Inner HIPT Chambers Occupancies

1
WS New Hadrons Facts and Fancy Milos,
Greece 19-20 September 2005
Search for the T pentaquark using kaon
secondary interactions at Belle
Roman Mizuk (ITEP, Moscow)

• Outline
• Detector, idea
• Search for inclusive production of T(1540)
• Search for exclusive production of T(1540)

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KEKB and the Belle detector
Mt. Tsukuba
KEKB
Belle
1 km in diameter
8 GeV e- x 3.5 GeV e
L peak 1.58 x 1034 sec-1 cm-2
Integrated Luminosity L 467 fb-1
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Idea

• ee- annihilations near ?(4S) provide an abundant
  source of kaons. Small fraction of these kaons
  interacts in the detector material ? use these
  secondary interactions to search for T(1540).
• K interactions are in the low energy domain,
  where most of the T(1540) evidences are
  reported.

Schematic view of event with secondary interaction
Momentum of primary K
N / 50 MeV
20cm
momentum (GeV/c)
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Selection of secondary pK pairs

• protons and charged kaons
• DO NOT originate from ee- interaction point
• positively identified based on dE/dx, TOF and
  Cherenkov information
• KS
• ??- detached vertex
• momentum IS NOT pointing to ee- interaction
  point
• significant impact parameters of daughter tracks
• Common pK vertex
• detached from ee- interaction point 1ltRlt11cm.

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Tomography of the detector

• XY distribution of secondary pKS vertices in
  data.
• Clear picture of detector structures ? selected
  pK vertices are dominated by secondary
  interactions.

SVD1 155fb-1
SVD2 242fb-1
y (cm)
x (cm)
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Search for inclusive production of T(1540)
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Mass spectra for secondary pK pairs
N / 2 MeV/c2
pK-
pKS
m (GeV/c2)
Fit m(pK-) to D-wave BW ? resolution function
threshold function ? N(?(1520))
(4.10.1)104, m 1518.4 0.1 MeV/c2
G 13.5 0.4 MeV
1519.5 1.0 15.6 1.0
consistent with PDG ?
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?(1520) production mechanism
?(1520) momentum
formation ? p?(1520)?400 MeV/c
p
p
?(1520)
N / 0.2 GeV/c2
K-
K-
production
p
formation
p
?(1520)

K-
K-
p?(1520) (GeV/c)
?(1520) momentum spectrum is hard ? inelastic
production dominates.
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?(1520) production mechanism (2)
Distance from pK- vertex - to nearest
track - to nearest K
Additional track is found in 0.5 of
?(1520), additional K - in only 0.5 of
?(1520). Strangeness conservation ? ?(1520)
produced by strange projectile.
1 / 0.5cm
peak at zero ? vx w/ additional track
Contribution of interactions of ?s lt a few
percent (? flux, cross section).
distance, cm
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Mass spectrum for secondary pKS pairs
N(T)
N / 2 MeV/c2
Upper Limit
Yield
m (GeV/c2)
m (GeV/c2)
Fit m(pKS) to resolution function (s2MeV/c2)
3rd order polynomial ? N(T)lt320 at the 90
C.L. for wide range of possible T(1540) masses.
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Upper limit on cross section ratio
epK epKs
NT N?
B(?(1520)? pK-) B(T(1540) ? pK0) B(K0? KS? pp-)
s(KN? T(1540) X) s(KN? ?(1520) X)

lt2.5 at the 90 C.L.
epKs/epK from MC assuming that T and ?(1520)
kinematics is similar.
Comparison with other experiments
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Search for exclusive production of T(1540)
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Method

• Use Kn?T(1540)?pKS
• Observed by DIANA NT / Nch 0.66
  0.19.Phys.Atom.Nucl 66,1715 (2003).
• Clear interpretation of the result NT / Nch
  ?GT. Cahn,Trilling,PRD69,11501 (2004).
• Projectile is not reconstructed ? background from
  KS, KL induced reactions and inelastic reactions.
  
• Use all available information to suppress
  inelastic reactions (main bg).
• Background still high ? determine the
  contribution of Kn?pKS indirectly.
• Conservatively assume that remaining inelastic
  reactions and KS, KL induced reactions do not
  produce T signal.

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Contribution of charge exchange reaction

• Problem M and epKs are complicated functions of
  coordinates (rely on MC?), calculation of P and
  S is model dependent.

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Reconstruction of D-?D0p-?(Kprojectilep-) p-
For elastic secondary interactions projectile
momentum can be determined based on (EpK, ppK)
and ?rrpK-rIP.
p
Sibirtsev et al.,EPJ A23,491(2005)
pF2 2mN
1. EN mN - 2e - , e7MeV
K
2. EK EpK - EN
iterations
detector material
3. pK from EK and ?r
4. pF ppK pK
K
? Iteratively find pK and pF.
ee- interaction point
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Reconstruction of D-?D0p-?(Kprojectilep-) p-
(2)
For every secondary pK pair determine pK,
combine with p- candidates to form D- and D0
candidates.
?mDm(Kprojp-p-)-m(Kprojp-)
m(Kprojp-)
N / 10 MeV/c2
N / 0.5 MeV/c2
mD0 50MeV
?mD 2MeV
D0 sidebands
m(Kproj p-) (GeV/c2)
m(Kproj p-) (GeV/c2)
NelD 47026 (from m(Kprojp-) fit), correct D0
mass, s?16 MeV/c2.
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Reconstruction of D-?D0p-?(Kprojectilep-) p-
(3)
Distance from secondary vertex to nearest track
Fermi momentum
hydrogen
N / 10 MeV/c2
D0 signal window
N / 10 MeV/c
D0 sidebands
m(Kproj p-) (GeV/c2)
pF (MeV/c)

• No additional tracks from secondary vertex for
  D0 signal,as expected for elastic scattering.

• Fit to oscillator model expectation.
• Extracted model parameter similar to other
  measurements.

Abramov et al.,JETP Lett.71,359(2000).
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Contribution of charge exchange reaction (2)
Number of D- ? D0 p- ? (Kprojectilep-) p- can
be expressed as
Kp elastic x-section
K flux
material
reconstruction efficiency
Nel ? FK (pK, ?) sel (mpK) M (R, ?) epK
(mpK, ppK, R, ?) dR d?
D
D
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Determination of Nel
FK sch epKs B FK sel epK
D
Determine D yield in mpK bins ?
D
N / 50 MeV/c2
mpK (GeV/c2)
217 per 50 MeV/c2 bin in T mass
region.
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Determination of FK / FK
FK sch epKs B FK sel epK
D
D
From direct reconstruction of K ?
N / 50 MeV/c2
mpK (GeV/c2)
mpK (GeV/c2)
FK / FK 850 20 in T mass region.
D
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Determination of sch / sel
FK sch epKs B FK sel epK
D
From published data on x-sections ?
sch / sel
sel (mb)
sch (mb)
charge exchange x-section
Kp elastic x-section
ratio
mpK (GeV/c2)
mpK (GeV/c2)
mpK (GeV/c2)
sch / sel 0.35 0.02 in T mass region.
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Determination of epKs / epK
FK sch epKs B FK sel epK
D
From GEANT based MC simulation ?
epKs / epK
efficiency
pK
pKS
mpK (GeV/c2)
mpK (GeV/c2)
epKs / epK (43 5) in T mass region.
? Nch (1.00.4)103 per 50 MeV/c2 bin in T
region
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Mass spectrum for secondary pKS pairs

• Reject pKS vertices with additional tracks
• Require 50ltpFlt300 MeV/c.

factor 4 suppression
DIANA
N / 2 MeV/c2
Fit mpKs to resolution function (s2MeV/c2)
3rd order polynomial
Nch
mpKs (GeV/c2)
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Upper limit on GT
Upper Limit
DIANA
Express NT / Nch via GT
GT
Cahn,Trilling,PRD69,11501 (2004).
mpKs (GeV/c2)

• GT lt 0.64 MeV at the 90 C.L. for m1.539
  GeV/c2.
• GT lt 1.0 MeV for wide range of possible T
  masses.

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Summary

• We searched for T(1540) pentaquark using kaon
  secondary interactions in the Belle detector
  material. No signal was found.
• For inclusive production we set upper limit
• For exclusive production we set upper limits
• GT lt 0.64 MeV at the 90 C.L. for m1.539
  GeV/c2.
• Similar sensitivity to DIANA do not support
  their evidence.
• GT lt 1.0 MeV for wide range of possible T
  masses.

(hep-ex/0507014, submitted to PLB)
s(KN? T(1540) X) s(KN? ?(1520) X)
lt 2.5 at the 90 C.L.
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FAQ Why no S in pKS mass spectrum?
s(K-p)
m(pK-)
the same structures are visible
pK (GeV/c)
m (GeV/c2)
m(pKS)
the only prominent peak is at 1.8GeV
pFlt300MeV/c
Cool et al.,PRD1,1887
m (GeV/c2)
pK (GeV/c)