10/2/2012

1

Stefan Baeβler

Fundamental Physics with Neutrons

The physicist’s view of a neutron

For most experiments, it is a point(with some properties: mass and spin).

dd

u

For neutron beta decay, it has (at least) the structure given by its valence quarks.

d

d

u

With more resolution, more structure appears

Different physicist’s have different views:

2

10/2/2012

2

What is our interest?

How? Fermilab’s view to this is:

David MacFarlane, Director of Particle Physics and Astrophysics division, SLAC

“The Intensity Frontier involves many diverse lower-energy precision experiments; and its discovery potential, being less direct, is therefore harder to understand.”

Answer: We want to find the fundamental laws of physics .

3

p+

n

e-

e

Table of contents

4

1. Production of Low Energy Neutrons

2. Experiments with Low Energy Neutrons:

• Neutron Beta Decay

• Spectroscopy of gravitationally bound quantum states

• Weak Hadronic Interaction in neutron capture on hydrogen

3. Future plans

10/2/2012

3

The Spallation Neutron Source SNS in Oak Ridge, TN

Linear H- accelerator Accumulator ring (buncher)

Target

Target

Guide Hall

1B - Disordered Mat’lsCommission 2010

2 - Backscattering Spectrometer Commission 2006

3 - High Pressure Diffractometer Commission 2008

4A - Magnetism Reflectometer Commission 2006

4B - Liquids ReflectometerCommission 2006

5 - Cold Neutron Chopper Spectrometer Commission 2007

18 - Wide Angle Chopper Spectrometer Commission 2007

17 - High Resolution Chopper SpectrometerCommission 2008

13 - Fundamental Physics Beamline Commission 2008

11A - Powder Diffractometer Commission 2007

12 - Single Crystal Diffractometer Commission 2009

7 - Engineering Diffractometer IDT CFI Funded Commission 2008

6 - SANS Commission 2007

14B - Hybrid Spectrometer Commission 2011

15 – Spin Echo

9 –VISION

Usage of neutrons @ SNS

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4

Transport (cold neutrons)

V

~ 100 neV

2

Fermin

2 big: V nb

m

Storage (ultracold neutrons)

Interactions of low energy neutrons with matter

2

Fermin

2( )i i

i

V b x xm

UCN

Typical properties:

Energy: EUCN ~ 100 neV

Velocity: vUCN ~ 5 m/s

Height: hUCN ~ 1 m 7

p+

n

e-

e

Table of contents

8

1. Production of Low Energy Neutrons

2. Experiments with Low Energy Neutrons:

• Neutron Beta Decay

• Spectroscopy of gravitationally bound quantum states

• Weak Hadronic Interaction in neutron capture on hydrogen

3. Future plans

10/2/2012

5

Beta Decay in the Standard Model

Parity Violation found by Wu et al, 1956

ud 5Fweak 5 h.c.

21 μ μ e

GH p γ γ γ n e γ γ γ ν

V

3. Helicity

… of elementary fermions: –p/E,

… of elementary anti-fermions: +p/E

60Co

I

e-

60Co

I

e-

≠

e-e

ep

μ- νμ

d u

b t

s c

1. Quark mixing

2

ud 95%V

2. Nucleon structure effects

gV = GF·Vud·1

gA = GF·Vud·λ

(No nuclear structure effects)

Fermi’s golden rule:

2

weak

2 decay probability i f f H i

9

d

2

eu2

e

221 3F V

dwG E

dE

Observables in Neutron Beta Decay

u1 2 2

e2

n d

21 3FG V E

pn

e-

e

n

e

Neutron lifetime

Jackson et al., PR 106, 517 (1957):

Observables in Neutron beta decay, as a function of generally possible coupling constants (assuming only Lorentz-Invariance)

2 ee

e

e en

e

ee

e

1 3 1

+

a b

A B

p p

E E

p p p

md E

E

Dp

E E E E

Beta-Asymmetry

Neutrino-Electron-Correlation

2

2

Re2

1 3A

2

2

1

1 3a

Fierz interference term 0b

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6

Search for Standard Model Parameters

-1.290 -1.280 -1.270 -1.260

λ = gA/gV

0.960

0.965

0.970

0.975

0.980

Vud

ft(0+→0+) [Hardy09]

ft(0+→0+) [Liang09 – PKO1]

ft(0+→0+) [Liang09 – DD-ME2]

PIBETA [Pocanic04]

λ[P

DG

201

2]

A[P

ER

KE

O I

I, 2

012]

Kaons+Unitarity [PDG 2012]

-1.667

(if neutron was aelementary particle)

-1.000

(if neutron was (udd))

Nab, goal

11

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7

13

~ GeV: quarks combine to form nucleons: → , → , ′ → , , …Problem: If nucleons were formed as many as anti-nucleons (CP-symmetry), nucleons and anti-nucleons would have annihilated and disappeared.Solution: Need (more) CP violation in theory

Experiments: Measure electric dipole moments, e.g. of neutron

14

. MeV: nucleons on thermal equilibrium: ~ ⁄ →

. MeV: heavier nuclei form:→ , → , → , …

(This is primordial nucleosynthesis, it stops at mass 5 and 8)We find element abundances from nuclear and particle physics!

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Neutron beta decay data in Primordial Nucleosynthesis

Experimental input from fundamental physics with neutrons:Stronger coupling constants in n ↔ p reactions (as determined by neutron lifetime)⇒ Phase transition later ⇒ nucleon density lower after phase transition ⇒ less 4He, more d

15

W±

e-

νen

p

n + νe ↔ p + e-

W±

e+

νe

n

p

n + e+ ↔ p + νe

Reactions in equilibrium

n ↔ p + e-+ νe

W±

e-

νen

p

Ee [MeV]

p p2

[MeV

2 /c2 ]

cos θeν = 1

Proton phase space (Dalitz plot) Probability (arb. units)

0

0.25

0.5

0.75

1

1.25

1.5

0 0.2 0.4 0.6 0.8

cos θeν = 0cos θeν = -1

1 cosee

e

pd a

E

n

e-

e

epKinematics in Infinite Nuclear Mass Approximation:

• Energy Conservation:

• Momentum Conservation2 2 2

e ep 2 cos ep p p p p

e,max eEE E

Idea of the cos θeν spectrometer Nab @ SNS

Ee =

75 keV

236 keV

450 keV

700 keV

22p emin, max

2ep

e

Edges:

Slope:

1 cos e

p p p

pa p

E

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SegmentedSi detector

decay volume (field rB,DV·B0)

0 kV

0 kV

30 kV

magnetic filterregion (field B0)

Neutronbeam

TOF region(field rB·B0)

Nab spectrometer principle: measurement of Ee and tp

• Measurement of Ee and tp for each event; protons only in upper detector

• Background suppression through coincidences of electron and proton.

• Long flight path improves spectrometer

Proton Trajectory

Magnetic Field

Adi

abat

ic

conv

ersi

on

p

||p

p

||p

18

Sim

ulat

ed c

ount

s [A

.U.]

0.002 0.004 0.0060

Ee = 300 keVEe = 500 keV

Ee = 700 keV

1/tp2 [µs-2]

Extraction of a in Nab

Data analysis: Use edge to determine or verify the shape of the detection function.

Then, use central part to determine slope and the correlation coefficient a.

pp2 [MeV2/c2]

p p2

dist

ribu

tion

0.0 0.5 1.0 1.5

2ep

e

1 cos e

pa p

E

Ee = 550 keV

2pcos 1e p

2pcos 1e p

pp

p pcos ( )

m dzt

p zq= ò

2p

2p,0 0

sin ( ) ( )

sin

z B z

B

q

q=

Nab spectrometer simulations:• J. Brown (2nd prize at Undergraduate Research Symposium

2011), T. Niu, D. van Petten (Mitchell Fellowship), S.B.• E. Frlez, L. P. Alonzi, D. McLaughlin, D. Pocanic(all UVa)• J. D. Bowman (ORNL) 19

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Nab: Spectrometer Magnet System

20

z [cm]

Mag

neti

cfi

eld

[T]

B

0

1

2

3

4

-1 0 1 2 3 4 5

neutrondecay volume

lowerdetector

upperdetector

z [cm]

Mag

neti

cfi

e ld

[T]

B

0

1

2

3

4

neutrondecay volume

Bz (on axis)Bz (off axis)

Filter

-30 -20 -10 0 10 20 30

Nab setup at Spallation Neutron Source (SNS)

FNPB beamline @ SNS

Spectrometer magnet

Si detectors

Neutron beam

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Uncertainty budget

PLANNED systematic uncertainty budget:PLANNED statistical uncertainty budget:

About 2×109 events can be detected in 6 weeks (Decay volume V = 246 cm3, decay density nd = 20 cm-3, 12.7 % of decay protons go to upper detector, 80% duty factor)

→ (Δa/a)stat < 1×10-3 can be reached

Compare to Δa/a = 5 % of existing experimental results

lower Ee cutoff none100 keV

100 keV

300 keV

upper tp cutoff none none 40 μs 40 μs

Δa 2.4/√N 2.5/√N 2.5/√N 2.6/√N

Δa (Ecal, lvariable)

2.5/√N 2.6/√N 2.7/√N 2.7/√N

Δa (Ecal, lvariable, inner 70% of data)

4.1/√N 4.1/√N 4.1/√N 4.1/√N

Experimental parameterSystematic

uncertainty Δa/a

Magnetic field... curvature at pinch 5·10-4

… ratio rB = BTOF/B0 2.5·10-4

… ratio rB,DV = BDV/B0 3·10-4

Length of the TOF region (*)Electrical potential inhomogeneity:… in decay volume / filter region 5·10-4

… in TOF region 1·10-4

Neutron Beam:… position 4·10-4

… profile (including edge effect) 2.5·10-4

… Doppler effect smallUnwanted beam polarization can be made smallAdiabaticity of proton motion 1·10-4

Detector effects:… Electron energy calibration (*)… Electron energy resolution 5·10-4

… Proton trigger efficiency 2.5·10-4

Residual gas smallBackground smallAccidental coincidences smallSum 1·10-3

0 50 100 150 200 250 300 3500

5

10

15

20

25

30

35

40

Angle [°]

Hei

ght [

mm

]

4900

4950

5000

5050

5100

Work Function [meV]

Kelvin Probe: First results from early work on aSPECT

In collaboration with Prof. I. Baikie, KP Technologies 25

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12

0 4 8 120

4

8

12

16

Hei

ght [

mm

]

Work Function [meV]

Width [mm]

0 50 100 150 200 250 300 3500

5

10

15

20

25

30

35

40

Azimuth angle [°]

Hei

ght [

mm

]

4900

4950

5000

5050

5100

In collaboration with Prof. I. Baikie, KP Technologies

Now: Better coating

Thanks to:Rachel Hodges (undergraduate research prize)Sean McGovern (M. Sc., 2010)Henry Bonner,Xuying Tong(all UVa)Gertrud Konrad(University of Mainz)

(arbitrary offset added)

26

Silicon detector for Nab / abBA / PANDA

Segmented ion-implanted silicon detector with fast readout electronics:

• Thickness 2 mm (less for testing)

• Thin dead layer of < 100 nm silicon (measured!):

Energy loss for 30 keV protons: < 11 keV (measured!)

• 127 channels

Sufficiently small count rate/pixel,

Allows to find electron and correlated proton.

Front side Back side

Ø 81 mm

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Si detector properties: proton detection

A. Salas-Bacci, P. McGaughey, Dinko Pocanic, S.B. et al @ NCSU proton source (A. Young et al.)

Threshold lost protons efficiency slope

8 keV 0.19% 110(30) ppm/keV

10 keV 0.20% 131(31) ppm/keV

12 keV 0.21% 165(32) ppm/keV

14 keV 0.28% 304(76) ppm/keV

For uncertainty in a, we assume a threshold of 10 keV and direct measurement of efficiency slope to 50%.

20 30 40 50 60 70 80 90energy [keV]

dead layer: 70-100 nm Si(corrected for nuclear defect,

charge recombination)

Cen

troi

dpu

lse

heig

ht [

chan

nels

]

0

50

100

150

200

250

10 20 30 40 50 60 70 80pulse height [channels]

Yie

ld [

A.U

.]

28

Ionization chamberin Faraday Cage

Bending magnet

Proton detector(in vacuum chamber)

Proton path

29

Proton source for detector tests (and advanced lab)

100

0.4 0.5 0.6 0.7

1000

10000

ion

coun

tra t

e[1

/s]

magnetic current [A]

mass 1(protons)

mass 2 (H)2+

Commissioning results:

Proton source is planned to be used for intermediate or advanced lab.

Support:Jeffress Memorial TrustJefferson TrustHEETFProton source team:Aaron Ross (Mitchell fellowship), Ryan Slater, Zia Tompkins, Americo Salas Bacci, Panaiot Zotev, S.B., Dinko Pocanic(all UVa)Martin Schlegel (DAAD fellowship), Y. Kahvaz

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14

Goal: Δb ~ 3×10-3

2 ee

e

1 3 1m

dw E bE

The determination of the Fierz Interference term

Electron spectrum:

Systematic uncertainties:1. Electron energy determination

2. Background

0 200 400 600 800Ee,kin (keV)

Yie

ld(a

rb.u

nits

)

b = +0.1SM

2% of events in tail(deadlayer,external bremsstrahlung)

Yie

ld

1

101

102

103

104

105

detected Ee [keV]

0 50 100 150 200 250 300

Detector response to decayelectron with Ee = 300 keV

30

Sensitivity to left-handed S-T couplings

Present limits (n decay data)SM is in the origin of this plot

Future limits,assuming a = -0.1059(1), A = -0.1186(1) ,B = 0.9807(30), C = -0.23785(24), τn = 882.2(13) s, b = 0±0.003

Model-dependent predictions: Supersymmetry, leptoquarks, …

Analysis similar to G. Konrad, S.B. et al., ArXiv:1007.3027

neutron and nuclear decays(survey, 68% C.L.)

superallowed0+→0+ decays(68% C.L.)

“present limits”(68% C.L.)

muon decay“90% C.L.”

nuclear decays

33

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15

Sensitivity to right-handed S-T couplings

Present limits (n decay data)SM is in the origin of this plot

Future limits,assuming a = -0.1059(1), A = -0.1186(1) ,B = 0.9807(30), C = -0.23785(24), τn = 882.2(13) s

Analysis similar to G. Konrad, S.B. et al., ArXiv:1007.3027

34

35

Relevance in the LHC aera

1

b0+=-0.0022≤0.0043

p Ø e n g

bn<0.001

-0.004 -0.002 0.000 0.002 0.004-0.02

-0.01

0.00

0.01

0.02

eT

e S

LHC7, 1 fb-1

LHC7, 5 fb-1

LHC8, 15 fb-1

LHC14, 50 fb-1

-0.004 -0.002 0.000 0.002 0.004-0.02

-0.01

0.00

0.01

0.02

eT

e S

1 ∙ CMS-Search for → after pp collisions

10/2/2012

16

The Nab collaboration

R. Alarcona, L.P. Alonzib , S.B.b,c (Project Manager), S. Balascutaa, L. Barrón-Palos n, J.D. Bowmanc (Co-Spokesmen), M.A. Bychkovb, J. Byrned, J.R. Calarcoe, T. Chupp, T.V. Ciancioloc, C. Crawfordf, E. Frležb, M.T. Gerickeg, F. Glückh, G.L. Greenec,i, R.K. Grzywaczi, V. Gudkovj, D. Harrisong, F.W. Hersmane, T. Itok, M. Makelak, J. Martinl, P.L. McGaugheyk, S. McGovernb, S. Pageg, S.I. Penttiläc (On-site Manager), D. Počanićc (Co-Spokesmen), K.P. Rykaczewskic, A. Salas-Baccib, Z. Tompkinsb, D. Wagnerf, W.S. Wilburnk, A.R. Youngm

a Department of Physics, Arizona State University, Tempe, AZ 85287-1504b Department of Physics, University of Virginia, Charlottesville, VA 22904-4714c Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831d Department of Physics and Astronomy, University of Sussex, Brighton BN19RH, UKe Department of Physics, University of New Hampshire, Durham, NH 03824f Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506g Department of Physics, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canadah IEKP, Universität Karlsruhe (TH), Kaiserstraße 12, 76131 Karlsruhe, Germanyi Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996j Department of Physics and Astronomy, University of South Carolina, Columbia, SC 29208k Los Alamos National Laboratory, Los Alamos, NM 87545l Department of Physics, University of Winnipeg, Winnipeg, Manitoba R3B2E9, Canadam Department of Physics, North Carolina State University, Raleigh, NC 27695-8202n Universidad Nacional Autónoma de México, México, D.F. 04510, Méxicoi University of Michigan, Ann Arbor, MI 48109

Tasks of UVa group: Spectrometer design, Superconducting magnet, Electrodes, Magnetometry, Proton Source36

37

From the 2011 NSAC report about priorities in “Fundamental Physics with Neutrons”

Scientific Priorities

Dec 1, 2011NSAC Neutron Physics Subcommittee

Report6

(Constant effort is discussed in more detail on a later slide…)

The only experiment that requires new funding

10/2/2012

17

p+

n

e-

e

Table of contents

38

1. Production of Low Energy Neutrons

2. Experiments with Low Energy Neutrons:

• Neutron Beta Decay

• Spectroscopy of gravitationally bound quantum states

• Weak Hadronic Interaction in neutron capture on hydrogen

3. Future plans

Bound States in Physics

proton

Sun

Mercury

Venus

Earth

Moon

Mars

neutron

electron

d

d

u

Responsible for binding:Electromagnetic interaction Strong interaction Gravitational interaction

39

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18

Gravitationally Bound states – The idea

n ; 0

; otherwise

m gz zV

Height [µm]

Ene

rgy

[peV

]

0 10 20 30 400

1

2

3

4

Ψ1

Ψ2

Ψ3

Ψ4

E1 = 1.41 peV

E2 = 2.46 peV

E3 = 3.32 peV

E4 = 4.08 peV

2 nΨ Ψ Ψ

Ψ ∝ Ai ; ∙ ; , n ∙

with 2.34, 4.09, 5.52, 6.79, … ~⁄

40

V.I. Lushikov,Physics Today, June 1977

Detection of the size of the quantum states

Collimator

Absorber/Scatterer

Neutron detector

L ~10-12 cm

Inclinometers

UCN

Slit Height Measurement

Bottom mirrors (Glass)

41

25Absorber height Δh [μm]

Cou

nt r

ate

N [

Hz]

5 10

background

15 200.00

0.01

0.02

0.03

0.04

0.05

Tunneling model fit

z1z2

Results (corrected for non-parallelism):

z1 = 12.2 ± 0.7(stat) ± 1.8(syst) μm

z2 = 21.6 ± 0.7(stat) ± 2.2(syst) μm

Comparison to theory, undisturbed wave functions:

z1 = 13.7 μm, z2 = 24.0 μm

V.V. Nesvizhevsky, H. Abele, S. B. et al., EPJC 40, 479 (2005)

10/2/2012

19

Development of gravity resonance spectroscopy

Accuracy of position-type observables: ~ 10%

Improvement: do spectroscopy

; 0

; otherwise

mgz zV

E1 = 1.41 peV

E2 = 2.46 peV

E3 = 3.32 peV

Ene

rgy

[peV

]

0 10 20 30 400

1

2

3

4

Ψ1

Ψ2

Ψ3

Ψ4 E4 = 4.08 peV

Absorber Height Δh [μm]

Induce state transitions through:

• Oscillating magnetic field gradients

• Vibrations (→ QuBounce, H. Abele et al.)

• Oscillating Masses

ΔE ~ h·kHz

42

Resonance transitions = Rabi oscillations

2 2

n2n

0

( ) cos2

, defines , N N

H m gz V z tm z

H N E

01

( ) e wit( h ) Ni tN

NNt Na t H N N

Schroedingerequation:

Ansatz:

Insert in Schroedingerequation, restrict to 2 states “1” and “3”:

13

13

13 33

1 33

3 111

3 11

( )( ) ( )

(

e cos cos

e cos co)

) ( ) s(

i t

i t

i t t

i

da ta t a t

dtda t

a t a tdt

t t

13 3 1 13 1 ( ) 3V z 11 1 ( ) 1V z

33 3 ( ) 3V z

2 passage2 213 13

23 1 passage 13 2 2

13 13

sin2

P

Rabi formula:

Neglect fast self coupling and fast oscillating terms:

43

10/2/2012

20

Resonance transitions = Rabi oscillations

2 passage2 213 13

23 1 passage 13 2 2

13 13

sin2

P

Rabi formula:

0.05 0.10 0.200.15t [s]

0.0

0.2

0.4

0.6

0.8

1.0

tran

sitio

n pr

obab

ility

ω = 0.95ω13

ω = ω13

“Rabi oscillations”

passagefor 0.05 s

Resonance behavior

0.2

0.4

0.6

0.8

1.0

max

. tra

nsit

ion

prob

abil

ity

0 200 400 600ω/2π [Hz]

t passage = 0.5 st passage = 0.05 s

3 → 1

4 → 12 → 1

Transition probability at maximum for and 13 passage 13

44

Oscillating potential: Fluctuating magnetic field

0I 0

1

2I 0 0

1

2I 0I 0

1

2I 0

• • •

0I0

1

2I

Bottom mirror

0

1

2I 0 0

1

2I 0I

1 mm

1 cm

Magneticholdingfield B0

100 µm above mirror surfaceat mirror surface

-130 -120 -110 -100 -90 -80

x [mm]

-1.0

-0.5

0.0

0.5

1.0

mag

. fie

ld g

radi

ent ∂

Bz/∂z

[T

/m]

-130 -120 -110 -100 -90 -80

x [mm]

-1.0

-0.5

0.0

0.5

1.0

mag

neti

c fi

eld

[mT

]

Bz

Bx

47

10/2/2012

21

First setup to detect magnetically induced resonance transitions in flow-through mode

New UCNSource

1. Prepare initial state,ground state suppressed

3. Filter ground state2. Induce transitions in periodic magnetic field gradient

Position-sensitive

Detector

4. Measure horizontal velocity in position-sensitive detector

Bottom mirror

1. Prepare initial state (mostly the 3rd), ground state suppressed

2. Induce Transitions 3→1 in time-dependent magnetic field gradient

3. Filter ground state

4. Detect neutrons in dependence of free fall height

(corresponding to horizontal velocity, corresponding to oscillation frequency)

1 mm

1 cm

Magnetic holding field B0

Hor

izon

tal U

CN

vel

ocit

yv h

or

Mag

. Fie

ld o

scil

latio

n fr

eq. ω

48

Velocity-selective detection

Filter ground state

Position-sensitive

Detector

Measure horizontal velocity

30 cm

3 → 1

4 → 1

Monte-Carlo-Simulation, takes into account:

• 10000 incoming neutrons per incoming state

• Background: 10% in ground state

• Filter: 80 mm long, slit height: 25 μm

• Wave function evolves in free fall

• Detector resolution: 0.2 mm

Not simulated: Interference effects, Stern-Gerlach shift

Main systematic effect: Geometry G. Pignol et al., Thesis UJF Grenoble, 2009

Filter height chosen

49

10/2/2012

22

50

Systematic effects

• 3D descriptionThe previous discussion assumes time-dependent fields (so: reference frame of the incoming neutron). In reality, loss of energy in the vertical component is transferred into gain of energy in the horizontal component. We have proven that at estimated precision of Δ ⁄ ~10 , both descriptions are equivalent.

• Depolarization:Need magnetic holding field of 13 Gauss in order to stabilize spin.

• Stern-Gerlach shift:At moderate magnetic field, interplay between magnetic holding field and rotating field with amplitude

and associated field gradient with amplitude

leads to spin-dependent frequency shift, that to the first non-vanishing order is given as

The sign of this term depends on the spin state, and our system can act as a UCN polarizer.In addition, the there is a slowing down of the transition frequency.

2600 2700 2800 2900 3000 3100 3200

resonance frequency [rad/s]

0

20

40

60

80

100

max

imum

tran

siti

onpr

obab

ilit

y[%

]

numerical simulation

Rabi formula

S.B. et al., CRP 12, 707 (2011)

Δ ⁄ ~6

∙ ⋯

S.B. et al., to be published

UCNproductionvolume(est: 1000 UCN/cm3)

coldshutter

Intermediate volume(est: 320 UCN/cm3)

Collimator channel optimization:A. Mietke, V. Nesvizhevsky, S.B., et al., CRP 12, 729 (2012)

GRANITexperiment

Installation of GRANIT: New UCN Source

O. Zimmer et al, arXiV:0708.1373v2

O. Zimmer et al, PRL 107, 134801 (2011)

warmshutter

cleanroom

51

10/2/2012

23

Installation of GRANIT: In the clean room

probably dual use, interest for a UCN reflectometer

52

UVa contributors:J. Prince, A. Mietke (DAAD fellowship), D. Morton, S.B. (vice spokesperson)

Search for Chameleon fields

Quintessence: Hypothetical scalar field φ that explains the accelerated expansionof the universe.

E.g., Potential density const +… with Λ 2.4 meV,

Chameleon field: Scalar field of the type above, position dependent, with a hypothetical coupling to matter (density ρ) of the type:

const with ,

Relevant properties:• Non-linear interaction, no superposition principle• Self-shielding of macroscopic bodies: only outer shell of macroscopic bodies contributes to the

force between macroscopic bodies (this evades constraints from torsion balance experiments) 54

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Search for Chameleon fields

55

(assumed to be ΔE/E ~ 10-3)

(assumed to be ΔE/E ~ 10-7)

Excluded, high β would cause extra quantum state of UCN

Chameleon field above mirror, for high β:

ΛΛ

⁄

Consequence:

Pl

P. Brax, G. Pignol, PRL 107, 111301 (2011)

V(z

)

1. Production of Low Energy Neutrons

2. Experiments with Low Energy Neutrons:

• Neutron Beta Decay

• Spectroscopy of gravitationally bound quantum states

• Weak Hadronic Interaction in neutron capture on hydrogen

3. Future plans

p+

n

e-

e

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57

npdgamma

Weak Hadronic Interaction in neutron capture on hydrogen:

UVa contribution:• A. Mietke, J. Schaedler, S. Schroeder (DAAD fellowships), J. Prince, S.B. (EC member

and magnetic field subsystem manager)• E. Askanazi, J. Hall, E. Frlez, D. Pocanic

18.00"

spin flipper

LH2 targetbeam monitor

supermirror polarizercompensation magnet

heavy concreteshielding

segmentedCsI(Tl) detector

segmentedCsI(Tl) detector

np

γ

Bea

mst

op

main magnet coils

1. Production of Low Energy Neutrons

2. Experiments with Low Energy Neutrons:

• Neutron Beta Decay

• Spectroscopy of gravitationally bound quantum states

• Weak Hadronic Interaction in neutron capture on hydrogen

3. Future research plans:

• G-2: Responsibility for trolley magnetic field measurement in g-2 at Fermilab

• nEDM: Purification of Helium, PULSTAR

• Nab: can be used with polarized neutron beam (abBA, PANDA), ~2020

• GRANIT: Use trapping mode to achieve ultimate accuracy

p+

n

e-

e

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Summary

• Fundamental physics with neutrons has many ways to make important discoveries

• Precision measurements take time

• Nab experiment promises to determine the coupling constants of weak interaction with high precision, allowing for Standard Model Tests and Searches for “Beyond the Standard Model”-physics

• GRANIT looks for new short-range interactions.