1. Stripping Plans for 2014 and 2015 Laurence Carson (Edinburgh), Stefano Perazzini (Bologna) 2 nd LHCb Computing Workshop, 07.11.13

2. Outline Plans for re-stripping of √s=7,8TeV data in 2014 – New features in stripping framework – Including new algorithm to improve CPU performance Ideas for stripping of √s=13TeV data in 2015 Automating testing of software for stripping releases 2

3. Plans for Re-stripping in 2014 Current plan is to have a full re-stripping of the 2011 and 2012 pp collision data sometime in late 2014 Schedule is driven by availability of final calibrations for the calorimeters – These calibrations can be applied at the DaVinci level, so there’s no need for a reprocessing (i.e. this will still be Reco14) This stripping will be labelled Stripping21 It will provide a legacy dataset for the 2011 and 2012 data It should merge the lines of the full Stripping20(r1) with the new lines added in Stripping20rXp{1,2,3} incremental re-strippings – Replacing buggy lines with the bug-fixed incremental versions – Should have significantly less bandwidth than the sum of Stripping20 + p1 + p2 +p3, due to removal of buggy lines and increased overlap between lines 3

4. Developments for Stripping21 Stripping21 will benefit from a number of new features that were not present in Stripping20, allowing further bandwidth gains – Though some are/will be present in some of the incremental restrippings Persistency of flavour tagging information (on both DST and μDST) is implemented since S20rXp2. Allows some lines to move to μDST. Generic MVATool functionality is now ready (in DV v33r8, released last week). Could be tested with S20rXp3 (deadline for p3 is January 19th) Some WGs want to explore removing the raw event info from the full DST. This should shave 20-30% off of the full DST size. Would be good to test this with S20rXp3. Plans to develop MDST.DST, which is a full DST holding all of the events selected by any line on μDST. Allows quick re-generation of μDST, to e.g. add extra info. Will keep a single copy of the MDST.DST on disk. (MDST.DST won’t need to contain all of the raw event info) 4

5. New Algorithm for Particle Combinations There is a new set of algorithms available from Vanya, called NBodyDecays, which aims to speed up the fitting of multi-particle vertices (compared to CombineParticles). These algorithms have combination cuts for the pairs, triplets etc within the multibody vertex – This allows to kill bad combinations at an early stage The performance of this algorithm is currently being tested by Ben. First results are promising; e.g. the timing of the 4h combination in StrippingB2D0KD2HHHHBeauty2CharmLine, drops from 5.8ms/evt to 2.4ms/evt. Testing will continue, to assess the performance of the new algorithm in different lines. If we decide to use this new algorithm in a future stripping production, we need to think about how to implement the switch- over in the stripping selections at large. 5

6. Strippings in 2015 Intense work will be needed at the start of 2015 running to understand the performance of the trigger, reco etc at the higher energy and 25ns bunch spacing, and with the split HLT Hence the prompt stripping will initially evolve rapidly to follow the changes in the trigger and reco Also in early running, preference may be given to lines aiming to make measurements based on early 2015 data (cross-sections etc) As more data is gathered, the prompt stripping should become more stable as the trigger and reco stabilises At the end of 2015 running, all the 2015 data will be re-stripped (but not reprocessed), with a stripping that should be similar to the stabilised prompt stripping (cf Stripping19f and Stripping20 in 2012) The prompt stripping will be labelled Stripping22, and the end-of- year re-stripping Stripping23 6

7. Preparing for 2015 Stripping Since there will be no √s=13TeV min. bias data to test the stripping retention before collisions start, and the multiplicities and momentum/p T distributions will be different from √s=8TeV data, it will be important to have min. bias MC to tune the stripping on – How much do we trust the extrapolations of the multiplicities and p T distributions from Pythia? – Also need to worry about ccbar and bbbar cross-sections Other necessary inputs for tuning the stripping will be the expected output rate of the trigger, and the allowed bandwidth (and timing) out of the stripping. 7

8. Automating Testing of Stripping Software Would be advantageous, during preparation for a production release, to run tests of bandwidth, timing etc in the nightlies. With new Performance & Regression (PR) framework, the nightlies should be able to cope with long tests such as these. These tests often need a “mix & match” setup, using the head of certain packages but tagged versions of others. Not clear how to take care of this in the nightlies. For the event size tests, the output (μ)DSTs are needed. Can these be persisted anywhere? Probably don’t need to run on all possible platforms/architectures. Other issues?... 8

9. Summary Plan to re-strip of all 2011 & 2012 pp data in late 2014 – Create legacy dataset, taking advantage of all framework developments since Stripping20 – Possibly using new algorithm for multibody vertices Starting to think about how to handle stripping of 2015 data Would like to automate some of the pre-production stripping tests in the nightlies, if possible. 9

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