A report on the analysis work in the Salerno Emulsion Laboratory is
presented. It is related to the search for nu_mu->nu_tau oscillations in CHORUS
experiment, the calibrations in the WANF (West Area Neutrino Facility) at Cern
and tests and preparation for new experiments.Comment: Proc. The First International Workshop of Nuclear Emulsion Techniques
  (12-24 June 1998, Nagoya, Japan), 15 pages, 11 figure

Amendola, S.

Barbuto, E.

Bozza, C.

D'Apolito, C.

Di Bartolomeo, A.

Funaro, M.

Grella, G.

Iovane, G.

Pelosi, P.

Romano, G.

English

arXiv

A report on the analysis work in the Salerno Emulsion Laboratory is presented. It is related to the search for nu_mu->nu_tau oscillations in CHORUS experiment, the calibrations in the WANF (West Area Neutrino Facility) at Cern and tests and preparation for new experiments

CERN Document Server

arXiv:hep-ex/9901034v1  25 Jan 1999Status of Salerno Laboratory(Measurements in Nuclear Emulsion)∗S. Amendola, E. Barbuto, C. Bozza, C. D’Apolito,A. Di Bartolomeo, M. Funaro, G. Grella, G. Iovane,P. Pelosi, G. RomanoUniversity of Salerno and INFN, Salerno, ItalyDecember 19, 2013AbstractA report on the analysis work in the Salerno Emulsion Laboratoryis presented. It is related to the search for νµ → ντ oscillations in CHO-RUS experiment, the calibrations in the WANF (West Area NeutrinoFacility) at Cern and tests and preparation for new experiments.1 INTRODUCTIONThe analysis work in the Salerno Emulsion Laboratory is running at presentalong the following main lines:• the search for νµ → ντ oscillations in CHORUS;• calibrations in the WANF;• tests and preparation for new experiments.The Salerno Group, having developed a new system [1] for a completelyautomatic system for search and the analysis of interactions in nuclear emul-sions, is also continuing to improve both hardware and software tools toincrease the efficiency and the speed of the system.This argument and some of the results obtained in CHORUS have beenpresented by E. Barbuto in this workshop.∗Presented in The First International Workshop of Nuclear Emulsion Techniques (12-14June 1998, Nagoya, Japan), http://flab.phys.nagoya-u.ac.jp/workshop.12 MEASUREMENT OF MUON FLUX IN THEWANFIn the West Area Neutrino Facility (WANF) [2] at CERN, a muon-neutrinobeam is obtained from the decay of a parallel beam of pions and kaonsof a given sign; the beam is then dumped in order to remove the chargedparticles.The neutrino beam thus obtained is monitored by means of suitablecounters inserted around the primary beam and the target, and inside thedump at different depths, where the muon flux is measured.As the neutrino flux is proportional to the number of detected muons,these measurements allow to center the neutrino beam on its target, andto estimate its intensity through a Monte Carlo simulation that takes intoaccount the muon absorption and scattering in the dump.In addition, this procedure constitutes a real on-line monitoring of theneutrino beam and allows to detect within a few seconds any fault that couldhave occurred along the beam line.The use of nuclear emulsions is mainly intended to give an absolutecalibration to few of the many Solid State Detectors (SSDs) inserted in theshielding, that are relatively calibrated one to the others. This techniquewas already used in past [3] to calibrate the detectors in the Wide-Band andin the Narrow-Band-Neutrino beam at CERN.The present automatic analysis, however, allows to handle much higherfluxes, with considerably increased statistics and in much shorter times.2.1 THE WANFThe CERN muon-neutrino beam was largely rebuilt in 1992 - 93, and op-timized for a new round of νµ → ντ oscillation experiments (CHORUS andNOMAD).450 GeV protons from the CERN-SPS are focused onto a primary targetin two spills, 6 msec long, separated in time by 2.7 sec. (fast-slow ejection),one at the start and one at the end of the flat top. The two spills collectabout 80% of the primary intensity.The target is made up of 11 beryllium rods (3 mm in diameter, 10 cmlong, spaced by 9 cm), aligned in a cast aluminum box; the rods are cooledby means of a closed flux of helium gas.An aluminum collimator, 2.75 m long, is placed 2.5 m downstream ofthe target to remove the wide angle secondaries (> 9 mrad).2After the first two years of successful operation, the station receivedmore than 2×1019 protons at 450 GeV/c, with a peak intensity of 2.8×1013protons per machine cycle.Positive (negative) hadrons are produced in the target and are focused(defocused) by the subsequent beam elements.The neutrino (antineutrino) beam is generated by positive (negative)hadrons decays, mainly pi+, K+ → µ+ + νµ, or c.c.In the case of a neutrino beam, a small contamination (about 5%) of isproduced by wrong sign hadrons (pi−, K−) present in the selected beam,while νe (about 1%) νeor (about 0.2%) are produced by semileptonic decaysof kaons.A much smaller fraction of ντ (about 10-6) is produced through theproduction and the prompt tauonic decay of Ds.The beam line of Cern West Area is divided in three principal regions.Figure 1: Target and beam line of CERN West Area.Figure 1 shows schematically, and not to scale, the beam line in the WestArea.The neutrino cave, 125 m long, contains the target and the focusingelements. These are the horn and the reflector, a system of two pulsed,3coaxial conductors with cylindrical symmetry, studied by S. Van der Meer.The decay tunnel, 290 m long and 60 cm in radius, is evacuated to apressure of about 1 torr in order to minimize secondary interactions. Here,a sizeable fraction of the focused hadrons decay along a line very close tothat of their parents.The shielding -iron and earth- 400 m long, absorbs the remaining hadronsand decay muons.In the shielding there are three pits about 15 m underground, 20, 40 and60 m downstream of the decay tunnel. In each pit there is an array of 43Solid State Detectors (SSD) to monitor the beam.2.2 SSDs AND THEIR ABSOLUTE CALIBRATIONSolide state detectors measure the charge (as an integrated electric current)produced by crossing particles and need an accurate calibration to converttheir electric signals into charged particles flux measurements.The absolute calibration is made using the counting provided by nuclearemulsions. The choice of nuclear emulsions is due to their very high efficiencyand to their excellent two track separation, that allow the detection of veryintense particle fluxes (up to more than 106 part/cm2 in our case).Our work refer to measurements in pit n◦3, the most downstream, inwhich muon flux is less than in the others, and for this reason, it has beenchosen for the emulsion set exposures.Solid State Detectors (silicon detectors - sensitive surface from 30 up to200 mm2 and thickness from 0.1 up to 1 mm) are placed in boxes on a rigidsupport, orthogonal to the beam line.Figure 2 shows a typical arrangement of the counters.A particular box with 5 SSDs, the calibration box (Cal.box), that canbe moved in front of the other counters, calibrates them. The calibrationsequence is automatically repeated every 8 hours, by successive movementsof the Cal.box.Another special box, the reference box (Ref.box), is moved from pit topit, and placed in front of the calibration boxes, to calibrate them.Finally, the absolute calibration of Ref.box, and hence of all the counters,is performed with emulsion measurements. To be safe, a set of 4 emulsionplates were used at the same time to calibrate also detector n◦40, on thecenter of beam line, and detector n◦2 (during 1994-95) and detector n◦42(during 1996-97).In the last 4 years, in pit n.3, 17 exposures of emulsion sets were per-formed.4Figure 2: SSDs arrangement in pit n.3.Emulsion plates were stuck on the center of a box containing SSDs andexposed perpendicularly to the beam direction, so that tracks cross theemulsions nearly perpendicularly and fully automatic scanning can be suc-cessfully performed.The location of the emulsion plates and their identification labels areshown in figure 3.We used 3 or 4 plates (3× 4 cm2) for each set, and two sets of emulsionswere generally exposed the same day, each to one spill of intensity between105 part/cm2 and 2 × 106 part/cm2, corresponding to 1012 ÷ 1013 protonson target (p.o.t.).We have used plates double coated on a 300 µm plastic base, with Fujior Nikfi gel. The thickness of emulsion pellicles were 100 µm (150 µm forthe last three exposures).A total of 66 emulsion plates were exposed; together with each exposedset, we produced a reference plate that was not exposed in the beam linebut was used for evaluating the background. In order to reduce the back-ground, due to environment radioactivity, to cosmic rays, etc., the emulsionplates were poured immediately before and developed soon after the expo-sure (within a period, typically, of one week).We used the automatic scanning, SYSAL (SYstem of SALerno). On eachemulsion 5×5 fields were scanned (about 0.39mm2), with a gap among fields5Figure 3: Emulsion plates (black boxes) exposed in pit 3 during Chorus -Nomad run. Empty boxes represent the Solid State detectors. The figure isout of scale.to prevent double counting of tracks.Typically, 35 to 35 tracks/field were found, and a total of about 4× 105tracks were measured.A two dimensional image as seen under a 50× magnification is shown infigure 4, corresponding to a density of about 80 tracks/field.2.3 ResultsTracks that cross the emulsion pellicle from one surface to the other arecalled passing - through tracks. In the data taking these tracks are built upwith at least 20 aligned grains, and are the only ones capable to contributeto the electric signal of SSDs. So, all other tracks present in emulsion mustbe excluded from flux evaluation, because they don’t reach the SSDs.Other tracks reconstructed by SYSAL are:6Figure 4: Emulsion layer as seen under a 50× magnification. Passing -through muons appear as black spots, their tracks being nearly perpendic-ular to the plane of the figure.• fake tracks due to association of random grains in emulsions, usuallywith few poorly aligned grains;• background tracks, like slow-energy electrons and cosmic rays, mostlywith wide angle;• mixed tracks, poorly aligned grains with an intermediate number ofgrains, contribute to both good and background tracks.Figure 5 shows the distribution of track grain multiplicity for a particularexposure.These plots show a peak at 28 - 30 grains due to passing through tracks;a flat region includes mixing tracks; another peak with a few grains is dueto fake and background tracks. The cut off at number of points equal to 20,to calculate muon flux, was chosen in order to reject the latter peak.7Figure 5: Track grain multiplicity on the top side of the plate of the 11thexposure. The emulsion thickness after development ranges between about50 and 60 µm.Figure 6 shows the distributions of the residuals from a parabolic fittingfor the three categories of segments, according to their grain multiplicity.To test the reproducibility of our measurements we have rescanned ev-ery time the same plate; such a scanning confirms that the measurementsreproducibility is within a few percent.For each plate we have also measured polar and azimuthal angle.Figure 7 shows polar and azimuthal angle distributions, after distortionand shrinkage corrections.8Figure 6: Residuals from a parabolic track fitting.We have studied the correlation between flux from SSDs (electric signalwas converted with the existing calibration) and flux measured on all emul-sion plates. We found a very good linear correlation. A linear correlation isalso confirmed between BCTs1 countings and emulsion measurements.These correlations are shown in Figure 8. The correlation between fluxmeasurements from Ref.box and flux measured from emulsion plate (Em 1)stuck on Ref.box gives a very good agreement (within about 1%).1The neutrino flux monitoring system also collects data about the primary proton beamand the secondary hadron beam from Beam Current Trasformers (BCTs) upstream of thetarget.9Figure 7: Polar (up) and azimuthal (down) angle measured on an emul-sion pellicle (plate n1, exposure n 11) after distortion and shrinkage cor-rections for passing - through (continuous line), mixed (dashed line) andfake/background (dotted line) tracks.The highest density of tracks is more than 2× 106 tracks/cm2.3 A TEST FOR TOSCA EXPERIMENTSysal was also used to test the set-up of possible, future experiments. Amongthese TOSCA [4], conceptually similar to CHORUS, aims to much betterdetection of charged particles, and foresees an emulsion target within a mag-netic field.An option for a wide-gap magnet could be the one built for UA1, atpresent in NOMAD (maximum field B=0.7 T).10Figure 8: Correlation between the SSD and the BCT counting with emulsionmeasurements. In plot (a) the emulsions are related to the SSDs on whichthey were exposed; the p.o.t. (proton on target) are compared with EM1(plot (b)) and EM2 (plot(c))An option for a suitable spectrometer is a Compact Emulsion Tracker(CET), a set-up already used in the past, for example in the study of high-energy heavy-ion experiments (EMU 08, 09,16, etc.)This set-up (fig. 9) was tested in September 1997 where an emulsiontarget 9 cm thick (3X0) was followed by silicon trackers and by a series of8 thin, parallel emulsion sheets spaced from 8 to 32 mm over a total lengthof 180mm.11Figure 9: Set up of CETs position. Figure is not in scaleA 15 GeV beam of pions was used to produce interactions in the target,whose particles have been traced in the external apparatus.A first alignment between pairs of CET sheets was realized by means ofX-ray guns (see fig. 9). A better approximation was obtained by measuringpositions and angles of a sample of primary particles, whose individual iden-tity was recognized from one sheet to the next by comparing the topologicalpattern.The angular spread of the beam (fig. 10) was found to be about 1.6mrad, in excellent agreement with that expected for a 15 GeV parallel beamafter having crossed a 3X0 target.This procedure allowed to place all sheets in a common reference frameby means of a fit of the rototraslational parameters.Finally, a random search was performed in the first pellicle for randomtracks out of the beam (θ > 50 mrad), and thus some tracks were searchedand measured in the following pellicles.A linear fit was performed for the transverse coordinates as functions ofthe longitudinal one: as a result, systematically the residuals on the bendingplane turned out to be about one order of magnitude larger with respect tothose in the non-bending planes, and these are compatible with the accuracy12Figure 10: Absolute angular distributions of primaries.in locating the pellicles with the location procedure described above.A parabolic fit in the bending plane allowed to determine the radius ofcurvature, hence the momentum of the particles.Now, the residuals turn out to be similar to those in the non-bendingplane.Fig. 11 shows a typical example of the results obtained on a particulartrack. Table n.1 shows the global results for a set of tracks.Radius of curvature (m) Momentum (GeV/c)20.7 ± 3.8 4.3± 0.8−26.3 ± 3.6 −5.5± 0.710.2 ± 0.9 2.1± 0.2−23.8 ± 2.4 −5.0± 0.5−18.5 ± 2.7 −3.9± 0.617.9 ± 2.0 3.7± 0.4−4.17± 0.07 −0.87± 0.0141.7 ± 6.9 8.7± 1.4−57.5± 11.9 −12.1± 2.5−55.6 ± 8.6 −11.7± 1.8−2.8 ± 0.09 −0.58± 0.0213Of course, this procedure assumes that the primary particles have straighttrajectories, but their curvature could be easily taken into account.In the near future it is planned to repeat these measurements on pre-dicted tracks, whose momentum has been also measured in the externalapparatus.From these results it is concluded that this set-up allows to measuremomenta with a minimum relative error ∆p/p ≈ 6%, essentially due tomultiple scattering in the emulsion sheets.The measurement error, that could be possibly lowered, gives at present∆p/p ≈ 1.4% × p.References[1] G.Rosa et al, Automatic Scan and Analysis of Digitized TV Images bya Computer Driven Optical Microscope, NIM A 394 (1997) 357-367.[2] C.Bozza, A. Di Bartolomeo, G.Iovane, P.Pelosi, Measurements of themuon flux in the CERN SPS wide band neutrino line, CHORUS InternalNote 97030, Geneva, January 1998.[3] E.H.M.Heijne, Muon flux measurements with silicon detectors in theCERN neutrino beams, CERN 83-06 Experiment Physics Facilities Di-vision, Geneva, 21 July 1983.[4] European Organization for Nuclear Research, Request for a testof emulsion-silicon configurations for a neutrino experiment, CERN-SPSC/97-4 SPSC/M596, 21 February 1997.14Figure 11: Linear fit of z and y coordinate versus x, parabolic fit of z coor-dinate versus x.15

Status of Salerno Laboratory: Measurements in Nuclear Emulsion

Status of Salerno Laboratory (Measurements in Nuclear Emulsion)

Status of Salerno Laboratory (Measurements in Nuclear Emulsion)

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