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Pile-up vertex finding in heavy ion collisions

Learn about pile-up vertex finding in heavy ion collisions, track incidence on the beam axis, vertex candidate identification, weight assignment for tracks, efficiency improvements, and future expectations for rates and lighter ions at RHIC II.

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Pile-up vertex finding in heavy ion collisions

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  1. Pile-up vertex finding in heavy ion collisions Marco van Leeuwen, LBNL

  2. Some numbers • TPC drift time ~40 ms • Time between events without pile-up: 80 ms • Interaction rate with single pile-up 12.5 kHz • Rate at Run 4 Au+Au: 3-10 kHz • Rate at Run 5 Cu+Cu: 8-25 kHz • Expected rate Au+Au RHIC II: ~ 60 kHz

  3. Pile-up vertex finding Incidence of tracks on beam axis (z-coord) Display (not the same event) Duncan Prindle Step 1: identify vertex candidates Resolution few cm # candidates: 1 triggered interaction + 2x pile-up

  4. Vertex selection parameters Number of BEMC hits Tracks crossing central membrane Mean-dip Red lines: parametrised ‘expected’ trends Step II: assign weights (rank) based on several properties

  5. Results Before Efficiencies After Anthony Timmins Confusion/inefficiency reduced to a few per cent in Cu+Cu

  6. Future expectations Anthony Timmins Method tested to 20-30 kHz rates (Cu+Cu) Will likely work up to expected RHIC II Au+Au rates, 60 kHz Lighter ions@RHIC II could be problematic (but see p+p experience) Caveat: track density for Au+Au @ 60 kHz larger than 25kHz Cu+Cu However, pile-up events are minbias, so not too worried

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