Università degli Studi di Bologna

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Neutrino Oscillation Neutrino Oscillation Studies with a Studies with a

Massive Magnetized Massive Magnetized CalorimeterCalorimeter

Università degli Studi di Università degli Studi di BolognaBologna

Marco Selvi

Massive Magnetized Detector M. Selvi – Università di Bologna

SummarySummary

• Neutrino Oscillations• Status of the experimental scenario

and need for new detectors• Magnetized calorimeter performances• Atmospheric neutrino physics• CNGS beam physics• -factory physics

Neutrino OscillationsNeutrino Oscillations

Neutrino OscillationsNeutrino Oscillations : 2 : 2 flavorsflavors

If neutrinos have mass the flavour eigenstates could not coincide with mass eigenstate:

|(0)> = cos |> + sin|>

|(0)> = -sin |> + cos|>

|(t)> = cos exp(-iE1t) |> + sinexp(-iE2t) |>

|(t)> = -sin exp(-iE1t) |> + cosexp(-iE2t) |>

After time evolution:

Oscillation Probability:P() = sin2 sin2(1.27 m2

m2 = m22- m1

Survival Probability: P() = 1 - P()

sin2m2 =0.003 eV2

Atmospheric neutrinosAtmospheric neutrinos

P + air --> (, K)

• < h > = 10 km

• ~ E-3.7

From Battistoni & Lipari (1998)

Updated NuMI beam

the LBL nightmareThe L/E rangeThe L/E range

L (down-going) ~ 10 km

L (up-going) ~ 104 km

E from 100 MeV up to 100 GeV

Status of neutrino studies Status of neutrino studies with Atmosphericswith Atmospherics

Status of atmospheric neutrino Status of atmospheric neutrino datadata

•Up/down asymmetry: robust indication of disappearance

(fixes the mixing in a model independent way)

•Disappearance occurs near the horizon

+ upgoing, througoing, multiring muon-like and NC-like, indication of appearance

+ MACRO, Soudan 2

Superkamiokande: 79.3 kty (Y. Totsuka, TAUP2001)

deficit increasing with Ldeficit increasing with L no anomalyfor eno anomalyfor e

Interpretation of atmospheric Interpretation of atmospheric neutrino dataneutrino data

• SK data interpreted as 2 oscillations in the channel • (Supported by MACRO,

SOUDAN2,CHOOZ)

• Pure–s oscillations excluded

• Pure –e oscillations excluded • Dinamycs of disappearance fit

an L/E law (FCNC, VLI, VEP excluded)

• Is pure - oscillation the end of atmospheric neutrino history?

Best fit:

m2 = 2.5 x 10-3 eV2 sin22 = 1

Explicit detection of Explicit detection of oscillation?oscillation?

• L/E resolution of SuperKamiokande not sufficient to detect oscillations explicitely

• Limited precision on m2

• There are viable alternative hypotheses with L/E law:

• Decay• Decoherence

• At least one full oscillation cycle has to be detected to prove oscillations (disprove alternative hypotheses).

The oscillation is damped by finite detector L/E resolution !!

Damped oscillationDamped oscillation

Perfect resolution

Damped Oscillation

Critical damping

sin2m2 =0.003 eV2

Physics Physics

with a Massive Magnetized with a Massive Magnetized Spectrometer Spectrometer

on Atmosphericon Atmospheric

New detector conceptsNew detector concepts

Overcome limitations of current atmospheric neutrino detectors:

•High L/E resolution•Fully exploit far/near source method

for disappearance•Systematic-free analysis of the oscillation pattern

Atmospheric: comparison Atmospheric: comparison up/downup/down

It is a good experimental rule that precise measurements are obtained by comparison with a reference

For E > 2 GeV • The atmospheric neutrino flux is up/down

symmetric at the source • The downward is not affected by oscillations (m2

< 10-2 eV2) reference near source• Upward flux is affected by oscillations: L/E goes

up to 6·104 km/GeV far source

Measurement of disappearanceMeasurement of disappearance

The disappearance probability can be measured with a single detector and two equal sources:

= P( ; L/E) N up(L/E)

N down(L’/E)

L(up) = 2Rcos(up) L’(down) = L( –down)

= 1 - sin2 (2) sin2 (1.27 m2 L/E)

An oscillation pattern should appear in the experimental ratio of up to down fluxes (*)

*) method first suggested by P.Picchi and F.Pietropaolo

What affects the L/E What affects the L/E resolutionresolution

The L/E resolution is determined by the capability of the experiment to reconstruct the neutrino energy and the neutrino direction of flight (L ~ 2R cos):

But is not measured; just ... so events near the horizon are of no use: resolution is

spoiled by the tan2 term

Low L/E values must be obtained with high E

A detector with a modest hadronic energy resolution, but a good muon momentum measurement can be effectively used provided that low-y events are selected

• Limitation of SK: due to the limited acceptance at high energies, oscillations occur near the horizon

Detector choiceDetector choice

• Magnetized tracking calorimeterMagnetized tracking calorimeter E by range measurement for fully contained events

E by tracking in magnetic field for partly-contained

events

by tracking

Up/Down by time of flight (plus vertex identification)

high time resolution (< 2 ns) is also required

The Monolith DetectorThe Monolith DetectorLarge mass 34 ktonMagnetized Fe spectrometer B = 1.3 TeslaTime resolution ~ 1 ns (for up/down discrimination)Space resolution ~ 1 cm (rms on X-Y coordinates)Momentum resolution p/p ~ 20% from track curvature for outgoing ~ 6% from range for stopping Hadron E resolution Eh /Eh ~ 90%/Eh 30%

~52000 m2 of detector : Glass Spark Counters

2.2 cm

29.5 m

14.5 m B B

Event selectionEvent selection

Event selection developed to optimise the observation of the oscillation pattern

(keep under control the relative L/E resolution)

1. E > 1.5 GeV

2. Fiducial selection of 40 cm on each side

FC events: inside fiducial volume

PC events: one single outgoing track with range > 4 m

3. Nb. of fired layers > 6

4. Selection on combination of the observables E, , Eh to ensure the required L/E resolution

L/E resolution in L/E resolution in MONOLITHMONOLITH

Contributions to L/E resolution

Angular spread

Energy measurement

Final L/E resolution

contribution of track fit error

Efficiencies and Efficiencies and resolutionsresolutions

• Selected CC (downgoing only!) after 4 y of data taking:

• Fully contained: 931

• Partially contained: 259

• Total: 1190

Effect of the Magnetic Effect of the Magnetic FieldField

Higher efficiency in the low L/E region Higher efficiency in the L/E region of physical interest (102-103) Slightly higher cost and complexity (anti-seismic rules for LNGS impose expensive mechanics anyway)

Expected L/E distributions Expected L/E distributions (1)(1)

Central value in each bin is obtained with a 26 years statistics.Event rates, error bars and contour lines correspond to 4 years.

99% C.L90% C.L.68% C.L.

m2 = 710-4 eV2

m2 = 210-3 eV2

Expected L/E distributions Expected L/E distributions (2)(2)

m2 = 510-3 eV2

m2 = 810-3 eV2

Monolith sensitivity – 4 yMonolith sensitivity – 4 y

•Comparison of MONOLITH sensitivity to oscillations with Kamiokande and SuperKamiokande• 90% C.L. allowed regions after 4 years for different m2 (left)• Exclusion regions if no effect is found (right)

Detection of the oscillation Detection of the oscillation patternpattern

Four simulated experiments of 4 years with m2 = 0.003 eV2

• best fit to oscillation• best fit to decay• best parametric fit

A staged approachA staged approach

13.1 m

14.5 m B

13.5 m B

1 module = 17 kt

Maximum size that fits in Gran Sasso Hall A (between LVD and GNO)

L 2REarthcosE= E+Eh

Resolution comparable to the full detector (34

Efficiencies and resolution in a Efficiencies and resolution in a 12 kt module12 kt module

Efficiency loss < 20% w.r.t. the full detector (fiducial cut against cosmic muon background)

34 kt 17 kt

A 12 kt detector (4 years)A 12 kt detector (4 years)

Kamiokande

0.007 eV2

0.003 eV2

0.001 eV2

90% C.L. allowed regions

Efficiency for decay model rejection at 95% C.L.

RMS Precision on sin22RMS Precision on m2

SK 90% C.L.

region

12 kt detector12 kt detector

3.0 10-3

1-3% precision in the oscillation parameters is achievable

Vertical vs horizontal Vertical vs horizontal layers for atmospheric layers for atmospheric neutrinos (FAQ)neutrinos (FAQ)

Selected atm. ’s events for fixed L/E resolution • Lower reconstruction

efficiency along the vertical direction with vertical plates

• About the same efficiency at small L/E (where the 1st minimum is expected):

• Events near the horizon filtered by resolution requirements!

• Need for an external VETO Pay on mixing, but marginally on m2

Physics Physics

with the with the

CNGS beamCNGS beam

• from , K

• < E > ~ 20 GeV

• L = 732 km

• Optimized for tau appearence

• Rate CC ~ 2600/kt y

Detector layoutDetector layout

CNGS event exampleCNGS event example

Efficiencies and Efficiencies and resolutionsresolutions

Almost flat around 50% for E>10 GeV

L/E RangeL/E Range

L/E distributions after selections• 4 y atmospheric (shaded)• 1 y CNGS beam

High sensitivity to m2 values down to a few 10-4 eV2

AtmosphericsThe L/E distribution, resulting after

selections, is populated up to 5·103 km/GeV

The Log(l/E) distribution is more populated at high L/E

The sensitivity of the experiment decreases for

increasing values of m2

Can the beam help at high m2 ?• atmospheric no systematic• beam systematic to be understood

Monolith on CNGS beamMonolith on CNGS beam

CNGS beam will cover with very high statistics the region L/E < 100 km/GeV: ~ 40,000 events/year CC after selections vs. ~ 200 events/year from up-going atmospheric.

Systematic effects: a tough job!

10% bin per bin systematics assumed

Accordingly with BMPT .

Impact of CNGS beamImpact of CNGS beam

Atmo’s alone

Atmo’s + Beam

m2 =0.007 eV2

CNGS beam: CC/NC ratioCNGS beam: CC/NC ratio

m2 = 0.003 eV2

MONOLITH 12ktx5y

Visible hadron energy (GeV)

Atm. full MONOLITH

90% allowed regions(includes uncertainties of beam shape and composition, detector effects, …)

CC/NC ratio can supplement atmospheric data constraints on sterile neutrinos

Physics at the Physics at the -factory-factory

with awith a

MonolithMonolith-like-like

DetectorDetector

If neutrinos have mass the flavour eigenstates could not coincide with mass eigenstate:

3 mixing angles: 12, 23, 13

2 mass differences: m212 m2

1 CP-violation fase:

One-mass scale One-mass scale dominancedominance

at terrestial distancesPe-= sin2(23 ) sin2(213) sin2(1.27 m2

23 L/E)

13 bounded by CHOOZ exp. to be smallsin2(213) < 0.1 (90% C.L.)

Very high intensity beam needed

factoryfactory

Features:

• High intensity

• Well-known beam

• Both flavors

• Different helicity

•Circulating 50 GeV in a NuFactory(1021 decays in 5 years)

•Beam made by and e (ee)

•Search at LBL for wrong sign muons () coming frome oscillated into

sign of m2, study of matter effects, CP violation

Physics at a Physics at a FactoryFactory

Golden channel: wrong sign Golden channel: wrong sign muonsmuons

CC rate (background)CC rate (background)

3.5 103.5 107 7

CCCCat 732 kmat 732 km

CC rate (signal)CC rate (signal)

oscillationoscillation

1.1 101.1 105 5 CCCCat 732 kmat 732 km

Two main sources:

•Fake WSM (due to charge misidentification)

• WSM from hadrons

BackgroundsBackgrounds

o Generate interaction using Pythia + q.e. + 1 corrections (Lipari code).o Simulate the whole event in Geant:o Multiple scattering with Moliere theory option ON

(not just gaussian approximation)o Full B field description o Fit muon track using GEANE and Kalman filter approach

(a real reconstruction, not just smearing)

both for signal and background

Charge identificationCharge identification

B field detailsB field details

Long FC event example Long FC event example ((--))

background event background event example (example (++))

Wrong event exampleWrong event example

Large Large angle angle scatterinscatteringg• Overestimated in GEANT (~30) ...see OPERA

• Recognizable via Kalman filter (change in slope)

Selection cuts:

• Pfrom range > 7.5 GeV

•In each region:• At least 4 points•Track lenght > 300 cm

•Same charge assigned in each region

Charge identification: Charge identification: resultsresults

Fractional bkg.1 x 10-6

Efficiency 35%

Wrong sign muonsWrong sign muons

from hadronsfrom hadrons

Wsm from hadronsWsm from hadrons

Large Magnetic Detector people (Dydak et al.) showed (see NuFact '00)that it is possible to reject such bkg up to

~ 2 x 10-6 with 30% efficiency

just using two cuts:

• P > 7.5 GeV

• Qt > 1. GeV

Wsm from hadronsWsm from hadrons

• P cut may be easily reproduced: • good muon momentum resolution

• Qt depends on hadronic angular resolution• in LMD analysis they assume to have the same performances of MINOS

(MINOS proposal - chapter 7)

... What can Monolith ... What can Monolith say?say?

Angular ResolutionAngular Resolution

• From true vertex to true shower’s center of gravity

• From

reconstructed vertex to rec. shower’s center of gravity

Vertex resolutionVertex resolution

• Transverse resolution x = 5.6 cm

• Longitudinal res. y = 5.8 cm

• Vertical res. z = 5.1 cm

hadronic angular hadronic angular resolutionresolution

Reconstructing vertex:Reconstructing vertex:about twice about twice MINOSMINOS

Monolith fitMonolith fit3232.. 8.28.2

Second approachSecond approach

• Use LMD cuts (P >7.5 GeV; Qt > 1 GeV)

And take into account the different smearing

Charge id. CC e CC e NC

MONOLITH

1. 10-6 7.5 10-7 2.5 10-7 5.2 10-6 16.5 %

35 30 15 160

Monolith fitMonolith fit

3232.. 8.28.2

ImprovementsImprovements

• Higher granularity• Planes orientation

... perform the same cuts (P >7.5 GeV; Qt > 1 GeV) and modify the fractional bkg accordingly with the obtained hadronic direction smearing

Efficiencies are considered to be the same (16.5%)

Very conservative hypothesis: improvements are expected in both cases

Horizontal plates – 4 cm Horizontal plates – 4 cm thickthick

Monolith fitMonolith fit2323.. 12.12.

Vertical planes – 8 cm Vertical planes – 8 cm thickthick

...Against ~5 cm in HOR configuration

Vertical plates – 8 cm Vertical plates – 8 cm thickthick

Monolith fitMonolith fit1515.. 12.12.

Test beam with the Baby-Test beam with the Baby-MonolithMonolith

prototype: prototype:

Hadronic angular resolutionHadronic angular resolution

Experimental setupExperimental setup

Beam of e, of2, 4, 6, 8, 10 GeV

Event display: Event display:

hadronic angular hadronic angular resolutionresolution

Resolution better than the Resolution better than the requested one.requested one.

Baby-Baby-Monolith fitMonolith fit1010..44 10.10.11

SinSin22(2(21313) sensitivity) sensitivity

• Oscillation probability:Pe-= s23

2 sin2(213) sin2(1.27 m2 L/E)

• Fix 23=45°, change 13 and m2

• Compare number of signal events (efficiency corrected) with the error in the surviving background events(statistical + 5% syst.)

• Draw a 4 region

SinSin22(2(21313) sensitivity – 4) sensitivity – 4

Strong muon momentum cut

P > 20 GeV

P > 7 GeV

Qt > 1 GeV

8 cm VERT plane

P > 7 GeV

Qt > 1 GeV

Baseline: 3500 kmBaseline: 3500 km

Baseline 732 km

Vertical layers

Baseline 3500 km

Vertical layers

Bkg ~ L-2 (fluxes)

Signal ~ L-2 (fluxes) x L2 (oscillation) = L0

... up to O(3000 km)

ConclusionsConclusions

We show that a massive magnetized calorimeter can significantly contribute to the actual and

future neutrino physics framework:

• Explicitely prove the oscillation pattern in L/E

• Precisely measure the osc. parameter values (if oscillations)

• CNGS beam can help in disappearence analysis and NC/CC ratio, especially if m2 > 0.005 eV2

• The proposed detector is well-suited for the wrong sign muons detection on a -factory beam.

Università degli Studi di Bologna

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