Héctor Alvarez Pol 16 December 2002 On the Multiwire Drift Chambers alignment of the HADES dilepton spectrometer

INDEX Part IThe HADES Physics Part IIThe HADES spectrometer Part IIIOverview of the drift chambers alignment Part IVAlignment using hardware methods Part VAlignment using software algorithms Conclusions

PART I THE HADES PHYSICS PROGRAM

THE HADES PHYSICS PROGRAM Heavy ion collisions at SIS energies

THE HADES PHYSICS PROGRAM Heavy ion collisions at SIS energies

THE HADES PHYSICS PROGRAM Heavy ion collisions at SIS energies

THE HADES PHYSICS PROGRAM Heavy ion collisions at SIS energies

Want to know!Observables Behavior of the High Density Phase Partial restoration of the chiral symmetry In-medium change of ρ, ω, φ masses M (MeV/c 2 )Γ (MeV/c 2 )cτ (fm) ρ0ρ ω φ 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

In-medium vector meson decay External vector meson decay Dilepton invariant mass spectra THE HADES PHYSICS PROGRAM

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 THE HADES PHYSICS PROGRAM

PART II THE HADES SPECTROMETER

THE HADES SPECTROMETER HADES installation at GSI

Flat acceptance in mass and in transverse momentum Rejection of hadronic and electromagnetic background which could obscure the dilepton signal Low mass materials are chosen in all detectors and support structures to minimize the multiple scattering A selective trigger scheme able to accept only those events with lepton pairs, mainly those of high mass Excellent mass resolution (  m/m  1 % (σ) at ω mass) should allow the individual identification of the vector mesons Capability to deal with high count rates and large particle multiplicities to accumulate enough significant events in a finite time Large dilepton acceptance (~40% for lepton pairs), required because of the tiny dilepton branching ratio, of the order of Allows the comprehensive studies of the behavior of vector mesons in the nuclear medium Large dilepton acceptance Excellent mass resolution High count rates Large particle multiplicities Rejection of hadronic and em. background Flat acceptance in mass and in m T Low mass materials A selective trigger scheme THE HADES SPECTROMETER HADES features

Large dilepton acceptance Excellent mass resolution High count rates Large particle multiplicities Rejection of hadronic and em. background Flat acceptance in mass and in m T Low mass materials A selective trigger scheme THE HADES SPECTROMETER

RICH: Ring Imaging Cherenkov Detector RICH THE HADES SPECTROMETER

RICH: Ring Imaging Cherenkov Detector RICH THE HADES SPECTROMETER

RICH MDCs: Multiwire Drift Chambers MDCs THE HADES SPECTROMETER

RICH MDCs: Multiwire Drift Chambers MDCs THE HADES SPECTROMETER

RICH MDCs: Multiwire Drift Chambers MDCs MDC features: High position resolution Two track detection ability THE HADES SPECTROMETER Operation on Isobutane-Helium mixture to reduce the multiple scattering

ILSE: Superconducting Toroidal Magnet RICH MDCs ILSE THE HADES SPECTROMETER

RICH MDCs ILSE TOF: Time-of-Flight Detectors TOF THE HADES SPECTROMETER

Pre-Shower: Electromagnetic/Hadronic Shower Detector With Lead Converters RICH MDCs ILSE TOF Pre-Shower THE HADES SPECTROMETER

RICH MDCs ILSE TOF Pre-Shower TOFino: lower angle Time-of-Flight TOFino THE HADES SPECTROMETER

PART III OVERVIEW OF THE DRIFT CHAMBERS ALIGNMENT

OVERVIEW OF THE DRIFT CHAMBERS ALIGNMENT 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 Steps towards the HADES alignment system

The tracking system OVERVIEW OF THE DRIFT CHAMBERS ALIGNMENT

Opposite directions for e - and e + Approx. linear behavior Dependent on the misaligned MDC OVERVIEW OF THE DRIFT CHAMBERS ALIGNMENT

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 Momenta between 400 and 600 MeV/c ElectronsPositrons MDC Δp/p (%/100μm) Δp (MeV/c/100μm) Δp/p (%/100μm) Δp (MeV/c/100μm) I II III IV OVERVIEW OF THE DRIFT CHAMBERS ALIGNMENT Simulation results

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 the external MDCs with respect to the inner ones, during the data taking period. OVERVIEW OF THE DRIFT CHAMBERS ALIGNMENT

PART IV ALIGNMENT USING HARDWARE METHODS

ALIGNMENT USING HARDWARE METHODS RASNIK: Red Alignment System from NIKHEF

Two emitters on the external MDCs frame Camera and lenses fixed to the internal MDCs frame IR light path ALIGNMENT USING HARDWARE METHODS

2. Aperture of the lens ALIGNMENT USING HARDWARE METHODS Parameters of the innovative setup 1. Angle between the sensor plane and the image plane

Experimental setup ALIGNMENT USING HARDWARE METHODS 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° Conclusions: Resolution analysis procedure Second order polynomial fit

Binocular design Epoxy Carbon Fiber: K T = - 0.5x10 -6 K -1 ALIGNMENT USING HARDWARE METHODS

Binocular ALIGNMENT USING HARDWARE METHODS Optical axis adjustmentsFocus adjustment

Mask and LEDs supports ALIGNMENT USING HARDWARE METHODS IR LEDs MatrixMask Mount

ALIGNMENT USING HARDWARE METHODS Stable calibration terms in different parts of the mask Stable calibration terms for different masks Calibration

RAHAD online monitor Internal raw data check ROOT graphics facilities EPICS Operator Screen Distributed monitor screens Archiver facilities ALIGNMENT USING HARDWARE METHODS

Complete data sample Reduced data sample X MDC Y MDC Z MDC Complete data sample σ( X MDC ) = 3.86 μm σ( Y MDC ) = 4.64 μm σ( Z MDC ) = 6.88 μm Reduced data sample σ( X MDC ) = 1.23 μm σ( Y MDC ) = 1.55 μm σ( Z MDC ) = 2.5 μm ALIGNMENT USING HARDWARE METHODS Resolution estimation

Correlation with the magnetic field Correlation with the temperature of the MDC frames ALIGNMENT USING HARDWARE METHODS Experimental results

PART V ALIGNMENT USING SOFTWARE METHODS

ALIGNMENT USING SOFTWARE METHODS Coordinate transformations MDC to Lab: MDC to MDC: where and for instance

Variables: Hit compatibility and sample selection Probability density function: Equiprobability volume (hyperellipsoids on α 4 ): ALIGNMENT USING SOFTWARE METHODS

Three MDCs alignment algorithm Then, minimize with: should be zero for each track. where, for instance: a b A B C ALIGNMENT USING SOFTWARE METHODS

If one parameter is fixed to the correct value The problem reduces to find out a set of histograms which univocally defines the correct value of the fixed parameter. ALIGNMENT USING SOFTWARE METHODS Convergence inside the allowable error Below 50 μm Simulation results

How to fix the angular parameter ALIGNMENT USING SOFTWARE METHODS bb a b cc c aa 8.6x x x10 -3 Abscissa for y=0 -6.6x10 -5

November 2001 alignment: three MDCs algorithm ALIGNMENT USING SOFTWARE METHODS 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). Differences in mrad

Two MDCs alignment ALIGNMENT USING SOFTWARE METHODS Minimization of the residuals: Analytical minimization with respect to the components of the translation vector: The solution is the relative translation vector V=(V 0,V 1,V 2 )

ALIGNMENT USING SOFTWARE METHODS Geometrical determination of the relative rotations, for instance, in-plane rotations: Two MDCs alignment θ

ALIGNMENT USING SOFTWARE METHODS Two MDCs alignment Iterative approach to the solution: 1.Sample selection 2.Analytical minimization of the translation (vector V) 3.Geometrical correction of the rotation (rotation matrix M) Below 50 μm Simulation results Convergence inside the allowable error

ALIGNMENT USING SOFTWARE METHODS The Target Finder algorithm 1. Analytical minimization of: 2. Iterative approach to the solution using bi-squared Tukey weights

ALIGNMENT USING SOFTWARE METHODS November 2001 alignment: two MDCs algorithm Mean: -7.8x10 -3 Mean: -4.5x10 -3

ALIGNMENT USING SOFTWARE METHODS Beam line reconstruction after alignment Beam line (Z) Track ρ θ

ALIGNMENT USING SOFTWARE METHODS November 2002 “Last minute” result Double target reconstruction 20mm Very preliminary alignment

CONCLUSIONS

In this work, several tools and methods have been developed to obtain the relative alignment of the Multiwire Drift Chambers (MDCs), the main tracking 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 solution for the hardware monitoring and a specific RASNIK configuration has been developed. The influence on the resolution of both the light incidence angle onto the camera and the lens aperture have been studied. CONCLUSIONS(1)

The implementation of the RASNIK devices in the spectrometer has required the design of custom-made pieces. This task has been accomplished from the mechanical design of all pieces up to the final installation in the spectrometer. A complete monitoring program (RAHAD) has been developed. It performs a data calibration and transformation, 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 below the requirements were confirmed. The RASNIK results have been successfully correlated with temperature changes and with the magnetic field forces. The RASNIK monitoring results have been used to correct the alignment parameters obtained by software methods. CONCLUSIONS(2)

Regarding the software methods, several iterative algorithms have been developed 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 use of 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 to obtain 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 alignment parameters fulfils the requirements. A set of data has been analyzed (Carbon beam at 1 GeV on a Carbon target, November 2001 run) using the alignment algorithms. The alignment parameters have been estimated, including their uncertainty intervals. CONCLUSIONS(3)