Φ(1020) Photoproduction in Φ(1020) Photoproduction in Neutral Decay ChannelNeutral Decay Channel

Heghine Seraydaryan

June 12, 2009

Outline

Theory Motivation Data and Selection of Events for p p

KSKLp’ Preliminary Results Summary

Φ(1020) Meson. Theory

Decay channels:

K+ K- (49.2%)

KS KL (34%)

0,+ - 0 (15.3%)

(1.3%)

p p’

,

Production mechanisms:

Kinematics and observables:

Θ - helicity angleΦ - azimuthal angle

,cos)()(),,( 0WtfEftE

Motivation and Observations for the Charged Channel

Charged Channel

• The peak at about 2 GeV with width 0.2 GeV• Theoretical curves fail to describe the data

Note:

• The cross sections were obtained without cut on (1520)

Previous results for p pΦ(1020) p K+

K- :

• No photo-production data for Neutral Channel • We can check the cross-section behavior and slope behavior

Motivation

D.Tedeschi

Events cleaning for p Φ(1020) p KS KL p

Also cuts on momenta of the particles:

P + > 0.1 (GeV/c), P - > 0.1 (GeV/c)

Pp > 0.35 (GeV/c)

The particle identification was done by using DC and SC information

Three particle events were selected (p, +,-)

The invariant mass of (+,-) was taken to be mass of KS

Missing mass of

( p->p + -)X was taken to be mass of KL

Generator

The generator for meson was created using several iterations method

The generator is based on data.

Cross section is generated as:

As initial energy distribution the K+K- energy distribution was taken

(using Tedeschi results).

f(E) and ρ00 parameters were varied to make Monte Carlo fit the data.

The same thing was done for t distribution.

Gen GSIM RECSISGen, GSIM, RECSIS were used several times to obtain generator-data agreement.

α =3.4

Acceptances

Accep

tan

ce

t- tmin

E = 1.6 E = 1.65

E = 1.7 E = 1.75

E = 1.8 E = 1.85

E = 1.9

E = 2.0

E = 1.95

E = 2.05

E = 2.1 E = 2.15

E = 2.2 E = 2.25

E = 2.3 E = 2.35

E = 2.4 E = 2.45

E = 2.5 E = 2.55

E = 1.6

1.6 GeV E 1.65 GeV

Efficiency calculations for -

To obtain the efficiency for - ,two reactions were used:

(γp->p +) -

(γp->p - + +) -

Four momentum slices(0.1-0.15),(0.15-0.2),(0.2-0.3),(> 0.3)

180 θ bins360 φ bins (1 degree each)

missing - detected -

To obtain the efficiency for +, were used: (γp->p -) +

(γp->p - + -) +

and to obtain the efficiency for p ,were used: (γp-> + -)p (γp-> + - + -)p

missingdetected

efficiency

p = 0.125 GeV/c

p = 0.175 GeV/c

p 0.3 GeV/c

p = 0.25 GeV/c

Cuts and Corrections

We used:

Cuts

On momenta of the particles: P + > 0.1 (GeV/c), P - > 0.1 (GeV/c)

Pp > 0.35 (GeV/c)

To select K : |M(KS)-0.49765| < 0.008 (GeV/c2)

|M(KL)-0.49765| < 0.015 (GeV/c2)

To select : M(φ) = 1.02 ± 0.02 (GeV/c2)

To select background: M(φ) = 1/2*N(1.06 ± 0.02 (GeV/c2) )

Corrections • Standard g11 momentum corrections

• Standard g11 photon energy corrections

• Energy loss corrections for + , - and p

• Photon timing : 1 photon in 2 ns interval

• Acceptance corrections

• Efficiency corrections

Preliminary Results

For the φ cross section in the Neutral decay mode we observe a peak , which is shifted to 1.9 GeV and is slightly smaller, compared to the peak at about 2 GeV in the Charged channel.

We also observe some difference for the slope values of the two channels. For the Neutral channel they are much smaller in photon energy region (1.6:2.4) GeV.

The Neutral channel cross section is multiplied by branching ratio (1.447)

A. Thomas et al

CLAS PRELIMINARY

Preliminary Results : Angular Distribution Function

CLAS PRELIMINARY

CLAS PRELIMINARY

Helicity Frame

Preliminary Results : Angular Distribution Function

CLAS PRELIMINARYCLAS PRELIMINARY

Gottfried-Jackson Frame

The fit function had to be modified with an addition of a linear term cos, to be able to fit the data correctly.

+ C cos

Preliminary Results : Spin-Density Matrix Elements

CLAS PRELIMINARYCLAS PRELIMINARY

Helicity Frame GJ Frame

Preliminary Results : Angular Distribution Function

CLAS PRELIMINARY

GJ Frame

Summary

We analyzed φ(1020) production in Neutral decay channel from g11 data.

We measured the cross section, the slope and the angular dependences of the

cross section. We extracted spin-density matrix elements in GJ and Helicity frames.

ConclusionsThe slope of the φ production in Neutral channel is much smaller than

the Charged channel slope for the photon energy interval (1.6:2.4) GeV.

The cross section peak at 2 GeV in Charged decay mode is slightly larger than the one observed in Neutral decay mode.

Comparison of the W between the Neutral and Charged channels shows agreement for two energy bins in the Helicity frame. For the Charged Channel data is used T. Mibe’s measurements from Spring-8 .

The difference between the two channels must be investigated further.

1/

Efficiency calculations for +

To obtain the efficiency for + ,two reactions were used:

(γp->p -) +

(γp->p - + -) +

Four momentum slices(0.1-0.15),(0.15-0.2),(0.2-0.3),(>0.3)

180 θ bins360 φ bins(1 degree each)

The ratio of two is the efficiency

missing + detected +

Efficiency calculations for protons

To obtain the efficiency for p ,two reactions were used:

(γp-> + -)p(γp-> + - + -)p

Four momentum slices(0.1-0.15),(0.15-0.2),(0.2-0.3),(>0.3)

180 θ bins360 φ bins(1 degree each)

The ratio of two is the efficiency

missing P detected P

Large angle efficiency (1) comes from the events with two detectedprotons (are mostly background)

+ Data Corrections with Efficiencies

- Data Corrections with Efficiencies

Proton Data Corrections with Efficiencies

Acceptance Calculation

• events were generated in 4 (figure a)

• GSIM was used to simulate the detector

• RECSIS was used to reconstruct the

events as in the experiment (figure b)

• The acceptance was calculated as the

ratio of reconstructed simulated data,

presented on figure b, over the simulated

data, presented on figure a.

It was done for different energy regions

and different t bins.

a)

b)

c)A

ccep

tan

ceE

ven

tsE

ven

ts

t - t min

generated events

reconstructed events

generated

tedreconstruc

Generator and Data Agreement

E = 1.65

1.6 GeV E 1.7 GeV

E = 1.65 E = 1.75 E = 1.85

E = 1.95 E = 2.05 E = 2.15

E = 2.25 E = 2.35 E = 2.45

Data eventsGenerated events

Generator and Data Agreement

Data eventsGenerated events