First Results from the HARP Experiment

1
First Results from the HARP Experiment

• Lara Howlett

University of Sheffield
On Behalf of the HARP Collaboration
2
Overview

• Physics Goals of HARP
• Experimental Setup
• Performance of Large Angle Detectors
• Goals of First Analysis
• Performance of Small Angle Detectors
• Results From First Analysis

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Physics Goals of HARP

• Systematic Study of Hadron Production
• Over the momentum range from 1.5-15 GeV/c
• Using solid and cryogenic targets from H to Pb
• As input For
• Calculations of atmospheric neutrino flux
• Design of neutrino factory targetry and pion
  capture
• Calculations of beam fluxes for K2K and MiniBoone
• Monte Carlo hadronic generators

4
Experimental Setup
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Status of Large Angle

• High statistics cosmic ray calibration and
  calibration with radioactive Fe were done in 2003
• This data has allowed
• Computation of gains and mapping of dead pads
• First evaluation of dE/dx
• First evaluation of the performance of correction
  for a cross talk effect
• Improvement in momentum resolution of 30
• As a first check of the improvements, data taken
  with a cryogenic H2 target and 3 GeV/c pions and
  protons is being analyzed, looking for elastic
  scattering
• p,(?) p -gt p,(?) p

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Aim of First Analysis
To be measured by HARP

• First Analysis focuses on the needs of K2K
  experiment
• Exploits the forward part of the spectrometer
  (NDCs, TOF, Cherenkov)
• One of the largest systematic uncertainties on
  oscillation parameters comes from the near/far
  ratio
• Range of interest qplt0.25rad ppgt1 GeV/c

oscillation peak
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Requirements for first analysis

• p and q measurements in range of interest
• provided by drift chambers
• Ability to identify p and reject p, K, e
• provided by TOF system, Cherenkov and electron id
• Appropriate data
• provided by data taken with K2K replica target
  taken at
• 12.9 GeV/c beam momentum

K2K interest
Geometrical Acceptance q
K2K interest
Geometrical Acceptance p
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Tracking
Top view
NDC4
NDC2
NDC1
NDC5
dipole magnet
target
1
beam
2
NDC3
case
1
Momentum bias for case 2 has now been solved
data
case
beam particles
2
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Tracking

• For this analysis only case 1 tracks shown in
  previous slide are used
• Lost efficiency can be recovered by the use of
  case 2 tracks which are now understood
• This will increase efficiency to 80-85
• Tracking efficiency for multi track events has a
  small dependency on the generator for now

Spread indicates Differences between 3 hadronic
generators
single track eff
single track eff
Case 1 Case 2
Case 1 only
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Particle ID TOF (p/p)

• p/p separation is provided by Time of Flight from
  0-4.5 GeV/c
• Tof wall resolution is 160ps -gt7s p/p at 3 GeV/c
• Beam resolution is 180ps for this analysis
  (150ps has now been achieved by additional
  calibration and further improvements are expected)

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Particle ID Cherenkov (p/p)

• Provides p/p separation above 3 GeV/c
• Provides p/k separation from 3 to 9 GeV/c

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Particle ID Cherenkov/ECal (e/hadron)

• Electron hadron separation is provided by
  Cherenkov up to 3 GeV/c
• At other energies this is provided by the
  calorimeter

3 GeV/c beam particles
12.9 GeV/c K2K thin target
data
h
hadrons
e
small electron contamination
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Raw Yields
Only 1/6 of the data for this setting has been
used
Only case 1 events have been used for this
analysis
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Cross section

• Definition of Cross Section

Pion Misidentification Background
Absolute Normalisation (Not included yet)
Bin Migration Matrix (Not included yet)
Pion Yield
Total Efficiency includes Geometrical
Acceptance Tracking Efficiency Pion Efficiency
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Yields Corrected for Efficiency
integrated over q
integrated over P
arbitrary units
arbitrary units
identified pions
identified pions
Proton background For TOF (3 MC generators) This
background can be Computed using data
No systematic errors have been Included at this
stage
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Conclusions

• HARP has completed an extensive data taking
  program
• 420M events were recorded over a large number of
  settings
• Significant progress has been made in the
  understanding of large angle detectors
• Forward PiD and tracking detectors are now well
  understood
• First physics results have been produced with the
  forward detectors using limited data and MC
  statistics
• This has allowed us to setup an analysis chain

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Future Aims

• The next step is to analyse full statistics of
  K2K and MiniBoone targets as well as large MC
  statistics
• A Detailed study of systematic errors and
  migration effects is also required
• Several ideas to recover efficiency are being
  implemented and giving promising results