Anselmo Cervera VillanuevaAnselmo Cervera VillanuevaUniversity of GenUniversity of Genevaeva

(Switzerland)(Switzerland)

Rencontres de Moriond Rencontres de Moriond 25 March 200425 March 2004

HARPHARP

On behalf of the HARP CollaborationOn behalf of the HARP Collaboration

FirstFirst

physics resultsphysics results

2

OverviewOverview

The experiment and its objectivesThe experiment and its objectivesDetector performanceDetector performance

TrackingParticle identification

Closing the first analysis cycleClosing the first analysis cycleUsing our K2K thin target dataEfficienciesMomentum and angular distributions

3

The HARP experimentThe HARP experiment

124 people 24 institutes

4

Physics goalsPhysics goalsSystematic study of Systematic study of HAHAddRRonon PProduction:roduction:

Beam energy: 2-15 GeV2-15 GeVTarget: from hydrogen to leadfrom hydrogen to lead

Motivation:Motivation:Pion/kaon yield for the design of the proton driver of neutrino factories neutrino factories and SPL-based super-beams super-beamsInput for precise calculation of atmospheric neutrino fluxatmospheric neutrino fluxInput for prediction of neutrino fluxes for the MiniBooNEMiniBooNE and K2KK2K experimentsInput for Monte CarloMonte Carlo generators (GEANT4, e.g. for LHC, space applications)

5

Motivation of this analysisMotivation of this analysis

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

GeVE 75.05.0

mrad

GeVP

250

1

K2KK2K

interestinterest

K2K

far

/nea

r ra

tio

K2K

far

/nea

r ra

tio

Beam MC Beam MCconfirmed byPion 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 K2K systematic One of the largest K2K systematic

errors errors

comes from comes from

the uncertainty of the far/near ratio the uncertainty of the far/near ratio

6

P > 1 GeV

mradsx

]200 ,200[

Geometrical acceptanceGeometrical acceptance

dipoleNDC1 NDC2

B

x

z

K2Kinterest

K2Kinterest

MCMC

7

TrackingTracking

MCMC

datadata

dipole magnetNDC1 NDC2

B

x

z NDC5

beam

target

Top view

momentum resolutionmomentum resolution

11

22

11

momentum biasmomentum biascase

NDC3

NDC4

No vertex No vertex constraint constraint includedincluded

11

22

datadatacase

case

beam particles

8

//pp byby Time of FlightTime of Flight

3 GeV beam particles3 GeV beam particles 12.9 GeV K2K thin target12.9 GeV K2K thin target

t0

tw

L

12

022

L

ttpm w

0-4.5 GeV

target

Tof Wall

Beam time detectors

datadata

pp

+light particles

mom < 4.5GeV

ta tb tc

Tof wall resolution is Tof wall resolution is ~160 ps ~160 ps

77 /p at 3 GeV/p at 3 GeVbeam time resolution is beam time resolution is ~180 ps ~180 ps

tof walltarget

9

//pp by by Threshold CerenkovThreshold Cerenkov

/ p above 3 GeV/ p above 3 GeV/ k from 3 to 9 GeV/ k from 3 to 9 GeV

2

20 /11

1 pmn

NN phel

P (GeV)

Nph

el

2.6 GeV

3-15 GeV

+

e+

9.2 GeVthreshold for pions threshold

for kaons

e++

3 GeV beam particles3 GeV beam particles

number of photoelectrons

p p

+

5 GeV beam particles5 GeV beam particles

number of photoelectrons

datadata

inefficiency

inefficiency

cerenkov

num

ber

of p

hoto

elec

tron

s

10

electron / hadronelectron / hadron

Above 3GeV the electron and pion

distributions have a serious overlap

12.9 GeV K2K thin target12.9 GeV K2K thin target3 GeV beam particles3 GeV beam particles

cere

nko

vce

ren

kov

calo

rim

eter

calo

rim

eter

0-3 GeV

datadata

e++

e+

h+

3 GeV beam particles3 GeV beam particles

p

small electronsmall electroncontaminationcontamination

hadronshadrons

datadata

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EfficienciesEfficienciesPion efficiency in the (p,) bin ij

trackij

ijaccij

trackij

trueij

accij

trueij

ijij

N

N

N

N

N

N

N

N

geometrical acceptance

tracking efficiency

pionefficiency

depends on correlation between particles

may depend on hadron generator

correlationindependent

computed with single particle MCverified with data

correlation independent

estimated with MCverified with databut can be compuded

using the data

12

Tracking efficiencyTracking efficiencydipole

NDC1 NDC2

B

x

z

NDC5

beam

target

3 MC hadron 3 MC hadron generatorsgenerators

Sources of inefficiencySources of inefficiency

hit efficiency (80%) high hit density in NDC1

PR confusion

Improvements to came:Improvements to came:

Use case

Vertex constraint

single track eff single track eff

11

22

22

13

Raw pion yieldRaw pion yieldall particlesall particles

identified pionsidentified pions

12.9 GeV K2K thin target12.9 GeV K2K thin target datadata

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… … corrected by efficiencycorrected by efficiency

These plots reflect the lack of MC statisticsThese plots reflect the lack of MC statistics

Integrated over Integrated over and p and p

No systematic errors includedNo systematic errors included

arbi

trar

y un

its

arbi

trar

y un

its

identified pions identified pions

integrated over integrated over P

proton background for Tof3 MC hadron generators

IMPORTANTIMPORTANTThis background This background can be computedcan be computed

with the data with the data

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Systematic sourcesSystematic sources Initial estimation

methodRelevance Reduction

Acceptance Data small

Tracking efficiency

Several hadron generators

+

User defined final state medium Measure with data

Momentum

& angular biases

Several hadron generators

+

beam data particlessmall Vertex constraint

(p,) bin migration(track purity)

(p and biases)

(p and finite resolution)

Several hadron generators small1.Optimize (p,) binning

2.Reduce biases

3.Improve resolution (vertex)

Proton

backgroundSeveral hadron generators small

Can be fully measured in the data

Electron background Several hadron generators negligibleCan be fully measured in

the data

Kaon background Several hadron generators smallMeasured with data above

3GeV

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ConclusionsConclusionsHARP was proposed in 1999HARP was proposed in 1999And recorded 420M events in 2 yearsAnd recorded 420M events in 2 yearsToday we present our first physics results Today we present our first physics results We have used 1/6 of our K2K thin target data …We have used 1/6 of our K2K thin target data …… … and very limited MC statistics …and very limited MC statistics …… … because we have used this analysis to set-up our MC because we have used this analysis to set-up our MC production mechanism (today 1M events/day) production mechanism (today 1M events/day) Pid detectors are well understoodPid detectors are well understoodThe vertexing algorithm already working (improve )The vertexing algorithm already working (improve )Several ideas for recovering efficiency to be implementedSeveral ideas for recovering efficiency to be implementedData statistics is not a problem (5.6 M events Data statistics is not a problem (5.6 M events after data qualityafter data quality))Small systematic error expectedSmall systematic error expected

pp /

420 million events

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Next steps Next steps

Analysis for K2K and MiniBooNE replica targetsAnalysis for K2K and MiniBooNE replica targets

Full data statisticsFull data statistics

Large MC statisticsLarge MC statistics2D distribution (p, 2D distribution (p,

Detailed study of systematic errors …Detailed study of systematic errors …

… … and migration effects (expected to be small)and migration effects (expected to be small)

This program will be completed in 3 months and presented at NEUTRINO 2004NEUTRINO 2004