expectations of the first 2 years of lhc operations a.rozanov itep winter school of physics february...

A.Rozanov ITEP Winter School of Physics February 2006 1

Expectations of the first 2 years of LHC operations

Outline

• LHC

• Experiments

• SM physics

• Higgs

• SUSY

• Exotics



LHC uses existing CERN complex

• LHC is being built in the existing tunnel previously used for LEP– Circumference = 27 km

• Radius = 4.3 km• Use existing accelerators as injection

system• Since the radius of the ring is fixed, one

has to use very high-field magnets to reach high energy: 7 TeV p + 7 TeV p– fill as large a fraction as possible of

the circumference with magnets• 2/3 of ring with dipole magnets• quadropole magnets for focusing• straight sections for acceleration,

detectors• beam injection and dump

systems



CERN LHC tunnel

Lake

Ring of 27 km



Four major “experiments”

• ATLAS and CMS are “general-purpose” detectors optimised for exploring new physics in pp collisions

• LHCb is a specialized detector for B-physics studies

• ALICE is a specialized detector for heavy-ion physics

Major experiments


Expectations of the first 2 years of LHC operationsMajor experiments


Expectations of the first 2 years of LHC operationsEnergy and intensity

Need very high energy and very high intensity to maximize the sensitivity to new physics

• Energy needed to produce new massive particles

• Intensity needed because: some of the processes that one would like to study are very rare and because the fraction of partons with high momentum is small



Need very high-field “two-in-one” magnets

• 15-meter long super-conducting magnet coils cooled to 1.9 K with super-fluid Helium

– Field > 8 Tesla

• Compared to 45 Tesla at Tevatron and HERA

• As LHC collides beams of protons (not proton-antiproton as at Tevatron), one needs double magnets



Luminosity

Want highest luminosity possible: Rate ×L

• Access to rare high momentum partons and to low cross-section processes

• Beam parameters at LHC

– N 1011 ; xy 15 m in ATLAS and CMS; f = 11 kHz; k = 2808



• From virtual reality to real reality



Some LHC parameters

• Centre-of-mass energy s = 14 TeV for proton-proton collisions

• c.f. 2 TeV at Tevatron collider

• Equivalent to ~100,000 TeV or 1017 eV fixed-target beam energy s = 6 TeV per nucleon for Pb-Pb collisions

• Luminosity

– L = 1034 cm-2s-1 for proton-proton collisions in ATLAS and CMS

• c.f. L = 1032 cm-2s-1 at Tevatron

– L = 1027 cm-2s-1 for Pb-Pb collisions (in ALICE and also ATLAS+CMS)

• Note: enormous energy stored in proton beams

– 331 MJ/beam (enough to melt 500 kg of copper)

• Rely on safe ejection of beams into beam dumps at end of coast

• Most of the protons used up in beam-beam collisions in experimental areas



More LHC Parameters

• Protons grouped in bunches – Bunch spacing is 25 ns in time (i.e. 7.5 meters in distance)

• Bunch-crossing rate is 40 MHz• Start-up with 75 ns bunch spacing

• Total proton-proton cross-section ~ 100 mb– Interaction rate at nominal L = 1034 cm-2s-1 is R ~ 109 Hz

• On average ~ 23 interactions per bunch crossing – Pile-up complicates analysis of what happened in the

interaction of interest– LHCb uses L = 2×1032 cm-2s-1 to maximize rate of single-interaction

bunch crossings• Different focussing of beams to ATLAS and CMS

– Rate much lower for heavy-ion case• R ~ 104 Hz for Pb-Pb (low luminosity)

– Much less than bunch-crossing rate (BC period = 125 ns for Pb ions)


Expectations of the first 2 years of LHC operationsCryodipole overview


Expectations of the first 2 years of LHC operationsCryomagnets interconnect in the tunnel



Optimistic LHC startup scenario

• End of dipole installation February 2007

• First collisions – July 2007

• 43+43 bunches, gradually increase up to L= 1032 cm-2 s-1

• Pilot run : 936+936 bunches of 75 ns, increase up to L= 1033 cm-2 s-1

• Switch to 25 ns with 2808+2808 bunches

• Collect in pilot 2007 run ~10-100 pb-1 - calibration

• 2-3 months shutdown ??

• In 2008 run with 2808+2808 bunches of 25 ns

• Gradual increase of luminosity up to L= 2 x 1033 cm-2 s-1

• Collect in the first physics run of ~7 months in 2008 ~10 fb-1



Luminosity assumptions

• First two years of LHC physics data taking 2008-2009

• Optimistic scenario: ATLAS and CMS get each 30 fb-1

• Moderate scenario: ATLAS+CMS get together 30 fb-1

• Pessimistic scenario: ATLAS+CMS get each 10 fb-1



Usual wisdom of 1980s:

• LHC accelerator is straight forward

• LHC experiments are challenging

• What is the status of detectors ?



ALICE



ALICE end of 2005



ALICE TPC



LHCb

• Detector to one side of the collision point

• Use large rate of high-momentum beauty hadrons in forward direction

• see lecture of N.Harnew this school



LHCb end of 2005



CMS



CMS November 2005



ATLAS



ATLAS November 2005


Expectations of the first 2 years of LHC operationsCaverne ATLASCaverne ATLAS



Inner DetectorPixels : silicon hybrid pixelsSCT : silicon stripsTRT : straw tubes traker with transition radiation function

solenoidal magnet(2T)



Silicon Tracking Detectors

• Silicon tracking detectors are reverse-biased junctions– The passage of a charged

particle produces electron-hole pairs that are collected on strips or pixels

• Since the detectors are thin, the charge collection time is small

– Signal processing is used to achieve a time resolution better than 25 ns

• Very large numbers of detector channels possible thanks to micro-electronics technology

– Of the order of 107 sensor elements sampled at 40 MHz bunch-crossing rate!



>80 millions of pixelsRadiation hard>80 millions of pixelsRadiation hard

1 pixel :50x400 μm²1 pixel :50x400 μm²

1 module :47232 pixels~62 cm²

1 module :47232 pixels~62 cm²

vertex and Impact parameters of charged particule

1,40 m1,40 m24 cm24 cm

3 discs

3 barrels



Pixels ATLAS

• Pixels 50 µm x 400 µm• R=5 cm , 9 cm and 12 cm

Destaged pixel layer



Pixel barrel ladders with 13 modules



Pixel disks of C-side



Barrel and one end-cap ready.

Introduction of layer B3

ATLAS Barrel Si Strips



Un bouchon du SCT

SCT endcap


Expectations of the first 2 years of LHC operations TRT barrel

Barrel and one end-cap ready.



Straw Tubes

• Straw-tube detectors achieve short charge collection time because of the small maximum drift distance (radius of straw)

– The detectors consist of an anode wire running along the centre of a conducting straw

– Electrons drift towards the wire and are amplified in the strong field near the wire surface

• ATLAS uses straw tubes for the outer part of its tracker

– Foil or foam is used to produce transition radiation X-rays from electrons

• Produce high energy hits in straws used in electron identification

• Full detector contains ~400k channels– Time of arrival of charge

measured and used to reconstruct tracks



“Exposure time” of one BC (25 ns)

Muons colouredin yellow



Additional material



Commissioning Detector Scenario

Initial ATLAS in DC1 layout (2 barrel pixels, 2 pixel disks, no TRT C-wheels)

• default inefficiency from the start-up 3% pixels, 2% chips, 1% modules

• b-layer inefficiency 1% chips, 0.5% modules

• but systematic error big, 2/4 % inefficiencies to be considered

• Pixel-SCT alignment after 3 months σRφ=20 μm , σz=60 μm

• Pixel-SCT alignment after 6 months σRφ=10 μm , σz=30 μm

• Pixel-SCT alignment after 9 months σRφ= 5 μm , σz=15 μm

• Direct simulations needed to prove the feasibility of this scenario

expectations of the first 2 years of lhc operations a.rozanov itep winter school of physics february...

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