The DCS role in the Luminosity measurement

1. The DCS role in the Luminosity measurement G de Cataldo

2. Basic information • The luminosity L is a quantity which relates the rate R of a process to its cross section s: R=L*s (for details: http://nayak.web.cern.ch/nayak/alice/alice_luminosity_1jun06.pdf ) • Due to the finite acceptance and efficiency (Acc and e) of a detector for a specific process, then using the relevant rate R the relative luminosity can be measured: L= R/(Acc * e* sspecific ). • For the absolute or total luminosity (all the known specific processes are included) the LHC beam parameters, the total cross section provided by TOTEM ( stot) and the vertex diamond size provided by SPD, will be used. • In the pp collisions the forward detectors V0 and T0 are the first candidates for the relative luminosity measurement . Pixel Trigger (PIT) will also contribute as soon as the trigger efficiency v.s. physics processes are known via simulation. • In PbPb collisions, ZDC (via the total hadronic cross section shad or mutual electromagnetic dissociation cross section) will be used for the relative luminosity first and later via a correction factors, the absolute one. • Average luminosity per bunch: The Central Trigger Processor (CTP) will provide the average luminosity per bunch since in that device the relevant rates (orbit number, buch crossing number) are available. G de Cataldo

3. Information sent from ALICE DCS to LHC *) the proposed production intervals are (on my knowledge) the same as proposed by/for CMS and ATLAS. *) later named Vertex Diamont. For information sent from LHC to Experiment please check: http://lhc-data-exchange.web.cern.ch/lhc-data-exchange/ G de Cataldo

4. Info. expected in OCDB from central DCS Background not mentioned G de Cataldo

5. The DCSs role in the L measurement • The ALICE total luminosity L will be calculated in the central DCS; • Each detector DCS (V0,T0, ZDC,PIT and CTP) has to archive and provide to the ALICE DCS only one relevant rate R. • Since the acceptance and efficiency depend on some parameter setting (HV, LV, th, gas….) then each DCS has also to provide and archive Acc and e at which the rate R is measured. Just as an example, in the hmpid a ‘detector status word’, summaries Acc information which are sent to the Offline Condition Database (OCDB). • L will be then calculated in the central DCS on the base of the single detector rates, corrective factors and relevant cross section. It will be archived, published via DIP for LHC and finally sent to the offline condition Database (OCDB) via shuttle. • The measurement of the vertex diamond will be carried out by SPD data in the DAQ environment. It will be sent to the OCDB (via fxs) and to the central DCS (via DIM). There it will be archived and published via DIP for LHC and other interested users. G de Cataldo

6. Dp’s set for each sub-detector • Each sub-detector is then requested to define the following PVSS data-point : • Datapoint Type: --->  AliLum_XXXType (where XXX is the detector identification: V00, T00, PIT, ZDC and CTP) • Datapoint: ---> aliLum_XXX • Datapoint elements:float rate float effCorrFactor (it contains e) • float accCorrFactor (it contains Acc) • float totCorrFactor (it contains Acc* e for those detectors that have only the product as the case of V0) • All the datapoint elements have to be archived; • In the central DCS node the total ALICE luminosity Lali = Lali(LV00, LT00, LPIT, LCTP….) will be calculated, monitored and compared with the one provided by LHC. • REM: the LHC luminosity, relevant for ALICE, is based on the BRAN-B system (CdTe detector) providing the average luminosity and average luminosity per bunch. G de Cataldo

7. Conclusion • the ALICE total luminosity L will be calculated in the central DCS on the base of the single detector rates, corrective factors and relevant cross section; • the concerned detectors/device are so far: V0, T0, PIT, SPD, ZDC and CTP; • Each sub-detector DCS provides in specified datpoint elements the trigger rate R, the acceptance Acc and efficiency e at which R is provided (corrective factors); • The measurement of the vertex diamond will be carried out by SPD data in the DAQ environment and archived in the central DCS. • L and the vertex diamond size will be published via DIP in the central DCS. G de Cataldo

8. Hmpid detector status words For each detector’s module binary information from the relevant subsystems are organized in 32 bit words. In the most significant 24 bits the sub-system status are reported while in the last 8 bit the module’s summary state (which module’s part is active or not) is provided. These seven status words are archived on change and at the end of each run sent to the OCDB. Summary module info: Binary information from Left and Right readout are provided with six module sectors status in one 8 bit word. G de Cataldo