K. Kadija

1
Observation of X pentaquark states at NA49

• K. Kadija
• for the NA49 Collaboration

2
Outline

• Pentaquark models
• NA49 experiment
• Analysis
• X -p -() and X p(-) invariant mass spectra
• Preliminary X(1530)0 p spectra
• Conclusion

1
3
Models Chiral Soliton
Suggested anti-decuplet of baryons JP1/2
D. Diakonov, V. Petrov, M. Polyakov, Z.Phys. A
359 (1997) 305
(ududs)
!
Q(1530)
(G 15 MeV)
Input
N(1710)
D m 180 MeV

10
S(1890)
(G X3/2? Xp 42 MeV)

X3/2(2070)

(dsdsu)
(ususd)

X3/2
- -
X3/2
4
Models Correlated quarks
Suggested 10f 8f of baryons JP1/2

R. Jaffe and F. Wilczek, arXivhep-ph/0307341
Input
MQ 1540 MeV /c2
Q (ud)2S gt
3
Input (the Roper)

MN 1440 MeV /c2
N (ud)2dgt
MN 1700 MeV /c2
NS (ud)(su)sgt
S

MS 1600 MeV /c2
S (ud)(su)dgt
3
MS 1850 MeV /c2
S S (su)2sgt
S
1- 1/2- 1/2 , 3/2
O
3
3
3
8f 10f
O
O
MX 1750 MeV /c2

X3/2 (us)2dgt
X03/2 X01/2
X-3/2 X-1/2
GX 1.5 GQ
- -

X3/2 (ds)2ugt
Note that the X3/2 and X1/2 have the same mass
5
Models

Chiral soliton model
Correlated quarks
PARITY
Uncorrelated quarks
-
Lattice QCD
X3/2
S
Ss
X3/2 X1/2
10
Chiral soliton model Heavy exotic cascades
Mass (arbitrary units)
Ns
N
??
SPECTRUM
L S
Q
Q
Quarks Light exotic cascades
10 8
N
quarks
soliton
More pentaquarks and their properties needed to
determine correct model
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NA49 Experiment
Only charged tracks detected
VTPC-1 (VTPC-2MTPC)
dp/p2 7 x (0.3) 10-4 (GeV/c)-1
3-6 dE/dx resolution
sTrig 28.1 mb
7
Data Sample
pp at 17.2 GeV
Before vertex cut After Vertex Cut
1999 1.2 M 0.66
M 2000 2.7 M 1.5
M 2002 2.9 M 1.6
M Total 6.8 M 3.76 M
Main vertex cuts
1.) fit converged 2.) x2y2lt 1
cm2 3.) -590.5 cm lt z lt -572.5 cm
i.e. within target
8
V0 and X Invariant Mass Spectra

X- peak
1640 events

L peak
M(Lp)-1.32131 lt 0.015 GeV
X peak
L peak
551 events
9
Primary pion selection
(?- ?, ? p)
p

• dbb lt 1.5 s, dbb .... distance to Bethe-Bloch
  curve
• position at main vertex (bx , by)
• bx lt 1.0 cm
• by lt 0.5 cm
• of point cut gt 10

10
X- p Invariant Mass Distribution
Structure at 1.86
Very small systematic error
X(1530)0
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X p Invariant Mass Distribution
No clear structures at 1.86 GeV/c2
X(1530)0
12
Primary p cuts opening angle
From the Monte Carlo simulation
X-
q gt 4.5 0
Signal
q
Background
p
q lab. angle between X- and p
13
Primary p cuts dE/dx and momentum
Negative tracks
e-
(X- p- ) events
p-
K
P
Positive tracks
(X- p ) events
large proton and K contamination
Purify with momentum and asymmetric dE/dx cut
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Summary of additional primary p cuts
cos(q) lt 0.997 (q gt 4.5)

X-
X p- -1.5 s lt dbb lt 1.5 s
-1.5 s lt dbb lt 1.5 s p
-0.5 s lt dbb lt 1. 5 s -1.5 s lt dbb lt
1.5 s pp gt 3 GeV/c
pp gt 3 GeV/c
p
p
p
p
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Final Xp Invariant Mass Distributions
C. Alt et al., hep-ex/0310014
X 3/2
Accepted by PRL
0
0
X 3/2 or X 1/2
0
0
X 3/2 or X 1/2
X 3/2
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Summed spectra
17
X5 search
X- selection
could also be the X 1/2

• Distance to Bethe- Bloch curve dbb lt 3 s
• M(pp-) - 1.115683 lt 0.015 MeV
• Z X- Zmain_vtx gt 12 cm
• X - position at main vertex (bx , by)
• bx lt 2 cm
• by lt 1 cm
• p (from X - decay) position at main vertex
• by gt 0.5 cm

L
18
Mass and width determination
M 1.862 0.002 GeV/c2
M 1.864 0.005 GeV/c2
M 1.862 0.002 GeV/c2
G 18 MeV/c2
19
Search for X- and X via X(1530)0 decay
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What do we expect in X(1530)0p ?
Q

X3/2
X3/2
- -
X3/2 X1/2
?
?
X(1530)0 p
X(1530)0 p-
X(1530)0 p-
R. Jaffe and F. Wilczek, hep/ph/0312369
21
X(1530)0 p- PRELIMINARY
X(1530)0
Entries / 7.5 MeV/c2
M1.855 0.003 GeV/c2
octet member
R. Jaffe and F. Wilczek
X-1/2
22
X(1530)0 p PRELIMINARY
No evidence for X3/2 to X(1530)0 p decay
X(1530)0 p
No cuts
X(1530)0 p-
No evidence for X3/2 to X(1530)0 p decay
X(1530)0 p
pp gt 3 GeV/c

- 0.5 s lt dbb lt 1.5 s
p
X(1530)0 p-
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Conclusion I

• Strong evidence for the existence of a narrow
  ?- ?- resonance
• at M 1.862 0.002 GeV/c2 ( ? 18
  MeV/c2) is observed
• At the same mass a peak is observed in the
  ?-? spectrum
• The corresponding antibaryon spectra show
  enhancement at
• the same mass

0
0
X3/2
- -
X3/2 X1/2
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Conclusion II

• There is preliminary evidence for existence of
  a narrow ?(1530)0 p- resonance at M 1.855
  0.003 GeV/c2
• There is no indication for a X(1530)0p
  resonance

0
0
-
X3/2
- -
X3/2 X1/2
X1/2
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Preliminary Conclusion

• Existence of the ?-1/2 octet member supports
  the diquark model, and seems to
  contradict the standard soliton model
• There is a possibility to add an octet to the
  anti-decouplet in the soliton model, but there
  seems to be no reason to expect, as is observed,
  similar masses for the X3/2 and X1/2 states
• In the diquark model, the X3/2 and X1/2
  naturally lie at the same mass

correlated quark
Soliton/Skyrme
?
?
26
Outlook
Open Questions

• Spin is unknown
• Parity is unknown
• Width ?
• Production mechanism?

NA49

• Further improvement of experimental resolution
• Data sample increase by up to 30
• Search for Ss0(-)? X- K (X- K0S)

NA49 Project
(Expression of Interest CERN-SPSC-2003-038)
In particular

• (3-6) 107 pp events (new DAQ system)
• Neutral pions

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The NA49 Collaboration

1