φphotoproduction from nuclear targets

T.Sawada

LEPS Collaboration Meeting in Academia Sinica, 2008.5.1

φ properties with A-dependence

・Modification studied by invariant mass spectra

・ Modification stdudied by A-dependence of the photo-production

dilepton: difficulty in the treatment of the background.

KK: distortion by the KN and KN interactions.

Mass Number AC

ross

Sec

tion

　 The modification of the spectral function implies the change of the pole position and the width.

　 When the effective in-medium width of the φ-meson becomes larger, then its decay probabilityalso increases, leading to a stronger absorption innuclear matter.

Thus, one might expect that the A-dependence indicates a in-medium modification of the imaginarypart of the phi-meson spectral function.

Within the Glauber formalism, we will analyze the φ-photoproduction data from nuclei and evaluatethe in-medium φ-N cross section.

φ- N total cross section

φ- N total cross section in free space

Quark model : 13.0mb

VDM relation : 7.7 - 8.7mb at Eγ= 4.6 - 6.7GeV

φ photo-production from nuclei

at Eγ = 1.5 - 2.4 GeV at forward angles (incoherent) T. Ishikawa et al., Phys. Lett. B608: 215-222(2005)

35 mb+17-11

Large φ-N interaction (σφN 　 =35mb) is obtained.

This result implies that the φ-N interaction is stronger than theoretical estimations due to the modification of the φ properties in the nuclear medium.

Introduction

Experimental setup at SPring-8/LEPS

1.5

Previous experiment(T. Ishikawa et al. Phys.Lett.B608:215-222,2005. )

This experiment

A systematic study over several kinematical region is very useful for a physical interpretation!

γ

γ

γ

K±

K±

K±

K

±

K

±

K

±

θ

the cross section of the incoherent φ-meson photoproduction with Angular dependence in the Glauber model

・ Eikonal approximation　 ( emission angle θ relative to γ-momentum = 0°)

・ The total reaction amplitude is built up from a sum of amplitudes on a single nucleon.

・ The incident particle is assumed to interact independently with each target nucleon.

・ The particle moves along a straight line trajectory through the nucleous.

・Angular dependence ( in the case of θ≠0°)

particle i(or photon)

particle f

the Eikonal formalism has been considered to Extract the in-medium properties of hadrons fromthe A-dependence of their production on nuclei.

・ In this experiments, the data are collected ata certain angular range determined by the detector acceptance.

・ A-dependence is effected by the emission angle.

-> We need to estimate how much it is effected.

azimuthal angle φ= 0°

azimuthal angle φ= 180°

θ

σi σf

nucleusnucleon

θ= 0 °

rdzbS ff exp2

1),,,(

ρA(r) : a nuclear density function taken 　　　　　　 as a Wood-Saxon distribution.

),,,(),(,2 zbSzbSzbdzbdN fiA

bTz

AiiZiezbzdzbS

,exp),(

dRrrA /exp1

0

fm8.076.028.1 3/13/1 AAR

fm/3 d

2222 cossinsinsincos zbr

θ : the emission angle of the φ-meson relative to γ-momentum

The last integration in equation being over the path of the produced φ-meson

φ : the azimuthal angle of the φ-meson

Si ; the attenuation probability of an i particle passing through the nucleus.

(b is impact parameter)

Sf ; the attenuation probability of an f particle passing through the nucleus.

J. Knoll , J. Randrup Nucl.Phys.A324: 445,1979.J. Blocki, J. Randrup, W.J.Swiatecki, and C.F.Tsang, Annal phys. 105, 427-462(1977)M. Effenberger, A. Sibirtsev Nucl.Phys.A632:99-108,1998.A. Sibirtsev , H.-W. Hammer , U.-G. Meissner,arXiv:0802.3373 [nucl-th]

bTbT

ifA

fi eebdN

21

zdzAT A ,bb

at θ= 0°limit

The effective nucleon number Aeff

the cross section of the incoherent φ-meson photoproduction with Angular dependence in the Glauber model

The slope of the Aα-dependence fitted tothe effective nucleon numbers(H,C,Cu) calculated using the above equation, for σi=0.14mb as a function of σf .

It is shown for the different emission angles; θ= 0°(black) , θ= 30°(blue), θ= 60°(purple), and θ= 90°(red).

Estimation of the effective nucleon number Neff 　 and the slope parameter α

0 10 20 30 40 50 60

0 10 20 30 40 50 600 10 20 30 40 50 60σf [mb]

σf [mb]

1

0.2

0.4

0.6

0.8

slop

eα

The effective nucleon number Aeff calculatedusing the above equation for H, C, and Cu nucleiand σi=0.14mb as a function of σf .

It is shown for the different emission angles; θ= 0°(black) , θ= 30°(blue), θ= 60°(purple), and θ= 90°(red). 1

10

102

NA

π- π+

pd

K-K+

dE/d

x (a

rb.)

momentum/charge (GeV/c)

TPC track (polar angle > 25. deg)

γ

K±

K

±

γ

K±

K

±

Analysis

both Kaon are identified by TPC.

one Kaon is identified by forwared spectrometer,and another one is detected by TPC.

Analysis

( now, only required charge information)

(use polar angle>25 degree track) +-

TPC K+ & TPC K-

number of tracks in TPC positive charged track >=1 && negative charged track >=1

track quality ; chi-square probability > 0.02

for good de/dx performance; numhits in track >= 6 polar angle > 25 deg

vertex quality ; cdist < 4.

target selection

Track cut

Event selection

Vertex cut

PID K+ & PID K-

chi-square probability cut : chi2prb > 0.02

number of hits in track : numhits >= 6

polar angle cut : polang > 25 deg.

run30000 (CH2) run30700 (C) run30200 (Cu)

track cutTPC K+ & TPC K-

0 1

0 10

closest distance < 4.

target selection ; sqrt(vtx**2+ vty**2) < 14.

target selection of vertex z

vertex cut

run30000 (CH2) run30700 (C) run30200 (Cu)

TPC K+ & TPC K-

invariant mass spectra of K+ K- from each targets

invariant mass(K+K-) GeV/c2

Cou

nts

/ 0.

002

GeV

/c2

invariant mass(K+K-) GeV/c2 invariant mass(K+K-) GeV/c2

CH2 target C target Cu target

683±77 events 397±57 events 117±23 events

TPC K+ & TPC K-

Height = 87.2±6.3Mean = 1017±0 MeVSigma = 6.2±0.5 MeVχ2/ndf = 62.16 / 38

Height = 50.2±6.3Mean = 1016±1 MeVSigma = 6.3±0.7 MeVχ2/ndf = 32.29 / 38

Height = 22.2±3.4 Mean = 1018±1 MeVSigma = 4.2±0.6 MeVχ2/ndf = 51.51 / 43

0.95 1 1.05 1.1 1.15 1.2 0.95 1 1.05 1.1 1.15 1.2 0.95 1 1.05 1.1 1.15 1.20

20

40

60

80

0

40

80

120

160

0

10

20

30

40

black : CH2

red : C(scaled by the number of photon)

invm (K+K-) [GeV]

| invm(KK) – Mφ| <0.02 GeV

| MM(KK) – Mp | < 0.1 GeV

black : CH2

red : C

free proton (CH2 - C)

Cou

nts

/ 0.

02 G

eV/c

2

Cou

nts

/ 0.

004

GeV

/c2

missing mass and invariant mass spectra of K+ K- from free proton TPC K+ & TPC K-

free proton (CH2 - C)

MissingMass (K+K-) [GeV] MissingMass (K+K-) [GeV]0 1 1.40.2 0.4 0.6 0.8 1.2

0.95 1 1.05 1.1 1.15 1.2 0.95 1 1.05 1.1 1.15 1.2

0 1 1.40.2 0.4 0.6 0.8 1.2

HCCu

arb.

MissingMass (K+K-) [GeV]

0 1 1.40.2 0.4 0.6 0.8 1.2

Monte Carlo

invm (K+K-) [GeV]

0

20

40

60

50

30

100

1020

30

40

0

20

40

60

-20

-20-10

50

30

10

-10

0

20

40

60

50

30

10

70

momentum of phi at Lab-flame [GeV/c]

free proton(CH2-C)

polar Angle at CM-system [deg]

t + |t|min [GeV2]

forward

backward

0 1 2

0-2 -1-3-4

0 18060 120

kinematics of phi | invm(KK) – Mφ| <0.02 GeV

&& | MM(KK) – Mp | < 0.1 GeV

TPC K+ & TPC K-

14

black : CH2

red : C (scaled by the number of photon)

1 2momentum of phi at Lab-flame [GeV/c]

polar Angle at CM-system [deg]0 18060 120

0-2 -1-3-4t + |t|min [GeV2]

Cou

nts

/ 0.

2 G

eV2

Cou

nts

/ 10

deg

C

ount

s /

0.1

GeV

/c

MC (proton)

polar Angle at CM-system [deg]0 18060 120

0 1 2momentum of phi at Lab-flame [GeV/c]

0

0

0

40

80

100

60

20

0

010

2030

40

-10

010203040

-10

010

2030

40

-10

40

80

60

20

40

60

20

mass/charge spectrum in spectrometer after K+K- PID(in tpc)

mass/charge [GeV/c2]

invm(K+K-)

invm(K-p)

invm(K+K-)

invm

(K- p

)

p

K-

K+

Cou

nts

/ 0.

033

GeV

/c2

Cou

nts

/ 0.

04 G

eV/c

2C

ount

s /

0.06

GeV

/c2

(CH2 target data)

phi(1020) , L(1520) in KKp identified events

TPC K+ & TPC K-φ→KKpΛ(1520)→KKpnon-resonant KKp

0 1 2-1

1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.3 1.4 1.5 1.6 1.7 1.8 1.9

0.9 1 1.1 1.2 1.30.9 1 1.1 1.2 1.3

0.9 1 1.1 1.2 1.31.31.41.51.61.71.81.9

spectrometer & TPC

number of tracks in TPC >=1

track quality cut ; chi-square probability > 0.02

target selection vtz & cdist < 4.

PID Kaon

K decay-in-flight rejection ; chi-square probability > 0.02

Target selection by z of vertex

number of tracks in spectrometer >=1

Event selection

LEPS track cut

TPC track cut

not required PID ( only charge )

spectrometer & tpc

K+ selection

chi2

vtz

chi2prob > 0.02

-1656 < vtz < -1386

spectrometer track cut (K+ ) spectrometer & tpc

K- selection

chi2

vtz

chi2prob > 0.02

-1656 < vtz < -1386

spectrometer track cut (K- )spectrometer & tpc

sqrt(vtx**2 + vty**2) <25

-1570< vtz <-1400

chi2 prob > 0.02

spectrometer & tpc

Cou

nts/

0.00

2GeV

/c2

invariant mass(K+K-) GeV/c2 invariant mass(K+K-) GeV/c2 invariant mass(K+K-) GeV/c2

forward spectrometer K+ & TPC K- event

CH2 target C target Cu target

Cou

nts/

0.00

2GeV

/c2

invariant mass(K+K-) GeV/c2 invariant mass(K+K-) GeV/c2 invariant mass(K+K-) GeV/c2

Cu targetC targetCH2 target

937±100 events 390±63 events 176±84 events

844±98 events 182±41 events386±53 events

invariant mass spectra of K+ K- from each targets spectrometer & tpc

Height = 126.7±8.5Mean = 1022±0 MeVSigma = 5.9±0.5 MeVχ2/ndf = 17.79 / 20

Height = 59.2±6.3Mean = 1021±1 MeVSigma = 5.3±0.9 MeVχ2/ndf = 29.97 / 20

Height = 15.1±3.2Mean = 1020±0 MeVSigma = 9.3±4.0 MeVχ2/ndf = 20.94 / 20

Height = 97.2±6.5Mean = 1024±1 MeVSigma = 9.0±0.7 MeVχ2/ndf = 37.23 / 25

Height = 50.4±4.5Mean = 1024±1 MeVSigma = 6.1±0.6 MeVχ2/ndf = 37.59 / 25

Height = 15.9±2.0Mean = 1026±1 MeVSigma = 9.2±0.2 MeVχ2/ndf = 16.12 / 25

0

100

200

300

400

500

600

0.95 1 1.05 1.1 1.15 1.2 0.95 1 1.05 1.1 1.15 1.2 0.95 1 1.05 1.1 1.15 1.2

0.95 1 1.05 1.1 1.15 1.2 0.95 1 1.05 1.1 1.15 1.2 0.95 1 1.05 1.1 1.15 1.2

10

20

30

0

20

40

60

80

100forward spectrometer K- & TPC K+ event

0

40

80

120

160

200

0

100

200

300

40

80

120

20

60

100

5

15

25

spectrometer K+ & TPC K-

Invariant Mass (K+K-)

free proton(CH2-C)

black : CH2

red : C(scaled by the number of photon)

Cut:| invm(KK) – Mφ| <0.02 GeV

Cut: | MM(KK) – Mp | < 0.1 GeV

Cou

nts

/ 0.

02 G

eV/c

2

Cou

nts

/ 0.

004

GeV

/c2

free proton(CH2-C)

black : CH2

red : C

missing mass and invariant mass spectra of K+ K- from free proton

Missing Mass (K+K-)0 0.2 0.4 0.6 0.8 1 1.2 1.4

Missing Mass (K+K-)0 0.2 0.4 0.6 0.8 1 1.2 1.4

0.95 1 1.05 1.1 1.15 1.2Invariant Mass (K+K-)

0.95 1 1.05 1.1 1.15 1.2

0

40

80

120

160

200

0

40

80

-40

100

200

300

400

500

0

50

100

150

-500

forward

backward

0 1 2

polar Angle at CM-system [deg]0 18060 120

t + |t|min [GeV2]

0-2 -1-3-4

free proton(CH2-C)

black : CH2

red : C

momentum of phi at Lab-flame[GeV]

| invm(KK) – Mφ| <0.02 GeV

&& | MM(KK) – Mp | < 0.1 GeVkinematics of φ spectrometer K+

& TPC K- C

ount

s /

0.2

GeV

2

Cou

nts

/ 10

deg

C

ount

s /

0.1

GeV

/c

MC (proton)

Cut:

0 1 2momentum of phi at Lab-flame[GeV]

0 1 2momentum of phi at Lab-flame[GeV]

polar Angle at CM-system [deg]0 18060 120

polar Angle at CM-system [deg]0 18060 120

t + |t|min [GeV2] t + |t|min [GeV2]0-2 -1-3-4 0-2 -1-3-4

0

200

400

600

0

100

200

50

150

250

0

100

200

50

150

0

40

8060

20

-20

100

300

500

100

spectrometer K-

& TPC K+

black : CH2

red : C

free proton (CH2 - C) Cut:

| invm(KK) – Mφ| <0.02 GeV

Cut: | MM(KK) – Mp | < 0.1 GeV

Cou

nts

/ 0.

02 G

eV/c

2

Cou

nts

/ 0.

004

GeV

/c2

missing mass and invariant mass spectra of K+ K- from free proton

Missing Mass (K+K-)0 0.2 0.4 0.6 0.8 1 1.2 1.4

Missing Mass (K+K-)0 0.2 0.4 0.6 0.8 1 1.2 1.4

Invariant Mass (K+K-)0.95 1 1.05 1.1 1.15 1.2

Invariant Mass (K+K-)0.95 1 1.05 1.1 1.15 1.20

40

80

120

0

40

80

120

160

0

0

40

80

-40

40

80

120

momentum of phi at Lab-flame[GeV]

forward

backward

polar Angle at CM-system [deg]0 18060 120

t + |t|min GeV20-2 -1-3-4

black : CH2

red : C

free proton (CH2 - C)

0 1 2

| invm(KK) – Mφ| <0.02 GeV&& | MM(KK) – Mp | < 0.1 GeV

spectrometer K-

& TPC K+ Kinematics of φC

ount

s /

0.2

GeV

2

Cou

nts

/ 10

deg

C

ount

s /

0.1

GeV

/c MC (proton)

Cut:

0 1 2

0 18060 120

t + |t|min GeV2

0-2 -1-3-4

0 1 2

0 18060 120

0-2 -1-3-4t + |t|min GeV2

polar Angle at CM-system [deg]

momentum of phi at Lab-flame[GeV]momentum of phi at Lab-flame[GeV]

polar Angle at CM-system [deg]

0

40

80

120

160

0

40

80

20

60

100

0

100

200

300

0

40

80

120

0

200

400

600

0

50100150200

invm(K+K-)

invm(K-p)

invm(K+K-)

invm

(K-p

)

K+

K-

p

Cou

nts

/ 0.

06 G

eV/c

2

(CH2 target data)

required PID K+K-p

φ(1020) , Λ(1520) in K+K-p identified events

φ→KKpΛ(1520)→KKpnon-resonant KKp

MC

1.3 1.4 1.5 1.6 1.7 1.8 1.91.3 1.4 1.5 1.6 1.7 1.8 1.9

0.9 1 1.1 1.2 1.30.9 1 1.1 1.2 1.3

0.9 1 1.1 1.2 1.31.3

1.5

1.7

1.9

1.4

1.6

1.8

Cou

nts

/ 0.

04 G

eV/c

2

0

20

40

60

0

10

20

invm(K+K-)

invm(K-p)

invm(K+K-)

invm

(K-p

)K-

K+

p

Cou

nts

/ 0.

04 G

eV/c

2C

ount

s /

0.06

GeV

/c2

(CH2 target data)

required PID K+K-p

φ(1020) , Λ(1520) in K+K-p identified events

φ→KKpΛ(1520)→KKpnon-resonant KKp

0.9 1 1.1 1.2 1.3 0.9 1 1.1 1.2 1.3

0.9 1 1.1 1.2 1.3

1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.3 1.4 1.5 1.6 1.7 1.8 1.9

1.3

1.5

1.7

1.9

1.4

1.6

1.8

0

10

20

0

10

20

30

Summary

We have performed hyperon photoproduction experiment at SPring-8/LEPS 　with CH2 , C and Cu target using 1.5 –2.4 GeV photons.

Time Projection Chamber surrounding the target extended the acceptance to backward region. LEPS standard detector system (forward spectrometer system) were used to detect forward going particles.

In this talk, the status of the analysis of φ(1020) photoproduction has been reported. The determination of theφ-N cross section will be done in near future.