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 νe 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 νµ νe + unexplained excess Antineutrino mode: does not rule out 'LSND anomaly'
LSND neutrino source
LSND neutrino source π DAR νµ µ+ νµ ν e e + π DIF νµ µ νµ ν e e + p 800 MeV or 1.5 GeV/c -
LSND neutrino source π DAR νµ µ+ νµ ν e e + π DIF νµ µ νµ ν e e + p 800 MeV or 1.5 GeV/c - DAR of µ competes with µ + (A,Z) νµ + (Α, Ζ 1)
LSND neutrino source π DAR νµ µ+ νµ ν e e + π DIF νµ µ νµ ν e e + p 800 MeV or 1.5 GeV/c - DAR of µ competes with µ + (A,Z) νµ + (Α, Ζ 1) νe flux prediction depends on: 1) Total number of pi2) Momentum spectra 3) Angular spectra 4) Geometrical layout and material composition
The HARP experiment
The HARP experiment
HARP-CDP cross sections
HARP-CDP: tuning hadron models Geant4 and FLUKA
HARP-CDP: tuning hadron models Geant4
HARP-CDP vs LSND parametrization
HARP-CDP simulation
Hadroproduction
Hadroproduction
HARP-CDP simulation Very complicated task Need differential pion production cross-sections of p, n, pi+, pi- on H2O, 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) st LSND used pions from 1 generation only LSND ignored pion production by neutrons LSND used MCNP simulation program only for geometry description
LSND Background I (geniune νe) LSND published DAR νµ 0.8 DAR νe 0.65 [10-9 / PoT / cm2] [10-12 / PoT / cm2]
LSND Background I (geniune νe) LSND published LSND emulation DAR νµ 0.8 0.60 DAR νe 0.65 0.59 [10-9 / PoT / cm2] [10-12 / PoT / cm2]
LSND Background I (geniune νe) LSND published LSND emulation Geant4 + Exp. data FLUKA + Exp. data DAR νµ 0.8 0.60 0.78 0.76 DAR νe 0.65 0.59 0.96 0.88 [10-9 / PoT / cm2] [10-12 / PoT / cm2]
LSND Background I (geniune νe) LSND published HARP-CDP estimate 19.5 ± 3.9 30.6 ± 8.8 LSND detector see this: νe + 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 and this 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 νµ (15% by LSND)
First reduction of the "anomaly"
LSND analysis strategy 2100 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... 2.7 events νe + 12C e- + 12Ngs followed by 12 Ngs 12C + e+ + νe
Comparison of R distributions When fit hypotheses comprise only correlated or accidental gammas 2.3 12Ngs 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 yielding 115.6 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 12Ngs beta decay were missed in LSND analysis We find significance of the "LSND anomaly" not large than 2.3 σ
The HARP-CDP group
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