1380b 50ns schemes
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Reminder:
– 25ns satellite-main collisions, why ?
– summer test
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New results from October:
– LDM measurements
– ALICE satellite-main collisions in 50ns physics
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Prospects for a test thursday this week
– see also Steve Hancock's presentation LMC_101
LBOC
25-Oct-2011
CERN
Massimiliano Ferro-Luzzi
1
The current "sat-main" 1380b scheme
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LBOC
25-Oct-2011
CERN
The intermediate 12b batch is
shifted by 25ns such as to
collide in IP8 (not IP2)
SPS injection gap: 250ns
instead of 225ns
No more space for keeping the
pilot => overinject
Massimiliano Ferro-Luzzi
2
Attempt in 12jul to 26jul
main-sat IP2 collisions
1380b
1380b N=1.05
1092b
normal scheme
840b
264b
48b
LBOC
25-Oct-2011
CERN
Massimiliano Ferro-Luzzi
3
Why bother ?
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Benefits:
all small gains, but all real
– 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
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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
 with 1-2% satellites could operate at 10m and tune lumi by separation
– Upgrade LHC: if choose 50ns and if 3 main-main collisions are too
much (beam-beam limits ?), this trick would maybe allow upgrade
operation with ATLAS / CMS / LHCb (5e34 vs 2e33 luminosities)
LBOC
25-Oct-2011
CERN
Massimiliano Ferro-Luzzi
4
Fill 2222 25ns satellite distribution
first 50 minutes
last 50 minutes
LDM, Enrico Bravin
fill average
all central RF buckets of the
nominal 25ns slots
After removing those more
than 1 slot away from a main
bunch (exact definition ?)
LBOC
25-Oct-2011
CERN
Massimiliano Ferro-Luzzi
5
Fill 2220 25ns satellite distribution
LBOC
25-Oct-2011
CERN
LDM, Enrico Bravin
Massimiliano Ferro-Luzzi
6
Fill 2219 25ns satellite distribution
LBOC
25-Oct-2011
CERN
LDM, Enrico Bravin
Massimiliano Ferro-Luzzi
7
Fill 2218 25ns satellite distribution
LBOC
25-Oct-2011
CERN
LDM, Enrico Bravin
Massimiliano Ferro-Luzzi
8
Fill 2217 25ns satellite distribution
LBOC
25-Oct-2011
CERN
LDM, Enrico Bravin
Massimiliano Ferro-Luzzi
9
Fill 2216 25ns satellite distribution
LBOC
25-Oct-2011
CERN
LDM, Enrico Bravin
Massimiliano Ferro-Luzzi
10
Fill 2215 25ns satellite distribution
LBOC
25-Oct-2011
CERN
LDM, Enrico Bravin
Massimiliano Ferro-Luzzi
11
Fill 2210 25ns satellite distribution
LBOC
25-Oct-2011
CERN
LDM, Enrico Bravin
Massimiliano Ferro-Luzzi
12
Fill 2208 25ns satellite distribution
LBOC
25-Oct-2011
CERN
LDM, Enrico Bravin
Massimiliano Ferro-Luzzi
13
Fill 2204 25ns satellite distribution
LBOC
25-Oct-2011
CERN
LDM, Enrico Bravin
Massimiliano Ferro-Luzzi
14
LDM, Enrico Bravin
25ns bucket population products
2222
2220
All 25ns slots, but cut at
0.01for filling the histograms
N1*N2*1e9

N1tot*N2tot
bucket_product to luminosity conversion
is approximately (for 0 separation):
L[i]=bucket_product[i]*3.4e26 Hz/cm2
assuming 100um beams
2219
LBOC
2218
25-Oct-2011
CERN
Massimiliano Ferro-Luzzi
15
LDM, Enrico Bravin
25ns bucket population products
2217
2216
2215
LBOC
2210
25-Oct-2011
CERN
Massimiliano Ferro-Luzzi
16
LDM, Enrico Bravin
25ns bucket population products
2204
2208
LBOC
25-Oct-2011
CERN
Massimiliano Ferro-Luzzi
17
Summary from LDM
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All in all, the satellite populations are reasonably stable!
(never believe in your machine colleagues' pessimism...)
For the relevant satellites (those which collide with a main)
 Mean population: 1.3 - 2.0 x10-3
(I take the start of fill)
 RMS population: 0.6 - 1.2 x10-3
 Mean population product: 0.4 - 1.0
 RMS population product: 0.4 - 0.7
LBOC
25-Oct-2011
CERN
Massimiliano Ferro-Luzzi
18
Paolo Martinengo & Co
ALICE: Vertex timing
From fill 2217 onward, ALICE has pure "sat-main" collisions (i.e. is asking,
I suppose) for zero separation
Fill 2216, main-main V0 vertex
vertex
Fill 2222, main-sat V0
Lateral peaks due to background
LBOC
25-Oct-2011
CERN
Massimiliano Ferro-Luzzi
19
Paolo Martinengo & Co
ALICE: Timing correlations
Fill 2216, main-main T0 vertex
Fill 2222, main-sat T0 vertex
LBOC
25-Oct-2011
CERN
Massimiliano Ferro-Luzzi
20
ALICE: Vertex distribution in XY plane
Main-sat
LBOC
25-Oct-2011
Paolo Martinengo & Co
Main-Main
CERN
Massimiliano Ferro-Luzzi
21
ALICE: Vertex distribution along Z
Paolo Martinengo & Co
Main-sat
Main-main
FWHM
LBOC
FWHM
25-Oct-2011
CERN
Massimiliano Ferro-Luzzi
22
Approximately expected total luminosity
bucket_product to luminosity conversion
is approximately (for 0 separation):
L[i]=bucket_product[i]*3.4e26 Hz/cm2
2217 and beyond
assuming 100um beams.
Here I used for the approximaley
expected total luminosity:
L = L[i]_mean * L[i]_entries
Get 0.5-0.9 1030 Hz/cm2
ALICE wish to have up to 2x1030 Hz/cm2
LBOC
25-Oct-2011
CERN
Massimiliano Ferro-Luzzi
23
ALICE lumi from TIMBER
ALICE operating lumi (levelled)
2217 and beyond
ALICE operating lumi (levelled)
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LBOC
0.5-0.9 1030 Hz/cm2
At start of fill, fair agreement with the approximately expected!
But too small lumi head-on => no levelling possible
25-Oct-2011
CERN
Massimiliano Ferro-Luzzi
24
What now ?
LMC 101 minutes:
"DECISION: LMC gave the green light for an artificial satellite-bunch trial in the LHC"
What would be desirable:
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Prepare PS and SPS enhanced 25ns satellite beams just before an injection of a
50ns fill
– about 1-2% satellite fraction is OK (essentially, anything you want which is bigger than
0.2% and smaller than 5%...)
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Inject into LHC
– check with LDM in the LHC
– if OK, use for physics fill
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Mike: "There might be a little cost in ATLAS/CMS peak lumi"
=> Fine for one fill, then we evaluate
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Shouldn't cost more than, say, about 2h of LHC beam time
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The window for this test is very narrow: Thursday morning to Friday morning, or
saturday morning to sunday afternoon
Would be nice to achieve this before end of the proton run!!
LBOC
25-Oct-2011
CERN
Massimiliano Ferro-Luzzi
25