Brient, J.C.

Gay, Pascal

Le Diberder, F.

Monteil, S.

Yermia, F.

HAL-IN2P3

Photon reconstruction statusPascal Gay, J.C. Brient, F. Le Diberder, S. Monteil, F. YermiaTo cite this version:Pascal Gay, J.C. Brient, F. Le Diberder, S. Monteil, F. Yermia. Photon reconstruction status.Workshop of the 2nd ECFA/DESY Study on Physics and Detectors for a Linear ElectronPositron Colliders 6, May 2000, Padova, Italy. 2000. <in2p3-00013854>HAL Id: in2p3-00013854http://hal.in2p3.fr/in2p3-00013854Submitted on 22 Jul 2003HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.L’archive ouverte pluridisciplinaire HAL, estdestine´e au de´poˆt et a` la diffusion de documentsscientifiques de niveau recherche, publie´s ou non,e´manant des e´tablissements d’enseignement et derecherche franc¸ais ou e´trangers, des laboratoirespublics ou prive´s.Photon Reconstruction StatusJ.C. Brient, P. Gay, F. Le Diberder, S. Monteil, F. Yermia9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionOutline• Framework• Approaches- TOWER- VICINITY- Photon FinDer- EMILE• Tests- Isolated Photons- π+/γ• Conclusions9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionFramework– GEANT 4– Projective Geometry (LINEAIRE)– Non-projective Geometry (MOKKA)- Interface of the CODES with the non-projectivegeometry is on progress and no diﬃculty is foreseen- The informations are centralized on the Web Sitehttp://lc-ecal.in2p3.fr9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionTOWER• Projective Geometry• Clusterisation is the collection of every pads in a5x5x40 (θ, φ, layer) tower around the most energeticpad if such a pad is not-isolated.If no not-isolated pad exits, the zone is reduced to a3x3X40 tower around the most energetic pad.• TestIsolated Photons from 250 MeV up to 30 GeVResolution obtained as a function of Eγ∆E/E=(10.3± 0.3)% /√E+(1.1±0.1)%• Acts as a benchmark• Indicates the intrinsic performances of the Si/Wecal9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionVICINITY• Projective Geometry• Clusterisation is based on vicinity rule between thepadsRule : 2 pads with at least a corner or/and a side incommon are connectedi) Clustering begins on the most energetic pad notalready involvedii) A cluster is the collection of all pads linked by thevicinity rule after iterative loop on all the padsalready collected.iii) goto i)• TestsIsolated Photons from 250 MeV up to 15 GeVFraction of collected energy as a function of Eγ→→→9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionVICINITY• Projective Geometry• Isolated Photons from 250 MeV up to 15 GeVFraction of collected energy as a function of theenergyThe cluster under consideration should have morethan 5 pads involved.The fraction of collected energy is less than 80% @250 MeV while it decreases to 60% when only themost energetic cluster is taken into account.• A rule to connect the clusters has to be deﬁned9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionPhoton FinDer : StructureWhich pads to use ?1 - reject from the list of pads, all pads within somedistance to the extrapolation of a charged track (1cm)VIRTUAL STACK 11 - Create a virtual stack by summing the ﬁrst 10 layers2- order by energy the virtual pad(s) of the virtual stack3- Start a new virtual cluster(s) as soon as a pad is nota neighbour of the previous virtual pad in the energyordered list.(GAMPEX - ALEPH photon package)CLUSTERING kernel1 - Start from the virtual cluster(s) as entry point toclustering for all real pad(s)2 - Use “equivalent distance” at the ECAL entry todeclare 2 pads are neighbours3 - Recover unassiocated pads by the angle between the“ direction ” of a cluster and the “direction” of a pad.see next transparancy for the deﬁnition of the direction9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionPhoton FinDer• What is ’direction’for a clusterVertex to COG of the clusterfor a padprojected COG to entrance of the ECALto Pad position• Tests- Use of MOKKA- Simulate photons from 0.15 to 100 GeV9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionResults from simulation    PHOTON simulated with GEANT4 and MOKKA Clustering efficiency % Photon energy     GeVEcl/Egen969798991000 0.25 0.5 0.75 1 1.25 1.5 1.75 29092.59597.51000 0.25 0.5 0.75 1 1.25 1.5 1.75 21 - PFD eﬃcency to ﬁnd photon in the low energy regionAbout 99% above 0.25 GeV2 - rate of fake electromagnetic cluster (created fromﬂuctuation of an electromagnetic shower)About few per mill - 4 10−3 at 0.5 to 9 10−3 at 100. GeV3 - fraction of the total energy in the clusterStable and about 95 % up to 4 GeV then slowly going to 99.5%at 100. GeV9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionResults from simulation    PHOTON simulated with GEANT4 and MOKKA  .2098    /     2A0   .2394E-01   .8991E-02A1   .1085   .6312E-02 1 /sqrt(E)∆E/E00.10.20.30 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5    PHOTON simulated with GEANT4 and MOKKA  .7118    /     3A0   .4783E-02   .1256E-02A1   .1367   .5804E-02 1 /sqrt(E)∆E/E00.10.20.30 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5    PHOTON simulated with GEANT4 and MOKKA  5.476    /     5A0   .2438   .1658E-01A1   .6290   .3731E-01 1 /sqrt(E)δΘ (mrad)00.511.520 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.54 - Energy and angular resolutionAFTER CLUSTERINGthe stochastic term is 11.4%/√Eup to few GeV then about13.7%/√Eδθ(mrad) = 0.63/√E + 0.24 downto few hundred MeV9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionEnergy Measurement Intended for Low Em showersBeside the Standard approaches, new one isdeveloped :Energy Measurement Intended for Low Em showersMain Directions– 3D– Democratic– Physical insight– No seed– Long range9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionEnergy Measurement Intended for Low Em showers• Two pads (i and j) are connected according a linkstrength dij deﬁned by terms which reﬂects the basicprocess (e→γ, γ→e)Long distance interaction e−ρij/XoEnergy relation Ei/EjAngular dependence 1/(1-βcosθij)whereρij is the 3D distance between the pads i and j,Xo is the interaction length,θij is the angle between the pad i and jβ=.99Thus dij is deﬁned asdij= e−ρij/Xo × Ei/Ej × 1/(1-βcosθij)9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionEnergy Measurement Intended for Low Em showers• dij– The dij terms are determined between every pair ofpads in the event but pad j should be on a layerouter than the pad i i.e. follows the development of thee.m. shower– All pads are connected without any initiate pad (incontrast with maximal energy pad rule)– The energy from a pad could be shared by manyobjects•An internal cut is appliedpreliminary Version !Cuts have to be tuned (or replaced by continuous function)9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionEMILE: Clustering• Clustering– def : Each pad j with dij=0 whatever i is a terminalpad– Rule : From the outer layer (i.e. 40th) the energy isdistributed on each pad according the dij down toeach terminal pad.→ A terminal pad deﬁnes a cluster→ Every characteristic of the cluster is builtthrough the dij weighting from the 40th layer to theterminal pad.1  layerstth40   layer Examples : Energy, terminal pad coordinates, core clustercoordinates...9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionEnergy Measurement Intended for Low Em showers•Cluster associationTwo clusters (a and b) are merged if‖Dentrya −Dentryb‖ ≤ 1.73 or ‖Dcorea,b‖ ≤ 0.5where Dentry stands for the Distance from the centerof the detector and the terminal pad point, andDa,bcore is the distance between the barycenter of thecluster a and b.Cuts have been tuned to ensure the best recoveringof photon energy• TestsProjective GeometryIsolated Photons from 100 MeV up to 15 GeV9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionEMILE: Low PhotonsEγ= 100 MeV Emeas/Eexpected02040600 0.5 1 1.5  Emeas/Etrue0501001502002500 0.5 1 1.5Eγ= 250 MeV Emeas/Eexpected0204060801000 0.5 1 1.5  Emeas/Etrue0501001500 0.5 1 1.59th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionFirst Preliminary Results02.557.51012.51517.52022.5250 0.25 0.5 0.75 1 1.25 1.5 1.75 2γ   θ=90 degrees1/√E (GeV)∆E/E (%)∆E/E=(11.± 0.3)% /√E+(1.4±0.2)%0.40.50.60.70.80.910 0.5 1 1.5 2 2.5 3 3.5 4√ E (GeV)F E(%)Fraction ofcollected energyis never less than92% even whenonly the mostenergetic clusteris taken intoaccount9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionFirst Preliminary Results0.940.960.9810 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1E (GeV)Clusterisation eff.9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionPhotons With Pions• Tests• Photons with noise coming from π+Samples with diﬀerent distances between the γ andthe π+Typically Eγ=1 GeV and Eπ=10 GeVDistance is 4, 3 and 2 cmThe clusters matching the MC photon direction areconsidered as photons@ 4 cm Emeas/Eexpected010203040500 0.5 1 1.5  Emeas/Etrue0204060801000 0.5 1 1.59th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionPhotons With Pions Eγ/Eγtrue02040600 0.2 0.4 0.6 0.8 1 Eπ/Eγtrue020400 0.2 0.4 0.6 0.8 10.50.60.70.80.910 0.1 0.2 0.3 0.4 0.5Eπ/Eγtrue E γ/EγtrueThe clusters matching the MC photon direction areconsidered as photons9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionPhotons With PionsPhoton with Pions@ 4 cm Emeas/Eexpected010203040500 0.5 1 1.5  Emeas/Etrue0204060801000 0.5 1 1.5to Simulate the Photon-Id a cut on (Ee.m./Emeas)cluster isappliedThe cut is ’tuned’(1) to render the distribution gaussian Emeas/Eexpected02040600 0.5 1 1.5  Emeas/Etrue0204060801000 0.5 1 1.5(1)typically .759th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionPhotons With PionsDisplay@ 3 cmknevt=36 dist=3cm-10-505100 5 10 15 20 25 30 35 405005055105155200 5 10 15 20 25 30 35 40knevt Emeas Eπ Eγ the phi lay Etrueπ Etrueγ36 1 2.768 1.413 1.355 0 513 1 6.071 1.47836 2 .014 .001 .013 -2 511 2 6.071 1.47836 3 .265 .240 .025 0 510 15 6.071 1.47836 5 2.870 2.785 .086 1 516 1 6.071 1.47836 6 .033 .033 .000 -11 510 39 6.071 1.47836 7 .403 .403 .000 -2 503 5 6.071 1.47836 9 .795 .795 .000 1 521 9 6.071 1.47836 10 .035 .035 .000 -3 519 17 6.071 1.47836 11 .050 .050 .000 4 516 1 6.071 1.47836 12 .013 .013 .000 -2 521 17 6.071 1.47836 13 .029 .029 .000 -4 521 24 6.071 1.47836 14 .009 .009 .000 -4 517 16 6.071 1.47836 15 .015 .015 .000 6 521 17 6.071 1.47836 16 .217 .217 .000 1 519 10 6.071 1.47836 17 .034 .034 .000 7 517 19 6.071 1.4789th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionFirst Preliminary ResultsPhoton with Pions@ 3 cm Emeas/Eexpected01020300 0.5 1 1.5  Emeas/Etrue02040600 0.5 1 1.5 Emeas/Eexpected01020300 0.5 1 1.5  Emeas/Etrue02040600 0.5 1 1.5With such assumptions Preliminary Results are@ 4cm γ=80%@ 3cm γ=50%@ 2cm γ=22%NB. No rejection of the π+ shower nor MipreconstructionMore realistic numbers will come with Photon-Id9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow SessionConclusion1 Standard approaches– Photon FinDer is an eﬃcient photon ﬁnder– It is a good starting point for photon– Could play the Benchmark roˆle, already interfaced w/ MOKKA2 New approach with EMILE– (3D, democratic, Physical insight, no seed, long range)– Preliminary version– Many switches have to be tunedNext• New Codes will be available from the Web Site• interfaced w/ MOKKA very soon• Included in BRAHMS• More investigation with noisy situation• Test the algorithms with jets, τ decays, etc.– Regular meeting are forseen (last one 13th April 2000)– KEK people are interested (F. Le Diberder will visit them onjuly)9th-may-2000ECFA-DESY WorkshopPhoton Reconstruction Status E-ﬂow Session

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