Parity Violating Electron Scattering and the HAPPEx III experiment - PowerPoint PPT Presentation

Parity Violating Electron Scattering and the HAPPEx III experiment Mark Dalton University of Virginia Acknowledgement
to
Kent
Paschke
for
many
slides.

Ma9er
and
Interac;ons Gravity Weak Electromagne;c Strong W + ,
W ‐ ,
Z 0 γ mediator (not
found) gluons acts
on all quarks
and
leptons Electrically
charged quarks
and
gluons Strength
at 
3x10 ‐17 
m 10 ‐41 10 ‐4 1 60 Nucleus Nucleon Quark 10 ‐14 
m 10 ‐15 
m <10 ‐18 
m Atom 10 ‐10 
m electron <10 ‐19 
m

Ma9er
and
Interac;ons Electroweak Gravity Weak Electromagne;c Strong W + ,
W ‐ ,
Z 0 γ mediator (not
found) gluons acts
on all quarks
and
leptons Electrically
charged quarks
and
gluons Strength
at 
3x10 ‐17 
m 10 ‐41 10 ‐4 1 60 One
unified
framework

for
weak
and
 electromagne;c
interac;ons Nucleus Nucleon Quark 10 ‐14 
m 10 ‐15 
m <10 ‐18 
m Atom 10 ‐10 
m electron <10 ‐19 
m

Introduc;on
to
electron
sca9ering e e Electron scattering: electromagnetic interaction, described as an exchange of a virtual photon. If
photon
carries
low
momentum
 ‐>
long
wavelength p p ‐>
low
resolu;on p p Q 2 : 4-momentum of the virtual photon

Introduc;on
to
electron
sca9ering e e Electron scattering: electromagnetic interaction, described as an exchange of a virtual photon. If
photon
carries
low
momentum
 ‐>
long
wavelength p p ‐>
low
resolu;on p p Q 2 : 4-momentum of the virtual photon e e p p e e Increasing
momentum
transfer
 ‐>
shorter
wavelength ‐>
higher
resolu;on
to
observe
 p p smaller
structures

What
is
Parity
Symmetry Parity transformation x, y, z → − x, − y, − z r r r r Right handed p → − r r Left handed p , L → L , S → S Parity
transforma;on
is
analogous
to
reflec;on
in
a
 mirror: .
.
.
reverses
momentum
but
preserves
angular
 Helicity: spin in direction of motion momentum h = � S · � p = ± 1 .
.
.takes
right‐handed
(helicity
=
+1)
to
le[‐handed
 (helicity
=
‐1). Parity
symmetry :
 





interac7on
must
be
the
same
a:er
parity
transforma7on

What
is
Parity
Symmetry Parity transformation x, y, z → − x, − y, − z r r r r Right handed p → − r r Left handed p , L → L , S → S Parity
transforma;on
is
analogous
to
reflec;on
in
a
 mirror: .
.
.
reverses
momentum
but
preserves
angular
 Helicity: spin in direction of motion momentum h = � S · � p = ± 1 .
.
.takes
right‐handed
(helicity
=
+1)
to
le[‐handed
 (helicity
=
‐1). Parity
symmetry :
 





interac7on
must
be
the
same
a:er
parity
transforma7on 60 Ni 1957 – Parity Violation observed 60 Co Weak decay of 60 Co Nucleus

Charge
and
Handedness Electric
charge
determines
strength
of
electric
force Neutrinos
are
“charge
neutral”:
 do
not
feel
the
electric
force observed not observed

Charge
and
Handedness Electric
charge
determines
strength
of
electric
force Neutrinos
are
“charge
neutral”:
 do
not
feel
the
electric
force observed not observed Weak
charge
determines
strength
of
weak
force Right‐handed
par,cles
 Le#‐handed
par,cles
 (le#‐handed
an,par,cles)
 (Right‐handed
an,par,cles)
 are
“weak
charge
neutral” have
weak
charge 60 Co 60 Ni 60 Ni 60 Co right‐handed R observed L an+‐neutrino le/‐handed not observed an+‐neutrino R L

Neutral
Weak
Force Electroweak
unifica;on
implied
a
pa9ern
of
neutral
weak
charges
 with
only
one
free
parameter:
 θ W Neutral
weak
force
first
measured
in
the
early
‘70s Z
bosons
produced
in
electron‐positron
collisions:
precise
 measurements
of
Z
charge
of
most
fermions Le[‐ Right‐ q = 0, ± 1, ± 1 3, ± 2 q = 0, ± 1, ± 1 3, ± 2 γ Charge 3 3 0 T = ± 1 W
Charge 2 Z
Charge − q sin 2 θ W T − q sin 2 θ W Measurements
of
Z
mass,
Z
charges
validated
the
electroweak
theory

Electron
sca9ering,
weakly Electron
sca9ering
is
(mostly)
 e e e e electromagne;c
sca9ering. Z 0 The
weak
amplitude
is
~10 ‐6 
smaller. The
weak
quark
charges
are
different
than
the
EM
charge.
The
weak
 interac;on
can
be
a
valuable
probe
of
nuclear
ma9er,
complementary
to
 the
extensive
electromagne;c
data
set.
 Fundamental
Weak
and
EM
interac;ons
are
predicted
with
very
high
 precision,
but
with
an
apparently
incomplete
model.
Can
we
find
a
crack
 in
the
Standard
Model
in
precision
measurements
at
low
energy? The
challenge:

Isolate
the
;ny
effect
of
the
weak
interac;on.

Accessing
parity
symmetry
in
the
lab
(using
 electron
sca9ering) Look
in
mirror
and
COMPARE
to
unreflected
 p p p p p p • Incident
beam
is
longitudinally
polarized • Change
sign
of
longitudinal
polariza;on • Measure
frac;onal
rate
difference

HAPPEx
III
Parameters 30
days
of
100
μA,
85%
longitudinally
polarised
electron
beam beam
energy
=
3.1
GeV 25
cm
long
liquid
hydrogen target elas;c
sca9ering angle
=
13.7
degrees energy
=
3.1
GeV Q 2 
=
0.6
GeV 2 size
of
asymmetry
22
ppm
±1%

Superconduc;ng
Accelerator
‐
Excellent
Beam Superconduc;ng,
con;nuous
wave,
recircula;ng
linac y g r e n E 
 
 m = oscilla;ng
voltage
(1.5
GHz) 
 u V m e G i x 
 2 a polarized
 . M 1 x 
 V 5 e source G 
 6 “Cold”
RF
makes
a
clean,
 A “quiet”
beam...
perfect
for
 B Electrons

travel
in
 C precision
experiments phase
with
+field • 
1500
MHz
RF,
with
3
 interleaved
500
MHz
 beams Bending
 Linac
 magnets
in
arc tunnel

Run
forever
or
run
differently 10 14 100 KHz = 10 9 seconds ∼ 30 years Solu;on:
instead
of
coun;ng
each
electron
individually,
integrate
charge Analog
integra;on
enables
very
high
flux
detec;on • Sca9ered
electrons
directed
to
detector. • Phototube
current
integrated
over
window. Requires
a
high
degree
of
linearity
in
photomul;plier
tubes
and
ADCs Heavily
restricts
post
experimental
data
analysis

Backgrounds:
inelas;c
sca9ering 1) to suppress background from inelastics and low-energy secondaries; 2) to study the backgrounds in separate runs at or near the HAPPEX kinematics; 3) to measure the momentum transfer Q2 ; 4) to measure and monitor the attenuation in the HAPPEX detector through the use of tracking; and 5) to measure the detector amplitude weighting factors for fine bins in Q2 Spectrometer Concept: Elastic Resolve Elastic detector Inelastic Quad target Dipole Q Q

Measuring
A PV HAPPEX‐II,
in
Hall
A
at
Jefferson
Lab Strange
quark
program,
ran
2004‐2005 Forward
Angle
~6 o ,
 Q 2 
~0.1
GeV 2 Par;cle
detectors 1 H ‐1.6 
(±0.1)
ppm 4 He +7.8
 ppm 
( ± 4%) Polarimeters Croyogenic
 High
Resolu;on
 target Spectrometers

Measuring
A PV HAPPEX‐II,
in
Hall
A
at
Jefferson
Lab Strange
quark
program,
ran
2004‐2005 Forward
Angle
~6 o ,
 Q 2 
~0.1
GeV 2 Par;cle
detectors 1 H ‐1.6 
(±0.1)
ppm 4 He +7.8
 ppm 
( ± 4%) Polarimeters Croyogenic
 High
Resolu;on
 target Spectrometers

Spectrometer
and
Detector Clean
separa;on
of
elas;c
events
by
magne;c
op;cs Integra;ng
Cerenkov
Shower
Calorimeter Focal plane dispersive axis (mm) • Electromagne;c
shower
through
brass
radiator 12
m
dispersion
 • Cerenkov
light
from
shower
in
quartz
layers sweeps
away
 • Analog
integra;on
of
PMT
signal inelas7c
events Overlap
the
elas;c
line
 and
integrate
the
flux Future
Experiments
require
 new
spectrometer
concepts 14

Backgrounds: rescattering in spectrometer Dedicated runs at very low current using track reconstruction of the HRS Dipole field scan to measure the probability of rescattering inside the spectrometer Acceptance Rolloff Helium Helium QE in detector: 0.15 +/- 0.15% Helium QE rescatter: 0.25 +/- 0.15% Al fraction: 1.8 +/- 0.2% Hydrogen: Al fraction 0.75 +/- 0.25 % Hydrogen Tail + Delta rescatter: <0.1% Total systematic uncertainty contribution ~40 ppb (Helium), ~15ppb (Hydrogen)

Reversing
helicity
as
quickly
as
possible
 minimises
noise Demanding
on
the
polarised
source Pockels
cell,
voltage
controlled
retarda;on
of
laser
beam
(i.e.
anywave
plate).

 Used
to
convert
linear
polarised
laser
to
right
AND
le[
handed
circular
light. Electronics
noise
(helicity
correlated
crosstalk
and
ground
loops):
a
major
issue
‐>
 delayed
helicity
concept,
fibre
op;cs Beam helicity pairs with fixed time intervals are ordered pseudo-randomly