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HBD Towards Run-9

HBD Towards Run-9. Itzhak Tserruya HBD meeting, April 2, 2008. Readiness of HBD for run-9. Request from Raphael H/L convener: “In the light of defining our beam use proposal, we need some input on

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HBD Towards Run-9

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  1. HBD Towards Run-9 Itzhak Tserruya HBD meeting, April 2, 2008

  2. Readiness of HBD for run-9 • Request from Raphael H/L convener: • “In the light of defining our beam use proposal, we need some input on • the HBD. Would it be possible to have a presentation on the subject? In particular, we'd like to hear : • - a quick summary of the run7 problems (HV, scintillation...) • - the status of the analysis (electron id up to which centrality?) • the honest status of the repairs, and the likelihood of the readiness for the run 9.” • Request from Tony Analysis coordinator: • “I would like to try to understand the status and plans for HBD offline software with a view towards Run 9… We will need, by the start of Run 9: • The ability to reconstruct HBD data within 2 weeks of physics collisions, earlier if possible. This will require that we have all necessary calibrations in place, and have working reconstruction code in place. It is not necessary that the reconstructed HBD data be final physics quality for this purpose, but it has to be good enough for meaningful conclusions to be drawn about performance and yields. • 2) The ability to match reconstructed tracks in the central arm to HBD hits and add the appropriate physics parameters to PHCentralTracks. • 3) Analysis code in place that extracts meaningful physics data from the HBD-matched central arm tracks, so that performance and yields can be evaluated during the run.”

  3. Reconstruction software • The HBD reconstruction software involves three main elements: • Gain equilibration • Cluster algorithm • Tracking to central arm • Close pair rejection

  4. Gain equilibration • is in excellent shape. • exploits the scintillation signals • has been used in run-7 off-line analysis • software exists. • a short time after the first collisions in run-9 we should be able to have the gain equilibration module ready.

  5. Gain derived from the scintillation (I) • Scintillation hit identification: • single pad hits not belonging to any track in peripheral events • Gain determination: • Fit the range (10-50) ADC channels with an exponential function • 1/slope increase with event multiplicity • 1/slope = Gain . <m> • (where <m> = avrg nr of scintillation photons in a fired pad) • Assuming the nr of scintillation photons per pad follows a Poisson distribution: • A fired pad measures: • <m> = • P(0) = probability to have no hit in a pad = • <m> =

  6. Gain derived from the scintillation (II) • P(0) is not measured • Determine the probability P(0,th) of not firing a pad for a given threshold and extrapolate to a zero threshold P(0,th) = 1 – [nr of fired pads (A>th)] / [total nr of pads]* * The large pads are excluded in this analysis i.e. the total nr of pads = 93 or 94.

  7. Cluster algorithm • Purpose: determine the location, size (number of pads) and total signal of each hit in the HBD. • A simple algorithm exists that has been used in the off-line analysis of run-7 Au+Au events with centrality > 50%. • Needs a lot of work: of optimization, cluster splitting and also conceptually in order to deal with more central events.

  8. Tracking to central arm • Software exists, has been used in run-7 off-line analysis, in excellent shape. • Hadrons selected in central arm: • Vertex +/- 20 cm • < 50 tracks • 3 matching to PC3 and EMCal • n0 < 0 • EMC energy < 0.5 • Projected onto HBD: • Z in HBD +/- 2 cm •  in HBD +/- 25 mrad • Position resolution: • z ≈  ≈ 1 cm • Dictated by pad size: • hexagon a = 1.55 cm • (2a/√12 = 0.9 cm)

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