Overview of the CMS experiment at LHC

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


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


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


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 ?


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.


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.


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.


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.


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).


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


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


96% of our universe is still a “dark thing”

WMAP

Convergence Model


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.


… 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.


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


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


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


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


The Higgs signal in CMSLow MH < 150 GeV Medium 130<MH<500 GeV High MH > ~500 GeV


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


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.


Particles through a CMS slice


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)


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.


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.


HF Lowering: the first one (the lightest baby)


YE1 Lowering: the most difficult one.


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.


An incredible series of complex activities


Three years later: no much room left over


25/08/2008: 16 years after the Letter of Intent, CMS is completed


10/09/2008: first beam in LHC2 shots of clockwise beam: 2x109 protons per beam


EB vs HB Energy correlationHCAL energy

ECAL energy

Good use also of the beam-on-collimators events


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.


CRAFT: 300 millions of cosmics to study the most subtle features of our detector


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.


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.


CMS has been opened again to repair defective components and install the last sub-detector

T. Virdee JOG Apr09 38


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


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 !


Possible scheme for LHC running 2009/2010

Run period ~ 1yearOctober 2009-September 2010Expectations for ~200pb-1 integrated luminosity at 10 TeV.


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 …


10pb-1 re-discovering SM In 10pb-1105W–> l,

In 10pb-12x104Z–> l+,l-


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.


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


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


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


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.

Overview of the CMS experiment at LHC

Documents

Transcript of Overview of the CMS experiment at LHC