Light Quark Vectors and Photoproduction

1
Light Quark Vectorsand Photoproduction

• Ryan Mitchell
• October 17, 2002
• Frascati, Italy

2
Outline

• I. Photoproduction and Spectroscopy
• II. A Short History of the Photoproduction of
  Higher Mass Vectors
• A. ?(1600)
• B. ??0(1250)
• C. ?(1650)
• D. ?(1680)
• III. Fermilabs FOCUS Experiment
• IV. FOCUS KK- Results
• V. The Future

3
I. Photoproduction and Spectroscopy
4
Light Meson Spectroscopy

• One of the oldest fields in High Energy Physics
• Why is it still important?

5
Light Meson Spectroscopy

• The QCD Lagrangian looks elegant
• but how does one solve it?
• What are the physical states?
• What types of states are possible?
• Meson spectroscopy is essential for understanding
  the strong force.

6
Methods of Meson Spectroscopy

• Hadroproduction with pion or kaon beams.
• Proton antiproton annihilation.
• Central production.
• ee- annihilation.
• ?? collisions.
• Radiative J/? decays.
• Photoproduction

7
Diffractive Photoproduction
Vector Meson Dominance
1-- Photon
0 Exchange (?)
Nucleon

• Unique production mechanism.
• Vector excitations? Hybrids?
• A dearth of data.

8
Photoproduction Theory

• Vector Meson Dominance.
• Diffraction. Pomeron exchange.
• S-channel Helicity Conservation.
• Relation to ee- annihilation.
• Plus all sorts of historical folklore.

9
II. A Short History of the Photoproduction of
the Higher Mass Vectors
10
Photoproduction of Light Mesons

• 1970s Diffractive photoproduction of ?, ?, and
  ? vector mesons was mostly as expected.
• Late 1970s to Mid 1980s Results are more
  unclear for the photoproduction of the vector
  excitations.
• ?(1600)
• ??0(1250)
• ?(1650)
• ?(1680)
• Very little has been done since.

11
State of Photoproduction in 1979
(See the comprehensive review article Bauer et
al., Rev. Mod. Phys. 50261 (1978).)
?(1200)
?(1600)
??-??-
??-
(Alexander et al, 1975)
??0
(MIT-DESY, 1971)
(LBL-SLAC, 1974)
12
Photoproduction since 1979

• The ?-Photon Collaboration at CERN.
• LAMP2 at Daresbury.
• SLAC Hybrid.
• E401 at Fermilab.
• (E687 and E831 at Fermilab.)

13
A. The Story of the ?(1600)
- Now considered two resonances ?(1450) and
?(1700).

• Photoproduced in ??-, ??-??-,
• and ??-?0?0.

• Early agreement with ee- annihilation led to a
  relatively
• stable history (the best-established of the
• photoproduced resonances).

14
1980 LAMP2 ??-??- Analysis
An attempt to fit with two resonances with masses
1200 and 1600 MeV/c2...
15
Later Observations of the ?(1600)
All subsequent fits use one very wide resonance
at 1600 MeV/c2
??-??-
Omega 1981
??-
??-?0?0
Omega 1980
Omega 1985
16
The ?(1600) Becomes the ?(1450) and the ?(1700).

• 1986 Erkal and Olsson argue two resonances are
  required for consistency of the 2? and 4?
  electromagnetic form factors. (Z. Phys.
  C31615(1986))
• 1987 Donnachie and Clegg fit the 2? and 4? ee-
  and photoproduction data with two resonances.
  (Z. Phys. C33407(1987)) They extend the fits in
  1988, 1990, 1994.
• 1988 New ee- results in ??? are fit with two
  resonances.
• The resonances are later established in other
  production mechanisms, especially ppbar from the
  Crystal Barrel in 1997.
• (But the last photoproduction results are from
  1985.)

17
Status of the Photoproduction of the ?(1600)

• The best established resonance in
  photoproduction is no longer a resonance.
• An important state, historically, as it provided
  easy comparison with ee- results.
• The last published photoproduction results were
  from 1985.

18
B. The Story of the ??0(1250)
19
It is 1--

• It was first thought to be a ?(1200). (Bauer et
  al 1978)
• 1980 LAMP2 analysis (assuming SCHC) favors 1-.
• Later in 1980, the ?-photon group confirms this
  analysis without their ? problem.

20
It is 1-

• In 1984, the ?-photon group has more statistics
  and analyzes ??0 without assuming SCHC. They
  find 1 dominant.
• In 1988, the SLAC Hybrid group confirms this
  result.

21
Status of the Photoproduction of the ??0(1250)

• It appears as if this is the b1(1235).
• The mass and width agree with the b1(1235) as it
  is produced in other production mechanisms.
• The most recent angular analyses favor 1.
• No corresponding resonance has been seen in ee-
  annihilation.
• However, there are still doubts. How is a 1-
  state diffractively photoproduced? Donnachie
  (hep-ph/0110191) this is inconsistent with
  all we know about diffraction

22
C. The Story of the ?(1650)
23
The Photoproduced Signal

• The only published observation in photoproduction
  is from the ?-photon group in 1983.

M 1670 ? 20 MeV/c2 ? 160 ? 20 MeV/c2

• Large cross section favors an ? interpretation.
• A 1984 re-analysis favors a ? interpretation
  based on comparisons to ee- ? ??-?0.

24
Search in ???

• In 1984, the ?-Photon group performed a search in
  ???, but found nothing.

? expectation divided by 3.
? expectation

• Superimposed are expectations using the results
  from ee- ? ??? and using the relation between
  ee- and photoproduction.

25
1992 ee- Results from DM2

• Branching fractions to the two modes are
  approximately equal.
• A simultaneous fit gives
• M 1662 ? 13 MeV/c2
• ? 280 ? 24 MeV/c2

??-?0
???
26
Status of the Photoproduction of the ?(1650)

• ee- annihilation
• ee- ? ?(1650) ? ???- data is strong.
• ee- ? ?(1650) ? ??-?0 data is less strong.
• Branching fractions to the two modes are nearly
  equal.
• Photoproduction
• Strong observation in ??-?0.
• Never observed in ???-.
• Mass and width comparisons are unhelpful.
• Comparisons to ?(1600) favor ? interpretation.
• Comparisons to ee- ? ??-?0 favor ?
  interpretation.

27
D. The Story of the ?(1680)
28
First Observation in the Photoproduction of KK-

• A simple Breit-Wigner fit results in a mass of
  1748 MeV/c2.
• ee- has reported a ? at 1680 in KsK?.
• A complicated fit, guided by the ee- ? KsK?
  results and using interference and Deck-type
  effects pulls the mass down to 1690 MeV/c2.

KK-
OMEGA 1981 1690 ? 10 MeV (1748 ? 11 MeV)
29
Search in KsK?

• 1984 ?-Photon.
• Calculate the expected cross section in
  photoproduction from the ee- ? ? cross section.
• Why doesnt the ?(1680) appear in photoproduction?

Total KsK?
KK
K0Ks
30
Further Observations in KK-

• The earlier 1981 fit is no longer credible with
  these statistics. The mass of the KK-
  enhancement is around 1750 MeV/c2.

E401 1989 1726 ? 22 MeV
OMEGA 1985 1760 ? 20 MeV
31
ee- Results

• ee- data is strong in KsK?, less strong in KK-.

DM2 1988 KK-
DM2 1991 KsK?
32
Status of the Photoproduction of the ?(1680)

• ee- annihilation
• ee- ? ?(1680) ? KSK? data is strong.
• ee- ? ?(1680) ? KK- data is less strong.
• Dominant decay mode is KSK?.
• Photoproduction
• The ?(1680) has never been observed in KSK?.
• The enhancement in KK- at 1750 MeV/c2 is not the
  ?(1680) at all, and is still to be interpreted.

33
Summary of Historical Photoproduction

• ?(1600)
• The best established of the photoproduced
  resonances is no longer a resonance at all.
• ??0(1250)
• Are we photoproducing a 1- b1(1235)?
• ?(1650)
• Are photoproduction and ee- consistent here?
• ?(1680)
• The photoproduced enhancement in KK- appears to
  be something completely different from the
  ?(1680) seen in ee-.

34
Light Vector Meson Excitations According to PDG
2002
Orbital excitations (13D1)
Radial excitations (23S1)
?(1700)
?(1450)
?(1420)
?(1650)
?(1680)
35
III. Fermilabs FOCUS/E831 Experiment
36
Fermilabs E831/FOCUS Experiment

• Charm photoproduction experiment with over one
  million reconstructed Ds.
• A continuation of the E687 experiment.
• In addition to charm, there is an enormous
  diffractive non-charm sample.

More than 2 million diffractive KK- pairs.
37
The FOCUS Photon Beam
38
(No Transcript)
39
E687 and E831/FOCUS Work in Light Quark
Spectroscopy

• A narrow dip in 6? around 1900 MeV/c2. (Phys.
  Lett. B 514240-246, 2001)
• Partial Wave Analysis of f1?. (Preliminary)
• An enhancement in KK- at 1750 MeV/c2.
• (Phys. Lett. B 54550-56, 2002)

40
IV. FOCUS KK- Results
41
Is the Photoproduced X(1750) the ?(1680)?

• Is the mass consistent?
• -- ee- measures 1680 20 MeV/c2
• -- photoproduction finds 1750 MeV/c2
• Is the KK-/KK branching fraction consistent?
• -- ee- measures 0.07 0.01
• -- photoproduction has never seen a
  corresponding enhancement in KK

42
FOCUS Data Selection

• Look at KK- and KSK? samples.
• Vertex in target
• No extra reconstructed photons
• No extra reconstructed tracks
• All particles are identified by Cerenkov
  information
• Beam energy between 20 and 160 GeV

43
Initial KK- Sample
Large ?(1020) signal, as expected.
44
? Production Characteristics
Diffraction
t t - tmin ? pT2 t ? (P? - PKK)2
45
The X(1750) SignalKK- at High and Low PT
Low PT
High PT (scaled)
46
Fitting the X(1750)
Using a non-relativistic Breit-Wigner and a
quadratic background Yield 11,700 ? 480 Mass
1753.5 ? 1.5 ? 2.3 MeV Width 122.2 ? 6.2 ?
8.0 MeV
47
Is the Photoproduced X(1750) the ?(1680)?

• MASS
• -- ee- measures 1680 20 MeV/c2
• -- FOCUS finds 1753.5 1.5 2.3 MeV/c2
• KK-/KK BRANCHING FRACTION
• -- ee- measures KK dominant

48
The KSK? Sample
Classic D and E regions
PT cut
Two K combinations
49
Fitting KK
With K to KS?, at 90 C.L. BF(KK/KK-) lt 0.183
With K to K?, at 90 C.L. BF(KK/KK-) lt 0.065
50
Is the Photoproduced X(1750) the ?(1680)?

• MASS
• -- ee- measures 1680 20 MeV/c2
• -- FOCUS finds 1753.5 1.5 2.3 MeV/c2
• KK-/KK BRANCHING FRACTION
• -- ee- measures KK dominant
• -- FOCUS finds KK- dominant

51
What is the X(1750)?

• By CP, it must be 0, 1--, 2, etc.
• Look at KSKS
• Angular analysis

52
Conclusions
Phys. Lett. B 54550-56, 2002.
Preprint hep-ex/0208027

• The X(1750) is not the ?(1680)
• The interpretation remains uncertain
• Watch for many more interesting results from
  photoproduction

53
V. The Future
54
Future of Photoproduction

• What is the vector spectrum?
• Is photoproduction really producing vectors or
  are there too many inconsistencies with ee-
  annihilation?
• An enormous E831 data set lies relatively
  untouched.
• The Hall D project at Jefferson Lab?
• The field is wide open.

55
(No Transcript)
56
Production of the X(1750)
Fit with two exponentials
57
The X(1750) Signal
58
Interference Scenarios?
The mass never drops below 1747 MeV/c2