WA104 - NESSiE R&D Plan1

Abstract2

The WA104-NESSiE Collaboration operating at the CERN Neutrino Facility3

aims at developing innovative solutions for the determination of the momentum4

and charge state of low energy muons. The ultimate goal is to provide high5

efficiency detectors and analysis tools for the study of neutrino interactions in6

the 1-10 GeV energy range.7

The NESSiE Collaboration8

A. Anokhina10, A. Bagulya9, M. Benettoni11, P. Bernardini7,6, R. Brugnera12,11,9

M. Calabrese6, S. Cecchini3, M. Chernyavskiy9, P. Creti6, O. Dalkarov9, A. Del Prete8,10

G. De Robertis1, M. De Serio2,1, L. Degli Esposti3, D. Di Ferdinando3, S. Dusini11,11

T. Dzhatdoev10, R. A. Fini1, G. Fiore6, G. Galati2, A. Garfagnini12,11, S. Golovanov9,12

C. Guandalini3, M. Guerzoni3, B. Klicek14, U. Kose11∗, K. Jakovcic14, G. Laurenti3,13

M. Laveder12,11, I. Lippi11, F. Loddo1, A. Longhin5, M. Malenica14, G. Mancarella7,6,14

G. Mandrioli3, A. Margiotta4,3, G. Marsella7,6, N. Mauri5, E. Medinaceli12,11,15

A. Mengucci5, M. Mezzetto11, R. Michinelli3, R. Mingazheva9, O. Morgunova10,16

A. Paoloni5, G. Papadia8, L. Paparella2,1, A. Pastore1, L. Patrizii3, N. Polukhina9,17

M. Pozzato4,3, M. Roda12,11, T. Roganova10, G. Rosa13, Z. Sahnoun3‡, S. Simone2,1,18

C. Sirignano12,11, G. Sirri3, M. Spurio4,3, L. Stanco11,a, N. Starkov9, M. Stipcevic14,19

A. Surdo6, M. Tenti4,3, V. Togo3 and M. Vladymyrov9.20

(a) Spokesperson21

1. INFN, Sezione di Bari, 70126 Bari, Italy22

2. Dipartimento di Fisica dell’Universita di Bari, 70126 Bari, Italy23

3. INFN, Sezione di Bologna, 40127 Bologna, Italy24

4. Dipartimento di Fisica dell’Universita di Bologna, 40127 Bologna, Italy25

5. Laboratori Nazionali di Frascati dell’INFN, 00044 Frascati (Roma), Italy26

6. INFN, Sezione di Lecce, 73100 Lecce, Italy27

7. Dipartimento di Matematica e Fisica dell’Universita del Salento, 73100 Lecce, Italy28

8. Dipartimento di Ingegneria dell’Innovazione dell’Universita del Salento, 73100 Lecce,29

Italy30

9. Lebedev Physical Institute of Russian Academy of Science, Leninskie pr., 53, 11933331

Moscow, Russia.32

10. Lomonosov Moscow State University (MSU SINP), 1(2) Leninskie gory, GSP-1,33

119991 Moscow, Russia34

11. INFN, Sezione di Padova, 35131 Padova, Italy35

12. Dipartimento di Fisica e Astronomia dell’Universita di Padova, 35131 Padova, Italy36

13. Dipartimento di Fisica dell’Universita di Roma “La Sapienza” and INFN, 00185 Roma,37

Italy38

14. Rudjer Boskovic Institute, Bijenicka 54, 10002 Zagreb, Croatia39

** Now at CERN, CH-1211 Geneva 23, Switzerland40

Preprint submitted to Elsevier February 28, 2014

‡ Also at Centre de Recherche en Astronomie Astrophysique et Gophysique, Alger, Algeria1

1. Introduction2

The WA104 activity is part of the CERN Neutrino platform that moving from3

the recommendation of the European Strategy Group to ”[...] develop a neu-4

trino programme to pave the way for a substantial European role in future long-5

baseline experiments” [1], includes neutrino detectors R&D and the study of a6

new neutrino beam [2].7

WA104-NESSiE aims at developing innovative solutions for the precise de-8

termination of the momentum and charge state of muons in the energy range9

from few hundreds MeV to several GeV.10

The immediate goal is the applications of identified solutions in the exper-11

imental search for sterile neutrinos beyond the Standard Model with a new12

CERN-SPS neutrino beam, as proposed in [3, 4].13

Two different approaches will be followed, a conservative one based on a14

light spectrometer seated in a 20 − 30 m3 magnetized air volume (Air Core15

Magnet), and an advanced one exploiting the novel superconducting (SC) cable16

technique for the magnetization of several hundreds cubic meter volumes. A17

novel intermediate system is also sketched for a SC-ACM.18

In the following we shall briefly recall the design of the NESSiE Air Core19

Magnet (Section 2), the required performances of the ACM Spectrometer (Sec-20

tion 2.1), the detectors to be used to instrument it (Section 3). The main21

features of the charged test beam are summarized in Section 6 while in Sec-22

tion 7 the EHN1 experimental hall facility is described. Our test program is23

outlined in Section 8. In Section 9 a proposal is advanced for a combined anal-24

ysis between ACM and liquid-Argon detector put in front of. In Section 10 we25

discuss the planned R&D on superconducting magnets for neutrino detectors.26

2. ACM for WA10427

The design of the Air Core Magnet (ACM) is optimized for the determination28

of the momentum and charge state of muons in the 0.5 - 3 GeV/c range (the mis-29

ID is required to be less than 3% at 0.5 GeV/c). Therefore a global small budget30

of low-density material along the beam direction should be envisaged. Provided31

the eventual use in a neutrino beam, a magnetic field over a relatively large32

volume is required as well. The ACM design has also to satisfy the requirements33

of large acceptance, modularity of construction, low power consumption and34

reduced costs.35

The ACM has been designed as a compromise between all these requirements36

and the measurement capability, the latter being maximized by the quantity37

B×∆z (magnetic field and size along the beam axis, respectively). The chosen38

ACM features are reported in Table 1. A suitable power supply can be the high39

current switch mode power converter PS-SMH57 [5]. It is extensively used in40

LHC, with output in the ranges 4-10 kA, 8-16 V. We may ask CERN to provide41

it.42

2

B ∆z Coils Single coil length Current density Power0.12 T 1.30 m 39 17.2 m 1.9 A/mm2 270 kW

Table 1: Values of the ACM design parameters.

In Fig. 1 and Fig. 2 the ACM 3D view and single coil view are shown,1

respectively. The mechanical structure contrasting the magnetic forces and the2

conductors are both made of Aluminum, which is a low density material. The3

volume of the bending magnetic field is in air. Single coils are all made in4

the same way and can be assembled one on top of the other. The tie-rods5

in the internal volume are placed in such a way to minimize the material in6

the magnetic volume available and to maximize the effective volume for the7

detectors.8

In Fig. 3 a sketch of the ACM equipped with a cage structure to allow safe9

and easy displacements with crane is shown. The single coil section is reported10

in Fig. 4. The heat due to the Joule effect is extracted from the coils by a water11

flow. Assuming the flow is 20 m3/h an increase of ∼ 10◦ C is expected for the12

water temperature going through the circuit.13

3

Figure 1: 3D view of the Air Core Magnet.

Figure 2: Single aluminum coil of the ACM.

4

Figure 3: ACM with the structure used for moving it by crane.

Figure 4: Section of the single ACM coil. The hole for the water flow is visible.

5

2.1. Expected performances of the ACM1

The mechanical stress due to the magnetic and gravitational forces have been2

carefully studied by means of finite element analyses. We have verified that3

Von Mises stress is always lower than the yield strength, thus the ACM (coils4

and load-bearing structure) is everywhere in the elastic range. Furthermore5

the strains induced by the forces on the ACM are lower than some tenth of6

millimeter.7

The magnetic field in the ACM volume is expected to be almost uniform. Its8

value versus different axes is shown in Fig. 5. In Fig. 6 the field value is shown9

also outside the ACM volume assuming a magnetic shielding (see Sec. 2.2 for10

details). The rapid change of the field magnitude at the two vertical edges11

forces a measurement of the non-bending coordinate(y). The y-coordinate can12

be coarsely measured via e.g. scintillator strips (see Section 4.2). We observe13

that it is lower than 10 G at few meters from the ACM. Indeed the fringe field14

value must be low in order to avoid any interference with the operation of the15

LAr detector.16

Fig. 7 shows the displacement with respect to the original path expected17

for a muon crossing different magnetic volume depths for different values of the18

magnetic field. In Fig. 8 the displacement versus incidence angle for the chosen19

130 cm volume depth and 0.12 T magnetic field is reported.20

Many simulations have been performed to foresee the capability of the ACM21

to distinguish the particle charge and to measure the momentum. The charge22

mis-identification shown in Fig. 9 as a function of the muon momentum is the23

result of a simulation assuming a realistic neutrino beam and CC interaction in24

the LAr detector. Twelve detector planes are used in the ACM volume with a25

resolution of 1 mm, a Kalman filter is applied for the charge measurement. The26

momentum measurement are expected with a resolution of the order of 30% or27

less, as depicted in the right plot of Fig. 9.28

6

Figure 5: The magnetic field in the ACM volume versus the vertical axis (left)and the beam axis (right).

7

Figure 6: Side view of the magnetic field. The white color corresponds to regionswith B > 50 G, the color palette is instead for B < 50 G. The shield and theACM are clearly visible.

8

Figure 7: Displacement of the muon path in the bending plane, as a functionof the momentum, for different values of magnetic field and its depth along thebeam axis. Particles are assumed to enter the ACM volume perpendicularly tothe detector planes.

9

)°angle in XY plane (50 100 150 200 250 300 350

)°

an

gle

wit

h r

esp

ect

to Z

axis

(

5

10

15

20

25

30

35

40

45

dis

pla

cem

en

t (c

m)

8

10

12

14

16

18

displacement (cm)

Figure 8: Shift of charged particle tracks with 0.5 GeV/c momentum versusimpinging angle (B = 0.12 T , ∆z = 130 cm).

Figure 9: Charge misidentification and momentum resolution as a function ofthe muon momentum. The ACM features are B = 0.12 T , ∆z = 130 cm, thespatial resolution of the assumed 5 detector planes is 1 mm. The error barscorrespond to the spread due to the multiple scattering and the intrinsic spatialresolution.

10

2.2. Magnetic shielding1

The experimental setup will be completed with a magnetic shield system2

made of iron and vacoflux-50 slabs. Vacoflux-50 is a cobalt-iron alloy widely3

used for magnetic shielding due to the high magnetic saturation (2.35 T).4

The aim of this configuration is to have a magnetic fringe-field lower than5

0.5 G where the LAr detector is. Many shield configurations have been studied6

taking into account also the request that the material in-between LAr and ACM7

must be as low as possible. It turned out that the magnetic shield shown in8

Fig. 10 is a suitable set-up. One iron slab (5 cm thick) is put in-between two9

vacoflux-50 slabs (each 1.5 cm thick). Another iron slab (50 cm thick) is put10

downstream the ACM to close the magnetic field lines.11

The magnetic field with this shielding has been already shown in Fig. 6. A12

zoom of the fringe field in the LAr detector position is shown in Fig. 11 and it13

results fully compatible with the standard PMT operation.14

Figure 10: The magnetic shield is made by iron and vacoflux-50 slabs. Thethickness of iron slabs is 5 (in front of the ACM) and 50 cm (behind), that ofvacoflux-50 slabs is 1.5 cm.

11

Figure 11: Magnetic field as a function of the distance from the ACM. The LAractive detector is expected to be at 2 m from the ACM (-2 m in this figure)where the fringe field is lower than 0.5 G (the 3 curves are referred to differenty heights).

3. Precision detectors1

The charge identification of low momentum muons cannot be done using an2

iron core magnet because of the multiple scattering they would undergo. This3

limitation is avoided if the magnetic field is in air. In Sec. 2.1 the expected4

effect of the magnetic field on muon tracks and the possible measurements are5

presented. As a consequence the resolution of the detectors to be used is of the6

order of 1 mm.7

Taking into account the beam energy and the short distance of the ACM8

detectors from the neutrino interaction point, a wide muon angular distribution9

with respect to the beam axis (z) is expected. Therefore two independent views10

(x, z and y, z) are necessary for a full reconstruction of the muon track bending11

and to check the association of the ACM-track with the LAr-track.12

The ACM will be instrumented with high precision tracking devices. Differ-13

ent detector options are being considered, which are discussed in the following.14

Also a combination of different detectors is possible in order to get a two-views15

reconstruction. Detailed Montecarlo simulations and test-beams are mandatory16

for the final choice of the precision trackers and of their configuration in the17

ACM volume.18

12

3.1. Scintillator Bar Tracking System1

The tracking detector comprises 5 planes of scintillator bar (SciBar) detec-2

tors 2 × 2 m2 size. The planes are equi-spaced inside the ACM depth of 1.33

m. Each plane is made of triangular shape scintillator bars aligned along two4

orthogonal directions (x,y when the beam is along the z direction). Two addi-5

tional planes are foreseen in order to resolve ambiguities in the hit position. The6

scintillator bar cross-section is a triangle 17 mm heigh and 33 mm wide, with a7

central hole 2.6 mm diameter to lodge the wavelength shifting fiber 12). Each8

bar is read by SiPMs, that can operate in a magnetic field; the hit position is9

determined by analog pulse readout and analysis. Preliminary R&D carried out10

on prototypes using laser beams, radioactive sources and cosmic ray particles11

for was aimed at12

• studying characteristics of different SiPMs;13

• determining their working conditions and efficiency dependence on vari-14

ables like temperature, Vbias etc;15

• calibrating;16

• determining the spatial resolution achievable with this tracking system.17

Results of the measurements made with a laboratory set-up that triggered on18

cosmic rays are shown in Figs.13; the corresponding predictions obtained by a19

pure geometrical Montecarlo reproducing the experimental tracking system is20

plotted in 14.21

Figure 12: Left: triangular scintillator bar and WLS fibers. Right: sketch of a2 plane scintillator bar tracker.

13

!Figure 13: Distribution of the reconstructed positions for cosmic rays selectedwithin 5.0 mm window trigger displaced by 4 mm is shown.

!Figure 14: Reconstructed position for cosmic rays selected within a 2.5 mmwindow (left): RMS 2.0 mm. Geometrical MC simulation (right): RMS 1.0mm

14

3.2. Resistive Plate Chambers with analog read-out1

Resistive Plate Chambers (RPCs) are suitable to reach the required 1-mm2

resolution for the charge ID. They are gas detectors [9] widely used in high3

energy and astroparticle experiments. Single gas gap delimited by bakelite re-4

sistive electrodes is the simpler set-up commonly used in streamer mode and5

digital read-out. The main operation features are excellent time resolution and6

high counting rate. Also the spatial resolution is very good. In particular con-7

ditions the centroid of the induced charge profile has been determined [10] with8

a FWHM resolution of ∼ 120 µm. In the case of the NESSIE experiment such9

resolution is not necessary and a simpler and cheaper set-up can be used.10

The analog read-out of RPC has been used in many experiments [13]. This11

technique allows to read the total amount of charge induced on the strips, so to12

get a more detailed information on the streamer charge distribution across the13

strips, resulting in a better estimate of the particle track across the detector.14

The charge profile has a Gaussian shape. The total charge depends strongly15

on the RPC high voltage and on the gas mixture. The width of the profile is16

∼ 5 mm and constant.17

The charge collected on the strips is proportional to the area and the solid18

angle involved. Then the choice of an adequate strip size allows to reach a19

mm resolution in the charge position determination. Also the dynamic range20

is improved, making possible to extend the capability to detect particle at a21

density of the order of 1000 particles/m2.22

We are willing to test the performances of these detectors in the WA104-23

NESSiE program. New electronics for the analog read-out will be implemented24

thanks to the expertise acquired in the ARGO-YBJ experiment [12]. A 10-bit25

5-kHz ADC should fit the required resolution with 1-cm strips. Strips of 0.5 cm26

would be more effective but the number of channels may come out to be too27

large.28

The gas system can be recovered from the OPERA experiment in Gran Sasso29

Laboratory. We will require to CERN the supply of the gas mixture and the30

security assistance.31

15

4. The Ancillary Systems1

4.1. The Iron-RPC System2

A mock-up of the iron core magnet of the NESSiE experiment instrumented3

with bakelite RPCs will be installed downstream of the ACM. It will be act4

mainly as muon range detector.5

The iron structure 1 was developed in 2003 for a CERN test-beam with6

glass RPCs in the context of the Monolith proposal. It is composed by a stack7

of twenty 5 cm thick iron plates separated by 2 cm wide gaps (total depth of8

138 cm). The cross section is 1 × 1 m2. The structure is held by a quadruplet9

of I-beams welded with the stack of slabs on two sides (Fig. 15).10

Figure 15: The Iron-RPC ancillary system.

The RPCs will be used also as trackers in the ancillary iron system. In this11

case the analog read-out and the signal amplification are not necessary and the12

digital operation in streamer regime is enough.13

This operation mode does not require a devoted R&D activity because it is14

widely used. Furthermore the NESSiE people acquired a lot of experience using15

digital RPCs in OPERA and ARGO-YBJ experiments. Standard 2-mm single-16

gap RPCs in streamer mode reach 3 MHz/m2 and this rate is fully compatible17

with the test-beam.18

In the ancillary device each RPC plane will be readout in two views by19

means of inductive strips. Therefore the tracks will be fully reconstructed to20

make easier an univocal association with LAr and ACM tracks.21

4.1.1. The Iron RPC FrontEnd22

A fully new front-end electronics of the RPCs instrumenting the iron mag-23

nets of the NESSiE Spectrometers has been designed to operate with an event24

rate of the order of several tens of events per spill. A trigger-less logic has been25

1The setup is currenly at the Laboratori Nazionali di Frascati (INFN).

16

implemented. According to the same design scheme adopted for the OPERA ex-1

periment, groups of 64 signals coming from the RPCs working in streamer mode2

are read-out by means of front-end boards (FEB) equipped with 4 16 -channel3

LVDS receivers and an Ethernet configurable Field Programmable Gate Array4

(FPGA). The LVDS receivers act as discriminators with programmable thresh-5

olds that can be set via Ethernet by 4 integrated 10-bit DACs. The output6

of each discriminator is sampled with a resolution of 10 ns and continuously7

stored in a 4096-sample circular buffer whenever a write-enable signal is ac-8

tive. A time stamp with a 10 ns resolution is provided for each stored signal.9

Each FEB provides 2 FAST - OR signals implementing the trigger of groups10

of 32 channels. FEBs are housed in crates controlled by a FPGA-based Crate11

Controller Board (CCB) with several tasks such as power supply management12

and monitoring, control signal distribution, masking, FAST-OR collection and13

management. Each CCB is able to manage up to 19 FEBs. The FAST-OR14

signals coming from the FEBs are stored in a circular buffer in a similar way as15

described above for the discriminated RPC signals in each FEB. The CCB pro-16

vides 4 configurable FAST-OR signals as input to a Trigger Supervisor Board17

(TSB) able to generate a programmable trigger which can be used for the acqui-18

sition of cosmic ray muons as well as for monitoring and calibration purposes.19

Prototypes of FEBs and CCB are currently under test in connection with a20

RPC set - up collecting cosmic rays.21

4.2. The scintillator sandwich system22

The incoming/outgoing directions of particles entering/exiting the ACM will23

be determined by planes of plastic scintillator strips placed upstream and down-24

stream of the ACM. The strips are arranged in horizontal and vertical planes25

(transverse to the beam direction) thus providing 3D track information. The26

scintillator strips are 2.5 cm wide, read on both sides using WLS fibers and27

multi-anode photomultipliers. (If made available we may re-use part of the28

target tracker system of the OPERA experiment.)29

17

Figure 16: The Front End board for the RPC readout.

18

5. Data Acquisition System1

The Data Acquisition system is built like an Ethernet network whose nodes2

are the FEB equipped with an Ethernet controller. The Ethernet network is3

used to collect the data from the FEB, send them to the event building worksta-4

tion and dispatch the commands to the FEBs for configuration, monitoring and5

slow control. This scheme implies the distribution of a global clock to synchro-6

nize the local counters running on the FEBs that are used to time stamp the7

data. The clock signal can be distributed either using a dedicated network or8

with the same Ethernet network implementing a White Rabbit protocol2. The9

DAQ clock is synchronized with the CERN General Time Machine signal in or-10

der to start the DAQ readout cycle during particle extraction time. Given the11

long duration (order of second) of the beam still a trigger system is needed to12

acquire the data associated with the passage of the beam particles and typically13

several FEB read-out cycle are performed within the same particle extraction14

time.15

Along the spill duration the FEBs store the status of the discriminators or16

the pulse height of the input signals, for digital and analog readout, respectively,17

in a circular buffer driven by an external clock. The readout of the buffer by the18

DAQ is triggered by a signal generated by a programmable logic (Trigger Board)19

on the basis of the FAST-OR signals generated by the FEBs. The trigger signal20

causes the FEB to disable the writing and the buffer content is transferred to21

the Ethernet controller. Here data are time stamped, eventually zero suppressed22

and sent through Ethernet to the event building. At the end of the read-out23

cycle an enable signal is used to reset the FEBs and start a new read-out cycle.24

In the inter-spill time the acquisition of cosmic ray muons and calibration data25

is triggered by a fake spill gate, possibly validated by a programmable logic26

(Trigger Board) on the basis of the FAST-OR signals generated by the FEBs.27

The start-of-spill signal is used to abort all the readout process on the FEBs28

and to start new data read-out.29

6. The charged beam30

The primary beam of 400 GeV/c protons are slowly extracted from the SPS.31

Typical SPS spill length varies from 4.8 to 9.6 s, while spills are repeated every32

14.8 s to 48 s depending on the number of SPS users. The extracted beam is33

transported over about 1 km by bending and focusing magnets and then split34

into three parts. Each one is directed towards the primary targets T2, T4 and35

T6 to provide secondary beam for experimental building in the North Area.36

EHN1 experimental hall hosts four secondary particle beam lines: the beam37

from target T2 splits into the lines H2 and H4, while T4 splits into the beam38

lines H6 and H8 (Figure 17). The H2, H4 and H8 beam lines can provide39

secondary hadrons, electrons or muons up to 400 GeV/c or primary protons of40

2http://www.ohwr.org/projects/white-?rabbit

19

up to 450 GeV/c. The height of the beam lines from the floor level is in the1

range 2.0-2.8 m.2

Since the detectors will be placed in the pit 9 m deep in the extended part,3

the beam lines have to be extended to transport the low energy particles. The4

length of H4 beam line is about 659 m, a few tens meter of extension is foreseen5

to provide tertiary beam to the experiment.6

Muons and pions test beams of positive and negative polarity and momenta7

between 0.5 and 5 GeV/c (with possibility of extending up to 7 GeV/c) are8

required to evaluate the ACM performances in a standalone configuration. An9

intensity of 1-2 kHz for each given momentum in a beam size of 10 × 10 cm210

would be required. A particle composition of > 99% for muon beams and ≥ 90%11

for pion beams is preferable. If the beam is a mixture of π and µ, particle tagging12

information from the Cherenkov counters or TOF is required to determine the13

ACM response separately to each particle type. Moreover, the π/µ, separation14

can be evaluated in the Iron-RPC system (see Section 4.1).15

Figure 17: Beam lines in EHN1 experimental hall.

20

7. EHN1 Experimental hall1

The NESSiE detectors will be placed in the extended part of the Exper-2

imental Hall 1 (EHN1) at the Super Proton Synchrotron (SPS) North Area3

(Figure 18) as agreed in the CERN Neutrino Platform and with a layout com-4

patible to the neutrino beam option. The total length of the extension is about5

70 m along the direction of beam lines. It includes two large pits of 7.3 and6

9.0 m deep devoted to WA105 and WA104, respectively. The extended EHN17

hall must be equipped with electrical power, air ventilation, water cooling and8

cranes. Depending on the test beam activity to be carried out, the detector will9

be moved downstream or upstream the LAr-TPC detector. Power converters10

of PS-SMH57&61 or LHC13kA-190V type could be used. They will be located11

in the vicinity of the detector setup. The power required to run the ACM, at12

the nominal field of 0.12 Tesla, is 8100 Amps for 35 Volts. Estimated power13

consumption would be around 270 kW plus 5% power loss in the supply for14

ACM and 30 kW for the electronic of the detector.15

The ACM coils are kept at a temperature of ∼ 20 0C by a water cooling16

system. A demineralised water flow of about 20 m3/h is required.17

Figure 18: EHN1 hall layout in neutrino beam configuration with NESSiE de-tectors placed downstream ICARUS-T150.

21

8. Test Program1

We plan to perform tests related to the structure and magnetic field of the2

ACM as well as to the performances of the spectrometer.3

8.1. Test on the ACM mechanical structure and magnetic fields4

The 39 coils ACM structure will be tested against5

• mechanical deformations under magnetic forces and weights6

• thermal expansion.7

Mapping of the magnetic fields in the ACM volume and the external fringe field8

will be performed by means of Hall probes, in different shielding configurations.9

8.2. Test beam10

The test will be performed using the 39-coils ACM. Different phases with11

the test-beam are foreseen. At the beginning the detectors will be tested on12

the charged beam. In a second phase the ancillary iron system will be used as13

a target upstream the ACM, finally the test will be performed with the muons14

emerging from the LAr volume.15

The ACM will be equipped with two different detectors (scintillator bars,16

analog RPCs) on the two sides. By means of the cranes the ACM will be moved17

in order to center the beam on scintillator or RPC part and to change the18

arrival angle of the charged particles. The scintillator sandwiches will be used19

to compare the tracks reconstructed inside the ACM with the tracks upstream20

and downstream the ACM. When necessary the addition of a copper plane will21

allow to enhance the pion/muon separation at low energy.22

The test-beam will be devoted to:23

• Check of DAQ, trigger and detector performances.24

• Optimization of the detector setup (number of planes and position in the25

ACM, scintillator bar geometry, RPC operation point and so on).26

• Estimate of the charge ID percentage as a function of detectors, energy,27

beam angle. This measurement is based on the track bending.28

• Measurement of the particle momentum as a function of detectors, energy,29

beam angle. This measurement is based on the bending in magnetic field30

complemented by the range measurement in the ancillary device.31

• Combined analysis of LAr-ACM events (see Sec. 9).32

22

9. Combined analysis of LAr-TPC - ACM events1

The following test program is foreseen to evaluate the global performance2

of ACM and LAr-TPC detectors. In this configuration the ACM is located3

downstream the LAr-TPC. The positioning of the setup with respect to the4

LAr-TPC detector is shown in Figure 18. We do not request any special beam5

operation. Beacuse of the average energy loss of the muon in argon (about6

210 MeV/m for a minimum ionizing particle), muons with Pµ > 3 GeV/c are7

energetic enough to emerge from the LAr volume (the length of T150 is about8

10 m), Figure 19.9

The momentum and sign of the tracks will be measured in ACM for each10

beam spill. This information will be provided to LAr-TPC data from the same11

spill using a timestamps common in both detectors. Therefore we need to access12

time stamp information as well as beam timing signal. All the tracks identified13

by ACM and LAr-TPC are then searched to identify the corresponding tracks14

in the two detectors.15

LAr-TPC tracks will be extrapolated along their directional three-vector16

from their exit position in the TPC to the ACM. The matching between two17

projections, by comparing the angle of the tracks and radial difference between18

the projected track, will be applied. Multiple scattering at the exits and entering19

to the detectors will be also taken into account.20

Assuming a beam spot of 5×5 cm2 containing 10 K muons with a momentum21

range 0f 2.5 to 5.5 GeV/c at the entrance of LAr-TPC, 1 m2 surface of ACM22

would be illuminated, as shown in Figure 20. In Figure 21 an example of the23

distribution of the reconstructed slopes in ACM is shown.24

In order to take detector resolution in account, gaussian smearing (1 mm)25

around the hits in ACM for all coordinates have been applied. All the hits26

recorded in the ACM within a time window would be used to form a track27

candidates in (x,z) and (y,z) planes. Charged particle tracks are bent in the28

ACM region due to presence of magnetic field, therefore a parabolic fit is applied.29

The track element in the LArTPC have been extracted by linear fit of muon30

hits at last 2 m.31

The angular matching for given momentum spectrum is found to be about32

50 mrad. Knowing the last point and slope of the track at LAr-TPC, the33

predicted position of the track on ACM evaluated. The position resolution34

(positions in ACM smeared) for a given momentum spectrum is found to be35

60 mm.36

The charge ID will be available at high sensitivity for all these kinds of37

tracks, allowing a substantial up-till-now unmeasured test of the possible charge38

identification in LAr.39

In case the neutrino beam will be granted, we would be ready to include40

ICM to exploit the full performances of the extended NESSiE system.41

23

Z (mm)-12000 -10000 -8000 -6000 -4000 -2000 0 2000 4000

X (

mm

)

-2500

-2000

-1500

-1000

-500

0

500

1000

1500

2000

2500

TOP ViEW

Z (mm)-12000 -10000 -8000 -6000 -4000 -2000 0 2000 4000

Y (

mm

)

-2500

-2000

-1500

-1000

-500

0

500

1000

1500

2000

2500

SIDE ViEW

Figure 19: Muon tracks with a momentum of 2.1, 2.8 and 3.5 GeV/c penetratingLAr-TPC. The track with Pµ > 3 GeV/c crossing ACM as well. Gray blocksrepresent passive materials (5 cm and 50 cm iron slabs).

x [cm]-100 -80 -60 -40 -20 0 20 40 60 80 100

y [c

m]

-100

-80

-60

-40

-20

0

20

40

60

80

100

0

1

2

3

4

5

6

7

8

9

10

Beam spot on ACM

Figure 20: Beam spot on the ACM.

24

xθ-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

Trac

ks

0

50

100

150

200

250

300

350

400

450

in ACMXθ

xθδ

-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2

Trac

ks

0

50

100

150

200

250

Xθδ

in ACMXθ

yθ-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

Trac

ks

0

50

100

150

200

250

300

350

400

450

in ACMYθ

yθδ-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2

Trac

ks

0

50

100

150

200

250

Yθδ

in ACMYθ

Figure 21: The angular resolution in the bending corrdinate of the ACM isreported for muon tracks of < Pµ >= 1.0GeV/c. The bias of about 50 mrad isclearly due to the effect of the magnetic field and the simplified reconstructionalgorithm, and it can properly accounted for.

25

10. R&D on Superconducting Magnets for Neutrino Detectors1

We will investigate the use of and feasibility of incorporating Superconduct-2

ing (SC) magnet systems in the design of the Air Core Magnet called SC-ACM,3

as well as magnet systems for Liquid Argon Chamber-like detectors. Several4

types of superconducting materials such as Niobium-Titanium (NbTi), operat-5

ing temperature 4.2 K, Magnesium-di-Boride (MgB2), operating at 20 K and6

Rare Earth Barium-Copper-Oxide (REBCO), operating at around 50 K will be7

investigated by considering the various options for coil design such as solenoids8

with rectangular section or sets of racetrack coils. Based on this study a con-9

ductor technology will be chosen.10

For the different superconductors the required operating conditions in terms11

of critical current density as function of peak magnetic field, forces, stress and12

thermal stability requirements will be optimized and evaluated. Crucial proper-13

ties like effective temperature margin for safe operation and quench protection14

options to handle the stored energy will be analysed in more detail. A second15

key issue is the choice of conductor technology and the impact on the coil wind-16

ing technology and cryogenic requirements. Depending on the Lorentz force17

produced due to magnetic field, a sufficiently rigid coil support structure has to18

be designed.19

Various tests to qualify the conductor technology are foreseen. Once the20

conductor technology is frozen, the construction of a short model coil is foreseen21

to validate the coil winding technology under realistic operating conditions in22

order to mitigate project risks.23

The magnetic and mechanical designs will be analysed using FEM codes like24

ANSYS and FIELD. The comprehensive R&D program on the use of supercon-25

ducting magnet technology will allow us to evaluate the options to reach a cost26

effective solution providing the best possible performance.27

We envisage to perform this activity in conjunction and supporting the28

CERN and ICARUS foreseen plans.29

10.1. A toroidal Super Conducting ACM30

We are studying the possibility to use a SC toroidal magnet to produce an31

average magnetic field of 1 T in air, by considering standard techniques already32

developed for the LHC experiments. It will be made by 8 Niobium-Titanium33

superconducting coils arranged in a toroidal configuration, as depicted in Fig. 22.34

The system owns an external diameter of 8 m. Detector can be inserted in front,35

inside and behind the toroid. It provides a large measuring surface free of any36

material, thus freeing of any limitation induced by multiple scattering. It can37

be operated with liquid Helium at 4.2 K.38

The sketched new system, provided its currently workable element-configuration,39

will allow to construct a magnetized setup for muons in a relatively short time,40

to provide large surfaces of measurements, and to couple in a standard way to41

Liquid Argon tanks. Needless to say this kind of configuration will have no42

outgoing fringe field.43

26

Figure 22: Design of a NbTi Superconducting Air Core Magnet

27

11. Conclusions1

The WA104 activity that is foreseen by the NESSiE Collaboration has been2

extensively described in this document. It will be part of the general frame3

endowed by the CERN Neutrino platform, which moves from the recommen-4

dation of the European Strategy Group to ... develop a neutrino program to5

pave the way for a substantial European role in future long–baseline experiments.6

R&D on neutrino detectors and the study of a new neutrino beam at CERN is7

therefore part of this program.8

WA104–NESSiE aims at developing innovative solutions for the precise de-9

termination of the momentum and charge state of muons in the energy range10

from few hundreds MeV to several GeV. The immediate goal is the applications11

of identified solutions in the experimental search for sterile neutrinos beyond12

the Standard Model with a new CERN-SPS neutrino beam, as already pro-13

posed. The two different approaches that we aim to develop, a conservative14

one based on a light–Z spectrometer (Air Core Magnet), and an advanced one15

exploiting the novel superconducting cable technique for the magnetization of16

several hundreds cubic meter volumes, have been described. In the latter case17

a relevant guideline will be taken into account, namely the overall cost for both18

its construction and the running mode.19

The foreseen prototyping of an ACM will allow to check the construction20

issues, in term of mechanical feasibility, optimization of the servicing modes21

and robustness. The magnetic system is foreseen to be operated in a standalone22

mode. In such a way it will be possible to place it in different positions, following23

different test–patterns and with different detectors, mainly Liquid–Argon ones.24

The R&D activity on the super–conducting cable will go all along the fore-25

seen time period and it will be conducted in parallel.26

The overall time schedule is reported in Figure 23.27

28

Figure 23: The foreseen time-table of the WA104-NESSiE activities.

Floor load capacity: 20 tons (concentrated loads 2 t/300 cm2)A crane of small capacity (5 t)A crane of large capacity (at least 30 t with auxiliary hook of 5 t)Control room, about 20 m2

General safety conditionsACM power supplyCooling services: heat exchangers, pumps and valvesDemineralized water (20 m3/h flow)Gas mixing, distribution and recirculation plant

Table 2: Required technical infrastructures at CERN

12. References1

[1] ...ref a documento strategy Group2

[2] ref a P5 Nov20133

[3] P. Bernardini et al., Prospect for Charge Current Neutrino Interactions4

Measurements at the CERN-PS, SPSC-P-343 (2011).5

[4] ICARUS and NESSiE Collaborations, M. Antonello et al.,6

[5] http://te-epc-lpc.web.cern.ch/te-epc-lpc/converters/SMH57-7

61/general.stm.8

[6] CERN - SBLNF - Study, EDMS Document No. 1260131 v. 10.09

[7] ...10

[8] G. Bari et al. Analysis of the performance of the MONOLITH prototype11

Nucl. Instr. and Meth. A 508 (2003) 170-17412

29

[9] R. Santonico, R. Cardarelli, Nucl. Instr. and Meth. A 187 (1981) 377.1

R. Santonico, R. Cardarelli, Nucl. Instr. and Meth. A 263 (1988) 20.2

[10] E. Ceron Zeballos et al, Nucl. Instr. and Meth. A 392 (1997) 150.3

[11] R. Arnaldi et al, Nucl. Instr. and Meth. A 490 (2002) 51.4

[12] G. Aielli et al, Nucl. Instr. and Meth. A 661 (2012) S56.5

[13] D. Autiero et al, RPC 2001 Workshop, Coimbra, November 2001.6

[14] P.K.F. Grieder ”Cosmic rays at earth”, Elsevier (Amsterdam, 2011).7

[15] ...8

30