1

K* Photoproduction off the proton

at CLAS

via

Ishaq Hleiqawi

OHIO UNIVERSITY

NSTAR2005 Oct. 12, 2005

p K *0 K

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• Experiment and Physics Motivation

• Background and Analysis Cuts

• Results: – Cross sections

– Systematic Uncertainties

• Conclusion

OUTLINE

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Experiment and Motivation “g1c” data set

Motivation: - K* production mechanism - Looking for N* resonances

Goal: Measuring Cross Sections

- dσ/dcosθ vs. E - dσ/dcosθ vs. cosθ

N*

E= 3.115 GeV

Target: LH2 (L=17.85 cm)

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Background

(signal)

( b.g.)

N*

K 0

K / YK K0* Y *

N*

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Analysis CutsParticle identification

- 2 detected particles: &

- 3 timing cuts: Δβ, (TOF-ST), and (TOF/Ttag )

Δβ = - < 0.1 ; =

TOF-ST = |TOF - (Start Counter) vtime | < 1.0 ns

TOF/Ttag = |TOF – (Ttag +zvertex/c) | < 1.0 ns

• Kinematic cuts– Kinematic coverage (cos vs. )

– zvertex & R at vertex cuts

– Fiducial cuts

• Mass cuts– missing mass

– K* invariant mass

K

K

E K*c.m.

ToF-Ttag (K)

zvertex (K)

TOFP P mX X X/ 2 2X X

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PID Timing cuts (kaons)

Kβ

P

P (before cuts) P (after cuts)

M (before cuts) M (after cuts)

K

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MM(K+)

IM(K*) vs. MM(K+)

K* and Σ+ Peaks

K* from IM( )

from MM( ) for a cut on K* peak

from MM( ) for a cut on K* SBs

peak From MM( )

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Kinematic Coverage

K* Cut

Y* Cut

cos(θ)

E

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Dalitz Plots

IM( )K

IM( Σ )

2

2+

E=1.8125 GeV E=2.00 GeV E=2.1625 GeV

E=2.300 GeV E=2.600 GeVE=2.475 GeV

E=2.9125 GeVE=2.8125 GeVE=2.7125 GeV

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Normalized cross section

Extracting Cross Sections

MH = number of grams/mole of target ρ and L = detector’s density and length Na = Avogadro’s number A = detector’s acceptance = photon flux

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Angular distribution of the diff. x-sec. (E=3.115 GeV)

dσ/dcosθ(nb)

cosθ

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dσ/d(cosθ) for K* photoproduction (E=3.115GeV)

E

(nb)

dσ/dcosθ

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dσ/d(cosθ) for K* photoproduction (E=3.115GeV)

E

(nb)

dσ/dcosθ

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Systematic

Uncertainties

6.65%

Cuts Uncertainty

3.11%

2.51%

2.17%

3.0%

2.0%

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Conclusion• We have measured the differential cross sections for the

K* Photoproduction.

• Our results agree with theory at the "middle to backward" angles

but disagree at forward angles.

- Small angles: forward-peaking

strongly correlated to the t-channel kaon exchange

- Large angle: backward cross sections

have less interferences from the t-channel meson exchange

• Our data are expected to play a role in constraining the

quark-vector-meson couplings and in improving the model

Q. Zhao, J. Al-Khalili, And C. Bennhold, Phys. Rev. C64(2001) 052210.

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