A search for strange tribaryonic states in the reaction Heejoong Yim Seoul National University For KEK-PS E549 collaboration

KEK-PS E549 Collaboration H. Bhang, J. Chiba, S. Choi, Y. Fukuda, T. Hanaki, R. S. Hayano, M. Iio, T. Ishikawa, M. Iwai, S. Ishimoto, T. Ishiwatari, K. Itahashi, M. Iwasaki, P. Kienle, J. Kim, Y. Matsuda, H. Ohnishi, S. Okada, H. Outa, M. Sato, S. Suzuki, T. Suzuki, D. Tomono, E. Widmann, T. Yamazaki, H. Yim

・ Deep! ・ Narrow! ～ 100 MeV ～ 20 MeV = meta-stable ・ Shrink! cf: B N ～ 10 MeV = high density? Embedding Ｋ in nucleus ？

4 He p p n K-p p n K- n Z : +1 T : 0 or 1 p p n n K-p n n K- Z : 0 Ｔ ： １ predicted unpredicted Missing mass measurement 3 How to produce ？

Possible states of the reaction Neutron spectrum Hard to confirm the structure due to low statistics Search for state (T=0) with 8 times better statistics than E471 Aim of ReactionZTTZTZ +11,00 Predicted by Akaishi spectroscopy E471 nucl-ex/ Motivation of E549 Neutron Measurement

Stopped K - method. ① Incident K - and its track by beamline detectors (K - /π - ratio ~ 1/200, K - ~ 5000/spill) ② Nucleon and its stop timing(TOF) by NC ③ Secondary charged particle and its track by TC-Tracking Chamber Same condition with previous experiment (Semi-Inclusive condition) ① ② ③ TC NC Overview of Experiment Setup T0 & BDC

TOF Analysis for Neutral Events Beam 1.T T0 : Measured time by T0 2.T kaon_flight : Beam (K - ) flight time from T0 to it’s stop 3.T NC : Measured time by NC Track viewed by VDC&BDC Liq. He veto TOF target→NC : Flight time from target vertex to NC TOF target  NC T NC T T0 T kaon_flight

1.5 times Improved Missing Mass Resolution 1/β ADC (MeVee) E471 Time Calibration and Resolution for Neutron Counter (NC) E threshold =7 MeVee 1/β σ=0.030 E549 E471 Missing Mass [MeV/c 2 ] Missing Mass resolution in σ [MeV/c 2 ] Black – previous (E471) Red – Present (E549) Resolution variation on a Missing Mass

Momentum scale and slewing correction are well tuned Σ+Σ+ n π+ π+ cos θ < (~185 MeV/c) (~0 MeV/c) K-K- N Σ QF π QF Check of TOF Analysis Threshold=2MeVee ADC (MeVee) MeV/c Σ decay P n ~ 185MeV/c Threshold=2MeVee Σ decay 1/β ~ /β Counts / (5 MeV/c) Neutron momentum

E471 E549 Much improved S/N ratio Threshold E471 = 10 MeVee Threshold E549 = 7 MeVee 10 MeVee 1/β Counts/0.025 Background Level Check 5 MeVee Counts/ /β

Semi-Inclusive Neutron Spectrum E471 (nucl-ex/ ) About 8 times higher statistics Neutron momentum (MeV/c) Counts / (10 MeV/c) E549 Neutron momentum (MeV/c) Semi-inclusive

Missing Mass Spectrum Counts / (5 MeV/c 2 ) Black – Data Red – Estimated background Missing Mass [MeV/c 2 ] Semi-inclusive neutron Background subtracted Pion coincidence is required to estimate upper limit of kaonic state

Counts/(5MeV/c 2 ) Missing Mass [1] R. C. Byrd et al. Nucl. Inst. Meth. A313 (1992) 437. Missing mass spectrum with pion coincidence Missing Mass [MeV/c 2 ] Black – 7 MeVee threshold Red – 10 MeVee threshold Blue – 13 MeVee threshold Missing Mass [MeV/c 2 ] Efficiency [ratio] Neutron detection efficiency estimation by DEMON code [1] Arbitrary Unit Efficiency corrected Missing Mass Missing Mass [MeV/c 2 ] Missing Mass resolution in σ [MeV/c 2 ] Black – previous (E471) Red – Present (E549) Resolution variation on a Missing Mass ΛπNN Λnp ΣNN

Develop a simulation for the semi-inclusive measurement with pion coincidence. Estimate number of stopped kaon in the target. Obtain upper limit of the kaonic tribaryon state. The further analysis is in progress ! Further analysis procedure Goal

IF exist, → YNN or πΛNN Y → π ± N Study spectrum using decay particle - Σ ± production by fast π (>~125 MeV/c) - Λ production by slow π (<~125 MeV/c) Event tagging can improve S/N ratio, selectively. Event tagging by TC

neutron momentum [MeV/c] Counts / (10 MeV/c) Neutron momentum spectra E471 (nucl-ex/ ) Counts / (10MeV/c 2 ) Neutron momentum [MeV/c] Fast π tagged E549 Counts / (10MeV/c 2 ) Neutron momentum [MeV/c] Fast π tagged At the present moment, the narrow (Γ~20 MeV/c 2 ) structure wasn’t observed.

Summary Neutron spectra was measured for the reaction with upgraded setup. At this stage, Narrow ( Γ ~20 MeV/c 2 ) peak structure of kaonic state did not appear on present result. Now, in progress status, analysis for upper limit estimation of kaonic tribaryon state.

Spare OHPs

Missing mass spectrum MeV/c 2 Pion triggered Semi-inclusive MeV/c 2

Neutron spectra (5MeV/c binning) Semi-inclusive Pion triggered MeV/c

Stopping kaon selection z K - T0 (light output ) Stop kaon selection region Target cell region BLC VDC Target cell Beam direction Stop kaon selection makes the acceptance to be correct Sine distribution for scattered particle by VDC tracking. T0 Kaon at rest In flight z

Semi-inclusive neutron momentum distribution Previous result (E471) 7 MeVee threshold 10 MeVee threshold Present result (E549) At 7 MeVee threshold, total statistics is about 8 times higher than E471 statistics.

IF exist, → YNN or πΛNN Y → π ± N Study spectrum using decay particle - Σ ± production by fast π (>~125 MeV/c) - Λ or Σ 0 production by slow π (<~125 MeV/c) π selection by using TC Event Selection using TC (I)

E549 TC setup TC_D layer TC_A layer TC_C layer TC_B layer Event Selection using TC (II) Pion E471 TC setup TC_A layer TC_B layer Upgrade Pion Proton

Cut for Pi/P separation(1) E b +E c (MeVee) Direction normalized E A (MeVee) Direction normalized E A (MeVee) Red - fast pion Green - fast proton Red - slow pion Green - slow proton E b +E c (MeVee) Direction normalized E A (MeVee) w/ D layer hit w/o D layer hit w/ no cut

Pi/P separation for A-layer vs (B-layer + C-layer) E b +E c (MeVee) Direction normalized E A (MeVee) Direction normalized E A (MeVee) Direction normalized E A (MeVee) no cut fast pi or slow pi fast p or slow p

PID definition by TC Pion Proton Blue – slow pion Red – fast pion TC 2 nd layer [MeVee] TC 1 st [MeVee] TC 2 nd layer [MeVee] TC 1 st [MeVee] TC 2 nd layer [MeVee] TC 1 st [MeVee]TC 2 nd layer [MeVee] TC 1 st [MeVee]

E549 MeV/c Counts / (10 MeV/c) E471 Neutron spectrum with pion trigger MeV/c 10 MeV/c binning

Detection efficiency correction Efficiency curve by DEMONS Efficiency corrected spectra

Less than 0.05%

Resolution variation MeV/c Momentum resolution (σ) [MeV/c]

Incoming K － proton 4 He target Neutron counters Iron plate Charged particle veto counter E471 Setup Upgrade in E549 Incoming K － proton Neutron counters 4 layers→7 layers neutron Proton TOF stop (σ ～ 70ps) Veto counter for neutron detection Smaller target TOF Start counter （ σ< 70ps) Proton chamber resolution improve 150ps→50ps Both proton/neutron σ ～ 300ps proton σ=100 ～ 150ps neutron σ=200ps Upgraded feature of E549 setup

Introduction

Neutral event analysis

Results