- Email: [email protected]
Search for the Kaonic Nuclear State, K−pp , in the exclusive pp→pΛK+ channel
Nuclear Physics A 827 (2009) 312c–314c www.elsevier.com/locate/nuclphysa
Search for the Kaonic Nuclear State, K −pp, in the exclusive pp → pΛK + channel K. Suzuki a,∗ , M. Berger b , P. B¨ uhler a , L. Fabbietti b , O. Hartmann a,b , N. Herrmann c , P. Kienle a,b , M. Kiˇs d,e , Y. Leifels d , J. Marton a , R. M¨ unzer b , M. Schafhauser a , E. Widmann a , T. Yamazaki f,g , J. Zmeskal a for the FOPI collaboration a Stefan
Meyer Institute for Subatomic Physics, Austrian Academy of Sciences, Vienna, Austria Cluster Universe, Technische Universit¨ at M¨ unchen, D-85748, Garching, Germany c University of Heidelberg, Heidelberg, Germany d Gesellschaft f¨ ur Schwerionenforschung, Darmstadt, Germany e Ruder Boˇ skovi´ c Institute, Zagreb, Croatia f Department of Physics, University of Tokyo, Bunkyo-ku, 113-0033 Tokyo, Japan g RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
b Excellence
Abstract We search for the most basic kaonic nuclear state, K − pp, by studying the exclusive p + p → K + + Λ + p process. Very recently data analysis of the DISTO experiment taken at Tp = 2.85 GeV found a broad peak component in the missing-mass ΔM (K + ) and the Λp invariant-mass M (Λp) spectra, which was enhanced by large-angle emission of protons, and thus assigned to the p + p → X + K + two-body reaction where X stands for K − pp. We are planning to study the same reaction making use of the SIS-18 synchrotron and the ∼ 4π acceptance FOPI apparatus at the GSI, Darmstadt, Germany at higher beam energies. The experiment is planned to take place in 2009. ¯ nuclei, strange dibaryon Key words: K
1. Introduction The possible existence of kaonic nuclear states has been extensively discussed recently, especially the issue of the K − pp system. The most basic kaonic nuclear state K − pp ∗ Present Address: Boltzmanngasse 3, A-1090, Vienna, Austria, Email address: [email protected]
0375-9474/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysa.2009.05.063
K. Suzuki et al. / Nuclear Physics A 827 (2009) 312c–314c
313c
was first predicted by Akaishi and Yamazaki based on the so-called Λ(1405) Ansatz ¯ quasi-bound state with BK = 27 MeV) to have (the Λ(1405) resonance as I = 0, KN 2 a mass M = 2322 MeV/c , an antikaon binding energy BK = 48 MeV and a width ΓΣπp = 61 MeV [1,2]. Recent Faddeev calculations also predict the K − pp to be deeplybound [3,4]. On the other hand, a theory based on chiral dynamics and the ”two-polestructure” Ansatz of the Λ(1405) prefers ”weak”-binding [5]. A detailed theoretical analysis of the structure of the K − pp suggested that the strongly bound K − pp system with a short p-p distance is populated quite favorably in a p + p → K − pp + K + reaction [6]. At large momentum transfer a high sticking probability of Λ∗ (1405) + p → K − pp is predicted. In response to this we prepare an experiment to measure the p + p → X + K + → (Λ + p) + K + reaction with FOPI at GSI [7,8]. 2. DISTO data analysis Preliminary results of the DISTO data analysis were first presented at the EXA08 conference in Vienna in September 2008 [9]. The DISTO experiment measured the p+p → p + Λ + K + channel at incident energies up to 2.85 GeV. The exclusive data set of pΛK + final state consists of the ordinary pΛK + three body final state channel (background channel), characterized by small emission angles of protons, and the exotic two-body process followed by X → Λ + p (signal channel), corresponding to large-angle emission of protons. In the ”deviation spectra” of ΔM (K + ) and M (pΛ), a broad peak structure on a rather flat background distribution is observed at the highest bombarding energy of 2.85 GeV. It represents a two-body exotic signal, since the events with large proton angles (cos θCM (p) > 0.6), which correspond to high momentum transfer emphasize the peak component, in agreement with the model of the K − pp formation in p + p reaction of Ref. [6]. 3. FOPI experiment In the year 2009 we perform a dedicated measurement to study the pp → pΛK + channel using the FOPI apparatus at GSI. Details of the experimental setup, beamline counter upgrade and newly developed Lambda trigger system are described in references [7,8] and Fig. 1. The FOPI apparatus is an azimuthally symmetric 4π detector complex with K + identification capability up to 1 GeV/c [10,11]. K+ Magnet Yoke (0.6T)
TOF Wall (plastic) TOF Wall (plastic) TOF Wall (RPC) Forward DC Start Counter Central DC
p
Target (LH2) proton beam Tp~3.0GeV, I=107/s Veto Counter Lambda Trigger Counters
p from (Λ)
y z
1m π− from (Λ)
Fig. 1. Schematics of the experimental setup
314c
K. Suzuki et al. / Nuclear Physics A 827 (2009) 312c–314c
Following the observation in the DISTO data analysis we performed a new simulation and optimized the experimental conditions once again, especially the incident proton beam energy. One limitation of the DISTO data is its ”low” beam energy which limits the kinematically allowed region of the background channel. This causes the background distribution to be similarly narrow as the X component. Although the simulation presented in the experimental proposal assumes the beam energy to be 3.0 GeV, the DISTO result suggests to increase the beam energy to a still higher value (see Fig. 2).
Minv2(K+Λ) [(GeV/c2)2]
σ [μb]
1.75
1.50
1.25
ppK− + K+
p+p
1.00
2.5
3.0
3.5
4.0
Tp [GeV]
4.5
DISTO Preliminary (2Γ)
5.0
2.00
4.5 4.0
p+p
p+Λ+K+
3.5 3.0 2.5
Tp=2.5, 2.75, 3.0, 3.25, 3.5
4
5
6
7
Minv2(pΛ) [(GeV/c2)2]
Fig. 2. Left: theoretical calculation of the total cross-section of p + p → ppK − + K + reaction [12]. A solid line is drawn to guide the region in between calculated points presented in dots. Right: kinematical limits of the p + p → p + Λ + K + reaction at different incident energies. The peak region of the X peak seen in the DISTO data in p + p → X + K + reaction at 2.85 GeV is indicated by the gray band (2Γ).
4. Outlook and Summary We search for the K − pp with an exclusive measurement of the pp → pΛK + channel. Further analysis of the DISTO data at Tp = 2.15 and 2.5 GeV will help in understanding the pΛK + background shape. New data at the most appropriate beam energy will be taken with FOPI. When both experiments show consistently the existence of such an exotic resonance, they will provide a strong argument for the issue of kaonic nuclear states and address the long standing question of deep or shallow binding of the system. References [1] [2] [3] [4] [5] [6] [7] [8] [9]
Y. Akaishi and T. Yamazaki, Phys. Rev. C 65 (2002) 044005. T. Yamazaki and Y. Akaishi, Phys. Lett. B 535 (2002) 70. N. V. Shevchenko, A. Gal, J. Mareˇs and J. R´evai, Phys. Rev. C 76 (2007) 044004. Y. Ikeda and T. Sato, Phys. Rev. C 76 (2007) 035203. A. Dot´ e, T. Hyodo and W. Weise, Nucl. Phys. A 804 (2008) 197. T. Yamazaki and Y. Akaishi, Phys. Rev. C 76 (2007) 045201. FOPI Collaboration, Experimental proposal to GSI (2007). K. Suzuki et al., EXA08 conference proceedings, submitted to Hyperfine Interactions. T. Yamazaki et al., EXA08 conference proceedings, submitted to Hyperfine Interactions [arXiv:0810.5182v1]. [10] J. Ritman, Nucl. Phys. B (Proc. Suppl.) 44 (1995) 708. [11] A. Sch¨ uttauf, Nucl. Instr. and Meth. A 533 (2004) 65. [12] Y. Akaishi, private communication.
Search for the Kaonic Nuclear State, K −pp, in the exclusive pp → pΛK + channel K. Suzuki a,∗ , M. Berger b , P. B¨ uhler a , L. Fabbietti b , O. Hartmann a,b , N. Herrmann c , P. Kienle a,b , M. Kiˇs d,e , Y. Leifels d , J. Marton a , R. M¨ unzer b , M. Schafhauser a , E. Widmann a , T. Yamazaki f,g , J. Zmeskal a for the FOPI collaboration a Stefan
Meyer Institute for Subatomic Physics, Austrian Academy of Sciences, Vienna, Austria Cluster Universe, Technische Universit¨ at M¨ unchen, D-85748, Garching, Germany c University of Heidelberg, Heidelberg, Germany d Gesellschaft f¨ ur Schwerionenforschung, Darmstadt, Germany e Ruder Boˇ skovi´ c Institute, Zagreb, Croatia f Department of Physics, University of Tokyo, Bunkyo-ku, 113-0033 Tokyo, Japan g RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
b Excellence
Abstract We search for the most basic kaonic nuclear state, K − pp, by studying the exclusive p + p → K + + Λ + p process. Very recently data analysis of the DISTO experiment taken at Tp = 2.85 GeV found a broad peak component in the missing-mass ΔM (K + ) and the Λp invariant-mass M (Λp) spectra, which was enhanced by large-angle emission of protons, and thus assigned to the p + p → X + K + two-body reaction where X stands for K − pp. We are planning to study the same reaction making use of the SIS-18 synchrotron and the ∼ 4π acceptance FOPI apparatus at the GSI, Darmstadt, Germany at higher beam energies. The experiment is planned to take place in 2009. ¯ nuclei, strange dibaryon Key words: K
1. Introduction The possible existence of kaonic nuclear states has been extensively discussed recently, especially the issue of the K − pp system. The most basic kaonic nuclear state K − pp ∗ Present Address: Boltzmanngasse 3, A-1090, Vienna, Austria, Email address: [email protected]
0375-9474/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysa.2009.05.063
K. Suzuki et al. / Nuclear Physics A 827 (2009) 312c–314c
313c
was first predicted by Akaishi and Yamazaki based on the so-called Λ(1405) Ansatz ¯ quasi-bound state with BK = 27 MeV) to have (the Λ(1405) resonance as I = 0, KN 2 a mass M = 2322 MeV/c , an antikaon binding energy BK = 48 MeV and a width ΓΣπp = 61 MeV [1,2]. Recent Faddeev calculations also predict the K − pp to be deeplybound [3,4]. On the other hand, a theory based on chiral dynamics and the ”two-polestructure” Ansatz of the Λ(1405) prefers ”weak”-binding [5]. A detailed theoretical analysis of the structure of the K − pp suggested that the strongly bound K − pp system with a short p-p distance is populated quite favorably in a p + p → K − pp + K + reaction [6]. At large momentum transfer a high sticking probability of Λ∗ (1405) + p → K − pp is predicted. In response to this we prepare an experiment to measure the p + p → X + K + → (Λ + p) + K + reaction with FOPI at GSI [7,8]. 2. DISTO data analysis Preliminary results of the DISTO data analysis were first presented at the EXA08 conference in Vienna in September 2008 [9]. The DISTO experiment measured the p+p → p + Λ + K + channel at incident energies up to 2.85 GeV. The exclusive data set of pΛK + final state consists of the ordinary pΛK + three body final state channel (background channel), characterized by small emission angles of protons, and the exotic two-body process followed by X → Λ + p (signal channel), corresponding to large-angle emission of protons. In the ”deviation spectra” of ΔM (K + ) and M (pΛ), a broad peak structure on a rather flat background distribution is observed at the highest bombarding energy of 2.85 GeV. It represents a two-body exotic signal, since the events with large proton angles (cos θCM (p) > 0.6), which correspond to high momentum transfer emphasize the peak component, in agreement with the model of the K − pp formation in p + p reaction of Ref. [6]. 3. FOPI experiment In the year 2009 we perform a dedicated measurement to study the pp → pΛK + channel using the FOPI apparatus at GSI. Details of the experimental setup, beamline counter upgrade and newly developed Lambda trigger system are described in references [7,8] and Fig. 1. The FOPI apparatus is an azimuthally symmetric 4π detector complex with K + identification capability up to 1 GeV/c [10,11]. K+ Magnet Yoke (0.6T)
TOF Wall (plastic) TOF Wall (plastic) TOF Wall (RPC) Forward DC Start Counter Central DC
p
Target (LH2) proton beam Tp~3.0GeV, I=107/s Veto Counter Lambda Trigger Counters
p from (Λ)
y z
1m π− from (Λ)
Fig. 1. Schematics of the experimental setup
314c
K. Suzuki et al. / Nuclear Physics A 827 (2009) 312c–314c
Following the observation in the DISTO data analysis we performed a new simulation and optimized the experimental conditions once again, especially the incident proton beam energy. One limitation of the DISTO data is its ”low” beam energy which limits the kinematically allowed region of the background channel. This causes the background distribution to be similarly narrow as the X component. Although the simulation presented in the experimental proposal assumes the beam energy to be 3.0 GeV, the DISTO result suggests to increase the beam energy to a still higher value (see Fig. 2).
Minv2(K+Λ) [(GeV/c2)2]
σ [μb]
1.75
1.50
1.25
ppK− + K+
p+p
1.00
2.5
3.0
3.5
4.0
Tp [GeV]
4.5
DISTO Preliminary (2Γ)
5.0
2.00
4.5 4.0
p+p
p+Λ+K+
3.5 3.0 2.5
Tp=2.5, 2.75, 3.0, 3.25, 3.5
4
5
6
7
Minv2(pΛ) [(GeV/c2)2]
Fig. 2. Left: theoretical calculation of the total cross-section of p + p → ppK − + K + reaction [12]. A solid line is drawn to guide the region in between calculated points presented in dots. Right: kinematical limits of the p + p → p + Λ + K + reaction at different incident energies. The peak region of the X peak seen in the DISTO data in p + p → X + K + reaction at 2.85 GeV is indicated by the gray band (2Γ).
4. Outlook and Summary We search for the K − pp with an exclusive measurement of the pp → pΛK + channel. Further analysis of the DISTO data at Tp = 2.15 and 2.5 GeV will help in understanding the pΛK + background shape. New data at the most appropriate beam energy will be taken with FOPI. When both experiments show consistently the existence of such an exotic resonance, they will provide a strong argument for the issue of kaonic nuclear states and address the long standing question of deep or shallow binding of the system. References [1] [2] [3] [4] [5] [6] [7] [8] [9]
Y. Akaishi and T. Yamazaki, Phys. Rev. C 65 (2002) 044005. T. Yamazaki and Y. Akaishi, Phys. Lett. B 535 (2002) 70. N. V. Shevchenko, A. Gal, J. Mareˇs and J. R´evai, Phys. Rev. C 76 (2007) 044004. Y. Ikeda and T. Sato, Phys. Rev. C 76 (2007) 035203. A. Dot´ e, T. Hyodo and W. Weise, Nucl. Phys. A 804 (2008) 197. T. Yamazaki and Y. Akaishi, Phys. Rev. C 76 (2007) 045201. FOPI Collaboration, Experimental proposal to GSI (2007). K. Suzuki et al., EXA08 conference proceedings, submitted to Hyperfine Interactions. T. Yamazaki et al., EXA08 conference proceedings, submitted to Hyperfine Interactions [arXiv:0810.5182v1]. [10] J. Ritman, Nucl. Phys. B (Proc. Suppl.) 44 (1995) 708. [11] A. Sch¨ uttauf, Nucl. Instr. and Meth. A 533 (2004) 65. [12] Y. Akaishi, private communication.