Study of the e+eη process at √s = 1 GeV

(main systematic error in the e+ee+eη analysis)

09-02-2010

N. expected events = L σ (e+eη) BR ( ) ε

Integrated luminosity L= 239.6 pb-1

σ (e+eη , η) = 0.23 nb

3

e+e-e+e-: systematics Output () value always 15% lower than expected

value Spread among results from different

cuts ~ 11% For a fixed

cut, the difference between pL and Mmiss

2 fits ~ 2% With or without pT<100 MeV cut, related to the

generated pT distribution for MC signal ~ 3%1 (no pT cut) = 0.209 ± 0.003

2 (pT cut) = 0.196 ± 0.003

(e+e e+es=1 GeV) = (50±2stat±9syst) pb

4

• TRIGGER, FILFO

• γγ filter (see KLOE Memo n.346), in detail:

• 2 tracks with opposite charge from a cylinder with ρPCA < 8 cm, |zPCA|< 8 cm, ρfirst-hit < 50 cm

Analysis criteriaAnalysis criteria

• at least 2 neutral prompt clusters with Eclu> 15 MeV

• 100 MeV < Σ Eγ < 900 MeV

• Eγ1 > 50 MeV

• 3 neutral prompt clusters• “Electron likelihood” cut• Cuts to reduce

“pathological” background:– “Split tracks” cut angle > 20°

+- mass < 425 MeV

Event selectionEvent selection

√s= ∑3 E + E + E

∑ p + p + p= 0

(3)

t - |r |/c = 0 (3)

15 variables : E,t,x,y,z for each

7 constraints:

M

j

kN

kj

kj

N

ii

measii PPCPP

1 11 2

22 )...(

)(

Lagrange multipliers method:

Kinematic fitKinematic fit MC signal

data

)cos1(2

2

1)(

)(

2

2

2 0

ijji

j

E

i

E

pair

EEM

EEM

M

M

MM

ji

Energy resolution

γγ pairing

QED + “pathological” backgrounds

data

data

e+ee+e e+e“split” tracks

“select” cut, “split” cut

angle

MC signal data

invariantmass

SL

invariantmass

SL

K+K 0 0 , e0

+0

KSKL00 +e

fD

B

N

Lf

A: M+- < 425 MeV B: |p+|+|p-| < 440 MeVC: E> 350 MeV

K+K- KSKL

N0 5.5 106 9.2 106 2.9 107 2.0 107 9.0 106

A 0.310 0.66 10-1 0.36 10-3 0.12 10-2 0.69 10-2

AB 0.310 0.43 10-1 0.31 10-3 0.11 10-2 0.40 10-2

AC 0.305 0.35 10-1 0.58 10-4 0.70 10-3 0.46 10-2

ABC 0.305 0.32 10-1 0.55 10-4 0.70 10-3 0.37 10-2

MC signal

MC signal

12

Kinematic fitMC signal

invariant mass

3 energy

M (MeV)

E3 (MeV)

e+e- 0

e+e-

e+e-

fit /d.o.f.= 193/169

N. final data = 172604

~ 9%, ~ 58%, ~ 22%

Fit (A)

fit /d.o.f.= 218/174

Fit (AB)

fit /d.o.f.= 170/169 fit /d.o.f.= 219/174

e+e- 0

e+e-

e+e-

M (MeV)

E3 (MeV)

N. final data = 115965

~ 13%, ~ 60%, ~ 19%

Fit (AC)

fit /d.o.f.= 197/169 fit /d.o.f.= 226/174

e+e- 0

e+e-

e+e-

M (MeV)

E3 (MeV)

N. final data = 105973

~ 14%, ~ 54%, ~ 24%

Fit (ABC)

fit /d.o.f.= 178/169 fit /d.o.f.= 222/174

e+e- 0

e+e-

e+e-

M (MeV)

E3 (MeV)

N. final data = 94939

~ 15%, ~ 55%, ~ 21%

E3 M+-

(nb) (A) 0.198 ± 0.002 0.202 ± 0.002

(nb) (AB) 0.200 ± 0.002 0.196 ± 0.002

(nb) (AC) 0.198 ± 0.002 0.197 ± 0.002

(nb) (ABC) 0.198 ± 0.002 0.196 ± 0.002

Results

e+eη ()

E3 M+-

(nb) (A) 6.28 ± 0.09 6.60 ± 0.07

(nb) (AB) 6.70 ± 0.08 6.89 ± 0.11

(nb) (AC) 6.89 ± 0.11 7.02 ± 0.10

(nb) (ABC) 6.80 ± 0.11 6.93 ± 0.03

e+e ()

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