2 The CDF Experiment at Fermilab Contents - Harvard University ...

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38 Section 2: CDF Physics Analysis g g ~g q g ~g g ~g q ~g Figure 17: Gluino production diagrams ~g q ~q q ~ 0 1 ~g q ~q q ~ 1 W ~ 0 1 ~g q q 0 q ~q q ~ 0 2 Z 0 ~ 0 1 q q Figure 18: Gluino decays Data Selection The data used for this search were recorded by CDF in 1993-5 and comprise 90 pb ,1 (Run Ib). A multi-level online trigger selected 2.6M events with 6E T > 35 GeV. On average there were 3.5 interactions per crossing, due to the high instantaneous luminosity. It is crucial that we understand the composition of the sample and identify the sources of missing
Section 2: Supersymmetry 39 transverse energy in the data. The main sources that can mimic the 6E T + jets signal, and therefore backgrounds to the search, are: Events with Main Ring accelator induced 6E T malfunctions (source of fake 6E T ) detector noise and other instrumental cosmic ray muon Bremsstrahlung (source of fake 6E T ) QCD events with 6E T arising from detector mismeasurements unistrumented regions (cracks), jet energy resolution (source of fake 6E T ) Z QCD associated production where the Z decays to (source of real 6E T ) W QCD associated production where the W decays to (source of real 6E T ) tt production where the top decays to a W and a b quark and the W decays to lepton and neutrino, (source of real 6E T ) We perform an aggressivemulti-stage clean-up of the trigger sample that rejects eciently cosmic background, instrumental background and jet mismeasurement backgrounds. At the rst stage it is important to improve the measurement of the 6E T in events with multiple vertices. This is implemented by identifying the main event vertex as the one associated with the highest momentum sum and reprocessing the data. At this stage the relative time stamp of the energy on the hadronic calorimeter and the beam crossing is used to reject Main Ring accelerator induced 6E T triggers and cosmic background. At the second stage the quality of the jets present in the event is tested by using the ratio of the electromagnetic to total energy in the event and the fraction of total transverse energy in charged particles (averaged over the tracks matching central clusters in the event). Residual cosmic ray background and overlap events with Main Ring hadronic splashes as well as other detector malfunctions are being eliminated at this stage. The eect of the clean up is shown in Fig. 19. The three distributions overlayed are the 6E T distribution of the trigger sample (largest tails), the sample derived after the rst cleanup selection is applied (6E T tail up to 300 GeV) and the corresponding one after the second clean up selection is applied. A signicant source of fake 6E T is due to jets landing in non-ducial regions of the detector (cracks) and causing energy imbalance in an event that would be otherwise a balanced QCD
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Page 3 and 4: Section 2: CDF 3 of Run I data. Rec
Page 5 and 6: Section 2: CDF Hardware Projects 5
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Page 36 and 37: 36 Section 2: CDF 2.3 Run I Physics
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Section 2: B Mixing and CP Violatio
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Section 2: B Mixing and CP Violatio
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Section 2: CDF 97 multijet trigger
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Section 2: CDF 99 The Jet Pseudora
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Section 2: CDF 101 while the proble
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Section 2: CDF 103 Talks at Confere
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Section 2: CDF 105 References [1] T
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