Pass1 & Pass2 Processing of Data

Overview

Good events are culled from the event stream amd reconstructed in the Pass1 and Pass2 processes. Pass1 eliminates about 97% (in '93) of the triggers and presents them to Pass2 for further classification and reconstruction. All physics events passing Pass1 are reconstructed in Pass2.

As of this writing, both passes through the data are performed on SLACVM, controlled by the SLDPM (SLD Processing Manager) service machine, owned by Len Moss. Catalogues of the output tapes from each pass are kept in Oracle and in DATACATs in DUCSDATACAT.

FILTER

This stage is intended to whittle the raw data down to a manageable size. It is the intention that the data that fails the filter need NEVER be looked at again. It also separates the data off into several streams for the subgroups that need them:

Compton
DC laser records
randoms triggers
120 Hz trigger records
(almost) all LUM triggers, stripped down to only contain LUM data

Physics and physics calibration events are streamed off into:

Z decay products (hadrons, taus, mu-pairs)
LUM bhabhas
track triggers with a good track

The calibration sources are stripped off to separate files; the physics events go into a single file. The filter results are written into SFCLASS.EVTCLASS and added to the RAWDATA.

The RAWDATA context is written out to the physics files. Output tapes from this stream can be found in DUCSDATACAT:HAD.DATACAT.

Z decays

Z decays are defined as passing

EITHER of the Energy-PASS1 (see SLD Physics Note 14; a requirement of some energy in both N & S has been added) or the '92 KAL (see SLD Physics Note 17. The cuts on energy imbalance and sphericity are disabled for the PASS1 filter) filter.
a mu-pair filter looking for a pair of WIC strip tracks roughly back-to-back (using routine MZ0FLT)
a tau pair filter, requiring at least one good track with p > 1 GeV.

Tracking cuts are made using pattern recognition (DCPTRK) tracks which have been found via a fast-PATREC option. DBQPATP.MinHit is set to 4.

Good tracks satisfy:

N(hits) > 30
p > 100 MeV
|z| < 20 cm
r_xy < 10 cm

LUM Bhabhas

The LUM bhabha filter accepts 'gross' and 'precise' events via routine MBHFLT.

Track triggers

These track triggers are quite useful for DC calibration. Accepted triggers have at least two good tracks, one of which must have p > 0.75 GeV. As for Z decays, these are DCPTRK tracks.

Source Files

SLDPM massages the file FILTER FRAMWORK on SLDPM 191 into a SANECTRL file. PASS1 IDA applies the physics filters. On VM, the loader information for the PASS1 is contained in FILTER SANEINCL.

IDA files

F_IOINI: initialize I/O for the filter
F_EVTINI: define non-event record handlers
F_VARINI(*): initialize variables, IDAL routines for PASS1
PASS1(*): physics filter
F_WRITE: write out the streams
F_IOSUM: summary of I/O
F_SUMMAR: write summaries of event to file; talk to STATUS

(*): all the user needs to run PASS1 on his/her own.

All the IDA files are available in DUCSSLD.

RECON

This stage reconstructs all the physics events to pass the FILTER and applies a PASS2 filter to tag WABs, hadrons, taus and mu-pairs.

The DST and PREPRO contexts as well as a smattering of RECON families (KUPHIT, KUPCLUS, KUPCHIT and DCFTHC) are written out.

Pass2 filters are applied to all the physics classes from PASS1.

The filter results are written into PHEVCL.EVTCLASS and added to the DST.

Good fitted tracks satisfy:

|cos(theta)| < 0.866
p > 100 MeV
|z| < 4 cm
r_xy < 2 cm

In '93, CRID and EDC reconstruction were turned off. The fitter was set to determine v_d and t0 from the tracks.

Hadrons

The PASS2 cuts as described in SLD Physics Note 14 are applied to the events that passed the PASS1.

The PASS2 for KZ0F applies the energy imbalance cut, but leaves the sphericity cut disabled. Energy trigger 'monojet' backgrounds are vetoed using KMONOJT (looking for front/back imbalance).

Each PASS2 class requires that the respective PASS1 class has been passed.

WABs

WABs are tagged via KWABID, looking at the highest energy towers.

Taus

PASS2 for taus requires that the sum of track momenta and good cluster energy exceed 10 GeV. This is really a tracking-hadron filter, not the standard tau Pass2 filter.

Mu pairs

PASS2 for mu pairs requires two CDC tracks that come within 0.2 cm of the IP in x-y.

Source Files

SLDPM massages the file RECON FRAMWORK on SLDPM 191 into a SANECTRL file. PASS2 IDA applies the physics filters. On VM, the loader information for the PASS2 is contained in RECON SANEINCL.

IDA files

R_IOINI: initialize I/O
R_VARINI(*): initialize variables, IDAL routines for PASS2
PASS2(*): physics filter
R_IOSUM: summary of I/O
R_SUMMAR: write summaries of event to file; talk to STATUS

(*): all the user needs to run PASS2 on his/her own.

All the IDA files are available in DUCSSLD.

Accounting

Results from the two passes are stored in the Pass1run, PAss2run and OFFLDAY Oracle tables.

Further statistics and diagnostic histograms are stored in STATS and HCOM files on the ZZERO 211 disk on SLACVM.

R.Dubois
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