Latest results from FroST at Jefferson Lab

Barry G. Ritchie*

Arizona State University

*Work at ASU is supported by the U.S. National Science Foundation B. G. Ritchie - MENU 2013 - October 2013 1

Nucleon excited states

• • As a composite system, the nucleon has a specific spectrum of excitations: the nucleon resonances.

This nucleon resonance spectrum has many broad overlapping states, making disentangling the spectrum difficult. 

γ p → π + n

B. G. Ritchie - MENU 2013 - October 2013 2

The state of our knowledge

Nucleon

• • •

Nearly half the states have only fair or poor evidence! Most states need more work to learn details Are there missing states?

• • • • 26 N

*

states: 10 with **** 5 with *** 8 with ** 3 with * • • • • 22 Δ

*

states: 7 with **** 3 with *** 7 with ** 5 with * B. G. Ritchie - MENU 2013 - October 2013 3

Models predict (lots of)excitations

• Many nucleon models have offered “predictions” for the nucleon resonance spectrum - • constituent quark model • diquark • collective models • instanton-induced interactions • flux-tube models • lattice QCD • (your favorite here) - BUT… •

THE BIG MYSTERY: Most models predict many more resonance states than have been observed.

B. G. Ritchie - MENU 2013 - October 2013 4

Example: Lattice QCD results for N

*

resonances

• Noticeable change as the π mass becomes more realistic • Number of low-lying states (boxed regions) remains the same for the two π-masses, and generally is the same as NRQMs • Many of these predicted states are poorly determined or missing. m π = 524 MeV Example: R.G. Edwards et al. Phys. Rev. D87 054506 (2013) B. G. Ritchie - MENU 2013 - October 2013 m π = 391 MeV 5

Solving a mystery: “The Case of the Missing Resonances”

EXPERIMENT

cross sections, spin observables

AMPLITUDE ANALYSIS

multipole amplitudes, phase shifts

BARYON MODELS

LQCD, quark models, etc…

REACTION MODEL

effective Lagrangians, Isobars, etc… B. G. Ritchie - MENU 2013 - October 2013 6

Gathering clues: helicity amplitudes

B. G. Ritchie - MENU 2013 - October 2013 7

Helicity amplitudes for γ + p → p + pseudoscalar

• 8 helicity states: 4 initial, 2 final → 4∙2 = 8 possible complex amplitudes • Parity reduces these to 4 complex amplitudes

H i

(8 W-dependent functions) • Overall phase unobservable → 7 W-dependent functions • Suggests complete determination possible with 7 observables/experiments •

HOWEVER

, not all possible observables are linearly independent →

a minimum of 8 observables / experiments

A

 

Initial helicity fin



A A

11 21

A A

12 22   

helicity +1 photons (ε + ):

3 2 1 2

A

   1 2 2 

H H

1 3

H H

2 4    

A

  ,    

e

     

A

 ,   → Parity →

A

helicity -1 photons (ε ):

 1 2     1 2 1 2    

H H

4 2  3 2 

H H

1 3    B. G. Ritchie - MENU 2013 - October 2013 8

Linkage between helicity amplitudes and the observables for single pseudoscalar photoproduction

Differential cross section Beam polarization S Target asymmetry T Recoil polarization P

Double polarization observables

• Need at least 4 of the double observables from at least 2 groups for a “complete experiment” • π

0 p, π +

complete n, and η p will be nearly • K

+

Λ will be complete!

B. G. Ritchie - MENU 2013 - October 2013 9

Conducting the investigation

FroST Photon beam

Unpolarized Linearly polarized Circularly polarized

x

0 H F

Target

y

T (-P) 0 g9b B. G. Ritchie – MENU 2013 – Rome

z

0 -G -E g9a 10

The detective’s tools: FroST and friends

B. G. Ritchie - MENU 2013 - October 2013 11

CLAS (1997-2012)

• • Lest we forget: CLAS was very good for detecting charged particles CLAS had large acceptance B. G. Ritchie - MENU 2013 - October 2013 12

Hall B Bremsstrahlung Photon Tagger

(not dead yet!)

61 backing counters

• Jefferson Lab Hall B bremsstrahlung photon tagger had: • E

γ

= 20-95% of E

0

• E

γ

up to ~5.5 GeV • Circular polarized

photons with longitudinally polarized electrons

• Oriented diamond

crystal for linearly polarized photons

B. G. Ritchie - MENU 2013 - October 2013 13

•

Frozen Spin Target - FroST

Doped butanol and dynamic nuclear polarization): • Butanol with paramagnetic radical TEMPO • Polarize unpaired TEMPO electrons to 99.999% with B = 5 T and T = 0.3 K • Transfer electron polarization to free protons with microwaves at ~140 GHz • • Remove microwaves Cool to T = 30 mK and use B = 0.5 T holding field • Put target in CLAS and run experiment B. G. Ritchie - MENU 2013 - October 2013 14

Holding coils

Transverse polarization – g9b Longitudinal polarization – g9a Complete assembly – g9a B. G. Ritchie – MENU 2013 - Rome 15

FroST performance

• Frozen spin butanol (C

4 H 9 OH)

• P

z

≈ 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

B. G. Ritchie - MENU 2013 - October 2013 16

FroST’s first clues: Single pion photoproduction

B. G. Ritchie - MENU 2013 - October 2013 17

Isospin combinations for reactions involving π

0

and π

+

• Differing isospin compositions for N* and Δ

+

for the π

0

p and π

+

n final states • The π

0

p and π

+

n final states can help distinguish between the Δ and N

* Δ + N *

 0 

p

: 2 / 3

I

 3 2 ,

I

3  1 2  1 / 3

I

 1 2 ,

I

3  1 2   

n

: 1 / 3

I

 3 2 ,

I

3  1 2  2 / 3

I

 1 2 ,

I

3  1 2 B. G. Ritchie - MENU 2013 - October 2013 18

Theoretical analyses

• • • In the plots that follow, you will see many curves from: SAID: A two-stage PWA where • stage 1 is the fit to data • stage 2 is the extraction of resonance parameters BnGa (Bonn-Gatchina): A single stage PWA MAID: Isobar analysis Note: The SAID results labeled “new” in this section of the talk include the new Σ data from ASU/CLAS. Later sections of the talk show SAID results that do not have the new Σ data included. B. G. Ritchie - MENU 2013 - October 2013 19

Observables: T and F

Reaction: γ p → n π

+

• • • • Configuration:

Circular photon polarization Transverse target polarization

Unpolarized photon (add circular beams) No recoil polarization • Experiment: g9b: FroST

Photon beam

Unpolarized Linearly polarized Circularly polarized

x

0 H F

Target

y

T (-P) 0

z

0 -G -E B. G. Ritchie - MENU 2013 - October 2013 20

T

for γ p → n π

+

(new) (new) (new) • • Early stage results CLAS results agree well with previous data

g9b:

Michael Dugger B. G. Ritchie - MENU 2013 - October 2013 21

F

for γ p → n π

+

(new) (new)

g9b:

Michael Dugger (new) • • • Early stage results Predictions get much worse at higher energies SAID13 are predictions based on preliminary fits to CLAS pion Σ measurements B. G. Ritchie - MENU 2013 - October 2013 22

Observable: E

Reactions :

γ p → p π 0

and γ p → n π

+

• • • Configuration:

Circular photon polarization Longitudinal target polarization

No recoil polarization • Experiment: g9a: FroST

Photon beam

Unpolarized Linearly polarized Circularly polarized

x

0 H F

Target

y

T (-P) 0

z

0 -G -E B. G. Ritchie - MENU 2013 - October 2013 23

E

for γ p → p π

0

(new)

g9a:

Michael Dugger B. G. Ritchie - MENU 2013 - October 2013 • Early stage results • Predictions better at lower energies 24

E

for γ p → n π

+

W = 1.25 GeV PRELIMINARY W = 1.27 GeV PRELIMINARY W = 1.29 GeV PRELIMINARY W = 1.31 GeV PRELIMINARY W = 1.37 GeV PRELIMINARY W = 1.49 GeV PRELIMINARY W = 1.39 GeV PRELIMINARY W = 1.51 GeV PRELIMINARY PRELIMINARY W = 1.61 GeV PRELIMINARY W = 1.63 GeV W = 1.41 GeV PRELIMINARY W = 1.53 GeV PRELIMINARY W = 1.43 GeV PRELIMINARY W = 1.55 GeV PRELIMINARY PRELIMINARY W = 1.65 GeV PRELIMINARY W = 1.67 GeV W = 1.33 GeV PRELIMINARY W = 1.45 GeV PRELIMINARY W = 1.57 GeV PRELIMINARY W = 1.35 GeV PRELIMINARY W = 1.47 GeV PRELIMINARY W = 1.59 GeV PRELIMINARY PRELIMINARY W = 1.69 GeV PRELIMINARY W = 1.71 GeV

SAID SAID (new) MAID Predictions worse at higher energies

PRELIMINARY W = 1.73 GeV W = 1.75 GeV PRELIMINARY W = 1.77 GeV PRELIMINARY W = 1.81 GeV PRELIMINARY W = 1.83 GeV PRELIMINARY W = 1.9 GeV PRELIMINARY PRELIMINARY g9a: W = 1.94 GeV W = 1.98 GeV PRELIMINARY W = 2.02 GeV PRELIMINARY PRELIMINARY W = 2.07 GeV PRELIMINARY W = 2.13 GeV PRELIMINARY W = 2.19 GeV

Cos(θ

π

c.m.

) Steffen Strauch B. G. Ritchie - MENU 2013 - October 2013 25

Observable: G

Reactions: γ p → n π

+

• • • Configuration:

Linear photon polarization Longitudinal target polarization

No recoil polarization • Experiment: g9a: FroST

Photon beam

Unpolarized Linearly polarized Circularly polarized

x

0 H F

Target

y

T (-P) 0

z

0 -G -E B. G. Ritchie - MENU 2013 - October 2013 26

W=1475-1500 MeV ◊ Bussey et al

G

for γ p → n π

+

W=1640-1680 MeV PRELIMINARY W=1840-1880 MeV PRELIMINARY W=2030-2080 MeV g9a:

Jo McAndrew

▬ SAID -- MAID • Bonn-Gatch

• Early stage results • Photon polarizations are approximate

PRELIMINARY PRELIMINARY

B. G. Ritchie - MENU 2013 - October 2013 27

Additional clues from FroST: Single eta or kaon photoproduction

B. G. Ritchie - MENU 2013 - October 2013 28

• •

“Isospin filters”

Final states of ηp and K

+

Λ systems have isospin ½ , and limit one-step excited states of the proton to be isospin ½. Thus, the final states ηp and K

+

Λ can serve as

isospin filters

to the resonance spectrum.

γ p → π + n γ p → η p

B. G. Ritchie - MENU 2013 - October 2013 29

Observables: T and F

Reaction: γ p → η p

• • • • Configuration:

Circular photon polarization Transverse target polarization

Unpolarized photon (add circular beams) No recoil polarization

Photon beam

Unpolarized Linearly polarized Circularly polarized

x

0 H F

Target

y

T (-P) 0

z

0 -G -E • Experiment: g9b: FroST B. G. Ritchie - MENU 2013 - October 2013 30

T

for γ p → η p

g9b:

Ross Tucker B. G. Ritchie – MENU 2013 – Rome 31

F

for γ p → η p

g9b:

Ross Tucker B. G. Ritchie – MENU 2013 – Rome 32

Observable: E

Reaction :

γ p → η p

• • • Configuration:

Circular photon polarization Longitudinal Target polarization

No recoil polarization

Photon beam

Unpolarized Linearly polarized Circularly polarized

x

0 H F

Target

y

T (-P) 0 • Experiment: g9a: FROST

z

0 -G -E B. G. Ritchie - MENU 2013 - October 2013 33

E

for γ p →

h

p

(new)

g9a:

Igor Senderovich • Predictions are generally inconsistent with data at all energies at more forward angles B. G. Ritchie - MENU 2013 - October 2013 34

Observables: T and F

Reaction: γ p → K

+

L

and γ p → K

0

S  • • • • Configuration:

Circular photon polarization Transverse target polarization

Unpolarized photon (add circular beams) No recoil polarization

g9b:

Natalie Walford B. G. Ritchie - MENU 2013 - October 2013 35

T for γ p → K

+

L W=1675 MeV E γ =1027 MeV

Bonn –data - purple GRAAL data - black

W=1725 MeV E γ =1117 MeV

Bonn-Gatchina: blue kaonMAID: pink

W=1775 MeV E γ =1210 MeV W=1825 MeV E γ =1306 MeV W=2125 MeV E γ W=1875 MeV E γ =1405 MeV W=1925 MeV E γ =1506 MeV W=1975 MeV E γ =1610 MeV W=2025 MeV E γ =1717 MeV =1938 MeV W=2175 MeV E γ =2053 MeV W=2225 MeV E γ =2170 MeV W=2275 MeV E γ =2290 MeV

W=1725 MeV E γ =1117 MeV

T for γ p → K

0

S 

Bonn-Gatchina: blue kaonMAID: pink

W=1775 MeV E γ =1210 MeV W=1825 MeV E γ =1306 MeV W=1875 MeV E γ =1405 MeV W=1925 MeV E γ =1506 MeV W=1975 MeV E γ =1610 MeV W=2025 MeV E γ =1717 MeV W=2075 MeV E γ =1826 MeV W=2125 MeV E γ =1938 MeV W=2175 MeV E γ =2053 MeV W=2225 MeV E γ =2170 MeV W=2275 MeV E γ =2290 MeV

A “complete” set of clues: Self-analyzing reaction K

+

Y (hyperon)

• Hyperon weak decay allows extraction of hyperon polarization by looking at the decay distribution of the baryon in the hyperon center of mass system:

I

(cos  )  1 2  1  

P Y

cos   where

I

is the decay distribution of the baryon, α is the weak decay asymmetry (α

Λ

is the hyperon polarization.

= 0.642 and α

Σ0

= -⅓ α

Λ

), and P

Y

• Get recoil polarization information without a recoil polarimeter: the reaction is

“self-analyzing”.

• No preliminary results yet, but data will be forthcoming. B. G. Ritchie - MENU 2013 - October 2013 38

More clues from FroST: multi-pion photoproduction

B. G. Ritchie - MENU 2013 - October 2013 39

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!

B. G. Ritchie - MENU 2013 - October 2013 40

γ p → p π

+

π

-

unpolarized beam and longitudinal target: δ l = Λ x = Λ y = 0 next slide slide after next longitudinal beam and longitudinal target: δ l ≠ 0, Λ x = Λ y = 0

B. G. Ritchie - MENU 2013 - October 2013 41

Spin observable P

z

for γ p → p π

+ π -

g9a:

Sungkyun Park FSU: Winston Roberts Fix & Arenhövel B. G. Ritchie – MENU 2013 – Rome 42

Spin observable P

z s

for γ p → p π

+ π -

Fix & Arenhövel

g9a:

Yuqing Mao B. G. Ritchie – MENU 2013 – Rome 43

FroST results in the full CLAS program for photoproduction from proton

pπ 0 nπ + pη pη’ K + Λ K + Σ 0 K 0 Σ + σ

✔ ✔ ✔ ✔ ✔ ✔ ✔

Σ

✓ ✓ ✓ ✓ ✓ ✓ ✓

T

✓ ✓ ✓ ✓ ✓ ✓ ✓

P

✓ ✓ ✓ ✓ ✔ ✔ ✓

E

✓ ✓ ✓ ✓ ✓ ✓ ✓

F

✓ ✓ ✓ ✓ ✓ ✓ ✓

G H T x

✓ ✓ ✓ ✓ Proton target ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

T z

✓ ✓ ✓

L x

✓ ✓ ✓ ✔ - published ✔ - acquired

L z

✓ ✓ ✓

O x O z C x

✓ ✓ ✓ ✓ ✓ ✓ ✔ ✔ ✔ Preliminary results shown in this talk

Not shown in table:

ω and ππ photoproduction observables

C z

✔ ✔ ✔ 44

Conclusions

• Spin observables will tremendously aid in sleuthing out resonance parameters and finding missing resonances (if they exist) • Photon experiments in Hall-B with FroST at JLab have acquired hundreds of data points yielding clues to the missing resonances • For most reaction channels, we will have data sufficient for a nearly complete experiment B. G. Ritchie - MENU 2013 - October 2013 45

Conclusions (cont’d)

• For K Λ and K Σ channels, we will have a complete experiment • Double-pion observables offer a “next generation” probe of reaction mechanisms and resonances • Data for some reactions and some observables are nearing the publication stage, but much work remains – STAY ON THE CASE!

B. G. Ritchie - MENU 2013 - October 2013 46

Acknowledgements

B. G. Ritchie - MENU 2013 - October 2013 47

Molte grazie!

B. G. Ritchie – MENU 2013 - Rome 48

Circular beam polarization

Circular polarization from 100% polarized electron beam

P

 

P e

 4  4

k

4

k

 

k

2 3

k

2

k = E γ /E e

H. Olsen and L.C. Maximon, Phys. Rev. 114, 887 (1959) B. G. Ritchie - MENU 2013 - October 2013 • Circular photon beam from longitudinally polarized electrons • Incident electron beam polarization > 85% 49

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 B. G. Ritchie - MENU 2013 - October 2013 50

FroST target

• Butanol composition: C

4 H 9 OH

• C and O are even-even nuclei → No

polarization of the bound nucleons

• Carbon target used to

represent bound nucleon contribution of butanol

B. G. Ritchie - MENU 2013 - October 2013 51

FroST target

Slide from Chris Keith B. G. Ritchie - MENU 2013 - October 2013 52

FroST target

Slide from Chris Keith B. G. Ritchie - MENU 2013 - October 2013 53

FroST target

Slide from Chris Keith B. G. Ritchie - MENU 2013 - October 2013 54

FroST target

Slide from Chris Keith B. G. Ritchie - MENU 2013 - October 2013 55

Slide from Chris Keith B. G. Ritchie - MENU 2013 - October 2013 56