The intermediate 12b batch is shifted by 25ns such as to collide in ip2 (not ip8)

The intermediate 12b batch is shifted by 25ns such as to collide in IP2 (not IP8)

• The intermediate 12b batch is shifted by 25ns such as to collide in IP2 (not IP8)

The intermediate 12b gives staggered crossings in IP8: 12b make LR encounters in IR8 at 3.75m instead of usual 7.5m

• 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)

Shown hear relative to average main bunch population

• 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.

IP2 lumi signal clearly visible, but on low side

• 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,

250ns gaps in SPS

• 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!

Benefits:

• 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)