LHC Update5/6/2010D Ingram

Photos: CERN unless otherwise noted

First -- What’s a Hadron?

Matter ConstituentsFermions (fractional spin)

Leptons Neutrinos (3) Electron Muon TauNever exist in composite particles

Quarks (6)Always exist in composite particles

Electroweak• Photon• W bosons• Z boson

Force CarriersBosons (0 or integer spin)

Strong force Gluons

Hadrons (quarks and/or antiquarks)

Mesons Pion Kaon B0

nc

Baryons Proton Neutron Lamda Omega

Is the Machine a Collider of Large Hadrons, or a Hadron Collider that is Large?

• 27 km circumference, 50-175m underground

• Two proton beams circling in opposite directions, crossing at four points along the path

• 1600(+) sc magnets, ~27t each, cooled to 1.9 K when operating

• Particle speeds < c by 1 part in 107

LHC Vacuum

• 54 km of beam line at ~7.5 e-07 torr

• 50 km (15,000 m3) of insulation vacuum around the magnets and LHe lines

• 48 of 54 km operated at 1.9 K

Heavy Ions

• For perhaps one month per year, the LHC will circulate beams of Pb ions (575 TeV per ion). The ion beam will be used in experiments related to the quark-gluon plasma that may have existed in the early universe

LHC Detectors• Compact Muon Solenoid (CMS): General-

purpose detector for studying proton-proton collisions

A Toroidal LHC Apparatus (ATLAS): Like CMS, a general-purpose detector capable of detecting

broad ranges of particles and energies

photo: Serge Bellegarde

A Large Ion Collider Experiment (ALICE): To be used for Pb-Pb ion collisions

Large Hadron Collider beauty (LHCb): “Measure the parameters of CP violation in the interactions

of b-Hadrons”

Total Cross Section, Elastic Scattering and Diffraction Dissociation (TOTEM): Uses the same

beam intersection as CMS

Large Hadron Collider Forward (LHCf): Relatively small, shares an intersection with ATLAS. Used

for cosmic ray physics.

Of course, nature might throw researchers a curveball. Martinus Veltman of the University of Michigan at Ann Arbor (Nobelist in 1999 with Gerard 't Hooft of Utrecht University in the Netherlands for work on the weak force that paved the way for the Higgs) suggested a gloomy but speculative scenario in which Higgs exists but fails to show up at the LHC. If that happens, he predicted, "it will probably be the end of particle physics."

Gross said that such a result, going against the standard model, would itself be "enormously exciting." What worried him was finding the Higgs and nothing else, because then it would be impossible to persuade world governments to fund future machines such as the proposed International Linear Collider , which took a hit in December when Congress yanked 2008 funding for the U.S. share of R&D on the project.

Without some hints from nature, physicists would not even know how big to build their machines to try to make new discoveries, Gross said. "My nightmare is we find the Higgs and nothing else," he said. "I have a lot of confidence that we won't, but that is a nightmare.“

The discussion touched at least one laureate's nerves. Theoreticians "have too much time to think" sometimes, Carlo Rubbia (awarded half the 1984 physics prize for experiments that led to the discovery of the W and Z bosons) charged. Rubbia, a former director general of CERN who is considered the father of the LHC for his early work on the project and now holds scientific advisory positions at several European institutions, asked if Veltman would return his share of the Nobel Prize money in the event the LHC found no sign of the Higgs. (Veltman replied that he had already spent it.)

Despite the excitement and sense of urgency, all of the Nobelists acknowledged that uncovering nature's secrets takes time. This, too, however, became a touchy subject. When asked how long before the LHC will perform its first experiments at full energy, Rubbia betrayed signs of exasperation, noting that glitches are to be expected. "This is not going to be a fault, this is not going to be a failure," he said, if there are unexpected delays. "The science community needs peace and tranquility to get over all these problems."

Gross noted that it would take at least several years before evidence of Higgs began to come in. An LHC timeline circulated in April at a physics meeting in St. Louis indicated that certain varieties of supersymmetry ought to show up even before the Higgs does.

Scientific American stirring the pot, July 2008

First Beam, 9/10/2008

The two beams were circulated separately

Sector 3-4 Failure, 9/19/2008

• Commissioners were verifying 5.5 TeV performance in the final sector to be tested

• Faulty electrical connection between two magnets, perhaps due to a glob of solder

• ~200 nΩ of resistance developed in a current ramp of 10 A/s, dissipating 10 W. Power supply tripped off, dump resistors activated to decrease current, quench detection and energy discharge worked as planned but an electrical arc punctured the helium enclosure, releasing He into the cryostat then into the tunnel through a relief valves, but the pressure rise damaged the vacuum barrier.

“Investigation teams confirmed the location of the electrical arc and, while they found no electrical or mechanical damage in neighbouring interconnections, they discovered contamination by soot-like dust, which propagated over some distance in the beam pipes. They also found damage to the multilayer insulation blankets of the cryostats. In addition, the forces on the vacuum barriers attached to the quadrupoles at the subsector ends were such that the cryostats housing these quadrupoles broke their anchors in the concrete floor of the tunnel and moved, with the electrical and fluid connections pulling the dipole cold-masses in the subsector from cold supports inside their undisplaced cryostats. The displacement of the quadrupole cryostats – short straight sections (SSS) – also damaged jumper connections to the cryogenic-distribution line.” Cern Courier Additional testing, verification and

changes stretched the time until the beam would return to service

2010 Return

• Beam returns on 11/20/2009. • Two beams circulated simultaneously on 11/23.

First collisons at 450 GeV• Fermilab Tevatron record of 0.98 TeV broken on

11/29.• Multibunch beam collisions at 1.18 TeV per

beam by 11/30. • All detectors received enough collisions to do

calibrations and gauge performance• ALICE, CMS and ATLAS submitted papers from

the November data (“Look Ma, it works!”)

Spring 2010

• March 30, 2010: Both beams at 3.5 TeV. 7 TeV collisions fed to all four principal detectors

• LHC will run at 3.5 TeV per beam for 18-24 months

• Subsequent lengthy commissioning will position the machine to deliver the design energy of 7 TeV per beam. (A 3.5 TeV beam requires a current of 6 kA in the magnets.)

• A new quench protection system required installation of 500 connectors in each of the eight sectors during the 08-10 down time. This system seems to be performing as designed.

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