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Positioning of IR2 collimators to intercept secondary beams from bound-free pair
production and electromagnetic dissociation at the ALICE interaction point
John Jowett
1 J.M. Jowett, Collimation Upgrade Specification meeting, 16/3/2012
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Ultraperipheral processes in Pb-Pb collisions
J.M. Jowett, Collimation Upgrade Specification meeting, 16/3/2012 2
208208 208
2
82 82 82
82 82 82
207
08208 20
82
20
8
2082
8 81
08 82 82 82
208 80
208
BFPP1: Pb Pb Pb e ,
281 b, 0.01235
BFPP2: Pb Pb Pb 2e ,
?? ,
P
0.02500
EMD1: Pb Pb Pb n ,
Pb
Pb
b
96
b
b
208208 20882 82 22 88 206 Pb
, 0.00485
EMD2: Pb Pb Pb 2n ,
29 , 0.00970b
Each of these makes a secondary beam emerging from the IP with rigidity change
Pb1 /
11 /
m m
Q Q
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Losses during Pb-Pb Collisions in 2011
J.M. Jowett, LHC Performance Workshop, Chamonix 7/2/2012 3
Bound-free pair production secondary beams from IPs
IBS & Electromagnetic dissociation at IPs, taken up by momentum collimators
??
Losses from collimation inefficiency, nuclear processes in primary collimators
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Parameters considered
J.M. Jowett, Collimation Upgrade Specification meeting, 16/3/2012 4
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6.5 TeV
0.5 m (Nominal optics for 2019)
Half-crossing angle 80 rady
E Z
p
IP2
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Secondary beams from Beam 1 in IR2
J.M. Jowett, Collimation Upgrade Specification meeting, 16/3/2012 5
Cannot separate BFPP and main beam in warm area (eg by Roman pots a la TOTEM).
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Optimum collimator position
J.M. Jowett, Collimation Upgrade Specification meeting, 16/3/2012 6
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Open gap so EMD1 passes (to IR3)
J.M. Jowett, Collimation Upgrade Specification meeting, 16/3/2012 7
Further opening or local bumps allow other selections.
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ATLAS and CMS ?
ATLAS and CMS also take high-luminosity Pb-Pb
The same problem of BFPP losses exists in the DSs around IP1 and IP5
– Details of loss locations may be slightly different
– Highest losses in 2011 were right of IP5
Similar motivation to install DS collimators to avoid a peak luminosity limit from quenches and/or long-term radiation damage
J.M. Jowett, Collimation Upgrade Specification meeting, 16/3/2012 8
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Conclusions
DS collimator for BFPP protection must be near Q9 in IR2
– Unless perhaps we insert bumps?
Detectors for BFPP ions must be located in cold section
– Incorporate in DS collimators?
Collimator gap can control selection of ultra-peripheral processes for physics purposes
J.M. Jowett, Collimation Upgrade Specification meeting, 16/3/2012 9
