Normal text - click to edit Large Hadron Collider og ATLAS @ CERN

Normal text - click to edit

Large Hadron Collider og ATLAS @ CERN


Part 1: LHC and LHC startup

Accelerator was proposed during the eighties

Project approved in 1994.



Some parameters

• 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

• 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?)



What happened on Sept 10th?

”It took an hour for the beam to make a full turn”

That’s just 27 km/h????….


• 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)

ATLAS was ready for first beam:

tertiarycollimators

140 m

BPTX175 m

Two LHC start-up scenarios:

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



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-PH-TH/2008-136)


Cosmic rays:

• have produced high energy proton-proton collisions for billions of years.

• We are still here….


From Ellis et al: ”Review of the Safety of LHC Collisions”” CERN-PH-TH/2008-136

LHC ENERGY


LHCPreparing for this talk last Friday I looked at some plots monitoring the magnet temperatures. I found…

This

..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 most likely cause of the problem was a faulty electrical connection 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

• Silicon detectors and detector modules for 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

SCT


The SemiConductor Tracker (SCT)


Some numbers:(Atlas in Bergen)

• 10 master students already completed ATLAS-related 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

The development of monitoring tools represents a large amount of work!


One shift pr. day (on average) must be taken by a Bergenperson.

Data quality shifts: Good for students!

The running of ATLAS:


Heidi ’supervises’ Katarina and Ole (from Oslo)

SCT, ROS and ID global monitoring shifters


Many Bergen people are involved in the development of monotoring tasks. Everybody

will take shifts during ATLAS operation

• 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?

Quark ’jets’ in reality


H →ZZ→μμee


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 are likely to be rare.• 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

• adds to the wealth of data collected by BaBaR on ’ordinary’ B-mesons, 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

Maren Ugland, Master thesis, (main study was to reconstruct Bs mesons)

τ


SUSY signals with taus:(Simulation study by Therese Sjursen)


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.

• 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 B-physics 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

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