search for exotic baryon resonances at na49 - jefferson lab

[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

The NA49 CollaborationThe NA49 Collaboration

[email protected] Jefferson Lab., November 2003.1

Motivation NA49 experimentData Sample and MethodApplied Cuts Invariant Mass SpectraSystematic Studies and checksConclusion and Outlook

OutlineOutline


Motivation I


Ξ

Σ

N

Motivation II


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


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


Λ

Ξ3/2 decay topology


1640 events

|M(Λπ)−1.32131| < 0.015 GeV

551 events

V0 and Ξ Invariant Mass Spectra


|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


Ξ- π Invariant Mass Distribution


Ξ+ π Invariant Mass Distribution


From the Monte Carlo simulation

θ: lab. angle between Ξ− and π+

θ > 4.5 0BackgroundSignal

Additional cuts:Opening Angle


Negative tracks

Positive tracks

(Ξ− π − ) events

(Ξ− π + ) events

e-

π−

K

P

Additional cuts:dE/dx+ momentum


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


Ξ π Invariant Mass Distributions


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− )


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


Ξ− π from the Venus MC

π : all negative particles

π : π−

Systematics study and checks


Ξ- π− invariant mass from shoulders


Summed spectra


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


Mwindow= M0window ± ∆M

(1.850 ≤ M0window ≤ 1.8725 ) [GeV/c2]

B0= 43

S0 ≥ 41S0 ≥ 38

S0 ≥ 35

Ξ-- Significance


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


Preliminary

Ξ(1530)0 π- :VERY PRELIMINARY

search for exotic baryon resonances at na49 - jefferson lab

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