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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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Hb

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q

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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

“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 Dipole

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LHC Accelerator

LHC dipoles

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LHC Dipoles

Coils

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LHC AcceleratorLHC RF cavities

RF = 400 MHz Rev f = 11246 Hz

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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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September 19th IncidentThe connecting busbar

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September 19th IncidentThe electrical arc destroyed the busbars

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September 19th IncidentThe large pressure forces resulted in

magnet displacements

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September 19th IncidentAnd more magnet displacements

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September 19th IncidentAs well as broken ground supports

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September 19th IncidentAnd beam vacuum

contamination

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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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Higgs Production at the LHC

GGF

VBF

AW

AT

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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 Modes

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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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Higgs Production at the Tevatron

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Higgs Production at the LHC

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Higgs Decay Modes

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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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LHC Dipole Interconnections

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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

3939

LHC Accelerator

LHC dipoles

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LHC

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LHC

The experiments (detectors) are located 100m underground

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LHC Accelerator

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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

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Higgs Boson Discovery

Unknown unknowns

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