1. Current status of estimation of Eγ resolution
12/19(Tue) analysis meeting
Y.Kato

2. To know the Eγ resolution is equal to know the momentum resolution!
Strategy
If reaction is assumed, Eγ is calculated analytically from
measured momentum.
In the case of γ p →　k+ Λ(1116),
To know the Eγ resolution is equal to
know the momentum resolution!

3. LLH2 run25452-25968 Analyzed data …LLH2 run23690-24058
Situation is different in these runs.
→later

4. ・σfromΔp is estimated from MC.
γ　p → k+ Λ(1116)
γ　p → π+ π- p
ΔEγ(GeV)
Momentum of k+(GeV/c)
Eγ(GeV)
・σfromΔp is estimated from MC.
・vertex,decay-in-flight,chi2probability,ybar cut is included.
It is neccesary to investigate momentum resolution of
MC and real data is differnte or not.

5. → MC γ p →k+ Λ(1116)→k+ p pi- Real data γ(p,p pi-)X line+gauss fit
Check the invariant mass of real data and MC
γ p →k+ Λ(1116)→k+ p pi-　
Real data
line+gauss fit →
3sigma cut
is applied
M(ppi-)
γ(p,p pi-)X
σ=1.30±0.03MeV MC
σ=1.24MeV

6. Smear the momentum resolution of MC
If ΔEγ is assumed , momentum resolution of real data can be obtained
from missing mass.
ΔEγ is assumed to be 12MeV MC
black:Real data
Red :MC
smear
ΔP(GeV/c)
σ=1.31MeV
Pk+(GeV/c)

7. γ p → k+ Λ(1116) ΔE after smear of MC for various mode
Red: Before smear
black: after smear
ΔEγ
Eγ（GeV）
Fit by constant value→11.9MeV±0.1

8. γ p →　pi+ pi- p
Red: Before smear
black: after smear
ΔEγ=11.8MeV±0.1

9. γ p →　k+ k- p
Red: Before smear
black: after smear
ΔEγ=10.7MeV±0.3

10. The hint for the reason of inconsistency between real data and MC
number of hits used in the tracking
Real data MC
number of hits removed in the tracking

11. γ p →k+ Λ(1116)
Red: nhits<16
Black: nhits>=16
ΔEγ(GeV)
Pk+(GeV/c)

12. Run dependence γp → k+ Λ γp → π+ π- p run23690-24058 run23690-24058
pk+(GeV/c) Eγ
change of ΔEγ or Δp ?

13. check the invariant mass
run
run
σ=1.30±0.03MeV
σ=1.26±0.04MeV

14. How large invariant mass change if run dependence of missing-mass
is all due to the change of momentum resolution?
smear to adjust run
smear to adjust run
σ=1.31MeV
σ=1.47MeV

15. γp→pi+pi-p vty(mm) VTY dependence run23690-24058 run25452-25968
black:
Red:
γp→pi+pi-p
ΔE(GeV)
vty(mm)

16. Summary
・Validity of momentum resolution in MC is essential to determine Eγ resolution.
・Invariant mass study indicates momentum resolution is under estimated in MC.
・Simple smearing makes inconsistency.
・Number of hits is different in real data and MC
・Run dependence of missing mass resolution can’t explain by the change of
momentum resolution.