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First data of the L (1405) in the charged ( Sp ) 0 decay channels for p+p reactions. Johannes Siebenson Technische Universität München and Excellence Cluster Universe. Outline:. 1. Λ(1405) in the different decay channels. 2. Analysis of the Λ(1405) in the charged channels.
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First data of the L(1405) in the charged (Sp)0 decay channels for p+p reactions Johannes Siebenson Technische Universität München and Excellence Cluster Universe
Outline: 1. Λ(1405) in the different decay channels. 2. Analysis of the Λ(1405) in the charged channels. 3. Analysis of the Σ(1385)+. 4. Summary and Outlook.
Separation of Λ(1405) and S(1385) 33.3% 5.8% 5.8% 33.3% 1.3% 33.3% 87.0% Г≈ 36 Г≈ 50MeV/c2 Г≈ 36 MeV/c2 Page 3 15.3.2010
Different decay channels of the Λ(1405) g + p → L(1405) + K+ : Final states: K+ g S p p Different cross sections: I=0 → L(1405) I=1 Page 4
Interference Effect g + p → L(1405) + K+ →(Sp)0 + K+ : J. C. Nacher et al., Phys. Lett. B455, 55, (1999) K. Moryaet al., arXiv:0911.0925v1 [nucl-ex] 4 Nov 2009 Line shape is different for the different decay channels! Page 5
Analysis of the Λ(1405) Λ(1405) in the charged decay channels: Steps of the Analysis: Page 6
Analysis of the Λ(1405) Λ(1405) in the charged decay channels: Steps of the Analysis: • Identify the four charged particles (p, K+, π+, π- ). Page 6
Analysis of the Λ(1405) Λ(1405) in the charged decay channels: Steps of the Analysis: • Identify the four charged particles (p, K+, π+, π- ). • Cut on the neutron mass and use kinematic refit on the neutron. Page 6
Analysis of the Λ(1405) Λ(1405) in the charged decay channels: Steps of the Analysis: • Identify the four charged particles (p, K+, π+, π- ). • Cut on the neutron mass and use kinematic refit on the neutron. • Cut on the Σ+ or Σ- mass. Page 6
Analysis of the Λ(1405) Λ(1405) in the charged decay channels: Steps of the Analysis: • Identify the four charged particles (p, K+, π+, π- ). • Cut on the neutron mass and use kinematic refit on the neutron. • Cut on the Σ+ or Σ- mass. • Try to understand background and subtract it. Page 6
Particle Identification • Proton, p+, p- are only identified via their energy loss in the MDCs. • Kaons are identified via their energy loss in MDCs and TOF or TOFino. Page 7
Particle Identification • Proton, p+, p- are only identified via their energy loss in the MDCs. • Kaons are identified via their energy loss in MDCs and TOF or TOFino. • And the mass of the kaons is reconstructed. Mass distribution of kaon candidates: • Mass resolution is very poor due to missing start detector. • Extract kaons by cut on the gray shaded mass area. • Misidentification of pions and protons as kaons rather high. counts preliminary Mass [MeV/c2] Page 8
Neutron After mass cut on the K+ (350 MeV/c2 < m K+ < 650 MeV/c2): • Clear neutron peak on top of large background. This is only misidentification of a proton or a pion as a K+. • Cut on the gray shaded area to extract Λ(1405) and apply kinematic refit. counts preliminary MM(p,K+,p+,p-) [MeV/c2] Page 9
First background reduction counts counts preliminary preliminary M(p,p-) [MeV/c2] M(p+,p-) [MeV/c2] These channels are extracted by cutting outside the red shaded area. Page 10
Effect of the kinematic refit The refit reduces the width of the Σ+ and Σ- , and thus the signal to background ratio is increased. Σ+ resonance Σ- resonance counts counts preliminary preliminary MM(p,K+,p-) [MeV/c2] MM(p,K+,p+) [MeV/c2] Page 11
Λ(1405) in Σ+ and Σ- channel Σ+ channel Σ- channel counts counts MM(p,K+) [MeV/c2] MM(p,K+) [MeV/c2] preliminary preliminary A peak near 1405 MeV/c2 is clearly visible, but to extract the pure Λ(1405), the background has to be understood and must be subtracted. Page 12
Understanding the background counts Mass [MeV/c2] preliminary Page 13
Understanding the background counts counts 0.5 1 Mass [MeV/c2] MM(p,K+, p+,p-) [MeV/c2] Describe background with a sideband analysis on the kaon mass distribution: preliminary preliminary Page 13
Understanding the background counts counts 0.5 1 Mass [MeV/c2] MM(p,K+, p+,p-) [MeV/c2] Describe background with a sideband analysis on the kaon mass distribution: counts • Red area includes almost only pions, `misidentified` as kaons. • Blue area includes almost only protons, `misidentified` as kaons preliminary preliminary preliminary Mass2 [MeV/c2]2 Page 13
Understanding the background But momentum distribution of kaon candidates is different for the different mass areas. counts 0.5 1 MM(p,K+,p+,p-) [MeV/c2] counts preliminary preliminary Mass2 [MeV/c2]2 Page 14
Understanding the background But momentum distribution of kaon candidates is different for the different mass areas. counts 0.5 1 1 MM(p,K+,p+,p-) [MeV/c2] counts counts preliminary preliminary preliminary Momentum [MeV/c] Mass2 [MeV/c2]2 Page 14
Understanding the background But momentum distribution of kaon candidates is different for the different mass areas. Imitate the black momentum distribution with the red and the blue distributions: a respects, that the relative contribution of pions and protons is not known. counts preliminary Momentum [MeV/c] Page 14
Understanding the background But momentum distribution of kaon candidates is different for the different mass areas. Imitate the black momentum distribution with the red and the blue distributions: a respects, that the relative contribution of pions and protons is not known. counts counts preliminary preliminary Momentum [MeV/c] Momentum [MeV/c] Page 14
Understanding the background Scale green distribution down to the black one by multiplying with a momentum dependent scale factor: Imitate the black momentum distribution with the red and the blue distributions. a respects, that the relative contribution of pions and protons is not known. counts preliminary Momentum [MeV/c] Page 14
Understanding the background Scale green distribution down to the black one by multiplying with a momentum dependent scale factor: Imitate the black momentum distribution with the red and the blue distributions. a respects, that the relative contribution of pions and protons is not known. counts counts preliminary preliminary Momentum [MeV/c] Momentum [MeV/c] Page 14
Understanding the background • Vary a and scale sideband data with: • a and g(p) for the pions • g(p) for the protons until the missing mass distribution fits best to the left figure. counts 0.5 1 MM(p,K+,p+,p-) [MeV/c2] preliminary Page 15
Understanding the background • Vary a and scale sideband data with: • a and g(p) for the pions • g(p) for the protons until the missing mass distribution fits best to the left figure. • The different contributions of pions and protons are resolved. • Analyze the scaled sideband sample in the same way, described before. counts counts preliminary MM(p,K+,p+,p-) [MeV/c2] Page 15
S+ and S- Understand the different contributions to the signals. Σ+ resonance Σ- resonance counts counts preliminary preliminary MM(p,K+, p+) [MeV/c2] MM(p,K+, p-) [MeV/c2] Page 16
S+ and S- Σ+ resonance Σ- resonance counts counts preliminary preliminary MM(p,K+, p+) [MeV/c2] MM(p,K+, p-) [MeV/c2] Page 16
S+ and S- Σ+ resonance Σ- resonance counts counts preliminary preliminary MM(p,K+, p+) [MeV/c2] MM(p,K+, p-) [MeV/c2] Page 16
S+ and S- Σ+ resonance Σ- resonance counts counts preliminary preliminary MM(p,K+, p+) [MeV/c2] MM(p,K+, p-) [MeV/c2] Page 16
misidentification of p or π+ as K+ S+ and S- Σ+ resonance Σ- resonance counts counts preliminary preliminary MM(p,K+, p+) [MeV/c2] MM(p,K+, p-) [MeV/c2] Page 16
misidentification of p or π+ as K+ S+ and S- Σ+ resonance Σ- resonance counts counts preliminary preliminary MM(p,K+, p+) [MeV/c2] MM(p,K+, p-) [MeV/c2] Page 16
Λ(1405) in Σ+ and Σ- channel Σ+ channel Σ- channel counts counts MM(p,K+) [MeV/c2] MM(p,K+) [MeV/c2] • Besides the fit to the S+ and S- resonances, also the mass range above the vertical dashed line is simultaneously fitted with the different contributions. • The different contributions can be subtracted in order to obtain a pure Λ(1405). For that purpose, further systematic studies of the background have to be carried out. preliminary preliminary Page 17
Analysis of the S(1385)+ S(1385)+ : Steps of the Analysis: • Identify the four charged particles (p, K+, π+, π- ) • Cut on the intermediate L and on the neutron. • Use kinematic refit on the neutron • Reconstruct S(1385)+ via invariant mass of L and p+ and subtract background. Page 18
Analysis of the S(1385)+ S(1385)+ : Steps of the Analysis: • Identify the four charged particles (p, K+, π+, π- ) • Cut on the intermediate L and on the neutron. • Use kinematic refit on the neutron • Reconstruct S(1385)+ via invariant mass of L and p+ and subtract background. Page 18
Analysis of the S(1385)+ S(1385)+ : Steps of the Analysis: • Identify the four charged particles (p, K+, π+, π- ) • Cut on the intermediate L and on the neutron. • Use kinematic refit on the neutron • Reconstruct S(1385)+ via invariant mass of L and p+ and subtract background. Page 18
Analysis of the S(1385)+ S(1385)+ : Steps of the Analysis: • Identify the four charged particles (p, K+, π+, π- ) • Cut on the intermediate L and on the neutron. • Use kinematic refit on the neutron • Reconstruct S(1385)+ via invariant mass of L and p+ and subtract background. Page 18
Intermediate L • Comparison between pure spectrum and spectrum with track quality cuts (distance between primary vertex and L decay vertex etc.). • Cuts reduce background essentially without decreasing the L signal too much. counts MM(p,p-) [MeV/c2] preliminary Cut on gray shaded area to separate the S(1385)+ events. Page 19
Neutron • Clear neutron peak on top of misidentification background. • This background (gray histogram) is again described with the momentum scaled sideband analysis. counts MM(p,K+ ,p- ,p+) [MeV/c2] preliminary Cut between vertical dashed lines further separates the S(1385)+ events. All the events are kinematically refitted. Page 20
misidentification of p or π+ as K+ S(1385)+ Background due to:. and due to: counts M(L,p+) [MeV/c2] preliminary Subtract gray histogram in order to obtain a pure S(1385)+ . Page 21
pure S(1385)+ S(1385)+ is a P13 state, therefore it should be described by a p-wave relativistic Breit –Wigner function: counts M(L,p+) [MeV/c2] preliminary Page 22
Comparison to other spectra S(1385)+ not corrected for efficiency and acceptance. S(1385)+ of HADES (with a total yield of ≈ 1500 entries) fits quite well into other spectra, which were used to determine the nominal quantities of this resonance. counts M(L,p+) [MeV/c2] preliminary PDG Entries - M. Baubillier et al., Z. Phy. C23 213 (1984) - S.R. Borenstein et al., Phys. Rev. D 9 3006 (1974) Page 23
Summary Reconstruction of the Λ(1405) in the charged decay channel was shown. • The kinematic refit is essential for an optimized background suppression. • New sideband analysis can describe the misidentification quite well. • The total background below the Λ(1405) understood and could be subtracted. Reconstruction of the S(1385)+ supplies a total yield of about 1500 entries. • The resonance can be described by a p- wave relativistic Breit-Wigner unction. • The results are in very good agreement with other experiments. Page 24
Outlook – Forward Wall FW Taking also into account the FW- data will increase our statistics essentially: Page 25 15.3.2010
HADES Collaboration G. Agakishiev8, C. Agodi1, A. Balanda3,e, G. Bellia1,a, D. Belver15, A. Belyaev6, A. Blanco2, M. Böhmer11, J. L. Boyard13, P. Braun-Munzinger4, P. Cabanelas15, E. Castro15, S. Chernenko6, T. Christ11, M. Destefanis8, J. Díaz16, F. Dohrmann5, A. Dybczak3, T. Eberl11, E. Epple11, L. Fabbietti11, O. Fateev6, P. Finocchiaro1, P. Fonte2,b, J. Friese11, I. Fröhlich7, T. Galatyuk4, J. A. Garzón15, R. Gernhäuser11, C. Gilardi8, M. Golubeva10, D. González-Díaz4, E. Grosse5,c, F. Guber10, M. Heilmann7, T. Hennino13, R. Holzmann4, A. Ierusalimov6, I. Iori9,d, A. Ivashkin10, M. Jurkovic11, B. Kämpfer5, K. Kanaki5, T. Karavicheva10, D. Kirschner8, I. Koenig4, W. Koenig4, B. W. Kolb4, R. Kotte5, A. Kozuch3,e, F. Krizek14, R. Krücken11, W. Kühn8, A. Kugler14, A. Kurepin10, J. Lamas-Valverde15, S. Lang4, J. S. Lange8,K. Lapidus10, L. Lopes2, M. Lorenz4, L. Maier11, A. Mangiarotti2, J. Marín15, J. Markert7, V. Metag8, B. Michalska3, D. Mishra8, E. Morinière13, J. Mousa12, C. Müntz7, L. Naumann5, R. Novotny8, J. Otwinowski3, Y. C. Pachmayer7, M. Palka4, Y. Parpottas12, V. Pechenov8, O. Pechenova8, T. Pérez Cavalcanti8, J. Pietraszko4, W. Przygoda3,e, B. Ramstein13, A. Reshetin10, M. Roy-Stephan13, A. Rustamov4, A. Sadovsky10, B. Sailer11, P. Salabura3, A. Schmah4, J. Siebenson11, R. Simon4, S. Spataro8, B. Spruck8, H. Ströbele7, J. Stroth7,4, C. Sturm7, M. Sudol4, A. Tarantola7, K. Teilab7, P. Tlusty14, M. Traxler4, R. Trebacz3, H. Tsertos12, I. Veretenkin10, V. Wagner14, H. Wen8, M. Wisniowski3, T. Wojcik3, J. Wüstenfeld5, S. Yurevich4, Y. Zanevsky6, P. Zumbruch4 Page 16 15.3.2010
Λ(1405) in Σ+ and Σ- channel To separate the Λ(1405) into the two different decay channels, the following method is used: • Two more kinematic refits are applied: • one with the constraint on the neutron and the Σ+ B) one with the constraint on the neutron and the Σ- • If the missing mass of proton, K+ and π- (MM(p, K+,π-)) lies in the appropriate mass region around the Σ+and the quality for the refit A) is higher than for the refit B), the event is identified as a Σ+-event. And the appropriate condition for the Σ--case.
Λ(1405) in simulations Σ+ channel Σ- channel counts counts MM(p,K+) [MeV/c2] MM(p,K+) [MeV/c2] Black distribution very similar to the experimental spectra.
Λ(1405) in simulations Σ+ channel Σ- channel counts counts MM(p,K+) [MeV/c2] MM(p,K+) [MeV/c2]