Large Hadron Collider og ATLAS @
CERN
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Part 1: LHC and LHC startup
Accelerator was proposed during the eighties
Project approved in 1994.
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Some parameters
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• 9600 magnets, out of which 1232 are large
dipole magnets
• Dipole current: 11850 A
• Magnetic field 8,33T
• Proton energy 7 TeV
• 120 Tonnes of Helium used to cool a mass
of 30000 tonnes.
…more parameters
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• Vacuum tube pressure10-13 atm
• Vacuum also serves as heat insulation, so in
total there is 9000 cubic meters of vacuum.
Price: 4.6 GCHF = 25GNOK
(Only the construction)
(how much per physicist per
year?)
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What happened on Sept 10th?
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”It took an hour for the beam to make a full turn”
That’s just 27 km/h????….
tertiary
collimators
140 m
BPTX
175 m
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ATLAS was ready for first beam:
Two LHC start-up scenarios:
• Muon system (MDT, RPC, TGC)
on at reduced HV
• LAr (-FCAL HV), Tile on
• TRT on, SCT reduced HV, Pixel off
• BCM, LUCID, MinBias Scint.
(MBTS), Beam pickups (BPTX)
• L1 trigger processor, DAQ up and
running, HLT available (but used
for streaming only)
1. Open all collimators, go around as far
as beam goes, correct as needed
• Little activity expected except for
accidents
2. Go step-by-step, stopping beam on
collimators, re-align with centre, open
collimator, keep going
• Splash event from collimators for
each beam shot
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Black holes in LHC?
• Black holes could, in principle, be arbitrarily small. However,
according to standard General Relativity, there is no chance to prodce
black holes at the LHC, since conventional gravitational forces
between fundamental particles are too weak.
• There is no established quantum theory for gravitation (certainly
needed for small ones).
• Some quantum gravity proposals (involving more than 3 spacial
dimensions) make speculative predictions on production of black
holes in proton.proton collisions at LHC
• But in these models they are always unstable, both because of
Hawking radiation, and because they always can decay back into the
particles that produced them.
• (I’m of course brainwashed by the Cern/LHC Safety Assesment
Group, Ellis,Guidice,Mangano,Tkachev,Wiedemann, CERN-PHTH/2008-136)
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Cosmic rays:
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• have produced high energy proton-proton
collisions for billions of years.
• We are still here….
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LHC ENERGY
From Ellis et al: ”Review of the Safety of LHC Collisions””
CERN-PH-TH/2008-136
Preparing for this talk last Friday I looked at some
plots monitoring the magnet temperatures. I found…
LHC
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..and this
Geneva, 20 September 2008. During commissioning (without beam) of
the final LHC sector (sector 34) at high current for operation at 5 TeV, an
incident occurred at mid-day on Friday 19 September resulting in a large
helium leak into the tunnel. Preliminary investigations indicate that the
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most likely causeNormal
of the problem
was- aclick
faulty electrical
between two magnets, which probably melted at high current leading to
mechanical failure. CERN ’s strict safety regulations ensured that at no
time was there any risk to people.
A full investigation is underway, but it is already clear that the sector will
have to be warmed up for repairs to take place. This implies a minimum
of two months down time for LHC operation. For the same fault, not
uncommon in a normally conducting machine, the repair time would be a
matter of days.
Further details will be made available as soon as they are known.
ATLAS in Bergen
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• SiliconNormal
detectorstext
and-detector
the track reconstruction system.
• Simulation studies of the physics potential.
• Development work for the detector control
systems and online monitoring.
• The daily running of the experiment
• Study the data
ATLAS
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SCT
The SemiConductor Tracker (SCT)
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Some numbers:
(Atlas in Bergen)
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• 10 master
students text
already
completed
ATLASrelated theses
• 3 completed PhDs
• 4 active doctoral students
• 5 active master students
• 2 postdocs (Burgess, Sandaker)
• 3 professors (Eigen,Lipniacka,Stugu)
• ATLAS was about 50% of the experimental
group’s activities; Now it is about 80% (Theory
research of Per Osland not included in above figures)
Detector control system (DCS) and
online monitoring
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The development of monitoring tools represents a large
amount of work!
The running of ATLAS:
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One shift pr. day (on average) must be taken by a Bergen
person.
Data quality shifts: Good for students!
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SCT, ROS and ID global monitoring shifters
Heidi ’supervises’ Katarina and Ole (from Oslo)
Many Bergen people are involved in the
development of monotoring tasks. Everybody
will take shifts during ATLAS operation
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• Developers: Heidi Sandaker, Arshak
Tonyan, Alex Kastanas...
• Bergen shifts are organised by Therese
Sjursen. She and two new master students
are currently at Cern for shifts ( Keep detector
alive and study cosmic rays)
What do the ATLAS events look like?
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Quark ’jets’
in reality
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H →ZZ→μμee
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Event with Supersymmetric Particles
Six jets of particles,
Two muons with momenta in the transverse direction of 74 and 84 GeV. They are visible in
the side view going to the left, but not in the end view (because the exited the detector in the
forward direction). They have opposite signs.
Missing energy in the direction transverse to the beam of 283 GeV. (Dark matter???)
Except for a few scenarios, the identification
of Higgses and/or Supersymmetry or other
new physics will be a painstaking process.
• Events from
new physics
likely toto
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rare.
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• Missing energy signals requires careful calibration and
proper accounting for escaping standard particles like
neutrinos.
• Must focus on abundant and known processes in the
beginning.
– B-mesons (quark-antiquark pairs where one of the
quarks is a b-quark)
– Z,W bosons
– top quarks
• Results from such studies will also give new insights that
can be published. (In particular about strange B-mesons
and the top quark)
Physics activities (present and planned
for the near future)
• B-physics with muons.
– In particular
Bs mesons
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• adds to the wealth of data collected by BaBaR on ’ordinary’ Bmesons, vital to understand CP-violation.
• Physics involving the tau lepton:
– Identification procedures (more difficult than muons
and electrons, but a number of interesting signatures
involve the tau lepton.
– Z→τ τ ( ’Light’ Higgses also decay to two taus)
– W→τν (SUSY also often have taus and missing energy)
– Top quark decays (these ’always’ involve W mesons
and b-quarks (i.e. B-mesons). top quark decays also
will produce the Standard Model physics signals with
the highest energies
Verification of track fitting procedures
by reconstructing mass of the J/psi
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τ
Maren Ugland, Master
thesis, (main study was to
reconstruct Bs mesons)
SUSY signals with taus:
(Simulation study by Therese Sjursen)
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Conclusion
• After a very promising start of the LHC, we are now set back a
few months due to a quench.
– Winter shutdown: Beams back in 2009.
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• Bergen takes an active part in the running of ATLAS, and
will do so also in the future.
• Aim is to contribute very actively to studies related to
muon and tau identification, with physics goals within Bphysics and searches for supersymmetric events and higgs
particles decaying to these particles.
• first thing: find and understand standard processes such as
–
–
–
–
J/psi -> μ+ μ –
B-decays
Z -> μ+ μ – , τ+ τ –
top quak decays