How large is the LSND anomaly? - University of Chicagoelagin/HARP-CDP_vs_LSND/Elagin...How large is...

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How large is the "LSND anomaly"? Andrey Elagin on behalf of the HARP-CDP group HEP lunch, UChicago, March 12, 2012

Transcript of How large is the LSND anomaly? - University of Chicagoelagin/HARP-CDP_vs_LSND/Elagin...How large is...

  • How large is the "LSND anomaly"?Andrey Elagin

    on behalf of the HARP-CDP group

    HEP lunch, UChicago, March 12, 2012

  • Outline

    ● 3.8 σ LSND Final Paper PRD 64, 112007 ● 3.8 σ → 2.9 σ HARP-CDP Paper I arXiv:1110.4265

    (accepted to PRD)● 2.9 σ → 2.3 σ HARP-CDP Paper II arXiv:1112.0907

    (accepted to PRD)

    ● LSND corrections: arXiv:1112.2181● HARP-CDP reply: arXiv:1112.3852

  • LSND● Beam dump experiment in Los-Alamos (1993-1998).

    ● Claimed 3.8 evidence of νµ→ν

    e oscillations with ∆m2 ~ 1 eV2. In

    stark conflict with three light neutrino flavours (solar and atmospheric oscillations and LEP N = 2.9840±0.0082).

    ● At least one 'sterile' neutrino is required: 800+ theoretical papers (700+ after 1998)

  • LSND● 1993-1994 data: 16.4 (+9.7 - 8.9) ± 3.3

    (alternative analysis by J.E. Hill do not find any excess PRL 75, 2654)

    ● 1993-1995 data: 51.0 (+20.2 – 19.5)

    ● Full dataset: 87.9± 22.4± 6.

    ∆m2 > 0.02 eV2.

    ● BNL-E776, CCFR, NuTeV and NOMAD

    exclude ∆m2 > 10 eV2.

    ● Bugey and CHOOZ ruled out

    ∆m2 < 0.2 eV2.

    ● KARMEN2 ∆m2 < 1 eV2 or ∆m2 ~ 7 eV2.

  • Test by MiniBoone

    Neutrino mode: exclude ν

    µ→ν

    e

    + unexplained excess

    Antineutrino mode: does not rule out 'LSND anomaly'

  • LSND neutrino source

  • LSND neutrino source

    π+DAR

    νµ µ+ ν

    µ ν

    e e+

    π-DIF

    νµ µ− ν

    µ ν

    e e−

    p

    800 MeV or 1.5 GeV/c

  • LSND neutrino source

    π+DAR

    νµ µ+ ν

    µ ν

    e e+

    π-DIF

    νµ µ− ν

    µ ν

    e e−

    DAR of µ− competes with µ− + (A,Z) → νµ + (Α, Ζ−1)

    p

    800 MeV or 1.5 GeV/c

  • LSND neutrino source

    π+DAR

    νµ µ+ ν

    µ ν

    e e+

    π-DIF

    νµ µ− ν

    µ ν

    e e−

    DAR of µ− competes with µ− + (A,Z) → νµ + (Α, Ζ−1)

    νe flux prediction depends on:

    1) Total number of pi-2) Momentum spectra3) Angular spectra4) Geometrical layout and material composition

    p

    800 MeV or 1.5 GeV/c

  • The HARP experiment

  • The HARP experiment

  • HARP-CDP cross sections

  • HARP-CDP: tuning hadron modelsGeant4 and FLUKA

  • HARP-CDP: tuning hadron modelsGeant4

  • HARP-CDP vs LSND parametrization

  • HARP-CDP simulation

  • Hadroproduction

  • Hadroproduction

  • HARP-CDP simulation

    Very complicated taskNeed differential pion production cross-sections

    ● of p, n, pi+, pi-● on H

    2O, Fe, Cu, Al, Mo, Air

    ● as a function of projectile momentum

  • Pions from different models

  • Pion generations

  • Pion production by 600 MeV neutrons

  • LSND Background I (geniune νe)

    ● LSND used pions from 1st generation only● LSND ignored pion production by neutrons● LSND used MCNP simulation program only for

    geometry description

  • LSND published

    DAR νµ

    [10-9 / PoT / cm2]

    0.8

    DAR νe

    [10-12 / PoT / cm2]

    0.65

    LSND Background I (geniune νe)

  • LSND published

    LSND „emulation“

    DAR νµ

    [10-9 / PoT / cm2]

    0.8 0.60

    DAR νe

    [10-12 / PoT / cm2]

    0.65 0.59

    LSND Background I (geniune νe)

  • LSND published

    LSND „emulation“

    Geant4 + Exp. data

    FLUKA + Exp. data

    DAR νµ

    [10-9 / PoT / cm2]

    0.8 0.60 0.78 0.76

    DAR νe

    [10-12 / PoT / cm2]

    0.65 0.59 0.96 0.88

    LSND Background I (geniune νe)

  • LSND Background I (geniune νe)

    LSND published HARP-CDP estimate

    19.5 ± 3.9 30.6 ± 8.8

    LSND detector see this: ν

    e + p → e+ + n

    „electron“ + delayed 2.2 MeV gamma from neutron capture

  • LSND Background II (fake νe)

    νµ + p → µ+ + n

    νµ + 12C → µ− + 12N

    νµ + 12C → µ+ + 12B

    Only π DIF can produce neutrinos above threshold

    If Tµ ~< 3 MeV, muons are not identified andthis reaction fakes signal

    νe + p → e+ + n

    We consider LSND uncertainty too optimistic

  • LSND Background II (fake νe)

    We estimate 35% uncertainty on νµ and 60% on ν

    µ

    (15% by LSND)

  • First reduction of the "anomaly"

  • LSND analysis strategy2100 „electron“ candidates

  • Correlated γ vs uncorrelated γ

  • Beam excess

    LSND finds „beam excess“ („beam on“ minus „beam off“) consists of 117.9+/-22.4 correlated events out of 2100 candidates

    Uncertainty of 22.4 is consistent with vanishingly small systematics, if any

  • Something is missing...

    νe + 12C → e- + 12N

    gs followed by 12N

    gs → 12C + e+ + ν

    e

    2.7 events

  • Comparison of R distributions

    When fit hypotheses comprise only correlated or accidental gammas 2.3 12N

    gs events will be interpreted as correlated

  • "Beam excess" calculation● Generate pseudodata with 120 correlated

    events and 1980 accidental events to study systematic uncertainty

    ● By varying "base distributions" and fitting R distribution we estimate 17.3% of systematic uncertainty

    ● 2.3 events subtracted from 117.9 LSND yielding115.6 events with total uncertainty of 27.9

  • Final reduction of the "anomaly"

  • Summary● The claim of a 3.8 σ significance of the LSND anomaly

    cannot be upheld● LSND didn't take into account pion production by

    neutrons● Improved simulation of the LSND beam stop shows that

    conventional background increases by a factor of 1.6● Positrons from 12N

    gs beta decay were missed in LSND

    analysis● We find significance of the "LSND anomaly" not large

    than 2.3 σ

  • The HARP-CDP group

  • Back-up

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