Realistic MC Needs/Status Mike Hildreth Université de Notre Dame du Lac Representing the Full Simulation Group 10 September, 2010 Mike Hildreth – XC Meeting

Mike Hildreth – XC Meeting Opening Statements Definition of “Realistic MC”: IOV-based (= run-number based) uses DB to control live/dead channels, calibrations, etc. Realistic “Conditions” beam spot in correct position for a given run pileup distribution matches “Realistic” Detector Geometry mis-alignments/smeared geometry matching the real detector NOT: realistic trigger simulation L1 Triggers are not in the release… One proposal: a set of “representative” runs should be decided upon by the Physics groups to give appropriate sampling of run-dependent epochs of detector conditions 10 September, 2010 Mike Hildreth – XC Meeting

Status of Necessary Pieces (I) Run-number setting (√ ) Simulation/Framework allows the specification of arbitrary lists of runs, each with a probability weight, to assign run numbers for Generation set before SIM step Run-number dependent code in Sim Packages (√) All subdetectors have code that reads conditions from the DB for simulation of masked/dead channels can easily be made run-dependent by assigning IOVs Beam Spot from DB (X) under discussion with experts to evaluate time scale not complicated, could be done quickly must be set in SIM step, matching Run number 10 September, 2010 Mike Hildreth – XC Meeting

Status of Necessary Pieces (II) Arbitrary Pileup Distributions (√ ) currently, distributions must be put in “by hand” either a root file or a list of numbers reading from the DB would obviously be better another relatively quick project actual distributions will have to be measured by someone correspondence number of vertices with true number of interactions, for example (See Charles’ work) Dedicated pileup studies needed 10 September, 2010 Mike Hildreth – XC Meeting

Status of Necessary Pieces (III) Geometry “Large” movements, such as mis-centering of pixels with respect to Silicon Tracker, beampipe, (Ecal?) should be put in Geant geometry would be new default Geometry DB would allow use of new and old samples does “smeared” tracker geometry represent our current understanding of alignment accuracy? For now: sidestep more complicated issue of making Data and MC tracker geometries ~ the same. Not relevant for pure MC pileup+signal samples. (progress on that: Strategy of absorbing local shifts of sensors in digitization can work with some modifications to Geant geometry evaluating difficulty of these modifications) will do this anyway 10 September, 2010 Mike Hildreth – XC Meeting

Mike Hildreth – XC Meeting Realistic Conditions A couple of items missing from previous discussion: Beam Backgrounds may be time-dependent should be taken directly from data if necessary we don’t know what the impacts are on analysis yet (personal statement: way too hard to simulate) Asynchronous HPD noise in Hcal Request (plan?) for Hcal to use data in simulation as default Thermal neutrons in cavern simulation plan evolving; may be difficult to get right All these may be easiest using DataMixer 10 September, 2010 Mike Hildreth – XC Meeting

Mike Hildreth – XC Meeting Philosophy Full Simulation should include all details that are relevant for physics analysis accurate representation of interaction of particles with detector tails on resolution distributions from all known effects to the extent that these tails are important… including noise, pileup, geometry, sensitivity, etc. just because we can make the simulation perfect doesn’t mean we have to currently victims of our own hard work things look “too good”, analysts will expect perfection in reality, it will never be perfect some a posteriori corrections will always be necessary Goal: reduce size of necessary corrections and the associated errors so that they have minimal impact on physics implies improvements to Simulation if needed needs to be “good enough” 10 September, 2010 Mike Hildreth – XC Meeting

Alternate example: DØ Approach Entirely Run-dependent MC All backgrounds, pileup, detector noise simulated by overlay of zerobias events from data (one zerobias per hard-scatter MC event) luminosity distribution roughly matches data samples re-weighting necessary Dead Channels in tracker MC hits killed using information stored in data overlay events no DB lookup necessary MC production does lag data significant? Does not seem to have hurt physics output too much Strategy isn’t optimal too few zerobias events used need better sampling of high-luminosity ZB need to be centrally processed in an efficient manner 10 September, 2010 Mike Hildreth – XC Meeting

Mike Hildreth – XC Meeting Comments on DataMixer Some attractive attributes: Backgrounds, multiple interactions, detector noise, etc. are automatically “correct” if samples are properly formulated no incorrect physics model of low-pT interactions taken directly from Nature Overlay is done at Digi level, so can be re-done without excessive computation But: it is the ultimate run-dependent MC beamspots must match between simulated and overlay events zerobias samples will need to be constructed before MC production representing a given time period can start some care necessary to make sure IOVs are correct for MC 10 September, 2010 Mike Hildreth – XC Meeting

Back to Run-Dependent MC Do we need it? Questions to answer: (not a complete list) Do we have “epochs” of dramatically different detector performance that have impacts on physics? either large correction factors or different simulation How much does beam spot motion affect tracking efficiency? tracking errors  B-tagging efficiency? NB: beam spot motion cannot be re-done at Digi time What are the effects of beam backgrounds on physics, and do they vary in time in a way that should be modeled? same for neutrons in cavern Are there significant differences in pileup distributions between Data and MC that we cannot simulate by modifying MC parameters? 10 September, 2010 Mike Hildreth – XC Meeting

Back to Run-Dependent MC Do we need it? Will need to explore both weighting and Run-Dependent options to decide which is necessary implies efforts from Physics, POGs, DPGs to study issues close coordination with simulation effort In particular, we now have sufficient quantities of events with large numbers of interactions in a single beam crossing need to have matching MC samples to make thorough comparison studies: Can we simulate pileup, or should we use data instead? need some sort of Pileup Study Group to coordinate again, close coordination between Physics and Simulation/Generators 10 September, 2010 Mike Hildreth – XC Meeting

Mike Hildreth – XC Meeting Conclusions MC will never be perfect Reweighting tools will be necessary and should be centrally developed Studies needed to determine how perfect a MC is necessary quite broad in scope pileup efficiency epochs beamspot effects need central coordination Technically, Run-Dependent MC is possible ~now some small updates needed validation needed 10 September, 2010 Mike Hildreth – XC Meeting