Long Baseline Accelerator Neutrino Oscillation Experiments

1
Long Baseline Accelerator Neutrino Oscillation
Experiments

• Teh Lee Cheng
• 1 May 2003

2
Outline

• Neutrino Mixing
• Long baseline neutrino experiments
• K2K
• MINOS
• CNGS (OPERA ICARUS)
• Discussion
• Conclusion

3
Neutrino Mixing

• If neutrino has mass, flavour states are
  combinations of mass eigenstates. For 3
  neutrinos,

Where sijsin?ij cijcos?ij
Atmospheric ?
Solar ?

• 3 angles 1 CP phase 2 mass difference ?m2
  (and signs) (true for Majorana neutrinos)

4
Two Flavour Mixing

• 1 parameter ?

• ? , ?m2 (eV2) theoretical parameters
• L(km), E(GeV) experimental parameters
• sensitivity ?m2 gt1.24 E/L
• to achieve ?m2 O(10-3) need L/E 1000
• E 1GeV, hence Long Baseline 103 km

5
Atmospheric vs accelerator ??

• Study ??? ?? (observed in Super-K)
• accelerator experiments try to confirm it, and
• observe oscillatory behavior,
• precise measurement of ? , ?m2.
• In 3 flavour mixing, if ?13 not zero, should be

Crucial for CP violation
6
First Generation of LBL ? Exp
K2K (250 km) started 1999
CNGS (732 km) mid 2006 ?

• MINOS (735 km) Dec 2004

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K2K KEK to Kamioka ? osc exp

• Goal detect ? osc, by measuring flux deficit and
  distortion of ? energy spectrum

? beam
Detectors

• ?? 98 pure (2 ?e)
• ltEgt ? 1.3 GeV
• 12 GeV protons
• 6x1012 protons/2.2 s
• want to collect 1220 protons on target (pot)

• Near detector
• 300 m from target
• Far detector Super-Kamiokande
• 250 km away
• Sensitive for
• ?m2 gt2x10-3eV2

8
K2K Detectors
Near detector

• measure beam flux and profile
• extrapolate to SK

1 kt has same technology with SK to minimise the
systematic error of analysis.
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Super-K a H2O Cherenkov detector

• 22.k ktons water
• measurement made by
• ??e? ?? e elastic scatt
• ??n? ?? p quasi el. Scatt
• select Full Contained (FC) events

13000 PMT
41.4 m

• Main Errors
• near-far extrapolation
• ? 5
• 1 kiloton systematic error 5

39.3 m
10
Recent K2K Data

• based on 4.8x1019 pot data
• (Jun 99 -- Jul 01)
• observed 56 events
• expected events (no oscillations)

11
K2K Analysis Results

• osc. best fit 2.8 x 10-3 eV2 and sin22? 1.0
• (1.5 - 3.9) x 10-3 eV2 for sin22? 1.0 _at_ 90 CL
• probability that observation was due to
  statistical fluctuation is lt 1 !

68.4 CL
90 CL

• cf SK atm ? result (Shiaozawa Neutrin 2002)
• best fit 2.5 x 10-3 eV2 sin22? 1.0
• (1.6 3.9) x 10-3 eV2 sin22? gt 0.92 _at_ 90 CL

99 CL
Allowed region
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MINOS (Main Injector Neutrino Oscillation Search)

• Under construction first magnetized neutrino
  detector
• Goal 1. Confirm definitely ? oscillations
• 2. Precise measurement of parameters
  3.determine relative strength of different osc
  modes
• How? Count the NC and CC events and look at the
  ? energy spectrum
• Implement 2 detectors
• Near (1040 m from target)
• Far (735 km away)

13
NuMI beam Neutrinos at the Main Injector

• Pure ?? beam (lt1 ?e)
• tunable energy 3 -18 GeV
• 120 GeV protons/1.9 s
• exposure rate, 4x1020 pot/year

14
MINOS Far Detector

• Iron/scintillating tracking detector
• steel absorber 2.54 cm
• (magnetized by 1.5 T B field)
• 2 sections, 15 m each
• 484 planes of scintillator (1 cm thick)
• 25,800 m
• provide 2-D tracking
• wavelength shifting fibres
• multi-anode PMT
• 5.4 ktons
• expected event rate 200/kt/year

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MINOS Near Detector

• Squeezed octagonal shape (3.8 m x 4.8 m)
• 282 steel absorber 153 scintillator planes,
• interleaving every 4 or 5 steel plates.
• 2 sections
• target
• muon tracking
• 12,300 scintillation strips
• 0.98 ktons

• Both Detectors have
• 60 / ? E hadronic showers
• 25 / ? E em showers
• expected event rate 200/kt/year

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MINOS physics sensitivity (1)

• If ??? ?? , ?? CC events suppressed

No Oscillations
Low energy beam, 2 year running, sin22? 0.9
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MINOS physics sensitivity (2)

• Exclusion region (no signal)

Allowed region
Cover all SK region
8x10-4 eV2
Low energy beam, 2 year running
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MINOS physics sensitivity (3)
Sensitivity to Ue32 sin22?13

• ?e appearance
• Background from NC events
• Expect and improvement to CHOOZ limit by a factor
  of 2
• Possible way to improve
• eliminate high energy tail
• improve the low energy flux

19
CNGS (OPERA ICARUS)

• Goal detect ??? ?? in appearance mode by
  searching for t
• 2 experiments implementing different detection
  concepts
• OPERA (nuclear emulsion sampling calorimeter)
• ICARUS (liquid argon TPC)

CNGS n beam
Event rate

• pure ?? with contamination 2.1 ??/?? 0.8 ?e
  /?? ?e /??
• ltEgt ? 17 GeV
• 40 GeV protons

• 2600 ?? CC events/kt/year
• 15 ?t CC events/kt/year
• (?m2 2.5x10-3eV2 and
• sin22? 1.0)

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OPERA (Oscillation Project with Emulsion-tRacking
Apparatus)

• 1.8 ktons lead target
• Good electron identification ability

56 lead plate emulsions --gt a brick 3328
bricks --gt a wall 31 walls --gt a target
section
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OPERA physics sensitivity

• Expected number of event in 5 years, assuming
  oscillation at full mixing (sin22q)

• Also try ??? ?e appearance, if no signal can
  constrain Ue32 lt 0.06 at 90CL for ?m2
  2.5x10-3eV2

22
ICARUS (Imaging Cosmic And Rare Underground
Signal)

• Modular concept, ultimate goal is to build a 5kt
  LiqAr detector.
• First 600 tons LiqAr (T600) is being installed.
• Made of two T300 half-modules.
• Can achieve bubble chamber precision.

23
ICARUS Physics sensitivity

• Expected number of event in 5 years, assuming
  oscillation at full mixing (sin22q)

• For ??? ?e appearance, if no signal can
  constrain Ue32 lt 0.04 at 90CL for ?m2
  2.5x10-3eV2

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Discussion

• All experiments study mainly ??? ?? mode, either
  appearance of disappearance.
• K2K first LBL accelerator based experiment to
  study neutrino oscillation confirmed the
  atmospheric neutrino deficit. Limited by
  statistic
• MINOS (Dec 2004) focus on disappearance mode
  determination of oscillation parameters up to
  10 precision. Highest sensitivity (near 10-4
  eV2)
• Both K2K and MINOS use a near and a far detector
  to minimise systematic effect on analysis.
• CNGS (mid 2006) aim at direct observation of ??
  mode
• both MINOS and CNGS would be able to improve the
  constraint Ue32 about a factor of 3 from the
  current CHOOZ limit (or order 10-2) the expected
  sensitivity needed for detection of ??? ?e is
  still out of reach.
• MINOS also plan to study CP violation by
  switching ?? beam to ?? beam after a few year.

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Conclusion

• The first LBL accelerator experiment has
  confirmed the atmospheric neutrino deficit and
  supported the neutrino oscillation hypothesis.
• Future experiments, including MINOS and CNGS will
  provide much larger statistics and more precise
  measurements of oscillation parameters are
  possible.
• Measurement of Ue32 (or equivalently q13) can
  only done by the next generation of LBL
  experiments, but improvement of the upper bound
  is foreseen.