMS Compact Muon Solenoid
ECAL
Tracker
HCAL
4T solenoid
Muon chambers
Total weight: 12,500 tOverall diameter: 15 mOverall length 21.6 mMagnetic field 4 T
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Muon System
195k DT channels210k CSC channels162k RPC channels
Gaseous planar ionisation detectors embedded in iron magnet return yoke to measure particle trajectories
YB0 Feb 2007
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December 2007
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YE-1 Jan 2008
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First data
First LHC Beam (10 Sept)
10 September 2008: beams were steered into collimators and secondary particles detected in CMSbefore and after September ~ 300 M cosmic ray events recorded
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The luminosity challenge
10331033
10351035
1032 cm-2 s-1 1032 cm-2 s-1
10341034
Full LHC luminosity~20 interactions/bx
Proposed SLHC luminosity~300-400 interactions/bx
HZZ ee, MH= 300 GeV for different luminosities in CMS
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TOBTOB
TIDTIDTIBTIB
TECTEC
PDPD
Tracker system
Radiation environment ~10Mrad ionising~1014 hadrons.cm-2
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Microstrip Tracker
automated module assemblyOuter barrel 3.1M channels
Inner barrel 2.4M channels
Endcaps3.9M channels
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Electromagnetic Calorimeter
Scine
Preshowerbased on Si sensors
ECAL Barrel17 xtal shapes
ECAL Endcap1 crystal shape
Preshowerbased on Si sensors
ECAL Barrel17 xtal shapes
ECAL Endcap1 crystal shape
Parameter Barrel Endcaps
Depth in X0 25.8 24.7
# of crystals 61200 14648
Volume 8.14m3 2.7m3
Xtal mass (t) 67.4 22.0
Scintillating crystals of heavy material – PbWO4
Light produced by electromagnetic showers
Light signal proportional to electron or photon energy
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Trigger and DAQ systems
Trigger selects particle interactions that are potentially of interest for physics analysis
DAQ collects the data from the detector system, formats and records to permanent storage
First-level trigger: very fast selection using custom digital electronics Higher level trigger: commercial computer farm makes more sophisticated
decision, using more complete data, in < 40-50 ms
Trigger requirements High efficiency for selecting processes of interest for physics analysis Large reduction of rate from unwanted high-rate processes Decision must be fast Operation should be deadtime free Flexible to adapt to experimental conditions Affordable
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p pH
jet jet
e+
e-
Z
Z
Triggering
Primary physics signatures in the detector are combinations of: Candidates for energetic electron(s) (ECAL) Candidates for µ(s) (muon system) Hadronic jets (ECAL/HCAL)
Vital not to reject interesting events Fast Level-1 decision (≈3.2 µs) in custom hardware
up to 100kHz with no dead-time Higher level selection in software
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What we hope to find
Higgs discovery (simplified!) Will be produced with many other particles ~20 events per beam crossing hundreds of secondary particles/25ns
p pH
µ+
µ-
µ+
µ-
Z
Z
Much new physics New forces New particles New symmetries
p p
e- e
q
q
q
q1
-
g~
~
20~
q~
10~
Machine incident
A superconducting cable connecting magnets and carrying ~9kA “quenched” – became resistive - and began to heat up
in < 1s the cable failed and an arc punctured the helium enclosure, releasing gas at high pressure
all the protection systems worked, but the pressure rose higher than expected
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improve monitoringrepair magnetsrestart summer 2009
Since September, impressive diagnosis of what happened…so: