Chiara Zampolli in collaboration with C. Cheshkov, A. Dainese ALICE Offline Week Feb 2009C. Zampolli 1

OFFLINE CALIBRATION – FIRST STRATEGY AND EXAMPLES

Chiara Zampolliin collaboration with C. Cheshkov, A. Dainese

ALICE Offline Week Feb 2009 C. Zampolli 1

Offline Calibration – a step forward

As LHC (re)start-up is approaching, the need for a clear definition of the detector offline strategies arises

Following the late ALICE Offline weeks, calibration was always mainly addressed to in terms of online calibration

Status of DAs

Status of DPs

Status of the preprocessor

OCDB objects

Apart from specific detector-related issues, the general schema for online calibration within the Shuttle framework is in place since long time, and “working smoothly since Dec 2007”

A new – well... not so new – question is now (re)asked to the detectors: What about offline calibration procedures?


What has come out...

From the ALICE Offline week – past and present – it looked as if not many clear ideas are already there

Procedures may be defined, but.....how to run them?......where?......when?......where to store the results?

The problem is in common between Calibration and AlignementA common approach/strategy should be defined


What we have now - examples

So far, EMCAL/PHOS, TOF, TPC, and TRD have some work done on the offline calibration, but many details are still missing.

TOF: offline calibration strategy first presented in the October ‘06 ALICE Offline Week

EMCAL/PHOS: offline calibration strategy outlined recently, presented last Monday, and also before at the February ‘09 PWG4 Meeting


The TOF Example


TOF Offline Calibration

On-the-Fly offline calibration redesigned wrt July Offline week, being splitted into two steps:

TTask (post-reconstruction process):Filling a tree:

one entry/TOF channel;Each entry being a 1D array with the necessary information to perform calibration;

Running at the EOR;Writing the tree into AliEn (as reference data) → don’t need CDB access

Job/Macro:Chaining the trees so far created over many runsRunning the calibration processWriting the calibration parameters on the CDB

8th October 2007 Chiara Zampolli – ALICE TOF 6

From Oct ‘07

TOF Offline Calibration: AliTOFCalibTask

Process, loop over events:

Applying quality cuts, and retrieving essential information from ESD tracks: ToT, measured time, expected times (π, K, p) → filling of a 2D array [TOF channels][# expected tracks/channel per run], as before;

Terminate:

Perform Combinatorial PID → reducing the 2D array size of a 1.7 factor (only one exp time stored), as before but added some improvements in the encoding of the algorithm;

Filling a run-level tree, one entry/TOF channel, changed;

Storing the tree in AliEn, new.


From Oct ‘07

Alberto, Jan Fiete 8Cern, July 19, 2007 OFFLINE Weekly meeting

TOF Offline calib strategy

Run 0

Chunk 0 Chunk 1 Chunk n

ESD 0 ESD 1 ESD n

Run 1

Chunk 0 Chunk 1 Chunk n

ESD 0 ESD 1 ESD n

Tree 0 Tree 1 Tree 2 Tree n

Calibrator 0 Calibrator 1 Calibrator 2 Calibrator n

OCDB From Oct ’07,

From A. Colla Jul ‘0

7

TOF Offline Calibration: AliTOFcalib

OCDB functionalities for Online/Offline Calibration: writing/reading of TOF CDB objects, both online and offline, both for decalibration (in MC) and calibration

Functionalities for Offline Calibration: Summing over the run-level trees stored into AliEn

Now, creating a TTree object, copying the entries of the existing ones (TTree::CopyEntries()):

Quite memory expensiveAllows to create the final tree also in case the run-level trees are stored in the reference data using the CDB classes

Thinking of using a TChain object:No memory expenseMany Log Info messages from TAlienFileOnly possible in case the run-level trees are stored in AliEn without using the CDB classes (but this seems to be the way..)


From Oct ‘07

TOF Offline Calibration – Computation of the Parameters

In the TOF schema:The Task should prepare the objects needed to calculate the offline calibration parameters......of which the job/macro should then be encharged Not so bad, but who should run the Task? When exactly? Where?


The EMCAL/PHOS Example


16/03/09 EMCal Status - Offline week 12/15

Offline Recalibration Strategy for PHOS and EMCal Task 2547: Implementation of online calibration procedures

PHOS and EMCAL had a joint meeting on 12.02.2009 to define a strategy for offline recalibration: http://indico.cern.ch/conferenceDisplay.py?confId=52643

PHOS and EMCAL offline calibration requires the full available statistics (~109 - 1010 events), therefore it can run with ESD only.

ESD produced after the first reconstruction pass should be filtered to extract branches CaloClusters, PHOSCells, EMCALCells. Some calibration algorithms using track matching require the Tracks ESD branch which also should be extracted from ESD in the filtering procedure.

The AOD with selected branches obtained by ESD filtering will be used for offline recalibration. Filtering and recalibration should be implemented as analysis tasks.

The output of the recalibration task is a file with the corrections to the cell amplitudes and can be stored in a private alien directory for expert use only.

Should this file have an structure depending on runs like OCDB? The OCDB to be used for further pass reconstructions will be corrected with

the cell amplitude corrections obtained, basically multiplying the coefficients.

We have to provide to the reconstruction managers macro that automatically do this.

EMCal has already a recalibration procedure that works with the analysis frame developed by Aleksei P. a year ago ($ALICE_ROOT/EMCAL/Calib) Need to see how to adapt it to this recalibration strategy.

From Gustavo, la

st monday

http://indico.cern.ch/conferenceDisplay.py?confId=52643

16/03/09 EMCal Status - Offline week 13/15

Besides creating the new OCDB object, we aim to recalibrate the ESD created after the first reconstruction pass. For this, this first ESD should pass through another filter, and parameters of the CaloClusters (energies, coordinates, shower shape) should be recalculated with the use of corrections to the cell amplitudes found by recalibration procedure.

As a result of this filtering, a new AOD will be created with better calibrated CaloClusters. This new AOD should be used for the official physics analysis.

A possibility to create online DA is being studied. This DA can create TTree of objects needed for recalibration. The total size of these objects accumulated from 109 acquired pp events is estimated as a 33 Gb. These objects in root files should be exported from DAQ or HLT network to the outside world for an express offline analysis. As a result of this express analysis, an OCDB needed for the first reconstruction pass can be created.

Question to core offline: is there a way to export root files produced by QA to a storage other than OCDB?

Offline Recalibration Strategy for PHOS and EMCal Task 2547: Implementation of online calibration procedures

From Gustavo, la

st monday

EMCAL/PHOS main points

A 1st Task would filter the ESDs obtained from pass1 to create new AODs with the necessary infoA 2nd Task should run on the new AODs to get the calibration parametersWith these calibration parameters, new AODs could be created from the same initial ESDs, to be used for analysis while waiting for the second pass reconstructionNot so bad, but who should run the Task? When exactly? Where?


Common Idea – using an AnalysisTask

Offline Calibration – as well as Alignment – could be organized as a “calibration/alignment train” to be run immediately after the reconstruction – in the same job, or in the same aliroot session:

Every detector providing its own wagon

Single loop over the events instead of once per detector calibration procedure

Possibility to run over every type pf available data

Automatization of the procedure

Running on the Worker Node

Every detector wagon should produce Calibration/Alignment data to be merged and from which to then extract the Calibration/Alignment parameters

Merging of Calibration/Alignment data could be done over several runs, depending on the detector’s needs


from a discussion with C. Cheshkov and A. Dainese

Offline Calibration – General Schema


Calibration/Alignment train

reconstruction

Chunk 0 Chunk 1 Chunk 2 Chunk 3

ESD 0 ESD 1 ESD 2 ESD 3

Cal/Alig data 0

Cal/Alig data 1

Cal/Alig data 2

Cal/Aligdata

3

Cal/Alig obj run in AliEn

(*) analogous to the existing merging procedure for ESD tags

Merging procedure (*)

i-th

Ru

n

j-th

Ru

n

Offline Calibration Strategy - Features

Size of Calibration/Alignment data after the merging must be small compared to the overall ESDs size! (if possible use QA data...) requirement for detector, up to them to keep this under control

Calibration/Alignment data need to be processed to obtain the real calibration parameters during a later step – macro? Job?

No automatization foreseen, at least for the beginning, since this would imply blind processing of different runs (if summing over runs is necessary) and storing the new Calib/Align objects in the OCDB w/ any check

Could also be done during the merging step – after a check (QA histo? ) of the data, the storing to the OCDB might be triggered

Calibration/Alignment data will be produced with no access to the OCDB – by definition

Can be run locally on the Worker Nodes

Need to store somewhere together with the Calib/Align objects the info about the OCDB objs used to produce the ESDs

Calibration/Alignment strategy seems to fit both TOF & EMCAL...

Possibility to test it during next cosmics runs, but also with old cosmics data


Any Comment?

Thanks to Andrea, Cvetan, Gustavo...


Back-Ups


TOF Offline Calibration: AliTOFcalib

Functionalities for Offline Calibration (cont’d): Perform Calibration (as before):

Calibration the whole TOF → default

Calibrating a selected channel → debug purpose

Calibrating summing over more than one channel → in case uniform behaviour between channels is expected

Calibrating a specific set of channels → partial TOF configuration

Calibrating using a dedicated algorithm to produce profile histogram → debug purpose

Still the same debugging functionalities:possibility to store control histos both during the 2-D array filling, and during calibration


From Oct ‘07

Cern, July 19, 2007 OFFLINE Weekly meeting

Managing the OCDB during reco

Run validity0 ∞1 2 3 54 101 102 103 104100

On

line

Offl

ine

Run 01234

100101102103104

Run 01234

100101102103104

Reset!Offline Calib obj

no more valid

Not valid

Not valid

Valid

Valid

Offline Calib obj validOffline Calib obj not validOffline Calib

obj valid

Alberto, Jan Fiete

From Oct ‘07

Offline Calibration Obj: fValidity

Handled by AliTOFcalib as a const char* member, fValidity;

Validity for offline calibration objects is written as a comment (AliCDBMetaData::SetComment()) in the MetaData of the obj;

“valid” is the key-word to activate the use of offline calibration params during reco;

fValidity set as “valid” when AliTOFcalib::Calibrate ends successfully (i.e. enough statistics), otherwise no new offline calibration objs stored;

During TOF reconstruction, both online/offline calibration objects are read: the first being always necessary to retrieve the status of the channel, the second being used only in case fValidity==“valid”.


From Oct ‘07

Documents

Chiara Zampolli in collaboration with C. Cheshkov, A. Dainese ALICE Offline Week Feb 2009C. Zampolli 1