Calibration of the COSY-TOF STT & pp Elastic Analysis

1. Calibration of the COSY-TOF STT & pp Elastic Analysis Sedigheh Jowzaee IKP Group Talk 11 July 2013

2. Outline • COSY-TOF Spectrometer • STT calibration goal • Calibration comparison • pp elastic analysis of data 2012

3. COSY-TOF Spectrometer p p π- K+ • Strangeness physics

4. 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

5. 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

6. 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

7. 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)

8. 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

9. 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

10. 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

11. Residual Comparison dl 5 dl 13 New calib. dl 5 dl 13 Old calib.

12. Resolution Comparison New calibration • Old calibration Resolution at 0.25 cm New: 142±8 µm Old : 174±18 µm

13. pp Elastic Analysis p1 φ Geometry of pp elastic events θ1 pbeam ptarget θ2 p2

14. pp Elastic Analysis After coplanarity cut After circular cut

15. Vertex Distribution • Dependent on the beam properties

16. Vertex Distribution • Dependent on the target dimension • target dimension=5.17±0.03 mm

17. 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

18. 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

19. Thank you

20. Backup slides

21. Straw hits

22. 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

23. Monte Carlo Comparison New calibration -2012 calibration-MC-2012

24. Beam Direction

25. 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