HARP (Hadron Production) Experiment at CERN

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1 HARP (Hadron Production) Experiment at CERN 2nd Summer School On Particle Accelerators And Detectors Sep 2006, Bodrum, Turkey Aysel Kayιş Topaksu Çukurova Üniversitesi, ADANA

2 Outline The Physics case for Harp Harp forward spectrometer Measuring a cross section Results for Al and preliminary results for Be Conclusions and Outlook

3 The Physics case for Harp (Based on Forward section) Computing ν fluxes Physics case for a hadroproduction measurement in the MiniBoone experiment Physics case for a hadroproduction measurement in the K2K experiment The Harp experiment

4 Neutrino Beam Fluxes Neutrino beams are produced in the laboratory by the weak decays of nuclei, nucleons, and µ, π, and K mesons. The spectrum of neutrinos from these decays is known extremely well The only significant flux uncertainty comes from the production cross section of the parent particle and its subsequent scattering in target materials. In decay-at-rest beams, this is simply an overall normalization factor. A single well-understood neutrino cross section is enough to completely determine the neutrino flux (e.g. νe elastic process, or an inverse β-decay transition) However, in decay-in-flight beams, the complete differential production cross sections of the parent particles are needed, along with their interactions in material along their flight paths

5 Decay-in-Flight ν Beams The calculation of secondary-production cross sections of π and K mesons in proton-nucleus collisions is not reliable, although new data is challenging modelers to make improvements Phenomenological parameterizations can be valid over limited energy and angle ranges, more useful at higher energies (> ~15 GeV) (e.g. Sanford-Wang or others) There are large discrepancies in the various hadron production models used in MC generators (MARS, FLUKA, MCNP, GHEISHA, etc.), although the situation is has been improving In order to predict fluxes with uncertainties less than ~10%, direct measurements in the appropriate energy and angular ranges are necessary

Conventional neutrino beams Ingredients to compute a neutrino flux (executive summary): Pion (and kaon) production cross section (use same target and proton energy than proton driver of ν

6 Conventional neutrino beams Ingredients to compute a neutrino flux (executive summary): Pion (and kaon) production cross section (use same target and proton energy than proton driver of ν experiment) Reinteractions (take data with thin and thick target) All the rest: Simulation of the neutrino line: An easy problem. Applies to: Past, present and future conventional ν beams

7 Example: The MiniBooNE Neutrino Beam Many studies have shown that the largest uncertainty in the ν flux prediction is the knowledge of the π/k production cross sections Various models are known to have large differences in neutrino rate predictions

Why you need hadro-production data MiniBoone MC: Prediction of pion yields for different models MiniBoone MC: Prediction of neutrino fluxes for different models

8 Why you need hadro-production data MiniBoone MC: Prediction of pion yields for different models MiniBoone MC: Prediction of neutrino fluxes for different models Notice: Large differences between models in final flux prediction Conclusion: the neutrino beam is sensitive to poorly understood, forward (small angle), pion production rates

Physics case for MiniBoone MiniBoone is looking for ν µ -->ν e oscillations using only one detector. They need, in consequence, an absolute calibration of their ν µ and ν e flux.

9 Physics case for MiniBoone MiniBoone is looking for ν µ -->ν e oscillations using only one detector. They need, in consequence, an absolute calibration of their ν µ and ν e flux. This implies the following measurements: π + production cross section (ν µ flux and part of ne flux) K production cross section (ν e flux) π - production cross section (anti ν running) Thick target measurements (effect of reinteractions in yields)

10 Example 2: The K2K experiment

11 Atmospheric neutrinos

12 Atmospheric neutrino oscillations L/E Analysis

13 Oscillation probability P νµ ν τ (L) = sin 2 (2θ)sin 2 (1.27 m2 (ev 2 ) E(GeV ) L(km)) P νµ ν µ (L) = 1 P νµ ν τ (t) E(GeV ) L osc = 2π 1.27 m 2 (ev 2 )

K2K: Disappearance experiment to confirm atmospheric oscillation Oscillation probability @ 250 km from source for atmospheric parameters: maximum ~1GeV

14 K2K: Disappearance experiment to confirm atmospheric oscillation Oscillation 250 km from source for atmospheric parameters: maximum ~1GeV Non-oscillated oscillated spectrum must be measured near the neutrino source In the case of oscillations one observes an energy-dependent suppression of the spectrum

15 Far-Near ratio ν beam 250km For a point-like source the flux, in the absence of oscillations scales like 1/R 2 Far/Near flux ratio x Φ(E ν ) far = R(E ν ) Φ(E ν ) near PIMON data analysis Simulation E ν (GeV) Integrated above 2.5GeV R(E ν ) If the near detector does not see a point-like source it is necessary to multiply by a factor R(E ν ) to obtain the predicted spectrum in the far detector. The correct determination of R(E ν ) is essential since the signal is a distortion of the energy spectrum (a wrongly determined R(E ) ν could fake oscillations)

16 K2K results No-oscillation excluded at >4σ Total 107 beam events observed; expect Terrestrial experiment confirms that atmospheric effect is disappearance of muon neutrinos

Physics case for K2K protons K2K is a disappearance experiment, with a near detector which provides a stringent constrain of the flux in the far detector provided that the Far/Near ratio is well

17 Physics case for K2K protons K2K is a disappearance experiment, with a near detector which provides a stringent constrain of the flux in the far detector provided that the Far/Near ratio is well measured. This in turn requires a good measurement of the ν µ flux. To compute the ν µ spectrum one must measure de p-n cross section for the production of positive pions at the energies of K2K proton driver (12.9 GeV) and with the same target material (Al). (Done by Harp) and Compute the transport of the produced π through the magnetic horns and its decay in the decay pipe. Transport the neutrinos. (K2K Beam Monte Carlo)

19 Motivations Systematic study of hadron production Beam momenta from GeV/c Targets from H to Pb Input for: Calculation of fluxes for conventional neutrino beams Neutrino factory design Atmospheric neutrino flux calculations Input for Monte Carlo hadronic generators

20 HARP data set Target material Target length (l%) Beam Momentum (GeV) #events (millions) Be 420 M events 30 TB of data > 100 settings Solid targets C Al Cu Sn Ta Pb 2 (2001) ±3 ± 5 ± 8 ± 12 ± 15 Negative only 2% and 5% K2K MiniBooNE Al Be 5, 50, 100, replica Cu button Cu +12.9, Cu skew Cu Cryogenic targets N D 1 H 1 6 cm ±3 ± 5 ± 8 ± 12 ± H 2 18 cm ±3, ±8, ± Water H , , +8(10%) 9.6

21 Harp Forward Spectrometer Beam detectors Drift chambers Tracking Momentum measurement Tracking efficiency Particle identification PID with the TOF PID with CHE Combined PID

22 Beam instrumentation: Counting protons on target MWPCs Beam composition and direction & Normalization (pot) T9 beam CKOV-A TOF-A CKOV-B 21.4 m TOF-B MWPCs Incident beam direction MiniBoone target Beam cherenkov K/π/p separation at high energy p 12.9 GeV K π Beam Tof K/π/p separation at low energy T0 π k p 3 GeV d Corrected TOF (ps)

Drift Chambers Cosmic rays Alignment Iter 1 Iter 2 Reused from NOMAD

per plane Plane efficiency studies also with cosmic rays and muons

23 Drift Chambers Cosmic rays Alignment Iter 1 Iter 2 Reused from NOMAD Tracking device for low angle region (<300 mrads) Alignment with cosmic and beam muons. Corrections on: Wire positions Wire time pedestal (t 0 ) Drift velocities per plane Plane efficiency studies also with cosmic rays and muons Performance drift distance resolution Iter 10 σ=340 µm eff~80% In NOMAD was >95% Due to the use of a different gas (non flammable) lateral modules plane efficiency

24 m 2 target TOF 2 2 tw t0 = p 1 L Tof ~160 ps 3.6σ π/p a 3 GeV Beam ~70 ps Particle ID π/p using TOF entries 3 GeV beam particles 5 GeV beam particles Beam TOF t a t b t c π + p m 2 (GeV 2 ) target t 0 data GeV π + L k t w Tof Wall

π/p using Cerenkov 3-15 GeV data entries 3 GeV beam particles 1400 1200 1000 800 600 400 200 p π + cerenkov π ineficiency e + entries 1200 1000 800 600 400 200 π / p p> 3 GeV π / k 3 <P< 9 GeV 5 GeV

25 π/p using Cerenkov 3-15 GeV data entries 3 GeV beam particles p π + cerenkov π ineficiency e + entries π / p p> 3 GeV π / k 3 <P< 9 GeV 5 GeV beam particles p π ineficiency π + N phel number of photoelectrons N 2.6 GeV Threshold pions e + phel α π GeV Threshold kaons P (GeV) 1 Pth N0 P N phe N phel N phe N phel

Particle identification P (GeV( GeV) 0 1 2 3 4 5 6 7 8 9 10 π/p TOF CERENKOV CAL π/k

entries 350 300 250 200 150 100 50 0 π + TOF p -1-0.5 0 0.5 1 1.

+ e + 0 0 5 10 15 20 25 30 35 40 45 50 N phe number of photoelectrons entries 250

26 Particle identification P (GeV( GeV) π/p TOF CERENKOV CAL π/k TOF CERENKOV TOF π/e CERENKOV CALORIMETER CERENKOV data 3 GeV/c beam particles entries π + TOF p m 2 (GeV 2 ) entries p CERENKOV π inefficiency π + e N phe number of photoelectrons entries E/p 0.4 CALORIMETER h + e E 1 /E

27 Computing a Cross Section 2 d σ α 1 A 1 α = M ijαi j α Ni j i θ j N pot N Aρt dp d Number of protons on target Physics constants for target properties Correction matrix including: Momentum resolution Geometrical acceptance Reconstruction efficiency Particle identification efficiency and migration Particles Observed

28 Event Selection RPC TPC MWPC BS HALO A ITC TDS BC B BC A target HALO B TOF B TOF A FTP Event selection for protons on target ( normalization trigger ): impact point and direction of primaries (BS, TDS, HALO A, HALO B) protons: identified bytof and Cherenkovs (TOF A, TOF B, BC A, BC B) Event selection for proton inelastic interactions ( physics trigger ): normalization trigger && forward trigger scintillator plane (FTP)

29 Reconstruction efficiency dipole magnet NDC2 target B

30 Downstream reconstruction efficiency dipole magnet NDC2 NDC5 B

31 Empty target subtraction To correct for backgrounds due to proton interactions in the material surrounding the target we take data in identical conditions than physics data but without the target. Yields are computed and corrected for empty target data and then subtracted from data yields.

32 Tertiaries x NDC1 dipole NDC2 NDC5 beam z target Particles arising from decay or nuclear interactions, making it to fiducial volume B

34 Results for Al Data Double differential π cross section for 12.9GeV/c protons hitting a 5%λ Al target Dotted line shows best fit to Sanford Wang parameterisation Nucl.Phys.B732:1-45,2006 hep-ex/

35 -the red line is the extrapolation of our best-fit Sanford-Wang parameterization Reasonable agreement between HARP and previous results

36 K2K Near/Far Ratio Predicted Flux Shape Predicted Far/Near Ratio Near Detector Near/Far Ratio Far Detector Near/far ratio errors are greatly reduced with the inclusion of Harp Data

37 Results - Be 90% of MiniBooNE neutrino flux comes from π->µ+ν µ HARP result covers 0.75<p π <6.5 GeV/c 30<θ π <210mrad More than 80% of the relevant pions come from this region

38 Results - Be Double differential π cross section for 8.9GeV/c protons hitting a 5%λ Be target

39 Comparison with older data: Be

40 Conclusions / Outlook Precision ν studies require a precise knowledge of ν production HARP Al results have been published and incorporated into K2K final oscillation analysis HARP results give a factor of 2 reduction in errors on F/N ratio predictions HARP Be results are close to completion and should be published later this year. These results will be used in MiniBooNE oscillation analyses HARP measurements have started to fill an important gap in ν flux predictions

41 Conclusions / Outlook Inclusion of C data will allow also a contribution to the measurement of the atmospheric flux. The on-going LA analysis will make fundamental contributions to the design of future neutrino installations such as the Neutrino Factory.

43 Momentum estimators (II) Good (~unbiased) and consistent (~ p 2 =p 4 ) estimators of P true Yields are measured in terms of p 2 (p 4 is used to compute tracking efficiency)

44 Detector response measured from data π + and π - have the same behaviour π - p k + π + π/p/k are clearly separated by the TOFW below 3 GeV Fit the inclusive beta distribution to a triple Gaussian with fixed shapes and free normalization π + and π - have the same behaviour Above pion Cherenkov threshold pions are suppressed to less than 1% by N phe <3 p k +

45 Sanford-Wang Parameterization X Particles in the final system P beam is the proton beam p and θ are the pion mom and angle c 1,c 2.c 8 are fits parameters

46 Errors - Al Typical error 8.2% on double differential cross section Dominant errors: overall normalisation, momentum scale and secondary interactions

47 Errors - Be Typical error 13.0% on double differential cross section Dominant errors: overall normalisation, statistics, momentum reconstruction and secondary interactions

48 HARP Forward Spectrometer 8.9 GeV/c π + beam

Results From The HARP Experiment

Results From The HARP Experiment Lara Howlett University of Sheffield Overview of HARP and forward analysis Al analysis for K2K experiment Be analysis for MiniBooNE experiment Motivations Systematic study