NUCLEAR FRAGMENTATION STUDIES WITH ANTIPROTONNUCLEUS ANNIHILATIONS J Kawada

NUCLEAR FRAGMENTATION STUDIES WITH ANTIPROTON-NUCLEUS ANNIHILATIONS J. Kawada on behalf of the AEg. IS collaboration. Albert Einstein Center for Fundamental Physics, Laboratory for High Energy Physics, University of Bern Contact e-mail: jiro. kawada@lhep. unibe. ch Abstract This work aims at collecting experimental data on low energy antiproton-nucleus annihilation, especially on nuclear fragmentation, by using emulsion films. In spite of their importance in many fields such as nuclear physics, astronomy and radiology, the characteristics ( e. g. hadronization and fragmentation multiplicities) of the stopping antiprotons annihilating on nuclei are not well known. For our study we exposed several thin targets (Al, Si, Ti, Cu, Ag, Au and Pb) to a very low energy antiproton beam from the CERN Antiproton Decelerator, delivering antiprotons to the AEg. IS experiment (AD 6). Nuclear fragment studies in p annihilation with emulsion films The AEg. IS experiment Nuclear fragmentation characteristics on p annihilation is not well known in spite of its importance in many fields, nuclear physics, radiotherapy, and cosmology. -Production Multiplicity -Energy deposit around the annihilation vertex(an issue of radiotherapy) -Dependency on various nucleon -Hyper-fragment production study The goal of the AEg. IS experiment (CERN AD 6) is to test the Weak Equivalence Principle (WEP) using antihydrogen. The gravitational sag of a beam will be measured with a precision of 1% on Dg/g by means of a moiré deflectometer and a position sensitive annihilation detector made of emulsion films. The required position resolution should be ~2 mm to achieve the 1% goal. Antiproton annihilation In emulsion film Nuclear Fragment Fig. 4 Left: Schematic view of the AEg. IS apparatus Right: Dg/g vs. number of reconstructed annihilations Emulsion film & techniques A nuclear emulsion film is photographic film with extremely high spatial resolution (better than 1 mm), and sensitive to MIP particles. In recent experiments, large area nuclear emulsions were used thanks to the developments of automated scanning systems(Fig. 2). Fig. 1. Left: Ag. Br crystals in emulsion layers observed by SEM. Right: A minimum ionizing track (MIP) from a 10 Ge. V/c pion. Antiproton exposure on metal foils with emulsion films Emulsion films were exposed to low energy antiprotons at the CERNAD beam line, the site of the AEg. IS experiment. Seven foils of pure materials were mounted in front of the emulsion film(Fig. 3 right). - Antiproton average kinetic energy: 150 ke. V - Beam density : 10 -20 antiprotons / mm 2 1 -2 k annihilations/foil UHV/OVC separation (2 mm titanium) 5 T/1 T magnet Vacuum flange In each material, 1 k vertices have been reconstructed. An analysis is going on for each vertices to collect data on p annihilation features. 260 microns Emulsion layer (44 micron) p 150 ke. V Fig. 5 Annihilation vertex detection in aluminum foil Lead MC(CHIPS) Data Gold MC(CHIPS) Data Multiplicity of minimum ionizing particles(MIPs) 5μm Cu Ti 20μm 5μm Si Emulsion 5 films Sample 1 Pb Au 5μm Si 400μm Sample 2 R&D on emulsion detector at LHEP 16 layers Analysis results MC(CHIPS) Data Ag 6μm Fig. 3 Left: Schematic view of the Antiproton exposure Right: Schematic view of target metal foils on emulsion films SUS 20 mm Silver Al 400μm Turbo pump Bare emulsion Flange Gate valve Fig. 2. Left: Emulsion scanning lab at LHEP, Bern University. Right: Schematic view of 3 D track reconstruction Janusz chamber (10 -5 mbar) Gate valve 68 mm 1 mm Aluminum Metal foils Aluminum MC(CHIPS) Data Lead MC(CHIPS) Data Silver MC(CHIPS) Data Gold MC(CHIPS) Data Multiplicity of heavily Ionizing particles Fig. 7 Multiplicity of MIPs(mainly charged pion) and heavily Ionizing particles(mainly protons) from p annihilation. Data points show the measured multiplicity for aluminum, silver, lead and gold and histograms show MC simulation based on the CHIPS model. The multiplicity of MIPs is in agreement with CHIPS model simulation. On the other hand, the multiplicity of heavily ionizing particle is in disagreement with CHIPS model for heavier nucleus than silver. - Highly sensitive new emulsion gel A new emulsion gel and its applications are (A) currently under R&D in Nagoya/Japan and LHEP/Bern. The new gel has a higher sensitivity and lower background density compared to the OPERA type (B) emulsion(Fig. 8, Tab. 1). 50 mm - Next generation scanning system with GPU Graphics Processing Unit with higher speed and Fig. 8. A 10 Ge. V/c pion track in flexible tracking. (A) OPERA type (B) new emulsion. The latest GPU(Ge. Force Titan) has been installed into the current scanning system, and software development is going on. - Other emulsion applications New emulsion techniques will be used in many Tab. 1. Comparison between OPERA-type applications. and the new emulsions(made by Nagoya AEg. IS experiment univ. ). Medical Application(precise beam monitor) Muon radiography Reference -C. Amsler et al. , ‘A new application of emulsions to measure the gravitational force on antihydrogen’. , JINST 8: P 02015, 2013. -M. Kimura et al. (AEg. IS collaboration), ‘Development of nuclear emulsions with 1 um spatial resolution for the AEg. IS experiment’, Nucl. Inst. and Meth. A. (in press). - C. Amsler et al. , (AEg. IS collaboration), ‘Prospects for measuring the gravitational free-fall of antihydrogen with emulsion detectors’, JINST 8: P 08013, 2013.