Determination of Polarization Transfer Coe cients Cx for ... Gleason.pdfz were extracted Simulations...

Determination of Polarization Transfer Coefficients Cx ′

and Cz ′ for Quasi-Free Hyperon Photoproduction off theBound Neutron

HUGS 2015

Colin Gleason

University of South Carolina

June 15, 2015

Colin Gleason (USC) Polarization Transfer Coefficients June 15, 2015 1 / 14

Overview

1 QCD and Baryon Spectroscopy

2 g13 Experiment at JLab

3 Analysis of ~γd → K 0~Λ(p)

4 Extraction of Cx ′ and Cz ′

5 Preliminary Results

6 Conclusion


QCD and Baryon Spectroscopy

Baryon Spectroscopy

Provides a way to measure the N* states

Excited atomic states → understanding of atom

Excited nucleon states → understanding of nucleon

At low energies, the strong coupling constantbecomes large and perturbation theory can not beused to solve QCD

Map N* spectrum to learn about the internalstructure of nucleons

Goal is to provide information about the relativedegrees of freedom

http://ebac-theory.jlab.org/

Constituent quark models three valence quarksDi-quark models bound quark pair → less degrees of freedom

Lattice QCD numerical solution to QCD

Many other approaches...Colin Gleason (USC) Polarization Transfer Coefficients June 15, 2015 3 / 14


Missing Resonance Problem

Constituent quark models predict many N* states that have yet to beobserved

Do these resonances exist?Some N* states have been observed thatdon’t appear in diquark models, but moreevidence is needed

Need more dataMajority of data out there is in the πN finalstateSome resonances couple weakly to thischannelFinal states with strangeness (KΛ,KΣ):

γp → K +Λ moving N(1900) 32

+from ?? to

? ? ?γn→ K 0Λ senstive to ?? N(2080) 3

2

−

f?

K.A. Olive et al., Review of Particle Physics



Polarization Observables in KΛ Photoproduction

Sfi = 12π2 ( MnMΛ

4EΛEK EnEγ)

12Mfiδ

(4)(pn + pγ − pK − pΛ)

16 Polarization observables are derived from the matrix elements Mfi

Sensitive to the physics involved in the resonant reaction

Unpolarized Cross Section σ0

Single P Σ TBeam-Recoil Cx ′ Cz ′ Ox ′ Oz ′

Target-Recoil Tx ′ Tz ′ Lx ′ Lz ′

Beam-Target E F G H

8 carefully chosen observables are needed to determine the fullscattering amplitude



Previous Studies for γn→ K 0Λ

Neil Hassall: Ph.D. Thesis for g13 (2010).Shown are his preliminary results for Ox′

Laboratory of Nuclear Science (LNS)in Japan

Measured cross sections of withEγ=0.8–1.1 GeV off 12C and LD2 targets

K. Tsukada et al., Phys. Rev. C 78,014001

In progress: cross sections from g13 and g10

g14 using a polarized target


g13 Experiment at JLab

Hall-B at Jefferson Lab

Photon Tagger

Photons are produced via thebremsstrahlung technique.

Eγ = E0 − Ee

Ee : 1.987 GeV and 2.649 GeV

Eγ ≈ 20− 95% of Ee

CEBAF Large AcceptanceSpectrometer (CLAS)

arXiv:1109.1720 [hep-ph]

D.I. Soberet al., The bremsstrahlung tagged photon beam in Hall B at JLab


Analysis of ~γd → K 0~Λ(p)

Analysis Overview: ~γd → K 0~Λ(p)

K 0 → π+π− and Λ→ pπ−

Select events which have 2 positive and 2 negative tracks

Particle Identification

1

10

210

310

410

Momentum (GeV/c)0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

β

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

vs. Momentumβ vs. Momentumβ

Particles were identified based on their velocity and momentumin CLAS

Photon Selection

time (ns)-5 -4 -3 -2 -1 0 1 2 3 4 50

100

200

300

400

500

600

700

800

310×

t)∆Coincidence Time ( h1Entries 3.189536e+08

Mean -0.03103

RMS 1.645

t)∆Coincidence Time (

time (ns)-5 -4 -3 -2 -1 0 1 2 3 4 50

100

200

300

400

500

600

700

310×

t∆Smallest h2Entries 2.298278e+07

Mean -0.01708

RMS 0.2718

t∆Smallest

∆t = tv − tγ where tv is the reconstructed event vertex timeusing the trajectory in CLAS of the fastest particle and tγ is the

time that the photon arrived at the event location



Selection of K 0 and Λ

Recall that Λ→ pπ− and K 0 → π+π−

The invariant masses of pπ− (Mpπ− ) and π+π− (Mπ+π− ) were used to reconstruct and

select the Λ and K 0

Filter out pπ+π−π− events that do not come from the K 0Λ final state

Mpπ− =

√(p̃p + p̃

π− )2 ≈ MΛ

Mπ+π− =

√(p̃π+ + p̃

π− )2 ≈ MK0

Cuts were calculated based on gaussian fitsto the projections of the x-axis and y-axis.

Events were kept if they fall within the redbox

Note: Some combinatorial background.

Arises when both π−’s yield a good K 0

and a good Λ

)2 (GeV/c-πp M1.08 1.09 1.1 1.11 1.12 1.13 1.14 1.15 1.16

)2 (

GeV

/c- π+ π

M

0.46

0.47

0.48

0.49

0.5

0.51

0.52

0.53

0.54

)-π) vs. M(p-π+πM(

1

10

210

)-π) vs. M(p-π+πM(



Identification of the Final State

The K 0Λ final state was identified using the missing mass (MX ) technique

γn→ K 0X where MX =√

(p̃γ + p̃n − p̃K 0 )2

γd → K 0ΛX where MX =√

(p̃γ + p̃d − p̃K 0 − p̃Λ)2

X = Λ

ORX = Σ→ Λγ → γpπ−

X = p OR X = γp

The black line ”separates” theK 0Λ events from K 0Σ events

)2 X) (GeV/cΛ0MM(K0.85 0.9 0.95 1 1.05 1.1 1.15

)2X

) (G

eV/c

0M

M(K

0.95

1

1.05

1.1

1.15

1.2

1.25

1.3

X)Λ0X) vs. MM(K0MM(K

1

10

X)Λ0X) vs. MM(K0MM(K

The quasi-free reaction is selected by accepting events of pX < 0.2GeV /c

K 0Λ

Background (K 0Σ events)


Extraction of Cx′ and Cz′

Extraction of Cx ′ and Cz ′

From the equation for the polarized cross section of KΛ photoproduction,the experimental asymmetry, A, can be derived:

A = N+−N−N++N− = αPcircCx ′/z ′ cos(θx ′/z ′)

N+(N−) is the number of events with right (left) handed helicityα = 0.642± 0.013 and is the self-analyzing power of Λ

n⇤

Kθ vs. cosγE

Kθ cos

1− 0.8− 0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8 1

γ E

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6h_e_gamma_vs_cosK_MM

Entries 225330Mean x 0.1661Mean y 1.465RMS x 0.3771RMS y 0.321

1

10

h_e_gamma_vs_cosK_MM

Entries 225330Mean x 0.1661Mean y 1.465RMS x 0.3771RMS y 0.321

Kθ vs. cosγE


Preliminary Results

Preliminary Results: Eγ Bins

Preliminary estimates of CX ′ and CZ′ for K 0Λ photoproduction are extracted for the first time

C 2X ′ + C 2

Z′ + P2 6 1

*K

θcos0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8

X'/Z

'C

1−

0.5−

0

0.5

1

<1.1γ

1.0<E <1.1γ

1.0<E

*K

θcos0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8

X'/Z

'C

1−

0.5−

0

0.5

1

<1.2γ

1.1<E <1.2γ

1.1<E

*K

θcos0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8X

'/Z'

C

1−

0.5−

0

0.5

1

<1.3γ

1.2<E <1.3γ

1.2<E

*K

θcos0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8

X'/Z

'C

1−

0.5−

0

0.5

1

<1.4γ

1.3<E <1.4γ

1.3<E

*K

θcos0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8

X'/Z

'C

1−

0.5−

0

0.5

1

<1.5γ

1.4<E <1.5γ

1.4<E

*K

θcos0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8

X'/Z

'C

1−

0.5−

0

0.5

1

<1.6γ

1.5<E <1.6γ

1.5<E

*K

θcos0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8

X'/Z

'C

1−

0.5−

0

0.5

1

<1.7γ

1.6<E <1.7γ

1.6<E

*K

θcos0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8

X'/Z

'C

1−

0.5−

0

0.5

1

<1.8γ

1.7<E <1.8γ

1.7<E

*K

θcos0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8

X'/Z

'C

1−

0.5−

0

0.5

1

<1.9γ

1.8<E <1.9γ

1.8<E

*K

θcos0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8

X'/Z

'C

1−

0.5−

0

0.5

1

>2.0γE >2.0γE


Conclusion

Conclusion and Outlook

Many resonant states predicted by constituent quark models have yetto be observed

Hyperon channels have a strong coupling to some of these resonances

First estimates of Cx ′ and Cz ′ were extracted

Simulations will be done to understand shape of Σ background in themissing mass

Estimate systematic uncertainties (photon polarization, α,background, analysis method)

Extract observables using different methods (2d fit, maximumlikelihood)


Conclusion

x'θcos-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

A

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1:[0.4, 0.6]

*

KθAsymmetry in x' for W:[2.0, 2.1] and cos :[0.4, 0.6]*

KθAsymmetry in x' for W:[2.0, 2.1] and cos

Momentum (GeV/c)0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

0

1000

2000

3000

4000

5000

6000

7000

8000

9000X

Missing Momentum pX

Missing Momentum p


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