Backward φ photo-production from C and Cu targets at Eγ = 1.5 - 2.4 GeV

Takahiro SawadaInstitute of Physics, Academia Sinica

Regular Seminar, AS, 17 May. 2013

2

・ Introduction

・ Experiment

・ Result & Discussion

・ Summary

Table of Contents

3

φ-meson properties in nuclear medium

Dropping mass

Width broadening

Brown & Rho (Brown & Rho scaling) m*/m = 0.8　　Hatsuda & Lee (QCD sum-rule) m*/m = 1 - 0.16ρ/ρ0 (for ρ/ω) m*/m = 1 - 0.03ρ/ρ0 (for φ) Muroya, Nakamura , Nonaka (Lattice calc.)

Klingl, Weise (Effective Chiral Lagrangian) 45MeV for φ (ρ=ρ0) 　Oset , Ramos (Renormalization of Kaon) 22MeV for φ (ρ=ρ0)Cabrera, Vicente (Renormalization of Kaon) 33MeV for φ (ρ=ρ0)

T. Hatsuda, S.H. Lee Phys. Rev. C 46, 34(1992)

E. Oset, M.J. Vicente Vacas, H. Toki, A. RamosPhys.Lett. B508 (2001) 237-242

in the nuclear medium

in free space

Normalize

y ; The strange contents in the nucleon𝑦=2<𝑠𝑠¿𝑁 /¿

Introduction

4More works are still required

Mass-Shape Measurement

CERES/NA45

GSI/HADES

CERN-SPS/NA60

RHIC/PHENIX

e+e- spectrum in high-energy heavy-ion collisions

e+e- spectrum in 2 GeV·A C-C collisions

μ+μ- spectrum in 158 GeV·A In-In collisions

e+e- spectrum in Au+Au collisions at √sNN = 200 GeV

No clear evidence for

the modification.

KEK/E325

e+e- spectrumin 12 GeV p+A

βγ < 1.25Excesses

・ Small FSI・ Small branching ratio (~10-4)・ Many backgrounds.

JLab/CLAS-g7No clear evidence

e+e- spectrum in Eγ < 3.8 GeV

Evidence for thedropping mass ?

In dilepton decay channel

Introduction

→ J-PARC E16

e+

e-

e+

e-

5

A-dependence Measurement

Mass Number A

Prod

uctio

n Ra

te o

f In

cohe

rent

φ P

hoto

-Pro

ducti

on

Photon

φ mesonAbso

rption

Mass Number A

Tran

spar

ency

Rati

o

σφN

σγN

～ 0.14 mb

OZI suppression

Expected

RφAT =

RφC

/ A

/ AC

12C

・ Dominant K+ K− Branching ratio ( ～50%)・ Cancellation of Systematic Errors

Nucleon

Nucleus

RφA ∝ Aα

Theoretical CalculationQuark model : 13.0 ± 1.5 mbVMD model : 8.2 ± 0.5 mb

Expected1

～ 10 mb

Introduction

6

A-dependence @ SPring-8/LEPS

+17-11σφN = 35 mb !!

Glauber multiple scattering theory

T. Ishikawa et al. Phys.Lett. B608 (2005) 215-222

photo-production at Eγ = 1.5 – 2.4 GeVφ → K+K- 　

< pφ > = 1.8 GeV/cLi, C, Al, and Cu targets.

Mass Number A

σA A∝ 0.72±0.07

Inco

here

nt φ

pho

to-

prod

uctio

n cr

oss

secti

on

(arb

)

Incoherent φ photo-production cross section

φ-N interaction cross section

Introduction

7

σφN ( φ-N interaction )

・ OZI suppression.Analogy to other mesons ( K+ , K- , π± )

・ φ-N resonance has not been reported.

ln2(s/s0) + ・・・total

・ Total hadronic cross section at a few GeV region

σφN < σK+N < σK-N , σπ+N , σπ-N 18 mb 30 mb 30mb 35mb

・ At 2 GeV/c

π+p total

π+p elasticσ π+p (m

b) π+ momentum (GeV/c)

Resonance

π production

?

Theoretical CalculationQuark model : 13.0 ± 1.5 mbVMD model : 8.2 ± 0.5 mb

Introduction

8

A-dependence @ CLAS/JLab

M. H. Wood et al. Phys.Rev.Lett. 105 (2010) 112301

Transparency ratios

photo-production at Eγ < 3.8 GeVφ → e+e- 　

< pφ > = 2 GeV/c .2H, C, Ti, Fe, and Pb targets.

e+e- invariant mass (GeV/c2)

Mass Number A

→ 　 σφN = 16-70 mb

ρ meson contribution

after subtractionfrom ρ meson contribution

Introduction

9

A-dependence @ ANKE-COSY

M. Hartmann et al, Phys.Rev. C85 (2012) 035206

2.83 GeV proton beam

C, Cu, Ag, and Au targetspφ ; 0.6 - 1.6 GeV/c

COSY

Transparency ratios φ-N cross section

Extracted

φ → K+K- 　

Momentum of φ meson (GeV/c)Transparency ratio decreases with φ momentum.

Momentum of φ meson (GeV/c)

(16-70 mb)

!?

Introduction

10

What does this result mean?

Nucleonp

φ-meson at slow speed.

Nucleonp × φ-meson at fast speed.Absorption

Transparent

Strongly Modified !?!?

Nucleus

Nucleus

The verification experiment using Photon-Beam is desired.

No Modified ?

Introduction

11

SPring-8 (Super Photon ring - 8 GeV)

• 3rd-generation synchrotron radiation facility

• 8 GeV electron beam• Circumference = 1436 m• RF = 508 MHz• One-bunch is spread within σ = 12 psec.• Beam Current = 100 mA• Top-up injection

Experiment

12

e 8GeV-

8 GeV Electron Experiment

13

Bremsstrahlung Photon

e 8GeV-

γ

γ

γ

Experiment

14

Beam Line Map

Operational; 54Planned or Under Construction; 3

The Number of Beamlines

April 3, 2012

Experiment

15

Backward Compton Scattering Photon

e 8GeV-

UV-Laser

Collide !!

γ

Experiment

16

Backward Compton Scattering Photon

e 8GeV-

UV-Laser

Collide !!

γ

Experiment

BCS photons

Bremsstrahlung photons

Photon Energy (GeV)

Coun

ts

・ Photon energy measurement・ Polarized photon beam・ Forward Detector

17

Laser hutch

SR ring

Experimental hutch

Backward Compton γ-ray

Laser light

8 GeV electron Recoil electron

Tagging counter

Collision

36m70m

LEPS facility

・ Photon energy measurement・ Polarized photon beam・ Forward Detector

(Laser Electron Photon Experiment at SPring-8)

Experiment

18

LEPS Detector Setup

Forward Spectrometer• TOF : RF signal - TOF wall, Δt = ~150 ps• Momentum : Δp ~ 6 MeV/c for 1 GeV/c K• Acceptance : Hori ±20o , Vert ±10o

TPC• 20o < θ < 160o

• Δp/p ~0.1• Δφ ~0.04 rad

Standard Setup w/ TPC

Experiment

19

Time Projection Chamber (TPC)

600mm

E (180 V/cm)

B (2 T)

beam

Charged Particle

Target

② Drift~ 5 cm/μsec

γ①

Ioni

zatio

n

③ Avalanche

④ M

easurement

3-dimensional Tracking Detector

・ Track Curvature → Momentum

・ Ionization Energy Loss (dE/dx) 　 → Particle Identification (π/K/p)

・ Avalanche Positions + Drift Times → 3-D Trajectory of the Charged Particle

(Gas-filled Cylindrical Chamber + MWPC)・ Large Acceptance・ Small Amount of Material

Experiment

20

Difficulty in This Experiment

・ TPC has the best performance for the tracks emitted in the sideward direction.

・ We have improved the analysis procedure to measure the tracks emitted in the forward direction.

Collider Experiment Cosmic Ray Experiment

Fixed Target Experiment

TPC TPC

TPC

Beam Beam

BeamTarget

Experiment

210 1 2 3 4 (m)

Collimator

Buffer Start

Dipole Magnet TOF Counters

DC1DC2 DC3

TPC

Solenoid Magnet

Up Stream e+e-

Veto Counter

Aerogel CherenkovCounter

^

Trigger Scintillator

Counter

(TPC-FWD)

Trigger Scintillator(TPC-SIDE)

γCollimator

Target

Start

Dipole Magnet TOF Counters

DC1DC2 DC3

Aerogel CherenkovCounter

^

SVTX

Counter

γ

Target

Detector Acceptance

Previous Experiment

This Experiment

Acceptance Forward + 20o < θ < 160o

Acceptance Hori ±20o

Vert ±10o

(w/ TPC)

(Standard Setup)

Experiment

22

Detection Modes for φ mesons

γ γKK

p

±

±γ

KK

p

+

-

TOF Counters

TPC

Drift Chambers

K

K+

-

TOF Counters

Drift Chambers

γ

Previous Experiment This Experiment

p

KK+

-

Momentum of φ meson in LAB system Fast Slow

(Standard Setup) (w/ TPC)

TPC TPC

Angle of φ meson in CM systemForward Backward

Experiment

φ Experiment with Nuclear Targets @Spring-8/LEPS

This experiment Previous experimentPeriod Sep.- Dec. in 2004 Nov. in 2001Beam 1.5-2.4 GeV photons

Targets C, Cu, and CH2 Li, C, Al, and Cu

Reaction φ → K+ K-

Main Detectors TPC + LEPS spectrometer LEPS spectrometer

φ momentum pφ = 0.3-2.0 GeV/c pφ = 1.0-2.2 GeV/c (Average 1.8 GeV/c)

23

Experiment

24

K+ K- Invariant Mass

0.6< pφ<1.3 (GeV/c)in tpc K P spK mode±

±

χ2/ndf = 149/102Nφ= 178±16

C target ー DATAー Fit resultー φ→K+K- (determined by the MC simulation)ー background (2nd-order polynomial)

Fit range ; 　 from 2mK±(0.987) to 1.2 GeV/c2

Summary Table

Contamination from miss-PID (π,p)

K+K- Invariant Mass (GeV/c2)

2 mK± (0.987 GeV/c2)Constraint

Coun

ts (/

2MeV

/c2 )

Result & Discussion

25

Transparency Ratio

● This experiment (C and Cu)Previous experiment (Li, C, Al, and Cu)

Transparency ratio decreases with φ momentum.

Here, the production rate of φ mesons 　

Tran

spar

ency

Rati

o

Momentum of φ meson (GeV/c)

Result & Discussion

26

Model Calculation

dRrrA /exp1

0

fm8.076.028.1 3/13/1 AARfm/3 d

Nuclear density distribution: Woods-Saxon

photon φ meson

σγN = 0.14mb σφN

nucleusnucleon

rdzbS exp2

1),,,(

),,,(),(,2 zbSzbSzbdzbdN effA γ

bTz

ANZNezbzdzbS γ

γγ

,exp),(

2222 cossinsinsincos zbr

𝑇𝑟𝑎𝑛𝑠𝑝𝑎𝑟𝑒𝑛𝑐𝑦 𝑅𝑎𝑡𝑖𝑜=𝑅𝐶𝑢

❑ / 𝐴𝐶𝑢

𝑅𝐶❑/ 𝐴𝐶

=𝑁𝐶𝑢

𝑒𝑓𝑓 / 𝐴𝐶𝑢

𝑁𝐶𝑒𝑓𝑓 / 𝐴𝐶here,

φ

φ

Glauber Approximation

The model calculation ; 　　 Transparency Ratio 　 　　 σφN

,

Systematic errors from “angle effect”

in tpc K P spK mode±

±

in tpc K+K- P , tpc K+K- spP modes

at σφN = 10mb~ 0.2%~ 0.9%

We calculated as the emission angle =0.

Result & Discussion

27

σφN = 21.7 mb+8.7-6.2

χ2/ndf = 6.95 / 3 ( χ2 prob.= 7 % )

Tran

spar

ency

Rati

o

pφ(GeV/c)

Blue: w/o KNRed: w/ Strong KN

σφN

Not So Good.

Momentum Dependent ?

Result & Discussion

28

Momentum Dependent ??

σφN = α (const.)

σφN = α ・ pφ

σφN = α ・ pφ2

Momentum Independent

Result & Discussion

29

σφN (Momentum Dependent)

σφN = α(const.) σφN = α ・ pφ

χ2/ndf = 6.95 / 3 ( χ2 prob.= 7 % )

χ2/ndf = 2.77 / 3(χ2 prob. = 43%)

σφN = α ・ pφ2

χ2/ndf = 1.32 / 3 (χ2 prob. = 72 %)

Tran

spar

ency

Rati

o

pφ(GeV/c)

Blue: w/o KNRed: w/ Strong KN

More Appropriate

Result & Discussion

30

σφN (Momentum Dependent)

σφN = α ・ pφ2

χ2/ndf = 1.32 / 3 (χ2 prob. = 72 %)

Tran

spar

ency

Rati

o

pφ(GeV/c)

σφN = 6.8 mb+3.4-2.3

σφN = 88.1 mb +43.7-29.8

At lower pφ (0.5 GeV/c)

At higher pφ (1.8 GeV/c)

Consistent with the theoretically predicted value in free space.

Unexplainable value !!!

α = 27.2 mb/(GeV/c)2+13.5-9.2

Result & Discussion

31

Discussion

This suggests that the cause of the transparency ratio reduction at higher pφ is not the φ-N interaction.

If so, Why ? What's happening ?

Result & Discussion

32

Discussion

● Propagation

Photon

φ meson

Absorp

tion

σφN

σγN Nucleon

Nucleus

● ProductionThe number of φ-mesons produced on nucleon is (almost) proportional to the target mass number A.

The flux of φ-mesons is decreased by the σφN .

Fixed

Measured

Unexplainable

In higher pφ , (= Diffractive) φ photo-production might have a strong A-dependence.

Result & Discussion

Discussion

R φCuTransparency Ratio =

R φC

/ ACu

/ AC

Decreasing ?

Increasing ?

( RA ; Production Rate)φ

33

Data-taking with many kinds of target nuclei.Improvement of the statistical precision.

For further study

●

●

Measurement of the absolute cross section for each target (not the “ratio”)

●

Measurement at higher pφ .●

( Decreasing )

Result & Discussion

34

Related Topic

W.C. Chang et al. Phys.Lett., B684:6–10, 2010.

Eγ (GeV)[ (dσ

d /dt

) / (2

*dσp /

dt) ]

t=tm

in

Tran

spar

ency

Rati

o

Transparency ratio for the deuteronat forward angles → A significant reduction

Some effect other than nuclear density ?

φ photo-production from the deuteron target @ SPring-8/LEPS

35

Summary

・ We have confirmed that the transparency ratio decreases with pφ.

・ The reduction of the transparency ratio shown in the high pφ region suggests that ・ σφN increases as pφ

2 . ・ a diffractive φ photo-production might have a strong A- dependence.

・ For further study, we point out the importance of the measurement of the absolute cross section for each target, of the improvement the statistical precision, of the data-taking with many kinds of target nuclei, and of the measurement until more higher pφ .

Summary

36

Thank you for your attention !!