photoproduction at SPring-8/LEPS Oct / 9 / 2018 RCNP Osaka - - PowerPoint PPT Presentation

Recent results of pion and kaon photoproduction at SPring-8/LEPS

Oct / 9 / 2018 RCNP Osaka University / Nagoya University Hideki Kohri

1

SPring-8 beamline map

LEPS2 LEPS beamlines

2

SPring-8 SR ring

Inverse Compton

g-ray Laser light 8 GeV electron Recoil electron Electron tagging Collision

LEPS facility constructed in 2000

Experiment hutch 10m 20m Laser hutch

Photon beam

Energy Eg = 1.5-2.95 GeV Intensity ~106 g/s Polarization linearly and circularly polarized beams. P~90% at the maximum photon energy.

3

g LEPS detector (optimized to detect f decaying to K+K-)

1m TOF wall MWDC 2 MWDC 3 MWDC 1 Dipole Magnet (0.7 T)

Target

LH2, LD2

Silicon Vertex Detector Aerogel Cerenkov (n=1.03)

Start counter

4

K+ K-

We are analyzing the data taken for K*0S+ photoproduction in 2007

• > K+p-

5

S.H. Hwang Ph.D. thesis Pusan National University (2012)

One of our physics objectives is to understand how hadrons are produced

(1) g p -> p+ n reaction dd production in the final state (2) g p -> K+L and K+S0 reactions ss production in the final state (3) g p -> p- D++ reaction uu production in the final state (4) g p -> p+ D0 reaction dd production in the final state I want to obtain unified understanding of various qq productions.

6

Another physics objective Missing resonance search

7

Simon Capstick and W. Robers Phys. Rev. D 58 074011 (1998)

Quark models predict more nucleon resonances than

• bserved experimentally.

Such missing nucleon resonances may be coupled to other channels than pN.

Reaction mechanisms of KY photoproduction

8

Very weak when a meson is produced at forward angles. Strong when a meson is produced at forward angles. s channel t channel u channel

Measurements of photon-beam asymmetry

(1) g p -> p+ n reaction (2) g p -> K+L and K+S0 reaction (3) g p -> p- D++ reaction (4) g p -> p+ D0 reaction We used linearly polarized photon beams. Photon-beam asymmetry (S) is sensitive to reaction mechanisms.

S

Positive p < r Natural parity exchange Positive K < K* Natural parity exchange Negative p > r Unnatural parity exchange Positive p < r Natural parity exchange

9

(1) Differential cross section and photon-beam asymmetry for the g p -> p+ n reaction at forward p+ angles at Eg=1.5-2.95 GeV

• H. Kohri, S.Y. Wang, S.H. Shiu, W.C. Chang, Y. Yanai et al.

LEPS Collaboration

Published in Phys. Rev. C 015205 (2018) on the 22nd of Jan.

10

Abstract

Missing mass p(g, p+)X

11

Neutron peaks are separately observed for 0.6 < cosq < 0.966. Positron mis-identification produces background between n and D0 for 0.966 < cosq < 1.

Differential cross sections for g p -> p+ n

12

Forward peaking cross sections are observed. t-channel reaction is found to be dominant.

13

Differential cross sections for g p -> p+ n

ds/dcosq decreases as Eg increases for 0.6 < cosq < 0.9. The energy dependence of Eg < 2.2 GeV is different for 0.9 < cosq < 1. This energy dependence might be due to N* or D*, as reported by the DESY group. Good agreement with CLAS(□) and DESY(▲) data.

(1996, 1997) (2009)

14

Ratio (NV – NH) / (NV + NH)

p+ prefers to scatter at fp angles perpendicular to the polarization plane. Photon-beam asymmetries for g p -> p+ n are found to be positive.

Photon-beam asymmetry S for g p -> p+ n

15

SLAC data (1979) Eg=3.4 GeV Eg=16 GeV

PLB 400 (1997) 6

First photon-beam asymmetry data for Eg > 1.9 GeV. Positive asymmetries are basically explained by r-meson exchange in the t-channel.

(2) Photoproduction of L and S0 hyperons off protons with linearly polarized photons at Eg=1.5-3 GeV

S.H. Shiu, H. Kohri, W.C. Chang et al. LEPS Collaboration

Published in Phys. Rev. C 97 015208 (2018) on the 31st of Jan.

16

Abstract

Missing mass p(g, K+)X

17

2018 data Eg=1.5-3.0 GeV 2006 data Eg=1.5-2.4 GeV

Background p+D0(1232) produces a peak at around 1.15 GeV if kaon mass is used in missing mass calculation

18

g + p → p+ + X

n

D0

Missing mass (GeV) calculated by pion mass

Differential cross sections for g p -> K+ L and K+ S0

19

First cross section data for LEPS at 2.4 < Eg < 3 GeV. K+L cross sections are larger than K+S0 cross sections. No evident structure due to N* or D*.

Ratio (nNV – NH) / (nNV + NH)

20

K+ prefers to scatter at fK angles perpendicular to the polarization plane. Photon-beam asymmetries are found to be positive for both the reactions, suggesting dominance of K*-exchange.

Photon-beam asymmetry for K+ L and K+ S0

21

First photon-beam asymmetries data for Eg > 2.4 GeV. The asymmetries increase gradually as Eg increases for both the reactions. K*-exchange contribution becomes larger. SLAC data (1979)

(3) Differential cross section and photon-beam asymmetry for the g p -> p- D++(1232) reaction at forward p- angles for Eg=1.5-2.95 GeV

• H. Kohri, S.H. Shiu, W.C. Chang, Y. Yanai, et al.

LEPS Collaboration

Published in Phys. Rev. Lett. 120 202004 (2018) on the 18th of May.

22

Abstract

Missing mass p(g, p-)X

23

2p/r 2p/r 3p

3p All BG All BG

D D

Differential cross sections for g p -> p- D++

24

First high-statistics cross section data. ds/dcosq decreases as Eg increases. Strong forward peaking (p-exchange). Theoretical calculations by S.i. Nam well reproduce the data by optimizing the cutoff mass parameter from 450 to 500 MeV. The energy dependence of Eg < 1.8 GeV cannot be reproduced for cosq > 0.9. N* or D* ?

Comparison of ds/dcosq between p- D++(●) and p+ n(■)

25

Strong forward peaking cross sections suggest t-channel reaction is dominant.

26

Ratio (NV – NH ) / (NV + NH )

p- prefers to scatter at fp angles parallel to the polarization plane. Asymmetries are found to be negative in most of LEPS kinematical regions.

Photon-beam asymmetry for g p -> p- D++

27

First asymmetry data for 1.5 < Eg < 2.8 GeV. Asymmetries are found to be negative for most of LEPS kinematical regions, suggesting p-exchange dominance. Theoretical calculations by S.i. Nam well reproduce negative asymmetries for cosq > 0.933. The calculations cannot reproduce the data for cosq < 0.9. Additional unnatural parity exchange is needed.

Why only p-D++ reaction favors light meson exchange ?

28

(1) g p -> p+ n (2) g p -> K+ L (3) g p -> p- D++

p(140 MeV) or r(770 MeV) p(140 MeV) or r(770 MeV)

spin 0 spin 1

K(490 MeV) or K*(890 MeV)

spin 0 spin 1 spin 0 spin 1

S

Negative Positive Other pseudoscalar meson photoproduction such as p+D0, p0p, hp has positive S. Heavy meson exchange is dominant.

dd production ss production uu production

Yukawa theory

29

Proton Neutron Neutron Proton Meson Strong interaction between nucleons is mediated by mesons. Meson

Uncertainty principle DE Dt ~ ℏ Energy conservation violates in a short time. A particle flying 1 fm with c has a mass, M ～ ℏc / (c Dt) = ~200 MeV fm / 1 fm. Light p meson can reach long distance. Interactions with heavy r, K* mesons are limited in short distances.

My personal interpretation for these results

30

p p p g g g p+ D++ n L p-

K+ We detected mesons at forward angles. Small momentum transfer suggests reactions occur near the surface

• f the proton.

(1) p+n reaction exchanges u quark with d. (2) K+L reaction exchanges u quark with s. (3) p-D++ reaction exchanges d quark with u. p meson exchange is long ranged. d quark may live in the central region

• f the proton ?

The difference in the asymmetries may suggest differences of u and d quark positions ?

p-meson exchange r-meson exchange K*-meson exchange

(1) (2) (3)

d-quark staying in the central region of the proton

31

p+

n

u and d quarks are coupled to spin=0. Good diquark.

: :

4 1 1

n

p+

p0 p0

p p

Proton in diquark model Proton in pion cloud model

Interpretation based on Vector-Meson-Dominance model

32

Annihilation Annihilation Quark exchange Quark exchange

uu production in the intermediate state dd production in the intermediate state

r, w r, w r, w r, w

p+ n p-D++

Summary

33

(1) g p -> p+ n reaction Published in Phys. Rev. C on Jan/22/2018 (2) g p -> K+ L and K+ S0 reaction Published in Phys. Rev. C on Jan/31/2018 (3) g p -> p- D++ reaction Published in Phys. Rev. Lett. on May/18/2018 (4) g p -> p+ D0 reaction Physics paper is prepared. We took high momentum charged pion data for the first time in 2007. It enables us to study uu, dd, and ss productions and we want to obtain unified understanding of these qq productions.

dd production ss production uu production dd production

Missing mass p(g, , p )X

p(g, p+)X p(g, p-)X

Eg=1.5-2.95 GeV Eg=1.5-2.95 GeV 0.7<cosqp<1 0.7<cosqp<1

34

Missing mass spectrum is fitted with relativistic Breit-Wigner shape for D, 2p / r, 3p, and e- or e+ curves.

uu and dd productions

Same acceptance Simultaneous measurements Same proton target

uu production is precisely compared with dd production by the γp→ π- Δ++ and π+Δ0 reactions

35

p- p+ g g

p p

D++ D0

I expect this comparison would give important information to understand how hadrons are produced.

Ratio s(p+D0)/ )/s(p-D++

++)

1/3 is expected from isospin=1 exchange in the t-channel

36

dd production is enhanced

• r

uu production is suppressed. (dd production / uu production )

Summary

37

(1) g p -> p+ n reaction data Published in Phys. Rev. C on Jan/22/2018 (2) g p -> K+L and K+S0 reaction data Published in Phys. Rev. C on Jan/31/2018 (3) g p -> p- D++ reaction data Published in Phys. Rev. Lett. on May/18/2018 (4) g p -> p+ D0 reaction data. Physics paper is prepared. We took high momentum charged pion data for the first time in 2007. It enables us to study uu, dd, and ss productions and we want to obtain unified understanding of these qq productions.

dd production ss production uu production dd production

SPring-8 SPring-8 RCNP RCNP RCNP -> SPring-8 T=10mK B=17 T T=4K B=0.2T T=2K B=1T T=4K B=0.2T T=300mK B=1 T IBC TC2 SC TC1 DRS

38

Refrigerators for polarized HD target

IBC(In Beam Cryostat)

Al wire 2.5cm

Combination of beam and target polarizations provides various physics

• bservables.

Rich information on hadron photoproduction can be obtained. g beam Circular or Linear Target Longitudinal or Transverse

Status of polarized HD target and future plan

40

• We are developing a polarized HD target for the near future LEPS experiments

using polarized photon beams and HD targets. We will be able to obtain rich information to understand hadron photoproduction.

• The polarization of H is 44+-1% and the relaxation time of the H polarization

is 8+-2 months. These performances are good enough for physics runs.

• We need skills to transport the HD target from the first cryostat to the last one.

After acquiring these skills, we will start the physics runs.

• Previously, SPring-8-II(8 GeV -> 6 GeV) planed to start in 2020.

But the schedule is delayed. We still have some years for the physics runs.

Thank you very much

41

42

In the simplest Regge picture involving the exchange of a single trajectory, the cross sections can be written as, a(t), C(t) are functions of t only. s0 = 1 GeV2.

s2 scaling

43

g p -> p+ n g p -> p+ n CLAS data

Effective a(t)

r(770) r3(1690) r5(2350)

p- p -> p0 n

pLab = 3.7, 5.9, 13.3 GeV/c

Successful example

44

a(t) values are obtained for each t by fitting to ds/dt with . a(t) values do not change largely. s dependence for LEPS data is close to that for SLAC data. a(t) for small | t | favors the single p-trajectory. t-channel is dominant

45

Photon-beam asymmetry S for gp -> p+n

The asymmetries become larger as | t | approaches 0. The r-meson exchange contribution is inferred to be small at small | t |. The p-meson exchange cannot explain positive asymmetries. Large asymmetries at small | t | could be due to p-exchange interference with the s-channel as shown by Nucl. Phys. A 627, 645 (1997)

• M. Guidal, J.-M. Laget, M. Vanderhaeghen.

SAPHIR total cross sections

46

Eg (GeV) s(mb)

• C. Wu et al.
• Eur. Phys. J. A 23 (2005) 317

Tail of s-channel resonances seems to continue up to ~Eg=2 GeV

d / u > 1 suggested by Drell-Yan experiments

Proton charge distribution Pion cloud model p+ (ud) may enhance p+D0 prodution(dd production)

• > Larger s(p+D0)/s(p-D++)

Bare proton Pion cloud

(ud)

47

(dd / uu )

Drell-Yan experiment

PRD 64 (2001) 052002

d / u