status of beam halo/gas simulation
DESCRIPTION
Status of Beam Halo/Gas Simulation. A.Stradling(Wisconsin) P. Steinberg(BNL) G. Usai (Chicago) Standard Model Group 6 December 2006. 1. Intro. Review of the practical issues surrounding beam halo and beam gas Simulation progress Initial plots of unweighted beam halo events. 2. - PowerPoint PPT PresentationTRANSCRIPT
Status of Beam Halo/Gas Simulation
Status of Beam Halo/Gas Simulation
A.Stradling(Wisconsin) P. Steinberg(BNL) G. Usai (Chicago)
Standard Model Group
6 December 2006
A.Stradling(Wisconsin) P. Steinberg(BNL) G. Usai (Chicago)
Standard Model Group
6 December 2006
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IntroIntro
Review of the practical issues surrounding beam halo and beam gas
Simulation progress
Initial plots of unweighted beam halo events
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Beam HaloBeam Halo
The LHC’s contribution to background
Results from proton losses, including:
Gases and impurities in the beampipe
Collimator impacts (less important)
Beam configuration and optics are taken into account
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Beam Halo DetailsBeam Halo Details
These effects are simulated in the IHEP MARS package
• I. Azhgirey, I. Baishev, K.M. Potter et al. Methodical Study of the Machine Induced Background in the IR8 of LHC. CERN LHC Project Note 258, Geneva, 2001;• I. Azhgirey, I. Baishev, K.M. Potter, V. Talanov, Cascade simulations for the machine induced background study in the IR1 of the LHC. CERN LHC Project Note 324, Geneva, 2003.
Particles were generated to represent one second of run, totaling 8.2 M particles
Particles are produced all along the accelerator, but most of those we see are produced in the inner triplet magnets just before the cavern
~10x more hadrons than muons, concentrated at a smaller radius
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Beam Halo FilesBeam Halo Files
The resulting file is specific to:
ATLAS, Side A (Beam 1), Optics v6.4, and possibly outdated collimator configuration
Design lumi (14 TeV, β* of 0.5 m and beam current of 0.54 A)
It includes nothing after the “scoring plane”, where the experimental volume is defined as beginning. This plane lies at 23000 mm from the IP, between the concrete wall and the beam shields
• /afs/cern.ch/atlas/project/MachineBackgrounds/Sam
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Beam Halo Scaling (1)Beam Halo Scaling (1)
Many of these previous assumptions have changed
LHC Optics version = 6.5, β* of 10 m or worse for initial runs
Collimators are still being finalized
Beam gas distributions account only for adsorbed gases (no other junk or impurities)
It should also be borne in mind that the LHC is not completely symmetric, and there will be differences in intensity between Beams 1 and 2
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Beam Halo Scaling (2)Beam Halo Scaling (2)
Most of these are relatively simple to handle:
Scaling for changes in beam intensity, β*, optics, beam gas density, beam asymmetries and other similar effects is linear - we just change the number of particles that come in at a time
We have 1.8 M particles per second total for 40 M bunch crossings - most bunch crossings will have little or no beam halo
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Beam Halo Scaling, 900 GeVBeam Halo Scaling, 900 GeV
The 900 GeV run is a problem, however - it requires a redo of the MARS simulation
Simple scaling is impossible - the differences lie not in the particle multiplicity, but in the produced particle energies and species proportions
The machine group is (obviously) fairly occupied now, and taking another crack at the simulation effort will take time
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Beam Halo Work in ProgressBeam Halo Work in Progress
Giulio Usai is working on getting the events unweighted and translated into HepMC format for simulation
Collaboration with the G4 community to get the odd detector volume issues (like having a vertex at 23 m) worked out
MC group is excited to have this in their production system
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Beam Halo Particles (1)Beam Halo Particles (1)
•Kinetic energy of beam halo particles
MeV
Ratio - Weighted/Unweighted
Weighted
Unweighted
Beam Halo Particles (2)Beam Halo Particles (2)
•Initial radius of halo particles on the scoring plane
Ratio - Weighted/Unweighted
Weighted
Unweighted
cm
Beam Halo Particles (3)Beam Halo Particles (3)
•PDG ID histogram of halo particles
1:1
Ratio - Weighted/Unweighted
WeightedUnweighted
Beam Gas GenerationBeam Gas Generation
HIJING (A+A, p+A generator) in Athena
Simulation of various gas species in the beampipe of the detector
Starting simple - will eventually make adjustments for gas density profiles and etc.
Generated events are vertex-shifted from 0,0,0 to other locations during simulation
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Beam Gas QuestionsBeam Gas Questions
The accelerator group did their work assuming that the only important gases in the beampipe were H2, CO2, CO, CH4
Other things may be present (N, Ti, V, Zr from the getter, Be from the beampipe, etc) - what will they look like? Will there be any significant presence?
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Timing Complications
Timing Complications
40 MHz bunch crossings give us a τ of 25 ns
25 ns at c translates to 7.5 m
Lots of bunches in flight
Timing the beam halo and beam gas relative to the physics event is crucial
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Beam Halo TimingBeam Halo TimingThe beam halo comes in with the same timing as the bunches themselves
Offsets of 25 ns
Use digitization to overlay beam halo events onto simulated events, as with pileup events for realistic TRT, LAr and Muon simulation
Differences - we will need to open up the number of bunch crossings to 3 on each side
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Beam Gas TimingBeam Gas Timing
More challenging - does not often happen in sync with the event (can be anywhere in the pipe)
Time offsets in the digitization need to be tunable (but are easy to calculate from the vertex position) - I have not yet determined whether this has been implemented in digi yet. Suggestions and recipes welcome.
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NextNext
Get good jobOptions for generation/simulation of the beam gas and beam halo, validate some output
Examine parameters (scaling of beam halo, proportions of beam gas components)
Pass to ProdSys
Start analyses of the effects of beam gas and beam halo on MinBias event triggering
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