fast and precise luminosity measurement at the ilc
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Fast and Precise Luminosity Measurement at the ILC
Ch.Grah
LCWS 2006Bangalore
LCWS2006, Bangalore Ch.Grah: Luminosity Measurement 2
Overview
The forward regionLuminosity measurement using
LumiCal Requirements Systematics Physics background
Fast luminosity monitor – BeamCal Using the pair background signal Beam parameter reconstruction
Summary and outlook
LCWS2006, Bangalore Ch.Grah: Luminosity Measurement 3
Forward Region – New Geometry20mrad geometry (LDC)
LCWS2006, Bangalore Ch.Grah: Luminosity Measurement 4
Forward Region - Tasks LumiCal (26 (43) mrad < θ < 153
mrad) Detection of low pT em interacting
particles Measure bhahba particles with high
precision BeamCal (5.6 mrad < θ < 28 (46)
mrad) Detection of low pT em interacting
particles Measure and analyse the deposition
from pairs originating from beamstrahlung.
LHCal (new idea) Low angle hadron calorimeter
PhotoCal (not drawn on this picture) Analyse beamstrahlung photons in the
range of ~100μrad
Minimize background from backscattering from pairs.
20mrad
2mrad
LCWS2006, Bangalore Ch.Grah: Luminosity Measurement 5
Backgrounds (Old 20mrad Geometry)
20mrad DID backscattering from pairshitting the LumiCal edge(K.Büsser)
Sketch of old BeamCalgeometry.
Projection of LumiCal‘sinner radius.
Energy depositedin LumiCal from pairs.
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LumiCalRequirements: 410
LL
Eve
nts
θ (rad)
Bhabha scattering
min
2LL
Energy (GeV)
Eve
nts
gen
gen
N
NN
N
N
L
L
rec
BHWIDE generated eventsprecision by:
LCWS2006, Bangalore Ch.Grah: Luminosity Measurement 7
Detector Performance
Detector performance can be included into MC.How well we have to know?
R.Ingbir
LCWS2006, Bangalore Ch.Grah: Luminosity Measurement 8
Systematic EffectsChanging the detector position
without
Including bias & resolution
Headon, 14,20 mrad X-angle outgoing beam
14 mrad X-angle detector axis
20 mrad X-angle detector axis
LCWS2006, Bangalore Ch.Grah: Luminosity Measurement 9
Compensating Systematic Effects by MC
X (cm)
Y (
cm) 20mrad X-angle
Detector axis
Before correction
after correction
ΔL/L~10-2
ΔL/L~10-3 This is assuming knowing in perfect precision many parameters!
So far these effects are all considered individually, so be careful!
LCWS2006, Bangalore Ch.Grah: Luminosity Measurement 10
Physics Background Four-lepton processes are the main source of physics background for luminosity measurement Simulation of e+e- -> e+e-l+l- (l=e, μ, τ) background with WHIZARD and Bhabha signal with BHLUMI detector simulation BARBIE for track hitting detector frontface (generated track information was used)
M.Pandurović/I. Božović-Jelisavčić
Energy [Gev] [deg]
Energy and polar angle of background
≈10-3 tracks/BX
LUMICALBEAMCAL
LUMICALBEAMCAL
LCWS2006, Bangalore Ch.Grah: Luminosity Measurement 11
Background Suppression
background can be effectively surpressed
x [cm]
x [cm]
x [cm]
x [cm]
y [c
m]
y [c
m]
signal/backgroundbefore (top) and after applying
the selection cuts (bottom)
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BeamCal
BeamCal: 4 < θ < 28 mrad(headon)
15000 e+e- per BX => 10 – 20 TeV
~ 10 MGy per year
“fast” => O(μs)
Direct photons for θ < 400 μrad (PhotoCal)
e+e- pairs from beamstrahlung are
deflected into the BeamCal
e+ e-
Deposited energy from pairs at z = +365 (no B-field)
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New Geometry
20mrad DID(Ri(LumiCal) = 10.0cm at z=2270mm)(Ro(BeamCal) = 16.5cm)
20mrad AntiDID(14mrad seems necessary for AntiDID)
An AntiDID configuration is close to the headon/2mrad design.BUT better be prepared for both possibilities.
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Fast Luminosity MonitoringWhy we need a fast signal from the
BeamCal?We can significantly improve L!e.g. include number of pairs hitting BeamCal
in the feedback system
0 100 200 300 400 500 6000
1
2
3x 10
34
Bunch #
Lu
min
os
ity
/ c
m-2
s-1
Luminosity development during first 600 bunches of a bunch-train.Ltotal = L(1-600) + L(550600)*(2820-600)/50
G.White QMUL/SLACRHUL & Snowmass presentation
position and angle scan
Improves L by more than 12% (500GeV)!
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Beamstrahlung Pair Analysis A lot of information is stored in the energy
distribution of beamstrahlung pairs hitting BeamCal. Observables (examples):
total energy first radial moment thrust value angular spread E(ring ≥ 4) / Etot E / N l/r, u/d, f/b asymmetries
detector: realistic segmentation, ideal resolution, bunch by bunch resolution
Beam parameters σx, σy, σz and Δσx, Δσy, Δσz
xoffset yoffset
Δx offset
Δy offset x-waist shift y-waist shift Bunch rotation N particles/bunch (Banana shape)
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Analysis Concept
Observables
Observables
Δ B
eamP
ar
Taylor
Matrix
nom
= + *
Beam Parameters
• determine collision
• creation of beamstr.• creation of e+e- pairs
guinea-pigguinea-pig
(D.Schulte)(D.Schulte)
Observables
• characterize energy
distributions in
detectors
FORTRANFORTRAN
analysis program analysis program
(A.Stahl)(A.Stahl)
and/orand/or
GEANT4GEANT4
11stst order Taylor- order Taylor-Exp.Exp.
Solve by matrix Solve by matrix inversioninversion(Moore-Penrose (Moore-Penrose Inverse)Inverse)
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Coefficients of the Taylor-Matrix
beam parameter i [au]
ob
serv
able
j [
au]
parametrization(polynomial)
1 point =1 bunch crossing
by guinea-pigslope at nom. value taylor coefficient i,j
LCWS2006, Bangalore Ch.Grah: Luminosity Measurement 18
Analysis for nominal ILC Parameters
ILCNOM, 20mrad DID
QuantityNominal Value
Precision
old new
x 553 nm 4.8 2.9
x 3.9 7.4
y 5.0 nm 0.1 0.2
y 0.1 0.4
z 300 m 8.5 8.5
z 6.7 6.3
y 0 2.0 0.6
single parameter analysis
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2mrad and 20mrad Analysis
QuantityNominal Value
Precision
2mrad 20mrad20mrad (2par)
x 553 nm 3.1 2.9 2.8x 5.2 7.4 7.6y 5.0 nm 0.3 0.2 0.2
y 0.3 0.4 0.4
z 300 m 4.8 8.5 11.1
z 3.7 6.3 7.4
εy40x10-
9mrad1.7 2.9 5.2
εy 0 4.2 4.1 4.7
x 17.7 9.3 10
y 0 0.5 0.6 0.6N 2x1010 0.01 0.01 0.01
N 0 0.01 0.02 0.03
...
LCWS2006, Bangalore Ch.Grah: Luminosity Measurement 20
BeamCal Geant4 Simulation Need precise simulation for showering/realistic bfield map.
Includes: flexible geometry (beam crossing angle, layer thickness,
variable segmentation, calorimeter tilt) simplified DiD/antiDiD magnetic field input – GP generated e+e- pairs output – root tree with energy distribution in segments 1 BX ~ 200min @ 2.4 GHz CPU
Shower visualization Energy/Layer distribution
A.Sapronov
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G4 Simulation with simplified B-field
σz, μm
20mrad DID
20mrad AntiDID
Deposited energy in sensorlayer
all layerslayer8
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Using Bfield Map
All layers Layer 8
Energy deposited in the sensors of the forward BeamCal.
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Summary Redesign of the forward region has been done to
cope with 20mrad DID (worst case). LumiCal
Investigated physics and selection cuts to effectively reduce background.
Investigated systematic effects (displacement, resolution, bias ....)...and recommend LumiCal to be centered around outgoing beam.
A luminosity measurement of ΔL/L ≈ 10-4 is feasible so far.
BeamCal Intratrain feedback of BeamCal has the potential to
increase the luminosity significantly. A fast beamdiagnostics has potential to access many
beam parameters (intratrain). This is also feasible for 20mrad. Have set up a G4 simulation of BeamCal for realistic
shower development and for realistic b-field map.
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Outlook LumiCal: extend background study by
detector simulation, crossing angle LumiCal Geant4 simulation for both design,
pad and strip version, are in workUse the BeamCal G4 simulation for the
beamdiagnostics Choose a subset of the detector information for
the analysis
Detector & Readout R&D => talk by W.Wierba (DAQ session)
Find more details at: http://www.ifh.de/ILC/fcal
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