the harp experiment at cern psharp.web.cern.ch/harp/classified/publications/... · 2004. 11. 2. ·...

NOW 04 Otranto, September 11-18 2004 M. Bonesini - The HARP expt at CERN PS /1

The HARP experiment The HARP experiment at CERN PSat CERN PS

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M�N OCP QSR TUWV U X Q P YZ[ \^] V T T R OV _R X `V N


Talk overviewTalk 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


Physics goals of HARPPhysics goals of HARP

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νν factory design factory design

• maximize π+(π-) production yield as a function of:

• proton energy• target material• geometry• collection efficiency (pL,pT)

• but different simulations show large discrepancies for π production distributions, both in shape and normalization. Experimental knowledge is rather poor (large errors: poor acceptance, few materials studied)⇒ � � ��

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νν beams flux prediction beams flux prediction

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Beam MC Beam MC confirmed byPion Monitor

0.5 1.0 1.5 2.0 2.50

Oscill. MAX

Eν (GeV)

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


Atmospheric Atmospheric νν flux flux

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Barton et. al.

Atherton et. al.NA56/SPY

Serpukov

Allaby et. al.

Abbott et. al.

Eichten et. al.

Cho et. al.

1 GeV 10 100 1 TeV

Parent energy

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Population of hadron-production phase-space for pA � �X interactions.

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µflux (represented by boxes) as a function of the parent and daughter energies.

Measurements.

1-2 pT points3-5 pT points>5 pT points

1 GeV

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100

1 TeV

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Dau

ghte

r en

ergy

Hadron production experimentsHadron production experiments

HARP


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Tuning of Montecarlo generatorsTuning 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


Data taking summaryData taking summary

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SOLID targets:

CRYOGENIC targets: ν EXP replica target:

HARP took data at the CERN PS T9 beamline in 2001-2002 Total: 420 M events, ~300 settings


The HARP detector layoutThe HARP detector layout

TRACKING + PARTICLE ID at Large angle and Forward


Detector PerformancesDetector Performances

1. Beam detectors2. Large angle detector3. Forward spectrometer


1. Beam instrumentation1. Beam instrumentation

Beam Tof

πK

Beam cherenkov

MBoone target

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MWPCs

• Beam TOF:– separate π/K/p at low

energy over 21m flight distance

– time resolution 70 ps – proton selection purity

>98.7%

• Beam Cherenkov:– Identify electrons at low

energy, π at high energy, K above 12 GeV

– ~100% eff. in e-π tagging

π

k

pd

Corrected TOF (ps)

3 GeV

Beam compositionand direction

TOF-A

CKOV-A CKOV-B

TOF-B

21.4 m

T9 beam

MWPCs


2. Large angle detector: status of TPC2. Large angle detector: status of TPC

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µ and πRelativistic rise

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Elastic scatteringElastic scattering

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2. Select p and π by beam TOF

3. BLUE: Simple selection

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RED: Additional cut on dE/dx in TPC (select proton)

Missing mass distributionsMissing mass distributions


3. Forward spectrometer: NDC tracking3. Forward spectrometer: NDC tracking

• 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 muons:drift distance resolution ~340 µm

Plane efficienciesSide modules

Plane number

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0.4

0.6

0.8

0

Resolution= 340 µm

TPC

NDC1 NDC2 NDC5

NDC4

NDC3

Dipole Cherenkov

TOF-wall

EM calorimeter

beam

reused from NOMAD


The momentum and angular resolutions are well within the K2K requirements

MCMC

datadata

11type

No vertex No vertex constraint constraint includedincluded

MCMC

momentum resolutionmomentum resolution angular resolutionangular resolution

Forward tracking: resolutionForward tracking: resolution


Forward PID: TOF WallForward PID: TOF Wall

TOF time resolution ~160 ps3σ separation: π/p up to 4.5 GeV/c

K/π up to 2.4 GeV/c

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7σ separation of π/p at 3 GeV/c

3 GeV beam particles3 GeV beam particles

datadataπ

p

Separate Separate ππ/p (K//p (K/ππ) at low momenta) at low momenta (0–4.5 GeV/c) (0–4.5 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)

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TOF Wall calibrationTOF Wall calibration

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2. Cosmic ray calibration (every 2-3 months):

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3. Laser calibration (many times a day):

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ics

70 ps


Forward PID: CherenkovForward PID: Cherenkov

Separate π/p at large momenta

• 31 m3 filled with C4F10 (n=1.0014)• Light collection: mirrors+Winston

cones � 38 PMTs in 2 rows

• LED flashing system for calibration

π mass is a free parameter

nominal threshold

Npe

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p (GeV/c)

Num

ber

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p

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Npheldatadata

Nphel


Forward PID: CalorimeterForward PID: Calorimeter

• Separate π/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

Energy resolution 23%/sqrt(E)• intrinsic resolution 15%/sqrt(E)• convoluted with beam spread

at detector entrance

electrons

pions

3 GeV3 GeV

datadata


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Forward Analysis for K2K targetForward Analysis for K2K target•

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Analysis for K2K: motivationsAnalysis for K2K: motivations


pion efficiency(data)

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pion purity (data)

pion yield(raw data)

tracking efficiency(data+MC)

migration matrix(not computed yet)Acceptance (MC)

depend on momentum resolution

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j = bin of recosntructed (p,θ)

The forward unnormalized cross sectionThe forward unnormalized cross section


P > 1 GeV

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K2Kinterest

K2K interest

Forward acceptanceForward acceptance

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NDC4

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• Aim: recover as much efficiency as possible and avoid dependencies on track density in 1st NDC module (hadron model dependent)


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N acc .

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Downstream trackingefficiency ~98%

Up-downstream matching efficiency ~75%

Tracking efficiencyTracking efficiency

ε track is known at the level of 5%

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Total Tracking Efficiency

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tof cerenkov calorimetermomentumdistribution

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 the “true” nature of the particle

Forward PID: Forward PID: ππ efficiency and purity efficiency and purity

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ε "π # $% &(' ) "π # %*+ , # - ./ 0 ) "π # %*+ , η "π # $% & ' ) "π # %*+ , # - ./ 0 ) "π # - ./

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

p-e/π misidentification background

5% 5% λλ Al target Al target

Raw dataRaw data(20% of stat)(20% of stat)

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Pion yield: K2K thin targetPion yield: K2K thin target


Pion yieldPion yield

After all After all correctionscorrections

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Conclusions and overlookConclusions and overlook

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the harp experiment at cern psharp.web.cern.ch/harp/classified/publications/... · 2004. 11. 2. ·...

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