the harp experiment physics goals and motivations summary of the experimental program

BEACH04 Chicago, June 28-July 3 2004 A.Tonazzo - HARP pion yields for neutrino beams /1

Hadron Production Cross-Sections and Hadron Production Cross-Sections and Secondary Particle Yields from 2 to 15 Secondary Particle Yields from 2 to 15

GeV using Neutrino Beam Targets GeV using Neutrino Beam Targets

• The HARP Experiment– Physics goals and motivations

– Summary of the experimental program

– Detector overview and performance

• The fist physics analysis: pion yields from K2K target – Goals

– Results

Alessandra Tonazzo, Università Roma Tre and INFN

On behalf of the HARP Collaboration


HARP physics goalsHARP physics goals

Precise (~2-3% error) measurement of

d2/dpTdpL

for secondary HAdRon Production by incident p and ± with– Beam momentum from 1.5 to 15 GeV/c– Large range of target materials, from

Hydrogen to Lead

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


Input for prediction of neutrino fluxes for the MiniBooNE and K2K experiments

Pion/Kaon yield for the design of the proton driver and target system of Neutrino Factories and SPL- based Super-Beams

Input for precise calculation of the atmospheric neutrino flux (from yields of secondary ,K)

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

HARP Physics MotivationsHARP Physics Motivations


Data taking summaryData taking summary

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

SOLID:

CRYOGENIC: EXP:

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


The HARP ExperimentThe HARP Experiment

124 physicists 24 institutes


The HARP ExperimentThe HARP Experiment


The HARP detector layoutThe HARP detector layout

TRACKING + PARTICLE ID at Large angle and Forward


Beam detectorsBeam detectors

• Beam tracking with MWPCs :– 96% tracking efficiency

using 3 planes out of 4– Resolution <100m

MiniBoone target

TOF-A

CKOV-A CKOV-B

TOF-B

21.4 m

T9 beam

MWPCs


Beam particle selectionBeam particle selection

• Beam TOF:– separate /K/p at low

energy over 21m flight distance

– time resolution 170 ps after TDC and ADC equalization

– proton selection purity >98.7%

• Beam Cherenkov:– Identify electrons at low energy, at

high energy, K above 12 GeV– ~100% eff. in e- tagging

3 GeV/c beam

K

12.9 GeV/c beam

K

p

d


Status of TPCStatus of TPC

pT/pT

pdE/dx

Elastic scattering of 3 GeV p and on H2 target

Missing mass mx

2 = ( pbeam + ptarget – pTPC )

Red: using dE/dx for

PID

pppp

pp


Analysis for K2K: motivationsAnalysis for K2K: motivations

• Computation of fluxes at SK is based on near/far ratio R– For pointlike source (no

oscillations), R~1/r2 – If the near detector does not

see a pointlike source, R depends on E

• Current K2K computation of R is based on MC– Confirmed by production

measurement (pion monitor) at E>1 GeV

– Extrapolated to E<1 GeV : the interesting region for oscillations !

beam 250km


Analysis for K2K: motivationsAnalysis for K2K: motivations


Analysis for K2K: interesting regionAnalysis for K2K: interesting region

K2K needs measurement of pions with E>1 GeV E<4.5 GeV <300 mrad

►Forward region • Main tracking detectors:

drift chambers• PID detectors: TOF,

Cherenkov, calorimeter

Dip from neutrino oscillations in K2K

they come from decay of these pions:


P > 1 GeV

mradsx

]200 ,200[

K2Kinterest

K2K interest

Forward acceptanceForward acceptance

dipoleNDC1 NDC2

B

x

z

A particle is accepted if it reaches the second module of the drift chambers


Forward Tracking: NDCForward Tracking: NDC

• 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

drift distance resolution ~340 m

Plane efficiencies

Side modules


Forward trackingForward tracking

dipole magnetNDC1 NDC2

B

x

z

NDC5

beam

target

Top view

11

22 NDC3

NDC4

Plane segment

33

• 3 track types depending on the nature of the matching object upstream the dipole1. Track-Track

2. Track-Plane segment

3. Track-Target/vertex

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


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


• Only particles with no track downstream the dipole do not enter into the game (~2%). – This 2% should be quite independent of the track density

(hadron model dependent) because tracks downstream the dipole are uncorrelated

downupdowntrack Downstream

tracking efficiency

~98%

Up-downstream matching efficiency

~75%

We have been working to improve it by:

1. Alignment2. Optimizing matching cuts

Tracking efficiencyTracking efficiency

track is known at the level of 5%


Total tracking efficiency as a function of p(left) and x (right) computed using MC (2 hadron generators) properly scaled by data

Total tracking efficiencyTotal tracking efficiency

Green: type 1 Blue: type 2 Red: type 3

Black: sum of normalized efficiency for each type


Forward PID: CherenkovForward PID: CherenkovSeparate /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

mass is a free

parameter

nominal threshold

Npe → 21

p (GeV/c)

Num

ber

of

pho

toe

lect

rons

e++

3 GeV beam particles3 GeV beam particles

p

p

+


Npheldatadata

Nphel


Forward PID: TOF WallForward PID: TOF Wall

Calibration / equalization– Cosmic ray runs (every 2-3 months)– Laser (continuous: monitor stability)

TOF time resolution ~160 ps =>3 separation of /p (K/)

up to 4.5 (2.4) GeV/c=>7 separation of /p at 3 GeV/c

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

by PMTs


datadata

p


Forward PID: CalorimeterForward PID: Calorimeter

• 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


ekpphe

phephe

pPEEpPNpPpP

pPEEpPNpPpPEENpP

,,,21

2121

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

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

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: efficiency and purity efficiency and purity

Iterative approach: dependence on the prior removed after few

iterations

j-(t) = Nj

-true-obs / Nj-

true j

-(t) = Nj-true-obs / Nj

-obs j-(t)/ j

-(t)


pion efficiency

3

1

)(

t

trackti

tracki

The 3 types of tracks must be treated separately because of the different momentum resolution

3

1

)()()(

)( 111

t

tj

tjt

j

tijtrack

iacci

i NM

)(

)()()(

kj

kbkgj

kjk

jN

NN

pion purity

pion yield

tracking efficiency

migration matrix(not computed yet)acceptance

depend on momentum resolution

i = bin of true (p,)

j = bin of recosntructed (p,)

The cross sectionThe cross section


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

p-e/ misidentification background

K2K replica targetK2K replica target

5% 5% Al target Al target

200% Al target

Raw dataRaw data

p > 0.2 GeV/c|y | < 50 mrad

25 < |x| < 200 mrad

Pion yieldPion yield


5% Al targetp > 0.2 GeV/c|y | < 50 mrad

25 < |x| < 200 mrad


After PID After PID correctioncorrection

After After efficiency efficiency correctioncorrection



After After acceptance acceptance correctioncorrection

5% Al target p > 0.2 GeV/c|y | < 50 mrad

25 < |x| < 200 mrad

Systematics are still to be evaluated:• tracking efficiency know to 5%• expect small effect from PID


ConclusionsConclusions

• The HARP Experiment has collected data for hadron production measurements with a wide range of beam energies and targets

• Status of detector– Forward region: good tracking and PID– Large angle: much recent progress

• First physics results are available: thin (5%) K2K target– Using forward region of the detector

• To do– Compute data deconvolution and migration matrix– Evaluate systematic errors– Analyse empty target data for background subtraction– Investigate =0 region: saturation effects due to beam particle removal– Introduce normalization for absolute cross-section (using min.bias trigger)– … go on to full statistics, and to the rest of the data !


BackupBackup


• 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 sensitive to these variations.

NDC 2 NDC 5NDC 4NDC 3datadata

NDC module efficiencyNDC module efficiency

NDC2 NDC5

NDC3

NDC4

dipole


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

mtracki

macci

NDCi

m module module

acceptanceacceptancemodule module

efficiencyefficiency

Module acceptance / Downstream eff.Module acceptance / Downstream eff.


datadata

MCMC

x2, x2

downi

recpidownup

iN

N

Up-downstream matching efficiencyUp-downstream matching efficiency

We need to convert x2 and x2 to p and .

For that we use the MC


• 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+

Up-down matching efficiencyUp-down matching efficiency


CalorimeterCalorimeterCkovCkovTOFTOF

• The different pid detectors are independent of each other

)|,,()|,()|,()|,,,,( 2121 EEpPNpPpPEENpP phephe

ekpphe

phephe

pPEEpPNpPpP

pPEEpPNpPpPEENpP

,,,21

2121

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

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

)()|(

)()|()|(

BPBAP

BPBAPABP ii

i

• Using the Bayes theorem

,...,,,

},,,,{ 21

kepB

EENpA phe

Measured quantities

Particle types

Forward PID: continuous probabilityForward PID: continuous probability


P( p , | ) from TOF = m2 / p2with

P( p ,Nphe | ) from Cherenkov

P( p , E1 , E2 ) from Calorimeter

Line : true PIDColored histograms: reconstructed PID

3 GeV

pe K

Step 1 Step 2

Step 3 Step 4

Step 5

Product of conditional probabilities and relative

abundances

Iterative Bayesian approach:

dependence on the prior removed after

few iterations

Forward PID: iterative procedureForward PID: iterative procedure

the harp experiment physics goals and motivations summary of the experimental program

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