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Where to Search for the Higgs
A direct search for the Higgs was carried out by the four LEP experiments from 1995-2000 CMS energy of 205-208 GeV The production and decay was
primarily by
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Where to Search for the Higgs
The combined result was
Of course there were interesting events
CL 95% @ GeV 4.114Hm
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Where to Search for the Higgs
“Triviality” sets an upper bound on the Higgs mass of O(1 TeV)
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Where to Search for the Higgs
Another upper limit can be found by considering the scattering amplitudes for Partial wave
unitarity yields
TeVmH 1
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Where to Search for the Higgs
Indirect constraints on the Higgs mass can be found by considering electroweak radiative corrections like
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Where to Search for the Higgs
Electroweak observables depend quadratically on the top quark mass and logarithmically on the Higgs boson mass
A global fit yields direct w LEPCL 95% @ GeV 191
CL 95% @ GeV 163
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Where to Search for the Higgs
Recently the DZero and CDF experiments at the Fermilab Tevatron excluded a new mass region Many different channels
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LHC (Large Hadron Collider)
CERN is located outside Geneva, Switzerland
The energy of the LHC will be 7 TeV x 7 TeV
The ring circumference is 27 km
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LHC Complex Duoplasmatron
at 300mA beam current at 92 keV
RFQ to 750 keV
Linac 2 to 50 MeV
PSB to 1.4 GeV
PS to 28 GeV
SPS to 450 GeV
LHC to 7 TeV at 180mA beam current
1111
What is the B Field?You might recall from your study of E&M that
a particle of momentum p in a uniform magnetic field B undergoes circular motion with radius
The LHC circumference is ~27 km Packing fraction of ~64% gives R~2.8 km Thus B needed for p=7 TeV is ~8.3 T Superconducting magnets using superfluid He at
1.8K are needed to reach this field Magnet current at this field is 11850 A
Bending achieved by 1232 15-m dipoles
GeVpTmBR 334.0
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LHC MagnetsSeptember 19, 2008
During powering tests, a fault occurred in the electrical bus connections between a dipole and quadrupole in Sector 3-4
The power supply tripped off due to a resistive zone and magnet quenches were triggered
An electrical arc developed that punctured the helium enclosure and led to the release of helium into the vacuum of the cryostat
The vacuum enclosure could not contain the pressure rise resulting in large pressure forces acting on the vacuum barriers separating subsectors
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Repairs
A total of 53 magnets (39 dipoles and 14 SSS) were removed and repaired
The number and size of relief valves on the cryostat vacuum vessels will be increased Designed to cope with a He discharge x2 the
September 19th incident
An enhanced quench detection and protection system (QPS) was developed to include interconnects and busbar splices
Floor jacks were reinforced on some quadrupoles
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Schedule
Schedule as of February 09 Beam in late September Collisions in late October 8-10 TeV run through autumn 2010
Experts say scheduled is tight but realistic Allows completion of all repairs Applies more stringent safety
constraints Acknowledges helium storage and
transfer constraints
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Higgs Production at the LHCGluon Fusion (GGF)
Dominant process
Vector Boson Fusion (VBF) Second largest cross
section Distinctive topology useful
for small mH
Associated W/Z (AW)Associated Top (AT)
Interesting topologies but smaller cross section
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VBF (Vector Boson Fusion)Higgs production with a distinctive
topology Forward jets No central activity because no color
Jet
Jet
Forward jets
Higgs Decay
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Higgs Decay Modes
The mass of the Higgs is unknown but the decay of the properties of the Higgs is a known
The Higgs boson likes mass It couples to particles proportional to
their mass It decays preferentially to the
heaviest particles kinematically allowed
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Higgs Decay ModesThe Standard Model rules say the Higgs
decays preferentially into the heaviest pair of particles that is kinematically allowed
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Cross Sections at the LHC
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Resonances - narrow width approximation:
e.g.
There is a factor > 1010 between the Higgs cross section and the total inelastic cross section. There is also the final state branching fraction to consider. This is why the LHC design luminosity is so high.
LHC Cross Sections:
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Kugelstossen: Kugelstossen:
The energy of one shot (5 kg) at 800 km/hour The energy of one shot (5 kg) at 800 km/hour corresponds to corresponds to
the energy stored in one bunch at 7 TeV. the energy stored in one bunch at 7 TeV.
There are 2808 bunches.There are 2808 bunches.Factor 200 compared to HERA, TEVATRON and SPS.Factor 200 compared to HERA, TEVATRON and SPS.
shot
Energy stored in one beam at 7 TeV: 362 MJoule
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Particle Accelerators
We study nature by using high energy collisions between particles
Particle accelerators can be thought of as giant microscopes that are used to study extremely small dimensions The higher the energy the smaller the
wavelength the better the resolution
Particle detectors are used to record the results of these high energy collisions
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LHC FODO
QF QD QFdipolemagnets
small sextupolecorrector magnets
decapolemagnets
LHC Cell - Length about 110 m (schematic layout)
sextupolemagnets
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LHC Accelerator
At four points around the ring the two beams are brought together where collisions occur
The beams are actually composed of many “bunches” of protons
These bunch crossings (collisions) occur every 25 ns
At an energy of 7 TeV it takes 90μs for a proton to make one revolution