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

YITP workshop MIN16 - Meson in Nucleus 2016 - 𝐿 0 Λ 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 1

𝐿 0 𝛭 photoproduction on the neutron studied with the FOREST detector at ELPH Outline - Baryon spectroscopy and 𝐿𝑍 channels Introduction - Narrow peak structures of special interest at W ∼ 1.67 and 1.71 GeV - ELPH & 4 𝜌 electromagnetic calorimeter FOREST Experiment Analysis - Particle identification, Kinematic fit - Yield counting, Background subtraction - Differential and Total cross sections Results - Reaction mechanism for the 𝐿 0 Λ photoproduction Summary 1, Aug, 2016 Y. TSUCHIKAWA 2

Baryon spectroscopy via 𝐿𝑍 photoproduction -> accessible highly excited baryons which hardly couple to 𝜌𝑂 (𝜃𝑂) • 𝐿 + Λ(Σ) : recently well studied (CLAS, LEPS, SAPHIR, MAINZ,…) • 𝐿 0 Λ(Σ) : few reports 𝑂 Allowed, 𝜹𝒐 → 𝑳 𝟏 𝚳 reaction Λ 𝐿 if 𝐿 ± Λ Isospin selective -> 𝑳𝚳: 1/2 , 𝐿Σ : 3/2 Expected few t-channel contributions s -channel u -channel t -channel All of the participants are NEUTRAL → no 𝐿 (not 𝐿 ∗ ) can be exchanged → Born term contributions are expected to be smaller than that of the 𝐿 + Λ case K. Tsukada et al. (NKS collaboration), Phys. Rev. C 83 039904 The previous measurement near the reaction threshold was done for 𝑀𝑏𝑐 = [0.9, 1.0) 𝐹 𝛿 = 0.9, 1.1 GeV and cos 𝜄 𝐿 Need the study with entire angle region 1, Aug, 2016 Y. TSUCHIKAWA 3

𝛿𝑂 → 𝜃𝑂 𝛿𝑜 → 𝜃𝑜 -> A narrow resonance-like structure @1670 MeV 𝑂(1670) 𝛿𝑞 → 𝜃𝑞 -> No such structure (but a dip?) LNS (ELPH) GRAAL FOREST SCISSORS II exp. V. Kuznetsov et al., Phys. Lett. B 647, 23 (2007) F. Miyahara et al., Prog. Theor. Phys. Suppl. 168, 90, (2007) T. Ishikawa et al., PoS (Hadron2013)025 A2@Mainz CBELSA/TAPS R.Wertmuller et al ., PRC 90, J.Jeagle et al , PRL 100 , 1, Aug, 2016 Y. TSUCHIKAWA 4 015205 (2014) 252002 (2008)

𝛿𝑂 → 𝜃𝑂 𝛿𝑜 → 𝜃𝑜 -> A narrow resonance-like structure @1670 MeV 𝑂(1670) 𝛿𝑞 → 𝜃𝑞 -> No such structure (but a dip?) LNS (ELPH) GRAAL FOREST SCISSORS II exp. V. Kuznetsov et al., Phys. The prominent structure observed in the 𝛿𝑜 → 𝜃𝑜 Lett. B 647, 23 (2007) Reported by many exp. groups LNS ( ELPH) , GRAAL , MAINZ , CB-ELSA/TAPS F. Miyahara et al., Prog. Theor. Phys. Suppl. 168, 90, (2007) → Consistent results: T. Ishikawa et al., Narrow width (∼ 𝟒𝟏 𝐍𝐟𝐖 ) and peak position ∼ 1670 MeV PoS (Hadron2013)025 A2@Mainz Observed in the 𝒐 𝜹, 𝜽 𝒐 reaction but not in the 𝒒 𝜹, 𝜽 𝒒 case CBELSA/TAPS R.Wertmuller et al ., PRC 90, J.Jeagle et al , PRL 100 , 1, Aug, 2016 Y. TSUCHIKAWA 5 015205 (2014) 252002 (2008)

Intrinsic narrow state 𝑂(1670) Recent theoretical interpretations – Intrinsic narrow state – Coupled-channel effects – Interference effects – 𝐿𝑍 threshold effects – … Interference effect Threshold effect (KY ch.) More experimental Anisovich et al., Eur. Phys. J. A 51 , 72 (2015) information is needed M. Döring and K. Nakayama, Phys. Lett. B 683, 145 (2010). -> How about the 𝐿 0 Λ case? Similarities between 𝜃𝑜 & 𝐿 0 Λ - Isospin 1/2 S(1535)&S(1650) - 𝜹𝒐 initial state - 𝒕 𝒕 component Confirmation of the N(1670) must be a valuable info. 1, Aug, 2016 Y. TSUCHIKAWA 6

𝑂 1710 ? Another narrow, but small, peak structure has been also observed in 𝜃(𝜌 0 ) photoproduction Re-analysis of the 𝛿 𝑜, 𝑜 𝜃 reaction (re-binned ver.) Σ asymmetry of the 𝛿 𝑞, 𝑞 𝜌 0 reaction Werthmuller et al., arXiv 1511.0829 (very recent!) Kuznetsov et al., Phys. Rev. C 91, 042201 (2015) GRAAL MAINZ 𝜃𝑜 𝜃𝑞 Γ = 15 ± 4 MeV 1, Aug, 2016 Y. TSUCHIKAWA 7

Experiment @ ELPH, Tohoku University, Sendai 1.2 GeV Electron Synchrotron and photon beam line @ Research Center for Electron Photon Science (ELPH) Layout of ELPH beam lines (~2012) ST retcher- B ooster Ring: 1.2 GeV electron synchrotron GeV- 𝛿 Beam line: 0.5-1.2 GeV photon 1.2 GeV Injector 1, Aug, 2016 Y. TSUCHIKAWA 8

4 𝜌 electromagnetic calorimeter complex FOREST 252 Lead/SciFi mod.s PS × 12 192 Pure CsI 24 PS × 3 layers 62 Lead/Glass PS × 18 (Forward) (Backward) 𝜏 𝐹 /𝐹 (1 GeV 𝛿 ) ~3 % ~ 7 % ~ 5 % Coverage 𝜄 5 ° ∼ 24 ° 30 ° ∼ 100 ° 110 ° ∼ 170 ° Target: liquid H2/D2 target (45.9 mm thick) 𝛿 𝐹 𝛿 = 750 − 1150 MeV 𝑢ℎ𝑠 𝐿 0 Λ = 915 MeV) ( 𝐹 𝛿 1, Aug, 2016 Y. TSUCHIKAWA 9

Particle identification 𝛿𝛿 invariant masses Focusing decay chains: 𝛿 𝜌 0 𝛿 𝛿 1 𝛿 2 𝛿 3 𝛿 4 𝐿 0 50% 0 𝐿 𝑇 30.69% 𝛿 𝜌 0 𝛿 𝑞 𝑞 Λ 63.9% 𝜌 − 𝜌 4 photons and 2 charged particles in the final state 𝑞𝜌 − 𝑞 → 4𝛿 𝑞𝜌 − 𝑞 𝛿𝑒 → 𝐿 0 Λ𝑞 → 𝐿 𝑇 0 Λ𝑞 → 𝜌 0 𝜌 0 Proton in the deuteron is assumed as a spectator 1, Aug, 2016 Y. TSUCHIKAWA 10

16 variables: Kinematic fit with 4 constraints 𝛿 𝑗 momentum, polar, and azimuthal angles: 𝐹 𝑗 , 𝜄 𝑗 , 𝜚 𝑗 (𝑗 = 1, … , 4) , same for proton: 𝑄 𝑞 , 𝜄 𝑞 , 𝜚 𝑞 , “ 𝜹𝜹 invariant mass = 𝒏 𝝆 𝟏 ” x2 and Photon beam energy : 𝐹 𝛿 1. 𝑁 2 𝛿 1 , 𝛿 2 ≡ 2𝐹 1 𝐹 2 1 − sin 𝜄 1 sin𝜄 2 cos 𝜚 1 − 𝜚 2 − cos 𝜄 1 cos 𝜄 2 = 𝑛 𝜌 0 2 2. 𝑁 2 𝛿 3 , 𝛿 4 ≡ 2𝐹 3 𝐹 4 1 − sin 𝜄 3 sin𝜄 4 cos 𝜚 3 − 𝜚 4 − cos 𝜄 3 cos 𝜄 4 = 𝑛 𝜌 0 2 2 − 𝑄 2 𝛿 1 , 𝛿 2 , 𝛿 3 , 𝛿 4 ≡ 𝐹 𝑌 2 − 𝑄 2 = 𝐹 𝛿 + 𝑛 𝑜 − 𝑗=1 “ 𝟓𝜹 missing mass = 𝒏 𝜧 ” : 3. 𝑁 𝑌 4 2 (𝐹 𝑗 , 𝜄 𝑗 , 𝜚 𝑗 , 𝐹 𝛿 ) = 𝑛 Λ 2 𝐹 𝑗 𝑌 𝑌 2 𝛿 1 , 𝛿 2 , 𝛿 3 , 𝛿 4 , 𝑞 = 𝑛 𝜌 − “ 𝟓𝜹𝒒 missing mass = 𝒏 𝝆 − ”: 4. 𝑁 𝑌 2 𝜌 0 𝜌 0 𝜌 − 𝑞 Selected events with detected values Contamination of accidental events -> sideband subtraction Accidentally triggered events 1, Aug, 2016 Y. TSUCHIKAWA 11

𝐿 0 signal Clear peak but S/N ~50% 𝐿 0 Clear peak but S/N ~50% 𝜈 = 494.9 3 MeV 𝜏 = 17.9(3) MeV About 8,400 𝐿 0 signals 𝐹 𝛿 [MeV] Acceptance 𝐷𝑁 Full coverage for cos 𝜄 𝐿 to the whole range of 𝐹 𝛿 1, Aug, 2016 Y. TSUCHIKAWA 12

Yield counting Examples of the fit results The simulated distributions (𝛿𝑜 → 𝜌 0 𝜌 0 𝜌 − 𝑞) well reproduce the BG distributions Fit for yield counting: Total (blue) = Gaussian (magenta) + BG dist. (red) 1, Aug, 2016 Y. TSUCHIKAWA 13

Differential Cross Sections 𝐷𝑁 : Kaon emission angle in the 𝛿𝑜 𝜄 𝐿 center-of-mass frame Legendre fit Angular distribution: Flat -> Backward enhancement This result supports the experimental remark in the previous measurement for the 𝛿𝑜 → 𝐿 0 Λ reaction reported by K. Tsukada et al. K. Tsukada et al., Phys. Rev. C 83 039904 1, Aug, 2016 Y. TSUCHIKAWA 14

Total Cross Section Comparable to the 𝐿 + Λ channel Systematic error (preliminary) Acceptance Geometry in the MC sim. Threshold energies for TDC for Trigger cond. Number of incident photon The target neutron is assumed at rest. Number of target 1, Aug, 2016 Y. TSUCHIKAWA 15

Total Cross Sections Excess? 𝑸 𝟐𝟐 (𝚫 = 𝟒𝟏 𝐍𝐟𝐖) A. Fix et al., Eur. Phys. J. A 32, 311 – 319 (2007). 1, Aug, 2016 Y. TSUCHIKAWA 16

Differential Cross Sections and theoretical curves Kaon-MAID Saclay-Lyon A Legendre fit Compared to two theoretical curves: Kaon-MAID and Saclay-Lyon A Present results favor the SLA model → u-channel Y* contribution may play an important role in the 𝜹𝒐 → 𝑳 𝟏 𝚳 reaction 1, Aug, 2016 Y. TSUCHIKAWA 17

Summary • The 𝛿𝑒 → 𝐿 0 Λ𝑞 photoproduction reaction is studied with electromagnetic calorimeter complex FOREST at ELPH, Sendai 𝑞𝜌 − 𝑞 → 4𝛿 𝑞𝜌 − 𝑞 • K 0 signals are well confirmed by 𝛿𝑒 → 𝐿 𝑇 0 Λ𝑞 → 𝜌 0 𝜌 0 reaction chains with an exclusive analysis • Shape of the background shown in the 𝜌 0 𝜌 0 invariant mass distribution can be well reproduced by the simulated distribution of 𝛿𝑜 → 𝜌 0 𝜌 0 𝜌 − 𝑞 non-resonant reaction • Differential cross sections show backward enhancement as 𝐹 𝛿 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 + Λ 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 𝛿𝑜 → 𝜃𝑜 reaction • The first measurement for the 𝐿 0 Λ photoproduction proposes new constraints for the theoretical interpretations on the mysterious 𝑂 1670 peak structure 1, Aug, 2016 Y. TSUCHIKAWA 18