LIGNOCELULÓSICOS
1.2.2. CARBONIZACIÓN DE MATERIALES LIGNOCELULÓSICOS
All recorded data and all simulated MC events are ultimately pro- cessed into the analysable xAOD format. Since the xAODs contain all reconstructed physical objects, the required amount of disk space is enormous. A single event of a simulated gluinoR-hadron sample averages at 326 kB per event. Most of the information contained in the xAOD, however, is irrelevant for the present study. The event data model as described in chapter3.3suggests the production of a derived format which is specific for a group of related analyses. The size of a single derivation (DxAOD) should be 1% of the whole xAOD. This can be achieved through three mechanisms which are also schematically shown in figure A.1:
Figure A.1: Schematic representation of how the size of an xAOD can be re- duced. Here, two input events are taken of which one is skimmed away. The re- maining event is slimmed and thinned to reduce its disk size. In a last augmen- tation step, new information is added to a collection.
• Skimming: Events are rejected if they do not fulfill certain selection criteria. In the simple most case this is achieved via a trigger se- lection, but object requirements or topological considerations are possible as well.
• Slimming: Individual variables or collections of variables are re- moved from the output if they are superfluous.
• Thinning: Removal of individual objects from collections in the data file. This could for example be the rejection of all muons which do not fulfill a certain momentum cut.
In addition to the procedures leading to a reduction of disk space, a derivation can also be subject to a fourth treatment which leads to an addition of information
• Augmentation: Additional information is appended to an object which was previously not available for a specific object.
Since the search for SMPs is unlike most ATLAS searches, the DxAOD used was solely produced for the present analysis and carries the name SUSY8derivation. Events which have not fired either a single- muon, di-muon, Emiss
T or jet+EmissT trigger are skimmed away. Since the analysis relies heavily on ID tracks and muon-like objects, all variables are kept for the associated objects. Further, SUSY8 con- tains all available EmissT information. Even though collections like photons or electrons are not needed for analysis, a rudimentary se- lection of associated variables is kept to ensure the reconstructability
of the event topology and the functionality of software tools sup- plied by dedicated ATLAS performance study groups. Lastly, since the biggest contributor to the derivation size are tracks ("‘track par- ticles"’), a mild thinning is applied and tracks are rejected if they posess no hits in the Pixel Detector, ptrack
T <10 GeV or longitudinal impact parameter |z0| > 10 mm. However, tracks which are asso- ciated to muons, electrons, jets or taus, are kept regardless of their properties.
In order to perform time-of-flight measurements in the calorime- ters it is necessary to have access to the hit information of all relevant cells. Upon first creation of the SUSY8derivation all calorimeter cells have been stored which led to very large derivations with≈ 85 kB per event.
Calo Clusters Trigger Track particles Truth information Muons and Staus MissingET Jets Photons Event shape Vertices Electrons Taus 51% 27% 8% 6% 3% 2% SUSY8 Derivation =1200 GeV g ~ stable R-Hadron m
Total size of derivation: 85.395 kB/event
Figure A.2: Content of the SUSY8 derivation upon first creation. The disk size is dominated by the stored calorimeter cell information.
To reduce the size, a tool has been written, which picks out the calorimeter cells associated to an ID track with ptrackT > 30 GeV (ptrack
T > 50 GeV throughout 2015 and early 2016) and augments the track with the necessary information. This way, considerably less calorimeter cell information has to be stored. This becomes apparent in the left panel of figure A.3, where the composition of the SUSY8 derivation in late2015has been plotted.
Figure A.3: Composition of the SUSY8 derivation in late2015(left) and 2017 (right). Changes to the derivation were made due to new requirements for common software tools and up- dated trigger specifications resulting in a slight increase of the derivation size per event.
Track particles Muons and Staus Truth information Jets Photons MissingET Trigger Calo Clusters Event shape Vertices Electrons Taus 31% 12% 11% 11% 11% 8% 6% 5% SUSY8 Derivation =1200 GeV g ~ stable R-Hadron m
Total size of derivation: 23.80 kB/event
Track particles Truth information Photons Muons and Staus Trigger Jets MissingET Calo Clusters Vertices Event shape Electrons Taus 31% 14% 12% 11% 8% 7% 7% 6% SUSY8 Derivation =1200 GeV g ~ stable R-Hadron m
Total size of derivation: 26.54 kB/event
The right panel of figure A.3 shows the SUSY8 composition in 2017. The composition has changed slightly due to updated re- quirements for common software tools. Since the trigger menu was changed in between data-taking in2015and2016, the changes in the derivation reflect the updated trigger selection and associated trigger elements. Lastly, a few variables which were found to be beneficial during analysis have been added to the derivation.