A study of A study of atmospheric neutrinosatmospheric neutrinos

at at India-based Neutrino ObservatoryIndia-based Neutrino Observatory

Abhijit Samanta Abhijit Samanta (INO Collaboration)(INO Collaboration)

abhijit.samanta@saha.ac.inabhijit.samanta@saha.ac.in

Saha Institue of Nuclear PhysicsSaha Institue of Nuclear Physics Kolkata, India Kolkata, India

PlanPlan Neutrino oscillationNeutrino oscillation

Neutrino parameters from present experimentsNeutrino parameters from present experiments

INO detectorINO detector

Detector simulationDetector simulation

Physics issues of INO:Physics issues of INO: Studies with atmosphericStudies with atmospheric ss ((INO Phase IINO Phase I)) . .

(Precision study of atmospheric oscillation (Precision study of atmospheric oscillation parameters only will be discussed in details parameters only will be discussed in details here.)here.)

Studies with beams fromStudies with beams from --decaydecay,, -factory-factory ((INO Phase INO Phase IIII).).

(in short)(in short) INO site INO site ConclusionConclusion

Neutrino stationary states: |1, |2 mass m1, m2

Neutrino flavour eigenstates: |e>, | µ>

Two different bases: |e = |1 cosθ + |2 sinθ

|µ = -|1 sinθ + |2 cosθ

|e produced at t = 0 |Ψ(0) = |e = |1 cos θ + |2 sinθ

At a later time: |Ψ(t) = |1 cos θ e-iE1t + |2 sinθ e-iE2t

Prob(e µ, t) = |µ |Ψ(t) |2 = 4 c2 s2 |e-iE1t - e-iE2t|2

Neutrinos are ultra-relativistic: p>>m Ei = (p2 + mi2)½ ≈ p + mi

2/2p

(E1 - E2)t = (m12 – m2

2)t /2p ≡ (∆/2p)t = L ∆/2E

Prob(e µ, L) = 4 c2 s2 sin2(L/ λ) where λ = 4 E/ ∆

Survival Prob. = Prob(e e, L) = 1 - Prob(e µ, L)

Quantum mechanics of neutrino oscillation

Neutrino parameters from present experiments

Neutrinos oscillate.

Neutrinos are massive and non-degenerate (m2 0) & sin2 0.

Solar m21 = 7.9 105 eV2,

12 = 36o (best-fit)

Atmospheric |m322|=2 10-3eV2 ,

23= 45o (best-fit)

Reactor KamLAND agrees with solar and CHOOZ constrain 1311o

Accelerator K2K confirms atmospheric results

tt

ee ee eeee

INO will have important role in

Confirmation of oscillation dip and rise

Sign of |m232|

Determination of 13

CP phase

Measuring the deviation of 23 from 45o

New physics ?

INO Detector

Mass: 50 kTonSize : 48 m (x) 16m (y) 12 m (z) 140 layers of 6 cm thick iron with 2.5 cm gap for active elements

Magnetic field ~ 1 Tesla along y-direction

Construction of RPCTwo 2 mm thick float GlassSeparated by 2 mm spacer

2 mm thick spacer

Glass plates

Complete RPC Graphite coating on the outer surfaces of glass

Pickup strips

INO will have the opportunityINO will have the opportunityto change the active part of to change the active part of the detector.the detector.

RPC test

Freon 134a : 62%Argon : 30%Isobutane : 8%

RPC Timing Studies

RPC Efficiency

Good time resolution Good up/down discrimination

Bending in magnetic field can also do this job.

INO prototype will be very soon at VECC, Kolkata.

Detector Simulation

Package: GEANT Version : 3.2214

Track reconstruction When a charge particle, say, ±, moves through ICAL, it gives

hits (very localized electric discharge in the gases) in the active detector elements; a track in the detector.

Energy for a track can be measured in two ways:

I) Energy calibration (FC only) II) curvature in a magnetic field (FC+PC).

(The case I & II have been studied separately. The case I will be discussed here.)

Energy can be calibrated with number of hits or with effective path-length (density geometric path).

It measures the amount of energy deposited in the detector.

Angle is determined from the first few hits of the track.

Calibration of E with effective path-length for a fixed zenith angle 40o

Calibration of E with number of hits for a fixed zenith angle 40o

Effective path-length and number of hits are proportional to E for a fixed zenith angle.

Variation of effective path-length with zenith angle for fixed E

Variation of number of hits with zenith angle for fixed E

Energy calibration with effective path-length is less dependent on zenith angle than that with number of hits.

The variation of muon energy The variation of zenith angle resolution for zenith angle 54o. resolution for E= 1 GeV.

(It will improve (worsen) (It will improve with increase with decrease (increase) of energy.) of zenith angle.)

Precision study with atmospheric neutrinos

Event generator: NUANCE Flux : Honda

Detector simulator: GEANT

Atmospheric neutrino fluxes

Low energy flux is not symmetric in up & down direction.

Oscillation of atmospheric

neutrinos L ~ 10 km for down going ~12000 km for up going

E~ few MeV-100GeV Down near detectorno oscillationUp far detector Oscillation

(Single detector with two equal sources.)

updown

L/E

Reduction of events (cuts)

To study the L/E resolution we generate a huge data set, say, 83000 events in the energy range 0.8 GeV to 200 GeV with almost equal weight up to 30GeV .

Study L/E resolutions in measured E & L/E bins.

For a particular L/E-bin, it improves with increase of E. (With increase of E the scattering angle ( - ) decreases.)

Again for a particular bin of E, resolution improves with increase of L/E. (L resolution improves as we go far from horizon.)

Let us fix a width of the resolution as a measure of goodness. With this criteria we find the minimum value of L/E for a given E.

We consider only longest track of an event (essentially the muon track). No hadrons are considered a very clean signal at ICAL detector.

Reduction of events (cut)

Applying the cuts defined above, we find the L/E resolutions and efficiency in neutrino (L/E – E) bins.

efficiency () = (selected events)/(nuance generated events)

L/E resolution

The shape and width of resolution change with E & L/E .The reasons have been discussed earlier.

The first four The first four figures are figures are obtained for a bin obtained for a bin of Eof E & (L/E) & (L/E)..

The last figure The last figure with all with all EE & (L/E) & (L/E) ofof 20 20 years un-oscillated years un-oscillated data.data.

Taking a given year of exposure we generate a GEANT simulated data Find up/down vs. L/E distribution (call it the “experimental data”)

Cut Number of surviving

Efficiency

hit 7 4313 events -------

Cut for L/E

resolution

2327 54

5-year run

Note: Efficiency must be improved if we consider zenith angle analysis for sin2 precision.

Confirm oscillation with dip and then rise

2-fit

We take an event and calculate the oscillation probability P.

We choose a random number X. If P > x, we keep it.

Identify the resolution function from the value of E & L .

If the efficiency of this bin is , smear over all L/E bins instead of smearing unity.

We thus obtain a up/down plot from 20 years un-oscillated data set. We call it a “theoretical data”.

If the bin size of E & L/E are made very small, we are then practically generating resolutions for every events.

Precautions in 2-fit

Up/down for plot obtained with Nuance and by random number technique from un-oscillated data as discussed above should match.

See the difference if Honda flux is with cosz bin 20 & 180 !!!Up/down plot from random number technique matches with 180 bin of

cosz

Allowed oscillation parameter regions

(upper limit – lower limit)( upper limit +lower limit)Precision =

INO (with FC events only) 7 19 10-yr

SKIII 10 20 10-yrMINOS 10 38 5-yrT2K 6 22 5-yr

SK (present experiment) 28 39 The precision at INO will improve with inclusion of PC. Note: We use multiple resolution functions; it is for each (E L/E ) bin.

The important features of INO

1. Large mass( high statistics) magnetized Iron CALorimeter

2. Tracks are obtained from the hits (electric discharge in the gases is very transient and localized unlike Cherenkov detector)

I) High angular resolution and high charge identification capability (bending of track in magnetic field) II) Good E resolution

III) Good time resolution ( ~ nanosec) up/down discrimination

3. INO to CERN baseline magic baseline (degeneracy in observables

due to CP-phase is negligible.)

Important role in the present open issues in neutrino physics e.g., determination of mass hierarchy, 13, CP-phase

search for new physics ……..

INO Site INO Site

PUSHEP (Pykara Ultimate Stage Hydro Electric Project) in South India

Reduction of muon background with depth

INO is in good depth !!!

PUSHEP selected,after a detailed comparison with Rammam

INO is growing up rapidly through

The INO training school Phase-I (April 10 – 25)

at Harish-Chandra Research Institute, Allahabad

on Theoretical and Phenomenological AspectsPhase-II (May 1 – 13)

Saha Institute of Nuclear Physics/Variable Energy Cyclotron Centre, Kolkata

on Experimental Aspects

URL: http://www.imsc.res.in/ ~ino

INO Collaboration

In the last year 41 Experimentalists

+ Engineers 22 Theorists

Acknowledgement

I am grateful to Dr. Michele Maltoni for arranging this talk. I want to express my gratitude to Professor Amitava Raychaudhuri, Professor Sudeb Bhattacharya and Professor Kamales Kar for all kind of supports, suggestions and discussions. I am also thankful to my collaborators Professor Ambar Ghosal and Professor Debasish Majumdar for discussions. Finally I want to acknowledge the supports from DST, India as well as from ASICTP.