PFAs – A Critical Look Where Does (my) SiD PFA go Wrong? S. R. Magill ANL ALCPG 10/04/07

A Systematic PFA Development Starting Point : 100% pure calorimeter cell population – 1 and only 1 particle contributes to a cell More practically, no overlap between charged particles and neutrals -> Defines cell volume – v(d IP,η,B?) -> Start of detector design optimization -> Perfect PFA is really perfect – no confusion to start 100% pure tracker hits (or obvious crossings) -> Defines Si strip size -> Start of design optimization -> Perfect Tracks are really perfect PFA is an intelligent mixture of high purity and high efficiency objects – not necessarily both together

Occupancy Event Display All hits from all particles Hits with >1 particle contributing

Defining Perfect PFA (Perfect Reconstructed Particles) Takes generated and simulated MC objects, applies rules to define what a particular detector should be able to detect, forms a list of the perfect reconstructed particles, perfect tracks, and perfect calorimeter clusters. Complicated examples : -> charged particle interactions/decays before cal -> photon conversions -> backscattered particles Critical for comparisons when perfect (cheated) tracks are used Extremely useful for debugging PFA Checks detector calibration procedure

Perfect Tracks Perfect Neutrals (photons, neutral hadrons) Perfect Cal Clusters SiD (SS/RPC)

Photons from Perfect PFA (ZPole events in ACME0605 W/Scin HCAL)  /mean ~ 18%/  E  /mean ~ 24%/  E Detector Calibration Check 24%/  E 18%/  E

Neutral Hadrons from Perfect PFA (ZPole events in ACME0605 W/Scin HCAL)  /mean ~ 47%/  E  /mean ~ 49%/  E  /mean ~ 46%/  E 46%/  E 49%/  E 45%/  E

Track/CAL Shower Matching This is an example of where high purity is preferred over efficiency -> will discard calorimeter hits and use track for particle -> better to discard too few hits rather than those from other particles -> use hits or high purity cluster algorithm Example : 1) Associate mip hits to extrapolated tracks up to interaction point where particle starts to shower. -> ~100% pure association since no clustering yet -> tune on muons to get extra hits from delta rays 2) Cluster remaining hits using high purity cluster algorithm – Nearest Neighbor with some fine tuning for neighborhood size -> iterate, adding clusters until ΣE cl /p tr in tunable range (0.65 – 1.5) -> can break up cluster if E/p too large (M. Thomson) -> err on too few clusters – can add later when defining neutral hadrons

ECAL Radius 175 cm (LDC-like) ESum of Charged Hadron Clusters per event Decent match of PFA to Perfect

Candidates for re-clustering? ECAL Radius 175 cm (LDC-like)

ECAL Radius 125 cm (SiD) PFA slightly larger than Perfect

Candidates for re-clustering? ECAL Radius 125 cm (SiD)

Now, high efficiency is desired so that all photons are defined – can optimize for both high efficiency and high purity by using multiple clustering. Example : 1) Cone or DT cluster algorithm (high efficiency) with parameters : radius = 0.04 seed = 0.0 minE = 0.0 2) Cluster hits in cones with NN(1111) to define cluster core (high purity for photons) mincells = 20 (minimum #cells in reclustered object) dTrCl = 0.02 (no tracks within.02) 3) Test with longitudinal H-Matrix and evaluate χ 2 Other evaluations are done in PhotonFinderDriver – like layer of first interaction if cluster fails mincells test, cluster E in HCAL, etc. Photon Finding

Photon Clustering

Photon Comparisons – ZPole events for ACME 0605 (SiD) detector On the left is the ESum of photons for each event, red is perfect and blue is from PFA – 20.1 GeV for perfect PFA compared to 19.2 GeV for real PFA. On right is the difference between real PFA and perfect PFA for each event, a -1 GeV difference on average per event.

Photon Comparisons – 500 GeV events for ACME 0605 (SiD) detector On the left is the ESum of photons for each event, red is perfect and blue is from PFA – 49.8 GeV for perfect PFA compared to 30.0 GeV for real PFA. On right is the difference between real PFA and perfect PFA for each event, now a - 20 GeV difference on average per event. From the plot on right, you can see that it’s the high energy photon events that are missing – probably consistent with the H-Matrix failing on large cluster (high E) photons or from overlapping clusters.

Photon Comparisons – ZPole events for ACME 0605, ECAL IR = 175 cm (LDC-like) On the left is the ESum of photons for each event, red is perfect and blue is from PFA – 20.5 GeV for perfect PFA compared to 19.8 GeV for real PFA. On right is the difference between real PFA and perfect PFA for each event, a GeV difference on average per event. As expected, this is slightly better than the smaller detector – probably less overlap.

Photon Comparisons – 500 GeV events for ACME 0605, ECAL IR=175 (LDC-like) On the left is the ESum of photons for each event, red is perfect and blue is from PFA – 49.9 GeV for perfect PFA compared to 31.2 GeV for real PFA. Very similar to the ~60% as before for ZZ events (slight improvement). On right is the difference between real PFA and perfect PFA for each event, now a -19 GeV difference on average per event. From the plot on right, you can see again that it’s the high energy photon events that are missing – probably consistent with the H-Matrix failing on large cluster (high E) photons or from overlapping clusters. Very slight improvement – needs to be investigated further.

Neutral Hadron ID Here again, high efficiency is desired – if previous algorithms have performed well enough, purity will not be an issue. Example : Cluster with Directed Tree (another high efficiency clusterer) -> clean fragments with minimum cells -> check distance to nearest track – if too close, discard -> merge remaining clusters if close Needs additional ideas, techniques – pointing?

AugustSeptemberOctoberNovemberDecemberJanuary Tools DigiSim DigiSim Calibration Calibration Perfect PFA Perfect PFA Photons Photons dM/M vs ESum (PPFA) PFA Res. ZZ->qq ZZ->qq ZZ->qqqq ZZ->qqqq tt->6 jets tt->6 jets dM/M vs Ejet ZH->4 jets B-field, ECAL IR, HCAL Tech., Det. variants 1 TeV Understand contribution to dijet mass resolution from energy, angles Results of PFA performance at 500 GeV CM for various n-jet processes - Performance vs Ejet or Ejetjet? - Detector parameter variations - Results for F’lab ALCPG FermiLab ALCPG