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Hunting the Missing Baryon Number Violation at the ESS

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Hunting the Missing Baryon Number Violation at the ESS Hunting the missing baryon number violation at the ESS n ? n D. Milstead Stockholm University Outline • Why look for neutron oscillations ? • How to look for neutron oscillations • Nnbar and HIBEAM at the ESS Baryon and lepton number violation • BN,LN ”accidental” SM symmetries at perturbative level – BNV, LNV in SM non-perturbatively (eg instantons) – B-L is conserved, not B, L separately. • BNV, LNV needed for baryogenesis and leptogenesis • BNV,LNV generic features of SM extensions (eg SUSY) • Need to explore the possible selection rules: BLBL 0 , 0, 0 BLBL 0 , 0, 0 LBBL 0 , 0, 0 ..... Neutron oscillation Mirror neutrons Neutron-antineutron oscillations R-parity violating supersymmetry, minimal flavour violation SUSY Unification models: M 1015 GeV Left-right symmetric models (nn and 0 2 ) Extra dimensions models Post-sphaleron baryogenesis etc, etc: arXiv:1410.1100 High precision n n search Scan over wide range of phase space for generic BNV + model constaints. Operator analysis Six quark operators i : n n, NN NN KK 1 Eg : n n neff n5 i n i n M X i Short distance (RPV SUSY): i 6 Long distance Hadronic ME: nni QCD 1 M 5 Oscillation time = X 6 nneff QCD Beyond the TeV scale Super-K ILL LHC, flavour Constraints vanish for >> TeV masses nnbar@ESS: extends mass range by up to ~400 TeV cf Super-K : pushes into the PeV scale : Reach beyond the LHC An experimentalist’s view (1) Hypothesis: baryon number is weakly violated. How do we look for it ? Need processes in which only BNV takes place. Single nucleon decay searches, eg, pe 0 ? BL 11 , ! Decays without leptons, eg, p , impossible due to angular momentum conservation. BL 00 , observables restricted by Nature. n n,' n and dinucleon decay searches sensitive to BNV -only. Free n n,' n searches cleanest experimental and theoretical approach. An experimentalist’s view (2) Few searches for BL 0, 0 Outline • Why neutron oscillations ? ✔ • How to look for neutron oscillations • Nnbar and HIBEAM at the ESS nn mixing formalism ? nn Emn i n n t n m En n 29 m n Heff n 10 MeV nn mixing physics 2 m 2 Pn nsin E t ; E E n E n E Two interesting cases: Free neutron oscillation:1 E t P m t2 Bound neutron oscillation:1 Et Searching with bound neutrons Nuclear disintegration after neutron oscillation nn nN n n + + ’s 2 m 2 Pnn sin E t , E E 100 MeV . 2 m 60 Suppression: 10 E 8 Best current limits (SuperKamiokande) free>2.5 10 s Irreducible bg's prevent large improvements. Model-dependent (nuclear interactions). Free neutron search at ILL Institute Laue-Langevin (Early 1990's). Cold neutron beam from 58MW reactor. 130 m thick carbon target Signal of at least two tracks with E 850 MeV 00 candidate events, background. 8 nn 0.86 10 s. Outline • Why neutron oscillations ? ✔ • How to look for neutron oscillations ✔ • Nnbar and HIBEAM at the ESS The European Spallation Source High intensity spallation neutron source Multidisplinary research centre with 17 European nations participating. Lund, Sweden. Start operations in 2023/2024. 2 GeV protons (3ms long pulse, 14 Hz) hit rotating tungsten target. Cold neutrons after interaction with moderators. HIBEAM 22 instruments/experiments with capability for more. Plan for staged experiment: (1) HIBEAM (high intensity baryon extraction and measurement) at Fundamental Physics Beam Port (2) NNbar at the Large Beam Port. Overview of the Experiment 2 Sensitivity = free neutron flux at targetP n n Nn t Cold neutrons (Ev <5 meV, <1000ms1) Low neutron emission temperature (50-60 K) Supermirror transmission and transit time Large beam port option, large solid angle to cold moderator. (4) (3) (1) (2) Neutronics (1) cold cold side Tungsten view target cold cold ESS moderators will be of “butterfly” design • Increase cold yield • Convenient beam extraction H Additional challenge for nnbar which could 2 benefit from extracting neutrons from all four visible cold surfaces Top • Conventional point-to-point focusing of a view H O cold neutron beam using ellipsoidal 2 mirrors inefficient. ambient • Ongoing studies on neutron optics (4) (3) (1) (2) Neutron supermirror Smooth surface Supermirror c =Critical angle for total internal reflection m Ni cC m 1 m 1 Need efficient focusing and minimal interactions (each interaction "resets the n-clock") Commercial supermirrors Commercial supermirrors with m 7 Acceptance for straight guide m2 ILL experiment used m 1 neutron optics. Increase from use of focusing reflector and optimised mirror arrays. Crucial contribution to increase of sensitivity wrt ILL. (4) (3) (1) (2) The need for magnetic shielding n nn 2 B E B 0 n Degeneracy of nn, broken in B-field due to dipole interactions: EB 2 Flight time 1s For quasi-free condition Et 1 B 5nT and vacuum 105 Pa. Shielding Magnetic shielding for flight volume BP 5nT, 105 mbar Aluminium vacuum chamber Passive magnetic shield from magnetizable alloy External coils for active compensation Background studied by turning on/off B-field. Overview of the Experiment (4) (3) (1) (2) Detector Expect n N 52 at s GeV. Cosmic Detector design for high efficiency 0.5 veto and low bg 0. Calorimeter Tracker TOF Annihilation target - carbon sheet Tracker - vertex reconstruction Neutron Target Time-of-flight system beam membrane - scintillators around tracker. Vacuum Calorimeter - lead + scintillating and clear fibre. Cosmic veto - plastic scintillator pads Trigger - Track and cluster algorithms GENIE: NNBar Final State Primaries Preliminary Final state list prepared by R. W. Pattie GENIE-2.0.0: intranculear propagation based on INTRANUKE C.Andreopoulos et al., The GENIE Neutrino Monte Carlo Generator, Nucl.Instrum.Meth.A614:87-104,2010. Final State Pionic Mode Nevents % Total π+π-2π0 530 10.60% 2π+π-π0 486 9.72% π+π-π0 417 8.34% 2π+π-2π0 409 8.18% π+π-3π0 329 6.58% 2π+2π-π0 315 6.30% π+2π0 290 5.80% π+3π0 219 4.38% π+π-ω 145 2.90% π+π0 137 2.74% π+2π-π0 132 2.64% 2π+2π- 124 2.48% 6/13/1429 A. R. Young, D. G. Phillips II, R. W. Pattie Jr. Annihilation event Capability of the experiment 3 Gain in Pnn 10 compared with ILL. Factor Gain wrt ILL Brightness 1 Moderator temperature 1 Moderator area 2 Angular acceptance/neutron 40 transmission Length 5 Run time 3 Total 1000 3 Increase in sensitivity for Pnn 10 compared to previous experiment (ILL) 35 Stability of matter ( life ) sensitivity10 yrs Discovery or new stringent limit on models of new physics and stability of matter. HIBEAM The proposed program HIBEAM/nnbar and ESS Particle Physics Strategy Consensus in the field is to pursue experiments with unique capabilities and physics reach. We live in interesting times Energy frontier Future discoveries or walking a few km in a desert ? ”Far future collider”: crystals, plasma wakefields… For the first time in 50 years, going to higher collision energies no longer offers a clear path to discoveries or fundamental insights. Need a complementary set of collider +non-collider experiments with unique physics potentials and reach of energy scale. EW instantons in the Standard Model Bosonic sector of EW theory Infinite no. of field configurations (vacua) Vacua distinguished by fermion energy levels. Instanton Instantons: Tunnelling between vacua minima Fluctuation of background W field. E Energy level raises above (or falls below) the surface of the Dirac sea. No. leptons and quarks changes t LBBLBL 0, =0, 0 Dirac sea 2 Exponentially suppressed: exp gW Maybe shielding isn’t needed Interesting discussion in the literature. .
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