analysis of beamstrahlung pairs ecfa workshop vienna, november 14-17, 2005 christian grah

Analysis of Beamstrahlung Analysis of Beamstrahlung Pairs Pairs

ECFA Workshop Vienna, November 14-17, 2005

Christian Grah

11/16/2005 Ch.Grah: Analysis of Beamstrahlung Pairs 2

OutlineOutlineVery Forward Calorimetry

Fast luminosity monitoring

Analyzing pairs from beamstrahlung with BeamCal

Pair distributions in different geometries and magnetic field configurations

Summary & outlook


Very Forward RegionVery Forward Region

LumiCal: 26 < θ < 82 mrad

BeamCal: 4 < θ < 28 mrad

PhotoCal: 100 < θ < 400 μrad


Very Forward CalorimetersVery Forward Calorimeters

LumiCal: Precise measurement of the luminosity by using Bhabha

events (very high mechanical precision needed). Extend coverage of the ILC detector.

Photocal Beam diagnostics from beamstrahlung photons.

BeamCal: Detection of electrons/photons at low angle.Beam diagnostics from beamstrahlung

electrons/positron pairs. Shielding of Inner Detector.


BeamCal: Beam DiagnosticsBeamCal: Beam Diagnosticsand Fast Luminosity Monitoringand Fast Luminosity Monitoring

15000 e+e- per BX => 10 – 20 TeV

~ 10 MGy per year

“fast” => O(μs)

Direct photons for < 400 rad (PhotoCal)

e+e- pairs from beamstrahlung are

deflected into the BeamCal

e+ e-

Deposited energy from pairs at z = +365 (no B-field, TESLA parameters)


BeamCal: W-Diamond BeamCal: W-Diamond SandwichSandwich

Length = 30 X0

(3.5mm W + .5mm diamond sensor)

~ 15 000 channels

~1.5/2 cm < R < ~10(+2) cm

Space for electronics


Fast Luminosity MonitoringFast Luminosity Monitoring Pair signal included into the fast 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

0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.220

5

10

15

Fractional Lumi Change After IP FB

= 0.12124 0.031719

0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.220

5

10

15

Fractional Lumi Change After ANG FB

= 0.12149 0.03356

L improvement for 500 GeV


Beamstrahlung PairsBeamstrahlung Pairs 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)


Analysis ConceptAnalysis 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)

11stst order Taylor- order Taylor-Exp.Exp.

Solve by matrix Solve by matrix inversioninversion(Moore-Penrose (Moore-Penrose Inverse)Inverse)


beam parameter i [au]

ob

serv

able

j [

au]

parametrization(polynomial)

SlopesSlopes

1 point =1 bunch crossing

by guinea-pigslope at nom. value taylor coefficient i,j


σx σy σz Δσx Δσy Δσz

0.3 % 0.4 % 3.4 % 9.5 % 1.4 % 0.8 %

0.3 % 0.4 % 3.5 % 11 % 1.5 % 0.9 %

0.9 % 1.0 % 11 % 24 %

5.7 % 24 % 1.6 % 1.9 %

1.8 % 1.1 % 16 % 27 % 3.2 % 2.1 %

Multi Parameter AnalysisMulti Parameter Analysis


Moving to 20mrad crossing Moving to 20mrad crossing angleangle

with DIDwith DID

Boost the generated pairs (GuineaPig) according to crossing angle. Shift center of detector to the outgoing beam. New segmentation of the detector and blind area for the incoming beam. Use a simplified implementation of DID field. (B.Parker & A.Seryi)

Coordinate system


Old Geometry for 20mradOld Geometry for 20mrad

QuantityNominal Value

Precision

x 553 nm 4.8nm

x 3.9nm

y 5.0 nm 0.1 nm

y 0.1nm

z 300 m 8.5 m

z 6.7 m

y 0 2.0nm

PRELIMINARY!Multi Parameter Analysishas also been done.

Applied the algorithm to the old 20mrad geometry, using TESLA parameters.


20mrad crossing angle 20mrad crossing angle – old geometry– old geometry

Here: ILC nom. beam parameters

Sketch of BeamCalgeometry.

Projection of LumiCal‘sinner radius.

Energy depositedin LumiCal from pairs.


BackgroundsBackgrounds

20mrad solenoid

20mrad DID backscattering from pairshitting the LumiCal edge

Background simulations by Karsten Buesser.


First try to fixFirst try to fix

Changed geometry:increased aperture of LumiCal by 3 cmincreased outer radius of BeamCal by 3 cmincreased apertures in between accordingly

Situation improved but still a factor of ~5 worse than in the 2mrad case.

Larger increase of the aperture is necessary, which will increase the background from backscattering from the BeamCal...Study is ongoing.

Hits in TPC


Options for 20mrad under Options for 20mrad under investigationinvestigation

DID, small aperture

DID, large aperture (Ri(LumiCal) > 13cm)

20mrad AntiDID 14mrad AntiDID


SummarySummary

A fast luminosity signal can significantly increase the luminosity.

Analyzing beamstrahlung grants access to many beam parameters.

Promising results also for 20mrad case.Single and Multiparameter analysis is

feasible.The Very Forward region design for large

crossing angles needs:The AntiDID field configuration ORA massively increased aperture (LumiCal’s

inner radius).


OutlookOutlook

The beam diagnostics, which was based upon a FORTRAN/HBOOK code is now being ported to a GEANT4 based simulation, including:Usage of b field map files.Realistic detector response.Fast shower parameterization.Optimization of observables.

Studies on the new 20mrad geometry are ongoing.

analysis of beamstrahlung pairs ecfa workshop vienna, november 14-17, 2005 christian grah

Documents

beamstrahlung photons

mrad photocal e e pairs

outgoing beam

incoming beam

photocal beam diagnostics

luminosity development

generated pairs guineapig

etot e n lr