Transcript +  ee Study of collisions with a hard initial state photon at BaBar E. Solodov (BINP, Novosibirsk) for the BaBar collaboration.

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
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Study of
collisions
with a hard initial state
photon at BaBar
E. Solodov (BINP, Novosibirsk)
for the BaBar collaboration

Initial state radiation (ISR) method
d (s, x)
 W (s, x, )  0 (s (1 x)),
dxd(cos )
2E
a 2  2x  x 2 x 2 
W (s, x, ) 
 , x 

 x  sin 2 
2 
s
•
•
•
•
•
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ISR
High PEP-II luminosity at s = 10.58 GeV precise measurement
of the e+e- cross section 0 at low c.m. energies with BaBar.
Improved hadron spectroscopy
Input to (gm-2) and aem calculations.
Few previous data in the 1.4-3.0 GeV range.
Comprehensive program at BaBar.
Today: preliminary results for +0, 2+2, K+K+, 2K+2K
from 89.3 fb-1
2
Events/0.01 GeV/c2
ee  0

Excited  states ?
Event selection:
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•
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Isolated ISR photon with ECM > 3 GeV
At least 2 good photons with E > 0.1 GeV
Two good, non-K tracks from IP
Kinematic fit:

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J/ •
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Energy and momentum balance enforced
Mass of two soft photons constrained to 0
2 < 40 for fit in  0 hypothesis selects
signal events
•
Reject events with extra photons if 2 < 40 for
  0 0  hypothesis
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Background for 3
Most dangerous backgrounds:
e+ e-  K+ K- 0, e+ e-  qq   00
Other backgrounds:
e+e-  2, 4, 5, …, +-, 0
MC
Two methods of background subtraction:
Data
1.
background mass distribution measured in
data, subtracted bin-by-bin from signal mass
2.
distribution
taken from simulation, corrected to real
experimental distribution
Total background level:
• (0.5 - 1.5)% in ,  regions
• (15 - 50)% at higher masses
• accuracy in background level
~25% up to 2 GeV
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Detection efficiency for 3
The detection efficiency (m):
• determined from a Monte Carlo
simulation that includes additional
corrections extracted from special
control event-samples
•quite uniform in 0.5<m<3 GeV/c2
• systematic error currently ~4% - will
be improved with more data
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
Fit of the 0 mass spectrum
dN 
dL


(m)
  (m) R(m),
 
3
dm th
dm
dN 
dN 
      f (m, m)
dm exp dmth
•
3(m) - Born cross section of e+e-  + - 0
is a coherent sum of 4 resonances: , , ,
•
•
R(m)~1 - radiative correction function from calculation
dL/dm - ISR luminosity taken from total integrated luminosity
and photon radiator function W(s,x); (checked with mm events)
f(m,m) - detector resolution taken from simulation
(with floating extra Gaussian smearing)
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•
•
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Fix ,
 widths to PDG values
Fix - relative phase to experimental value (1637)
Fix - relative phase to 180,  -  to 0
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Fit results:  -  region

2/d.f.=146/148
consistent with known properties
of these resonances

(,  widths fixed to PDG values)
The resolution is about 6, 7, 9
MeV/c2 at , , J/ masses.
Fitted resolution smearing is
~1 MeV/c2
BaBar Preliminary
PDG
B(ee)B(3)=(6.700.06 0.27)10-5 (6.350.11)10-5
B(ee)B(3) =(4.300.08 0.21)10-5 (4.590.14)10-5
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Fit results: higher mass region
•
Good fit obtained for the range up
to 1.8 GeV/c2.
•
Extending the fit to masses above
1.8 GeV/c2 may require a more
complicated fitting function taking
into account non-resonant 3
production.


•
Mass and width parameters are
dependent upon our assumed
phases - interference effect is strong
BaBar Preliminary
B(ee)B(3)=(0.820.050.06)10-6
B(ee)B(3)=(1.30.10.1)10-6
PDG
M()= 13502020 MeV/c2
1400 - 1450
()= 4507070 MeV
180 - 250
M()= 1660102 MeV/c2
1670  30
()= 2303020 MeV
315  35
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e+ e-  +  0 cross section
SND
BaBar Preliminary
DM2
• coverage of wide region in this experiment -
 3  (m) 
dN dm
 (m) R(m) dL dm
no point-to-point normalization problems
• consistent with SND data E C.M. < 1.4 GeV
• inconsistent with DM2 results
• overall normalization error ~5% up to 2.5 GeV
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Events/0.004 GeV/c2
J/  3 decay
• The
J/ meson is narrow - clean
signal
• After sideband subtraction NJ/ = 92034
sideband
=(9.20.6)%
•
Detection efficiency -
•
The result: (J/ ee)B(J/ 3)=
0.1220.0050.08 keV
sideband
•
We previously measured (mm)
(J/ ee)=5.610.20 keV
Phys. Rev. D69,011103 (2004)
B(J/ 3) = (2.180.19)%
(1.500.20)%
(2.100.12)%
BaBar Preliminary
PDG
BES 2003
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e e  22 , KK , 2K2K
Event selection:
•
•
•
•
Isolated ISR photon with ECM > 3 GeV
At least four good tracks from IP
Kinematic fit:
Energy and momentum balance enforced
Energy and angles of hard ISR photon are not
used - 1C fit
•
Fit in 3 hypotheses:
4 for all events
2K2 if 1 or 2 identified kaons
4K if 2, 3 or 4 identified kaons
Background subtraction:
•
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Other ISR processes (5, …) – using
difference in 2 distributions
e+e-  qq – using JETSET simulation
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ee  2 2 cross section
Systematic errors:
BaBar
Preliminary
• 12% for m4 < 1 GeV,
• 5% for 1 < m4 < 3 GeV,
• 16% for higher masses)
• best measurement above 1.4 GeV
Coverage of wide region in one
experiment
No point-to-point normalization
problems
Intermediate states:
• a1(1260) - dominant, structure which
may be f0(1370) final state is seen.
• For detailed study, a simultaneous
analysis of 22 and 20 final
states is required.
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e e  2 2 cross section
Good agreement with direct e e measurements
Most precise result above 1.4 GeV
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 substructures
BaBar preliminary
MC generator:
• H.Czyz and J.H.Kuehn,
Eur.Phys.J C18(2000)497-509
• Includes a1(1260) and f0(1370)
a1(1260)
• Does not include J/
J/
f0(1370)
(770)
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e e  K K  
Systematic error – 15% (model
dependence, kaon identification)
J/
Much more precise than previous
measurement
Substantial resonance sub-structures
observed:
• K*(890)K dominant
• ,KK contribute strongly
• K*2(1430)K seen.
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KK substructures
BaBar preliminary
K*(890)K dominated
No studies in previous
e+e- experiments!
K*K MC generators
are not available yet
K* regions excluded


f0(980) ?
No signal from f0(980) yet
Connection to f0(980)?
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Events from band
e e  2K 2K
BaBar preliminary
J/
First measurement
Overall normalization systematic
error – 25% (model dependence,
kaon identification)
No clear mass structure in the
two- or three-body subsystems
No ’ s !
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J/ and (2S) decays
2+2-
+- J/
K+K-+-
2K+2K-
m+m-
BaBar preliminary
B(J/ =(3.610.26 0.26)10-3
B(J/ K+K- =(6.090.50 0.53)10-3
B(J/ K+K-K+K-) = (6.71.1 1.0)10-4
PDG
(4.01.0) 10-3
(7.22.3) 10-3
(9.23.3) 10-4
B((2S)  J/ +-)=0.3610.015 0.028
0.3170.011
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Summary
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Using ISR method the cross sections of e+e  0, 22, K+K,
2K+2K reactions have been measured from threshold to 4.5 GeV.
•
These are the most precise measurements to date for c.m. energies greater
than 1.4 GeV.
•
Example: contribution to amhad (1010) from 2+ 2 (0.56 – 1.8 GeV)
from all e+ e exp.
14.21  0.87exp  0.23rad
Davier-Eidelmanfrom all  data
from BaBar
12.35  0.96exp  0.40SU(2) Hoecker-Zhang 2003
12.95  0.64exp  0.13rad
696.37.2
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Several B(J/ -> X) measurements better than current world average
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Detailed papers to be submitted to PRD
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More modes to come; aim for systematic errors 1% (in +)
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