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Luminosity measurements and forward physics in ATLAS
• forward detectors • luminosity calibration and monitoring• forward physics beyond luminosity
Hasko Stenzel
on behalf of the
ATLAS Luminosity
& forward physics WG
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Forward physics in ATLAS
ATLAS proposes a two-stage program:
1: Luminosity calibration with Roman Pot detectors from elastic scattering in the Coulomb region using special beam optics with high β*.
Relative luminosity monitoring by an integrated Cerenkov detector LUCID up to highest luminosity.
2: Hard diffractive physics, exclusive central diffraction, double-Pomeron exchange, requiring proton tagging and momentum-loss measurements at collision optics.
Studies for radhard RP detectors at 220m are ongoing, complementing FP420 studies.
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The ATLAS detector
TAS
R
50 1 2 43 6 7 8
Barrel
FCAL LUCIDTracking
EndCap
RP ZDC/TAN
Diffraction/Proton Tagging Region
y109
-chambers
inelastic
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Motivation for a precise Luminosity determination
Relative precision on the measurement of HBR for various channels, as function of mH, at Ldt = 300 fb–1. The dominant uncertainty is from Luminosity: 10% (open symbols), 5% (solid symbols).
(ATLAS-TDR-15, May 1999)
Determination of Standard Model cross sections ● heavy quark production● W/Z production ● QCD jet cross sections
Background for searches, constraints of PDFs
Theorectical predictions at the level of 5%
with prospect for improvements (NNLO).
New physics manifesting in deviation of x BR
relative to the Standard Model predictions
Important precision measurements● Higgs production x BR● tan measurement for MSSM Higgs
pp
bgdobs
LA
NN
exp
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Methods of Luminosity measurements
Absolute luminosity ● from the parameters of the LHC machine● rate of ppZ0/ W± l+ l- / lν
● rate of ppγγμ+ μ-
● Optical theorem: forward elastic+total inelastic rate, extrapolation t0 (but limited |η| coverage in ATLAS)
● cross-check with ZDC in heavy ion runs● from elastic scattering in the Coulomb region● combinations of all above
Relative luminosity● LUCID Cerenkov monitor, large dynamic range, excellent linearity
ATLAS aims for 2-3% accuracy in L
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Luminosity from elastic scattering
Measure elastic pp-scattering down to
very small angles (~3 μrad)
● operate tracking detectors very
close to the beam, 10 σ = 1.2 mm
● high β* optics
parallel-to-point focusing
● reconstruct the t-spectrum
● fit L to the t-spectrum
Coulomb region: FC≈FN
UA4 measurement
2
2
0
2
4
2 t
eit
aFFL
dt
dN EMNC
t
B
ρσ
L tot
radGeVtot
EMa
t
5.3
min24106
8
min
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Detector requirements
Physics & operation requirements
• detector resolution d = 30 m , beam spot size =120 m at RP
(t-resolution dominated by beam divergence) • detector sensitivity up to the edge towards the beam
(‘edgeless detector’, insensitive region d0 100≲ m at the edge)
• position accuracy ~ 10 m relative between top and bottom detector (stringent survey and metrology requirements)• radiation tolerance 100 Gy/yr (dominated by beam halo)• rate capability O(1 MHz) and time resolution O(5 ns)• insensitive to EM pulse from the bunched beam
Integration & construction constraints
• integration in the readout/DAQ/trigger scheme of ATLAS• LHC safety, control and interlock requirements• limited resources and tight schedule
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Roman Pots for ATLAS
RP
IP
240m 240m
RPRP RP
RP RP RP RP
Roman Pots
Two RP stationswith top and bottom
vertical pots, separatedby 4 m, at each side 240
from IP1
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Roman Pot detectors
Roman Pot mechanics
(TOTEM design)
PMT baseplate
optical connectors
scintillating fibre detectors
overlap&trigger
Roman Pot
MAPMTsFE electronics
& shield
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The Roman Pot (modified TOTEM design)
Overlap extrusions brazed on bottom
Top flange with helicoflex joint
Pumping hole
Rectangular body out of centerBrazing of beam
windows
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Top view
Fiber detectorTrigger scintillator (detector)
Overlap detectorTrigger scintillator (overlaps)
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detector principle
LHC
beam
key features:
square scintillating fibres 0.5x0.5 mm2
U/V geometry 45o stereo layers 64 fibres per module plane 10 double sided modules per pot staggering of modules by n√2x0.5mm/10 trigger scintillator in the crossing area overlap detectors for relative vertical alignment overlap triggers in the beam halo
Fiber detector: 10 plates of
2x64 fibers
Trigger for detector: 1 plastic scintillator 3mm thick
Overlap detector: 3 plates of
2x30 fibers
Trigger for overlap detector: 2 plastic scintillator 3mm thick
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detector prototypes
0.5mm spacers
reference edge
0.17mm Al2O3
ceramic substrate
Principle Protoype: 20 Planes u and v of 6 fibres
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Beam tests of ALFA prototypes
Trig.
Trig.
Si1Si2
Si4 S1 x S2
S3
Purpose of the testbeam:
- photoelectric yield- efficiency- cross talk- edge sensitivity- track resolution
proof of principle
At DESY22, 6 GeV e-
October/November 2005
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testbeam results: photoelectric yield and cross talk
OPERA readout(900 V)
<Npe>/MIP=4-4.5
total opticalcross talk = 4%
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testbeam results: efficiency
single fibre efficiency 90-94% (depends on cut)
insensitive area at the edge < 30 μm
(limited by resolution)
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testbeam results
?29.529.9Si telescope
98.9936.5636.00ALFA
ε[%]σy [µm]σx[µm]At Ee = 6 GeV resolution scales like 1/E large multiple scattering contribution expect σx,y≈20µm from MC at LHC
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Transversal displacement of particles in the ring away from the IP:
Special optics with high * and parallel-to-point focusing:
independent of the vertex position
properties at the roman pot (240m)
y*
y*
parallel-to-point focusingydet
IP Leff
advance phase 90 ,point -to-parallel
; o
2**,
**det ptLy yyeffy
Beam optics
09
0
m 119
m 2625
*y
*****
sinsincos yyy
2max
2min
max
min
d
GeV 098.0
GeV 0004.0
rad 7.44
rad 7.2
mm 12.0
t
t
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Simulation of elastic scattering
t=-0.0007
t=-0.001
10 σ
15 σ
2
,
2
,
2
2222*
yeffxeff
xx
L
y
L
xp
ppt
t reconstruction
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L from a fit to the t-spectrum
2
222/
2
22
2
16
14
c
e
t
e
t
cL
FFLdt
dN
tBtot
tBtot
NC
input fit errorcorrelation
L 8.124 1026 8.162 1026 1.5 %
σtot 100 mb 101.1 mb 0.74% -99%
B 18 Gev-2 17.95 Gev-20.59%
64%
ρ 0.15 0.15024.24%
92%
Simulating 10 M events,running 100 hrsfit range 0.00055-0.03
large stat.correlation between L and other parameters
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experimental systematic uncertainties
divergence
divergence
divergence
divergence
Currently under re-evaluation
beam divergence σ’=0.23µrad detector resolution detector alignment background from
Halobeam-gasbeam-wallnon-elastic
beam optics uncertainties
Δexp≈2-3 %
impact of beam divergence
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LUCID:Luminosity measurement using Cerenkov integrating detector
Front face of LUCID end is ~17m from the IP - covering 5.4 <|η|< 6.1 Front face of LUCID end is ~17m from the IP - covering 5.4 <|η|< 6.1
LUCID region 67 Mrad/year at 1034 cm-2s-1
from J.Pinfold
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LUCID detector principle
Winston Cones Fibres
Two detectors x 168 Al tubes filled with C4F10 or Isobutane at 1 or 2 Bar pressure
Two detectors x 168 Al tubes filled with C4F10 or Isobutane at 1 or 2 Bar pressure
Winston cones at the end of the tubes bring the Cerenkov light onto quartz fibers.
Winston cones at the end of the tubes bring the Cerenkov light onto quartz fibers.
LUCID Cross-sectionLUCID Cross-sectionBeam pipe
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LUCID test beam performance
<Npe>/Cerenkov tube = 5.3, a bit lower than anticipated from simulation triggered design improvements for tubes/winston cones/fibre coupling
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LUCID luminosity monitoring
No Saturation
Linear response
Sensitive to primaries – projective geometry – smaller signals for secondaries & soft particles:
● shorter paths length for secondaries● Cerenkov thresholds
No Landau fluctuations in Cerenkov emission counting multiple tracks/tube – no saturation
Excellent time resolution ● ~140ps @ CDF● Luminosity bunch-by-bunch
Linear relationship between lumi & track counting
Segmentation in tubes gives position sensitivity
Radiation hard – light – compact
Sensitive to primaries – projective geometry – smaller signals for secondaries & soft particles:
● shorter paths length for secondaries● Cerenkov thresholds
No Landau fluctuations in Cerenkov emission counting multiple tracks/tube – no saturation
Excellent time resolution ● ~140ps @ CDF● Luminosity bunch-by-bunch
Linear relationship between lumi & track counting
Segmentation in tubes gives position sensitivity
Radiation hard – light – compact
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Forward physics beyond luminosity
From the luminosity run and elastic scattering we get
the total cross section σtot
the nuclear slope B the ρ-parameter
... to some accuracy
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hard diffraction with ATLAS + RP220
A new project for RP detectors at ~220 m to study DPE at high luminosity has started
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RP220 project
Place two horizontal RP stations around 220m Run at high luminosity with collision optics Si strip / micromegas detectors studied Cerenkov counters for timing considered extension of the luminosity program, complementary to FP420
beam spot calculated with MADX in the RP region
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acceptance for t and ξ
0<ξ<0.18
acceptance for ξ from ~0.01 to ~0.16
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conclusion
ATLAS luminosity program
● with roman pot detectors from elastic scattering for absolute calibration
● complemented by W/Z counting and γγ-processes● and machine parameters● with LUCID for luminosity monitoring● gaining experience in operation close to the beam ● 2006: testbeams for ALFA and LUCID, final design● construction 2006/2007, installation 2007/2008
Upgrade options
● RP220 under study to explore hard diffraction & DPE● complementing/extening FP420● time scale 2008-2009
ATLAS luminosity program
● with roman pot detectors from elastic scattering for absolute calibration
● complemented by W/Z counting and γγ-processes● and machine parameters● with LUCID for luminosity monitoring● gaining experience in operation close to the beam ● 2006: testbeams for ALFA and LUCID, final design● construction 2006/2007, installation 2007/2008
Upgrade options
● RP220 under study to explore hard diffraction & DPE● complementing/extening FP420● time scale 2008-2009