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Tracking for lepton physics

Tracking for lepton physics

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Tracking for lepton physics

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  1. low - momentum Tracking for lepton physics Tetyana GalatyukGoethe-Universität, Frankfurt

  2. The challenge… No electron identification in front of tracking Background due to material budget of the STS Reduction of background by reconstructing pairs from g conversion and p0 Dalitz decay Radial vs. z position (eγ) and By along the beam axis Introduction

  3. Characteristic of the e+ and e- Invariant e+e- spectrum in 25 AGeV Au+Au collisions (b = 0, full phase space) Momentum distribution Introduction Opening angle distribution 1 signal decay / 400 background events

  4. Combinatorial background topology Small (moderate) opening angle  “close pairs” if there is no field Asymmetric laboratory momenta Introduction

  5. Momentum correlation plot plab identified e- vs. plab identified e+ plab identified e- vs. plab nrec e+ Introduction Track Segment Identified e+/- Identified e+/- Track Fragment

  6. Wish N1 : Increase the size of the tracking detectors STS1STS2 STS2 STS3 STS3 STS4 x vs. y position of the extrapolated tracks Wish N1 Done! By now standard geometry

  7. Wish N2 : The choice of the proper magnetic field Trade: Acceptance vs. Resolution Currently a scaling of the filed is used. Our choice is 70% of the nominal field value Dp as a function of the magnetic field value Wish N2

  8. Wish N3 : Good tracking performance Reconstruction efficiency ~93% (p < 1 GeV/c) Momentum resolution < 2% Number of primary tracks with momentum < 500 MeV/c increased by 26% Reconstruction efficiency Momentum resolution Wish N3

  9. Wish N4 : Field free region between the target and 1st MVD Distance to closest neighbor hit in the 1st MVD station • Excellent double-hit resolution (<100mm) provides substantial close pair rejection capability • A realistic concept to suppress the field between the target and first MVD station has to be worked out Wish N4 With magnetic field = 30% of its nominal value

  10. Wish N5 : Refined field profile in the target region RICH ~ 0 kG target ~ few kG ~ 7 kG Vertical magnetic field strength (i.e. By) along the beam axis • Magnetic field map was developed (E. Litvinenko) • Problems with the tracking, most likely do to the strong field gradient at around 10 cm downstream of the target? • Trade: • Suppression of delta-electrons vs. opening of close pairs Wish N5

  11. Summary Past: Optimize tracking performance for tracks with momentum < 1 GeV/c Changes to the the detector setup Present: Proposed STS geometry is “standards” by now High track reconstruction efficiency for low-momentum tracks Future: Tracking within the field free region between the target and MVD 1 Track reconstruction with MVD (using the 3/4 MVD setup) Reconstruction of the g conversion on the detector material (using KF article) Thank you