HARPHARP

Anselmo Cervera Villanueva

University of Geneva(Switzerland)

K2KK2K

Neutrino CH MeetingNeuchâtel, June 21-22, 2004

OverviewOverview

HARPHARP K2KK2K HARP contribution to K2KHARP contribution to K2K Geometrical acceptanceGeometrical acceptance Tracking efficiencyTracking efficiency Particle identificationParticle identification Pion yieldsPion yields

HARPHARP

The HARP experiment (CERN)The HARP experiment (CERN)

124 people 24 institutes

Physics goalsPhysics goals

Systematic study of Systematic study of HAHAddRRonon PProduction:roduction: Beam momenta: 1.5-15 GeV/c1.5-15 GeV/c

Target: from hydrogen to leadfrom hydrogen to lead

Motivation:Motivation: Pion/kaon yield for the design of the proton driver of neutrino neutrino

factories factories and SPL-based super-beams super-beams

Input for precise calculation of atmospheric neutrino fluxatmospheric neutrino flux

Input for prediction of neutrino fluxes for the MiniBooNEMiniBooNE and K2KK2K experiments

Input for Monte CarloMonte Carlo generators (GEANT4, e.g. for LHC, space applications)

K2kK2k

K2K Experiment (Japan)K2K Experiment (Japan)

First long base line neutrino experiment (250 km)First long base line neutrino experiment (250 km) To confirm with beam neutrinos the Super-K To confirm with beam neutrinos the Super-K

resultsresults

250 km

250 km

<E<E> = 1.3 GeV> = 1.3 GeV almost pure almost pure : ~98%: ~98%

-like event at Super-K-like event at Super-K

Overview of K2KOverview of K2K

12.9 GeV 12.9 GeV proton proton beambeam

++

++

pp

Target + HornTarget + Horn

pion monitorpion monitor(cerenkov)

decay pipe

muon monitor near detectorsnear detectors Super-KSuper-K

200m 100m 250km

no oscillationno oscillation

oscillationoscillation

predicted

10 2 43 5E (GeV)

4

8

12

x1010

measured

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 1 2 3 4 5Neutrino Energy (GeV)

(xL

)/(

xL

)

SK

SK

FD

FD

22

Far/Near spectrum ratio ≠ 1Far/Near spectrum ratio ≠ 1

confirmed bypimon

Beam MC

1Kt

HARP HARP contribution contribution

to to K2KK2K

Motivation of this analysisMotivation of this analysis

GeVE 75.05.0

mrad

GeVP

250

1

K2KK2K

interestinterest

K2

K f

ar/

ne

ar

rati

oK

2K

fa

r/n

ea

r ra

tio

Beam MC Beam MC,confirmed by Pion Monitor

To be measured To be measured by HARPby HARP

0.5 1.0 1.5 2.0 2.50 E(GeV)

oscillationoscillationpeakpeak

One of the largest One of the largest systematic errorssystematic errors

on the neutrinoon the neutrino oscillation parametersoscillation parameters

measured by the measured by the K2K experimentK2K experiment

comes fromcomes from

the uncertainty on thethe uncertainty on the far/near ratiofar/near ratio

pions producing neutrinos pions producing neutrinos in the oscillation peakin the oscillation peak

Forward AcceptanceForward Acceptance

MCMC

dipoleNDC1 NDC2

B

x

z

xz

y

top view

The ingredientsThe ingredients

trackingtracking p and measurement (at the interaction vertex) connect tracks with particle identification (PID) measurements

PIDPID Identify pions Reject protons, kaons and electrons

(p,)absolute

normalization

bin migration matrix

total efficiency pion yield

pion purity(background)

To measure all this one needs:

datadata We have reproduced in HARP the exact K2K conditions:

12.9 GeV/c proton beam An exact replica of the K2K target (2 aluminium)

jjj

ijtracki

acci

normi NMF 111

acceptance

pion id efficiency

Forward TrackingForward Tracking

dipole magnetNDC1 NDC2

B

x

z

NDC5

beam

target

Top view

11

22 NDC3

NDC4

2D segment

33

We distinguish 3 track types depending on We distinguish 3 track types depending on the nature of the matching object upstream the nature of the matching object upstream the dipolethe dipole1.1. 3D-3D3D-3D2.2. 3D-2D3D-2D3.3. 3D-Target/vertex 3D-Target/vertex (independent of NDC1)(independent of NDC1)

The idea is to recover as much efficiency as The idea is to recover as much efficiency as possible to avoid hadron model possible to avoid hadron model dependencies.dependencies.

Saturation of NDC1 in the beam Saturation of NDC1 in the beam spot regionspot region

High density of hits in NDC1 High density of hits in NDC1 provokes correlation between provokes correlation between particles particles

hadron model dependencieshadron model dependencies

problemsproblems solutionssolutions

systematic errorsystematic error

Momentum and angular resolutionsMomentum and angular resolutions

The momentum and angular resolutions are well inside the K2K requirements

MCMC

datadata

11type

No vertex No vertex constraint constraint includedincluded

MCMC

momentum resolutionmomentum resolution angular resolutionangular resolution

Tracking efficiencyTracking efficiency

It can be computed with the DATA as a function of x2 and x2

We use the MC to perform the conversion:

once demonstrated that DATA and MC agree in their x2 and x2 distributions

downi

recpi

acci

downi

acci

recpitrack

iN

N

N

N

N

N

downupi

downi

dipole magnetNDC1 NDC2

B

x

z

NDC5

beamtarget

Top view

11

2D segment

22

33

,, 22 px x

extrapolation to this plane

Module efficiencyModule efficiency

The efficiency of NDC2 and NDC5 is flat within ~5%. The efficiency of the lateral modules (3 and 4) is flat

within 10% The combined efficiency is not sensible to these

variations.

NDC2 NDC5

NDC3

NDC4

NDC 2 NDC 5NDC 4NDC 3

datadata

dipole

Downstream efficiencyDownstream efficiency

5

2

5

2

5

2

5

2

5

2

5

2

nmpp

NDCi

mmn

n

NDCi

NDCi

mmn

n

NDCi

NDCi

m

NDCi

downi

pnm

nm

m

NDC2 NDC5

NDC3

NDC4

)%298(

MCMC

dipole

Up-down matching efficiencyUp-down matching efficiency

Is the probability of matching a downstream track with the other side of the dipole

downi

recpidownup

iN

N

dipole magnetNDC1 NDC2

B

x

z

NDC5

beamtarget

Top view

11

NDC3

NDC4

2D segment

22

33

MC and data agree MC and data agree within ~3% in their within ~3% in their

shapesshapes

We tune to the DATA We tune to the DATA the absolute scale of each track type the absolute scale of each track type

MCMC datadata+

Total tracking efficiencyTotal tracking efficiency The MC reproduces the up-down

matching efficiency in terms of x2 and x2 within ~3%

The downstream efficiency is flat

We can use the MC to We can use the MC to compute the total efficiency compute the total efficiency

as a function of p and as a function of p and downup

idowni

tracki

)%298(

MCMC datadata+

Particle identificationParticle identification

e++

p

number of photoelectrons

inefficiency

e+

h+

0 1 2 3 4 5 6 7 8 9 10

p

P (GeV)P (GeV)

e

k

TOF CERENKOVCALORIMETER

3 GeV/c beam particles3 GeV/c beam particles

TOFCERENKOV

TOF ?CERENKOV

CERENKOV

CALORIMETER

TOF

CERENKOV

CAL

+

p

datadata

Pion ID efficiency and purityPion ID efficiency and purity

ekpphe

phephe

pPEEpPNpPpP

pPEEpPNpPpPEENpP

,,,21

2121

)|()|,,()|,()|,(

)|()|,,()|,()|,( ),,,,|(

toftof cerenkovcerenkov calorimetercalorimetermomentummomentumdistributiondistribution

Using the Bayes theorem:Using the Bayes theorem:

1.5 GeV 3 GeV 5 GeV 1.5 GeV 3 GeV 5 GeV

datadata

we use the beam detectors to establish we use the beam detectors to establish the “true” nature of the particlethe “true” nature of the particle

Pion yieldPion yield

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

datadatap-e/p-e/ misidentification misidentification background background

K2K replica targetK2K replica target

5% 5% Al target Al target

200% Al target

jjj

ijtracki

acci

i NM 111

datadata

ConclusionsConclusions The The tracking efficiencytracking efficiency is known at the level of is known at the level of ~5%~5% The pion ID correction factor is fully computed with The pion ID correction factor is fully computed with

data (except kaon contamination below 3GeV)data (except kaon contamination below 3GeV)

Small systematic errorSmall systematic error However, a detailed study of the PID systematic error However, a detailed study of the PID systematic error

is still missing is still missing

NextNext Increase tracking efficiency Increase tracking efficiency reduce systematic (<5%)reduce systematic (<5%) Use the MC to compute the systematic error on the pion Use the MC to compute the systematic error on the pion

ID correction factorID correction factor Larger MC and data statistics Larger MC and data statistics (p,(p,) 2D distribution) 2D distribution Detailed study of migration effectsDetailed study of migration effects Replica target Replica target z dependencez dependence