The HARP Experiment

1
The HARP Experiment

• Physics goals and motivations
• Summary of the experimental program
• Detector overview and performance
• Large angle
• Forward region
• Towards physics analysis
• Alessandra Tonazzo, Università Roma Tre
• On behalf of the HARP Collaboration

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
• Acceptance over the full solid angle
• Final state particle identification

3
Motivation 1 Neutrino Factory

• Aim maximize p production rate (/proton/GeV)
• Optimize
• target material and geometry
• primary beam energy
• collection scheme
• Existing simulation packages show large
  discrepancies on pion yields and distributions
• Experimental data are poor (small acceptance, few
  materials) and old (Allaby et al.1970, Eichten et
  al. 1972)
• Measure pT distribution with high precision (lt5)

? Thick target program high Z, large p
4
Motivation 2 Input to MC generators

• Lack of experimental data and large uncertainties
  in the calculations,
• in particular for thick and high Z target
  materials

Differential distributions for pion production
NIMA451(2000)327
NIMA472(2001)557
NO DATA !
? Thin and thick targets, scan in Z
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Motivation 3 Atmospheric neutrinos

• Calculation of neutrino fluxes for atmospheric
  neutrino experiments

• Main uncertainty (30) secondary hadron
  production
• Lack of experimental data

? Low Z materials cryogenic targets
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Motivation 4 MiniBooNE and K2K
K2K case (by Issei Kato)
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Motivation 4 MiniBooNE and K2K
K2K Near/Far ratio

• K2K Largest uncertainty (5) on neutrino fluxes
  arises from Near/Far spectrum ratio, mainly for
  Enlt1 GeV
• MiniBoone Large uncertainties on MC calculation
  of n fluxes
• Measure p and K fluxes in the forward direction
  with precision 3
• K2K Al target, 12.9 GeV/c protons
• MiniBooNE Be target, 8.9 GeV/c protons
• Official collaboration with
• K2K and MiniBoone

MiniBoone n spectrum
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A byproductBeam related background of LSND
n
H2O target
p 1.46 GeV/c
LSND detector
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• Expect nenm 7.5x10-4
• But LSND measures a signal of ne25x10-4
• 4.1s evidence for nm?ne oscillations?
• Try to verify the beam related backgrounds
• pp- production ratio (expect 81)
• Measure thin (10l) H2O target with 1.5 GeV/c
  protons (easy)
• ee- ratio look for anomalous m- decay in
  water target
• Measure thick (100l) H2O target with 1.5 GeV/c
  protons (need sensitivity 10-3)

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Data taking summary
SOLID
n EXP
CRYOGENIC
K2K Al MiniBoone Be LSND H2O
5 50 100 Replica 5 50 100 Replica 10 100
12.9 GeV/c 8.9 GeV/c 1.5 GeV/c
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Data taking summary
HARP has been taking data at the CERN East Hall
on the PS T9 beamline in 2001 and 2002

• Total
• 30 Tbytes of data
• 420 M events
• 13000 physics runs
• 300 settings
• High performance of DAQ system

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The HARP experiment
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The HARP experiment
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The HARP detector layout
TRACKING PARTICLE ID at Large angle and Forward
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Beam detectors
T9 beam

• Beam tracking with MWPCs
• 96 tracking efficiency using 3 planes out of 4
• Resolution lt100 mm

extrapolation to target
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Beam particle selection

• 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 gt98.7

p
3 GeV/c beam
p
d
K
12.9 GeV/c beam

• Beam Cherenkov
• Identify electrons at low energy, p at high
  energy, K above 12 GeV
• 100 eff. in e-p tagging

p
K
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Large angle region
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TPC

• Diameter 82.0cm outer, 10.2cm inner
• Drift length 156 cm
• Magnetic field 0.7 T
• Electric field gradient 110 V/cm
• Gas Ar-CH4 91-9
• Drift velocity 5 cm/ms
• Total drift time 32 ms 320 time samples
• 3972 pads in 20 rows, 5.5x15mm2 each

• Efforts to understand the detector are going on
• dead/hot pads
• energy calibration
• cross-talk
• E and B field distrortions

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TPC calibration

• Laser system (continuous)
• drift time monitoring
• drift velocity measurement
• study of distortions
• 83Kr (periodical injections)
• channel equalization (spread 25)
• energy calibration measured resolution lt14
• Dedicated runs with cosmics and X-ray sources
  (Fe,Kr) in summer 2003

Drift velocity vs time
83Kr specturm (few pads with similar response)
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TPC cross-talk

• Due to capacitive coupling between the output of
  one preamplifier and the input of another
• Measurement
• Individual pulse
• injection in one sector
• Modelling
• Capacitive coupling preamp transfer function
• preamp signal
• Introduce in simulation and estimate effect
• Correct !
• Subtract cross-talked signal

Energy response Simulated Fe data
s9.6
s14.9
s9.8
correct
X-talk
Energy response Fe data 2003
correct
Preliminary !
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TPC track reconstruction and resolution
Momentum resolution (at present)
3 GeV/c p on Ta target (100l)
Hot/dead pad and equalizations applied No X-talk
corrections
PL (GeV/c)
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TPC dE/dx
Preliminary !
Cosmic data 2003 (1 run)
Protons
Muons and pions
Relativistic rise
Electrons?
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RPCs

• TOF measurement in the large angle region for
  particle identification when TPC dE/dx cannot
  distinguish
• e/p(K,p) lt300 (500,1000) MeV/c
• 30 barrel 16 forward chambers 8m2
• 4-gap glass stack with 0.1 mm gap

Time (35 ps)
Slewing corrections
Charge (0.1 fC)

• Studies on 12 GeV p- beam
• Time-charge dependence of response
• Response vs impact position
• Calibration from physics tracks
• absolute time scale for each channel spread 100
  ps
• Charge resol. vs impact point
• Time resolution in overlaps
• Efficiency (in progress)

Width of RPC
Time response (ps)
Small charges
Very large charges
PA
PA
Vertical impact point position (mm)
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RPCs
Time difference of two RPCs hit by same particle

• Performance
• Single track efficiency
• gt97
• Time resolution
• 180 ps
• independent of impact point position
• Preliminary PID results

Horizontal scan
Efficiency
Impact point position (strip)
Impact point position (mm)
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Next physics analysis goalneutrino experiments

• K2K needs measurement of p with
• Egt1 GeV
• Elt4.5 GeV
• qlt300 mrad
• Forward region
• Tracks reaching forward PID detectors
• p/p separation with TOF and Cherenkov
• Focus on forward detectors
• Efficient tracking
• Calibration
• PID

Dip from neutrino oscillations in K2K
they come from decay of these pions
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Forward region
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Forward region
CHERENKOV
ECAL
NDC4
TOF
NDC1
NDC2
NDC5
MAGNET
NDC3
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Forward acceptance
K2K interest
MC
NDC2
NDC1
dipole
K2K interest
B
x
P gt 1 GeV
z
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Forward Tracking NDC
P 3,5,8,15 GeV/c High intensity

• 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
• gt drift distance resolution 340 mm

Side modules
nominal
Eff. vs time in spill
Plane efficiencies
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Forward track reconstruction
Track segment eff
Hit eff

• Entirely new track reconstruction method
  developed to achieve high efficiency for track
  reconstruction in spite of low hit efficiency
• Algorithm based on plane segments rather than
  triplets testing all possible combinations of
  matching objects, with the help of Kalman
  algorithm
• Matching of segments before/after dipole magnet ?
  track with momentum determination

Data MC
Track eff 95 for all momenta and angles
Lower at borders due to large angular bias
30
Forward tracking performance
Momentum resolution
5
K2K interest
eloss?
P (GeV)
K2K requirements
Data MC
15 mrads
Angular resolution dq2.5 mrad at p2 GeV/c
P (GeV)
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Forward tracking performance
Matching to other subdetectors
NDC - TPC
NDC - ECAL
NDC - TOF
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Cherenkov

• Separate p/p at large momenta
• 31 m3 filled with C4F10 (n1.0014)
• Light collection mirrorsWinston cones ? 38 PMTs
  in 2 rows
• LED flashing system for calibration

nominal threshold
Number of photoelectrons
Npe ? 21
p mass is a free parameter
p (GeV/c)
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TOF Wall
Variation of equalization constants 2001-2002
cosmics vs laser

• Separate p/p (K/p) at low momenta
• 42 slabs of fast scintillator read at both ends
  by PMTs

PMT response to Laser vs time

• Calibration
• Cosmic ray runs (every 2-3 months)
• Laser (continuous monitor stability)
• Equalization gt
• overall time resolution 210 ps
• gt3s separation of p/p (K/p)
• up to 4.5 (2.4) GeV/c

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Electron identifier

• 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

• Energy resolution 23/sqrt(E)
• intrinsic resolution 15/sqrt(E)
• convoluted with beam spread at detector entrance

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Forward particle identification
Calorimeter
5 GeV electrons DATA
5 GeV electrons MC
TOF 3 GeV/c
Associated ECAL Energy (GeV)
p
p
Track momentum (GeV/c)
Cherenkov vs Ecal
electrons
E(EM1)/E(Ecal)
electrons
Nphel
Ecal Energy (a.u.)
pions
all
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Conclusions

• The HARP data taking programme has been
  successfully completed in 2002
• Large angle
• Reconstruction chain ready
• Focus on understanding of TPC
• Forward region
• All detectors calibrated and understood
• Preliminary PID
• On the road to results for K2K/MiniBoone

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RPC PID electrons
Electron enriched sample photon conversion
candidates 2 tracks with same production angle
and coming from same origin
1.4
1
0.6
8 GeV/c 0.05 l Be target
0.2
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LSND

• pN?Xp / pN?Xp- 8/1
• p?mnm / p-?m-nm 1/0.05
• m?enmne / m-?e-nmne 1/0.12
• nenm e-e 1/8 x 0.05 x 0.12 7.5x10-4

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