Today's Progress 23. May 2010

Normalized Λp spectra (1)

Here, we present normalized Λp spectrum by generalized acceptance discussed in the 2009 Aug 18th report for back-to-back events (case1-180deg). First of all, we present the summary of total numbers of Λp events. Since we have updated the proton selection procedure after 2007 June 11th report at 2007 July 11th report, we compare the event number cycle-by-cycle as the first step, for the case1 topology.

E549/E570 cycle-by-cycle &Lambda N event statistics

For the primary neutron, selection A is defined by detection software threshold (3 MeVee) and 1/&beta selection (1.6-9.0) to define "physical" neutrons. For the primary proton, it is defined by successfull energy loss correction with 'reaction vertex' and layer B hit if the proton is measured on TC. For 6th and 7th column, the values in the round brackets are the events numbers before the improvement of proton selection procedure at 2007 July 11th report. For 8th column, the numbers in the quotation marks are the number if bad PB counter hits (L-3, R-15 for E549, nothing for E570-1, and R-15 for E570-2) are removed from the event accumulation.
YN pair(dibaryon/tribaryon channel) case ID(Selection) Angler acceptance (cos(ΛN)) PA/PB/NT particle TC particle No. of reconstructed &Lambda No. of event after selection A yield of well-defined &Lambda N pair
&Lambda p (X+/S0) 1(A-b-1-x) (-1,-0.7)p + p&pi 1415(1329)/1380(1294)/549(514) 1352(1271)/1339(1256)/525(494) 1352+1339+525=3216 "1241+1339+496=3076"
&Lambda p (X+/S0) 1(A-b-x-1') (-0.9,0.9)p&pi + p 1250(1217)/1208(1186)/498(490) 966(937)/935(916)/384(379) 966+935+384=2285 "910+935+376=2221"
&Lambda n (X0/S+) 1(A-b-3-x) (-1,-0.7)p + n&pi 12535(12200)/12640(12289)/4822(4678) 4657(4555)/4675(4550)/1915(1875) 4657+4675+1915=11247 "4447+4675+1881=11003"
&Lambda n (X0/S+) 1(A-b-x-3') (-0.9,0.9) p&pi + n 3819(3711)/4033(3908)/1417(1389) 1723(1675)/1713(1678)/623(614) 1723+1713+623=4059 "1639+1713+608=3960"

Below, we show Λp coincidence spectrum, under the thress conditions:

1. pΛ≥320 MeV/c,

2. pp≥320 MeV/c,

3. cosθpΛ≤-0.75.

Ap, Bp and Cp components are represented by green, red, and blue, respectively.

Λ momentum.
Proton momentum.
Angle by 3-momenta of Λ and proton.
Angle by 3-momenta of Λ and proton. Now each component is normalized to 1.
Invariant mass of Λ and proton.
4He(K-stopped,p) missing mass = 3S0 mass.

Following several important conclusions are almost immediately derived :

  • Per-stopped-K- fraction of Ap and Bp are ≈0.86% and ≈1.31%, respectively.
  • The back-to-back correlation is the strongest for Ap component, as expected. But it is not the "real" back-to-back, as was observed for 4ΛHe -> d+d or (4He-K-)atomic->Λ+t processes.
  • Bp component peaks at 2S+ mass ≈2230 MeV/c2, which corresponds to "K-pp" binding energy of ≈140 MeV. The HWHM is then ≈70 MeV.
  • Bp component peaks at 3S0 mass ≈3140 MeV/c2, which corresponds to "K-pnn" binding energy of ≈170 MeV. The HWHM is then ≈80 MeV.

    • Of course, the nature of the Bp process must be carefully examined with other information, like Λn and/or ΣN results.