FP420 Proposal Document: Alignment Section

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FP420 Proposal Document Alignment Section
Mainly Jo Pater and Mike Albrow, KP

• Highest resolution charged particle spectrometer
  ever!
• 420 m of vacuum, 120 m of 8 T dipoles, 10 m at
  start, 1 rad at back.
• Want (ideally) MM measurements to be limited by
  beam momentum spread,
• not detector resolutions or alignment or
  calibrations.
• (Then well ask for electron cooling of the beams
  to beat that limit!)
• Issues
• ? Optics of the machine, how well we know it,
  changes with time. (Peter)
• ? Detector resolution and track resolution
  (including multiple scattering)
• ..... not this section.
• ? Alignment and positioning of detectors w.r.t.
  each other and beam.
• Calibration of momentum scale, linearity, and
  resolution ( , and MM)
• Alignment (space) calibration (momentum) are
  distinct things

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Optics Peter wrote section but we include some
here.
Beam position and slope known
Known magnetic elements Each has a matrix IN ?
OUT
BEAM
Track known to 5 um and 1 urad in x,y
and well enough in z
Vertex known to lt 10 um in x,y and well enough
in z
vector x,x,y,y,p
vector x,x,y,y,p
FP420
HECTOR (Louvain) X(s) M1.M2... X(0) checked
with MAD-X
CMS top view CMS side view ATLAS top view ATLAS
side view
FP420
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Chromaticity grids at 420 m Top
plot Displacement from the beam (dx) for
different energy losses from 10 100 GeV and
scattering angles from 0 500 murad. Really a
trapezoid, do not be fooled by scale, 1 mm 1000
um / tick mark! Bottom plot Opens it up by
showing x vs x Now you see you need BOTH
x and x to get energy loss. Note scale 1 tick
in x is 10 urad. We should do 10x better 8 um
over 8 m 1 urad. Have the resolution (4 layers
of 10 um) but need also the alignment.
10 GeV, 0 deg
100 GeV, 0 deg
100 GeV, 500ur
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• Alignment
• Internal, all planes known relative to each
  other.
• Precision construction
• Important to have planes very well
  parallel to remove 2 degrees of freedom.
• Important to have strips (pixel axes)
  parallel (or perpendicular)
• These should come from precision engineering,
  at few micron level.
• (Microscope) alignment of strips on layers
  within a station (3 stations).
• (b) Three stations aligned relative to each other
  with wire position sensors

Capacitative measurement, relative to
C-fibre wire, sub-micron, as used for LHC
alignment.
Off-line, straight (7 TeV) tracks ... can zero
residuals (x1,y1,x2,y2) remain.
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Do not (phew!) need to know track w.r.t.
ATLAS/CMS to microns! The 7 TeV beam is good to
tie these coordinate systems together. (Bent
laser) What we need to know is the distance, dx
and dy, between the beam centroid and the track,
at the front (dx1,dy1) and back (dx2,dy2) of the
420 arm. Thus we need precision beam position
monitors (BPMs) at front and back. Ideally 2 BPMs
at each end, fixed w.r.t. beam and fixed w.r.t.
420 detectors.
Schematic 2 BPMs not 4
GARAGE
OPERATING
LVDT measurement
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Arc BPM - Button Feed-through
Rhodri Jones talk
1158 button BPMs in LHC Transfer lines. Issue
is not precision but calibration
Button Feedthrough
Beam Screen
Liquid Helium Cooling Capillary
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Front End Electronics (BPMs)
LHC BPMS mostly cryogenic we want warm. We want
better calibration. Higher precision
mechanics(?) and precision balance between L R
gains. E.g. Duplex Make L R signals both go
through A B electronics, so gains etc must be
equal (time averaged).
This is not quite same, but similar in spirit(?)
Rhodri Jones talk
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Rhodri Jones talk
BPMs can be calibrated on bench before
installation with pulsed wire centre, linearity,
slope. Will do, but want to check before-after
installation
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From HECTOR (de Favereau, Rouby and Piotrzkowski)
Misalignment seems to have minor impact on
resolution, but we need also mass scale, ability
to remove time-varying misalignments, etc. I.e.
we must have a CALIBRATION.
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Calibration with Physics Processes
Check and adjust if necessary momentum
scale. Test its linearity. Measure the resolution.
Needs a process with momentum or mass range
Essential, to know sensitivity and to measure
widths of resonance

• We know of, and discuss, 3 physics processes that
  can contribute
• pp ? p p gamma (bremss, forward, ? ZDC)
• p p ? p X single diffraction, optimise
  t-distribution
• p p ? p ll- p exclusive di-lepton
  production

(Elastic scattering even at high-t is not
accepted) Exclusive di-lepton is the only one
with the needed 10-4 precision, but others can
be useful controls.
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Calibration with Bremsstrahlung
Beam proton
420
ZDC EMcal
Photon brems from collision point 100 GeV
Say ZDC EMcal resolution 20/sqrtE, i.e 2 or
2 GeV, not uninteresting. Need calibration of ZDC
energy scale (how?), and questions of backgrounds
multi-photons, pios, radiation from
elsewhere. ? Could be useful, it remains to be
seen
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Exclusive Dilepton Calibration
l
p
p
l-
Energy and longitudinal momentum conservation
Dilepton measurement ? both p momenta (only need
to see one!) Mass of dilepton measured to 100
MeV (pT,eta) (?) and that gives order of
precision on protons ? Missing Mass, except for
p-beam spread, which dominates in both
cases. But cross section falls fast with
M(ll-) want low mass/pT threshold ( 10 GeV/5
GeV) , forward leptons. Probably v. difficult for
electrons (trigger, backgrounds), possible for
muons. Must do it with pile-up Background can be
tolerated.
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Exclusive dimuon rates, coverage
Want coverage to low mass, for cross section,
thus statistics. Want coverage to forward
rapidities to increase on that side Example
CDF Run II Preliminary
Expect 8500 events(?)/
twice that if pT gt 4 GeV/c because of Upsilon
photoproduction Sigma.B 6,000 fb Goncalves
Machado 20,000 fb Klein
Nystrand Upsilons also ? nice check on mass
scale
pT(min) 5
pT(min) 4
CDF Run II Preliminary
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Goncalves and Machado, arXiv0710.4287
Goncalves and Machado, arXiv0707.2523
Photo-production of Z
But other modes, ee-, b-bbar (x4) !
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Off-line optimization of x,y offset, maximizing
slope (and intercept) of single diffractive
t-distributions (Gallinaro and Goulianos, CDF7877)
0.2 mm
Resolution (Tevatron) 1mm (x), 0.2mm(y)
But this is integrated over a wide range of
xi. If one selected a small band of xi as
determined by the calorimeters (single
interaction, no PU) it should be sharper. (Dino,
was this tried in CDF? How does this scale to
LHC?)
1 mm
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Conclusions, in document (have text)
Along with crucial importance of high precision
detectors, it is vital to have high
precision Internal and stable alignment of all
detectors, in manufacture and in operation
(movements). Beam position monitors have the same
requirements, to know tracks w.r.t. beam in
displacement and angles. (The beam itself ties
ATLAS/CMS to FP420) . Also vital is CALIBRATION
with physics processes. We know three Brems
photons to ZDC Single diffraction
t-distributions Exclusive muon pair production
lowest rate but best precision. WE CAN
ACHIEVE WHAT IS NEEDED but with great care