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On the Multiwire Drift Chambers alignment of the HADES dilepton spectrometer. Héctor Alvarez Pol. 16 December 2002. INDEX. Part I The HADES Physics. Part II The HADES spectrometer. Part III Overview of the drift chambers alignment. Part IV Alignment using hardware methods.

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On the multiwire drift chambers alignment of the hades dilepton spectrometer
On the Multiwire Drift Chambers alignment of the HADES dilepton spectrometer

Héctor Alvarez Pol

16 December 2002


INDEX dilepton spectrometer

Part I The HADES Physics

Part II The HADES spectrometer

Part III Overview of the drift chambers alignment

Part IV Alignment using hardware methods

Part V Alignment using software algorithms

Conclusions


Part i the hades physics program
PART I dilepton spectrometerTHE HADES PHYSICS PROGRAM


THE HADES PHYSICS PROGRAM dilepton spectrometer

Heavy ion collisions at SIS energies


THE HADES PHYSICS PROGRAM dilepton spectrometer

Heavy ion collisions at SIS energies


THE HADES PHYSICS PROGRAM dilepton spectrometer

Heavy ion collisions at SIS energies


THE HADES PHYSICS PROGRAM dilepton spectrometer

Heavy ion collisions at SIS energies


THE HADES PHYSICS PROGRAM dilepton spectrometer

Want to know!

Observables

Behavior of the High Density Phase

In-medium change of ρ, ω, φ masses

  • Partial restoration of the chiral symmetry

  • Equation of State (EOS)

  • Astrophysics: neutron stars and inner stars structure

In-medium dilepton decays are not affected by strong interactions!


THE HADES PHYSICS PROGRAM dilepton spectrometer

Dilepton invariant mass spectra

In-medium vector meson decay

External vector meson decay


THE HADES PHYSICS PROGRAM dilepton spectrometer

These series of experiments, exploiting the full range of

primary and secondary beams available at GSI,

are expected to make important contributions to our

understanding of Quantum Chromodynamics in the non-perturbative regime and, in particular, will provide information on the origin of hadron masses.

From The HADES Physics Program, J. Friese and V. Metag


Part ii the hades spectrometer
PART II dilepton spectrometerTHE HADES SPECTROMETER


THE HADES SPECTROMETER dilepton spectrometer

HADES installation at GSI


THE HADES SPECTROMETER dilepton spectrometer

HADES features

Capability to deal withhigh count rates

and large particle multiplicities

to accumulate enoughsignificant events in a finite time

Low mass materials

are chosen in all detectors and supportstructures to minimize the multiple scattering

Excellent mass resolution

( Dm/m » 1 % (σ) at ω mass) should allow the individual identification of the vector mesons

A selective trigger scheme

able to accept only those events withlepton pairs, mainly those of high mass

Rejection of hadronic and electromagnetic background

whichcould obscure the dilepton signal

Large dilepton acceptance

(~40% for lepton pairs), required because of the tiny dileptonbranchingratio, of the order of 10-5. Allows the comprehensive studies of the behavior of vector mesons in the nuclear medium

Flat acceptance

in mass and in transverse momentum

Large dilepton acceptance

Rejection of hadronic and em. background

Excellent mass resolution

Flat acceptance in mass and in mT

High count rates

Large particle multiplicities

Low mass materials

A selective trigger scheme


THE HADES SPECTROMETER dilepton spectrometer

Large dilepton acceptance

Rejection of hadronic and em. background

Excellent mass resolution

Flat acceptance in mass and in mT

High count rates

Large particle multiplicities

Low mass materials

A selective trigger scheme


THE HADES SPECTROMETER dilepton spectrometer

RICH: Ring Imaging Cherenkov Detector

RICH


THE HADES SPECTROMETER dilepton spectrometer

RICH: Ring Imaging Cherenkov Detector

RICH


THE HADES SPECTROMETER dilepton spectrometer

MDCs: Multiwire Drift Chambers

MDCs

MDCs

RICH


THE HADES SPECTROMETER dilepton spectrometer

MDCs: Multiwire Drift Chambers

MDCs

MDCs

RICH


THE HADES SPECTROMETER dilepton spectrometer

MDCs: Multiwire Drift Chambers

MDCs

  • MDC features:

  • High position resolution

MDCs

RICH

  • Operation on Isobutane-Helium mixture to reduce the multiple scattering

  • Two track detection ability


THE HADES SPECTROMETER dilepton spectrometer

ILSE: Superconducting Toroidal Magnet

MDCs

MDCs

RICH

ILSE


THE HADES SPECTROMETER dilepton spectrometer

TOF

TOF: Time-of-Flight Detectors

MDCs

MDCs

RICH

ILSE

TOF


THE HADES SPECTROMETER dilepton spectrometer

Pre-Shower: Electromagnetic/Hadronic Shower

Detector With Lead Converters

TOF

MDCs

Pre-Shower

MDCs

RICH

ILSE

Pre-Shower

TOF


THE HADES SPECTROMETER dilepton spectrometer

TOF

TOFino: lower angle Time-of-Flight

MDCs

Pre-Shower

MDCs

RICH

TOFino

ILSE

Pre-Shower

TOF


Part iii overview of the drift chambers alignment
PART III dilepton spectrometerOVERVIEW OF THE DRIFT CHAMBERS ALIGNMENT


OVERVIEW OF THE DRIFT CHAMBERS ALIGNMENT dilepton spectrometer

Steps towards theHADES alignment system

  • Revision of the momentum reconstruction methods in the spectrometer

  • Simulation of the misalignment effects on the reconstructed momentum

  • Analysis of the architectural design and evaluation of the technical resources

  • Definition of a specific alignment scheme


OVERVIEW OF THE DRIFT CHAMBERS ALIGNMENT dilepton spectrometer

The tracking system


OVERVIEW OF THE DRIFT CHAMBERS ALIGNMENT dilepton spectrometer

Opposite directions for e - and e+

Dependent on the misaligned MDC

Approx. linear behavior


OVERVIEW OF THE DRIFT CHAMBERS ALIGNMENT dilepton spectrometer

Simulation results

Momenta between 400 and 600 MeV/c

Electrons Positrons

MDC Δp/p (%/100μm) Δp (MeV/c/100μm) Δp/p (%/100μm) Δp (MeV/c/100μm)

I-0.21-1.1 -0.32 -2.2

II 0.130.7 0.19 1.3

III0.341.70.473.3

IV -0.27 -1.4-0.37-2.6

  • Maximum misalignment of the MDCs (according to Physics criteria):

  • Δy ~ 50 μm along the particle magnetic kick direction

  • Also allows the determination of maximum deviation in the tilt angles


OVERVIEW OF THE DRIFT CHAMBERS ALIGNMENT dilepton spectrometer

After the analysis of the architectural design and the evaluation of the allowable displacements of the support structures and other constraints, the proposed and implemented alignment scheme consist of:

  • Software algorithms, based on the analysis and minimization of residuals or other functions of the hits in the drift chambers, using data samples with the magnetic field off.

  • Hardware sensors (RASNIK), monitoring the relative displacements of theexternal MDCs with respect to the inner ones, during the data taking period.


Part iv alignment using hardware methods
PART IV dilepton spectrometerALIGNMENT USING HARDWARE METHODS


ALIGNMENT USING HARDWARE METHODS dilepton spectrometer

RASNIK: Red Alignment System from NIKHEF


ALIGNMENT USING HARDWARE METHODS dilepton spectrometer

Two emitters on the external MDCs frame

Camera and lenses fixed to the internal MDCs frame

IR light path


ALIGNMENT USING HARDWARE METHODS dilepton spectrometer

Parameters of the innovative setup

1. Angle between the sensor plane and the image plane

2. Aperture of the lens


ALIGNMENT USING HARDWARE METHODS dilepton spectrometer

Resolution analysis procedure

Experimental setup

Second order polynomial fit

Conclusions:

  • The resolution improves for the smallest apertures

  • The resolution is practically independent of the incident angle

  • For α≥30°, the analysis module starts to fail

Selected setup

Lens aperture 15 mm

Angle with sensor plane 25°


ALIGNMENT USING HARDWARE METHODS dilepton spectrometer

Epoxy Carbon Fiber:

KT = - 0.5x10-6 K-1

Binocular design


ALIGNMENT USING HARDWARE METHODS dilepton spectrometer

Focus adjustment

Optical axis adjustments

Binocular


ALIGNMENT USING HARDWARE METHODS dilepton spectrometer

IR LEDs Matrix

Mask Mount

Mask and LEDs supports


ALIGNMENT USING HARDWARE METHODS dilepton spectrometer

Calibration

Stable calibration terms in different parts of the mask

Stable calibration terms for different masks


ALIGNMENT USING HARDWARE METHODS dilepton spectrometer

EPICS Operator Screen

RAHAD online monitor

  • Distributed monitor screens

  • Archiver facilities

  • Internal raw data check

  • ROOT graphics facilities


ALIGNMENT USING HARDWARE METHODS dilepton spectrometer

Complete data sample

Reduced data sample

Complete data sample

σ( XMDC ) = 3.86 μm

σ( YMDC ) = 4.64 μm

σ( Z MDC ) = 6.88 μm

Reduced data sample

σ( XMDC ) = 1.23 μm

σ( YMDC ) = 1.55 μm

σ( Z MDC ) = 2.5 μm

ZMDC

Resolution estimation

XMDC

YMDC


ALIGNMENT USING HARDWARE METHODS dilepton spectrometer

Experimental results

Correlation with the temperature of the MDC frames

Correlation with the magnetic field


Part v alignment using software methods
PART V dilepton spectrometerALIGNMENT USING SOFTWARE METHODS


ALIGNMENT USING SOFTWARE METHODS dilepton spectrometer

MDC to Lab:

MDC to MDC:

where

and

for instance

Coordinate transformations


ALIGNMENT USING SOFTWARE METHODS dilepton spectrometer

Variables:

Probability density function:

Equiprobability volume (hyperellipsoids on α4):

Hit compatibility and sample selection


ALIGNMENT USING SOFTWARE METHODS dilepton spectrometer

b

a

Three MDCs alignment algorithm

should be zero for each track.

Then, minimize

with:

where, for instance:

A

B

C


ALIGNMENT USING SOFTWARE METHODS dilepton spectrometer

Simulation results

If one parameter is fixed to the correct value

Convergence inside the allowable error

Below 50 μm

The problem reduces to find out a set of histograms which univocally defines the

correct value of the fixed parameter.


ALIGNMENT USING SOFTWARE METHODS dilepton spectrometer

b

b

b

a

a

a

c

c

c

How to fix the angular parameter

2.06x10-3

8.6x10-5

Abscissa for y=0

-6.6x10-5

-1.93x10-3


ALIGNMENT USING SOFTWARE METHODS dilepton spectrometer

Differences in mrad

November 2001 alignment: three MDCs algorithm

  • The uncertainties in the calibration procedures and hit fitting tasks lead to hits with incompatible slopes on the MDCs.

  • As a consequence, the uncertainty intervals for the alignment results in Nov01 are slightly larger than expected (~100 μm for MDCs I-II, ~300 μm for MDCs II-III).


ALIGNMENT USING SOFTWARE METHODS dilepton spectrometer

Two MDCs alignment

Minimization of the residuals:

Analytical minimization with respect to the components of the translation vector:

The solution is the relative translation vector V=(V0,V1,V2)


ALIGNMENT USING SOFTWARE METHODS dilepton spectrometer

Two MDCs alignment

Geometrical determination of the relative rotations,

for instance, in-plane rotations:

θ


ALIGNMENT USING SOFTWARE METHODS dilepton spectrometer

Two MDCs alignment

Simulation results

  • Iterative approach to the solution:

  • Sample selection

  • Analytical minimization of the translation (vector V)

  • Geometrical correction of the rotation (rotation matrix M)

Below 50 μm

Convergence inside the allowable error


ALIGNMENT USING SOFTWARE METHODS dilepton spectrometer

The Target Finder algorithm

1. Analytical minimization of:

2. Iterative approach to the solution using bi-squared Tukey weights


ALIGNMENT USING SOFTWARE METHODS dilepton spectrometer

November 2001 alignment: two MDCs algorithm

Mean:

-4.5x10-3

Mean:

-7.8x10-3


ALIGNMENT USING SOFTWARE METHODS dilepton spectrometer

Beam line reconstruction after alignment

Track

θ

ρ

Beam line (Z)


ALIGNMENT USING SOFTWARE METHODS dilepton spectrometer

November 2002

“Last minute” result

20mm

Double target reconstruction

Very preliminary alignment


Conclusions
CONCLUSIONS dilepton spectrometer


CONCLUSIONS(1) dilepton spectrometer

  • In this work, several tools and methods have beendeveloped to obtain therelative alignment of the Multiwire Drift Chambers (MDCs), the maintracking detectors in the HADES spectrometer.

  • In a first step, the requirements on the resolution in the reconstructed momentum and the invariant mass of the lepton pair, have been expressed as maximum deviations in the knowledge of the relative displacements and rotations of the MDCs.

  • A set of RASNIK devices has been considered as optimal solutionfor the hardware monitoring and a specific RASNIK configuration hasbeen developed.

  • The influence on the resolution of both the light incidence angleonto the camera and the lens aperture have been studied.


CONCLUSIONS(2) dilepton spectrometer

  • The implementation of the RASNIK devices in the spectrometer hasrequired the design of custom-made pieces. This task has been accomplished from the mechanical design of all pieces up to the final installationin the spectrometer.

  • A complete monitoring program (RAHAD) has been developed. It performs a data calibration andtransformation, according to the coordinate systems of the MDCs,as well as the interface with the EPICS “HADES Slow Control System”.

  • Once the RASNIK setup was installed on the spectrometer, its performances belowthe requirements were confirmed.

  • The RASNIK results have been successfully correlatedwith temperature changes and with the magnetic field forces. The RASNIK monitoring results have beenused to correct the alignment parameters obtainedby software methods.


CONCLUSIONS(3) dilepton spectrometer

  • Regarding the software methods, several iterative algorithms have beendeveloped in order to obtain the relative alignment parameters between MDCs.

  • Two different algorithms has been developed, for those sectors with three or two MDCs.

  • The useof the “Two MDCs algorithm” includes the determination of the target position, implemented in the so-called “Target Finder” algorithm. The “Three MDCs algorithm” has been chosen as the main method toobtain the position parameters.

  • The different algorithms have been first tested under simulation, checking their convergence to the correct parameters. The errors have been estimated and the resolution in the determination of the relative alignmentparameters fulfils the requirements.

  • A set of datahas been analyzed (Carbon beam at 1 GeV on a Carbon target, November2001 run) using the alignment algorithms. The alignment parameters have been estimated, including their uncertainty intervals.


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