0 photoproduction on the neutron studied with the FOREST detector - - PowerPoint PPT Presentation

β–Ά
0 photoproduction on the neutron studied with the forest
SMART_READER_LITE
LIVE PREVIEW

0 photoproduction on the neutron studied with the FOREST detector - - PowerPoint PPT Presentation

Oct 13, 2022 368 likes β€’572 views

YITP workshop MIN16 - Meson in Nucleus 2016 - 0 photoproduction on the neutron studied with the FOREST detector at ELPH Yusuke TSUCHIKAWA for the FOREST collaboration Department of Physics, Nagoya University 1, Aug, 2016 Y. TSUCHIKAWA

slide-1
SLIDE 1

𝐿0Ξ› photoproduction on the neutron studied with the FOREST detector at ELPH

1, Aug, 2016

  • Y. TSUCHIKAWA

1

Yusuke TSUCHIKAWA for the FOREST collaboration

Department of Physics, Nagoya University YITP workshop MIN16 - Meson in Nucleus 2016 -

slide-2
SLIDE 2

Outline Introduction

  • Baryon spectroscopy and 𝐿𝑍 channels
  • Narrow peak structures of special interest

at W ∼ 1.67 and 1.71 GeV Experiment

  • ELPH & 4𝜌 electromagnetic calorimeter FOREST

Analysis

  • Particle identification, Kinematic fit
  • Yield counting, Background subtraction

Results

  • Differential and Total cross sections
  • Reaction mechanism for the 𝐿0Ξ› photoproduction

Summary

1, Aug, 2016

  • Y. TSUCHIKAWA

2

𝐿0𝛭 photoproduction on the neutron studied with the FOREST detector at ELPH

slide-3
SLIDE 3

Baryon spectroscopy via 𝐿𝑍 photoproduction

  • > accessible highly excited baryons which hardly couple to πœŒπ‘‚ (πœƒπ‘‚)
  • 𝐿+Ξ›(Ξ£): recently well studied (CLAS, LEPS, SAPHIR, MAINZ,…)
  • 𝐿0Ξ›(Ξ£): few reports

1, Aug, 2016

  • Y. TSUCHIKAWA

3

  • K. Tsukada et al. (NKS collaboration), Phys. Rev. C 83 039904

The previous measurement near the reaction threshold was done for 𝐹𝛿 = 0.9, 1.1 GeV and cos πœ„πΏ

𝑀𝑏𝑐 = [0.9, 1.0)

Need the study with entire angle region

𝐿 𝑂 Ξ›

πœΉπ’ β†’ π‘³πŸπš³ reaction

Isospin selective -> π‘³πš³: 1/2, 𝐿Σ: 3/2 Expected few t-channel contributions

All of the participants are NEUTRAL β†’ no 𝐿 (not πΏβˆ—) can be exchanged β†’ Born term contributions are expected to be smaller than that of the 𝐿+Ξ› case

s-channel t-channel u-channel

Allowed, if 𝐿±Λ

slide-4
SLIDE 4

J.Jeagle et al, PRL 100, 252002 (2008) R.Wertmuller et al., PRC 90, 015205 (2014)

  • F. Miyahara et al., Prog. Theor.
  • Phys. Suppl. 168, 90, (2007)

CBELSA/TAPS A2@Mainz LNS (ELPH)

𝛿𝑂 β†’ πœƒπ‘‚ π›Ώπ‘œ β†’ πœƒπ‘œ -> A narrow resonance-like structure @1670 MeV

π›Ώπ‘ž β†’ πœƒπ‘ž -> No such structure (but a dip?)

  • T. Ishikawa et al.,

PoS (Hadron2013)025

𝑂(1670)

FOREST

SCISSORS II exp.

1, Aug, 2016

  • Y. TSUCHIKAWA

4

  • V. Kuznetsov et al., Phys.
  • Lett. B 647, 23 (2007)

GRAAL

slide-5
SLIDE 5

J.Jeagle et al, PRL 100, 252002 (2008) R.Wertmuller et al., PRC 90, 015205 (2014)

  • F. Miyahara et al., Prog. Theor.
  • Phys. Suppl. 168, 90, (2007)

CBELSA/TAPS A2@Mainz LNS (ELPH)

𝛿𝑂 β†’ πœƒπ‘‚ π›Ώπ‘œ β†’ πœƒπ‘œ -> A narrow resonance-like structure @1670 MeV

π›Ώπ‘ž β†’ πœƒπ‘ž -> No such structure (but a dip?)

  • T. Ishikawa et al.,

PoS (Hadron2013)025

𝑂(1670)

FOREST

SCISSORS II exp.

1, Aug, 2016

  • Y. TSUCHIKAWA

5

  • V. Kuznetsov et al., Phys.
  • Lett. B 647, 23 (2007)

GRAAL

The prominent structure observed in the π›Ώπ‘œ β†’ πœƒπ‘œ Reported by many exp. groups LNS (ELPH), GRAAL, MAINZ, CB-ELSA/TAPS β†’ Consistent results: Narrow width (∼ πŸ’πŸ ππŸπ– ) and peak position ∼ 1670 MeV Observed in the 𝒐 𝜹, 𝜽 𝒐 reaction but not in the 𝒒 𝜹, 𝜽 𝒒 case

slide-6
SLIDE 6

1, Aug, 2016

  • Y. TSUCHIKAWA

6

Recent theoretical interpretations

– Intrinsic narrow state – Coupled-channel effects – Interference effects – 𝐿𝑍 threshold effects – …

  • M. DΓΆring and K. Nakayama,
  • Phys. Lett. B 683, 145 (2010).

More experimental information is needed

  • > How about the 𝐿0Ξ› case?

Similarities between πœƒπ‘œ & 𝐿0Ξ›

  • Isospin 1/2
  • πœΉπ’ initial state
  • 𝒕

𝒕 component Confirmation of the N(1670) must be a valuable info.

Anisovich et al., Eur. Phys. J. A 51, 72 (2015)

S(1535)&S(1650)

Threshold effect (KY ch.) Interference effect

𝑂(1670)

Intrinsic narrow state

slide-7
SLIDE 7

𝑂 1710 ?

1, Aug, 2016

  • Y. TSUCHIKAWA

7

Kuznetsov et al., Phys. Rev. C 91, 042201 (2015)

Werthmuller et al., arXiv 1511.0829 (very recent!)

Another narrow, but small, peak structure has been also observed in πœƒ(𝜌0) photoproduction Ξ£ asymmetry of the 𝛿 π‘ž, π‘ž 𝜌0 reaction

Re-analysis of the 𝛿 π‘œ, π‘œ πœƒ reaction (re-binned ver.)

MAINZ πœƒπ‘ž πœƒπ‘œ GRAAL Ξ“ = 15 Β± 4 MeV

slide-8
SLIDE 8

1.2 GeV Electron Synchrotron and photon beam line @ Research Center for Electron Photon Science (ELPH)

1, Aug, 2016

  • Y. TSUCHIKAWA

8

STretcher-Booster Ring: 1.2 GeV electron synchrotron GeV-𝛿 Beam line: 0.5-1.2 GeV photon

Experiment @ ELPH, Tohoku University, Sendai

1.2 GeV

Layout of ELPH beam lines (~2012)

Injector

slide-9
SLIDE 9

𝐹𝛿 = 750 βˆ’ 1150 MeV (𝐹𝛿

π‘’β„Žπ‘  𝐿0Ξ› = 915 MeV)

𝛿

𝜏𝐹/𝐹 (1 GeV 𝛿) ~3 % ~ 7 % ~ 5 %

192 Pure CsI 24 PSΓ— 3 layers 252 Lead/SciFi mod.s PSΓ—12 PSΓ—18 62 Lead/Glass Target: liquid H2/D2 target (45.9 mm thick)

4 𝜌 electromagnetic calorimeter complex FOREST

(Forward) (Backward)

  • Y. TSUCHIKAWA

9 1, Aug, 2016

Coverage πœ„ 5Β° ∼ 24Β° 30Β° ∼ 100Β° 110Β° ∼ 170Β°

slide-10
SLIDE 10

1, Aug, 2016

  • Y. TSUCHIKAWA

10

Particle identification

𝐿𝑇 𝜌0 𝜌0

Focusing decay chains: 4 photons and 2 charged particles in the final state

𝛿 𝛿 𝛿 𝛿 Ξ› π‘ž πœŒβˆ’

30.69% 63.9%

𝛿𝑒 β†’ 𝐿0Ξ›π‘ž β†’ 𝐿𝑇

0Ξ›π‘ž β†’ 𝜌0𝜌0

π‘žπœŒβˆ’ π‘ž β†’ 4𝛿 π‘žπœŒβˆ’ π‘ž

Proton in the deuteron is assumed as a spectator

𝐿0

50% 𝛿1 𝛿2 𝛿3 𝛿4

𝛿𝛿 invariant masses π‘ž 𝜌

slide-11
SLIDE 11

1, Aug, 2016

  • Y. TSUCHIKAWA

11

Kinematic fit with 4 constraints

β€œπœΉπœΉ invariant mass = π’π†πŸβ€ x2

  • 1. 𝑁2 𝛿1, 𝛿2 ≑ 2𝐹1𝐹2 1 βˆ’ sin πœ„1 sinπœ„2 cos 𝜚1 βˆ’ 𝜚2 βˆ’ cos πœ„1 cos πœ„2 = π‘›πœŒ0

2

  • 2. 𝑁2 𝛿3, 𝛿4 ≑ 2𝐹3𝐹4 1 βˆ’ sin πœ„3 sinπœ„4 cos 𝜚3 βˆ’ 𝜚4 βˆ’ cos πœ„3 cos πœ„4 = π‘›πœŒ0

2

β€œπŸ“πœΉ missing mass = π’πœ§β€ : 3. π‘π‘Œ

2 𝛿1, 𝛿2, 𝛿3, 𝛿4 ≑ πΉπ‘Œ 2 βˆ’ 𝑄 π‘Œ 2 = 𝐹𝛿 + π‘›π‘œ βˆ’ 𝑗=1 4

𝐹𝑗

2 βˆ’ 𝑄 π‘Œ 2(𝐹𝑗, πœ„π‘—, πœšπ‘—, 𝐹𝛿) = 𝑛Λ 2

β€œπŸ“πœΉπ’’ missing mass = π’π†βˆ’β€: 4. π‘π‘Œ

2 𝛿1, 𝛿2, 𝛿3, 𝛿4, π‘ž = π‘›πœŒβˆ’ 2

16 variables:

𝛿𝑗 momentum, polar, and azimuthal angles: 𝐹𝑗, πœ„π‘—, πœšπ‘— (𝑗 = 1, … , 4) , same for proton: 𝑄

π‘ž, πœ„π‘ž, πœšπ‘ž,

and Photon beam energy: 𝐹𝛿

Selected events with detected values

π‘ž πœŒβˆ’ 𝜌0𝜌0

Accidentally triggered events

Contamination of accidental events

  • > sideband subtraction
slide-12
SLIDE 12

1, Aug, 2016

  • Y. TSUCHIKAWA

12

Acceptance

Full coverage for cos πœ„πΏ

𝐷𝑁

to the whole range of 𝐹𝛿 𝐹𝛿 [MeV] 𝐿0 Clear peak but S/N ~50%

𝐿0 signal

Clear peak but S/N ~50% 𝜈 = 494.9 3 MeV 𝜏 = 17.9(3) MeV About 8,400 𝐿0 signals

slide-13
SLIDE 13

1, Aug, 2016

  • Y. TSUCHIKAWA

13

Examples of the fit results

The simulated distributions (π›Ώπ‘œ β†’ 𝜌0𝜌0πœŒβˆ’π‘ž) well reproduce the BG distributions Fit for yield counting: Total (blue) = Gaussian (magenta) + BG dist. (red)

Yield counting

slide-14
SLIDE 14

πœ„πΏ

𝐷𝑁: Kaon emission angle in the π›Ώπ‘œ

center-of-mass frame

1, Aug, 2016

  • Y. TSUCHIKAWA

14

Differential Cross Sections

Legendre fit

This result supports the experimental remark in the previous measurement for the π›Ώπ‘œ β†’ 𝐿0Ξ› reaction reported by K. Tsukada et al.

  • K. Tsukada et al., Phys. Rev. C 83 039904

Angular distribution: Flat -> Backward enhancement

slide-15
SLIDE 15

1, Aug, 2016

  • Y. TSUCHIKAWA

15

Total Cross Section

Systematic error (preliminary)

The target neutron is assumed at rest. Acceptance Geometry in the MC sim. Threshold energies for TDC for Trigger cond. Number of incident photon Number of target

Comparable to the 𝐿+Ξ› channel

slide-16
SLIDE 16

1, Aug, 2016

  • Y. TSUCHIKAWA

16

Total Cross Sections

  • A. Fix et al., Eur. Phys. J. A 32,

311–319 (2007).

Excess?

π‘ΈπŸπŸ(𝚫 = πŸ’πŸ ππŸπ–)

slide-17
SLIDE 17

1, Aug, 2016

  • Y. TSUCHIKAWA

17

Differential Cross Sections and theoretical curves

Kaon-MAID Saclay-Lyon A Legendre fit

Present results favor the SLA model β†’ u-channel Y* contribution may play an important role in the πœΉπ’ β†’ π‘³πŸπš³ reaction Compared to two theoretical curves: Kaon-MAID and Saclay-Lyon A

slide-18
SLIDE 18

Summary

  • The 𝛿𝑒 β†’ 𝐿0Ξ›π‘ž photoproduction reaction is studied with electromagnetic

calorimeter complex FOREST at ELPH, Sendai

  • K0 signals are well confirmed by 𝛿𝑒 β†’ 𝐿𝑇

0Ξ›π‘ž β†’ 𝜌0𝜌0

π‘žπœŒβˆ’ π‘ž β†’ 4𝛿 π‘žπœŒβˆ’ π‘ž reaction chains with an exclusive analysis

  • Shape of the background shown in the 𝜌0𝜌0 invariant mass distribution can be well

reproduced by the simulated distribution of π›Ώπ‘œ β†’ 𝜌0𝜌0πœŒβˆ’π‘ž non-resonant reaction

  • Differential cross sections show backward enhancement as 𝐹𝛿 increases

(This result supports the remark of the previous measurement)

  • Comparison with the theoretical calculations may indicate that the hyperon

resonance plays an important role in this reaction at higher energies

  • The total cross section shows comparable order of magnitude to the 𝐿+Ξ›

photoproduction cross section

  • An excess-like structure was observed in the vicinity of 1670 MeV it may be related

to the prominent structure observed in the π›Ώπ‘œ β†’ πœƒπ‘œ reaction

  • The first measurement for the 𝐿0Ξ› photoproduction proposes new constraints for

the theoretical interpretations on the mysterious 𝑂 1670 peak structure

1, Aug, 2016

  • Y. TSUCHIKAWA

18