ISR Physics at Bfactories

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ISR Physics at B-factories

• Vladimir Druzhinin
• BINP, Novosibirsk

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Initial State Radiation (ISR) Method

• High luminosity at B-factories allows to use
  this method for measurements of ee-? f cross
  sections at energies below ?s
• Wide energy interval in single experiment
• Greatly reduced point-to- point uncertainty

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Initial State Radiation Studies at BABAR

• Rely on tagged photon for identification, loose
  hadronic selection
• High fiducial efficiency
• Wide-angle ISR forces hadronic system into the
  detector fiducial region
• Collimated hadronic system due to boost.
• Weak dependence on details of fragmentation
• Harder momentum spectrum due to boost
• fewer problems with soft particles.
• Kinematic fit
• excellent mass resolution
• background suppression
• Most dangerous background, ee-? f?0, can be
  estimated from data and subtracted

• ??????????? ???? ???????? ??????.
• 10 ??????? ????????????? ????????
• ??? ?? ee- ? ?????? ??? ?10 ???, ?0 ?????????
  ?????
• ?????? ??????????? ????????????? ??????????? ??
  ????? ? ???????? ????????
• ????????? ??????? ?? ?????? ?? 3-5 ???
• ??? ??????????? ??????
• ????? ?????? 3 ???
• ??????? ? ?????????? (5-8 ???) ??????? ? 3.5 ???
• ??? ???? ?? ee- ? ??????, ?? ???? ????????????,
  ee- ? ee- ??????
• ???????? ?????? ????????? ??? ??????? ???? 3.5
  ???
• 10 ??? - ???????????? ???????? ??????? ???? ? ???
  ?????? ????????? ???????? ??????

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Initial State Radiation Studies at BABAR

• Objective
• Precise cross section measurements for all
  significant processes,
• e e- ? f , from threshold to c.m. energy
  4.5 GeV
• Purpose
• Significantly improve understanding of the
  spectroscopy of JPC 1--
• states, and of their resonant substructure
• Combine the cross section measurements to
  obtain improved
• precision on the c.m. energy dependence of R
  in this region
• Reactions for which results have been published
  
• e e- ? p p
• e e- ? ? ?- ?0
• e e- ? 2? 2?-, K K- ? ?-, 2K 2K-
• e e- ? 2? 2?- 2?0, K K- 2? 2?-
• Work in progress on
• p p- , K K , K K p0 , K K h , p p- p0 p0 ,
  p p- 3p0 , L L ,
• L S , S S , d d ,..

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s(ee- hadrons)
Burkhardt, Pietrzyk 2001
?s GeV/c2
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Build R from Sum Over Exclusive Final States
Analyses in Progress
Results published by BABAR
pp-p0
KK- K0SK0L
pp-
KK-p/hK0Kp
DD
6p2K4p
y(2S)
KK-pp-KK-KK-
pp-pp- pp-p0p0
R Units
pp
J/y
vs' GeV
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ee- pp
(232 fb-1)
Phys. Rev. D 73, 012005 (2006)
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The cross section depends on two form factors,
electric and magnetic.
Ratio of form factors can be extracted from
analysis of angular dependence
From the total cross section we obtain effective
form factor
Advantage of ISR measurement weak dependence of
detection efficiency on mass and proton polar
angle Model-independent measurement of cross
section.
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Mass spectrum
J/?
232 fb-1
?(2S)
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Angular distributions
GE dominates near m2 GeV/c2 Inconsistent with
PS170 measurements
GM in Blue GE in Red
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Cross section
In reasonable agreement with ee- previous
measurements Negative steps at M 2.2 and 3 GeV
(!?)
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pp effective form factor

• Reasonable agreement with pp-annihilation
  results
• Steep behaviour at threshold can be manifestation
  of subthreshold pp-bound state

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ee- pp-p0
(90 fb-1)
Phys. Rev. D 70, 072004 (2004)
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ee- p p - p 0g
Key process for study excited ?-like state
?
?
PDG 1400-1450 ???/c2 PDG 180-250 ??? PDG 1670
30 ???/c2 PDG 315 35 ???
??
???
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ee- p p -p 0g
NJ/? 920?34
SND
BaBar90 fb-1
DM2
M3pGeV/c2

• systematic error - 5
• ? and ?-meson parameters are in agreement with
  world averages
• Consistent with SND data for Mlt1.4 GeV
• Inconsistent with DM2 results

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ee- 4h pp-pp- KK-pp- updated
KK-p0p0 new (232 fb-1) KK-KK-
(90 fb-1)
Phys. Rev. D 71, 052001 (2005)
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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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ee- KK-pp-, KK-p0p0, KKK-K-
232 fb-1
ee- KK- KK- Systematic error 25
90 fb-1
Systematic error 7-15 Intermediate states
K(890)K? dominant, f??, ?KK Structures in
KK-pp- cross section near 1.8, 2.2, 2.4 GeV.
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ee- 6h 3(pp-) 2(pp-)p0p0KK- 2(pp-)
(232 fb-1)
Phys. Rev. D 73, 052003 (2006)
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6p final states

• pp-pp-pp-
• Large improvements upon existing measurements.
• Structure around 1.9 GeV, already seen by DM2 and
  FOCUS (diffractive photoproduction)
• Little substructure (1r/event)

J/?

• pp-pp-p0p0
• Large improvement in precision
• Similar Structure around 1.9 GeV
• substantial substructure
• wh, w3p, h3p seen
• r, r0, fo(980), . present

J/?
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Fit to ee-?6p cross section data
ee- 3(pp-)
J/?
ee- 2(pp-) p0p0
J/?
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ee- KK-2(pp-)
s(KK-2(pp-)) (nb)

• Clear signals for K0, J/y and y(2S)
• f signal in KK- spectrum
• mainly from J/y decay

J/y
y(2S)
K0
K0
J/y
f Band
J/y
y(2S)
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J/y and y(2S) decays
BES (2.100.12)

• We actually measure
• BF(J/y?f)xGee
• Branching fractions
• are obtained using
• Gee (5.400.18) keV
• PDG

New
New
New
better
New
worse
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DD mass spectrum

• Mass spectrum fitted with interfering
• Presence of structure at 3.9 GeV
• (Not due to a new charmonium state
• but to a threshold effect predicted by
• E. Eichten et al.,Phys.Rev. D21
• (1980) 203.)

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ee-?Y(4260)? ? ? ? -J/? ?
PRL 95, 142001 (2005)

• ISR photon need not be detected
• Confirmation by CLEO-c e e- scan
• Y(4260)
• 125 ? 23 ???????
• Mass - 4258?8 ???
• Width - 88?23 ???
• ?max ? 50 ??

232 fb-1

• Not seen in total hadronic cross section ? small
  electron width, but large ?(? ? -J/? )
• Exotic structure 4q, hybrid, mesonic or baryonic
  molecular
• Search for similar states containing light quarks
  (???).

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ee- ? f0 (980)
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ee- ? f0 (980)
Fitted resonance parameters
M21751015 MeV ?581620 MeV ss partner of
Y(4260)? f0 have large ss content ssss state
Phase space ?2/?81/51
Resonance ?2/?38/47
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• Cross section measurements
• Continuous coverage from threshold to Ecm4.5 GeV
  for many processes.
• Eventually combine exclusive cross section
  measurements to obtain precise s dependence of R
  1 below 1 GeV, 5 for 1-3 GeV
• Spectroscopy of JPC 1-- states
• Parameters of excited ?-, ?-, ?-states
• New, possibly exotic states dip at 1900 MeV
  in ee-?6p cross section, Y(4260), structure in
  ?f0 at 2175 MeV
• Large luminosity is needed both for R measurement
  (1-2 accuracy can be reached for 1-5 GeV range)
  and for spectroscopy.

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ISR luminosity for 50 ab-1
VEPP-2000 2 fb-1
BES-III 20 fb-1
Resonances produced and detected J/? -
0.25x109 ? (2S) 0.14x109 ?(1S) 0.6x109 ?(2S)
0.5x109 ?(3S) 0.8x109