Accelerators and Physics at CERN
Accelerators and physics, 2005. Bengt Lund-Jensen
Accelerators
Bending in magnetic field
momentum p charge q radius of curvature ρ magnetic field B
p = q B ρ
with unit charge and momentum in GeV
p = 0.3 B ρ
Example: Large Hadron Collider (LHC)
p = 7⋅103 GeV/c, ρ = 4.3⋅103 m (27 km circumference)
⇒B ≈ 5.4 T
Not all the tunnel is filled with bending magnets, so need a bit higher field: B ≈ 8.3 T
Accelerators and physics, 2005. Bengt Lund-Jensen A top quark factory Required for the discovery of the Higgs boson.
NEW PHYSICS!!
Parameters Value Circumference 26.7 km Dipole Field 8.4T Collision energy 7.0 TeV Injection energy 450 GeV Stored beam energy 332 MJ Bunch spacing 25 ns Number of bunches 2835 Particle per bunch 1011 Circulating current per beam 540 mA Excellent for CP violation Bunch radius 16 μm Bunch length 75 μm Beam lifetime 22 h studies with B-hadrons! Luminosity 1034 cm-2s-1 Luminosity lifetime 10 h
Accelerators and physics, 2005. Bengt Lund-Jensen
Synchrotron radiation
Particles in circular orbit emit ”synchrotron radiation”
Radiated energy per turn:
4π q 2β2γ 4 ∆E = 3ε0 ρ For relativistic particle with energy E (= mγ)
∆E ~ m -4
Electron with β ≈ 1
∆E = 88.5 E 4/ρ ( keV, E in GeV)
E.g. E = 100 GeV, ρ = 1000 m
⇒∆E = 8.9 GeV/turn
(not feasible to build e- accelerator for 100 GeV with such small radius)
Accelerators and physics, 2005. Bengt Lund-Jensen The CERN Large Hadron Collider, a new accelerator in the old LEP tunnel
Accelerators and physics, 2005. Bengt Lund-Jensen
Accelerators and physics, 2005. Bengt Lund-Jensen Accelerators and physics, 2005. Bengt Lund-Jensen
Electron cooling
Accelerators and physics, 2005. Bengt Lund-Jensen Accelerators and physics, 2005. Bengt Lund-Jensen
”Antiatomic” physics
Antiproton decelerator (AD) delivers slow antiprotons for:
ATHENA & ATRAP: antihydrogen studies
ATHENA
Accelerators and physics, 2005. Bengt Lund-Jensen ASACUSA: hyperfine structure of antiprotonic helium
Accelerators and physics, 2005. Bengt Lund-Jensen
i.e. antimater is made at CERN, though only in extremely small quantities.
Bu we have NO X33
Accelerators and physics, 2005. Bengt Lund-Jensen The LHC programme
The LEP (Large Electron Positron) collider gave precision physics studies for more than a decade: • There are 3 neutrino families • Predicting the top quark mass • The energy dependence of the coupling constants ⇒ Grand Unification requires new physics • Lower limits on Higgs boson mass and Supersymmetric particles • A prediction of the Higgs boson mass. The Higgs boson still has to be found! (the last LEP data did not include real signs of the higgs)
LEP was stopped in November 2000 to build LHC
Accelerators and physics, 2005. Bengt Lund-Jensen
For non particle physicists: the Standardmodel
Describes the particle content, their properties and interactions as far as we know them today.
Matterparticles (spin = ½ ): quarks and leptons Leptons
Charge mass leptonnumber Quarks M (GeV/c2) q
-3 2 up 1.5 - 4,5•10 +2/3 None < 3 eV/c Le = + 1 u νe -3 e 2 down d 5 - 8,5•10 -1/3 -1 511 keV/c Le = + 1
2 charm c 1,0 - 1.4 +2/3 νμ None < 0.19 MeV/c Lμ = + 1 μ 2 strange s 0.08 - 0.155 -1/3 -1 106 MeV/c Lμ = + 1 top ± 2 t 174 5 +2/3 ντ None < 18.2 MeV/c Lτ = + 1 τ 2 bottom b 4,0 - 4,5 -1/3 -1 1777 MeV/c Lτ = + 1
Quarks can only be found in bound states: qqq, qq och qqq
Baryonnumber = +1/3 for quarks. Accelerators and physics, 2005. Bengt Lund-Jensen The CERN Large Hadron Collider
Accelerators and physics, 2005. Bengt Lund-Jensen
A top quark factory
Parameters Value Circumference 26.7 km Dipole Field 8.4T Collision energy 7.0 TeV Injection energy 450 GeV Stored beam energy 332 MJ Bunch spacing 25 ns Number of bunches 2835 Excellent for CP violation Particle per bunch 1011 Circulating current per beam 540 mA Bunch radius 16 μm studies with B-hadrons! Bunch length 75 μm Beam lifetime 22 h Luminosity 1034 cm-2s-1 Luminosity lifetime 10 h
Accelerators and physics, 2005. Bengt Lund-Jensen What about: the Higgs boson ?
The electroweak symmetry is broken in the way that the photon is massless, while W and Z are heavy.
Introducing a 4 component Higgs field, results in spontanously broken (hidden) local gauge invariance, giving masses to the W and Z bosons.
The interactions are still gauge invariant.
One degree of freedom still remains resulting in a new particle, the Higgs boson. Expected higgs mass from fit to data The Higgs boson couple to the fermions in proportion to their masses.
Accelerators and physics, 2005. Bengt Lund-Jensen
The decay of the Higgs boson depends on its mass 2 ●100 < mH < 150 GeV/c H→ bb dominates, but large background !! Possible if H is produced in association with W, Z or tt. H→γγ rare decay but little background. The most promising channel, but requires excellent calorimeter resolution.
Expected H→γγ signal for mH = 120 GeV (1 year at high luminosity). Left: signal on top of irreducible background. Right: after background subtraction.
Accelerators and physics, 2005. Bengt Lund-Jensen 4 experiments will be built for LHC:
General purpose: ATLAS and CMS (Compact Muon Solenoid)
Heavy ions: ALICE
B-hadron physics: LHCB (also done by ATLAS and CMS)
LHC will start May 2008.
Accelerators and physics, 2005. Bengt Lund-Jensen
The ATLAS Detector
xcellent Standalone Muon measurement
Accelerators and physics, 2005. Bengt Lund-Jensen Accelerators and physics, 2005. Bengt Lund-Jensen
Nov 2005
Accelerators and physics, 2005. Bengt Lund-Jensen Accelerators and physics, 2005. Bengt Lund-Jensen The KTH contribution
KTH is together with LPSC, Grenoble, and groups in Morocco responsible for the presampler, that, placed just in front of the barrel EM calorimeter, compensates for energy oss in upstreams material . Required for sufficient resolution for H →γγ
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Accelerators and physics, 2005. Bengt Lund-Jensen The official LHC schedule
Accelerators and physics, 2005. Bengt Lund-Jensen
SM Higgs at the LHC (several production/decay channels) g fusion VBF WW/ZZ fusio ssociated associated WH, ZH t t H
Uncertainties on x-sections • gg 10-20 (NNLO) k~2.0 • VBF ~ 5%(NLO) k~1.1 • WH,ZH ~<5%(NNLO) k~1.4 • ttH 10-20 % (NLO) k~1.2
Accelerators and physics, 2005. Bengt Lund-Jensen H→γγ in the EM calorimeter
Accelerators and physics, 2005. Bengt Lund-Jensen
H→WW→l+νl-ν
Important channel for mH~160 GeV (H→WW BR ~ 95% ) •No mass peak •Need exact knowledge of bgk shape
Backgrounds: tt, tWb : rejected by jet-veto WW,WZ,ZZ: rejected by kinematical cuts + - Recently: l l +MET gg → WW contribution tt, single top@NLO Extra sensitivity by adding exclusive VBF →WW
Accelerators and physics, 2005. Bengt Lund-Jensen ATLAS discovery potential in 3 yrs low L
Beware: 2003 result LO calculation New on-going LEP limit
Accelerators and physics, 2005. Bengt Lund-Jensen
SUSY
Each Standard Model particle has a supersymmetric (SUSY) partner with ½ a unit difference in spin. The Higgs field is now more complex giving 5 physical Higgs bosons.
4 2 ~ ~0 ~ 0 ~ 0 χ = N1γ + N2Z + N3H1 + N4 H 2 ; Ni =1
H ∑
T i=1
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- d • SUSY so far not observed.
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• there are e.g. no boson partners of the leptons at the same mass.
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Accelerators and physics, 2005. Bengt Lund-Jensen The lightest sparticle is stable?
It is possible that the lightest SUSY particle (LSP) is stable. (This would prevent too fast proton decay, but isnot strictly required) In that case, the LSP must be neutral, otherwise it would have been seen as a heavy charged particles in cosmic rays.
χ∼ 0 ⇒ LSP = 1
A stable LSP might be part of the explanation for dark matter (WIMP)
To quantify the stability, introduce R-parity such that normal SM particle have R=1 and sparticles R=-1 :
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, 3B+L+2S n R = (1-) (B= baryon number, L=lepton number, S=spin)
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Accelerators and physics, 2005. Bengt Lund-Jensen
How to discover SUSY?
R-parity ⇒ SUSY created in pairs, final state contain 2 LSPs.
In experiments, this leads to the creation of two heavy neutral particles that can carry large transverse energy that will not be detected ⇓ missing transverse energy (momentum)
LSP has gravitational interaction. May gather in the sun (earth) and annihilate giving high energy γ localizable to the sun.
At accelerators: need higher energy.
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T ⇒ The Large Hadron Collider (LHC) at CERN.
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Accelerators and physics, 2005. Bengt Lund-Jensen SUSY at LHC SUSY created in pairs, normally gluino-gluino or squark-squark dependent on sparticle mass. Often complex decay chains:
• Event selection guided by typical decay chain of SUSY particles ~0 χ 1 ~ qR ~ q g p p ~ _ ~ χ0 ~ q ~0 ~ 1 q g L χ 2 l q q l l χ 0 In the end two 1 that give missing transverse energy.
The complex decay chain ⇒
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T • Large jet multiplicity
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. Also event with two leptons of same charge.
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Accelerators and physics, 2005. Bengt Lund-Jensen
Alice: heavy ion physics
Accelerators and physics, 2005. Bengt Lund-Jensen Search for quark gluon plasma
Accelerators and physics, 2005. Bengt Lund-Jensen
Neutrino Oscillation Experiments If the neutrino interaction eigenstates and mass eigenstates are not the same, neutrinos can change interaction eigenstate during travel.
Accelerators and physics, 2005. Bengt Lund-Jensen Seen in cosmic ray exepriments (Superkamiokande). Next step:
Send neutrino beams from accelerators towards neutrinodetectors far away.
Two detectors: OPERA and ICARUS (ICANOE)
Accelerators and physics, 2005. Bengt Lund-Jensen
Accelerators and physics, 2005. Bengt Lund-Jensen CLIC Test Facility 3
Accelerators and physics, 2005. Bengt Lund-Jensen
The Baseline Machine (500GeV)
~30 km 20mr ML ~11.2km (G = 31.5MV/m) RTML ~1.6km
2mr BDS 5km
e+ undulator @ 150 GeV (~1.2km) R = 955m x2 E = 5 GeV
not to scale
Accelerators and physics, 2005. Bengt Lund-Jensen The ILC Accelerator
nd 2 generation electron-positron Linear Collider
Parameter specification
Ecms adjustable from 200 – 500 GeV Luminosity Æ ∫Ldt = 500 fb-1 in 4 years Ability to scan between 200 and 500 GeV Energy stability and precision below 0.1% Electron polarization of at least 80% Options for electron-electron and γ−γ collisions The machine must be upgradeable to 1 TeV
Three big challenges: energy, luminosity, and cost
Accelerators and physics, 2005. Bengt Lund-Jensen
Scope of the 500 GeV machine
Main linacs length ~ 21 km, 16,000 RF cavities (total) RF power ~ 640 10-MW klystrons and modulators (total) Cryoplants ~ 11 plants, cooling power 24 kW (@4K) each Beam delivery length ~ 5 km, ~ 500 magnets (per IR) Damping ring circumference ~ 6.6 km, ~400 magnets each Beam power ~ 22 MW total Site power ~ 200 MW total Site footprint length ~ 47 km (for future upgrade > 1 TeV) Bunch profile at IP ~ 500 x 6 nm, 300 microns long
Accelerators and physics, 2005. Bengt Lund-Jensen Elements of the BCD
Parameter plane established
TESLA designed for 3.4e34 but had a very narrow operating range
ILC luminosity of 2e34 over a wide range of operating parameters
Bunch length between 500 and 150 um
Bunch charge between 2e10 and 1e10
Number of bunches between ~1000 and ~6000
Beam power between ~5 and 11 MW
Superconducting linac at 31.5 MV/m
Cavities qualified at 35 MV/m in vertical tests
Expect an average gradient of 31.5 MV/m to be achieved
Rf system must be able to support 35 MV/m cryomodules This still requires extensive R&D on cavities and rf sources
Accelerators and physics, 2005. Bengt Lund-Jensen
5GeV
inal ILC design?
1 TeV -10 years away, omewhere
Accelerators and physics, 2005. Bengt Lund-Jensen Conclusions:
• CERN’s effort is now concentrated at LHC • Large parts of the LHC experiments have been made and assembly into complete detectors is starting. Almost every week some new and impressive detector structrure can be seen at CERN !!! • Other experimental programmes still continue.
We are looking forward to the first LHC beams in 2008 and the world class physics studies for which CERN will continue to stand
Accelerators and physics, 2005. Bengt Lund-Jensen