Experimental Aspects of Precision Luminosity Measurement

Experimental Aspects of Precision Luminosity

Measurementcontributions from

Forward Calorimetry Collaboration

L.Suszycki

AGH University of Science and Technology Cracow

L. Suszycki LCWS 04: Paris 19-23 April 2004 2

Forward Calorimetry Collaboration

H. Abramowicz11, K. Afanaciev8, S. Denisov10, R. Dollan5, D. Drachenberg5, V. Drugakov8, I. Emeliantchik8, S. Erin10, R. Ingbir11, S. Kananov11, A. Kowal4, E.

Kousnetsova5, R. Kwee5, W. Lange5, A. Levy11, W. Lohmann5, J. Lukasik4, M. Luz5, D. Miller7, I. Minashvili6, U. Nauenberg1, B. Pawlik4, N. Rusakovich6, A. Rybin10, N.

Shumeiko8, A. Stahl5, L. Suszycki4, K. Suzdalev10, V. Vrba9, W. Wierba2, J. Zachorowski3, L. Zawiejski2, F. Zyazyulya8

1 University of Colorado, Boulder, USA, 2 Institute of Nuclear Physics, Cracow, Poland, 3 Jagellonian University, Cracow, Poland, 4 University of Science and Technology, Cracow, Poland, 5 DESY, Zeuthen, Germany, 6 Joint Institute of

Nuclear Research (JINR), Dubna, Russia, 7 University College London, London, UK, 8 NC PHEP, Minsk, Belarus, 9 Institute of Physics of the Academy of

Sciences of the Czech Republik, Praha, Czech Republik, 10 Institute of High Energy Physics, Protvino, Russia, 11 Tel-Aviv University, Tel-Aviv, Israel.


Forward Calorimetry Layout

LAT functionally is nowLuminosityCalorimeter

LumiCal– z = 305-325 cm– R= 8-28 cm – 26.2<<82 mrad– 0<<360 deg

TESLA TDR design (postponed)

Low Angle Tagger(LAT)

New mask design l*=4m


Luminosity measurement

Based on Bhabha scattering e+e- e+e-()

At 250 GeV, =5.5 nb,

For L = 3.4 · 1034 cm-2s-1 rate R 180 Hz `one minute` luminosity possible on-line

Goal precision: L/L = 10-4

Can it be done?

LCWS 04: Paris 19-23 April 2004 5

• Si/W calorimeters on both sides of the IP

• 16/64 concentric cylinders (in r)• 30 rings (in z)• 24/120 sectors (in )• Detector simulation with

Geant3.21 Two calorimeter structures considered:• Si pads • Si strips

LumiCal Design Simulation

beam pipe

Tungsten mask


Polar angle reconstruction• Polar angle reconstruction – good resolution, uniformity, no

bias• Fiducial volume definition min is crucial:

d/d ~1/3 , so tot(min, max) ~ min-2 , min = 26.2 mrad

L/L = 2min/ min -> min = 1.3 rad


Angle reconstruction - Pad Design

• „oscillations” around rec vs gen linear dependence due to detector granularity

• resolution in is -dependent due to cylindrical geometry


LumiCal – reconstruction

24 sectors

48 sectors Resolution as function of the number of cylinders (in r) and sectors (in φ)

Angle reconstruction with simple energy weighting

Both large bias and bad resolution ~0.2 – 0.3 mradobserved even using large numbers of cylinders/sectors

A.Kowal (UST Cracow)

HEP Tel Aviv UniversityA Luminosity Detector for the Future Linear Collider

Reconstruction Algorithm

)]}ln([,0max{T

ii E

EconstW

i

ii

E

EXX

i

ii

W

WXX

Events Num.

)(radgenrec

)(radgenrec

)(radgen

We explored two reconstruction algorithms: Energy weighting and logarythmic weghting

The log. weight fun. was designed to reduce steps in a granulated detector :

1. Selection of significant cells.

2. Log. smoothing.

Log. weight.

E weight.


Logarithmic Constant

Constant value

Constant value

)]}ln([,0max{T

ii E

EconstW

After selecting:

We explored a more systematic approach.

The first step is finding the best constant to use under two criteria:

1. Best resolution.

2. Minimum bias.

400 GeV

))(_( radmean genrec

))(( rad


Energy dependent constant

)]}ln()([,0max{T

ibeami E

EEconstW

The goal is to find a global weight function.

Is the log. weight really a constant ?

Constant value


Beam Energy (GeV)

))(( rad

Angular resolution

Results using ‘pure electron’ simulation

Can we maintain same detector properties using a more ‘real’ MC ?


Azimuthal resolution

)]}ln([,0max{T

ii E

EconstW

Events Num.E weight.

Log. weight.

(deg)genrec


LumiCal – Stripped design

• 30 tungsten rings

• every second ring has either 120 radial or 64 concentric Si strips

• 2960 readout channels

• but necessary sectioning of Si sensors will give factor of ~3 - 4

B.Pawlik (INP-PAN, Cracow)


Stripped LumiCal reconstruction results

• Accuracy in -reconstruction is ~50

rad

• Energy measurement with accuracy of

5 GeV (E~0.31√E)• low segmentation level

seems to be sufficient (~3000 readout channels)

B.Pawlik (INP-PAN, Cracow)


Stripped LumiCal - Bhabha events

Reconstruction : energy 7GeV (0.44√E) Angle ~0.09 mrad ACOLINEARITY ~1MRAD

Egen - Erec

B.Pawlik (INP-PAS, Cracow)

θL – θR (mrad)θgen – θrec (mrad)


Detector mechanics

• Calorimeter assembling - perfect homogenity, - stable

• Calorimeter positioning (rmin =8 cm), rmin = 4 m, z = 0.2mm

Challenging for mechanics and thermal stability! rmin = 1m x T for steel support ( factor 1/3 for W support)

• Monitoring of calorimeter shift and/or deformation due to:- temperature- ageing- ground motionLaser method for on-line control is being developed


Laser monitoring of the LumiCal detector displacement

(very preliminary)

reconstruction of He-Ne laser spot on CCD camera

Requirements on alignment:Inner Radius of LumiCal < 4 μmAxial LumiCal position < 60 μm

possible resolution of ~1m if the center of the light spot is determined with accuracy better than 0.1 pixel

J.Zachorowski (UJ),W.Wierba (INP-PAN) Cracow

Laser scan of x and y positions

slope 0.127pixel/m

To be done:• Small-pixel BW camera, • Manually controlled sensitivity,• Semiconductor laser,• Piezoelectric movement of

camera,• Independent measurement of

displacement,

• Multiframe statistics.


Monitoring of the beam parameters

Generator level Bhabha simulation (A.Stahl, Desy-Zeuthen) yields permissible beam deviations:

beam offset r = 650 m

IP longitudinal offset z = 150 mbeam tilt = 0.2 mrad

Beam Calorimeter (BeamCal) foreseen for fast beam diagnostics may help


Conclusions• High precision luminosity measurement involves

numerous experimental and technical problems• First MC results indicate ways of the future work• Angle reconstruction must be done very

carefully minimizing the bias• Special system for monitoring the detector

possible moves and/or deformations has to be built

• Limited space for detector makes mechanics and electronics still more difficult

• Optimized design of LumiCal is strongly dependent on choice of the LC option

The end

Thank you

Detector Design

0.34 cm Tungsten

0.31 cm Silicon

Cell Size1.3cm*2cm>1.3cm*6cm<

~1 Radiation length

~1 Radius Moliere


15 cylinders * 24 sectors * 30 rings = 10800 cells

RL

8 cm

28 cm

6.10 m


LumiCal pad–design optimization

• # of active rings around the shower maximum

• logarithmic weighting in angle reconstruction

• () ~ 70 rad feasible

resolution

# of cylinders

R. Ingbir (TAU)

Documents

Experimental Aspects of Precision Luminosity Measurement