Mariyan Bogomilov CERN, (Switzerland) University of Sofia and INRNE, (Bulgaria)

1. Mariyan Bogomilov CERN, (Switzerland) University of Sofia and INRNE, (Bulgaria) THE HARP EXPERIMENT On behalf of the HARP Collaboration 13-20 June 2005 GAS@BS, Kiten, Bulgaria

2. Motivation for HAdRon Production experiment Pion/kaon yield for the design of the proton driver and target systems ofneutrino factories

3. n factory design • Maximizing p+(p-) production yield as a function of • Target material • Proton energy • Geometry • Collection efficiency • Poor experimental knowledge: • Few material tested • Large errors (small acceptance) • Different simulations show large discrepancies for p production distribution, both in shape and normalization. • need to measure p yield and p+/p- ratio better than 5% • need differential distributions (PL,PT)

4. Motivation for HAdRon Production experiment Pion/kaon yield for the design of the proton driver and target systems ofneutrino factories Input for prediction of neutrino fluxes for the MiniBooNE and K2K experiments

5. MC only Analysis for K2K: motivations

6. n beam 250km 2.0 1.5 2.5 0 0.5 1.0 K2K interests One of the largest K2K systematic errors on the neutrino oscillation parameters comes from the uncertainty on the far/near ratio pions producing neutrinos in the oscillation peak To be measured by HARP oscillation peak K2K far/near ratio K2K interest En(GeV) Beam MC, confirmed by Pion Monitor Beam MC

7. Motivation for HAdRon Production experiment Pion/kaon yield for the design of the proton driver and target systems ofneutrino factories Input for prediction of neutrino fluxes for the MiniBooNE and K2K experiments Input for precise calculation of the atmospheric neutrino flux (from yields of secondary p,K)

8. Atmospheric n flux Primary flux is now considered to be known better than 10% Most of uncertainty comes from the lack of data to construct and calibrate a reliable hadron interaction model Model-dependent extrapolations from the limited set of data lead to about 30% uncertainty in atmospheric fluxes Need measurements on cryogenic targets (N2, 02) covering the full kinetic range in a single experiment

9. Motivation for HAdRon Production experiment Pion/kaon yield for the design of the proton driver and target systems ofneutrino factories Input for prediction of neutrino fluxes for the MiniBooNE and K2K experiments Input for precise calculation of the atmospheric neutrino flux (from yields of secondaryp,K) Input for Monte Carlo generators (GEANT4, e.g. for LHC or space applications)

10. HARP physics goals Precise (~2-3% error) measurement of differential cross-section for secondary hadrons by incident p and p± with: • Beam momentum from 1.5 to 15 GeV/c • Large range of target materials, from Hydrogen to Lead • Thin and thick targets, solid, liquid and cryogenic • K2K and MiniBooNE replica targets • Acceptance over the full solid angle • Final state particle identifications

11. The HARP Collaboration Bari University ,  CERN ,  Dubna JINR ,  Dortmund University ,  Ferrara University ,  Geneve University , P.N. Lebedev Physical Institute ,  Legnaro /INFN ,  Louvain-la-Neuve  UCL ,  Milano University/INFN ,  Moscow INR ,  Napoli University/INFN ,  Oxford University ,  Padova University/INFN ,  Protvino IHEP, Protvino ,  Paris VI-VII University ,  RAL , Roma I University/INFN Roma Tre University/INFN , Sheffield University , Sofia  Academy of Sciences ,  Sofia  University ,  Trieste  University/INFN ,  Valencia University 24 institutes 124 physicists

12. Data taking summary HARP took data at the CERN PS T9 beam-line for 2 years Total: 420 M events, ~300 settings SOLID: Element Thickness, l Beam momentum CRYOGENIC: n EXP:

13. Detector layout Large Angle spectrometer Forward spectrometer

14. MWPCs TOF-B TOF-A CKOV-A CKOV-B T9 beam 21.4 m Beam detectors MWPC: incident beam direction with σ<100μm, e=96% Beam TOF: p/K/p at low energy T0 with σ~70ps Proton selection purity > 98.7% Two beam Cherenkov: p/K above 12 GeV ~100% e-p tagging efficiency 12.9 GeV/c 3 GeV p p d K Corrected TOF (ps)

15. pt = abs(1 +2) pt √2(tot) DPT/PT PT (GeV/c) p dE/dx p P (GeV/c) Large angle spectrometer: TPC

16. p Beta=v/c p P(GeV/c) Large angle spectrometer: RPC • Two groups: barrel and forward plane • 46 chambers; • 2 layers; • 368 pads • Intrinsic barrel time resolution: ~220 ps • Combined resolution (RPC+TPC+BEAM) ~ 330 ps

17. NDC4 Top view NDC2 NDC1 dipole magnet NDC5 3 target B 1 beam x Plane segment 2 NDC3 z K2K interest K2K interest Forward acceptance A particle is accepted if it reaches the second module of the drift chambers P > 1 GeV

18. NDC4 Top view NDC2 NDC1 dipole magnet NDC5 3 target B 1 beam x Plane segment 2 NDC3 z Forward tracking Downstream Upstream • 3 track types depending upstream information • Track-Track • Track-Plane segment • Track-Target/vertex • recover efficiency and avoid dependencies on track density in 1st NDC module (model dependence) • Calculate efficiency separating downstream system first:

19. Tracking efficiency P, GeV/c x, rad y, rad

20. Tracking efficiency P, GeV/c x, rad y, rad

21. Reconstruction efficiency P, GeV/c x, rad y, rad

22. 3 GeV/c beam particles CALORIMETER TOF p CHERENKOV p+ h+ p inefficiency e+ p+ p e+ number of photoelectrons Forward spectrometer: PID 0 1 2 3 4 5 6 7 8 9 10 P (GeV) p/p TOF CHERENKOV CAL TOF p/k CHERENKOV TOF CHERENKOV p/e CHERENKOV CALORIMETER

23. Analysis for K2K Oscillation max In K2K: En : 0 ~ 5 GeV • Pp < 10 GeV/c • qp < 300 mrad Most important region oscillation max: En ~ 0.6 GeV • 1 GeV/c < Pp < 2 GeV/c • qp < 250 mrad En Pp qp Pp vs qp Study interactions of 12.9 GeV protons on Al with the HARP Forward Spectrometer

24. Combined PID probability Bayes theorem: TOF cherenkov where j = p, p • By MC: • electrons have a peak in low energy; • the particle is rejected if p<2.6 GeV/c and Nphe >15; • By data: • Kaons are estimated • And subtracted

25. 5% l Al target 200% l Al target K2K replica target Raw yield for K2K thin target • where: • M– unfolding momentum matrix - between true and measured momentum • J – Jacobian of transformationbetween measured and ‘true’  • -inverse tracking efficiency • -inverse geometrical acceptance

26. True pion and proton yields • Then: • Corrections for absorption (not reaching downstream detector) ~ 10-20% • Correction for secondary interactions( in the target and not coming from vertex) ~5% • Empty target subtraction • Subtraction of electrons and kaons • PID criteria by • where ij is the fraction of observed j to be true i

27. Pion cross-section Pion yield • A - atomic number • N0 - Avogadro number • - density Z – target thickness Npot – number of protons on target Cross-section calculation

28. + cross-section (graphics) + data … Stanford-Wang fit • 7 mln. triggers • 3.054 mln. incoming protons • 170 000 secondary tracks PRELIMINARY

29. + cross-section (table) PRELIMINARY

30. Conclusions • The HARP Experiment has collected data for hadron production measurements with a wide range of beam energies and targets • Detector, PID, tracking efficiency well understood and robust • First cross-section data are available: thin (5%l) K2K target, using forward region of the detector In the near future HARP will provide many important results, not only for n physics!

31. MiniBooNE beam phase space 8.9 GeV beam interactions on MiniBooNE replica Be target cooling fins Momentum and Angular distribution of pions decaying to a neutrino that passes through the MB detector. Acceptance of HARP forward detector

32. yield for the MiniBooNE thin target Iterative PID algorithm on Be 5% target data to extract raw pion yields. PRELIMINARY