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The investigation of L (1405) state in the stopped K - reaction on deuterium

The investigation of L (1405) state in the stopped K - reaction on deuterium. 1. Motivation and theoretical basis 2. Principle of the measurement 3. Experimental setup 4. Monte-Caro simulation and expected result 5. Summary.

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The investigation of L (1405) state in the stopped K - reaction on deuterium

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  1. The investigation of L(1405) state in the stopped K- reaction on deuterium 1. Motivation and theoretical basis 2. Principle of the measurement 3. Experimental setup 4. Monte-Caro simulation and expected result 5. Summary Takatoshi Suzuki1, Jafer Esmaili2,4 and Yoshinori Akaishi3,4 　　　　　　　　　　　　　1The University of Tokyo 　　　　　　　　　　　　　2Isfahan University of Technology 　　　　　　　　　　　　　3Nihon University 　　　　　　　　　　　　　4RIKEN

  2. Physics Motivation ★ To give the final solution of yet unresolved problem of Kbar-nuclear interaction. Low energy Kbar N scattering L(1405) (I=0 KbarN bound state?) Critical reconsideration of the basis of so attractive potential Resolution of “unti-kaonic hydrogen puzzle”(KEK E228) Prediction of deeply bound narrow Kbar nuclei L(1420) :two-pole hypothesis? Various search experiments L(1405)? L(1420)? The most fundamental question Many experimental results/plans. Results: E548,E549, FINUDA, OBELIX, FOPI, DISTO,… Plans: E15/P28, P27, AMADEUS, FOPI,… Serious Problems: Interpretations are complicated and unsettled. Sometimes results are conflicting each other.

  3. L(1405) VS L(1420): difference in the I=0 KbarN scattering amplitude ★The“peak” potitions of Im(FKbarN): Single pole ->1405 Double pole ->1420 E<0 E>0

  4. Observables of KbarN-Sp coupled channels See, Prof. Akaishi’s talk, or D. Jido, E. Oset, T. Sekihara, arXiv:0904.3410v3 Im(FKbarN) ∝Im T11(in general) = |T21 |2q (in KbarN boundregion) |T21 |2q :KbarN->Sp Invariant mass spectra. Hyodo-Weise’s Chiral SU(3) dynamics z1: 1432-17i MeV (KbarN-Sp) z2: 1398-73i MeV (Sp-Sp) 2nd pole? No effect on the KbarN->Sp spectra. KbarN->Sp spectra is sensitive only to the 1st/single pole position!!! Measurement of the KbarN->Sp reaction is essential .

  5. (K-stopped, n)(Sp)0 reactions KbarN I=0 scattering amplitude (model dependent) +realistic Fermi momentum distribution -> uniquely calculated (Sp)0 spectrum shape!! by the neutron spectator process K- + p -> S+(1660) + p- pK- =4.2 GeV/c

  6. d(K-stopped, n)(Sp)0 reaction and dependence on the pole number? The spectrum shape is much different in two cases. The spectrum shape depends only on z1 position.

  7. The Experiment

  8. n n p  * K‾  Objective of the experimental study Discrimination of L(1405) and L(1420) by measuring the spectrum shape of the IM((Sp)0) from the d(K-stopped, n) (Sp)0 reaction , the simplest reaction with no ambiguity/the weakest FSI. Neutron spectator process Key Issues: 1. Mass Resolution 2. Statistics 3. Clean ID of real events

  9. Experimental Principle Investigation of the reaction, K-stopped + d -> L(1405) + nprimary -> (Sp)0 -> S-+ p+primary:mode 1 -> ndecay + p-decay -> S++ p-primary:mode 2 -> ndecay + p+decay *MM(nprimary) = IM((Sp)0) for (Sp)0n final states => Investigation of the M((Sp)0) via 1. Precision measurement of nprimary 2. Selection of (Sp)0n final states by equalities, MM(nprimaryp±primary) = M(S∓) for ZS= ∓1 => energy loss effect of S±is avoidable. MM(nprimary) = M(L(1405))

  10. Experimental Setup (Overview) J-PARC K1.8BR beamline (op. 2’) ~ 0.7 GeV/c K- beam E15->Dr. Outa’s talk E17->Dr. Sato’s talk K- : E0-BLC3. nprimary : CDH (E0-CDH TOF). pprimary : CDC-CDH (with Bz = 0.5T ). Modification from E17: 1. Target: liq. 3He -> liq. d 2. Magnetic field off -> on (Bx=0, By=0, Bz=0.5T : E15 mode). 3. SDD (Xray detector) removal.

  11. Expected Results

  12. Sensitive Region/Resolution: Summary Point 1. Sensitive region -> wide enough. Point 2. Mass resolution -> extremely high.

  13. Expected Spectra • Here, we consider • Realistic statistics, • (ii) Realistic sensitive region, • (iii) Realistic mass resolution, • and • (iv) Physical BG (like direct QF, • S(1385) etc.), • (v) Combinatorial BG, • are neglected. 1.0×105 (1420) / 0.74×105 (1405) events Both of mass resolution and statistics are perfect.

  14. Sensitivity The result of c2fitting of the theoretical curve with M and G as the arguments, to the Monte-Carlo data in the previous slide -> Enough sensitivity. Any result (spectrum shape) is welcome, as it is available to determine the PDG value of poorly-known E and W of L*

  15. Experimental Detail

  16. Basic studies • 0. Statistics with the beamline (K1.8BR) and setup. • Sensitive region (Calculation/Monte-Carlo) • The detection threshold of neutron (by TOF window and discriminator threshold) and pion (by energy loss in the target materials) strictly define the sensitive IM region. It is vitally important to check whether the “window” is wide enough to judge the models or not. • M((Sp)0) resolution (Calculation) • The M((Sp)0) resolution is just defined by the neutron TOF resolution. Is it enough to discriminate two models? • Event ID (Monte-Carlo) • Availability of MM(np) for the clean ID of event. As neutron and pion • also originate from S decay and stopped p- on the surroundings, and • substantial constant neutron BG is expected, this must be studied carefully. • Feasibility of acceptance correction (Monte-Carlo) • In the experiment, the acceptance correction is indispensable as the spectrum shape is examined only after that. As this is coincidence measurement, it is non-trivial.

  17. Realistic Yield Estimation • Yi = Nstop K × Bri × ep × en× eDAQ× eANA : mode 1(S-p+n) /2(S+p-n) • Nstop K : Total number of stopped K- = 1.9×107 (14 days with 27kW-equivalent -10% of phase-1 goal- primary beam intensity at K1.8BR op.2’ beamline ) • Bri : reacton branching ratio. Measured values, 0.22,0.30 for i=1,2 • (IL NUOVO CIMENTO 39 538 (1977)). • ep : pion detection efficiency ~ 0.6 (solid angle) • en : neutron detection efficiency ~ 0.08×0.6(solid angle) ~0.05 over 5 MeV • neutron(if the threshold can be set to 1 MeVee, efficiency is ~3%/g • for 5 MeV kinetic energy. If the threshold can be smaller, then it increases) • eDAQ : DAQ live time ratio = 0.7 • eANA : Analysis efficiency = 0.9 • => Y1 = 7.9 × 104, Y2 = 1.1 × 105

  18. Sensitive Region (Time Gate/Efficiency) Time window: TOF is acceptable up to ~40 nsec by the cable length and trigger scheme of E15/E17. Acceptable mass is up to ~1427 MeV/c2. by the constraint. TOF max (nsec) Neutron Detection Efficiency: ~5.4 MeV is the light output by MIP. ~0.6 MeVee hardware threshold should be set safely to apply 1.0 MeVee or lower software threshold. (cf. 9 MeV MIP VS ~1.2 MeVfor E549). Detectable mass is up to 1421 MeV/c2 (5MeV by neutron energy scale) for 1 Mevee software threshold. (Sp)0 Invariant Mass (MeV/c2) 79(L)*10(W)*3(T) cm NE102=BC400 Attenuation Length 329cm Hardware Th. 0.6 MeVee Neutron accidental rate must be moderate for applying such low thresholds.

  19. Calibration of neutron TOF * g-ray from stopped K- reaction (time-0, 1/bn=1.0 ) * S+stopped -> n p+ (185.02 MeV/c, 1/bn=5.176) g (1/b = 1.0) KEK-E549 n (1/b = 5.176) n (1/b = 4.968) Point 1. TOF calibration is robust by two intense monochromatic peaks by g and n. Point 2. “Neutron” energy resolution is directly and exactly determined by “neutron” at the energy region of interest. 1/b for neutral particles p± momentum calibration and PID -> E15 issue.

  20. IM((Sp)0) = MM(nprimary) Resolution DTOF = 400 psec LTOF = 60cm (minimum) ✓Resolution is fine (due to small b). ✓The light output dependence of DTOF will make the dependence more moderate in real case. 0.4 MeV/c2@1420MeV/c2 2.3 MeV/c2@1400MeV/c2 Mass Resolution (MeV/c2) (Sp)0 Invariant Mass (MeV/c2)

  21. Event ID (1): MM(np+) =M(S-)?->mode1 ✓M(Y*)=1.40 GeV/c2 ✓Large S/N ratio. ✓Blue/Yellow BG is avoidable if i) we require 2 pion coincidence, and ii) ndecay is eliminated by IM(np-) = M(S-) . MM(nprimaryp+primary) MM(nprimaryp+decay) MM(ndecayp+primary) MM(ndecayp+decay) MM spectrum (S/N) is Y*-mass dependent.

  22. Event ID (2): MM(np-) =M(S+)?->mode2 ✓M(Y*)=1.40 GeV/c2 ✓Large S/N ratio. ✓Blue/Yellow BG is avoidable if i) we require 2 pion coincidence, and ii) ndecay is eliminated by IM(np+) = M(S+) MM(nprimaryp-primary) MM(nprimaryp-decay) MM(ndecayp-primary) MM(ndecayp-decay) MM spectrum (S/N) is Y*-mass dependent.

  23. Acceptance Correction ✓In the np coincidence measurement, acceptance of any physical quantities can be corrected by generalized-acceptance function defined by 3-variables(acceptance matrix), for instance, pn,pp, cosqnp. ✓The generalized-acceptance matrix, enp ,does not depend on specific dynamics to produce np, and applicable to any process. ✓The reproducibility of the original spectra from various processes by the sole acceptance matrix has been already studied and verified in KEK-E549. ✓For 3-body final state like Spn, the acceptance matrix is reduced to be defined by 2-variables. ✓The cylindrical symmetry of the setup makes the calculation very easy.

  24. Summary and Concluding Remark • KbarN->Sp reaction is the most relevant and direct tool to determine the • 1st /single pole position corresponding to “L(1405)”　resonance. 2nd pole in the • Sp->Sp channel does not affect the KbarN->Sp spectra. •  We have discussed on the measurement of • d(K-stopped, n) (Sp)0 reaction • with E17 experimental setup at K1.8BR, and investigated the followings: • 0. Statistics (Calculation) • 1. Sensitive region (Calculation/Monte-Carlo) • 2. M((Sp)0) resolution (Calculation) • 3. Event ID (Monte-Carlo) • 4. Feasibility of acceptance correction • They were all found to be satisfactory, and the result is enough to discriminate • two hypotheses of L(1405), and more precise mass and width will be obtained. • Therefore, we propose it as a new experimental proposal at J-PARC, and • the data will come on within FSY 2010 just after E17(Kaonic atom). •  Accidental and synchronized (from p-absorption, nuclear g, etc) neutron/g • BG was not considered here. The accidental BG, which is strongly • dependent on the available beam intensity unknown so far, may introduce • difficulty to reduce the software P.H. threshold of neutron detection, and • synchronized BG may cause further combinational BG of MM(np).

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