r. michaels, jlab doe s&t 2012 parity violation at jefferson lab prex, moller, & pvdis...

R. Michaels, JlabDOE S&T 2012

Parity Violation at Jefferson Lab PREX, MOLLER, & PVDIS

Experiments

Robert Michaels Hall A

1/16


Parity Violating Asymmetry 2410~ QALR

LRPV

0Ze e

+

2

Applications of APV at Jefferson Lab

• Nucleon Structure

• Test of Standard Model of Electroweak

• Nuclear Structure (neutron density)

W2sin

APV from interference

Strangeness s s in proton (HAPPEX, G0 expts)

e – e (MOLLER) , e – q (PVDIS) elastic e – p at low Q2 (QWEAK)

208Pb 208Pb

PREX

This talk

e - 208Pb2/16


How to do a Parity Experiment

Flux Integration Technique:HAPPEX: 2 MHzPREX: 500 MHz

(integrating method)

Example : HAPPEX

3/16


• Offline asymmetries nearly identical to online.

• Corrections tiny (here, 3 ppb)

• Errors are statistical only

Parity Violating Asymmetry

Asy

mm

etr

y (p

pm

)

Slug

Small beam-related Systematics -- thanks to Jlab beam quality

(HWP = optical element used to flip beam helicity, helps suppress some systematics)

HAPPEX-II data

HAPPEX-II data

Araw = -1.58 ppm 0.12 (stat) 0.04 (syst)

4/16

(~1 day)

D. Lhuillier, K. Kumar spokespersons


Slug # ( ~ 1 day)

Un

its:

m

icro

ns

RLhelicityforXX LR ,

Parity Quality Beam : Unique Strength of JLab

Helicity – Correlated Position Differences

Sign flips provide further suppression : Average with signs = what experiment feels

achieved < 5 nm

Points: Not sign-corrected. 20-50 nm diffs. with pol. source setup & feedback

Araw

= Adet

- AQ +

E+

i x

i

Plotted below

Measured separately

Sign flips using ½ wave plate & Wien filter ++ -+ +- --This BPM, Average = 2.4 3.1 nm

PREX data

5/16


PREX : Z0 of weak interaction : sees the neutrons

proton neutron

Electric charge 1 0

Weak charge 0.08 1

Neutron form factor

)()(4

1)( 0

32 rqrjrdQF NN

Parity Violating Asymmetry

)(

)(sin41

22 2

22

2

QF

QFQGA

P

NW

F

0

T.W. Donnelly, J. Dubach, I. Sick

C.J. Horowitz

Nucl. Phys. A 503, 589, 1989

C. J. Horowitz, S. J. Pollock, P. A. Souder, R. Michaels Phys. Rev. C 63, 025501, 2001

6/16


PREX & Neutron Stars

pn RR

Crab Pulsar

C.J. Horowitz, J. Piekarewicz

RN calibrates equation of state (pressure vs density) of Neutron Rich Matter

Combine PREX RN with Observed Neutron Star Radii

Some Neutron Stars seem too cold

Strange star ? Quark Star ?

Explained by Cooling by neutrino emission (URCA process) ?

0.2 fm URCA probable, else not

Phase Transition to “Exotic” Core ?

7/16


Physics Asymmetry

CEBAFHall AJLAB

Pol. Source Statistics limited ( 9% ) Systematic error goal

achieved ! (2%)

)(014.0)(060.0

656.0

syststat

ppmA

Septum Magnet

HRS + septum

Pb target

HRS

Pb target

50

PREX PRL 108 (2012) 112502Results

8/16


Neutron Skin = RN - RP = 0.33 + 0.16 - 0.18 fm

Establishing a neutron skin at ~95 % CL

Asymmetry leads to RN

proposed

published

Also considering a new 48Ca proposal

Spokespersons K. Kumar R. Michaels K. Paschke P. A. Souder G. Urciuoli

9/16


12 GeV Parity Program

• MOLLER (e-e scattering)

• PVDIS (e-q scattering)

• Fundamental tests of electroweak theory

10/16

R. Michaels, JlabDOE S&T 2012 11

MOLLER

Ebeam = 11 GeV

APV = 35.6 ppb

δ(APV) = 0.73 parts per billion

δ(QeW) = ± 2.1 % (stat.) ± 1.0 % (syst.)

75 μA 80% polarized

Moller (e-e) Scattering: Search for New Physics at the TeV Scale

best contact interaction reach for leptons at low OR high energy

To do better for a 4-lepton contact interaction would require: Giga-Z factory, linear collider, neutrino factory or muon collider

Luminosity: 3x1039 cm2/s!

+

LH2 5-10 mrad11 GeV Beam

Credit: Krishna Kumar

11/16


Error bar σA/A (%) at bins in Q2, x

Standard Model test in the e – quark couplings.

Novel window on QCD using a broad kinematic scan to unfold

hadronic effects (CSV, higher twist)

Project is still at an early planning stage

Credit: Paul Souder

SOLID Spectrometer for PVDIS

Q2

(Ge

V2)

12/16


Interplay with LHC: New Physics

Does Supersymmetry provide a candidate for dark matter?

RPVSUSY

MSSM

Ramsey-Musolf and Su, Phys. Rep. 456 (2008)

•Virtually all GUT models predict new Z’s•LHC reach ~ 5 TeV, but....•For ‘light’ 1-2 TeV, Z’ properties can be extracted

Suppose a 1 to 2 TeV heavy Z’ is discovered at the LHC

•Can we point to an underlying GUT model?

J. Erler and E. Rojas

Assume either SUSY or Z ’ discovered at LHC

Not if Nature lies in RPV SUSY space rather than MSSM space

TeV-Scale Z/

13/16


Interplay with LHC: EW Physics

precise enough to affect the central value of the world average

MOLLER projected δ(sin2θW) = ± 0.00026 (stat.) ± 0.00012 (syst.)

mW and sin2ϴW are powerful indirect probes of the mH

use standard model electroweak radiative corrections to evolve best measurements to Q ~ MZ

14/16


MOLLER Status

• ~ 150 GHz scattered electron rate– Idea is to flip Pockels cell ~ 2 kHz– 80 ppm pulse-to-pulse statistical

fluctuations

• 1 nm control of beam centroid on target– Improved methods of “slow helicity

reversal”

• > 10 gm/cm2 liquid hydrogen target– 1.5 m: ~ 5 kW @ 85 μA

• Full Azimuthal acceptance with ~ 5 mrad– novel two-toroid spectrometer– radiation hard, highly segmented

integrating detectors

• Robust and Redundant 0.4% beam polarimetry– Compton and Moller Polarimeters

• MOLLER Collaboration

– ~ 100 authors, ~ 30 institutions

– Expertise from SAMPLE A4, HAPPEX, G0, PREX, Qweak, E158

– 4th generation JLab parity experiment

Director’s Review chaired by C. Prescott: positive endorsement

Technical Challenges

•~ 20M$ project funding sought• 3-4 years construction• 2-3 years running

thanks, Krishna Kumar15/16

lab


Conclusions : Parity-Violation at Jefferson Lab

Jefferson Lab is a great place to do parity-violation. Leverages the strengths of the polarized source and superconducting RF accelerator.

Parity experiments provide• Unique information about structure of

nucleon ( strangeness content )

nuclei ( neutrons ) PREX

• Precision Frontier of Standard Electroweak Model

complementary to LHC.

Robert Michaels Hall A

not discussed

MOLLER, SOLID-PVDIS


appendix


Property Upstream MollerConcept 2

Qweak

Field Integral (Tm) 0.15 1.1 0.89

Total Power (kW) 40 765 1340

Current per wire (A) 298 384 9500

Voltage per coil (V) 19 285 18

Current Density (A/cm2) 1200 1550 500

Wire cross section (ID: water hole) (in)

0.229x0.229(0.128)

0.229x0.229(0.128)

2.3x1.5 (0.8)

Weight of a coil (lbs) 44 555 7600

Magnetic Forces (lbs) 100 3000 27000

Magnet Concepts :• increased the size of the water cooling hole• simplified layout with slightly larger conductor• current density fine with sufficient water flow• water-cooling achievable• weight and magnetic forces modest• still need work on support structure and water/electrical connections

Ongoing studies (students/postdocs) :• optimize the optics• position sensitivity studies• magnetic forces for asymmetric coils

MOLLER Spectrometer Design Progress


SoLID PVDIS Progress• CLEO-II magnet fulfills requirements of SoLID PVDIS and SoLID SIDIS.

Preliminary discussions about procuring magnet from Cornell have been started.

• Baffles: workable concept has been developed for the baffle assembly.

• GEM prototyping on going at UVa and several Chinese institutions (USTC, CIAE, Tsinghua U, Lanzhou U,IMP).

• Cherenkov conceptual design with two readout options (PMT/GEM).

• Shashlyk type EM Calorimeter R&D ongoing by user institutions, collaboration with IHEP from Russia.

• A Geant4 simulation framework, GEMC, is successfully applied.• Analysis Software: Tracking framework and calibration methods

being developed • Aiming for a Director’s Review in Fall 2012


( R.J. Furnstahl )

Measurement at one Q is sufficient to measure R

2

N

proposed error

Why only one parameter ?

(next slide…)

PREX:


ZN

Nuclear Structure: Neutron density is a fundamental observable that remains elusive.

Reflects poor understanding of symmetry energy of nuclear matter = the energy cost of

xn

)21()()2/1,(),( 2xnSxnExnE

n.m. density

ratio proton/neutrons

• Slope unconstrained by data

• Adding R from Pb will significantly reduce the dispersion in plot.

N208

Slide adapted from J. Piekarewicz


Skx-s15Thanks, Alex Brown

PREX Workshop 2008

E/N

N



PREX Workshop 2008

E/N

N


Diamond LEAD

Lead / Diamond Target

• Three bays

• Lead (0.5 mm) sandwiched by diamond (0.15 mm)

• Liquid He cooling (30 Watts)


Performance of Lead / Diamond Targets

Last 4 days at 70 uA

Targets with thin diamond backing (4.5 % background) degraded fastest.

Thick diamond (8%) ran well and did not melt at 70 uA.

meltedmelted

NOT melted

Solution: Run with 10 targets.


Error Source Absolute (ppm)

Relative ( % )

Polarization (1) 0.0083 1.3

Beam Asymmetries (2) 0.0072 1.1

Detector Linearity 0.0076 1.2

BCM Linearity 0.0010 0.2

Rescattering 0.0001 0

Transverse Polarization 0.0012 0.2

Q2 (1) 0.0028 0.4

Target Thickness 0.0005 0.112C Asymmetry (2) 0.0025 0.4

Inelastic States 0 0

TOTAL 0.0140 2.1

Systematic Errors

(1) Normalization Correction applied

(2) Nonzero correction (the rest assumed zero)

)(014.0)(060.0

656.0

syststat

ppmA

PREX-I Result

Statistics limited ( 9% )

Systematic error goal achieved ! (2%)

Physics Asymmetry

A physics letter was recently accepted by PRL.

PRL 108 (2012) 112502


Collimators

Septum Magnet

target

HRS-L

Q1

HRS-R

Q1

Improvements for PREX-II

Location of ill-fated O-Ring which failed & caused significanttime loss during PREX-I

PREX-II to use all-metal seals

Tungsten Collimator & Shielding

Region downstream of target


Geant 4 Radiation CalculationsPREX-II shielding strategies

Number of Neutrons per incident Electron

Strategy

• Tungsten ( W ) plug

• Shield the W

• x 10 reduction in 0.2 to 10 MeV neutrons

00 37.0

0 - 1 MeV

Energy (MeV)

Energy (MeV)

Energy (MeV)

--- PREX-I--- PREX-II, no shield--- PREX-II, shielded

1 - 10 MeV

10 - 1200 MeV

beamline

shielding

scattering chamber

49


Halfwave plate (retractable, reverses helicity)

LaserPockel Cell flips helicity

Gun

GaAs Crystal

e beam-

• Based on Photoemission from GaAs Crystal

• Polarized electrons from polarized laser

• Need :

Polarized Electron Source

• Rapid, random helicity reversal• Electrical isolation from the rest of the lab• Feedback on Intensity Asymmetry


P I T A Effect

)sin( IA Laser at Pol. Source

Polarization Induced Transport Asymmetry

yx

yx

TT

TT

where

Transport Asymmetry

Intensity Asymmetry

drifts, but slope is ~ stable. Feedback on

Important Systematic :

28/53


Methods to Reduce Systematics

A rotatable /2 waveplate downstream of the P.C. allows arbitrary orientation of the ellipse from DoLP

A simplified picture: asymmetry=0 corresponds

to minimized DoLP at analyzer

Perfect DoCP

Scanning the Pockels Cell Scanning the Pockels Cell voltage = scanning the voltage = scanning the residual linear polarization residual linear polarization ((DoLPDoLP))

Inte

nsit

y A

sym

metr

y

(pp

m)

Pockels cell voltage offset (V)


/)( AA

Pull Plot (example)

PREX Data


Corrections to the Asymmetry are Mostly Negligible

• Coulomb Distortions ~20% = the biggest correction.

• Transverse Asymmetry (to be measured)

• Strangeness

• Electric Form Factor of Neutron

• Parity Admixtures

• Dispersion Corrections

• Meson Exchange Currents

• Shape Dependence

• Isospin Corrections

• Radiative Corrections

• Excited States

• Target Impurities

Horowitz, et.al. PRC 63 025501

r. michaels, jlab doe s&t 2012 parity violation at jefferson lab prex, moller, & pvdis...

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