To calculate relative luminosity for online display

L = (dN/dt) /(б * A * ε )

L = Beam luminosity

(dN/dt) = Rate of precisely calculable physics process (total inelastic cross-section)

Lfactor = Luminosity Factor = 1/(б * A * ε )

A = Detector acceptance for the physics process

б = бpp = Total inelastic pp cross-section

ε = εeff = Effective Efficiency = Detector Efficiency (εdet) * Other efficiency

factors

ALICE On-line Luminosity

9/26/2008 1Luminosity Calculation in ALICE - Premomoy Ghosh

How do we proceed?

L = (dN/dt) /(б * A * ε )

Cross-section (б) for inelastic pp @ 900 GeV as 52.1 mb (confirmed with Karel Safarik)

• We get the rate, (dN/dt) from Detector-DCS• Need to know the acceptance (A) and the efficiency (ε) of the detector for the

process.

• Proposed to have options for luminosity measurement from different DCSs –

VZERO, TZERO, PIT and CTP – to start with.

Where to calculate ?

Options: 1) To get the rate from detector-DCS and calculate at ALICE-DCS

2) Luminosity calculation in respective detector-DCS and then imported by ALICE-DCS

Status of related detector-DCS ?

9/26/2008 2Luminosity Calculation in ALICE - Premomoy Ghosh

Readiness of PIT-DCS w.r.t. luminosity calculation

• Discussed with Cesar Torcato De Matos

PIT has 1200 Fast-OR input signals available from 1200 pixel chips-400 in inner layer and 800 in outer layer

PIT has 10 output counters developed with different algorithms and they are connected to CTP. All these counters exist in hardware but datapoints for PVSS are not yet created.Datapoints from the output counters can be made available within a few days. To understand and decide which of the output counters can be used for luminosity calculation.A few more days are required if the datapoint for rate for luminosity calculation has to be developed from input counters.

Could not contact T0-DCS. Roman will discuss CTP-DCS. Readiness of V0-DCS follows.

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Readiness of V0-DCS w.r.t. luminosity calculation

• Scalers on 16 triggers exist in V0-DCS.

T1: BBA AND BBC or

T2: BBA OR BBC

The flag BBA (BBC) is “ON” if the number of fired segments on the disk-A (disk-C) exceeds a programmed threshold TH_BBA (TH_BBC)

What is the value of TH_BBA or TH_BBC?

• Simulation result on Acceptance * Efficiency (efficiency for a given acceptance)

for full geometrical acceptance exists

1) For V0A AND V0C = 82.0 %

2) For V0A OR V0C = 93.4 %

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More on V0 simulation follows

V0 Simulation

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We have simulation results from Fabien Nandez• The efficiency*acceptance factor is from simulation assuming full active detector.

• If one segment is inactive - it is relatively easy to estimate the loss in the factor efficiency*acceptance.

• If more than one segment is inactive - because of different sizes and shapes of all 32 segments in each of the two disks, the problem becomes complicated and it is not possible to correct the efficiency for partial acceptance by any simple method online.

•For a given RUN: we start with whatever is known about the LIVE segments from before. Then at the end of the run, we analyze and find if any new segment is DEAD and try to find out the efficiency for corresponding acceptance. This correction can be incorporated afterwards in the database and published.

V0 Simulation Plan for acceptance correction

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Simulation Plan• We run say about 1M events with full V0 detector ACTIVE.

• We save all the numbers at SDIGITS level. May be ESD level is also OK.

• From these data we can calculate the efficiency for any acceptance of V0.  For example, if one set of segments are not working - we can turn those off in the SDIGITS and recalculate the efficiency for respective partial geometrical acceptance.

• Discussed with Peter Hristov and he is in agreement with the approach .

•To work in collaboration with Fabien Nandez.

Luminosity from V0 – some questions

• For full geometrical acceptance of V0, we can have luminosity script ready in the ALICE-DCS – to start with.

• How do we account for deadtime of the detector?

• Can the time-windows for BBA and BBC flags restrict signals on VZEROs due to direct beam-particles?

• Does the width of time-windows cause reduction in efficiency? Is it estimated?

• Can there be some impurity-factor in BBA, BBC due to beam-gas or beam-particles ? Do we need to estimate?

• Any other aspect / factor that we missed here ?

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Acknowledge discussions with Karel Safarik