Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 50 (2017)

Status report on the developement of the high-resolution
missing-mass spectroscopy for the (p,2p) reaction in inverse
kinematics
S. Reichert,¤1,¤2 M. Sako,¤2 M. Sasano,¤2 R. Gernhäuser,¤1 H. Baba,¤2 C. Berner,¤1 M. Böhmer,¤1 N. Chiga,¤2W. F. Henning,¤4 T. Kobayashi,¤2,¤5 Y. Kubota,¤2,¤6 R. Lang,¤1 L. Maier,¤1 D. Mücher,¤3 V. Panin,¤2L. Stuhl,¤2 E. Takada,¤7 T. Uesaka,¤2 L. Werner, ¤1 and J. Yasuda¤2,¤8¤1¤2¤3¤4¤5¤6¤7¤8Department of Physics, Technical University Munich
RIKEN Nishina Center
Department of Physics, University of Guelph
ANL
Department of Physics, Tohoku University
Center for Nuclear Studies, University of TokyoNIRS
Department of Physics, Kyushu University

16O(p, 2p)15 N, we were able to demonstrate themissing-mass spectroscopy based on our setup by reconstructing kinetic curves for the ground state andthe excited states at 6.3 MeV and 9.9 MeV with an uncertainty better than σ = 1.7 MeV, as shown in Fig. 1.
# of counts

A new detector setup for high-resolution missingmass measurements was tested at the HIMAC facility in February 2016 with the reaction 16 O(p, 2p)15 N
in inverse kinematics at E = 290 MeV/nucleon andwith a beam intensity of 105 pps. The concept is adetector setup having two arms each to measure themomentum vector of a proton emitted from the (p,2p)
reaction. Each arm consists of three layers of singlesided 100 μm thick silicon detectors featuring a strip
pitch of 100 μm. Two arrays of 9 scintillator rods for
TOF mounted at a distance of 2 m outside the vacuum chamber for the target and silicon trackers complete each arm. Measuring the light particle’s velocity| | and their directions v/| |, the missing-mass in aquasi-free scattering kinematic is deﬁned rather well.
Downstream in the beam-line, a dE−dE detector measures the remaining heavy residues and therefore, one
is even able to determine the exclusive excitation function. In the experiment, background especially arises
from inelastic (p, 2p) reactions in the CH2 target. Fora detailed description of the setup, see1) .
The major goal for the test experiment at HIMAC
was to prove the capability of the setup to reach aresolution of σEX ∼ 1 MeV for the excitation energy.
Achieving such a high excitation energy resolution is amajor prerequisite for studying ﬁssion barrier heights
induced by the (p, 2p) reaction in future experiments
at RIBF/RIKEN.2)
Preliminary results for the resolution are for anopening angle of 3.2 mrad (σopen ) and for an energyof 3.3% (σEN Y ). They are slightly greater than thetargeted values of 3.0 mrad (σopen ) and 2.5% (σEN Y ),respectively. The opening angle depends strongly on
the inner-target multiple scattering. Therefore, 125μm-thick target foils and vertical ﬁber targets (D =150 μm) were accurately positioned to evaluate thevertex-position reconstruction performance of the silicon trackers. Geant4 simulations predict a vertex resolution of σpos = 165 μm. In the experiment we could
reconstruct reactions in the ﬁbers with a precision ofσpos = 175 μm3) .
As a result of the quasi-free knockout reaction

35PRELIMINARY

302520151050−30−20−100102030Exc. eny [MeV]Fig. 1. Distribution of the excitation energies in 15 N, reconstructed from the missing-mass spectroscopy. Data arecompared to a superposition of the three most prominent states and a constant background (red dotted line).
Signal shapes were empirically ﬁt by a gaussian (purpledotted) and a left tail (blue dotted).

The diﬀerential cross sections dσ/dEX are listed inTable 1 and so far do not match with the ratio of thespectroscopic factors in (e, e p ) reactions in4) .
Table 1. Comparison between preliminary diﬀ.
CSdσ/dEX and spectroscopic factors for the ﬁrst discretepeaks
Ex (MeV)
0.00
6.32
9.93

Jπ1−23−
23−2

CS Exp. (mbarn)
4.6±1
5.2±1
3.1±1

Sα Ref.4)
1.260(13)2.348(19)0.133(15)The next step is the replacement of the ﬁrst layer
with new 50 μm silicon wafers to reduce multiple scattering and to improve the resolution of the missingmass.
References
1) S. Reichert, M. Sako et al.: RIKEN Accel. Prog. Rep.
48, 47 (2015).
2) D. Mücher, M. Sasano et al.: RIBF NP-PAC-12 (2013).
3) L. Werner, Master’s Thesis, A silicon tracker system for(p,2p) reactions , TU Munich (2016).
4) M. Leuschner et al.: Phys. Rev. C, 49,955 (1994).

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