Status of the 3-Body NMWD study and E18 H. Bhang (Seoul National University) KJ-PARC WS SNU, Sep , 2011 Outlines I. E18 Proposal status; 2 nd stage Approval in Jan. PAC II. Precision to improve III. Can we make some improvement to accept higher beam intensity? IV. Status of E18 preparation (Dr. Kim’s talk)

Proposal status;

FIFC Report and the Revised two-step Plan

Simulation Study Double coincidence eff. at E N =75MeV → Much increased!!!!!!!! beam p n pp cos   cos  pp np nn E18 cos  np cos  nn E508 pp np nn  np  NN  pp  nn  np E18 Decay Counter pair nucleon detection efficiency

E508 (2T)E18_orig (5T) E18_insitu (1T) N  tot 2T5T0.8T n  /spill4M/4sec10M/spill(6sec)2M/spill(6sec) d.f.( duty fac) ~1 ~0.3 N Y (hyp.n)60K150K24K N nm 46K115K18K  ch  n   0.45 N np (bb)116(  7  2.5) ~2030(  7 .5) ~320 N nn (bb)43(  3.5  2.5) ~376(  3.5 .5) ~60 N pp (bb)8(4  4  2.5) ~320(4x4 .5) ~51 N np (nbb)9(  12  2.5) ~270(  12 .5) ~43 N nn (nbb)16(  4.5  2.5) ~280(  4.5 .5) ~45 N NNN 6(  12  1.8  2.5) ~325(  12  1.8 .5) ~52 Reduced insitu E18 proposal Proposal ; Divide the experiment into two runs as - 1 st Run for 0.8 tera pion with d.f. ~ (~70 shifts) - 2 nd Run for 4 tera pion with d.f. ~ 1

The PAC recommended 2 nd stage approval of E18 and encouraged the efforts; 1. To clarify the precision expected in extracting TN-NMWD signal including the INC calculation. 2. The efforts to tolerate higher beam intensity to reduce the precious beam time. PAC approval and the homeworks

1.Quenching in both p and n spectra from those of INC(1N). 2.What would be the mechanism for the nucleon Quenching?  FSI & 3-Body process.  The 3-body NMWD (or 2N-NMWD) has been calculated first by Alberico-Ericson for Nuc. matter (‘91). Then Ramos-Oset extended to finite nuclei (‘94). Recently Bauer-Garbarino further extended it.  Γ 2N =~0.27 Γ Λ ( 12 Λ C) INC(1N) E p (MeV)E n (MeV)

Γ 2N and the quenching of yields How to disentangle the effect of FSI? Renormalize INC so that it can fit to the experimental data. It is a fitting function, rather than a model prediction. Total sum of the yields under 300 MeV/c is reproduced with the branching ratio, b 2N =0.29. b 2N  Γ 2N /Γ nm =0.29±0.13 Phys. Rev. Lett. 103 (’09) Present Experiment Γn/ΓpΓn/Γp 0.51±0.13±0.05 Γ nm 0.95  0.04 b 2N 0.29±.13 Γ 2N 0.27±.13 ΓnΓn 0.23±0.08 ΓpΓp 0.45± Errors are large, Need a better measurement.  E18 (J-PARC)

Inclusive and Exclusive nature

Recent progresses on Γ 2N (Finuda experiment) A hig h A low Mass dependence of A low /(A low +A high )  2N /  nm =0.24  0.10 Phys. Lett. B685 (’10) 247 (K stop -,π - ) reaction

Theo. Prediction of 3-body process (Γ 2N ) of NMWD. Λ N π Model for 2N-NMWD; Alberico-Ericson for Nuc. matter (‘91), and Ramos-Oset extended to finite nuclei (‘94). Absorption of virtual pion by 2p-2h states. - Λ  pπ - is dominant at the weak vertex and - Pions are absorbed dominantly on the pn pair. In the process 3 nucleons are emitted; 1p(LE) + 2n (HE) Γ 2N = 0.27 Γ Λ ( 12 Λ C) Bauer and Garbarino; Recently, extended the model to include K, ,  mesons and pp and nn pairs also. Γ 2N → 0.37 Γ Λ ( 12 Λ C) [Bauer et al., NPA836 p199] Extended to K, ρ, ω..

Decay widths; agree well with theoretical ones (Bauer et al., NPA836 p199). However, there remains significant discrepancies in the spectra and the coincidence correlation data.

Γ 2N Status

FSI independent observables to extract  

How to improve to accept higher beam intensities

Multiplicity at BDC and SDC; Rate limitation of the drift chamber; ~200k/signal wire Data Acquisition system. Can we make some improvement to accept higher beam intensity?

E18 preparation Decay Counter; - Scintillators/PMT/LG/Mag shieldings - Chambers - Supporting holders - Cables Electronics DAQ program Space for setup/storage Moving abroad - Custom - What logistics scheme? -... T4: 20 cm x 100 cm x 5cm T3: 10 cm x 100 cm x 2cm T2: 4 cm x 20 cm x 0.4 cm

Summary 5. We need both more accurate measurements and calculations to understand NMWD. 6. E18 preparation is going on. ( Dr. Kim’s talk) Λ N π

Thank you for your attention

EXTRA

Other ways to derive b 2N is to look at the pair yields in nbb region where the 3-body NMWD would increase the pair yields. Here we expect the yields would increase as b2 increases as can be seen in the figure. Triple coincidence yields are also expected to increase as b 2N. Exclusive observables to extract  

III. Models for NMWD Two classes for short range behavior, 1.Heavy meson exchange model (HME); K, ρ, ω etc. with ΔI=1/2 rule. 2.Hybrid models; π, K exchange + Direct quark int.(DQ) w/o ΔI=1/2 rule. or π, K exchange + Q. Bag model 3. Point interaction model (phenomenological model) π OPEHME Meson-quark Hybrid Mod. Λ N N N 4-point int. OPE; Dalitz and Adams first calculated Γ nm

5 Λ HeΓ nm (Γ Λ )Γn/ΓpΓn/Γp  nm (p) OBE(all) Parreno et al. π+K+DQ Sasaki et al. π+K+w+2π( ,  ) (0.12)Itonaga et al. Experiment0.42   0.11   0.08  0.04 KEK-PS E462 Upgraded Γ n /Γ p theoretical values After the correction of the phase error in K exchange term, Γ n /Γ p ratio was enhanced significantly. Now the theoretical Γ n /Γ p ratios of various models agree with the recent exp. ratio quite well. The Γ n /Γ p ratio puzzle was finally resolved. Models of NMWD and the Γ n /Γ p puzzle (III)

Proton Energy spectrum (KEK-PS E307)

Coincidence Meas. (KEK-PS E462/E508) and Γ n /Γ p resolution - Measure; n, p  N n (E), N p (E) - Measure Pair coin. yields in  ; N nn (θ), N np (θ) - Seperate back-to-back(bb) and non-bb(nbb) kinematic events. - Require back-to-back (cosθ<-0.7) condition.  to supress FSI and 2N-NMWD. EpEp EnEn n,  p, 

Coincidence Yields (NN angular correlations) Г n /Г p = 0.45±0.11±0.03 B.Kang et al., PRL 96 (’06) (N nn /N np ) bb  Г n /Г p 12 Λ C 5 Λ He - bb ; cosθ < FSI/3-B broaden the angular corr. 1.Well agreed with those of Th. 2.Г n /Г p puzzle finally solved. 3.Why the exp. Г n /Г p ratio has been so high? Г n /Г p = 0.51±0.13±0.05 M. Kim et al., PLB (’06)

Summary 1.It turned out that the reason behind the long standing Г n /Г p puzzle was the strong contribution of the 3-body NMWD process. 2.Its branching ratio obtained in the previous exp was b 2N ~0.29±0.13, only a 2σ confidence level. It has to be measured more accurately, for which E18 is proposed. 3.The purpose of E18 (J-PARC) is to measure Γ 2N (3-body decay process), Γ n,Γ p for 12 Λ C accurately. 4.Another important issue in NMWD is the asymmetry parameter, α nm. Now there are serious inconsistencies among experimental and theoretical values. The best target to study it is 13 C. The feasibility to adopt it to measure b 2N and α nm accurately and simultaneously has been discussed. The production cross section and the polarization of 13 Λ C are ~1/2 times smaller and 5 times higher than those of 12 Λ C. 5.The current preparation status of E18 was reported.

Physics Outputs and the Run request and Strategy 1.First-run ; - total 0.8x10 12 π+ beam (~60 shifts), - 3 kW, - 2x10 6 π/2s(spill) with d.f.~ 30%. 2. Physics Output; - The direct and exclusive confirmation of b 2N (=Γ 2N /Γ nm ) with triple coin and N NN (nbb). - A solid confirmation of Γ 2N of at least 3-4 σ confidence level. - N NNN ~ 52(6), N NN (nbb) ~90(25), N pp (bb) >50(8).

Recent progresses on Γ 2N (Theory) Our scheme for the decay rates, developed in [25--28], puts on the same ground the microscopic evaluation of one?and two 춂 ody stimulated decay mechanisms and includes the channels #nn nnn and #pp npp besides the standard mode #np nnp. This scheme uses the same OME weak transition potential (containing #, #, K, K, # and # exchange) of [23].

Inclusive and Exclusive nature

Before this coincidence experiment, np ratio was determined from the proton spectrum relying on the INC model calculation on FSI on the outgoign proton. However, such procedure is quite INC model dependent.

OPE  +K+DQ  +K+   +K+  +DQ At present, only π+K+s+DQ model reproduce both G n /G p and a NM.  +K OME Theoretical models, such as π +K and OBE, can explain our G n /G p ratio, but not a NM. Status of Γ n /Γ p & α nm puzzle

(2N-NMWD)

Models of ΛN  NN interaction (I) I. Meson Exchange Models; ΔI=1/2 rule adopted. OPE model(1967) ; V π by Adams. Heavy meson exchange(HME) model; Dubach, Oset, Ramos, Parreno.. - Due to large momentum, they involve short distance behaviors. - pseudo-scalar and vector mesons; π, ,K,... - No drastic effect. 2π(σ,  channel) Exchange Model; Itonaga, Schmatikov - 2π exchange is important in nuclear force. - found its contribution important. π OPE N π

Models of NMWD and the Γ n /Γ p puzzle (II) II. Hybrid quark-hadron Model 6-q Bag model + V π ; Cheung et al., Direct Quark(DQ) Mechanism; V DQ + V ME - ΔI=1/2, 3/2 both allowed. - Oka, Sasaki,.. - considerable improvement on Γ n /Γ p - Phase problem in K exchange amplitude; Sasaki, III. Contact four fermion interaction model Block and Dalitz; prl 11 ('63) 96 Jun J., prc 63 ('01) Parreno A.; prc 70 ('04) Λ N N N

Parreno EFT calc.; long range; ,K exch., short R; PV and PC contact terms K exch. ; important for n/p ratio.

Decay Counter Setup (J-PARC E18) Setup  n ~47 %  p ~40% T4: 20cmx 100 cm x 5cm T3: 10 cm x 100 cm x 2cm T2: 4 cm x 20 cm x 0.4 cm J-PARC 50GeV E18 E18 Decay Counter Setup

Original run; - High Beam intensity; ~5x10 6 π + /s (~10 7 π + /2s(spill)) To meet this high beam intensity, - BDC(1-4) ; - 1/1/3/3 mm wire spacing. - BDC4 needs further consideration. - SDC(1,2) ; 1mm chambers.(Osaka coll.) Technical Issues; High rate capabilities of Beam line detectors. In ’10 autumn run, all beamline detectors (BDC, SDC) were working fine with 1x10 6 π/2s spill(10% d.f.) beam, which corresponds to - ~5x10 6 π + /s (100% d.f.) = 10 7 π + /spill - ~1.5x10 6 π + /s (30% d.f.)= 3x10 6 π + /spill All SKS detectors are ready except A(erogel)C, for which a new wider acceptance AC will be installed by the Osaka collaboration in this month.

Neutron random background; E508 Neutral particle TOF spectrum ~2% nn background n singles nn pair

E508E18_orgE18(1 st -step) Instant beam rate 4M/1.8s =2.2 M/s (* df~1.0) 10M/1.8s=5.5 M/s (* df~1.0) 2M/(2  0.3)s=3.3 M/s (* df~0.3) n det. rate11.8x5/21.8x3/2 nn random bg 1(1.8x5/2) 2 (1.8x3/2) 2 nn Yields x5/ x3/2 Y B /Y nn x5/2= x3.2 = 0.03 (Y B /Y nn ) nbb 0.02x(13/16)/(16/59) =0.06 (* Y nn (bb/nbb)=43/16) =0.135 (with improved  (nbb) ) 0.08 (* with improved  (nbb) ) With 2 M  /spill and df~0.3, we can maintain the instant beam current and the random background rate below those of original E18 proposal. However, it is important to keep the neutron random background rate below the level of 2-3% of singles neutron. (Need n background check in the area.) We can maintain the  bg below 10% level with a similar neutron background. Neutron Backgrond

WC Target Trigger rate; A WC counter to reject proton Cerenkov light R tot ~270/spill R πK ~150/spill Need to maintain R πK but increase the real K trigger. Most of the K trigger was proton. Need to remove p contamination. 1 mm thickness Water C.

e + 450MeV t4 t3 t5 t6 e+e+ Beam Trigger: t3  4  t5  t6 Cerenkov light Trigger: BeamxWČ 11 Test Exp. at the e-LINAC of Tohoku Univ.

 N pe =18.6(3”), 5.7(2”)  This gives 7 pe for K so that an efficient WC counter can be made.  The incident position and angle dependence varies down to 60%, but acceptable. WC light collected

Decay Counter Status Repairment

Collaboration

1. Revised Two-step Run plan; - Current duty factor of K1.8 beamline remains %. - Expected improvement; at most ~ 30 % in a couple of years, 1) E18_1 st -step run; for solid confirmation of 2N-NMWD with ~30% df beam. 2) E18_Main run; for full statistics run for 10% stat. error for Γ 2N, Γ n, Γ p, Γ n /Γ p with high df beam. 2. First-step run ; total 0.8x10 12 π+ beam (70 shifts) on 4g/cm 2 12 C target, 3kW, 2x10 6 π/2s(spill), 30% duty factor beam. 3. Physics Output; - can achieve a direct and exclusive confirmation of 3-body NMWD by measuring the triple coin and N NN (nbb). - can achieve a solid confirmation of the branching ratio b 2N of at least 3-4 σ confidence level instead of the current 2σ. 4. N NNN ~ 52(6), N NN (nbb) ~90(35), N pp (bb) ~ 50(8). These results can be published to meet the urgent need of a solid confirmation of 2N-NMWD in the weak decay research community. The Revised Two-step Plan

E508E18_main E18_1 st -step N  tot 2T5T (80shifts)0.8T (70 shifts) n  /spill4 M/4sec10 M/spill(6sec)2 M/spill(6sec) d.f.~1 ~0.3 N np (bb)116(  7  2.5) ~2030(  7 .5) ~320 N nn (bb)43(  3.5  2.5) ~376(  3.5 .5) ~60 N pp (bb)8(4  4  2.5) ~320(4x4 .5) ~51 N np (nbb)9(  12  2.5) ~270(  12 .5) ~43 N nn (nbb)16(  4.5  2.5) ~280(  4.5 .5) ~45 N NNN 6(  12  1.8  2.5) ~325(  12  1.8 .5) ~52 Summary of the Two-step Plan

Decay Counter Setup (J-PARC E18)

Reproduction of Angular correlation and singles yields Present Experiment Γn/ΓpΓn/Γp 0.51±0.13±0.05 Γ nm 0.95  0.04 b 2N 0.29±.13 Γ 2N 0.27±.13 ΓnΓn 0.23±0.08 ΓpΓp 0.45±0.10 Г nm -Г 2N =Г p (1+Г n /Г p ) - Errors are large, Need a better measurement.  E18 (J-PARC)

Γ 2N and the quenching of yields Total sum of the yields under 300 MeV/c is reproduced with the branching ratio, b 2N =0.29. b 2N  Γ 2N /Γ nm =0.29±0.13

Theo. Prediction of 3-body process (Γ 2N ) of NMWD. Λ N π Model for 2N-NMWD; Alberico-Ericson for Nuc. matter (‘91), and Ramos-Oset extended to finite nuclei (‘94). Absorption of virtual pion by 2p-2h states. - Λ  pπ - is dominant at the weak vertex and - Pions are absorbed dominantly on the pn pair. In the process 3 nucleons are emitted; 1p(LE) + 2n (HE) Γ 2N = 0.27 Γ Λ ( 12 Λ C) Bauer and Garbarino; Recently, extended the model to include K, ,  mesons and pp and nn pairs also. Γ 2N ; similar values. Extended to K, ρ, ω..