Transcript First data with FROST Michael Dugger* Arizona State University *Work at ASU is supported by the U.S.

First data with FROST
Michael Dugger*
Arizona State University
*Work at ASU is supported by the U.S. National Science Foundation
M. Dugger, Jlab User Meeting, June 2012
1
Outline
• General motivations
• Polarization observables to be discussed
• Experimental details
• Preliminary results for several
polarization observables
• Conclusions
M. Dugger, Jlab User Meeting, June 2012
2
Motivation: Baryon resonances
• Masses, widths, and coupling constants
not well known for many resonances
• Many models: relativised quark model,
Goldstone-boson exchange, diquark and
collective models, instanton-induced
interactions, flux-tube models, lattice
QCD…
• Big Puzzle: Most models predict more
resonance states than observed
M. Dugger, Jlab User Meeting, June 2012
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Observables to be shown
• γ p → p π0
• γ p → n π+
•γp→pη
• γ p → K+ Λ
• γ p → K+ Σ0
• γ p → p π + π-
E
E, G
E
E, Σ, G
E
Is, Pz, P○z
M. Dugger, Jlab User Meeting, June 2012
Single
pseudoscalar
photoproduction
4
Isospin overlaps for reactions
involving π0 and π+
• Differing isospin overlaps of N* and Δ+ for the π0 p and π+ n final states
• The π0 p and π+ n final states can help distinguish between the Δ and N*
Δ+
N*
 0  p : 2 / 3 I  32 , I 3  12  1 / 3 I  12 , I 3  12
   n : 1 / 3 I  32 , I 3  12  2 / 3 I  12 , I 3  12
M. Dugger, Jlab User Meeting, June 2012
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“Isospin filters”
• Resonance spectrum has many broad overlapping states
• The ηp and K+Λ systems have isospin ½ and limit one-step
excited states of the proton to be isospin ½. The final states ηp
and K+Λ act as isospin filters to the resonance spectrum.
γ p → π+ n
γp→ηp
M. Dugger, Jlab User Meeting, June 2012
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Self-analyzing reaction K+ Y (hyperon)
• The weak decay of the hyperon allows the extraction of the
hyperon polarization by looking at the decay distribution of the
baryon in the hyperon center of mass system:
I i (cosi )  12 1  PYi cosi 
where Ii is the decay distribution of the baryon, α is the weak decay
asymmetry (αΛ= 0.642 and αΣ0 = -⅓ αΛ), and PYi is the hyperon
polarization.
• We can obtain recoil polarization information without a recoil
polarimeter and the reaction is said to be “self-analyzing”
M. Dugger, Jlab User Meeting, June 2012
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Helicity amplitudes for γ + p → p + pseudoscalar
• 8 helicity states: 4 initial, 2 final → 4∙2 = 8
• Amplitudes are complex but parity symmetry reduces independent numbers to 8
• Overall phase unobservable → 7 independent numbers
•HOWEVER, not all possible observables are linearly independent and it turns out
that there must be a minimum of 8 observables / experiments
 A11
A
 A21
A12 
A22 
Final helicity
Initial helicity
helicity +1 photons (ε+):
3
2
A  
1
2
1
2
 H1

 H3
1
2
helicity -1 photons (ε-):
A
 , 
 e   A ,

H 2
 Parity symmetry → A  
H 4
M. Dugger, Jlab User Meeting, June 2012
1
2
1
2
1
2
 H4
H
2

3
2
 H 3

H1 
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Helicity amplitudes and observables for single
pseudoscalar photoproduction
Differential cross section
Beam polarization
Target asymmetry
Recoil polarization
g9a
g9b
Double polarization observables
• Need at least 4 of the double
observables from at least 2 groups for a
“complete experiment”
• π0p, π+ n, and η p will be nearly
complete
• K+ Λ will be complete!
M. Dugger, Jlab User Meeting, June 2012
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Photoproduction of π+ π- p states
• 64 observables
• 28 independent relations related to helicity amplitude magnitudes
• 21 independent relations related to helicity amplitude phases
• Results in 15 independent numbers
Good for discovering
resonances that decay
into other resonances!
M. Dugger, Jlab User Meeting, June 2012
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Finding missing resonances
requires lots of different
observables. Cross sections are not
enough.
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Outline
• General motivations
• Polarization observables to be discussed
• Experimental details
• Preliminary results for several
polarization observables
• Conclusions
M. Dugger, Jlab User Meeting, June 2012
Bremsstrahlung photon tagger
• Jefferson Lab Hall B
bremsstrahlung
photon tagger
• Eγ = 20-95% of E0
• Eγ up to ~5.5 GeV
• Circular polarized
photons with
longitudinally
polarized electrons
• Oriented diamond
crystal for linearly
polarized photons
61 backing counters
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Counts
Circular beam polarization
• Circular photon beam
from longitudinally
polarized electrons
Circular polarization from 100% polarized electron beam
Circular polarization
• Electron beam
polarization > 85%
4k  k 2
P  Pe 
4  4k  3k 2
k = Eγ/Ee
H. Olsen and L.C. Maximon, Phys. Rev. 114, 887 (1959)
M. Dugger, Jlab User Meeting, June 2012
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Linearly polarized photons
• Coherent bremsstrahlung from
50 μ oriented diamond
• Two linear polarization states
(vertical & horizontal)
•Analytical QED coherent
bremsstrahlung calculation fit to
actual spectrum
(Livingston/Glasgow)
• Vertical 1.3 GeV edge shown
• Currently, only very preliminary
values of Pγ
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FROST in Hall B
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FROST target
• Butanol composition: C4H9OH
• Each bound proton is paired with a
bound neutron → No polarization of
the bound nucleons
• Carbon target used to
represent bound nucleon
contribution of butanol
M. Dugger, Jlab User Meeting, June 2012
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Target polarization
• Frozen spin butanol (C4H9OH)
• Pz ≈ 80%
• Target depolarization: τ ≈100 days
• For g9a (longitudinal orientation) 10% of allocated time was used
polarizing target
• For g9b (transverse orientation) 5% of allocated time was used
polarizing target
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S. Strauch
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FROST running conditions
g9a: First running of FROST
g9b: Second running of FROST
• Longitudinally polarized target • Transversely polarized target
• Circular and linear photon
polarization
• Circular and linear photon
polarization
M. Dugger, Jlab User Meeting, June 2012
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Outline
• General motivations
• Polarization observables to be discussed
• Experimental details
• Preliminary results for several
polarization observables
• Conclusions
M. Dugger, Jlab User Meeting, June 2012
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Dilution factor and helicity asymmetry E
Theoretically:
d d 0
1  Pz PC E 

d d
Experimentally:
→
1
E
PZ PC d
E
 1/ 2   3 / 2
Pz PC  1/ 2   3 / 2 
 Y1/ 2  Y3 / 2 


Y

Y
 1/ 2 3 / 2 
where Y represents yield and d is the dilution, which is the
ratio of hydrogen events to total events:
YH
d
Ybound  YH
Note: Bound nucleons have no polarization → Ebound = 0
M. Dugger, Jlab User Meeting, June 2012
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γp→pη
• Arizona State University
• Brian Morrison, Michael Dugger, and Barry Ritchie
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Helicity asymmetry for η
photoproduction at threshold
• S11(1535) dominates at threshold
• Since the S11(1535) is an L=0, s = ½,
resonance, this resonance can only
couple to helicity = ½ initial state.
• S11 dominance forces E ≈ 1.0 at, and
near, threshold for all scattering angles
• Provides an analytic check
M. Dugger, Jlab User Meeting, June 2012
 1/ 2   3 / 2
E
 1/ 2   3 / 2
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Counts
Scale factors
Butanol
γ p →p π+ π- X
m2X(GeV2)
Bound nucleon events
Counts
Butanol
Carbon
z (cm)
Scale factors = Butanol/Carbon
M. Dugger, Jlab User Meeting, June 2012
Sample η fits from γ p → p X
N1/2 - N 3/2
Counts
Counts
N1/2 + N 3/2
• W = 1525 MeV
• cos(θc.m.) = -0.3
mX (GeV)
mX (GeV)
Counts
Scaled carbon
mX (GeV)
M. Dugger, Jlab User Meeting, June 2012
E at threshold for p η
γ+ p → p + X
p0= 1.00 ± 0.04
PRELIMINARY
γ + p → p + X (n.c.)
p0= 1.02 ± 0.04
SAID
MAID
Bonn-Gatchina
PRELIMINARY
• W = 1525 MeV
γ + p → p + X (γ det.)
p0= 0.99 ± 0.04
PRELIMINARY
γ + p → p + X (γ det. n.c.)
p0= 0.98 ± 0.04
PRELIMINARY
cos(θc.m.)
*n.c. implies no charged particles other than the proton.
M. Dugger, Jlab User Meeting, June 2012
• All have E=1,
within statistical
uncertainties
☺
E
Helicity asymmetry at fixed energies
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
SAID
MAID
Bonn-Gatchina
Preliminary data
prefers SAID for
W >1.75 GeV
cos(θc.m.)
M. Dugger, Jlab User Meeting, June 2012
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γ p → π+ n
• University of South Carolina
• Steffen Strauch
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E: γ p→π+ n for W = 1.25 to 1.70 GeV
Preliminary
Data
Preliminary
Data
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E: γ p → π+ n for W = 1.70 to 2.25 GeV
Preliminary Data
For W< 1.75 GeV all of the models represent the data fairly well.
For W> 1.75 GeV none of the models represents the data well.
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γ p → p π0
• The George Washington University
• Hideko Iwamoto and Bill Briscoe
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First data with FROST
W = 1.465 GeV
W = 1.433 GeV
W = 1.528 GeV
W = 1.497 GeV
W = 1.558 GeV
M. Dugger, Jlab User Meeting, June 2012
W = 1.588 GeV
First data with FROST
W = 1.617 GeV
W = 1.674 GeV
W = 1.646 GeV
W = 1.702 GeV
W = 1.730 GeV
W = 1.809 GeV
W = 1.756 GeV
W = 1.783 GeV
M. Dugger, Jlab User Meeting, June 2012
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First data with FROST
W = 1.835 GeV
W = 1.885 GeV
W = 1.959 GeV
W = 1.860 GeV
W = 1.910 GeV
W = 1.934 GeV
W = 1.994 GeV
W = 2.041 GeV
• Agreement with models breaks down for W > 1850 MeV
M. Dugger, Jlab User Meeting, June 2012
γ p → K+ Λ and γ p→ K+ Σ0
• Catholic University of America
• Liam Casey and Franz Klein
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Helicity asymmetry E for K+ Λ
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Helicity asymmetry for K+ Λ
• None of the models represents the data well
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Helicity asymmetry for K+ Σ0
• Models represents the data better than for K+ Λ
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Σ and G observables
d d 0
1  PT  cos( 2 )  PT Pz G sin( 2 ) 

d d
• Σ is a single polarization observable (beam asymmetry)
• G is a double polarization observable
M. Dugger, Jlab User Meeting, June 2012
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γ p → π+ n
• The University of Edinburgh
• Jo McAndrews and Dan Watts
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+n
Example
of
extraction
for
G
for
π
G Observable Extraction
Create an asymmetry and fit a function to obtain G:
p3 = pγpzfG
PRELIMINARY!
PRELIMINARY!
Asymmetry -ve polarised target
Asymmetry +ve polarised target
M. Dugger, Jlab User Meeting, June 2012
Preliminary results of G for π+ n
PRELIMINARY
PRELIMINARY
PRELIMINARY
Early stage results
with very preliminary
linear beam
polarization values

PRELIMINARY
PRELIMINARY
M. Dugger, Jlab User Meeting, June 2012
γp→
+
K
Λ
• University of Glasgow
• Stuart Fegan and Ken Livingston
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Σ for K+ Λ
• Since the beam asymmetry Σ
does not rely upon target
polarization, bound nucleons
can have Σ ≠ 0
PRELIMINARY
• Dilution must be carefully
determined
• The beam asymmetry is used
only for purposes of checking
data consistency
PRELIMINARY
M. Dugger, Jlab User Meeting, June 2012
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PγPzG for K+ Λ
• Eγ = 1.5 GeV
PRELIMINARY
• Can clearly see sign change
between +z and –z target
polarization data
PRELIMINARY
M. Dugger, Jlab User Meeting, June 2012
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γ p → p π+ π• Florida State University
• Sungkyun Park and Volker Crede
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γ p → p π+ π-
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γ p → p π+ π-
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IS for p π+ π-
φπ+
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P○z for p π+ π-
M. Dugger, Jlab User Meeting, June 2012
φπ+
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Pz for p π+ π-
φπ+
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Pz for p π+ π-
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φπ+
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FROzen Spin Target “FROST” (g9b)
 Transversely polarized target
• Beam: Circular polarization; Linear polarization; Un-polarized
• Data obtained for Σ, F, H, P and T (for pseudoscalars)
• Data is in calibration phase right now
Beam
Target
Circular Transverse
Linear Transverse
Observable
d d 0

1  Pxylab P F cos(    )  PxylabT sin(    )
d d


d d 0

1  PT  cos( 2 )  Pxylab PT H cos(    ) sin( 2 )
d d

 PxylabT sin(  )  Pxylab PT P sin(  ) cos(2)
σ0 = unpolarized cross section, PT = transverse beam polarization
P0= circular polarization, Pz= longitudinal target polarizaion
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
A very early look at
T for γ p → π+ n
• Arizona State University
• Michael Dugger and Barry Ritchie
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A quick attempt at T from
uncalibrated CLAS data
• Used only 2 uncalibrated runs
T = -0.34 ± 0.09
• Eγ from 0.65 to 1.2 GeV
• cos(θπc.m.) = 0.95
TSAID = -0.440
• Target offset (in φ) is within one
standard deviation of the set value (60 degrees)
• The measured value of T is within
1.14 standard deviations of SAID
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Conclusion
• Models fit preliminary FROST pion helicity asymmetry data best when
W < 1.75 GeV
• Preliminary FROST helicity asymmetry data for η p favors SAID for
W > 1.75 GeV
• None of the models shown represents the K+ Λ data well but do much better for
K+ Σ0
• Σ and G measurements are at an early stage of analysis and use very preliminary
linear beam polarization values, but are progressing nicely
• There is lots of data for the π+ π- p channel, and the preliminary IS observable
from FROST compares well with g8b
• Very preliminary looks at data from the second running of FROST (transverse
target) are promising
M. Dugger, Jlab User Meeting, June 2012
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Acknowledgements
✦ NSF
✦ DOE
✦ CLAS Collaboration
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Status of meson photoproduction
σ Σ
T
P E
F
G H Tx
Tz Lx
Lz O O C C
x
z
x
z
Proton target
pπ0
✔ ✓ ✓
✓ ✓
✓
✓
✓
nπ+
✔ ✓ ✓
✓ ✓
✓
✓
✓
pη
✔ ✓ ✓
✓ ✓
✓
✓
✓
pη’
✔ ✓ ✓
✓ ✓
✓
✓
✓
pω
✔ ✓ ✓
✓ ✓
✓
✓
✓
K+Λ
✔ ✓ ✓
✔ ✓
✓
✓
✓
✓
✓
✓
✓
✓ ✓ ✔ ✔
K+Σ0
✔ ✓ ✓
✔ ✓
✓
✓
✓
✓
✓
✓
✓
✓ ✓ ✔ ✔
✓
✓
K0*Σ+ ✔ ✓
Neutron target
pπ-
✔ ✓ ✓
✓
✓
✓
✓
pρ-
✓ ✓ ✓
✓
✓
✓
✓
K-Σ+
✓ ✓ ✓
✓
✓
✓
✓
K0Λ
✓ ✓ ✓
✓ ✓
✓
✓
✓
✓
✓
✓
✓
✓ ✓ ✓ ✓
K0Σ0
✓ ✓ ✓
✓ ✓
✓
✓
✓
✓
✓
✓
✓
✓ ✓ ✓ ✓
K0*Σ0 ✓ ✓
✔ - published, ✔ - acquired,
planned