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Calibration of the COSY-TOF STT & pp Elastic Analysis. Sedigheh Jowzaee IKP Group Talk 11 July 2013. Outline. COSY-TOF Spectrometer STT calibration goal Calibration comparison pp elastic analysis of data 2012. COSY-TOF Spectrometer. p. p. π -. K +. Strangeness physics.

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Calibration of the cosy tof stt pp elastic analysis
Calibration of the COSY-TOF STT & pp Elastic Analysis

Sedigheh Jowzaee

IKP Group Talk

11 July 2013


Outline

  • COSY-TOF Spectrometer

  • STT calibration goal

  • Calibration comparison

  • pp elastic analysis of data 2012


COSY-TOF Spectrometer

p

p

π-

K+

  • Strangeness physics


COSY-TOF STT

  • Installed in vacuum tank

  • Consists of 2704 straw tubes with Ø=10 mm & 1050 mm length

  • Organized in 13 double-layers

  • Filled with Ar/CO2 gas at 1.2 bar overpressure

  • Fixed in 3 orientations with angle 60˚ to each other for 3D track reconstruction


Calibration Procedure

  • Motivation for precise STT calibration

    • Reconstruction of events with STT at COSY-TOF

    • Event analysis based on the vertices reconstruction of the charged final state particles (p, K, Λ p, π-)

  • Calibration steps

    • TDC correction

      • Multiple hits removal

      • Signal width cut

      • Electronics offset correction

    • Estimation of correlation between drift time and radius

    • Straw layers position correction

  • pp elastic events measured in Fall 2012 at pbeam=2.95 GeV/c are analyzed for the calibration of the STT

    • Data taking in November 2012 for 4 weeks


TDC Correction

  • First hit selection

  • Signal width cut

    • 5ns width limit of readout electronics

Using the common-stop readout of the TDCs, higher values correspond to shorter drift times

raw TDC spectrum for 5.106 hits in the 3 double layers straw tubes

TDC spectrum after first hit selection and width cut


Turning point

σ

TDC Correction

  • Electronics offset correction

    • Different readout modules

    • Correction with fit method

      • Ref. point=turning point of error function + 1σ

      • Offset= 780 ns(arbitrary)-Ref. point

Due to applying 3 racks of readout electronics

Due to the positioning of readout board

Due to the positioning of tubes in dls (Time of flight)


Track

Straw Tube

Self-Calibrating Method

  • Main aim: determination of the correlation between the drift time and the isochrone radius

  • Isochrone radius was calculated for each bins of drift time (homogeneous illumination assumption in whole straw)

Isochrone radius: cylinder of closest approach of the particle track to the wire

Risochrone


Auto-Calibration Method

  • Track reconstruction with averaged r(t) curve of 3 groups of double layers from self-calibrating method was done

  • Track parameters were analyzed to find the most probable correlation between drift time and isochrone radius (track to wire distance)

shift vs. isochrone radius

distance to wire vs. drift time


STT Resolution

  • Residual=|d| – rd: track to wire distance, r: isochrone radius

  • Spatial resolution: width of the Gaussian fit functions to the residual distribution as a function of drift time or radius

  • The resolution at 0.25 cm averaged over all double layers is 142 ± 8 µm

Residual vs. isochron radius

resolution vs. isochron radius

residual vs. drift time


Residual Comparison

dl 5

dl 13

New calib.

dl 5

dl 13

Old calib.


Resolution Comparison

New calibration

  • Old calibration

Resolution at 0.25 cm

New: 142±8 µm

Old : 174±18 µm


pp Elastic Analysis

p1

φ

Geometry of pp elastic events

θ1

pbeam

ptarget

θ2

p2


pp Elastic Analysis

After coplanarity cut

After circular cut


Vertex Distribution

  • Dependent on the beam properties


Vertex Distribution

  • Dependent on the target dimension

  • target dimension=5.17±0.03 mm


Closest Approach of Tracks

  • Minimum distance of the two proton tracks of selected pp elastic scattering events

    • Independent on the beam properties

    • Dependent on the STT reconstruction precision

  • Improvement of FWHM 7.6%

  • FWHM=1780 µm new calibration

  • FWHM=1920 µm old calibration

  • Improvement in reconstruction accuracy


Summary

  • Signal width cut is effective to remove noise

  • Electronics offset correction reduced the systematic error from different electronics modules and time of flight

  • Improved spatial resolution 142 ±8 µm at 0.25 cm averaged over all double layers compared to the old calibration with same beam momentum (174 ±18 µm)

  • The new calibration improved track reconstruction accuracy for pp elastic scattering events





Corrected drift time spectra

Maximum drift time 145 ns

Same drift time spectrum within each double layer

Irregular shape and tail part in first 4double layers

Improper recognition of first hits due to low sensitivity of their electronics

Events mixing and tail pile-up

Drift time


Monte Carlo Comparison

New calibration -2012

calibration-MC-2012



Beam Polarization

  • distribution of asymmetry is fitted with the ā(θ*)cos(φ)

  • The analyzing power A(θ*) is taken from the partial wave analysis Said

  • calculated beam polarization

  • (69.9±10.0)%

Azimuthal asymmetry of elastic scattering events in


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