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Anselmo Cervera Villanueva University of Gen eva (Switzerland)

First. HARP. physics results. Anselmo Cervera Villanueva University of Gen eva (Switzerland). On behalf of the HARP Collaboration. 25 March 2004. Rencontres de Moriond. Overview. The experiment and its objectives Detector performance Tracking Particle identification

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Anselmo Cervera Villanueva University of Gen eva (Switzerland)

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  1. First HARP physics results Anselmo Cervera Villanueva University of Geneva (Switzerland) On behalf of the HARP Collaboration 25 March 2004 Rencontres de Moriond

  2. Overview • The experiment and its objectives • Detector performance • Tracking • Particle identification • Closing the first analysis cycle • Using our K2K thin target data • Efficiencies • Momentum and angular distributions

  3. The HARP experiment 124 people 24 institutes

  4. Physics goals • Systematic study of HAdRonProduction: • Beam energy:2-15 GeV • Target:from hydrogen to lead • Motivation: • Pion/kaon yield for the design of the proton driver ofneutrino factories and SPL-based super-beams • Input for precise calculation ofatmospheric neutrino flux • Input for prediction of neutrino fluxes for theMiniBooNEandK2Kexperiments • Input forMonte Carlogenerators (GEANT4, e.g. for LHC, space applications)

  5. 2.0 1.5 2.5 0 0.5 1.0 Motivation of this analysis One of the largest K2K systematic errors comes from the uncertainty of the far/near ratio pions producing neutrinos in the oscillation peak To be measured by HARP oscillation peak K2K far/near ratio En(GeV) K2K interest Beam MC confirmed by Pion Monitor Beam MC

  6. NDC2 NDC1 dipole B x z Geometrical acceptance K2K interest MC K2K interest P > 1 GeV

  7. B x z Tracking NDC4 Top view NDC2 NDC1 NDC5 dipole magnet target 1 beam 2 NDC3 momentum resolution momentum bias case MC 1 No vertex constraint included case 1 data data case 2 beam particles

  8. 0-4.5 GeV p/pbyTime of Flight Beam time detectors tw target L t0 ta tb tc tof wall Tof Wall target data Tof wall resolution is ~160 ps 7sp/p at 3 GeV beam time resolution is ~180 ps 3 GeV beam particles 12.9 GeV K2K thin target light particles p+ mom < 4.5GeV p p

  9. Nphel P (GeV) p/pby Threshold Cerenkov 3-15 GeV e+ • p / p above 3 GeV • p / k from 3 to 9 GeV p+ number of photoelectrons cerenkov 2.6 GeV data threshold for pions 9.2 GeV 3 GeV beam particles threshold for kaons 5 GeV beam particles p p p inefficiency p inefficiency p+ p+ e+ number of photoelectrons number of photoelectrons

  10. electron / hadron 3 GeV beam particles 0-3 GeV p data Above 3GeV the electron and pion distributions have a serious overlap cerenkov p+ e+ 3 GeV beam particles 12.9 GeV K2K thin target data h+ hadrons calorimeter e+ small electron contamination

  11. Efficiencies • Pion efficiency in the (p,q) bin ij pion efficiency tracking efficiency geometrical acceptance depends on correlation between particles correlation independent correlation independent may depend on hadron generator estimated with MC verified with data computed with single particle MC verified with data but can be compuded using the data

  12. B x z Tracking efficiency NDC2 NDC5 NDC1 dipole target 1 beam Sources of inefficiency • hit efficiency (80%) • high hit density in NDC1 PR confusion 2 Improvements to came: • Use case • Vertex constraint 2 single track eff single track eff 3 MC hadron generators

  13. data Raw pion yield 12.9 GeV K2K thin target all particles identified pions

  14. … corrected by efficiency integrated over q integrated over P arbitrary units arbitrary units • These plots reflect the lack of MC statistics • Integrated over q and p • No systematic errors included identified pions identified pions proton background for Tof 3 MC hadron generators IMPORTANT This background can be computed with the data

  15. Systematic sources

  16. Conclusions 420 million events • HARP was proposed in 1999 • And recorded 420M events in 2 years • Today we present our first physics results • We have used 1/6 of our K2K thin target data … • … and very limited MC statistics … • … because we have used this analysis to set-up our MC production mechanism (today 1M events/day) • Pid detectors are well understood • The vertexing algorithm already working (improve ) • Several ideas for recovering efficiency to be implemented • Data statistics is not a problem (5.6 M events after data quality) • Small systematic error expected

  17. Next steps • Analysis for K2K and MiniBooNE replica targets • Full data statistics • Large MC statistics • 2D distribution (p, q) • Detailed study of systematic errors … • … and migration effects (expected to be small) This program will be completed in 3 months and presented at NEUTRINO 2004

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