A search for free oscillations at the ESS n n ? n n - - PowerPoint PPT Presentation

• D. Milstead

Stockholm University

n n

?

π π π

A search for free

• scillations at the ESS

n n →

π π

Why baryon number violation ?

• Baryon number is not a ”sacred” quantum number

– Approximate conservation of BN in SM

• ”Accidental” global symmetry at perturbative level

– Depends on specific matter content of the SM

• BNV in SM by non-perturbative processes

–Sphalerons

– B-L conserved in SM, not B,L separately.

– Generic BNV in BSM theories, eg, SUSY. – BNV a Sakharov condition for baryogenesis

Why baryon number violation ?

? n n → Why

n n →

• Theory
• Baryogenesis via BNV (Sakharov condition)
• SM extensions from TeV mass scales scale-upwards
• Complementarity with open questions in neutrino physics
• Experiment
• One of the few means of looking for pure BNV
• Stringent limit on stability of matter

Neutron oscillations – models

6 5 15

2, 1000

QCD n n

c B L m M M R M δ

→

• Λ

∆ = ∆ = ⇒ = ⇒

• ∼

∼ Back-of-envelope dimensional reasoning: 6 q operator for TeV

• parity violating supersymmetry

Unification models: 10 GeV Extra dimensions models Post-sp

[ ]

n n BNV

• ⇒

→ ⇒ arXiv:1410.1100 High precision search haleron baryogenesis etc, etc: Scan over wide range of phase space for generic + model constai nts.

Extend sensitivity in RPV-SUSY

CMS dijet ATLAS multijet Displaced jets ESS

RPV-SUSY – TeV-scale sensitivity

Arxiv:1602.04821 (hep-ph)

( )

2 2, 0, 2 Neutrinoless

• decay

Eg seesaw mechanism for light L B B L β ν ∆ = ∆ = ∆ − =

( )

0, 2, 2 Eg Unification models n n L B B L → ∆ = ∆ = ∆ − =

⇔ Neutrino physics neutron oscillations

2

• n

n B L β ⇔ → Neutrinoless

• decay

linked under violation. Eg Left-right symmetric models.

Neutron oscillations – an experimentalist’s view

BNV p e L p π

+

→ + ⇒ → Hypothesis: baryon number is weakly violated. How do we look for ? Single nucleon decay searches, eg, ?

• violation, another (likely weakly) violated quantity.

Decays without leptons, eg, , BNV n n BNV n π π + → impossible due to angular momentum conservation. Nature may well have chosen albeit with few processes to observe it. and dinucleon decay searches sensitive to

• only processes.

Free n → ⇒ searches cleanest experimental and theoretical approach.

35

0, 10 New experiment: sensitivity yrs Discovery or new stringent limit on stability of matter.

life

B L τ ∆ ≠ ∆ = ∼

Previous searches for BNV and nnbar@ESS

30 34

0, 10 10 Few searches for Limits on from all searches yrs

life

B L τ ∆ ≠ ∆ = ∼ −

n n

?

( ) ( )

29 2 2 2

10 sin : 1 MeV mixing physics ; Two interesting cases: Free neutron oscillation Bound neutron

n n eff n n n n

E m n n i n m E n t m n H n nn m P E t E E E E E t P m t δ δ δ δ δ

− →

      ∂ =       ∂       = < =   = ∆ × ∆ = −   ∆  

• ∆ ×

⇒ ×

• ℏ

≪ ∼ : 1

• scillation

E t ∆ × ≫

mixing formalism n n →

Searching with bound neutrons

( )

2 2 2 60 8

sin , 100 10

n n free

m P E t E E m E δ δ τ

→ −

  = ∆ ×   ∆   ∆   ⇒ <   ∆   ⇒ × ∼ MeV . Suppression: Best current limits (SuperKamiokande) >2.5 10 s Irreducible bg's prevent large improvements. Model-dependent (nuclear interactions). Nuclear disintegration after neutron oscillation

n n

n n → n N +

+ π’s +

Free neutron search at ILL

8

850 0.86 10 Institute Laue-Langevin (Early 1990's). Cold neutron beam from 58MW reactor. 130 m thick carbon target Signal of at least two tracks with MeV candidate events, background. s.

n n

E µ τ → > ⇒ > × ∼

The European Spallation Source

High intensity spallation neutron source Multidisplinary research centre with 17 European nations participating. Lund, Sweden. Start operations in 2019. 2 GeV protons (3ms long pulse, 14 Hz) hit rotating tungsten target. Cold neutrons after interaction with moderators.

The European Spallation Source

22 instruments/experiments with capability for more. ∼

Overview of the Experiment

( ) ( )

2 1) n

P n n N t E v

−

× → ∝

• Sensitivity = free neutron flux at target

Cold neutrons ( <5 meV, <1000ms Low neutron emission temperature (50-60 K) Supermirror transmission and transit time Large beam port opt

3 nn

P

• ∼

ion, large solid angle to cold moderator. Increase in sensitivity for 10 compared to previous experiment (ILL) Neutron guiding, larger opening angle, higher flux, particle ID technologies, running time.

(1) (2) (3) (4)

Top view side view Tungsten target H

2

H2O ambient ESS moderators will be of “butterfly” design

• Increase cold yield
• Convenient beam extraction

Additional challenge for nnbar which could benefit from extracting neutrons from all four visible cold surfaces

• Conventional point-to-point focusing of a

cold neutron beam using ellipsoidal mirrors inefficient.

• Ongoing studies on neutron optics

Neutronics (1)

cold cold cold cold

(1) (2) (3) (4)

Neutron supermirror

Smooth surface Supermirror

=Critical angle for total internal reflection

c

θ

1 m = 1 m >

Need efficient focusing and minimal interactions (each interaction "resets the -clock") n

Ni c C

m θ θ →

Commercial supermirrors

2

7 1 Commercial supermirrors with Acceptance for straight guide ILL experiment used neutron optics. Increase from use of focusing reflector and optimised mirror arrays. Crucial contribution to incr m m m ∝ ∼ ∼ ease of sensitivity wrt ILL.

(1) (2) (3) (4)

The need for magnetic shielding

5

, 2 1 5 n n E B E t B µ

−

∆ =

• ≤

∆ × ⇒ ≤ ≤

• ≪

Degeneracy of broken in B-field due to dipole interactions: Flight time 1s For quasi-free condition nT and vacuum 10 Pa.

( )

n µ ↓

( )

n µ ↑

2 B µ •

• (

) ( )

n n µ µ ↓ ↑

E

B ∼

Shielding

5

5 B P

−

• <

∼

• Magnetic shielding for flight volume

nT, 10 mbar Aluminium vacuum chamber Passive magnetic shield from magnetizable alloy External coils for active compensation Background studied by tu B

• rning on/off -field.

Maybe shielding isn’t needed

Interesting discussion in the literature.

Overview of the Experiment

(1) (2) (3) (4)

(4) Detector

( ) ( )

5 2 0.5 Expect at GeV. Detector design for high efficiency and low bg . Annihilation target - carbon sheet Tracker - vertex reconstruction Time-of-flight system

• scintillators aro

n N s π ε + →∼ >

• ∼

∼ und tracker. Calorimeter

• lead + scintillating and clear fibre.

Cosmic veto - plastic scintillator pads Trigger - Track and cluster algorithms

• Neutron

beam Target membrane Tracker Calorimeter Vacuum TOF Cosmic veto

28

GENIE: NNBar Final State Primaries

• A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

6/13/14

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%

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 list prepared by R. W. Pattie

Preliminary

29

Energy Threshold Acceptance (Signal)

ILL Trig. Thresh.

6/13/14

• A. R. Young, D. G. Phillips II, R. W. Pattie Jr.

Annihilation event

Collaboration and approximate timescales

Several workshops (CERN, Lund, Gothenburg) Collaboration formed – interim spokesperson G. Broojimans Expression of Interest submitted to ESS. Signatories from 26 institutes , 8 countries. Sweden: Stockholm, Uppsala, Lund, Chalmers. More collaborators are welcome!

ESS

nn

Commissioning, Intensity ramp, early experiments Initial user program Routine operations 2019 Construction, commissioning, early data-taking 2023 Physics runs 2026 End run, complete analysis

Particle Physics Strategy

Consensus in the field is to pursue experiments with unique capabilities and physics reach.

Summary

• The search for neutron-antineutron oscillations addresses open

questions in modern physics.

• An experiment at the ESS offers a new opportunity to extend

sensitivity to neutron oscillation probability by several orders

• f magnitude and set a new limit on the stability of matter.
• Collaboration formed and EOI submitted
• Provisional schedule made.

Potential gains

Factor Gain wrt ILL Brightness Moderator temperature Moderator area

2

Angular acceptance/neutron transmission

40

Length

5

Run time

3

Total

1 ≥ 1000 ≥ 1 ≥

(RPP)

0, B L ∆ ≠ ∆ ≠ 0, B L ∆ ≠ ∆ =

Baryon number violation searches

30 34 35

0, 10 10 10 Few searches for limits yrs limit from new experiment yrs B L τ τ ∆ ≠ ∆ = ∼ − ∼

Decay mode Partial mean life (x 1030 yrs)

BNV searches

L and B violated B violated

RPP

Poor experimental coverage of ”pure” B violation tests

( )

1, 1, Single nucleon decay Eg unification models L B B L ∆ = ∆ = ∆ − =

( )

2 2, 0, 2 Neutrinoless

• decay

Eg seesaw mechanism for light L B B L β ν ∆ = ∆ = ∆ − =

( )

0, 2, 2 Eg Unification models n n L B B L → ∆ = ∆ = ∆ − =

Complementary searches for and BNV LNV

• Each search tests complementary conservation laws.

Neutrinoless double -decay linked under violation. Eg Left-right symmetric models. n n B L β ⇔ →

( )

'' 2 2 11 , 2 2 1 , '' 11 '' '' '' 111 '' '' 112 113

, , , , 1 16 | | 3 . , Reduced particle content: + ; Yukawa coupling: steered by . Flavour mixin

R R R R R

k d s b s nn g d s b k ijk ikj

u d g d s b m g C C n n m m m nn λ τ λ λ λ λ λ λ = = ⇒ = − ⇒ = ⇒ ⇒

ɶ ɶ ɶ ɶ ɶ ɶ ɶ

ɶ ɶ ɶ ɶ

• (

)

( )

2 , 2 1

, g Mixing parameters: eg

R R R R

d s b d RR k d

s d b d m m δ   → →   ⇒ = ≠

ɶ ɶ ɶ ɶ

ɶ ɶ ɶ ɶ

in a SUSY framework n n →