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\section{Triggering on Single Charged Particle}
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For the purpose of Hcal calibration, a dedicated trigger path has been
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designed in order to record a high rate of single charge particle
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(mainly pions). Using these data, Hcal will be able to obtained an
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intercalibration of the cells as well as an energy scale. The momentum
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of such particle will be equalized using appropriate weight to the sum
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of the energy deposited in Ecal and Hcal. It is clear that such events
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can also be used in order to have a clean sample of charged pions. The
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study of the energy deposition respectively in Ecal and Hcal can then
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be compared to the simulation in order to tune it.
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\subsection{Specificity of the Trigger}
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In order to perform a sensible calibration, Hcal detector needs a
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important amount of events. Single charge particle will be mainly
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produced within multijet production and such production is highly
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prescale at the trigger level.
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The trigger path has been modified in order to keep the bandwidth low:
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even if the rate of such events is high, the information kept is
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minimal. These kind of triggers are named AlCaRaw as their purpose is
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the calibration of the detector. The selection of the event is strong
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and the content of it is simply the minimal need request by Hcal
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calibration.
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\subsection{Selection of the Events}
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The High Level Trigger path is seeded using an OR of L1 single jets
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and L1 single tau jet. The corresponding level 1 rate for a
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instantaneous luminosity of $2\times 10^{30}$ or $2\times 10^{31}$ is
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of the order of 4.5 kHz.
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The selection is based on a L1TauJet object with a matching within a
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cone of 0.5 to a pixel track with a $p_T > 20$GeV. In a cone of 0.5
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around this object also no pixel track with $p_T > 2$GeV should be
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found.
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Once such candidate is found, the FED collections to be written out is
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reduced. Only tracker FEDs around the nominal tracks are recorded as
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well as for the Ecal while most of the FEDs of Hcal are written. This
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gives the possibility to access to all timing information needed to
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perform Hcal calibration.
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The total rate of such events is expected to be around 20Hz which
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should give a bandwidth occupation of around 2MB/s.
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Such events require tracker measurement, so they will cover at maximum
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the calibration up to $|\eta| \leq 2.4$.
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