fast and precise luminosity measurement at the ilc

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


Forward Region – New Geometry20mrad geometry (LDC)


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


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.


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:


Detector Performance

Detector performance can be included into MC.How well we have to know?

R.Ingbir


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


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!


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


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)


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)


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.


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)!


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 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

...


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


G4 Simulation with simplified B-field

σz, μm

20mrad DID

20mrad AntiDID

Deposited energy in sensorlayer

all layerslayer8


Using Bfield Map

All layers Layer 8

Energy deposited in the sensors of the forward BeamCal.


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.


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

fast and precise luminosity measurement at the ilc

Documents

luminosity measurementbeamstra

grah lcws

precise luminosity measurement

rad photocal e e pairs

ilc ch

number of pairs

radminimize background

angle scanimproves