The BaBar Mini

1
The BaBar Mini

• BaBar
• BaBars Data Formats
• Design of the Mini
• Mini Performance and Status
• The Mini in BaBars New Computing Model

2
BaBar

• 5-layer Si Vertex tracker
• 40-layer Drift Chamber
• DIRC Cherenkov Counter
• CsI Crystal Calorimeter
• Muon Chambers in Fe

3
BaBar Event Data Formats (2001)
4
A Gap in the Formats

• Raw, Reco, and ESD formats were not useful
• Reading any of these required staging many large
  files
• Time to read reco is comparable to running
  reconstruction
• A better persistent model was needed the Mini

Transient
Persistent


ESD Reco
Reco Track
Reco Track
ESD
Kalman Fit
Kalman Fit
Kalman Fit
Kalman Fit
DC Hit
Si Hit
Si Hit
DC Hit
Si Hit
Si Hit
Reco
Cluster
Cluster
Cluster
Cluster
Raw
digi
digi
digi
digi
digi
digi
digi
digi
5
Mini Design Goals

• Support detector studies
• Provide low-level detector details to support
  common tasks
• calibration, alignment, diagnostics, and
  algorithm development
• Provide Reconstruction Object interfaces
• Support detailed Physics analysis
• Provide access to the full reconstruction results
• EG track fits using Kaon mass for material
  effect predictions
• Allow users to follow calibration and alignment
  changes
• Allow detector-level systematic error checks
• Support a detailed event display
• Support the standard BaBar analysis interface
• Make it easy to access
• A disk size of 10KBytes/event or less
• A readback speed comparable to the Micro
• Allow customized output to fit specific needs

6
Mini Design

• Directly persist high-level reconstruction
  objects
• Tracks, calorimeter clusters, PID results,
• Indirectly persist lower-level reconstruction
  objects
• Track hits, calorimeter crystals,
• Store raw detector quantities (where possible)
• Digitization values, electronic channel id,
• Pack data to detector precision
• Aggressively filter detector noise
• Avoid overhead in low-level persistent classes
• Used fixed-size classes
• Align all data members
• No virtual functions in low-level classes

7
Mini Persistence

• Pack data from low-level classes into compact
  objects
• Persist the entire transient tree in one
  persistent object
• References become indices into embedded arrays
• Every event fully described by 13 persistent
  objects

Transient
Persistent

Reco Track
Kalman Fit
Kalman Fit
Si Hit
Si Hit
DC Hit
Cluster
Cluster
digi
digi
digi
digi
8
Data Packing

• Digitize floating point values
• Eg track fit parameters and covariance matrix
• Set packing precision at 1 of detector
  resolution
• Use locally flat, globally logarithmic packing
  algorithm
• Packing precision depends on the value being
  packed
• Supports histograms without binning artifacts
• Bitwise OR small fields into packed data words

• Track Impact parameter
• Pack into 17 bits
• longword alignment
• Pack parameter error into remaining 15 bits

9
Mini Analysis Interface

• The BaBar Analysis Framework is entrenched
• Huge investment in Physicist code after 3 years
  of operation
• The original design supported multiple data
  formats
• But it had evolved to depend on details of the
  Micro
• Providing Mini-compatibility was a major effort
• Changes in the base classes, new subclasses,
• The BaBar Mini Analysis interface is now working
• Physics (Micro) objects are built from native
  Mini objects
• Fully compatible with existing user code
• Provides access to most Mini-specific features
• Performance is comparable to reading the Micro

10
Mini Performance

• Data size (after ootidy gzip compression)
• 6.5 Kbytes per generic physics event
• 10 Kbytes per multi-hadron event (10 tracks)
• Readback speed
• 20 mSec per generic event (1GHz pentium III Linux)

Readback operation time
Transient creation deletion 35
Objectivity data read 1030
Physics object creation 20
Framework overhead 10
Data field unpacking 0.1
11
(No Transcript)
12
Mini Status

• The Mini was released for production in 2002
• All components of BaBar detector represented
• Trigger, MC truth matching, Particle ID,
• 2002 Reprocessing is nearly complete
• Should finish this week!
• Will provide the full Mini for BaBars full data
  sample
• Reco, Raw, and ESD were not written in this
  processing
• A Large savings in cpu, IO, tape, lock traffic,
• Mini data is available at BaBar Tier-A sites
• The total Mini sample will be 10 TeraBytes
• Access is through dynamic staging
• Small samples can be exported to smaller sites
• Physicists are starting to use it

13
BaBars New Computing Model

• BaBar has recently revised its computing model
• Prompted (partly) by the need to integrate the
  Mini
• The Mini will be ported to use RootIO
• Allows interactive (CINT) access to production
  output
• Embedded arrays will be converted to Root columns
• Embedded object classes will be directly reused
• A Reduced Mini will replace the existing Micro
• Cluster Mini objects used directly in analysis
  into New Micro
• Cluster other objects separately to complete the
  Mini
• The Analysis interface will be re-implemented
• Optimized for Mini access

14
Conclusions

• BaBar has implemented a new Event format the
  Mini
• Replaces inefficient Raw, Reco, and ESD formats
• Provides access to detector detail for average
  users
• The full BaBar data sample will soon be available
  in Mini format
• BaBar is implementing a new Computing Model
• The Mini will be ported to RootIO
• The Micro will be replaced with a Reduced Mini
• The Analysis interface will be re-implemented
• The new model will be deployed in late 2003
• We are close to achieving our original goal of a
  flexible, unified, efficient event data format