Fake MET

• Noisy channels– Online/offline

strategies

• Non-collision backgrounds– Beam halo– Beam loses– Cosmics

Hot channels

From Song Ming Wang: Joint D0/CDF/CMS Jet/MET Workshop, Jan 28th 2004

First Look at Beam Halo Muons in CMS

• Just a preliminary, qualitative look at what is seen in the detector– No rates or cross-sections calculated– No overlay with pile-up

• Used 6000 events (out of 8000) from Beam Halo Muon samples generated by Volker Drollinger for his studies– CMKIN_4_2_0, OSCAR_3_6_5– Digitised privately at Florida using ORCA_8_7_1

• Looked at:– Stand Alone Muon Reconstructor (default)– Iterative Cone Jets, R = 0.5 (default)– MET and Sum ET from EcalPlusHcalTowers (default)

(see B. Scurlock’s talk, CMS Week, March 2005)

Beam Halo Muon Distributions: First Look

METMET Sum ESum ETT

IC5 Jet IC5 Jet

STA Muon STA Muon

IC5 Jet EIC5 Jet ETT

• Qualitatively what one expects– MET – End-cap Muons– Barrel Jets

• Even at low lumi, nearly every beam halo is overlaid with collisions (e.g. 3.5 non-diff collisions for L=2x1033)

• Next step - Develop MET cleaning algorithms

– Form rejection criteria based on ECAL vs. HCAL energy

5999 events5999 events

81 events81 events

861 events861 events

(see B. Scurlock’s talk, CMS Week, March 2005)

Why so large?Investigating!

EcalPlusHcalTowers

Plan

• Develop MET “Cleaning” tools/algorithms/strategies– Useful for early physics

• Overlay beam halo simhits with cosmic simhits with minbias simhits and digitise with ORCA– Individually and all together

• use PU code developed by Heavy Ion Group

– Do for a variety of beam halo rates

Plan (cont.)

• Study effect of beam halo & cosmic muons on trigger rates

• Study various cleaning algorithms (currently inspired from CDF & D0). E.g.:– Event charged fraction– Event EM fraction– Narrow longitudinal strip of “hit” HCAL towers

(constant in phi)• Aiming for

– CMS Note for September– Contributed JetMET Section in P-TDR Vol. 1

Future

• Investigate how MET might be used in online Data Quality Monitoring

• Etc,

• etc