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Beam Backgrounds

Beam Backgrounds. Itaru Nakagawa RIKEN/RBRC. cogged w/ collimator. Rates from clock trigger sample. Towards beam. Towards beam. Tsutomu’s MUID backgroud study. Towards beam. Towards beam. 2. Rates from clock trigger sample. 3. Run08 pp backgrounds. BBC rates ~ 91 kHz.

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Beam Backgrounds

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  1. Beam Backgrounds Itaru Nakagawa RIKEN/RBRC

  2. cogged w/ collimator Rates from clock trigger sample Towards beam Towards beam Tsutomu’s MUID backgroud study Towards beam Towards beam 2

  3. Rates from clock trigger sample 3

  4. Run08 pp backgrounds BBC rates ~ 91 kHz

  5. Away from beam Away from beam Away from beam • Things to notice: • Gap 4 much higher for upper panels (beam background worse due to lack of protection from concrete mezzanine) • Structure shows where the shielding kicks in. • Average hits/channel ~ 100. West East Small Toward beam Toward beam Toward beam South Horizontal

  6. Away from beam Away from beam Away from beam • Things to notice: • Average hits/channel ~ 10. • Gap 4 no higher than Gap 0. West East Small Toward beam Toward beam Toward beam North Horizontal

  7. What does this mean? • 100,000 events corresponds to 1e-2 seconds of time. • On the south we have: • ~100 hits/channel/1e-2sec, • or a hit rate of ~10 kHz/tube. • On the north we have: • 10 hits/channel/1e-2sec, • or a hit rate of 1 kHz/tube. • In MB events we have 14 hits/arm in the South and 1.4 hits/arm in the North. • During the clock trigger run the MB rate was 91kHz. • There are 3160 tubes/arm, so we would expect from beam 14*91kHz/3160 tubes = 400 Hz on the South (and, similarly, 40 Hz on the North). • Meaning that something like 96% of the hits in each arm are not in coincidence with collisions. • Caveat – the MB rate is with a vertex cut, without this cut the rate was nearly twice as high, which would up the expected rates to ~1 kHz and 100 Hz for each arm. But this still leaves 90% of the hits from non-collision background.

  8. What we know so far • Backgrounds situation isn’t serious at STAR • MUID rates @ clock trigger barely changes by collimation • As soon as steer beam from collision, the backgrounds disappear • Collision repopulates beam halo/beam backgrounds • MuID rates are highest Gap-0 next Gap-4 • Gap-0 backgrounds come from IP? • Gap-4 backgrounds come from upstream? • RPC proto indicates some components comes from upstream.

  9. Some observations: nice signals, but at two times, “late” signal at high/low thresholds, and lower voltages From Ralf’s meeting slide 2014/8/25 R.Seidl: RPC design R.Seidl: RPC design 9

  10. Second peak reduced in muon coincidence 2014/8/25 R.Seidl: RPC design R.Seidl: RPC design 10

  11. So, where is the source of backgrounds?

  12. Background Scintillators Layout

  13. North Tunnel Scintillators Counts < 200kHz Already achieved in Run09

  14. Beamline Diameter

  15. Beam Spacial Size at Triplet 5mm @ 35 m ~ 12  Smaller than 200 GeV

  16. Beam Size at IP

  17. Plan • Some space between shielding and beam pipe • Move background counter closer • Pin diodes in IP?

  18. Backups

  19. Beta Tune

  20. Magnets Layout

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