EXPERIMENTAL STUDY OF THREE-NUCLEON DYNAMICS IN PROTON–DEUTERON BREAKUP REACTION∗ 
A. Rusnoka, I. Ciepałb, B. Jamra, N. Kalantar-Nayestanakic 
G. Khatrid, St. Kistrynd, B. Kłosa, A. Kozelab, J. Kubo±e 
P. Kulessab, A. Liptake, W. Parolb, I. Skwira-Chalotf 
E. Stephana, A. Wilczeka, B. Włochb, J. Zejmad 
aInstitute of Physics, Universityof Silesia, Katowice,Poland bThe H. Niewodnicza«ski Insitute of Nuclear Physics,PAN, Krakw,Poland cKVI-CART, Universityof Groningen, Groningen, The Netherlands dThe M. Smoluchowski Inst. of Physics, Jagiellonian University, Krakw,Poland eFacultyof Physics and Applied Computer Science AGH Universityof Science andTechnology, Krakw,Poland f Facultyof Physics, UniversityofWarsaw,Warszawa,Poland 
(Received December 14, 2016) 
Ameasurementof the di˙erential cross sections for the proton–deuteron elastic scattering and the deuteron breakup in collision with a proton was carried out at Cyclotron Center Bronowice using the BINA detection system. Thevery preliminary analysisoftheexperimentaldatatakenat three protonbeam energies: 108, 135 and160 MeV is presented. 
DOI:10.5506/APhysPolB.48.485 
1. Motivation 
Research in the domain of few-nucleon systems is the basis for understanding of nuclear interactions and properties of nuclei. The proton– deuteron breakupreaction can serveasatoolfor testingmodernapproaches to describenuclearinteractionsbetween threenucleons[1–3].Atintermediate energies, below the threshold for pion production, a comparison of the data with exact theoretical calculations is possible and e˙ects of the dynamics beyond the pairwise nucleon–nucleon interaction, the so-called three-nucleon force (3NF), are signifcant. Beside the 3NF, the Coulomb interaction and relativistic e˙ects also a˙ect the di˙erential cross section of the breakup reaction. 
∗ Presented at the Zakopane Conference on Nuclear Physics “Extremes of the Nuclear Landscape”, Zakopane,Poland, August 28–September4, 2016. 
(485) 
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Aseriesof experimentswas carried outat KVI Groningen and FZ-Jich to determine cross section andpolarization observablesof the 1H(d, pp)n and 2H(p, pp)n breakup reactions at intermediate energies[4–10]. The experimental data confrmed importance of the 3NF andhuge infuence of the Coulomb interaction between protons at certain kinematic confgurations. There are also regions and observables where pd elastic scattering and/or breakup reaction data are notwell-describedbythe state-of-the-art theoretical calculations. The database for the breakup reaction is still limited in studied energies, which hinders the conclusions on the role of 3NF and on the defcienciesofthe descriptiongivenbythe current models.Asa continuation of the studies, the measurements are carried out at the new Cyclotron Center Bronowice (CCB, Krakw), at three protonbeam energies (108, 135, 160 MeV). 
The combination of large phase space coverage of the BINA detector systemand wide rangeof accessiblebeam energiesprovidesa uniquepossibilityto study various aspects of the dynamics in the three-nucleon system, in regions of their maximum visibility. 
2. Experiment and preliminary results 
TheBINAdetection systemis defnedby alarge angular acceptanceand low-energy threshold for the particle detection[11, 12]. It is composed of two detector groups —Wall and Ball. TheWall, covering the forward scat-tering angles(12◦–35◦ inthe lab-frame),consistsofamultiwire proportional chamber (MWPC) and scintillation hodoscope system ΔE–E. MWPC pro-vides information for exact reconstruction of the momentum direction of the charged particles, whereas the ΔE–E system is applied for charged par-ticle identifcation and total energy measurement. The backward angles (35◦–160◦ in the lab-frame) are coveredbythe second detector group, Ball, consisting of 149 “phoswich”-type scintillation detectors dedicated to mea-surement of the particle energy and to approximate determination of the momentum direction. Theliquid D2 target is located inside the Ball detec-tor which serves also as a vacuum chamber. 
The frst data have been collected for elastic scattering and the pd breakup reaction at three protonbeam energies: 108, 135 and 160 MeV. The Ballpartwasnotfullyoperationalatthetimeofthe measurements,sothe preliminary analysis is devoted to checking consistency of the data collected in theWall part. The high eÿciencyof MWPC hasbeen demonstrated. A sample particle identifcation spectrum, obtained for one “virtual telescope”, 
i.e. the combination of overlapping elements of the ΔE and E detectors, is presented in Fig. 1 (left panel). Proton and deuteron bands and spots are well-visible allowing for clear defnition of corresponding graphical cuts. The simplifed energy calibration has been applied leading to a proper distribution of proton–proton coincidences alongthe corresponding three-body breakup reaction kinematics (see Fig. 1 (right panel)). The clean spectrum below the breakup kinematics proves low level of accidental coincidences. Thenumberofevents collectedatbeam energyof108MeV correspondsto anaverage statistical accuracyofabout 4–5%in one bin (defnedbythe bins in the proton emission angles: Δθ1 =Δθ2 =2◦ , Δφ12 = 10◦ and the bin in energy of2 MeV). 

Fig.1. Left panel: Sample particle identifcation spectrum measured with one virtualtelescopeatthebeamenergyof135MeV —aprotonbandanda deuteron spot are very well-separated. Right panel: Kinematical spectrum measured for a sample confguration of the proton pair(θ1 = θ2 = 20◦ , φ12 = 140◦)originating from the breakupreaction; data measured at thebeam energy of 108 MeV. 

Fig.2.ParticlesregisteredintheWall presentedontheplaneofpolarangle versus energy. The spectra have been produced separately for particles identifed as protons (leftpanel) and deuterons (right panel); the lines represent dependences calculated for elastic scattering kinematics at 108 MeV. 
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After the PID selection, energy versus angle θ dependences have been checked for protons and deuterons separately, see Fig. 2. Bandsof elastically scattered protons and deuterons are in agreement with the corresponding kinematical curves. 
3. Outlook 
The very preliminary analysis of the data taken with the BINA detector at CCB demonstrates a proper and eÿcient functioning of the forward part of this detector. The aim of the further analysis is to obtain di˙erential cross section of the breakupreaction at 108 MeV as a function of kinematic variables. In a frst step, a number of angular confgurations of outgoing protons will be chosen. The absolute normalization relies on the elastic scattering data measured in parallel to the breakup reaction and the known elastic scattering cross section[13]. 
Thisworkwas partially supportedbythePolish National Science Center (NCN) from grant DEC-2012/05/B/ST2/02556 . 
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