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The HARP Experiment Physics goals and motivations Summary of the experimental program

Hadron Production Cross-Sections and Secondary Particle Yields from 2 to 15 GeV using Neutrino Beam Targets. The HARP Experiment Physics goals and motivations Summary of the experimental program Detector overview and performance The fist physics analysis: pion yields from K2K target Goals

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The HARP Experiment Physics goals and motivations Summary of the experimental program

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  1. Hadron Production Cross-Sections and Secondary Particle Yields from 2 to 15 GeV using Neutrino Beam Targets • The HARP Experiment • Physics goals and motivations • Summary of the experimental program • Detector overview and performance • The fist physics analysis: pion yields from K2K target • Goals • Results Alessandra Tonazzo, Università Roma Tre and INFN On behalf of the HARP Collaboration A.Tonazzo - HARP pion yields for neutrino beams

  2. HARP physics goals Precise (~2-3% error) measurement of d2s/dpTdpL for secondary HAdRon Production by incident p and p± with • Beam momentum from 1.5 to 15 GeV/c • Large range of target materials, from Hydrogen to Lead • Acceptance over the full solid angle • Final state particle identification A.Tonazzo - HARP pion yields for neutrino beams

  3. HARP Physics Motivations Input for prediction of neutrino fluxes for the MiniBooNE and K2K experiments Pion/Kaon yield for the design of the proton driver and target system of Neutrino Factories and SPL- based Super-Beams Input for precise calculation of the atmospheric neutrino flux (from yields of secondary p,K) Input for Monte Carlo generators (GEANT4, e.g. for LHC or space applications) A.Tonazzo - HARP pion yields for neutrino beams

  4. Data taking summary HARP took data at the CERN PS T9 beamline in 2001-2002 Total: 420 M events, ~300 settings SOLID: n EXP: CRYOGENIC: A.Tonazzo - HARP pion yields for neutrino beams

  5. The HARP Experiment 124 physicists 24 institutes A.Tonazzo - HARP pion yields for neutrino beams

  6. The HARP Experiment A.Tonazzo - HARP pion yields for neutrino beams

  7. The HARP detector layout TRACKING + PARTICLE ID at Large angle and Forward A.Tonazzo - HARP pion yields for neutrino beams

  8. MWPCs TOF-B TOF-A CKOV-A CKOV-B T9 beam 21.4 m Beam detectors • Beam tracking with MWPCs : • 96% tracking efficiency using 3 planes out of 4 • Resolution <100 mm MiniBoone target A.Tonazzo - HARP pion yields for neutrino beams

  9. Beam particle selection p 3 GeV/c beam p d K 12.9 GeV/c beam • Beam TOF: • separate p/K/p at low energy over 21m flight distance • time resolution 170 ps after TDC and ADC equalization • proton selection purity >98.7% • Beam Cherenkov: • Identify electrons at low energy, p at high energy, K above 12 GeV • ~100% eff. in e-p tagging p K A.Tonazzo - HARP pion yields for neutrino beams

  10. Status of TPC Elastic scattering of 3 GeV p and p on H2 target Missing mass mx2 = ( pbeam + ptarget – pTPC ) pppp p DpT/pT dE/dx Red: using dE/dx for PID pppp  A.Tonazzo - HARP pion yields for neutrino beams

  11. n beam 250km Analysis for K2K: motivations • Computation of n fluxes at SK is based on near/far ratio R • For pointlike source (no oscillations), R~1/r2 • If the near detector does not see a pointlike source, R depends on En • Current K2K computation of R is based on MC • Confirmed by p production measurement (pion monitor) at En>1 GeV • Extrapolated to En<1 GeV : the interesting region for oscillations ! A.Tonazzo - HARP pion yields for neutrino beams

  12. Analysis for K2K: motivations A.Tonazzo - HARP pion yields for neutrino beams

  13. Analysis for K2K: interesting region K2K needs measurement of pions with • E>1 GeV • E<4.5 GeV • q<300 mrad • Forward region • Main tracking detectors: drift chambers • PID detectors: TOF, Cherenkov, calorimeter Dip from neutrino oscillations in K2K they come from decay of these pions: A.Tonazzo - HARP pion yields for neutrino beams

  14. Forward acceptance K2K interest NDC2 NDC1 dipole x z B K2K interest A particle is accepted if it reaches the second module of the drift chambers P > 1 GeV A.Tonazzo - HARP pion yields for neutrino beams

  15. Forward Tracking: NDC • Reused NOMAD Drift Chambers • 12 planes per chamber, wires at 0°,±5° w.r.t. vertical • Hit efficiency ~80%(limited by non-flammable gas mixture) • stable in time • lowered by high particle flux • recovered between spills • correctly reproduced in the simulation Alignment with cosmics and beam muons • drift distance resolution ~340mm Side modules Plane efficiencies A.Tonazzo - HARP pion yields for neutrino beams

  16. B x z Forward tracking NDC4 • 3 track types depending on the nature of the matching object upstream the dipole • Track-Track • Track-Plane segment • Track-Target/vertex • Aim: recover as much efficiency as possible and avoid dependencies on track density in 1st NDC module (hadron model dependent) Top view NDC2 NDC1 dipole magnet NDC5 3 target 1 beam Plane segment 2 NDC3 A.Tonazzo - HARP pion yields for neutrino beams

  17. Forward tracking: resolution The momentum and angular resolutions are well within the K2K requirements angular resolution momentum resolution MC type MC 1 No vertex constraint included data A.Tonazzo - HARP pion yields for neutrino beams

  18. Tracking efficiency • Only particles with no track downstream the dipole do not enter into the game (~2%). • This 2% should be quite independent of the track density (hadron model dependent) because tracks downstream the dipole are uncorrelated Downstream tracking efficiency ~98% Up-downstream matching efficiency ~75% • We have been working to improve it by: • Alignment • Optimizing matching cuts etrack is known at the level of 5% A.Tonazzo - HARP pion yields for neutrino beams

  19. Total tracking efficiency Total tracking efficiency as a function of p(left) and qx (right) computed using MC (2 hadron generators) properly scaled by data Green: type 1 Blue: type 2 Red: type 3 Black: sum of normalized efficiency for each type A.Tonazzo - HARP pion yields for neutrino beams

  20. Forward PID: Cherenkov 3 GeV beam particles Separate p/p at large momenta • 31 m3 filled with C4F10 (n=1.0014) • Light collection: mirrors+Winston cones → 38 PMTs in 2 rows • LED flashing system for calibration p p+ e+ nominal threshold data Nphel 5 GeV beam particles p Number of photoelectrons Npe → 21 p+ p mass is a free parameter p (GeV/c) Nphel A.Tonazzo - HARP pion yields for neutrino beams

  21. Forward PID: TOF Wall Calibration / equalization • Cosmic ray runs (every 2-3 months) • Laser (continuous: monitor stability) TOF time resolution ~160 ps =>3s separation of p/p (K/p) up to 4.5 (2.4) GeV/c =>7s separation of p/p at 3 GeV/c Separate p/p (K/p) at low momenta • 42 slabs of fast scintillator read at both ends by PMTs 3 GeV beam particles data p p A.Tonazzo - HARP pion yields for neutrino beams

  22. Forward PID: Calorimeter • Pb/fibre: 4/1 • EM1: 62 modules, 4 cm thick • EM2: 80 modules, 8 cm thick • Total 16 X0 • Reused from CHORUS • Calibration with cosmic rays: • Measurement of attenuation length in fibers • Module equalization 3 GeV electrons data pions Energy resolution 23%/sqrt(E) • intrinsic resolution 15%/sqrt(E) • convoluted with beam spread at detector entrance A.Tonazzo - HARP pion yields for neutrino beams

  23. Forward PID: p efficiency and purity Using the Bayes theorem: momentum distribution tof calorimeter cerenkov Iterative approach: dependence on the prior removed after few iterations data we use the beam detectors to establish the “true” nature of the particle 1.5 GeV 3 GeV 5 GeV 1.5 GeV 3 GeV 5 GeV j-(t) = Nj-true-obs / Nj-true j-(t) = Nj-true-obs / Nj-obs j-(t)/ j-(t) A.Tonazzo - HARP pion yields for neutrino beams

  24. The cross section The 3 types of tracks must be treated separately because of the different momentum resolution i = bin of true (p,) j = bin of recosntructed (p,) depend on momentum resolution migration matrix (not computed yet) pion yield acceptance pion efficiency tracking efficiency pion purity A.Tonazzo - HARP pion yields for neutrino beams

  25. Pion yield 5% l Al target • To be decoupled from absorption and reinteraction effects we have used a thin target 200% l Al target K2K replica target p > 0.2 GeV/c |y | < 50 mrad 25 < |x| < 200 mrad Raw data p-e/p misidentification background A.Tonazzo - HARP pion yields for neutrino beams

  26. Pion yield 5% l Al target p > 0.2 GeV/c |y | < 50 mrad 25 < |x| < 200 mrad After PID correction After efficiency correction A.Tonazzo - HARP pion yields for neutrino beams

  27. Pion yield After acceptance correction 5% l Al target p > 0.2 GeV/c |y | < 50 mrad 25 < |x| < 200 mrad • Systematics are still to be evaluated: • tracking efficiency know to 5% • expect small effect from PID A.Tonazzo - HARP pion yields for neutrino beams

  28. Conclusions • The HARP Experiment has collected data for hadron production measurements with a wide range of beam energies and targets • Status of detector • Forward region: good tracking and PID • Large angle: much recent progress • First physics results are available: thin (5%l) K2K target • Using forward region of the detector • To do • Compute data deconvolution and migration matrix • Evaluate systematic errors • Analyse empty target data for background subtraction • Investigate q=0 region: saturation effects due to beam particle removal • Introduce normalization for absolute cross-section (using min.bias trigger) • … go on to full statistics, and to the rest of the data ! A.Tonazzo - HARP pion yields for neutrino beams

  29. Backup A.Tonazzo - HARP pion yields for neutrino beams

  30. NDC module efficiency NDC4 • The efficiency of NDC2 and NDC5 is flat within ~5%. • The efficiency of the lateral modules (3 and 4) is flat within 10% • The combined efficiency is not sensitive to these variations. NDC5 NDC2 dipole data NDC3 NDC 2 NDC 4 NDC 3 NDC 5 A.Tonazzo - HARP pion yields for neutrino beams

  31. Module acceptance / Downstream eff. NDC4 NDC5 NDC2 module acceptance module efficiency dipole MC NDC3 A.Tonazzo - HARP pion yields for neutrino beams

  32. Up-downstream matching efficiency data x2, qx2 MC We need to convert x2 and qx2 to p and q. For that we use the MC A.Tonazzo - HARP pion yields for neutrino beams

  33. Up-down matching efficiency NDC4 Top view • Probability of matching a downstream track with the other side of the dipole NDC2 NDC1 NDC5 dipole magnet 3 target 1 beam B 2D segment 2 NDC3 x z We tune to the DATA the absolute scale of each track type MC and data agree within ~3% in their shapes MC data + A.Tonazzo - HARP pion yields for neutrino beams

  34. Forward PID: continuous probability • Using the Bayes theorem • The different pid detectors are independent of each other Measured quantities Particle types Ckov Calorimeter TOF A.Tonazzo - HARP pion yields for neutrino beams

  35. Forward PID: iterative procedure P( p ,  | ) from TOF with  = m2 / p2 3 GeV P( p ,Nphe | ) from Cherenkov Step 1 Step 2  p e K P( p , E1 , E2 ) from Calorimeter Step 3 Step 4 Product of conditional probabilities and relative abundances Iterative Bayesian approach: dependence on the prior removed after few iterations Step 5 Line : true PID Colored histograms: reconstructed PID A.Tonazzo - HARP pion yields for neutrino beams

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