GuidoTonelli /IPM/Isfahan/20-24 April 2009 1
Overview of the CMS experiment at LHC
Guido TonelliUniversity of Pisa/INFN/CERN
• Why and how CMS was designed
• Status of the experiment
• Preparation for physics
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CMS and LHC@ CERN
LHC
CERN Site (Meyrin)CERN Site (Meyrin)
SPS
LHC: 9300 Superconducting Magnets; 1232 Dipoles (15m), 448 Main Quads, 6618 Correctors. Operating temperature: 1.9o K; 26.7 km tunnel
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Why everything is so complex?
We are trying to solve some of the main puzzles of nature
•What is the origin of mass•What could be the dark matter that keeps together the clusters of galaxies•Why the main interactions are so different in strength•Why gravity is not included so far in our picture•How many are really the dimensions of our world
The answer to some of these questions is probably hidden in the so far unexplored TeV region
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What is wrong with the Standard Model?
The SM is still among the most successfull theories tested so far(accuracy <10-
4).
LEP, CDF-D0: we really understand physics up to 100GeV.
Why we are not happy with it ?
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Why the masses of elementary constituents (matter and fields) are so different ?
The bare SM could be consistent with massless particles but matter particles range from almost 0 to about 170GeV while force particles range from 0 to about 90GeV.
How can it be that a massless photon can carry the same electroweak interaction of a 80-90 GeV W or Z?
The simplest solution (Higgs, Kibble, Brout, Englert 1960’s)
All particles are massless !! A new scalar field pervades the universe.
Particles interacting with this field acquire mass: the stronger the interaction the larger the mass.
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Mathematical (in)-consistency of the SM
WL
WL
WL
ZL
ZL
time
WL
WL
ZL
H
At energies larger than 1TeV the probability of scattering of one W boson off another one becomes >1 ?!
The SM gives nonsense!
An elegant solution would be to introduce a Higgs exchange that would cancel the bad high energy behaviour.
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How heavy is the Higgs: the TeV scale.
LEP+ CDF-D0 data indicate Higgs could quite light (but logarithmic dependences are tricky).
To be sure to be able to catch it (if it does exist) a safe attitude is to explore the entire region between 100 and 1000GeV.
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Hierarchy problem and supersymmetryBut a Higgs boson “alone” would bring with him new problems.There would
be large quantum mechanics corrections to its mass thus leading to large instabilities for > > 1/ √GF.
The “standard trick” to remove instabilities is to introduce new massive particles:
If each SM particle has a partner with spin differing by 1/2 unit, infinities “magically” disappear.
Fantastic! but this implies the existence of a completely new form of matter:
“super-matter” or SUSY particles.
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Super-symmetry
Since none of them have been discovered yet they must be heavy and SUSY must be a broken symmetry! But if SUSY is supposed to solve the issue of
naturalness they must populate the TeV mass region:
|M2spart - M2
part| < O (1 TeV2)
Each SM particle could have a super-symmetric (SUSY) partner with spin 1/2 difference. In super-matter the carriers of the interactions are fermions and the particles are bosons. Elegant and nice symmetry of nature (similar to matter-antimatter where the spin plays the role of the charge).
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The production cross sections could be high in the √s=14TeV region
In one of the simplest SUSY model we have gluinos, squarks, sleptons, 4 neutralinos, 2 charginos and a whole family of
Higgs bosons
h0, H0, A0, H
Sparticles would be produced in pairs to conserve R-parity. The Lightest Super-symmetric Particle would be a massive, stable and weakly interacting neutralino: ideal candidate to explain dark matter.
A gas of heavy neutralinos could hold together clusters of galaxies (including ours).
Major breakthrough in our understanding of the universe.
Susy and cosmology
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25-30% of our universe is made of “unknown matter”
Collision of two galaxies“Bullet Cluster” Clowe et al.
Direct evidence for collisionless Dark MatterChandra, Magellan, HST, Gravitational Lensing
Dark Matter
Gaseous Matter
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96% of our universe is still a “dark thing”
WMAP
Convergence Model
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Other exciting possibilities for naturalness
If the Higgs boson is discovered and Super-symmetry does not manifest itself in the TeV region again we have to find other mechanisms to fight against the radiative corrections to the Higgs mass.
MH2 MH
2 (o) + c 2
is the scale of the theory. If ~MGUT ~ 1015 GeV an incredible, un-natural fine tuning would be needed to allow for a “light” Higgs
Two major sets of possibilities to save naturalness:
Protected by other new forces/particles? (Z’, W’, technicolor).
Protected by (compactified) extra dimensions?
….
New signatures of new physics.
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… and if no Higgs boson will be found
Several dynamical mechanisms have been proposed for the symmetry breaking.
QCD inspiredWL and ZL could be sort of ‘pions’ of a new interactionrescale f to 1/√GF leading to strong interaction in TeV range VL- VL scattering analog of - scattering
TechnicolourThe Higgs-less SM is saved by a techni-Whole family of new states predicted
Strong breaking of E-W symmetryNo Higgs boson but a triplet of massive bound states - vector
bosons V0, V (similar to techni-)
New particles and new signatures.
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SUSY, Large Extra Dimensions and GUT• The coupling constants "run" in quantum
field theories due to vacuum fluctuations. For example, in EM the e charge is shielded by virtual fluctuations into e+e- pairs on a distance scale set by, le ~ 1/me. Thus increases as M decreases, (0) = 1/137, a(MZ) = 1/128.
• If SUSY is really a symmetry of nature and the mass of the super-partners is ~ 1 TeV, then the GUT unification is good - at 1016 GeV. A local SUSY GUT could incorporates naturally gravity.
• But, if gravity does change at some mass scale 1/R, then the Planck mass could be a “mirage”. The law of gravity depends on the number of space dimensions. Space-time may have more than 4 dimensions: extra-dimensions that are not visible because they are curled-up.
Standard Model
Supersymmetry (MSSM)
Large Extra Dimensions
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MH ~ 1000 GeV
EW ≥ 500 GeV
Eq ≥ 1000 GeV (1 TeV)
Ep ≥ 6000 GeV (6 TeV)
Proton Proton Collider with Ep ≥ 5-7 TeV
p pq
q
q
q
Z0
Z0
HWW
Higgs Production in pp Collisions14TeV
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SM Higgs production at LHC
10 fb-1 (104 pb-1) O(105) events for MH<200 GeVBR(HZZ)*BR(ZZ4l) ~ 10-4, 10-5
Few tens of H4l events for 30 fb-1
NLO
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SM Higgs Branching ratios
Low mass (MH<2MZ):
bb dominant, but huge QCD background only ttH accessible
Also accessible: H, HZZ*4l, HWW*ll, H
MH>2MZ:
HZZ4l, WW modes
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The Higgs signal in CMSLow MH < 150 GeV Medium 130<MH<500 GeV High MH > ~500 GeV
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Signal and background1034
Cross sections for various physics processes vary over many orders of magnitude
Higgs (600 GeV/c2): 1pb @1034 10–2 HzHiggs (100 GeV/c2): 10pb @10340.1 Hzt t production: 10 HzW l : 102 HzInelastic: 109 HzSelection needed: 1:1010–11
Before branching fractions...CDF and D0 successfully found the top quark facing similar rejection factors
Fast detectors: 25ns bunch crossingHigh granularity: 20 overlapping complex eventsHigh radiation resistance: 10 years of operation
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Basic principles
Need “general-purpose” experiments covering as much of the solid angle as possible (“4”) since we don’t know how New Physics will manifest itself detectors must be able to detect as many particles and
signatures as possible: e, , , , , jets, b-quarks, ….Momentum / charge of tracks and secondary vertices (e.g. from b-
quark decays) are measured in central tracker (Silicon layers). Energy and positions of electrons and photons measured in
electromagnetic calorimeters.Energy and position of hadrons and jets measured mainly in hadronic
calorimeters. Muons identified and momentum measured in external muon
spectrometer (+central tracker).Neutrinos “detected and measured” through measurement of missing
transverse energy (ETmiss) in calorimeters.
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Particles through a CMS slice
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MUON BARREL
CALORIMETERS
Silicon MicrostripsPixels
ECAL Scintillating PbWO4
Crystals
Cathode Strip Chambers (CSC)Resistive Plate Chambers (RPC)
Drift Tube Chambers (DT)
Resistive Plate Chambers (RPC)
SUPERCONDUCTING
COIL
IRON YOKE
TRACKERs
MUON ENDCAPS
Total weight : 12,500 tOverall diameter : 15 mOverall length : 21.6 mMagnetic field : 4 Tesla
HCAL Plastic scintillator copper
sandwich
The Compact Muon Solenoid (CMS)
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The CMS Collaboration
1772 physicists.134 universities and research centers.38 countries and regions of all continents.
CERN
France
Italy
UK
Switzerland
USA
Austria
Finland
GreeceHungary
Belgium
Poland
Portugal
SpainPakistan
Georgia
Armenia
Ukraine
Uzbekistan
CyprusCroatia
China, PR
Turkey
Belarus
EstoniaIndia
Germany
Korea
Russia
Bulgaria
China (Taiwan)
Iran
Serbia
New-Zealand
Brazil
Ireland
Mexico ColombiaLithuania
Iran participation in CMS 7 physicists from IPM.Important contribution to the construction of HF. Strong commitment for physics.Interest in participating in the RE up-scope project.
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UXC/USC5: CMS caverns
Delivered to the experiment onFebruary 1-st 2005.The main components of the whole experiment assembled in the surface halland lowered 100m underground.
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HF Lowering: the first one (the lightest baby)
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YE1 Lowering: the most difficult one.
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YB0 lowering: the heaviest one (1920t)
Touchdown after 11 hours.
Two days to align it better than a fraction of a mm in all coordinates.
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An incredible series of complex activities
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Three years later: no much room left over
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25/08/2008: 16 years after the Letter of Intent, CMS is completed
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10/09/2008: first beam in LHC2 shots of clockwise beam: 2x109 protons per beam
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EB vs HB Energy correlationHCAL energy
ECAL energy
Good use also of the beam-on-collimators events
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19/09/2008: our black fridayAn incident occurred during a powering test of one LHC sector for
commissioning beam operation to 5 TeV. Massive helium loss in one arc of the tunnel; cryogenics and vacuum lost and important mechanical damage to tens of dipoles and quadrupoles
The cause of the incident was determined to be a faulty electrical connection (“bus bar”) between a dipole and a quadrupole.
Superfluid helium inquick expansion caneasily displace a string of many 20t magnets…
… and these are the consequences:~1 year of work to replace/repair/re-check 53 magnets and to put in place any sort of test and all possible preventive actions to avoid the same incident could happen again.
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CRAFT: 300 millions of cosmics to study the most subtle features of our detector
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CRAFT Results: tracker and calorimetry.
rms=24umrms=24um
BarrelPixelsBarrelPixels
Si TrackerTOB
Si TrackerTOB
rms=47umrms=47um
Energy deposited by muons
Energy deposited by muons
HCALHCAL
ECALECAL
radiativeradiativeionisationionisation
Points- dataPoints- data
totaltotal
Alignment in Inner TrackerAlignment in Inner TrackerThe whole tracking system aligned with an accuracy planned to be achieved only after the first 50pb-1 of data.
Detailed cross-check of timing and calibration issues in our calorimetry response.
Excellent starting points for many early physics goals.
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CRAFT results: Muon DT chambers
~250um~250um
MB4MB4
MB3MB3
MB2MB2
MB1MB1
Muon Chambers Point ResolutionMuon Chambers Point Resolution
240 chambers aligned; magnetic field simulation corrected; TDR resolution (250m) achieved before data taking.
Another excellent starting point for many early physics goals.
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CMS has been opened again to repair defective components and install the last sub-detector
T. Virdee JOG Apr09 38
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Installation of the pre-shower: the very last component of CMS
39
The two separate ES DeesThe two separate ES Dees
Transporting ES towards EETransporting ES towards EE
ES attached to support coneES attached to support cone
ES cabledES cabled
Installation and commissioning finished Friday April 17 99.9% of the 136K channels are OK
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Latest news from LHC• Repair work is going on as scheduled• Good understanding of the incident and better diagnostic tools put in place to prevent any kind of additional problem.
• 39 dipoles and 14 quadrupoles of the Short Straight Sections have been replaced/repaired. All magnets back in the tunnel since Friday April 17-th. 2-3 weeks of delay accumulated wrt the schedule foreseen in December•Action to pass from 2shifts/dayx5 days/week to 3 shift/day 7 days/week to recover the delay•Expect beam in September !
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Possible scheme for LHC running 2009/2010
Run period ~ 1yearOctober 2009-September 2010Expectations for ~200pb-1 integrated luminosity at 10 TeV.
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First pb-1
• Careful cross check of the trigger performance• Improved calibration and quality control (efficiencies)• Reconstruction of the basic physics objects: muons, electrons, photons, jets…• Re-discovery of 0, Ko, J/psi, Upsilon …
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10pb-1 re-discovering SM In 10pb-1105W–> l,
In 10pb-12x104Z–> l+,l-
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100pb-1 Z’--->ee, µµ
Z’Z’
Discovery potential for new massive bosons through dilepton invariant mass distributions and detailed understanding of the Drell-Yan continuum.
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100pb-1 Supersymmetry
Large missing momentum from escaping invisible particles
Classic signature of minimal supersymmetric models with a dark matter candidate
Energetic “jets” from supersymmetric particle decays.
SUSYSUSY
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First few hundred pb-1 starts the Higgs hunting
Signals and backgrounds are scaled from 14 TeV Plots are indicative of CMS reach
HiggsHiggs
With 200 pb-1, reach current Tevatron sensitivity for
Higgs
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Our Schedule
Software, Computing & Physics
Maintenance & Operation
Install ES1Install ES2
Tracker Cooling Plant Revised
Close CMS
Magnet Tests
CRAFT
Full validation of 3_1 (incl. production and
physics)
Deadline for Input for 3_1 CRAFT, Trigger Review (menu), Phys…
Use 3_1 widely CMS gets familiar with 3_1
CMS READY for Beam CMS READY for Beam
Release CMSSW3_0 (limited validation, step towards 3_1)
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Start Fullsim production 3_1
Release CMSSW3_1 (LHC Startup)
Start Fastsim production 3_1CRAFT Contingency & pre-beam maintenance
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Conclusion
Within a few months we shall start the systematic exploration of the TeV region with an excellent scientific instrument.
My hope is that there will be many un-expected results and our current understanding of nature will change in depth thereafter.
Excellent time for brilliant students and post-docs to join the effort and contribute to it with their enthusiasm and (hopefully) new ideas.