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 0  (search for a 0 (980)). C.Bini, P.Gauzzi, D.Leone. Channel 1:  0  5  () Channel 2:  0  +  - 5  (  +  -  0 ) Combined fit to the M  spectra Conclusions KLOE General Meeting 20/12/2001 – Roma 3.

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0 search for a 0 980
0(search for a0(980))

C.Bini,P.Gauzzi,D.Leone

  • Channel 1: 05 ()

  • Channel 2: 0+-5 (+-0)

  • Combined fit to the M spectra

  • Conclusions

  • KLOE General Meeting 20/12/2001 – Roma 3


5 channel
5  channel

  • Signal:

  • (a0+00)0

  • Background: S/B

  • e+e-0 00 0.2

  • (f0+00)00 0.3

  • 3 1.5 (0.4% = fraction of 5 events)

  •  000 0.3 (2.5% = fraction of 5 events)


Analysis scheme
Analysis scheme

  • Preliminary selection: no tracks, 5 prompt photons (5t),

  • Eprompt> 700 MeV, > 21o

  • First kinematic fit: 30 parameters with 9 constraints 9 ndf

  • Best photon pairing in the following hypotheses:

  • 1) 0

  • 2) 00

  • 3) 000 ( mass , E0=218 MeV in the selection 2)

  • 4) 3 ( mass , Erad=363 MeV in the selection 2)

  • Second kinematic fit : 30 parameters, 11 constraints

  • ( 9 +  and 0 masses for 1) or two 0 masses for 2) 3) )

  • For each event this fit is performed three times

  •  hyp. 1) , 2) and 3)

  • Final cuts

  • All the events pass through the whole chain: cuts are applied

  • at the end


Rejection
 rejection

  • 0

  • 00

  • 

E (MeV)

Data

M (MeV)

M (MeV)

  • Photon pairing in the 3 hyp.

  •  rejection : Erad<340 MeV

  • To reduce the sample: |M-M| < 3

  • cut at 2/ndf < 3to reject  000


Mc 0 0 sample
MC: 00 sample

  • 00

  • 0

  • 

E (MeV)

Events

M (MeV)

  • Get spectrum from data:

  • |M-M|>3 to get a clean

  • 00 sample

  • Alternative way: use the spectrum

  • from Simona’s analysis

M (MeV)


Mc 0 0 sample1
MC: 00 sample

  • Correct for efficiency

  • Get scale factors bin by bin

  • from the ratio of the

  • experimental spectrum to the

  • MC generated one

  • It takes into account for both

  • f0 and 00 00

  • No need for MC

  • 0000

M (MeV)


0 0 rejection
00 rejection

Data

  • 0

  • 000

  • 00

|M(1)- M (2)| (MeV)

M (MeV)

(0 wrong pairing)

  • Parabolic cut to reject 0 (equivalent to 2 cut on M)

  •  M < 760 MeV to reject f0 + 0 wrong pairing


Data mc comparison
Data-MC comparison

  • Data

  • — MC

  • — bckg

  • Data

  • — MC

Events

Events

2/ndf

Etot/E

  • Second fit: 2/ndf >3 dominated by background

  • (mainly 000)  cut at 2/ndf < 3


Data mc comparison1
Data-MC comparison

  • Data

  • — MC

  • — bckg

Events

  • 3  cut on M removed

  • Good agreement up to 10 

(M-547)/

(M-135)/


Final sample
Final sample

  • Data

  • — 00

  • —000 

  • —000

  • —

  • Data

  • — MC

Events

Events

M (MeV)

cos

  • 916 events in the final sample


Efficiency and luminosity
Efficiency and luminosity

Efficiency:

Average efficiency = 32.4%

  • Luminosity:

  • Run number range: 15174 – 17330

  • Integrated luminosity: (16.45 0.33) pb-1

  • use VLAB, uncertainty 2%

  • if there is no VLAB, use LAB x (1 – 1.2%)

  • if there is no LAB use TRGLUMI,

  • uncertainty  5%

M (MeV)

LVLAB = 15.78 pb-1

LLAB = 0.58 pb-1

LTRG = 0.09 pb-1


Background subtraction
Background subtraction

Rej. factor Cross sect. or Br.(*) Expected events

e+e-0 00 140  = 0.460.05 nb 54  6

00 40 Br = 10-4  10% 152  16

  6  104  = 17.2  0.6 nb5  2

 000 2.5  103  = 13.8  0.4 nb98 10

———

tot. bckg. 309  20

The errors include MC statistics and cross section (or Br) uncertainties

((*) Only KLOE measurements)

Signal (0) : 916 – 309 = 607 events

with =(3.370.12) b (from  )

and Br() = (39.33 0.25) % (PDG 2000)

Br(0) = (8.51  0.43 (stat.)) x 10 -5


Systematics
Systematics

  • Analysis cuts: evaluated by moving the cuts by 1 on the variable

  • and cuts on 2 by 1

  • Cut Uncertainty

  • >21o (1o) 1.5 %

  • first fit 2 1.2 %

  • 3  on M 4.0 %

  • E < 340 MeV 2.0 %

  • Parabolic cut (M) 3.0%

  • M < 760 MeV 1.7 %

  • second fit 2 1.2 %

  • ———

  • Combining in quadrature 6 %


Uncertainty summary
Uncertainty summary

  • Absolute (10-5 units) Relative

  • Statistics 0.43 5.0 %

  • Bckg subtraction 0.28 3.3 %

  • Analysis cuts 0.51 6.0 %

  • Luminosity 0.17 2.0 %

  • cross section 0.31 4.0%

    (L contribution subtracted)

    Br() 0.05 0.6 %

    Trigger to be evaluated ( negligible)

    Photon counting to be evaluated (1—2 % ?)

    Br(0) = (8.510.51(stat.+bckg))0.62(syst.)) x 10 –5

    Br(0) = (8.8 1.40.9) x 10 –5 SND (2000)

    Br(0) = (9.0 2.41.0) x 10 –5 CMD-2 (1999)


5 channel1
+-5 channel

  • No background with exactly the same final state

  • Main backgrounds:

  • 2 Tracks + 3/4 photons + splitting/accidental

  • 2 Tracks + 6 photons + acceptance loss/merging


Event selection

  • ECL (ppfilt)

  • 1 vtx in IR with 2 tracks

  • 5 prompt photons E>10 MeV, q>21o

  • kinematic fit 1 E/p cons., c-speed

  • Minv(p+p-) < 425 MeV

  • to reject KSp+p-

M (MeV)

Large rejection factors

few expected bckg events


Data-MC comparison

Before cut on

Minv(p+p-)

  • h and w peaks clear.

  • MC signal + bckg well reproduces

  • data

  • gg and ppgg combinations

  • invariant masses after fit-1

gg and ppgg combinations

invariant masses after fit-2

(variables from fit-1)

M (MeV)

M (MeV)

After cut on

Minv(p+p-)

M (MeV)

M (MeV)

M (MeV)

M (MeV)

M (MeV)

M (MeV)


Final sample

197 events selected:

Lint=16.4 pb-1

BR(0)=(7.960.60(stat+bckg)

0.47(syst))  10-5

Statistics 0.58

Bckg subtraction 0.15

Efficiency(*) 0.30

Br(+-0) 0.14

Luminosity 0.16

 cross section 0.28

(*)work in progress

Raw Minv(hp) spectrum

and cos(qg) distribution


Fit to the m spectra
Fit to the Mspectra

  • Contributions:

    • a0(980) with a00

    • 00 with 0

    • Br() 1/3 Br(0) =1.2  10-5 (PDG)

    • Br( 0) = 0.54  10-5 (Bramon, Grau, Pancheri,

    • Phys.Lett.B283(1992),416)

    • = 5.18  10-5 (Fajfer, Oakes,

    • Phys.Rev.D42(1990),2392)

    • 3)e+e-0 with

    • (e+e-0)  Br()  0.12  10-5  negligible

  • 1) and 2) can interfere


Shape
 shape

 momentum

in the  c.m.

Phase space

( angle in the  c.m.)

Achasov-Gubin Phys.Rev.D63

094007(2001)


Shape1
 shape

a.u.

M (MeV)

Good agreement with Bramon et al., Phys.Lett.B283,416 (1992)


A 0 flatte phys lett b63 224 1976
a0 (Flatte’,Phys.Lett.B63,224,(1976))

Above KK threshold

Below KK threshold


A 0 0 0 interference achasov gubin
a000 interference (Achasov-Gubin)

a0 only

a0+ no interf.

interference (+)

interference (-)

M (MeV)


Fit method
Fit method

  • Combined fit to the two spectra

  •  shape fixed + Br()/Br(+-0) fixed

  • Ni = number of events (data) i=1,Nexp bin in Mexp

  • Mij = smearing matrix, takes into account for resolution and photon

  • pairing effects j=1,Ngen bin in Mgen (from MC)

  • f = theoretical function

  • i2 = 2(data) + stat2(MC)

  • Free parameters: Br1=Br( 0), Br2=Br(a0),

  • a0 (PDG: 50—100 MeV)

  • Fixed : Ma0 = (984.8 1.2) MeV (PDG) ; gk = 0


Fit results
Fit results

  • Br1(10-5) Br2(10-5) a0(MeV) 2/ndf

  • Combined 1.780.40 6.220.43 12915 20.3/25

  • Only ch. 1 1.310.54 6.520.57 13922 15.5/15

  • Only ch. 2 2.450.69 6.000.74 11724 2.7/7

  • Comb., +int. 2.200.44 5.920.47 12316 19.7/25

  • Comb., - int. 1.510.42 6.620.48 13816 22.3/25

  • Br(a0) = (6.220.43(stat+bckg))  10-5

  • Agreementbetween the two samples

  • Very large a0 width, but it is model

  • dependent

  • Interference: not significant with this

  • statistics

  • Br1 close to Br() 1/3 Br(0)


Fit to a 0 only flatte
Fit to a0 only (Flatte’)

  • From Bramon et al.,

  • Br1 = 0.54  10-5

  • Try to fit the spectra to a0 only

  • 2 free parameters:

  • Br(a0) = (7.650.33)  10-5

  • a0 = (192  18) MeV

  • 2/ndf = 37/26


Fit to a 0 only ii
Fit to a0 only (II)

  • Flatte’ formula has no p3

  • dependence, as expected for a

  • V  V S decay

  • Try a simple B.W. with p3 and

  • with a damping factor:

  • Br(a0) = (7.890.34)  10-5

  • a0 = (36.9  5.2) MeV

  • = (890  100) MeV

    2/ndf = 24.3/25


Conclusions
Conclusions

  • The analysis of the two channels is well defined

  • The two samples are in good agreement

  • Systematics evaluation is almost done

  • The combined fit procedure is working:

    • The two channels are consistent

    • Separation of the two contribution a0(980) and

       0 is difficult, because the fit cannot be

      performed in a model independent way


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