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1380b 50ns schemes

1380b 50ns schemes. 12b staggered, LR encounters in IP8 ALICE satellite-main collisions in 50ns physics. The "standard" 2011 1380b scheme. The intermediate 12b batch is shifted by 25ns such as to collide in IP2 (not IP8). LR collisions at 3.75m. 7.5m. colliding. staggered.

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1380b 50ns schemes

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  1. 1380b 50ns schemes 12b staggered, LR encounters in IP8 ALICE satellite-main collisions in 50ns physics

  2. The "standard" 2011 1380b scheme • The intermediate 12b batch is shifted by 25ns such as to collide in IP2 (not IP8)

  3. LR collisions at 3.75m 7.5m colliding staggered • The intermediate 12b gives staggered crossings in IP8: 12b make LR encounters in IR8 at 3.75m instead of usual 7.5m • with negative LHCb polarity (net angle of 40urad), the encounters are closer than with the positive (1040urad). • Is this an issue for operation / performance ? • Note that most bunches make such LR collisions at 3.75m in IR2 • This 12b staggered pattern in IR8 can be removed • either in the standard scheme (remove 24 collisions from ALICE and add them to LHCb), not very nice for ALICE • or by using the IR2 sat-main scheme (clearly preferred if we would have to make a choice) 7.5m

  4. 12jul to 26jul main-sat IP2 collisions 1380b 1380b N=1.05 1092b normal scheme 840b 264b 48b

  5. Size of 25ns satellites fills 1900 and 1901 Courtesy Adam Jeff • Shown hear relative to average main bunch population • Scaling from 1.2e33 Hz/cm2 at IP1 (* = 1.5m) and assuming 2x1300 collisions in IP2 and homogeneous emittance, we need Nsat25ns  = 0.14% Nmain for reaching 5e29 Hz/cm2 at IP2 (* = 10m), head-on. • Caveat: absolute value of measured fraction has systematics (under study) related to baseline subtraction.

  6. ALICE sat-main with 48b main-sat IP2: ~23 main-main IP1: 9 ATLAS/ALICE 9.5/0.007 = 1360 expect 2600 for 0.1% sat fraction

  7. ALICE sat-main with 264b main-sat IP2: ~427 main-main IP1: 249 ATLAS/ALICE 250/0.054 = 4630 expect 3900 for 0.1% sat fraction

  8. ALICE sat-main with 840b and 1380b 840b "best" lumi ratio ATLAS/ALICE = 8800 expect 4000 for 0.1% sat fraction 1380b best lumi ratio ATLAS/ALICE = 5000 expect 4000 for 0.1% sat fraction

  9. Rough summary • IP2 lumi signal clearly visible, but on low side • Unfortunately: • no LDM measurement (?) • no AFS summary files from ALICE (coming ?) • NB: was ALICE asking/hoping for 2e30 Hz/cm2 ??? (was never advertised for a 0.1-0.2% sat fraction) • Prospects: • improved control of sat fraction in PS ? • smaller emittance, caveat: very coarse

  10. 1380b with sat-main collisions in IP2 • 250ns gaps in SPS • all bunches are staggered in IR2, hence each main collides with an "empty" 25ns slot... unless there is a satellite at that place!

  11. Why bother ? all small gains, but all real • Benefits: • ALICE luminosity diluted over all 25 ns slots: perfect, minimize pile-up! • More collisions in ATLAS (1%), CMS (1%) and LHCb (2%) • SPS 250ns gap: "more relaxed operation" w.r.t. 225ns gaps • And... (but is this really a benefit ?) no more LR encounters at 3.75m for the 12b in IP8 • Prospects: • PS RF (Steve Hancock): potentially could control the 25ns satellite intensity! • Next year: could squeeze ALICE according to achievable population of 25ns satellites, • e.g. b*=1m would allow operating with current satellite populations • Upgrade: if choose 50ns and if 3 main-main collisions are too much, this trick would maybe allow upgrade operation with ATLAS / CMS / LHCb (5e34, 5e43, 2e33 lumies)

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