Fast Beam Diagnostics at the ILC Using the Beam Calorimeter Christian Grah, Desy FCAL Workshop 12-13 February Cracow

Fast Beam Diagnostics at the ILC Using the Beam Calorimeter

Christian Grah, DesyFCAL Workshop12-13 FebruaryCracow

FCAL Workshop Cracow, 12-13 Feb 2006

C.Grah: Beamdiagnostics 2

Contents

Very forward region and BeamCalBeam parameter reconstruction

• Principle

• Results on 20mrad geometry with the nominal ILC parameter set.

Summary and outlook



Very Forward Region

LumiCal: 26 < θ < 82 mrad

BeamCal: 4 < θ < 28 mrad

PhotoCal: 100 < θ < 400 μrad



BeamCal

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)

W:diamond sandwich calorimeter



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.



ILC B-Field Configurations

20mrad DID(Ri(LumiCal) = 13.5cm)(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.

DID: Detector integrated Dipole, B-field aligned with the incoming beam

AntiDID: B-field aligned with the outgoing beam



Fast Luminosity Monitoring Why 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)!



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)



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)



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



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



2mrad and 20mrad Analysis

QuantityNominal Value

Precision

2mrad 20mrad 20mrad (2par)

x 553 nm 3.1 2.9 2.8

x 5.2 7.4 7.6

y 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

εy 40x10-9mrad 1.7 2.9 5.2

εy 0 4.2 4.1 4.7

x 17.7 9.3 10

y 0 0.5 0.6 0.6

N 2x1010 0.01 0.01 0.01

N 0 0.01 0.02 0.03

...



Status of AnalysisGuineaPig files for ILCNOM ready

(~400 pair files).New geometry ready.Single and multiparameter analysis

started. Mostly done for• 2mrad

• 20mrad DID

Good progress in the Geant4 implementation (A.Sapronov‘s talk).



Summary & Outlook Including a fast signal of number of pairs or total energy into the

feedback system can significantly increase luminosity of the accelerator.

Analyzing the spatial energy distribution of beamstrahlung pairs hitting the BeamCal grants access to many beam parameters. For highly correlated parameters measurements from other systems can be included (e.g. PhotoCal).

20mrad geometry is implemented with DID field approximation. ILCNOM investigation is in work. Geant4 simulation is running, BC observable calculation and beam

parameter reconstruction can be done with some limitations. Next:

Geant4 simulation with realistic b-field map and compare to simplified one.

Hopefully no fast shower simulation has to be included (cpu time dependent). Fast shower simulation is implemented in Geant4 for homogenous detector….

Find most interesting regions (layers) in the BeamCal segments. Need background calculation for our 20mrad geometry.

Documents

Fast Beam Diagnostics at the ILC Using the Beam Calorimeter Christian Grah, Desy FCAL Workshop 12-13 February Cracow