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HERMES Recoil Detector

HERMES Recoil Detector. Roberto Francisco P é rez Benito. On behalf the HERMES Collaboration. European Graduate School Lecture Week on Hadron Physics Jyväskylä, Aug 25-29, 2008. Outline. Motivation The Hermes Recoil Detector Performance Outlook. The Spin Structure of the Nulceon.

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HERMES Recoil Detector

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  1. HERMES Recoil Detector Roberto Francisco Pérez Benito On behalf the HERMES Collaboration European Graduate School Lecture Week on Hadron Physics Jyväskylä, Aug 25-29, 2008

  2. Outline • Motivation • The Hermes Recoil Detector • Performance • Outlook

  3. The Spin Structure of the Nulceon Nulceon Spin: Accss to via Deeply Virtual Compton Scattering (DVCS) • Spin of quarks measured in DIS HERMES: • Spin of gluons, first Measurements • expected to be small • Orbital angular momentum of quarks • Orbital angular momentum of gluons unknown

  4. Generalized Parton Distributions (GPDs) Ji Sum Rule – Ji, PRL 78(1997)610 GPDs parton longitudinal momentum fractionsfraction of the momentum transferinvariant momentum transfer to the nucleon

  5. GPDs and the DVCS process DVCS final state is indistinguishable from theBethe-Heitler Process (BH) → Amplitudes add Coherently • Photon-Production cross section: Interference Term

  6. DVCS Measurements • calculable in QED with the knowledge of the Form Factors • is parameterized in terms of Compton Form Factors (convolutions of GPDs ) • At HERMES kinematics: GPDs accessible through cross-section differences and azimuthal asymmetries via interference term I → Magnitude + Phase(GPDs enter in linear combinations)

  7. The HERMES Spectrometer (before 2006) • Fixed target experiment (uses 27.6 GeV/c HERA lepton Beam) • Recoiling proton undetected large background contamination (15%) • Polarize gas targets: H,D,He • Unpolarize gas targets: H,D,N,He,Ne,Xe,Kr

  8. Exclusivity for DVCS via Missing Mass • Exactly one DIS lepton and one photon detected in the Calorimeter. • Recoiling proton undetected. • Exclusivity via Missing Mass exclusive region Overall background contribution in exclusive region

  9. The HERMES Spectrometer (2006 - 2007) • Recoil detector installed for the last two years of data taking • Recoiling proton detected background contamination <1%

  10. HERA BEAM Recoil Detector 1 Tesla Superconducting Solenoid Photon Detector • 3 layers of Tungsten/Scintillator Scintillating Fiber Detector • 2 Barrels • 2 Parallel & 2 Stereo-Layers in each barrel Silicon Detector • 2 Layer of 16 double-sides sensors • 97×97 mm2 active area each • Inside HERA vacuum Target Cell

  11. Alignment of the SFT

  12. Measurements of dedicated SFT run were used and tested on cosmic data collected with Recoil detector Residuals (280 µm) are in good agreement with expectations from ideally aligned Monte-Carlo (220 µm) Results of Alignment of SFT SFT Parallel top =0.28mm Si and PD alignment respect SFT

  13. Detect scattered electron in the Forward spectrometer and protons in the Recoil Correlation of angles reconstructed in the Forward spectrometer and the Recoil Detector can be used for the relative alignment of these detector systems Ep Elastic Scattering

  14. Momentum Reconstruction

  15. Momentum Reconstruction

  16. Momentum Reconstruction

  17. Energy Deposit of MIP‘s HERMES magnet • Energy loss of single fiber from pions • Leading fibers from tracks were selected • MIP’s position are stable from different time periods Recoil detector

  18. Recoil Particle Identification HERMES magnet Recoil detector

  19. Collected statistic (preliminary) with recoil detector Electron beam 2006 (only SFT operational): H : 5k DVCS (3Mio. DIS), D : 1k DVCS (0.8Mio. DIS) Positron beam 2006/07 (all subdetectors fully operational) H : 41k DVCS (38Mio. DIS), D : 7.5k DVCS (10Mio. DIS) Data tacking and Performance 2 2 2 2

  20. Analysis of data with Recoil Detector for exclusive photons and mesons Exclusive meson cross-sections Exclusive meson cross-section ratios Spin Density Matrix Elements Exclusive πˉ and π° impossible without Recoil Detector! Outlook

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