Incoherent φ 　 photo-production from deuteron at SPring-8/LEPS

M. Miyabe博士論文審査５人委員会

contents

• Physics motivation• Experiment• Analysis• Results • Conclusion and discussion• summary

Vector Meson Photo-production

● Vector Meson Dominance

● Meson Exchange

● Pomeron Exchange

N

N

(~ss)

q

_q

_qq =

Dominant　at　low　energies

Slowly　increasing　with　energyAlmost　constant　around　threshold uud

p p

p p

M.A.　Pichowsky　and　T.-S.　H.　LeePRD　56,　1644　(1997)

Prediction　from　Pomeron　exchange

Prediction　from　meson　exchange

Data from: LAMP2('83), DESY('76), SLAC('73), CERN('82),FNAL('79,'82), ZEUS('95,'96)

Prediction : dominant contribution formpseudo scalar meson exchangenear threshold

Vector Meson Photo-production

Titov,　Lee,　Toki　Phys.Rev　C59(1999)　2993

Data from: SLAC('73), Bonn(’74),DESY(’78)

Natural parity exchange

Unnatural parity exchange

Important to distinguish natural parity exchanges from unnatural ones

P2: 2ndpomeron ~ 0+glueball

(Nakano, Toki (1998))

=0

deg

ree)

photo-production near threshold

Polarization observables with linearly polarized photon

Decay　Plane　//　natural　parity　exchange　(-1)J　(Pomeron,　Scalar　mesons)

Polarizationvector of

K+

K+

K-

In　　meson　rest　frame

Decay　Plane　　　　　　unnatural　parity　exchange　-(-1)J　

(Pseudo　scalar　mesons　)

Relative contributions from natural, unnatural parity exchanges

Decay angular distribution of meson

K+

K+

K-

p’

meson rest frame (Gottfried-Jackson(GJ) frame)

K+

K+

K-

polProduction

planez

Decayplane

z-axis

K+-pol

direction of linear polarization

Decay angular distribution of meson

Decay angular distribution

● W0,W1,W2 are parameterized by the 9 spin density matrix elements. Re() Im() andIm()

),(),,( 0 WW

),()2sin(),()2cos( 21 WPWP Unpolarized part

Polarized part

K.Schilling et al. Nucl. Phys. B15(1970) 408

Spin density matrix elements

)(2cos~12

1)( 3

PW

2

12

1 cos~sin~121

23

)(cosW

22 cos~21

2

1)( W

)(2cos~12

1)( 4

PW

2cos~12

1)( 5 PW

1-dimensional　projections

100

1115

211

1114

211

1113

0112

0001

2~Im2/1~Im2/1~

~

~

Relations　to　standard　definition

distribution

Prediction by A. Titov (PRC,2003)

Pure naturalparity exchange

Pure unnaturalparity exchange

0

P, glueball, , f2’

p

)(2cos~12

1)( 3

PW

11

LEPS result (proton)

Peak structure around 2GeV.Natural parity exchange is dominant　→　 0+ glueball ?Pseudo scalar meson exchange is not negligible.

T. Mibe, et al. nucl-ex/0506015

Explore the exotic process• Is the bump structure candidate of 2nd Pomeron

(glueball)?– Only decay asymmetry can explain using Pseudo

scalar exchange, But for cross section enhancement, Need to natural parity exchange comparable effect from Pseudo scalar exchange process.

– Detailed study for pseudo scalar π-η exchange is important.

To study incoherent photo-production from deuteron is unique tool.

2005/09/21 HAW05 13

φ photo-production of Deuteron

1. Coherent production– Interact with deuteron

itself.

2. Incoherent production– Interact with proton or

neutron in deuteron.

2005/09/21 HAW05 14

Coherent production• Deuteron is iso-scalar target

– Iso-vector π exchange is forbidden.• Pure natural parity exchange except for η-exchange process.

LEPS result

Differential cross section Decay asymmetry

Differential cross section at t=tmin showsDecreasing with energy. Dashed line shows theoretical calcuration.

Decay asymmetry showsnatural parity exchange is dominant

From coherent result

• Differential cross section– Increase with energy– Not only Pomeron and η-exchange

• Decay asymmetry– Pure natural-parity exchange– η-exchange is weak?

Additional natural parity process is required!

Incoherent production• Due to isospin effect,

– gπnn = - gπpp → destructive– gηnn = gηpp → constructive π-η interference effectDetail Information for unnatural (π/η) exchange process

2005/09/21 HAW05 17

g(π, η)NN

gφγ (π, η)

π,η

φγ

N N

Differential cross section for as a function of energy and angle.

For πη interference effect, neutron cross section decrease at low energy and forward angle.

Decay asymmetry as a function of energy and η-exchange strength

Decay asymmetry Σφ=2ρ3

Eγ=2 GeV

Large difference for decay asymmetry cause large η-exchange process

Aim of this thesis

• Differential cross section for incoherent process– (π 、 η)-interference

• Decay asymmetry for γ+N→φ+N – η-exchange process magnitude

Extract clearly quasi-free γ+N→φ+N eventExplore the exotic pomeron exchange in the Bump

structure.

Nuclear transparency ratio

• T=σA/(A*σN ) (=Pout)• Mass number

dependence is larger than theoretical calculation.

• Large σφN in nuclear medium.– How about duteron

case?

EXPERIMENT

The LEPS beamline

Linearly polarized Photon

• Backward Compton scattering by using UV laser light• Intensity (typ.) : 2.5 * 106 cps• Tagging Region : 1.5 GeV< E < 2.4 GeV• Linear Polarization : 95 % at 2.4 GeV

E (Tagger) (GeV)E (GeV)

Cou

nts

Line

ar

pola

rizat

ion

Charged particle spectrometer

1m

TOF wall

MWDC 2

MWDC 3

MWDC 1

Dipole Magnet (0.7 T)

Liquid Hydrogen Target50mm-long (2000 Dec.-2001June)150mm-long (2002May-July)

Start counter

Silicon VertexDetector

AerogelCerenkov(n=1.03)

Summary of data taking

● Trigger condition : TAG*UpVeto*STA*AC*TOF● Run period

I (50mm-long LH2) 2000,Dec. – 2001, June

II (150mm-long LH2) 2002,May - 2002.JulyIII (150mm-long LD2) 2002,July – 2003 Feb, Apr-Jun

● Total number of trigger I 1.83*108 trigger (~50% Horizontal, ~50% Vertical pol.) II 1.71*108 trigger III 4.64*108 trigger

ANALYSIS

φ Event selection

• Number of track ≧1• K+ , K- Particle Identification cut (PID)• Decay in flight cut (DIF)• Vertex cut• Tagger• Invariant Mass K+K- cut• Missing Mass cut

Particle identification and decay in flight cut

Kaon identification is 4σ

• Consistency of TOF hit position– Difference of y-position of

TOF ≦80mm– Difference TOF slat number

≦ 1

• Number of outlier– Noutl ≦ 6

• χ2 probability– Prob(χ2)≧0.02

Decay in flight cut

Vertex cut

-1120. < Vertex z < 880. -30< Vertex(x,y) < 30

Invariant mass K+K-

• Fit with Gaussian convoluted breit-weigner

• Resolution~1.5MeV

Cut point for invariant mass is 10MeV

Missing Mass cut

• Missing mass distribution forγ + p → φ X (MMp)

• From the fermi motion effect

• Cut for MMp at LD2 set to 80 MeV

Summary of φ selection

Procedure analysis for quasi-free like Incoherent γ+N→φ+N production

• LEPS spectrometer has designed for forward φ→K+K- event– Exclusive γ+n→φ+n event can’t accept.

Precisely analysis for possible reactions is required.Coherent processFinal State Interaction(FSI)Fermi motion effectFortunately, exclusive γ+p→φ+p has a small

acceptance.

Energy Definitions

For cross section

For decay asymmetry

Minimum momentum spectator approxmation

γ

np

n

p

φ

n

p

PCM

np

γ PKK

EKK

PγEγ

Pmiss

Emiss

In the lab system, the missing momentumBecome minimum at the direction is anti-parallel to photon

The momentum of pn system as

Pmin characteristic

• coherent process– Pmin ~ +0.15

– Dominant Pmin ≧0.1

• Quasi-free process make peak around zero.

• Other inelastic reactions distribute large negative value.

Monte-Carlo simulation for Pmin

• coherent process– Dominant > 0.1GeV

• Quasi-free process clear symmetric peak around zero.

• around Pmin ~ 0.1GeV cut point for quasi-free process

Pmin distribution in MC

Extract quasi-free incoherent process

Pmin distribution Real with MCContamination from coherent as a function of Pmin cut

Coherent contamination is large in High energy region about 10% at Pmin≦0.09 in this estimation

Validity check for Quasi-free process cut |Pmin |≦ 　 0.9

slope Differential cross section

Pmin cut dependence is flat |Pmin|=0.9 at Slope and cross section except for 2-Highest energy bin. In E8, about 10% fluctuation from the tighter cut.

Introduce the effective photon energy

• Pmin strongly correlated to z-component of fermi momentum inside deuteron.

• Pmin could be used for estimating Fermi momenta of target nucleons.Total center of mass

energy s of KKN system

Pmin vs. Fermi momentum z

Conversion Eγeff from Eγ

• Effective photon energy Eγeff as

s is the center of mass total energy of KKN system.

• Resolution for Eγ is improved. (~50%)

Eγ resolution

Conversion to effective photon flux

Photon flux ωγ for each Eγ as ωγ(Eγ)=εTag(Eγ) ＊ Ntag

εTag(Eγ) : Tagger efficiencyNtag : corrected tagger scalar count

In nucleon at rest frame,

At one specific Eγeff, it depends on some Eγ which spread over because of fermi motion.Conversion ratio from each Eγ bin is calculated using Monte-Carlo.

Conversion ratio

originalEmin Emax Frac

1.573 1.673 .31905E+12

1.673 1.873 .32266E+12

1.773 1.873 .36441E+12

1.873 1.973 .39824E+12

1.973 2.073 .50882E+12

2.073 2.173 .53101E+12

2.173 2.273 .62225E+12

2.273 2.373 .53687E+12

2.373 2.473 .18670E+12

Eγeff = 1.973-2.073

0.005

0.26

0.56

0.20

New Frac (1.973-2.073) = 0.005*0.364E+12 + ・・・ +0.20*0.53E12

Eγ

Estimate the Final state interaction

• In the threshold energy, momentum of outgoing nucleon is small.– Final state interaction?

• Strength of FSI is enhanced in small relative momentum p and n. (similar kinematics in coherent)

np

n

φγ

p

Monte Carlo simulation

• Real data fitted with Monte Carlo simulation coherent, incoherent and FSI.

• FSI contribution is very weak at all energy bin.

Missing Mass distribution MMD

Black :real, red coherent green: incoherent, blue: FSI

P-N relative momentum fitP-n relative momentum fitted FSI.

χ2/ndf distributionas a function of FSI strength

Weak FSI effect become better χ2weak

FSI effect is negligible small

Background subtraction

• Assuming the Background shape is non-resonant KK event.

• Estimate the number of background with side band region.

Non-resonant K+K- invariant mass

RESULT

Differential cross section t dependence. Fitted function as dσ/dt = C*exp(-b*t)

Fitted result of slope parameter bAs a function of Eγeff

Not monotonic behavior of slope,Slope b = 3.74 +/- 0.12 (free proton b=3.38+/-0.23)

Differential cross section at t=tmin

dσ/dt at (θ=0) with Constant slope b=3.74

Differential cross section at forward angle.Not clearly seen the bump like structure.

Differential cross section with tighter Pmin cut

Not monotonic behavior of slope,Slope b = 3.45 +/- 0.13 (free proton b=3.38+/-0.23)

dσ/dt at (θ=0) with b=3.45 t dependence Pmin ≦50

Cross section decrease at E1~E3

3-particle KKp mode

dσ/dt at (θ=0) with Constant slope b=3.38

Cross section for Exclusive K+K-p event. Very limited statistic. The bump like structure was seen same as free proton

Decay angular distribution

ρ1~5 as a function of EγDecay angluar distribution

Conclusion and Discussion

• Differential cross section at t=tmin

– About 30% reduction from free proton

• Not a simply nuclear density effect since deuteron is loosely bounded.– φ→ω 　 conversion?

Red : incoherent γN→φNBlack: free proton

Lower Histgram Td = (dσ/dt)N/2*(dσ/dt)p

Differential cross section in KKp mode

• Similar degree of reduction such as incoherent process– π-η 　 interference is small

Red : exclusive KKp eventBlack: free proton

Lower Histgram Td = (dσ/dt)KKp/(dσ/dt)free p

Spin density matrix element

• ρ3N is little bit higher than free proton.

• Theoretical prediction of ρ3n is 0.25~0.30.– ρ3N is 0.23~0.25 good agreement

• Small difference ρ3

p and ρ3n

– η-exchange is small

ρ3 　 as a function of Eγ

ρ3

Red : γ+N→φ+NBlack : γ+p→φ+p

Tighter Pmin cut

Differential cross section at t=tmin

Red : incoherent γN→φNBlack: free proton

Red : γ+N→φ+NBlack : γ+p→φ+p

ρ3 　 as a function of Eγ

Decrease in Highest energy region

Summary• Differential cross section for incoherent φ photo-production shows a

significant reduction from free proton– Some effect other than nuclear density is necessary (ex, φ-ω conversion).

• From analysis for exclusive KKp event, – π-η interference is small.

• Decay asymmetry ρ3 is similar with free proton one– η 　 exchange component is weak.

　　　 Bump structure around Eγ= 2GeV for γ+p→φ+p→ a new natural parity candidate (glueball).

Pmin≦90 MeV(50MeV) selection cut occurs a large systematic err in

highest energy bin. More detailed study is needed.

Backup figures

Eγ vs. Eγ(n)

Eγ

Eγ(n)

Spin density matrix

Horz Vert

Spin density matrix

ρ

Horz, Vert Horz+Vert

Spin density matrix element

Spin density matrix element

Vert

Horz

Pmin dependence

slope Differential cross section

Photon flux

Photon flux

Comparison to LEPS result

Tagger cut

Coherent contamination

Lambda(1520)

Non-resonant BG

2005/09/21 HAW05 76

Experiment at Spring-8

•8GeV electron storage ring Harima Hyogo

Liquid hydrogen target150mm

Drift Chamber calibration

• Depth of the multi hit TDC ~3 (before 8)

• High Voltage value of sense wire is large.

• Threshold for discri-amp is low.– Noisy level is high

t0 calibration

• Large fluctuation in TDC offset value t0 .– Every 10 run calibration.

DC-t0 run dependencerun

tdc

xt-calibration

• Xdrift = c1t+c2t2+c3t3+c4

• Correct the origin-point• Calcurate parameters

when resolution and efficiency are down

Result of calibration

Number of outlier Χ^2 probability

LH2(short)

LH2(long)

LH2(long)