ISR physics at BaBar

1
ISR physics at BaBar

• Vladimir Druzhinin
• (BINP, Novosibirsk)
• for BaBar Collaboration

2
ISR method

• High PEP-II luminosity ? precise measurement of
  the ee- cross section ?0 at low c.m. energies
  with BaBar.
• Few previous data in the 1.4-3.0 GeV range.
• Improved hadron spectroscopy.
• Input to (gm-2) and aem calculations.

3
ISR program at BABAR

• pp-
  pion form factor
• pp- pp-
• pp- ?0 ?0 r resonance recurrences
• pp- h
• pp- ?0 w resonance recurrences
• 5?
• 6?
  structure near 2 GeV
• KK-pp, KK-KK-
• KK-pp pp
• KK- , KSKL kaon
  form factor
• KK- h, f h f resonance recurrences
• KK?
• pp baryon form factors
• ??

4
Selection of e?e? ? h ? candidates

• All final particles are detected
• Charged particle identification with the use of
  Cherenkov angle and dE/dx measurement
• Kinematic fit with requirement of energy and
  momentum balance and mass constraint for ?0
  candidates.

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Background subtraction
signal region

• Main sources of background
• ISR events with misidentified particles
• KK-?0? for ??-?0?
• KK-?, ??-? for pp?
• events with ?0 instead of ISR photon
• ??-?0?0 for ??-?0?
• pp?0 for pp?
• other ISR and ee-?qq events
• ??-?, ??-?0?0? for ??-?0?
• pp?0? for pp?

??-?0? KK-?0?, ??-?0?0 ??-?, ??-?0?0?,
sideband
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??-?0 mass spectrum
PRD 70, 072004 (2004)
?
90 fb-1
f
B(V?ee)B(V?3?) PDG ?
(6.70?0.06 ?0.27)?10-5 (6.35?0.11)?10-5 f
(4.30?0.08 ?0.21)?10-5 (4.59?0.14)?10-5 ??
(0.82?0.05?0.06)?10-6 ??? (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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ee- ? ??-?0 cross section
PRD 70, 072004 (2004)

• coverage of wide region in this experiment - no
  point-to-point normalization
• problems
• consistent with SND data E C.M. lt 1.4 GeV
• inconsistent with DM2 results
• overall normalization error 5 up to 2.5 GeV

8
e? e? ? 2??2?? cross section
PRD 71, 052001 (2005)

90 fb-1

• Systematic errors
• 12 for m4? lt 1 GeV,
• 5 for 1 lt m4? lt 3 GeV,
• 16 for higher masses

Good agreement with direct e? e?
measurements Most precise result above 1.4 GeV

• a1(1260)? - dominant, f0(1370)? final state is
  seen.

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e? e? ? K? K? ?? ??, 2K? 2K? cross sections
PRD 70, 072004 (2004)
J/?
J/?
First measurement Systematic error 25 No
clear mass structures in the two- or three-kaon
subsystems No ? s !

• Systematic error 15
• Substantial resonance sub-structures observed
• K(890)K? dominant
• f??, ?KK contribute strongly
• K2(1430)K? seen.

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The cross section depends on two form factors,
electric and magnetic.
From the total cross section we obtain effective
form factor
Ratio of form factors can be extracted from
analysis of angular dependence
Advantage of ISR measurement low mass and
angular dependence of detection efficiency.
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J/?
232 fb-1
?(2S)
??-? KK-? pp?0 pp?0? uds pp? data
5.9 2.5 2.5 1.0 229 32 13 3 26 4 3737 75 4025
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Angular distribution
1
4
Mpp, GeV/c2 N Nbkg GE/GM
1.877-1.950 533 27
1.950-2.025 584 3712
2.025-2.100 602 5015
2.100-2.200 705 4214
2.200-2.400 592 6116
2.400-3.000 464 4512
2
5
preliminary
6
3
Dominant contribution of electric form factor
near threshold
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BaBar GE/GM measurements vs previous ones
and dispersion relation prediction (yellow) based
on JLab space-like GE/GM and analyticity
DM2FENICE

• BaBar preliminary
• LEAR
• hep-ph/0507085

E835
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Cross section
preliminary
preliminary
In reasonable agreement with ee- previous
measurements Negative steps at M 2.2 and 3 GeV
(!?)
15
Effective proton form factor
preliminary
preliminary

• Steep behaviour at threshold confirmed
• Similar behaviour at threshold is seen in other
  processes with different quantum numbers

preliminary
16
e?e? ? 3(????), K?K?2(????), 2(?????0) cross
sections
preliminary
preliminary
preliminary

• e?e? ? 3(????)
• Systematic error 6-8
• ?4? intermediate state

e?e? ? 2(?????0), Systematic error
11, Substantial substructure ?4?,?3?,??,?3?
e?e? ? K?K?2(????) First measurement Systematic
error 15 Complex substructure weak ?, strong
K?(890)
232 fb-1
17

Fit of 6? cross sections
preliminary
3(????) 2(?????0)
FOCUS M, GeV 1.88?0.03 1.86?0.02 1.91?0.01
?, GeV 0.13?0.03 0.16?0.02 0.037?0.013 ?,
deg. 20?40 -3?15 10?30
preliminary
Dip near 1.9 GeV is confirmed but wider than in
DM2 (ee-) and FOCUS (diffractive
photoproduction) experiments.
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J/? and ?(2S) decays

PDG B(J/? ???-?0)
(2.18?0.19)?10-2 (1.5?0.2) ?10-2
BES 2.10?0.12 B(J/? ?2?2?-)
(3.61?0.37)?10-3 (4.0?1.0) ?10-3 B(J/? ?
3?3?-) (4.40?0.41)?10-3 (4?2)
?10-3 B(J/? ?2?2?-2?0) (1.65?0.21)?10-2
B(J/? ?KK-??-)
(6.09?0.73)?10-3 (7.2?2.3) ?10-3 B(J/?
?2K2K-) (6.7?1.5)?10-4
(9.2?3.3) ?10-4 B(J/? ?KK-2?2?-)
(5.09?0.55)?10-3 (3.1?1.3) ?10-3 B(J/?
?pp) (2.22?0.16)?10-3
(2.17?0.08) ?10-3 B(?(2S) ?2?2?-2?0)
(5.3?1.7)?10-3 B(?(2S)
?KK-2?2?-) (2.1?1.0)?10-4
B(?(2S) ?pp) (3.3?0.9)?10-4
(2.36?0.24) ?10-4
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Summary

• Using ISR method the several eeannihilation
  cross sections 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.
• The proton form factor has complex mass
  dependence.
• Near-threshold enhancement.
• Two mass regions, near 2.25 and 3 GeV, with the
  rapid decrease of the form factor.
• Noticeable deviation of GE/GM ratio from unity.
• The existence of the dip in ee? ? 6? cross
  section near 1.9 GeV is confirmed.
• Several B(J/?, ?(2S) -gt X) measurements are
  better than current world averages.