The NPDGamma Experimentbattlestar.phys.utk.edu/~rcgillis/presentations/rcgillis...NPDGamma!n + p !d...

NPDGamma−→n + p → d + γ

R. Chad Gillis

Outline

Introduction

Motivation

The Weak Interaction

Flavour-ConservingHadronic ParityViolation

The DDHMeson-ExchangeModel

Effective Field TheoryApproach

The Measurement

The GammaAsymmetry AγApparatus Overview

A Gamma AsymmetryMeasurement

The Beam Monitors

Spin Flipper

The Liquid HydrogenTarget

The Detector Array

Status: Present andFuture

.

The NPDGamma Experiment

R. Chad Gillis

Indiana University Department of Physics

on behalf of

The NPDGamma Collaboration

XXXIII Symposium on Nuclear PhysicsCocoyoc, Morelos, Mexico

January 2010


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

Introduction

MotivationThe Weak InteractionFlavour-Conserving Hadronic Parity ViolationThe DDH Meson-Exchange ModelEffective Field Theory Approach

The MeasurementThe Gamma Asymmetry Aγ

Apparatus OverviewA Gamma Asymmetry MeasurementThe Beam MonitorsSpin FlipperThe Liquid Hydrogen TargetThe Detector ArrayStatus: Present and Future

.


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.


The NPDGamma Reaction

+pn + d(2.2 MeV)

γ

I Incident nucleon energies of meV.

I Although partons are relativistic, ΛQCD ≈ GeV is bigenough to prevent us from using perturbation theorywhen studying the nucleon.

I Some mysteries associated with the nucleon give usideas of what measurements to make anyway.

I NPDGamma is a low-energy probe of parity violationin a purely hadronic system.


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

The Weak Interaction g

purely leptonic

νµνµ νe

µ−

−

W−

e


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.


∆S = 1 hadronic

∆I = 12 ,

32

u s

u u d u d

p

s

u

u

d

W-

d

A

π


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.


∆S = 0 hadronic

∆I = 0, 1, 2 12 ,

32

u d d

u u d u d d

u u d

n

np

d

u

u

d

W-

p


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

Flavour-Conserving Hadronic Parity Violation

I ∆I = 0, 1, 2 may give interesting results in the sameway that ∆I = 1

2 ,32 does

I The weak interaction is short range

I It is also weak enough to probe strongly-interactingsystems without affecting strong dynamics

I Since the neutral weak current conserves quark flavour,flavour-conserving processes are needed formeasurements of neutral-current weak processes inhadronic systems

I A successful theory of hadronic parity violation may giveinsight into nuclear structure by allowing for a betterunderstanding of other parity-violating effects such asanapole moments


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

The DDH Meson-Exchange Model

I In 1980, Bertrand Desplanques, John F. Donoghueand Barry R. Holstein published calculations of aweak internucleon meson exchange model

I Desplanques, Donoghue, Holstein, Annals of Physics, Vol. 124, 1980, pp. 449-495

I Analogous to a similar description that has been usedfor the residual strong interaction.

ρ, , ωπ

N

N

N

N

parity−conservingstrong vertex

+−parity−violating

weak vertex


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

Effective Field Theory Approach

I More recently, an effective field theory framework hasbeen developed

I Zhu, Maekawa, Holstein, Ramsey-Musolf, and van Kolck, Nucl. Phys. A748, 435 (2005)I C.-P. Liu, Phys. Rev. C 75, 065501 (2007)

I Unlike the meson-exchange theory, this framework ismodel independent

I EFT hides what happens at the vertex so is restricted tolower energies but is constructed to respect allnecessary symmetries

I Both pionless and pionful versions of the EFT theoryexist

I Both the meson-exchange model and the EFTframework can be constrained using difficult butpossible experiments


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

A Parity-violating Gamma-ray Asymmetry

Directional distribution of gamma-ray emission in−→n + p → d + γ:

dω

dΩ(θsk)

∝ 1 + Aγcos(θsk) + · · ·

Aγ ≈ 10−8

is mostly isotropic but also depends on the angle θskbetween neutron spin ~sn and gamma momentum ~kγ :

cos(θsk) ≡~sn · ~kγ

|~sn||~kγ |


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.



dω

dΩ(θsk) ∝ 1

+ Aγcos(θsk) + · · ·

Aγ ≈ 10−8



|~sn||~kγ |


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.



dω

dΩ(θsk) ∝ 1 + Aγcos(θsk) + · · ·

Aγ ≈ 10−8



|~sn||~kγ |


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.


pn +


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.


skθ

γ

d


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.


skθ

γ ωdd Ω sk(θ )

dd


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

The NPDGamma Apparatus

beampolarizer

monitorbeam60 Hz

Helmholtz coils provide uniform vertical magnetic field.

neutron guide

monitorbeam

monitorbeam

spin

flipper

pulsed coldneutrons

gamma detectors

2

target

LH

60 Hz SNS beam


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.


beampolarizer


neutron guide

monitorbeam

spin

flipper

neutrons

gamma detectors

pulsed cold60 Hz beam

monitor

2

target

LH

60 Hz SNS beam


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.


beampolarizer


neutron guide

monitorbeam

monitorbeam

spin

flipper

pulsed coldneutrons

gamma detectors

60 Hz

2

target

LH

60 Hz SNS beam


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.


gamma detectors


neutron guide

monitorbeam

spin

flipper

pulsed coldneutrons

60 Hz

beampolarizer

beammonitor

2

target

LH

60 Hz SNS beam


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.


gamma detectors

beampolarizer

monitorbeam60 Hz


neutron guide

monitorbeam

monitorbeam

spin

flipper

pulsed coldneutrons

2

target

LH

60 Hz SNS beam


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.


beampolarizer

monitorbeam60 Hz


neutron guide

monitorbeam

monitorbeam

spin

flipper

pulsed coldneutrons

gamma detectors

2

target

LH

60 Hz SNS beam


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

A Gamma-ray Asymmetry Measurement

AγPncosθ =[N(θ)− N(θ + π)]↑ − [N(θ)− N(θ + π)]↓[N(θ) + N(θ + π)]↑ + [N(θ) + N(θ + π)]↓

Pn= average beam polarization

Pn> 0

nn

n nnn nn

nn

n nn

CsI

nn

n

2LH

pp

pp

ppp

p

p

p

p

pppp

pp

p

π + θ

θ

I Reverse the polarization pulse-by-pulse to compare signalsin the same detector Aγ

I Flip according to the sequence ↑↓↓↑↓↑↑↓ to cancel linearand quadratic time-dependent gain drifts


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.




Pn< 0

n nn

CsI

nnnn

n

2LH

pp

p

ppp

p

p

p

p

pp

p

p

π + θ

θ

I Reverse the polarization pulse-by-pulse to compare signalsin the same detector Aγ

I Flip according to the sequence ↑↓↓↑↓↑↑↓ to cancel linearand quadratic time-dependent gain drifts


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.




Pn< 0

n nn

CsI

nnnn

n

2LH

pp

p

ppp

p

p

p

p

pp

p

p

π + θ

θ

I Other signals besides Aγ are correlated with thepolarization state and could create a false signal

I These can be catalogued and are either suppressed bydesign or can be measured


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

The Beam Monitors

I Ionization chambers containing 3HeI Placed directly in the beam.

I Produce a current signal that for a monochromaticbeam is proportional to beam flux


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

The Beam Monitors

I Ionization chambers containing 3HeI Placed directly in the beam.

I Produce a current signal that for a monochromaticbeam is proportional to beam flux

0

0.5

1

1.5

2

2.5

3

3.5

4

130 120 110 100 90 80 70 60 50 40 30 20 10

beam

mon

itor

prea

mpl

ifier

out

put (

volts

)

time (ms)

Beam Monitor Signal

(20 Hz Los Alamos beam)


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

The RF Resonant Spin Rotator

I Operates by magnetic spin resonance

I 10 gauss holding field provides vertical static field

I RF field from a 30 cm × 30 cm aluminum-shielded solenoid

I Spins precess about a horizontal axis at a rate proportional

to the oscillating field amplitude

I Since time spent

inside the solenoid is

proportional to time

of flight, the

amplitude of the RF

field is ramped as

1/tof .


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

The Liquid Hydrogen Target

I Hydrogen must be in the para molecular state to not

depolarize the beam

I Hydrogen is maintained as liquid at 17 K and is circulated

through an ortho-to-para converter by boiling off and

recondensing

I 30 cm × 30 cm cryogenic vessel


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

The Detector ArrayI 4 concentric rings of 15 cm-wide CsI cubes

I 12 detectors per ring

I Amplification is performed by vacuum photodiodes and low

noise preamps which are negligibly affected by magnetic

field fluctuations from the spin flipper


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

A Gamma Asymmetry Measurement

In agreement with past chlorine measurements:I V.A. Vesna et al.. JETP Lett. 36 (1982), p. 209.

I M. Avenier et al.. Nucl. Phys. A 436 (1985), p. 83.


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

A Gamma Asymmetry Measurement


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

Status

I We have measured the gamma asymmetry for para-hydrogenat Los Alamos:

−1.2± 2.1(stat)± 0.2(sys) × 10−7

[ M. T. Gericke et al., to be published ]

matching the precision of the only other measurement of Aγ

that was carried out at the ILL in the 1970s[ Cavaignac,Vignon,Wilson, Phys. Lett., Vol. 670, Number 2 (1977) ]

I We have measured the gamma asymmetry for chlorine which

agrees with measurements by other experimental groups

I We have measured the beam-off asymmetry to be zero at the

desired level

I We have catalogued all possible beam-on asymmetries. The

apparatus has been constructed so that they are either known

to be negligible or so that they will be measured


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

Present and Future

I We are in the process of preparing for data-taking at the SNS

in Oak Ridge, Tennessee


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.


J.D. Bowman (spokesman), S. Penttila Oak Ridge National LaboratorySalas Bacci, W.S. Wilburn, V. Yuan, G.S. Mitchell Los Alamos National LaboratoryT.R. Gentile National Institute of Standards and TechnologyR.D. Carlini Thomas Jefferson National Accelerator FacilityS. Santra Bhabbha Atomic Research CenterT. Ino, Y. Masuda, S. Muto High Energy Accelerator Research Org. (KEK)E. Sharapov Joint Institute of Nuclear ResearchB. Lauss Paul Scherrer InstitutR. Alarcon, S. Balascuta Arizona State UniversityG.L. Jones Hamilton CollegeP.-N. Seo North Carolina State UniversityS.J. Freedman University of California at BerkeleyTodd Smith University of DaytonW.M. Snow, R.C. Gillis, B. Losowki, W. McCarthy, J. Mei, H. Nann, Z. Tang Indiana UniversityC.B. Crawford University of KentuckyM.T. Gericke, S.A. Page, W.D. Ramsay University of Manitoba and TRIUMFS. Covrig, M. Dabaghyan, F.W. Hersman University of New HampshireT.E. Chupp University of MichiganG.L. Greene, R. Mahurin, J. Dadras, N. Fomin, M. Musgrave University of TennesseeL. Barron Palos Universidad Autonoma de Mexico


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

Supplementary Slides


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

The ∆I = 12 ruleg

I Consider two similar strangeness-violating decays.

I Look at possible isospin changes.

Λ0 → pπ−

Λ0 → nπ0

I = 0 → I =1

2,

3

2

I pπ− and nπ0 are of definite I3, but not of definite I

I Predict the ratio of rates, for each isospin-changingchannel separately.

if ∆I = 12 if ∆I = 3

2 PDGΓ(Λ0→pπ−)Γ(Λ0→nπ0)

2 12 1.78± 0.03

I The same issue exists for other ∆S = 1 decays.


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

Beam-dependent systematic effects

reaction correlation direction size−→n + p → d + γ sn · kγ U-D 1 ×10−8

−→n + p → −→n + p k′n · sn × kn L-R 2 ×10−10

−→n + p → d + γ k′γ · sn × kn L-R 2 ×10−11

−→n + p → d + γ sγ · sn U-D 1 ×10−10

−→n → p + e− + νe sn · ke U-D 3 ×10−11

−→n + d → t + γ sn · kγ U-D 1 ×10−10

−→n + p → −→n + p k′n · sn × kn L-R 1 ×10−10

−→n + 6Li→ α + t sn · k′ U-D 2 ×10−11

(µn · 5) B (sn · 5) B U-D 1 ×10−10

−→n + A→−−−→A + 1→ sn · ke U-D 1 ×10−10

(A + 1) + e− + νe

Table from: W. M. Snow et al., Fundamental Physics with Pulsed Neutron Beams, World Scientific,2001, pp. 203-213, Editors C. R. Gould, G. L. Greene, F. Plasil, W. M. Snow


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

The n + 3He reactionI Cross section is huge (kilobarns at thermal energies) with

clean 1/v dependence.

I Only kinetic energy is released. Products do not leavethe chamber.

I Response to gamma background is negligible.

n + 3He p + t + 764 keV

He4

Jπ 0+=

Jπ 0+=

20.6 MeV

0.5 MeV

energy

0 MeV

ground state

20.2 MeV


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

3He As a Polarization Analyzer

I Resonance occurs only if J=0 (antiparallel spins)

I Allows 3He to be used to polarize the beam, to measure

beam polarization and to measure the efficiency of the spin

flipper

I Use beam monitors to measure the transmission of the

beam through a glass cell containing polarized 3He

Jπ 0+=

12

π = +J 12

π = +J

n + 3He p + t + 764 keV

He4

Jπ 0+=

20.2 MeV

20.6 MeV

0.5 MeV

energy

0 MeV

ground state


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

3He As a Polarization Analyzer

I Resonance occurs only if J=0 (antiparallel spins)

I Allows 3He to be used to polarize the beam, to measure

beam polarization and to measure the efficiency of the spin

flipper

I Use beam monitors to measure the transmission of the

beam through a glass cell containing polarized 3He

A beam polarizerused at LANSCE.


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.


Ratio of axial vector to vector

couplings is altered by QCD from the

Standard Model’s V-A law.

u d

u u d

p

d

u

W-

d

n

e νe

e νe


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.


I In 1980, Bertrand Desplanques, John F. Donoghueand Barry R. Holstein published calculations of aweak internucleon meson exchange model

I Desplanques, Donoghue, Holstein, Annals of Physics, Vol. 124, 1980, pp. 449-495

I Analogous to a similar description that has been usedfor the residual strong interaction.

ρ, , ωπ

N

N

N

N



weak vertex


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.


I Based on the quark model, it involves the π+, π−, ρand ω mesons.

I One vertex is strong (PC) while the other is weak(PV).

I Weak couplings strong couplings.

ρ, , ωπ

N

N

N

N



weak vertex


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.


I Considerable theoretical uncertainty (≈ 100%)remains in the calculated weak couplings.

I Of particular interest is pion exchange whichcharacterizes the long-range component of theinternucleon interaction.

π+−

N

hπ1 gπΝΝ

N N

N


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

Current Status of h1π knowledgeunits: ×10−7

-2 0 2 4 6 8 10 12 14

h1

- 0.12 h1

- 0.18 h1

-5

0

5

10

15

20

25

30

-(h

0+

0.7

h0 )

p

133Cs

19F

205Tl

18F

Haxton, Liu, Ramsey-Musolf. Phys. Rev. Lett. 86, 5247− 5250 (2001)


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

Requirements for the NPDGamma Apparatus

I Aγ ≈ 10−8 → need N ≈ 1010 events/s in gammadetectors

I Detectors must run in current modeI Detectors must subtend a large solid angle about the

target

I The observable is dependent on the orientation of theneutrons

I To extract Aγ , the neutron beam must have a knownnonzero polarization

I The beam must not lose its polarization between thepolarizer and a capture in the target


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

Requirements for the NPDGamma Apparatus

I The apparatus must observe tiny differences in gammasignal despite physical limitations such as variations inthe gain of gamma detectors.

I The apparatus must not be prone to false signals fromsources such as

I electronic noise that is correlated with beampolarization state;

I background from capture in materials of the apparatusthat possess their own Aγ ;

I other beam polarization-dependent observables that arenot Aγ .


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

The Supermirror PolarizerI Compared to 3He polarizers, supermirror polarizers

provide:I higher beam polarization ≈ 95 %I higher transmission ≈ 30 %I wider beam acceptance for our 10 cm × 12 cm guide

allowing for a factor of 4 improvement in polarizerfigure of merit

I Recent improvements in supermirror technology allowthe entire phase space of our beam to be polarized

Supermirrors used in the n-4He spin rotation experiment at NIST


R. Chad Gillis

Outline

Introduction

Motivation





The Measurement



The Beam Monitors

Spin Flipper


The Detector Array


.

Systematic Errors

I The polarization-dependent signal is isolated by rapidlyreversing beam polarization

I Other signals besides Aγ are correlated with thepolarization state and can contribute a false signal

I Beam-off false asymmetries may existI These are caused by changes in the gain or offset in the

detectorsI They are verified to be zero at the desired level by quick

beam-off measurements (in ≈ a day)

I Polarization-dependent beam-on signals that are not Aγ

also existI These can be catalogued by examining all possible

cartesian invariants that depend on neutron spin andenergy deposition in the detector

I They involve known physics or can be measuredI They can be suppressed by appropriate construction of

the apparatus

The NPDGamma Experimentbattlestar.phys.utk.edu/~rcgillis/presentations/rcgillis...NPDGamma!n + p !d...

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Transcript of The NPDGamma Experimentbattlestar.phys.utk.edu/~rcgillis/presentations/rcgillis...NPDGamma!n + p !d...