Sampling Detectors for e Detection and Identification

Adam Para, Fermilab

NuFact02

Imperial College

Interest de jour: what is sin2213 • oscillations -> e

• ‘superbeams’

• ‘Current’ generation of experiments

• How can we do better

• Sampling detectors for e detection

Different baselines: where the oscillation peaks are ?

L(km)/n 1 2 3

300 0.73 GeV

0.24 GeV

0.15 GeV

750 1.82 GeV

0.60 GeV

0.36 GeV

1500 3.64 GeV

1.21 GeV

0.73 GeV

E < 1 GeV (KEK/JHF to SuperK, CERN to Frejus

0.3 < E < 3 GeV (NuMI)

0.5< E < 6 GeV (CERN to Taranto, BNL to ?)

Flux/rates drop

Neutrino Cross Sections

N+leptonN+l+

Many particles

Det. 2

What will MINOS do?

Two functionally identical neutrino detectors

Det. 1

e Interactions in MINOS?

NC, Eobs = 3 GeVe CC, Etot = 3 GeV

NC interactions:

Energy distributed over ‘large’ volume

Detector Granularity:

•Longitudinal: 1.5X0

•Transverse: ~RM

e CC interactions (low y) :•Electromagnetic shower:

•Short•Narrow

•Most of the energy in a narrow cluster

energy

Needle in a Haystack ? NC Background

e (|Ue3|2 = 0.001)e background

NC (visible energy), no rejection

spectrumSpectrum mismatch: These neutrinos contribute to background, but no signal

MINOS Limits on to e Oscillations

Sample of e candidates defined using topological cuts

10 kton-yr exposure,

m2=0.003 eV2, |Ue3|2=0.01:

Signal (= 25%) - 8.5 ev

e background - 5.6 ev

Other (NC,CC,) – 34.1 ev

M. Diwan,M. Mesier, B. Viren, L. Wai, NuMI-L-

714

90% CL: | Ue3|2< 0.01

Limit comparable to a far superior detector (ICARUS) in CNGS beam

Receipe for a Better Experiment

More neutrinos in a signal region Less background Better detector (improved efficiency, improved rejection

against background) Bigger detector

Lucky coincidences:

• distance to Soudan = 735 km, m2=0.025-0.035 eV2

• Below the tau threshold! (BR(->e)=17%)

2 21.27 2.541.6 2.2

2

m L m LE GeV

E

Two body decay kinematics

* * *

* *

( cos )

sin

L

T

p p E

p p

‘On axis’: E=0.43E

At this angle, 15 mrad, energy of produced neutrinos is 1.5-2 GeV for all pion energies very intense, narrow band beam

Off-axis ‘magic’ ( D.Beavis at al. BNL Proposal E-889)

2

2

22 412

zA

Flux

1-3 GeV intense beams with well defined energy in a cone around the nominal beam direction

NC/ e /0 detectors

CHARM II (e scattering)

Challenges: Identify electrons Small cross section,

large background from NC interactions

Solution:

•Low Z, fine grained calorimeter

Detector(s) Challenge

Surface (or light overburden) High rate of cosmic ’s Cosmic-induced neutrons

But: Duty cycle 0.5x10-5

Known direction Observed energy > 1 GeV

Principal focus: electron neutrinos identification

• Good sampling (in terms of radiation/Moliere length)

Large mass:

• maximize mass/radiation length

• cheap

A possible detector: an example

Cheap low z absorber: recycled plastic pellets

Cheapest detector: glass RPC (?)

Constructing the detector ‘wall’

Containment issue: need very large detector Engineering/assembly/practical issues

On the Importance of the Energy Resolution

M. Messier, Harvard U.

Cut around the expected signal region too improve signal/background ratio

Energy resolution vis-à-vis oscillation pattern

First oscillation minimum: energy resolution/beam spectrum ~ 20% well matched to the width of the structure

Second maximum: 20% beam width broader than the oscillation minimum, need energy resolution <10%. Tails??

Energy Resolution of Digital Sampling Calorimeter

Digital sampling calorimeter:

1/3 X0 longitudinal 3 cm transverse

Energy = Cx(# of hits) DE ~ 15% @ 2 GeV DE ~ 10% 4-10 GeV ~15% non-linearity @

8 GeV, no significant non-gaussian tails

Improve energy resolution?

Total Absorption Calorimeter: HPWF

Energy resolution limited by fluctuations of the undetected energy: nuclear binding energy, neutrinos and not by sampling fluctuations

‘Crude’ sampling calorimeter (CITFR), 10 cm steel, better energy resolution than total absorption one (HPWF)

Neutrino energy, Quasi-elastics ?

E(reconstruct) – E (True) (MeV)

=80MeV

E(

reco

nst

ruct

)

events

cos

22

pEm

mEmE

N

N

+ n → + p

p

(E , p)

~ 2 GeV: CC e / NC interactions

~ 2 GeV: CC interaction

~ 7 GeV: CC e / NC interactions

CC e vs NC events: example

Electron candidate: Long track ‘showering’ I.e. multiple

hits in a road around the track

Large fraction of the event energy

‘Small’ angle w.r.t. beam

NC background sample reduced to 0.3% of the final electron neutrino sample (for 100% oscillation probability)

35% efficiency for detection/identification of electron neutrinos

Detector questions/issues

What is the optimal absorber material (mostly an engineering/cost question, if X0 kept constant)

What longitudinal sampling (X0)? What is the desired density of the detector?

(containment/engineering/transverse segmentation) Containment issues: fiducial volume vs total volume,

engineering issues: what is the practical detector size? What is the detector technology (engineering/cost issue

if transverse segmentation kept constant) What is the optimal transverse segmentation (e/p0,

saturation,…) Can a detector cope with cosmic ray background? What

is the necessary timing resolution?