Expectations of the first 2 years of LHC operations A.Rozanov ITEP Winter School of Physics February...
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![Page 1: Expectations of the first 2 years of LHC operations A.Rozanov ITEP Winter School of Physics February 2006 1 Outline LHC Experiments SM physics Higgs SUSY.](https://reader037.fdocuments.net/reader037/viewer/2022110206/56649f575503460f94c7bbb9/html5/thumbnails/1.jpg)
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
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A.Rozanov ITEP Winter School of Physics February 2006 2
Expectations of the first 2 years of LHC operations
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
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A.Rozanov ITEP Winter School of Physics February 2006 3
Expectations of the first 2 years of LHC operations
CERN LHC tunnel
Lake
Ring of 27 km
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A.Rozanov ITEP Winter School of Physics February 2006 4
Expectations of the first 2 years of LHC operations
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
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A.Rozanov ITEP Winter School of Physics February 2006 5
Expectations of the first 2 years of LHC operationsMajor experiments
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A.Rozanov ITEP Winter School of Physics February 2006 6
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
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A.Rozanov ITEP Winter School of Physics February 2006 7
Expectations of the first 2 years of LHC operations
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
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A.Rozanov ITEP Winter School of Physics February 2006 8
Expectations of the first 2 years of LHC operations
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
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A.Rozanov ITEP Winter School of Physics February 2006 9
Expectations of the first 2 years of LHC operations
• From virtual reality to real reality
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A.Rozanov ITEP Winter School of Physics February 2006 10
Expectations of the first 2 years of LHC operations
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
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A.Rozanov ITEP Winter School of Physics February 2006 11
Expectations of the first 2 years of LHC operations
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)
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A.Rozanov ITEP Winter School of Physics February 2006 12
Expectations of the first 2 years of LHC operations
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A.Rozanov ITEP Winter School of Physics February 2006 13
Expectations of the first 2 years of LHC operationsCryodipole overview
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A.Rozanov ITEP Winter School of Physics February 2006 14
Expectations of the first 2 years of LHC operationsCryomagnets interconnect in the tunnel
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A.Rozanov ITEP Winter School of Physics February 2006 15
Expectations of the first 2 years of LHC operations
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A.Rozanov ITEP Winter School of Physics February 2006 16
Expectations of the first 2 years of LHC operations
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
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A.Rozanov ITEP Winter School of Physics February 2006 17
Expectations of the first 2 years of LHC operations
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
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A.Rozanov ITEP Winter School of Physics February 2006 18
Expectations of the first 2 years of LHC operations
Usual wisdom of 1980s:
• LHC accelerator is straight forward
• LHC experiments are challenging
• What is the status of detectors ?
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A.Rozanov ITEP Winter School of Physics February 2006 19
Expectations of the first 2 years of LHC operations
ALICE
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A.Rozanov ITEP Winter School of Physics February 2006 20
Expectations of the first 2 years of LHC operations
ALICE end of 2005
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A.Rozanov ITEP Winter School of Physics February 2006 21
Expectations of the first 2 years of LHC operations
ALICE TPC
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A.Rozanov ITEP Winter School of Physics February 2006 22
Expectations of the first 2 years of LHC operations
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
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A.Rozanov ITEP Winter School of Physics February 2006 23
Expectations of the first 2 years of LHC operations
LHCb end of 2005
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A.Rozanov ITEP Winter School of Physics February 2006 24
Expectations of the first 2 years of LHC operations
CMS
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A.Rozanov ITEP Winter School of Physics February 2006 25
Expectations of the first 2 years of LHC operations
CMS November 2005
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A.Rozanov ITEP Winter School of Physics February 2006 26
Expectations of the first 2 years of LHC operations
ATLAS
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A.Rozanov ITEP Winter School of Physics February 2006 27
Expectations of the first 2 years of LHC operations
ATLAS November 2005
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A.Rozanov ITEP Winter School of Physics February 2006 28
Expectations of the first 2 years of LHC operationsCaverne ATLASCaverne ATLAS
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A.Rozanov ITEP Winter School of Physics February 2006 29
Expectations of the first 2 years of LHC operations
Inner DetectorPixels : silicon hybrid pixelsSCT : silicon stripsTRT : straw tubes traker with transition radiation function
solenoidal magnet(2T)
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A.Rozanov ITEP Winter School of Physics February 2006 30
Expectations of the first 2 years of LHC operations
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!
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A.Rozanov ITEP Winter School of Physics February 2006 31
Expectations of the first 2 years of LHC operations
>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
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A.Rozanov ITEP Winter School of Physics February 2006 32
Expectations of the first 2 years of LHC operations
Pixels ATLAS
• Pixels 50 µm x 400 µm• R=5 cm , 9 cm and 12 cm
Destaged pixel layer
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A.Rozanov ITEP Winter School of Physics February 2006 33
Expectations of the first 2 years of LHC operations
Pixel barrel ladders with 13 modules
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A.Rozanov ITEP Winter School of Physics February 2006 34
Expectations of the first 2 years of LHC operations
Pixel disks of C-side
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A.Rozanov ITEP Winter School of Physics February 2006 35
Expectations of the first 2 years of LHC operations
Barrel and one end-cap ready.
Introduction of layer B3
ATLAS Barrel Si Strips
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A.Rozanov ITEP Winter School of Physics February 2006 36
Expectations of the first 2 years of LHC operations
Un bouchon du SCT
SCT endcap
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A.Rozanov ITEP Winter School of Physics February 2006 37
Expectations of the first 2 years of LHC operations TRT barrel
Barrel and one end-cap ready.
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A.Rozanov ITEP Winter School of Physics February 2006 38
Expectations of the first 2 years of LHC operations
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
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A.Rozanov ITEP Winter School of Physics February 2006 39
Expectations of the first 2 years of LHC operations
“Exposure time” of one BC (25 ns)
Muons colouredin yellow
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Expectations of the first 2 years of LHC operations
Additional material
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A.Rozanov ITEP Winter School of Physics February 2006 41
Expectations of the first 2 years of LHC operations
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