The HARP experiment at CERN PS

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The HARP experiment at CERN PS
Neutrino Oscillation Workshop Conca
Specchiulla, Otranto, September 11-18 2004
M.Bonesini INFN, Sezione di Milano, Italy

Dipartimento di Fisica G. Occhialini, Universita
di Milano-Bicocca On behalf of the HARP
collaboration
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Talk overview

• The HARP Experiment
• Physics goals and motivations
• Data taking summary
• Experimental setup and program
• Detector overview and performance
• First physics analysis pion yields for K2K
  target
• Motivations
• Results
• Conclusions and overlook

3
Physics goals of HARP

• Input for prediction of neutrino fluxes for the
  MiniBooNE and K2K experiments
• Pion/Kaon yield for the design of the proton
  driver of neutrino factories and SPL- based
  super-beams
• Input for precise calculation of the atmospheric
  neutrino flux
• Input for Monte Carlo generators (GEANT4, e.g.
  for LHC or space applications)

2000 2001 Installation 2001- 2002 Data taking

• Systematic study of hadron production
• Beam momentum 1.5-15 GeV/c
• Target from hydrogen to lead
• Acceptance over full solid angle
• Final state particle identification

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n factory design

• maximize p(p-) production yield as a function
  of
• proton energy
• target material
• geometry
• collection efficiency (pL,pT)
• but different simulations show large
  discrepancies for p production distributions,
  both in shape and normalization. Experimental
  knowledge is rather poor (large errors poor
  acceptance, few materials studied)

• aim measure pT distribution with high precision
  ( lt 5) for high Z targets

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n beams flux prediction

• Energy, composition, geometry of a neutrino beam
  is determined by the development of the hadron
  interaction and cascade ? needs to know ?
  spectra, K/ ? ratios

Precise pT and pLspectra for extrapolation to far
detectors and comparison between near and far
detectors
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Atmospheric n flux

• Primary flux is now considered to be known to
  better than 10
• Most of the 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 ,
  O2) covering the full kinematic range in a single
  experiment

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Hadron production experiments
NA56/SPY
Population of hadron-production phase-space for
pA ? pX interactions. ?µ flux (represented by
boxes) as a function of the parent and daughter
energies. Measurements. 1-2 pT points 3-5 pT
points gt5 pT points
Atherton et. al.
Barton et. al.
Serpukov
Allaby et. al.
Eichten et. al.
Cho et. al.
Abbott et. al.
HARP
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Tuning of Montecarlo generators

• General problem little exp. data and large
  uncertainties in calculations
• In particular for high Z materials and low
  primary energy

?Thin and thick targets, scan the periodic system
and momenta
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Data taking summary
HARP took data at the CERN PS T9 beamline in
2001-2002 Total 420 M events, 300 settings
SOLID targets
CRYOGENIC targets
n EXP replica target
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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The HARP detector layout
TRACKING PARTICLE ID at Large angle and Forward
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Detector Performances

1. Beam detectors
2. Large angle detector
3. Forward spectrometer

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1. Beam instrumentation
MWPCs
TOF-B
TOF-A
Beam composition and direction
CKOV-A
CKOV-B
T9 beam
21.4 m
Beam Tof
MWPCs
Beam cherenkov

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

• Beam TOF
• separate p/K/p at low energy over 21m flight
  distance
• time resolution 70 ps
• proton selection purity gt98.7

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

12.9 GeV
3 GeV
p
p
d
k
MBoone target
Corrected TOF (ps)
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2. Large angle detector status of TPC
dE/dx
DpT/pT
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Elastic scattering
Elastic scattering

• Measure elastic cross-section
• To normalise the data (elastic cross section is
  well known)
• To evaluate the acceptance efficiency in TPC
• To check momentum scale
• Calibration tool for merging forward and large
  angle analysis

Missing mass mx2 ( pbeam ptarget pTPC )2

• Target liquid H2 (cryogenic target)
• Target length 18 cm
• 3 GeV/c beam

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Missing mass distributions
p p -gt p p
? p -gt ? p
Red using dE/dx for PID

• missing mass for p p?p p and ?p ? ? p
• Select p and ? by beam TOF
• BLUE Simple selection
• Only 1 pos. track in the TPC coming from the
  target
• RED Additional cut on dE/dx in TPC (select
  proton)

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3. Forward spectrometer NDC tracking
NDC4
Plane efficiencies
TOF-wall
Side modules
NDC1
NDC2
NDC5
TPC
beam
0.8
0.6
Dipole
Cherenkov
reused from NOMAD
0.4
EM calorimeter
NDC3
0.2

• Reused NOMAD Drift Chambers
• 12 planes per chamber (in total 60 planes)
• wires at 0,5 w.r.t. vertical
• Hit efficiency 80 (limited by non-flammable gas
  mixture, it was 95 in NOMAD)
• correctly reproduced in the simulation
• Alignment with cosmics and beam muonsdrift
  distance resolution 340 mm

Plane number
0
Resolution 340 mm
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Forward tracking resolution
angular resolution
momentum resolution
MC
MC
type
1
No vertex constraint included
data

• The momentum and angular resolutions are well
  within the K2K requirements

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Forward particle identification
0 1 2 3 4 5 6
7 8 9 10
P (GeV)
p/p
TOF
CERENKOV
CAL
TOF
p/k
CERENKOV
TOF
CERENKOV
p/e
CERENKOV
CALORIMETER
data
3 GeV/c beam particles
CALORIMETER
TOF
p
CERENKOV
h
p
p inefficiency
e
p
p
e
number of photoelectrons
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Forward PID TOF Wall

• Separate p/p (K/p) at low momenta (04.5 GeV/c)
• 42 slabs of fast scintillator read at both ends
  by PMTs
• Calibration / equalization
• Cosmic ray runs (every 2-3 months)
• Laser (continuous monitor stability)

3 GeV beam particles
data
PMT
p
Scintillator
p

• TOF time resolution 160 ps
• 3s separation p/p up to 4.5 GeV/c
• K/p up to 2.4 GeV/c
• ? 7s separation of p/p at 3 GeV/c

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TOF Wall calibration

• A good and redundant system is needed for good
  TOFW timing measurements
• Cosmic ray calibration (every 2-3 months)
• Measure the relative time-offset between
  photomultipliers
• Laser calibration (many times a day)
• TOF wall stability check
• Good agreement with cosmic ray calibration

70 ps
cosmics
laser
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Forward PID 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

3 GeV beam particles
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
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Forward PID Calorimeter

• Separate ?/e
• 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

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Forward Analysis for K2K target

• Focuses on the needs of K2K experiment
• Exploits the forward part of the spectrometer
  (NDCs, TOFW, CKOV)

?(E?)SK R(E?) . ?(E?)ND
Range of interest 1 GeV/c lt p? lt 8 GeV/c ?? lt
250 mrad
oscillation peak
1.5
2.0
2.5
0.5
0
1.0
Beam MC confirmed by pion monitor
Beam MC
0.5 lt E? lt 0.75 GeV
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Analysis for K2K motivations
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The forward unnormalized cross section
i bin of true (p,?) j bin of recosntructed
(p,?)
depend on momentum resolution
migration matrix (not computed yet)
pion yield (raw data)
Acceptance (MC)
pion efficiency (data)
tracking efficiency (dataMC)
pion purity (data)
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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 gt 1 GeV
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Forward tracking
NDC4
Top view
NDC2
NDC1
dipole magnet
NDC5
3
target
1
beam
Plane segment
2
NDC3

• 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)

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Tracking efficiency
Downstream tracking efficiency 98
Up-downstream matching efficiency 75
Total Tracking Efficiency
1.0
1.0
0.8
0.8
Green type 1 Blue type 2 Red type 3
Total tracking efficiency
Total tracking efficiency
0.6
0.6
0.4
0.4
Black sum of normalized efficiency for each type
0.2
0.2
0
2
4
6
8
10
-200
-100
0
200
100
P (GeV/c)
qx (mrad)
etrack is known at the level of 5
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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)
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Pion yield K2K thin target
p gt 0.2 GeV/c ?y lt 50 mrad 25 lt ?x lt 200
mrad

• To be decoupled from absorption and reinteraction
  effects we have used a thin target

5 l Al target
Raw data (20 of stat)
p-e/p misidentification background
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Pion yield
After all corrections
5 l Al target p gt 0.2 GeV/c ?y lt 50 mrad 25
lt ?x lt 200 mrad
To do Correction for resolutions, absolute
normalisation, empty target subtraction full
statistics
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Conclusions and overlook

• Status of HARP detector
• Forward region good tracking and solid PID
• Large angle much recent progress (TPC
  calibration campaign in 2003)
• First preliminary results are available thin
  (5?) K2K target (mainly as an example of the
  many HARP analysis capabilities)
• Using forward region of the detector
• We plan to have a detector paper (incorporating
  performances of all subdetectors, that are now
  well understood) and a first physics paper on
  thin K2K target on a 2 month timescale. A first
  large-angle analysis (H/Tn targets for ?-factory
  study) will be shown at the Villars SPSC meeting