clas hadron 090926hadron.physics.fsu.edu/.../Sep2609/strauch_clas_hadron_090926.pdf · CLAS Hadron...

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CLAS Hadron Spectroscopy Group Meeting, JLab, September 26, 2009 Steffen Strauch University of South Carolina π + Photoproduction from FROST Analysis Update

Transcript of clas hadron 090926hadron.physics.fsu.edu/.../Sep2609/strauch_clas_hadron_090926.pdf · CLAS Hadron...

Page 1: clas hadron 090926hadron.physics.fsu.edu/.../Sep2609/strauch_clas_hadron_090926.pdf · CLAS Hadron Spectroscopy Group Meeting, JLab, September 26, 2009 Steffen Strauch University

CLAS Hadron Spectroscopy Group Meeting, JLab, September 26, 2009

Steffen StrauchUniversity of South Carolina

π+ Photoproduction from FROSTAnalysis Update

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Polarized cross section (beam/target polarization)g9 Experiment

PT : transverse beam polarizationP⨀ : degree of circular beam polarizationPX, PY : transverse target polarizationPZ : longitudinal target polarization

I.S. Barker, A. Donnachie, and J.K. Storrow, Nucl. Phys. B75, 347 (1975)

Single- and Double Polarization Observables

dσdΩ

⎛⎝⎜

⎞⎠⎟

dσdΩ

⎛⎝⎜

⎞⎠⎟ unpol

= 1− PTΣ cos(2φ)

+PX[−PTH sin(2φ) + P°F]−PY [−T + PTP cos(2φ)]−PZ [−PTG sin(2φ) + P°E]

π+

p

xy

z

2

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Polarization Observable E

dσdΩ

⎛⎝⎜

⎞⎠⎟=

dσdΩ

⎛⎝⎜

⎞⎠⎟ unpol

1− PZP°E( )

E = −xi∑

hPZP° x∑ i

2

σ 2 (E) ≥ 1− h2PZ

2P°2E2

h2PZ2P°

2N

Circularly polarized beam / longitudinally polarized target

3

xi = +1xi = −1

beamspin

targetspin

The sum is running over all events from the butanol targetBound-nucleon background is accounted for by the dilution factor h.

Estimator

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π+ Photoproduction - Event Selection

One and only one positively charged particle detected with:

hit in ST, SC, and DCβ > 0, p > 0, and l > 0crude pion ID

No negatively charged particles detectedPhoton with good tagger status, and vertex time closest to that of the pionNo energy-loss correction, yet

4

γ p→π +n

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Vertex-time difference (ns)-4 -2 0 2 4

Coun

ts

0.05

0.10

0.15

610×

(ns)!t"-4 -2 0 2 4

Coun

ts

0.02

0.04

0.06

610×

(ns)!t"-4 -2 0 2 4

(ns)

#t"

-4

-2

0

2

4

Particle Identification and Photon Selection

Vertex-time difference: |Δtγ| < 1 ns Particle ID: |Δtπ| < 1 ns

5

Δtπ =lc1β−

mπ2

p2+1

⎝⎜

⎠⎟

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Vertex-z Position (cm)0 10 20

Coun

ts

1

10

210

310ButanolCarbon

2CH

Transverse Vertex Position (cm)-10 -5 0 5 10

Coun

ts

210

310

410

MVRT-XMVRT-Y

Reaction Vertex

6

Butanol events from Z ∈ [-3, 3] cm, r < 2 cmCarbon events from Z ∈ [5, 7.5] cm, r < 2 cmButanol background under carbon ≈ 1.3% of total

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Missing Mass (GeV)0.5 1.0 1.5 2.0

Coun

ts

0

1

2

610×

ButanolC (unscaled)12

W = 1.200 - 2.250 GeV

γ(p,π+)X - Missing Mass Distribution

7

Identification of reaction channel;mX ≈ mN

Background from reactions off bound (unpolarized) nucleons ⇒

quenching of the asymmetry signalπ+ production off free and bound nucleons

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Dilution factor

For the butanol target (C4H9OH) thesimple estimate is ≈ 10/74 ≈ 0.14Statistical uncertainty in E scales as

Figure of merit

Summer project, UG student Garry Hollis (USC)

Dilution Factor

8

h =SB= 1− C

B

F = h2B

Carbon

Butanol

free-proton events

Signal

mX

σ E ∝1F

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Missing Mass Bin (GeV)0.6 0.8 1.0

C) ]

12No

rmal

izat

ion

[ N(B

utan

ol) /

N(

4

5

6

7

5%

Butanol/Carbon Normalization

Missing mass distributions for butanol and carbon data are of the same shape up to 0.8 GeV.Relatively more butanol events at ≈ mN (expected)Depletion at 0.8 - 0.9 GeV?

9

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W (GeV)1.0 1.5 2.0 2.5

C) ]

12No

rmal

izat

ion

[ N(B

utan

ol) /

N(

4

5

6

7

DataNormalization s (fit)

5%±s

Energy Dependence of Normalization

Normalization factor is energy independent within ±5%Fit Χ2/d.o.f = 35/20Angular dependence not studied, yet

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Missing Mass (GeV)0.5 1.0 1.5 2.0

Coun

ts

0.0

0.2

610×

Butanol

C12

Missing Mass (GeV)0.5 1.0 1.5 2.0

Diffe

renc

e

0.0

0.1

0.2

610×

W = 1.450 - 1.500 GeV

Missing Mass (GeV)0.5 1.0 1.5 2.0

Coun

ts

0

10

310×

Butanol

C12

Missing Mass (GeV)0.5 1.0 1.5 2.0

Diffe

renc

e

0

1

2

3310×

W = 1.950 - 2.000 GeV

Free-Proton Missing Momentum Distribution

Carbon data normalized to butanol data for mX < 0.8 GeVThe difference distribution is for illustration only and not used in the further analysis.

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W (GeV)1.0 1.5 2.0 2.5

Dilu

tion

Fact

or

0.4

0.6

0.8

Dilution factor h (fit) 5%±h

= 0.93 to 0.97 GeV Xm

Dilution Factor

h ≈ 0.51; i.e. factor four improvement in this reactionDilution factor decreases for larger WModulation of dilution factor not yet understoodAngular dependence of the dilution factor to be tested

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# Run Numbers E0 (GeV) Pe (?) HWP Holding Field

Target Polarization

1 55521 - 55536 1.645 - + + -

2 55537 - 55555 1.645 - - + -

3 55556 - 55595 1.645 - + + +

4 55604 - 55625 2.478 + + - +

5 55630 - 55678 2.478 + + - -

6 56164 - 56193 2.478 + + + +

7 56196 - 56233 2.478 + + + -

g9a Runs with Circularly Polarized Beam

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Runs0 50 100 150

Asym

met

ry0

0.5

Butanol DataC Data12

55512 - 55595 55604 - 55676 56164 - 56193

Confirm Polarization Orientations

14

Status of half-wave plate, helicity signal, sign of electron-beam polarization, proton-target spin orientation understood on a per run base (up to an even number of sign changes).Pion data may help study the time dependence of electron / target polarization

A =Pi∑ xiP∑ i

2

Page 15: clas hadron 090926hadron.physics.fsu.edu/.../Sep2609/strauch_clas_hadron_090926.pdf · CLAS Hadron Spectroscopy Group Meeting, JLab, September 26, 2009 Steffen Strauch University

Run Nunmber55600 55800 56000 56200

Elec

tron

Beam

Pol

ariz

atio

n

0.7

0.8

0.9

1.0

Beam and Target Polarizations

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Photon beam polarization

Target polarization

) e / E! Photon Beam Energy (E

0.0 0.5 1.0

) e

/ P

! Ph

oton

Bea

m P

olar

izat

ion

(P

0.0

0.5

1.0

Pe ≈ 85%

Pγ = Pe4x − x2

4 − 4x + 3x2

PZ ≈ 80%

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Beam-Charge Asymmetry

Helicity-gated beam-charge signals from the synchrotron light monitor in the HLS bankAll runs have beam-charge asymmetries within ± 0.5%.

16Summer project, UG student Theo DuBose (USC)

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)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0E

-1

0

1W = 1.450 - 1.500 GeV

SAID (SP09)MAID (2007)SAID (SM95)

)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0

E

-1

0

1W = 1.400 - 1.450 GeV

SAID (SP09)MAID (2007)SAID (SM95)

)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0

E

-1

0

1W = 1.350 - 1.400 GeV

SAID (SP09)MAID (2007)SAID (SM95)

)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0

E

-1

0

1W = 1.300 - 1.350 GeV

SAID (SP09)MAID (2007)SAID (SM95)

)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0E

-1

0

1W = 1.250 - 1.300 GeV

SAID (SP09)MAID (2007)SAID (SM95)

)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0

E

-1

0

1W = 1.200 - 1.250 GeV

SAID (SP09)MAID (2007)SAID (SM95)

Preliminary Results (I)

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)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0E

-1

0

1W = 1.750 - 1.800 GeV

SAID (SP09)MAID (2007)SAID (SM95)

)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0

E

-1

0

1W = 1.700 - 1.750 GeV

SAID (SP09)MAID (2007)SAID (SM95)

)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0

E

-1

0

1W = 1.650 - 1.700 GeV

SAID (SP09)MAID (2007)SAID (SM95)

)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0

E

-1

0

1W = 1.600 - 1.650 GeV

SAID (SP09)MAID (2007)SAID (SM95)

)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0E

-1

0

1W = 1.550 - 1.600 GeV

SAID (SP09)MAID (2007)SAID (SM95)

)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0

E

-1

0

1W = 1.500 - 1.550 GeV

SAID (SP09)MAID (2007)SAID (SM95)

Preliminary Results (II)

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)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0E

-1

0

1W = 2.050 - 2.100 GeV

SAID (SP09)SAID (SM95)

)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0

E

-1

0

1W = 2.000 - 2.050 GeV

SAID (SP09)SAID (SM95)

)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0

E

-1

0

1W = 1.950 - 2.000 GeV

SAID (SP09)SAID (SM95)

)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0

E

-1

0

1W = 1.900 - 1.950 GeV

SAID (SP09)MAID (2007)SAID (SM95)

)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0E

-1

0

1W = 1.850 - 1.900 GeV

SAID (SP09)MAID (2007)SAID (SM95)

)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0

E

-1

0

1W = 1.800 - 1.850 GeV

SAID (SP09)MAID (2007)SAID (SM95)

Preliminary Results (III)

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)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0

E

-1

0

1W = 2.200 - 2.250 GeV

SAID (SP09)SAID (SM95)

)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0E

-1

0

1W = 2.150 - 2.200 GeV

SAID (SP09)SAID (SM95)

)! cm"cos(

-1.0 -0.5 0.0 0.5 1.0

E

-1

0

1W = 2.100 - 2.150 GeV

SAID (SP09)SAID (SM95)

Preliminary Results (IV)

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Very preliminary results for E in π+ photoproduction covering a wide energy and angular range.-0.9 < cos(θπcm) < +0.91.20 GeV < W < 2.25 GeVPresently more than 730 data points.

Page 21: clas hadron 090926hadron.physics.fsu.edu/.../Sep2609/strauch_clas_hadron_090926.pdf · CLAS Hadron Spectroscopy Group Meeting, JLab, September 26, 2009 Steffen Strauch University

Systematic Uncertainties

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Quantity UncertaintyElectron-beam polarization 5%Beam-charge asymmetry < 0.5%Photon-beam polarization from Pe ?Target polarization ?Dilution factor 5%Kinematics (W, cos(θ)) ?Total < 10%

present best guesses

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Summary

Very preliminary results for E in π+ photoproduction

Issues:Obtain improved values for electron beam and target polarizations on a per run-period baseStudy of systematic effects in dilution factor (carbon/butanol normalization, butanol contamination of carbon data, energy and angular dependence)Implement energy-loss corrections and study of the reconstruction of event kinematics

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