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Upgrading L2Cal Clustering Algorithm for Better Performance

This upgrade entails hardware-based changes in the L2Cal team with a refresher on existing L2 clustering methods. Problems like high jet rate and seed positions are addressed using new algorithms. The Pass0, Pass1, and Pass4 procedures are detailed with specific criteria for tower clustering. Isolation and jet configurations have been improved with the adoption of cones for jets and new Missing Et calculations. The status of the upgrade shows hardware and software implementation progress. The rewritten L2 code now incorporates alpha clustering for Pass1 and Pass4 scenarios.

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Upgrading L2Cal Clustering Algorithm for Better Performance

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  1. L2Cal Upgrade L2cal team 041807

  2. Refresher on existing L2 clustering • Hardware based • Pacman: looks for seeds then clusters all contiguous towers that satisfy a shoulder threshold • Problems-Jets: high rate due to jets being artificially energetic at high lumi, position of seed is used as position of jet • -Photons/electrons- 2 high Et passes

  3. Current clustering algorithms • Pass0-Look for seed tower: Em >= 2 GeV and Had/Em < 0.125-One tower per “cluster” • Pass1-Seed has Em >= 8GeV-Shoulder Em >=7.5 GeV ( no limit on number of towers , marked towers as used and don’t use again ) • Pass2 jets • Pass4 (alpha clustering )-Use Pass1 seed position then cluster using pass0 tower info (towers have Had/Em cut )-In central ( clusters do not open in phi; eta+-1 wrt to seed)-Plug ( 3x3 box )-No crossing eta = zero boundary etc

  4. Current isolation • Calculated for Pass1, Pass4 • Start with seed position-find iso for 3X3 and (4) 3x4 tower configurations-Use smallest of the 5 sums

  5. Status of algorithms ( upgrade ) • Pass0 is unchanged • Pass 1 is no more… • Pass4 ( alpha ) is unchanged • Isolation is unchanged (Pass 4) • Jets will be new (pacman→cones) • Missing Et will be new • If there are other improvements now is a good time to let us know…

  6. Offline tools • Have L2Cal simulation ( TrigSim ) which includes Pass0,Jets,Pass4, Iso, MET • Also have Stntuple version of code which will be available within HTTF tools-can also make available independent of Higgs tools-If your ntuples have DCAS info you can run new clustering • Tools already available for testing/optimizing new triggers

  7. What is the status of the upgrade • Have all hardware in hand • About half of the hardware is already installed • Software (as described) is written- beginning to run it parasitically • So things are starting to come together

  8. What happens when pass 1 is used in L2 code • Rewritten level-2 code to use alpha clustering if passed 1 or 4, 4 is used in the code.

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