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[email protected] Jefferson Lab., November 2003.
K. Kadija
Ruđer Bošković Institute, Zagreb, Croatia
Search for Exotic BaryonSearch for Exotic Baryon Resonances Resonances at NA49at NA49
[email protected] Jefferson Lab., November 2003.1
Motivation NA49 experimentData Sample and MethodApplied Cuts Invariant Mass SpectraSystematic Studies and checksConclusion and Outlook
OutlineOutline
[email protected] Jefferson Lab., November 2003.
dp/p2 = 7 x (0.3) 10-4 (GeV/c)-1 VTPC-1 (VTPC-2+MTPC)
3-6 % dE/dx resolution σTrig= 28.1 mb
NA49 Experiment
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Before vertex cut After Vertex Cut
1999 1.2 M 0.66 M2000 2.7 M 1.5 M2002 2.9 M 1.6 M
Total 6.8 M 3.76 M
Main vertex cuts: 1.) fit converged2.) x2+y2< 1 cm2
3.) -590.5 cm < z < -572.5 cm (i.e. within target)
p+p at =17.2 GeV s
Data Sample
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1640 events
|M(Λπ)−1.32131| < 0.015 GeV
551 events
V0 and Ξ Invariant Mass Spectra
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|dbb| < 1.5 σ, dbb .... distance to Bethe-Bloch curveposition at main vertex (bx , by):
|bx| < 1.0 cm|by| < 0.5 cm
# of point cut > 10
((ΞΞ−− ππ, , ΞΞ++ π)π)
Primary pion cuts
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From the Monte Carlo simulation
θ: lab. angle between Ξ− and π+
θ > 4.5 0BackgroundSignal
Additional cuts:Opening Angle
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Negative tracks
Positive tracks
(Ξ− π − ) events
(Ξ− π + ) events
e-
π−
K
P
Additional cuts:dE/dx+ momentum
[email protected] Jefferson Lab., November 2003.
cos(θ) < 0.997 (θ > 4.5)
Ξ- Ξ+
π- -1.5 σ < dbb < 1.5 σ -1.5 σ < dbb < 1.5 σ
π+ -0.5 σ < dbb < 1. 5 σ -1.5 σ < dbb < 1.5 σptot > 3 GeV/c ptot > 3 GeV/c
Additional cuts
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By changing:- mass cuts around Ξ and Λ- dE/dx cuts - number of point cuts- bx, by cuts- e.t.c.
Peak remains robust !
Systematics study (Ξ- π− )
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events with
1520.0 ±15 1115.7 ±10p
1520.0 ±151019.0 ±10 892.0 ±30 K+
1115.7 ±10 892.0 ±30 497.6 ±10769.0 ±60
π+
pK-π−
Systematics study:Resonances
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Ξ− π from the Venus MC
π : all negative particles
π : π−
Systematics study and checks
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M = 1.862 ± 0.002 GeV/c2
M = 1.864± 0.005 GeV/c2
M = 1.862 ± 0.002 GeV/c2
Γ ≤ 18 MeV/c2
Mass and width determination
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Mwindow= M0window ± ∆M
(1.850 ≤ M0window ≤ 1.8725 ) [GeV/c2]
B0= 43
S0 ≥ 41S0 ≥ 38
S0 ≥ 35
Ξ-- Significance
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A strong evidence for existence of a narrow Ξ− π− resonance at M = 1.862 ± 0.002 GeV/c2 ( Γ≤ 18 MeV/c2) is observed
At the same mass a peak is observed in the Ξ−π+ spectrumThe corresponding antibaryon spectra show enhancement atthe same mass
Σ
N
Ξ(1862)
Conclusions and outlook
