Today's Progress 29. May. 2007

&Lambda reconstruction/&Lambda N correlation analysis: E570

p&pi invariant mass spectra constructed from (p onNT, &pi onTC) and (p onTC, &pi onNT) events

p&pi invariant mass spectra constructed from (p onNT, &pi onTC) and (p onTC, &pi onTC) events from E570 1st cycle. The black-colored spectra are results when &Lambda decay vertex is adopted to calculate 1/&beta and energy loss inside, while the red-colored ones are the result with Kaon stopping point defined by BLC-PDC.

p&pi invariant mass spectra constructed from (p onNT, &pi onTC) and (p onTC, &pi onTC) events from E570 2nd cycle.

Suppression of combinatorial background by vertex information

p&pi invariant mass spectra constructed from (p onNT, &pi onTC) and (p onTC, &pi onTC) events for E570 1st cycle. The events with positive vec(v&Lambda)*hat(p&Lambda) are plotted by red, while green if not.
p&pi invariant mass spectra constructed from (p onNT, &pi onTC) and (p onTC, &pi onTC) events for E570 2nd cycle. The events with positive vec(v&Lambda)*hat(p&Lambda) are plotted by red, while green if not.

p&pi invariant mass spectra for specific event sets

p&pi invariant mass spectra constructed from (p onNT, &pi onTC) and (p onTC, &pi onTC) events from E570 1st cycle. The events with positive vec(v&Lambda)*hat(p&Lambda) are plotted by red, while green if not. Event topology is explicitly written on the spectra.
p&pi invariant mass spectra constructed from (p onNT, &pi onTC) and (p onTC, &pi onTC) events from E570 2nd cycle.

&Lambda N correlation analysis

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 ones. 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. Selection B is defined by the elimination of unhealthy PB counter hit(nothing for 1st cycle, R-15 for 2nd cycle).
YN pair(dibaryon/tribaryon channel) case ID(Selection) Angler acceptance PA/PB/NT particle TC particle No. of reconstructed &Lambda No. of event after ANo. of event after B (yield of well-defined &Lambda N pair)
&Lambda p (X+/S0) 1(A-b-1-x) 180 +- 30p + p&pi 1294/5141256/494 1256/467
&Lambda p (X+/S0) 1(A-b-x-1') 90 +- 45p&pi + p1186/490916/379 916/372
&Lambda n (X0/S+) 1(A-b-3-x) 180 +- 30p + n&pi 12289/46784550/18754550/1841
&Lambda n (X0/S+) 1(A-b-x-3') 90 +- 45p&pi + n3908/13891678/6141678/600
&Lambda p (X+/S0) 2(B-a-1-x) 90 +- 45&pi + pp 337/157 323/149 323/142
&Lambda p (X+/S0) 2(B-a-x-1') 180 +- 45&pip + p3002/1277 2476/1050 2476/1027
&Lambda n (X0/S+) 2(B-a-3-x) 90 +- 45&pi + np 6626/2434 1357/532 1357/516
&Lambda n (X0/S+) 2(B-a-x-3') 180 +- 45&pip + n4438/1678 2489/989 2489/950

The definition of variables are as follows:

&Lambda 4-momentum p&Lambda(0:3)/3-momentum p'&Lambda(3):p'&Lambda(i)=pp(i)+p&pi(i), p&Lambda(i)=p'&Lambda(i) (i=1,2,3), p&Lambda(0)=sqrt(M&Lambda2+|p'&Lambda|2),

Nucleon 4-momentum pN(0:3)/3-momentum p'N(3):pN(i)=p'N(i) (i=1,2,3), pN(0)=sqrt(MN2+|p'N2|)

cos(N&Lambda):p'&Lambda*p'N/(|p'&Lambda|*|p'N|)

N&Lambda total 3-momentum Ptot:sqrt((p&Lambda(1)+pN(1))2+(p&Lambda(2)+pN(2))2+(p&Lambda(3)+pN(3))2)

N&Lambda total energy Etot:p&Lambda(0)+pN(0)

N&Lambda invariant mass Minv:sqrt(Etot2-Ptot2)

4He(stopped K-,N&Lambda)X missing mass Mmiss:sqrt((M4He+MK--Etot)2-Ptot2)

The results are exhibitted below for every event topologies:
  • &Lambda case 1 p 180degree
  • &Lambda case 1 p 90degree
  • &Lambda case 1 n 180degree
  • &Lambda case 1 n 90degree
  • &Lambda case 2 p 180degree
  • &Lambda case 2 p 90degree
  • &Lambda case 2 n 180degree
  • &Lambda case 2 n 90degree