MINOS: a vertex tracker coupled to a thick liquid hydrogen target for in-beam spectroscopy of exotic nuclei A. Obertelli1 , A. Delbart1 , S. Anvar1 , L. Audirac1 , G. Authelet1 , H. Baba2 , B. Bruyneel1 , D. Calvet1 , F. Château1 , A. Corsi1 , P. Doornenbal2 , J.-M. Gheller1 , A. Giganon1 , C. Lahonde-Hamdoun1 , D. Leboeuf1 , D. Loiseau1 , A. Mohamed1 , J.- Ph. Mols1 , H. Otsu2 , C. Péron1 , A. Peyaud1 , E.C. Pollacco1 , G. Prono1 , J.-Y. Rousse1 , C. Santamaria2 and T. Uesaka2 1

2

CEA, Centre de Saclay, IRFU, F-91191 Gif-sur-Yvette, France RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan December 6, 2013 Abstract MINOS is a new apparatus dedicated to in-beam nuclear structure experiments with low intensity exotic beams in inverse kinematics at intermediate energies above 150 MeV/nucleon. The device is composed of a thick liquid hydrogen target coupled to a compact time projection chamber (TPC) serving as a vertex tracker. Either used for in-beam gamma spectroscopy of bound excited states or invariant-mass spectroscopy of unbound states, MINOS aims at improving the luminosity by a very significant factor compared to standard solid-target material experiments while improving experimental resolutions.

− Report to the editor − 1

1

Summary

This article describes in details the MINOS project which is devoted to the nuclear structure experiments using exotic nuclei beams. By using a Time Projection Chamber (TPC) surrounding a liquid hydrogen target, MINOS aims to improve the luminosity and resolution. The paper provides the detector and target specifications needed to achieve the latter and obtained by simulations. It details the hydrogen target and TPC geometry, the TPC parameters (gas choice, field cage, Micromegas amplification structure, etc.), the readout electronics, trigger and the Data Acquisition Software.

2

General comments • Make sure that the words are well divided at end of line. Here are some examples which should be modified: – Introduction, p. 2: . . . a typ–ical length of . . . ) – §2.1.3: The signal is anal–yszed by a mathemathical . . . – §3: The mechan–ical support . . . drft veloc–ity calibration of physics events during . . . – §4.1: A power of 10 W at 20 K is needed for the oper–ation . . . – §7.3: TCP server thread that trans–codes . . . • §2.2.3: Replace CH4 by CH4 , iCH4H10 by i-CH4 H1 0 • §4.4: I will recommend, if the editor agrees, to remove the list of requirements which guarentee the Safety of the target cell. • §8: It could have great to add a few results/comments about the cosmic-ray tests (t0 , spatial resolution, drift velocity, etc.)

3

Specific corrections • Figure 2: In the caption: . . . incident energy as obtained . . . • §2.2.1: . . . will be affected by angular straggling in the target. Also, higher the total kinetic energy is, better are the acceptance and the resolution of the spectrometer. Energy loss and . . .

2

• §2.2.2: Two main results are retained. Add a dot after this sentence. And remove the (iii) after: This means that a compact geometry is preferred. • §2.2.5: . . . when both protons are detected. Indeed, for most events, one of the two protons has a kinematics that leads to a degraded resolution . . . • §2.2.5: Is it 1300-mm upstream or 130-mm upstream? • §2.2.5: . . . in order to reach a better efficiency and quality of vertex reconstruction. • Table 2: in gas table: Composition (upper case). • §4.2: (CABTF): explicit the acronym or quote a reference • §4.2: . . . the Systems Engineering (SIS) of IRFUt also manages . . . • §4.2: . . . 110 µm-thickness in polyethylene terephthalate (PET) film referred in the text as the trademark Mylar, and . . . • In this configuration, the remote user is able to remotely display the system without possibilities to pilot it. • §4.3: . . . at least of 2.8 bars (internal differential pressure). Crash tests have been performed with liquid nitrogen five times. The burst pressures reached were from 5.5 to 6.3 bars, well above . . . • Figure 10: Re-do the picture by writing the legend outside the bonding box in order to . • §5.1: . . . hydrogen target. The TPC is read out on one side . . . Beside the need of compacity, the design of the TPC vessel requires a light structure to keep a radiation length low. Reformulate the second part of the sentence: . . . due to . . . the TPC vessel. R • §5.1: precise for Rohacell (polymethacrylimide low density rigid structural foam) and Kapton (poliymide) foil.

• §5.1: replace kapton by Kapton (2 times). • §5.1: replace FR4 or FR4 epoxy by glass epoxy. • Figure 12: Both unreadable. The readability of the legend, axis and axis titles must be improved. • Figure 13: 3

• Figure 13: the readability could be improved. • §5.2: rather well contained in this fast gas if its content stays below a few ten ppm(see Fig. 12). • §5.2: . . . at the CEA/Irfu Micromegas workshop. Layouts of projective and constant geometry pad planes are shown in Fig. 14. • Figure 14: a) projective pads (in the legend of the top figure) • §5.3: replace kapton by Kapton (2 times). TM R • §5.1: Rohacell instead of Rohacell

• §5.3: Mean values of the measured impedance for the resistors is 3889.8 kΩ ... • §6.5: . . . 40 mW/channel. Active air cooling . . . • §7.3: . . . and sends the configuration event. • §8: XY detection plane is composed of two 500 × 500 mm2 Micromegas detector

4

Final recommendation

As a well written and a very detailed description of the MINOS project, I recommend this paper for publication after minor revision that I have listed above.

4