Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 47 (2014)

Development of the tracking detector with large GEM foils for theJ-PARC E16 experiment
Y. Komatsu∗1,∗2 for the J-PARC E16 Collaboration
The J-PARC E161) experiment is proposed to measure the mass spectrum of the ϕ meson in nuclear
matter. In the spectrometer, the momentum ofcharged particles is measured using the tracking detectors(called “GEM trackers”) in a magnetic ﬁeld. The
details of the GEM tracker are described elsewhere2)3) .
The development of the tracker with an eﬀective areaof 300 mm × 300 mm is reported in this article. Aschematic view of the 300 mm×300 mm readout board
is shown in Fig. 1. Cartesian strips called “X” and “Y”
are made of copper and patterned on the top and thebottom of a polyimide sheet of thickness 25 µm. For
charge sharing between X and Y, the base polyimide isetched using the chemical method, except just underthe X strips. The glass epoxy of thickness 100 µm is
laid under the Y strips as a support.

Fig. 1. Schematic view of the 300 mm × 300 mm readoutboard. Only a part of the readout board is shown inthis magnified view.

The positions of the strips were measured using acoordinate measuring machine (Nikon VMR-10080).
The coordinates of the cross-points of the left edge ofthe X strips and the upper edge of the Y strips (xij ,yij )(i,j=0,...,71) were measured for every 12 strips. The
subscripts i and j denote the row and column numbers. The deviations of the coordinates of the crosspoints from the mean values were calculated for each
strip and plotted in Fig. 2. The deviationsof the X∑71
and Y strips are deﬁned as xi,j − i=0 xi,j /72 and∑71yi,j − j=0 yi,j /72. The maximum deviation of the Xand Y strips were 43 µm and 42 µm, respectively. Thedeviations were small compared to the spatial resolution of the X and Y strips, which are 100 µm and 400µm, respectively. The precision of the readout strips
was conﬁrmed. GEM foils with an eﬀective area of 300
mm × 300 mm were also fabricated. The average diameters of the holes were 65 µm for copper and 33 µm forpolyimide in the top and the middle GEM of the stack,∗1∗2Department of Physics, University of Tokyo
RIKEN Nishina Center- 223 -Fig. 2. The measured deviations of the X and Y strips ofthe 300 mm × 300 mm readout board. The unit ofthe color bar is mm and the right (up) direction is thepositive direction in the left (right) figure.

and 56 µm and 27 µm in the bottom for copper andpolyimide, respectively. The spatial resolution of theGEM tracker was evaluated using positron beams at
the Research Center for Electron Photon Science, Tohoku University. The setup is shown in the left panelof Fig. 3. The GEM tracker was located between twoSilicon Strip Detectors (SSDs). The position resolution was evaluated on the basis of the residual of thehit positions calculated from the hits on SSDs and theGEM tracker. The obtained residual distribution for
the 0◦ beam is shown in the right panel of Fig. 3. The
residual distribution was ﬁtted with a Gaussian, andthe standard deviation was 73 µm. The requirementof the position resolution is 100 µm, and the 300 mm
× 300 mm GEM tracker has suﬃcient resolution for
the experiment.

Fig. 3. Setup of the beam test (left) and residual distribution of the 300 mm × 300 mm GEM tracker for 0◦beam(right).

References
1) S. Yokkaichi et al.: In this report.
2) Y. Komatsu et al.: RIKEN Accel. Rep. 45 (2011).
3) Y. Komatsu et al.: RIKEN Accel. Rep. 46 (2012).