Summary of Physics Analysis
Perspectives and Detector
Performance Interests
SLUO LHC
Workshop SLAC
July 16-17,2009
Peter Loch
University of Arizona
Tucson, Arizona
USA
This Talk
2
P. Loch
U of Arizona
July 17, 2009
Scope
Some input from what I heard yesterday
West Coast physics analysis interest
Jason, Anna,…
German analysis facility at DESY
Wolfgang
More emphasis on first data performance evaluation
Underlying event & pile-up
Fast access to systematics of hadronic final state energy scales
Jets, taus, missing Et
Some focus on possible analysis facility role of SLAC
Resources and critical mass
Meetings & educational efforts
Biased views
“Small” university group experience
Arizona is locally below critical mass for most studies of interest
But excellent and long standing connections to CERN and ATLAS (PL)
SLUO LHC
Workshop SLAC
July 16-17,2009
Personal connections to CERN > 20 years
Arizona is ATLAS member since ~15 years
Well established collaborations with INFN Pisa, INFN Milan, MPI Munich, CERN,
ATLAS Canada,…
Sometimes limited to intellectual input role so far!
Longstanding (continuing) and short-lived (need-driven) collaborations
Some personal connections to theorists/phenomenologists
West Coast (SLAC – Peskin, Oregon – Soper, Washington – S.D. Ellis), FNAL/CERN
(Skands, Mrenna), BNL (Paige), LPTHE/Paris VI (Salam/Cacciari),…
Not limited to client role!
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Critical Mass & Resources
What does critical mass
mean?
Sufficient local expertise
around the corner
Detector, software, physics
analysis
Peers facing similar problems
and/or challenges
Low communication thresholds
for new graduate students etc.
Common group interests
Significant number of experts
and soon-to-be experts work
closely together on related
topics
E.g., Ariel’s Jet/MET/b-tag group
SLUO LHC
Workshop SLAC
July 16-17,2009
Fast senior and peer review of
new ideas and general
progress
Less time lost with “wrong
approaches”
Willingness to share new ideas
at early stages and “help out”
Collaborative work environment
Usually not available to
university groups
Some exceptions!
P. Loch
U of Arizona
July 17, 2009
(Computing) Resources
Locally available computing
CPU power, storage
Often limited for university
groups
Historically no or little
dedicated funding for
computing requested
“Hardware group” tag with
funding agents
Different visions on group
contribution to ATLAS
Distributed computing
resources often deemed
sufficient
Grid etc. – see next slide!
Funding crunch at state
level does not help
Recently implemented new
charges to groups at state
universities
Cooling & power for larger
systems
Not so much an issue for
Arizona so far!
Loss of “free” operation
support
Loss of system manager may
become a problem for Arizona
Physics Analysis Resources
4
P. Loch
U of Arizona
July 17, 2009
SLUO LHC
Workshop SLAC
July 16-17,2009
ATLAS Computing
Model for Physics
Analysis
(long term)
Graph from Jim Cochran, this meeting
5
Physics Analysis Aspects
P. Loch
U of Arizona
July 17, 2009
Mostly needs critical mass
Intellectual guidance, exchange and progress review
essential
Assuming we want to keep significant analysis activity in the
US/at the West Coast
I think we should (entry point for new graduate students, already
significant investments,…)!
Resources provided by ATLAS distributed computing
Data extraction, compression by official production system…
Managed by ATLAS physics groups
…or on Tier2 “around the corner” for different filters
Reflecting local (US ATLAS etc.) group interest
SLUO LHC
Workshop SLAC
July 16-17,2009
Local refined and final analysis needs much less resources
DnPD as simple as root tuples
Tier3g cluster, desktop, laptop can be sufficient depending on
analysis
May have somewhat relaxed time scale
Not always true, in particular for early data (competition with
CMS, conferences, graduation deadlines,…)
But what about performance?
On the Side…
6
P. Loch
U of Arizona
July 17, 2009
Tier3 in US ATLAS
Tier3’s are not a US ATLAS resource
They are a local group resource!
US ATLAS spends money to help with setting up Tier3’s…
Help with dataset subscriptions, some software support (my understanding)…
Hardware and configuration recommendations to simplify support role
…but they are not running it for you!
Tier2’s or larger groups may offer to host smaller group’s computing
At a price: $ or fractional use of equipment by host are discussed
Helpful if no or little local computing support
Contractual limitations in base programs may require funding agent
agreements/permissions
Requests for American Recovery & Reinvestment Act (ARRA
2009) funds by universities
Not only computing
SLUO LHC
Workshop SLAC
July 16-17,2009
Arizona: ~25% requested for computing, rest replacement of obsolete
electronic lab equipment
Not a direct competition to US ATLAS Tier1/2 funding
Invitation to apply fully supported by US ATLAS – including per group
recommendations for scale of computing hardware to acquire!
Thanks to Jim!
Unique chance for university groups to get ready for analysis of first data!
Performance Tasks for First Data
7
Need flat jet response rather quickly
P. Loch
U of Arizona
July 17, 2009
1.6  pT  2.4 GeV
Basis for first physics analyses
E.g., inclusive jet cross-section
Systematics can dominate total error already
at 10-200 pb-1
Depending on final state, kinematic range
considered, fiducial cuts,…
single   simulations
  extracted from
minbias
Requires understanding of hadronic
response (Jason, Ariel,…)
Minimum bias
Single charged hadron response of calorimeter
Pile-up with tracks and clusters
Di-jets
Underlying event with tracks and clusters
Direction dependent response corrections

Prompt photons
SLUO LHC
Workshop SLAC
July 16-17,2009
Absolute scale by balancing, missing Et
projection fraction, etc.
Initial focus on simple approaches
Least number of algorithms
Least numerical complexity
Realistic systematic error evaluation
Conservative ok for first data!
But also try new or alternative
approaches!
(plots from CERN-OPEN-2008-020)
jet
calo
R

calo signals
ptcalo  pt
pt
pt
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P. Loch
U of Arizona
July 17, 2009
JES Systematics (Example)
figures from K. Perez,
Columbia U.
Systematic error evaluations for JES
Requires understanding of effect of calorimeter signal choice in
real data
Towers, noise suppressed towers, topological cell clusters
Corresponding algorithm tuning
SLUO LHC
Workshop SLAC
July 16-17,2009
Noise selection criteria, mostly
Need to consider at least two different final states
Can be di-jets, photon+jet(s), single track response
May need repeated partly or full event re-reconstruction
Need calorimeter cells to study different signals
Dataset with most details – ESD or PerfDPD
Considerations for MC based calibrations
Study change of response from calibrated (jet) signals for
different hadronic shower models
Determined with one model, applied to simulated signals from other
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JES Systematics Resource Needs (1)
Iterative reconstruction with quick turn-around
Large (safe) statistics to focus on systematic effects
Can be several 100k of ESD events each for different final state patterns
(photon triggers, jet triggers, MET triggers, combinations…)
>1M for minimum bias!
CPU ~1 min/event, disk size ~1.5 Mbytes/event
Need to save at least 2 iterations
Change configurations from default reconstruction
Run on cells from default reconstruction
Need for cell signal re-reconstruction (RAW data) not obvious in jet context
Maintenance of configurations
Book-keeping
Potentially several rounds to explore parameter space(s)
Semi-private production scenarios feeding back to official reconstruction
Highly efficient access to significant resources
Speed is an issue
SLUO LHC
Workshop SLAC
July 16-17,2009
Maybe not quite within the 24-48 hours gap between data taking and
reconstruction, but close!
Local CPU and disk space
Cannot afford dependence on grid efficiency
Need clear tracebacks in case of problems
Reports/output files lost on the grid?
Database access
Latest conditions data need to be available locally
E.g., from CAF etc.
P. Loch
U of Arizona
July 17, 2009
JES Systematics Resource Needs (2)
10
P. Loch
U of Arizona
July 17, 2009
Changing hadronic shower models in G4
Not clear that appropriate resources are available in
production system…
Especially after data taking starts!
… but important part of evaluation of systematic
uncertainties!
All jet calibrations will likely use some MC input – admittedly
with different sensitivities to hadronic shower models
Long term fully MC based?
Big project
SLUO LHC
Workshop SLAC
July 16-17,2009
Setting up full simulation, digitization, and reconstruction
chain
Severe disk space requirements if truth level detector
information is turned on (probably needed)
~2.4 MByte/event → 5.7 Mbyte/event, 8% increase in CPU
Dedicated resources preferred
Especially if not part of the standard ATLAS production
May not be taken on by other international institutions
Maybe MPI Munich – resource limitations?
Potential Role of SLAC
11
P. Loch
U of Arizona
July 17, 2009
Physics analysis
Clearly potential to provide critical mass as an analysis facility
Involvement of West Coast institutions required
See Wolfgang’s talk: existence of analysis facility needs community to fill with life
(providing expertise, attendants…)
Does not seem to be a big problem!
Physics interest for initial data well aligned at the West Coast
E.g., lots of common interests in various standard model hadronic final states,
minbias/pile-up, b-jets, W/Z production…
SLAC Tier2 can be resource to extract user data
Need some organization to handle request
Just the grid? Analysis groups? Individuals?
Extension of Tier2 to allow some interactive/local batch analysis capabilities?
Depends on final university Tier3 funding
Hosting computers for West Coast (and other) institutions?
Meeting and office space
SLUO LHC
Workshop SLAC
July 16-17,2009
Accommodate visitors working on specific aspects of an analysis
Provide meeting space for groups working on same/similar projects
Seems to be possible
Certainly desirable from my standpoint!
Some coordination with LBL?
Analysis facility extension to analysis center?
Going to SLAC instead of CERN saves $$$ for Arizona!
Reduce amount of time grad student spends at CERN by better preparation!
Role in Performance Evaluation
12
P. Loch
U of Arizona
July 17, 2009
Bigger task
Needs critical mass and significant resources
Would need dedicated computing resources for a unique contribution to ATLAS
Critical mass not a problem at all
C.f. Ariel’s group
SLAC meetings have been a significant source of new ideas in hadronic final state
reconstruction
Already two very productive US ATLAS Hadronic Final State Forums (2008 and 2009)
~30 attendants in very informal environment – low threshold for contributions & discussions
Want to continue with 1-2/year meetings
New convenership for HFSF – PL likes to continue to be involved in organization
Several concepts seriously worked on today were initially discussed at these meetings
Latest: data driven jet calibration, some jet substructure focus
Workshops have “real work” portion with educational perspective
First access to ATLAS jet simulations for some attendants, thanks to huge effort of Ariel’s group – Bill L.,
Stephanie M. etc. may remember!
Computing resources – a wish-list?
Dedicated task or project assigned computing resources need extension of Tier2
center
SLUO LHC
Workshop SLAC
July 16-17,2009
Don’t believe typical Tier3 computing does the job – very similar infrastructure and
maintenance levels as Tier2 may be required
Something for Richard to work on!
Resource needs not completely out of scope, even for re-reconstruction
But also needs organization, local batch management, disk space management, i.e. $$
SLAC seems to be able to provide infrastructure – in principle!
How can potential clients help? How much do funding agents allow us to help?
Personal opinion
I see a clear potential for a very significant contribution to the timely improvement
of the hadronic final state reconstruction in ATLAS with SLAC hosting the intellectual
and resource center for the related activities
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Educational Role
P. Loch
U of Arizona
July 17, 2009
Education beyond software tutorials (e.g., “ATLAS 101”
lectures)
I like DESY’s approach of “lower level” schools
E.g., focusing on detectors principles and reconstruction approaches,
selected (early) physics & performance topics
Mostly aim at new graduate students and post-docs
Also good source to refresh knowledge for senior collaborators
Good opportunity to capture knowledge within the collaboration
Original designers or other specialists can lecture on detector physics
in the context of the actual ATLAS designs
Preserve knowledge potentially lost due to people leaving ATLAS
Not everything is written down!
SLAC could help to organize and host such schools
Need to involve external experts to help with lectures
E.g., ATLAS calorimetry, some physics topics…
SLUO LHC
Workshop SLAC
July 16-17,2009
Probably need modest financial support
Not clear – I imagine mainly for the lecturers’ travel and some local
infrastructure
Scope of support? Possibly from US ATLAS project??
Helps grad students in smaller groups to get into ATLAS faster
Education beyond the local expertise useful for full physics analysis
Can improve and accelerate understanding of data
Knowledge of detector principles often weak point in analyses