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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
slide16

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

slide17

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)

slide18

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