Data analysis of April'2002 SVD-2 run. Pentaquark searches

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• Data analysis of April'2002 SVD-2 run.
  Pentaquark searches
• Detection capabilities
• Charmed mesons
• Pentaquark searches
• A.Kubarovsky, V.Popov, V.Volkov
• SINP MSU Moscow

Talk at VHMP 2004, Dubna, Russia 16-17 April 2005
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• 53,000,000 events collected
• 7 are beam only/non-useable
• Basic way of pre-analysis
• Finding a primary vertex
• Search for a secondary one(s) within different
  regions and with different detectors/methods to
  use/CPU time to be consumed ?
• Average CPU time per event up to 7 PIII-1000
  seconds
• Facilities SINP and SRCC MSU old clusters.

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K-
?
??
Region II (5-60 cm)
?
??
P-beam
K-
?
??
??
p
??

Region I(1-35 mm)
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Primary vertex Z-coordinate in SVD-2 active target
Si 300?m Pb 220 ?m ? 500 ?m
SVD-2 data analysis
Pb
C
Si
Si
Si
Si
Si
sz 70130µm, sx,y 710µm
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K0s and ?0 effective masses

• K0s M 497.61 0.09 (stat.), s4.4 MeV/c2
• ?0 M 1115.32 0.05 (stat.), s1.6 MeV/c2

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• Reconstruction of V0s with the spectrometer
  (distant ones)
• K0 s5.8 MeV/c2
• ?0 s3.0 MeV/c2

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• The well-known resonances of the same topology as
  ?
• Arrows correspond exactly to the PDG data

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(No Transcript)
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Near-threshold D0 production

• Search for the D0? Kp- decays
• Different reconstruction methods used (not
  cross-checked yet)
• 24 events over background of 12

V.Volkov
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A start of pentaquark history

• An idea of five-quark states was discussed since
  late 60s (Jaffe, Lipkin, Strotteman, )
• First estimates in the Skyrme model (Chemtob,
  Praszalowicz, Walliser) 1985...
• There were no conclusive results from
  experimental searches
• The general prejudice against baryons not
  made of three quarks and the lack of any
  experimental activity in this area make it likely
  that it will be another 15 years before the issue
  is decided. (PDG, 1986)

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PDG in Particle listings under revision
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In the 2003 fall...

• uudds quark content
• Predicted by Diakonov,Petrov and Polyakov Z.Phys
  A 359, 305(1997)
• Supposed to be of 1530 MeV/c2 mass, width lt15
  MeV/c2 and to decay into nK or pK0
• Observed by several experiments
  (LEPS,DIANA,CLAS,) in both decay modes
• The pK0 mode can be searched for by SVD-2good
  resolution for K0s and proton identification

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Experiments zoo
Spring8
DIANA
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PENTA-I Data sample

• 35,000 events sample for D-meson searches was
  used
• Primary selection mainly based on the presence of
  well-defined secondary vertices in the
  close-to-target region
• Secondary tracks are measured by vertex detector
• Allowed decay length is 135 mm (av. 20 mm),
  means that only 10 of K0s to be reconstructed

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Penta-IEvents selection

• 5 charged tracks from primary vertex to reduce
  combinatorial background
• K0s selection
• 2 oppositely charged tracks from secondary vertex
• 490 Mpp 505 MeV/c2
• Mpp 1120 MeV/c2 (? not ?0)
• Proton selection
• Positive track from primary vertex
• Momentum of 421 GeV/c
• Absence of a Cerenkov detector hit

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Penta I pK0s spectrum analysis

• Cut applied pK0s system goes forward in
  center-of-mass system
• Narrow peak at 1526 MeV/c2 is observed
• FRITIOF simulated background fails to reproduce
  the real shape
• Peaks in higher mass region can be attribu-ted to
  S bumps

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Penta I Cut applied PpgtPK0 to eliminate bumps
(cf. B.Levchenko, arXivhep-ph/0401122)

• Background can be described in different ways
• FRITIOF simulations
• Plain polynom fitting
• Random-star (not shown)
• All three give the shape compatible to the
  experimental one

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Penta I Pentaquark parameters at SVD-2

• Number of events within a peak 50 over
  background of 78, gives a significance of 5.6 s
• Mass 1526 3(stat.) 3(syst.) MeV/c2
• Width G lt 24 MeV/c2 (below experimental
  resolution)
• Strangeness could not be defined directly, but
  there are no reported S -1 states in this mass
  region

We interpret this state as T pentaquark
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Penta I Cross section and A-dependence

• We estimate the total cross-section of pA?T X
  as30120 µb/nucleon
• We fail to find the difference in A-dependence
  of T events from that of total for inelastic
  events (A0.7)

The ratio of T peak events to the total of K0
events for different target materials
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Theta masses from different experiments
1520
1540
1560
Spring-8
Kn
CLAS-d

• Certain mass shift can be observed between the
  Kn and K0p modes

CLAS-p
SAPHIR
ITEP
HERMES
K0p
COSY
ZEUS
SVD-2
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Penta I second analysis

• To be checked
• Possibly could result in a much more narrow peak

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Penta II event selection

• Distant K0 used
• Cuts applied
• Number of primary charged tracks 4 to 6
• Proton candidate momentum 9 Pp 15 GeV/c
• No Cerenkov detector hit for a proton
• A total of 9,000 events selected

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Penta II results

• Peak is well pronounced (6 s)
• No significant change in the effective mass
• Cross-section and systematic errors are yet to be
  evaluated

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Hadron nicknames
K-
s
u
Meson quark-antiquark
-1/3
-2/3
p
u
2/3
Baryon three quarks
d
u
-1/3
2/3
Pentaquark 4 quarks 1 antiquark Exotic if
antiquark is of the different flavour
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Anti-decuplet of q4q-bar states

• DPP model modified
• (DP hep-ph/0310212)

(1530) G lt 15 MeV
M1760-1810
M1650-1690
M1862 G 5 GQ
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H1 charmed pentaquark?

• M 3099 3 5 MeV
• Minimal quark content uuddc
• To be confirmed!

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Exclusive reaction searches
LEPS ?n ? KK-n
CLAS ?d ? KK-pn
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Pentaquark observations
A table from E.Klempt, hep-ph/0404270
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Current status

• New analysis software is able to process
  distant V0s
• K0 - 10 times more statistics (for T analysis
  and charm searches)
• ? up to 100 times more statistics, allowing ?
  - decays reconstruction to search for ? 3/2
  pentaquark claimed by NA49
• Better kinematical fitting for secondaries to
  improve effective mass resolution

The end
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Theta mass with another set of cuts applied

• Peak width

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18 MeV/c2
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Pentaquark II (distant K0)

• M1524 2.3 MeV/c2
• s 12.0 2.3 MeV/c2
• Nevents 187
• Significance 5.9 s
• No significant mass difference from the previous
  analysis