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Micromegas detectors for the Muon Spectrometer upgrade of the ATLAS experiment

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Please note that terms and conditions apply. 2015 JINST 10 C02026 of the 2 EDIALAB M October 20, 2014 December 2, 2014 February 16, 2015 : ISSA : : S . Together with the 2 ECEIVED CCEPTED R UBLISHED A P ETECTORS D UBLISHINGFOR doi:10.1088/1748-0221/10/02/C02026 IOPP ENSITIVE S ,U.K. for a total active area of 1200 m OSITION URREY UBLISHEDBY 2 P P ,S UILDFORD ,G ONFERENCEON C 2014, URREY S : Gaseous detectors; Micropattern gaseous detectors (MSGC, GEM, THGEM, : Through the years the Micromegas (MICRO MEsh GAseous Structure) devices have CERN 2015 for the benefit of the ATLAS collaboration, published under the terms [email protected] c of the Creative Commons Attribution 3.0 License by IOP Publishing Ltd and Sissa EPTEMBER NTERNATIONAL I th NIVERSITYOF EYWORDS BSTRACT INFN Sezione di Roma Tre, Via della Vasca Navale, 84 - 00146 Rome, Italy E-mail: U 10 7–12 S K A Medialab srl. Anypublished further article’s distribution title, journal of citation this and work DOI. must maintain attribution to the author(s) and the RETHGEM, MHSP, MICROPIC, MICROMEGAS, InGrid,detectors etc); Gaseous imaging and tracking small-strips Thin Gap Chambers, they will composethe the innermost two New stations Small of Wheels, the which ATLAS will Endcapbreakthroughs replace and Muon developments tracking of system this in type the ofwith Micro 2018/19 the Pattern shutdown. Gas path The Detector towards will the be construction reviewed,sites along of starting in the 2015. modules, An which overview of willin the take detector recent place performance years obtained in at in several the CERN production test will beam be campaigns also presented. proven to be reliable detectors withMicromegas excellent will space be resolution employed for and the highupgrade first rate time of capability. in Large the high-energy area physics ATLAS for experiment the at Muon Spectrometer the CERN LHC. A total surface of about 150 m M. Iodice on behalf of the ATLAS Muon collaboration forward regions of the Muon Spectrometer willEach be module equipped covers with a 8 surface layers from of 2 Micromegas modules. to 3 m Micromegas detectors for the Muon Spectrometer upgrade of the ATLAS experiment 2015 JINST 10 C02026 – 1 – In figure1 the present Small Wheels are shown together with the layout of the NSW, divided The sTGC are primarily devoted to the Level-1 trigger. However they also have the ability 4.1 Construction of the first four plane Micromegas prototype8 5.1 Spatial resolution5.2 for perpendicular tracks and Spatial efficiencies resolution for inclined tracks. The micro-TPC method 10 10 2.1 Bulk3 Micromegas 2.2 The resistive-strip spark protection scheme4 detector planes. 2 into eight small and eightin large the sectors. NSW Similarly in theEach 16 MM module sectors, and is in sTGC a detectors a(precision) quadruplet, will sandwich and composed be in configuration by arranged the of four azimuthalSpectrometer), four coordinates. planes the wedges total for For number sTGC-MM-MM-sTGC. the position of two MM measurements quadruplets wheelsm to in (one be the on built is each radial 128, endcap for a side total of active the area of 1200 to measure offline muon tracks withtracking, good but precision. can, at The the MM same are time,cap confirm primarily middle the dedicated existence stations, to of thus precision track segments exploitingforms found trigger by a capabilities. the muon fully end- In redundant this detectorfunctions. way, system the for sTGC-MM combination triggering and tracking with both online and offline 1 Introduction The Micromegas (MM) istracking one and trigger of purposes the for theiment detector upgrade [1] technologies of in the that view forward of has muonexcellent the detectors been high LHC of rate chosen luminosity the capability ATLAS increase. for exper- andlutions. precision MM good are performance Together micro-pattern in with gaseous terms small-strips detectors of ThinSmall with Wheel efficiency, Gap spatial (NSW) Chambers that and (sTGC), will time the replacein reso- the MM the present will LHC Small Long compose Wheel Shutdown the of in New the 2018/19 ATLAS [2]. Muon Spectrometer 3 Further improvements towards large area Micromegas4 for5 ATLAS Layout and construction of Micromegas for the New Small Wheel6 5 Performance of the Micromegas with high energy particle beams9 6 Conclusions 12 Contents 11 Introduction 2 History and breakthroughs in the Micromegas technology2 2015 JINST 10 C02026 m. This µ m and the position µ 40–50 kV/cm), while the electric field between the m per plane, the position of the read-out strips along – 2 – ∼ µ m accuracy. Given the large surfaces of the individual detector elements, the µ m, sustained by special pillars built on the strip plane, a stretched metallic mesh is µ 1 TeV with the Muon Spectrometer in ATLAS, each track segment in the NSW needs m is required for each of the MM and sTGC planes. Considering the 16 measurement ∼ µ T : Left: photo of the present Small Wheels before entering the cavern. Despite the name, p Charged particles traversing the drift space ionize the gas. The electrons liberated by the The anode is segmented in metallic strips with a pitch of a few hundreds microns. At a distance This detector combination has been designed to be able to also provide excellent performance ionization process drift towards thethe mesh. metallic mesh Due is essentially to transparent the for high the ratio electrons between so that the they two drift electric to fields, the mesh, pass in the precision coordinate should be known with an accuracy better than 30 mesh and the cathode (the so called drift region) is much lower (few hundreds V/cm). of about 100 positioned. This gap, aswith well a as a gas few mixture.amplification mm region) gap is The between held electric at the a field mesh large and value between ( a the cathode mesh plane and are filled the metallic strips (the so called to be reconstructed withperformance a should position not resolution degrade even inbackground if the particles a or bending considerable if some fraction plane detector of to planesthan the are better 100 not detected operational. than hits Thus, are 50 a caused spatialplanes resolution by (sTGC+MM) better with a resolution of 100 of each plane onknown the within coordinate 80 perpendicular to the chamber surface (out-of-plane) should be 2 History and breakthroughs in the Micromegas technology The concept of the Micromegas has beenPattern developed Gaseous in Detectors the (MPGD). ‘90s A [3] sketch in of the context the of MM R&D operating on principle Micro is shown in figure2. for the High Luminosity15% LHC at upgrade. In order to ensure a momentum resolution better than mechanical precision requirements of thedesign, readout construction, modeling planes and positioning control represent of a all possible challenge deformations. in the Figure 1 its size is about 9.3 metersradial in segmentation diameter. of Centre: the Layout MM ofcomposed the modules of New is a Small central visible. Wheel. spacer In Right: and one a View sector sandwich of the of one MM sector and sTGC of modules. the wheel. It is 2015 JINST 10 C02026 – 3 – ) with excellent spatial resolution. However, MM chambers were not 2 . 2 mm / kHz 34 cm . Other medium-size MM were also produced for the T2K TPC readout [6] with – 80:10:10) and by operating the detectors at a moderate gain. × 10 2 4 ∼ /CF : Principles of operations of Micromegas chambers. The sketch shows a MM with the 6 40 cm H 2 × Despite the good performance of the MM in these experiments, it was soon realized that the While the drift of the electrons in the conversion gap is a relatively slow process the amplifi- Micromegas detectors have been successfully used in a number of High Energy Particle (100 ns) for them to reach the mesh, which is the typical duration of the slower signal induced on 2.1 Bulk Micromegas Due to the very narrowsmall amplification variations gap in the MM gap, are imply particularly significantin variations vulnerable in a to the higher amplification, sparking. probability which of in Moreover, sparks turn can (narrower result gaps) or in inefficiencies (larger gaps). The positioning dimensions 36 yet produced in large quantitiesof and 40 the dimensions were limited in COMPASS to an active area greatest problem to solve forparticles this (hadrons) technology leading was to the sparks discharges betweenand with the aging high mesh issues. flux and of In the highly COMPASS the strips(Ne/C ionizing discharge planes, rate thus has to been inefficiencies minimized by using a low density gas cation process happens in athe fraction readout of strip. a Contrary nanosecond to the [4],moving electrons, resulting back the in to ions a the that fast amplification areand pulse produced mesh. therefore in of close Most the electrons to avalanche of on process the the are O readout ions strip. are Given produced the in relativelythe the low strips. drift last velocity avalanche Still of step very the fastwhich ions, compared makes it to the takes other MM particularly detectors. suited It to is operate the at very fast high evacuation particlePhysics of fluxes. the experiments. positive ions COMPASS was2002, the equipped first with experiment, MM detectors since [5] thement and beginning has (up shown of to to data operate in taking very in high particle rate environ- Figure 2 reference operational parameters used during the first yearsupgrade. of R&D at CERN in view of the ATLAS the amplification region, where the avalanchemetallic takes read-out place, strips. and finally the signal is collected by the 2015 JINST 10 C02026 m pitch. All dimen- µ m thick) of insulator (e.g. kapton foil) on top of – 4 – µ electrons in the avalanche, where sparks start to occur, can easily be 7 . In case of highly ionizing particles (as for example, slowly-moving 4 /cm. Geometrically, the resistive strips match the pattern of the readout strips and Ω : Left: Sketch of the detector concept, illustrating the resistive protection scheme; Right: The proof that the principle works was obtained operating a bulk MM chamber with resistive In order to explore the potential of the MM technology to be adopted for the NSW upgrade, are electrically insulated from them.readout strips. The In signals case aredown of induced hence sparks, through damping the the capacitive resistive discharge. coupling strips to charge the up and the electric field locally drops which resistive strips aretens deposited. of M The resistivity of the strips should be of the order of few an R&D activity, called Muonthe ATLAS MicroMegas first Activity years (MAMMA) most starteddischarge of in problem the has 2008 been R&D [9]. overcome work with In the the at amplification implementation CERN of gap. was a layer dedicatedof This of to the resistive was strips address resistive-strip a facing the protection breakthrough sparkref. scheme in issue. [10]. is the illustrated technology The It in development. consists figure3 ofand The described a principle in thin more layer detail (50–70 in Figure 3 Principle of operation for a resistive MM chamber with readout strips of 400 reached. This was immediately recognizedthe to LHC be luminosity a upgrade. limiting factor to operate MM in ATLAS after charged debris from a neutronRaether limit - [8] or of other about 10 - interactions in the gas and/or detector materials), the sions are not to scale. of the mesh inchallenge order in to the construction. obtain The arepresented introduction good of a flatness the new “bulk and method Micromegas” parallelism by ofis Giomataris embedded with producing et into MM respect al. the elements [7] to readout PCBmuch in the simpler structure. one procedure. anode This The single was production allowed process of a to bulkcould in make MM be the based which extended on mounting to the the of printed medium mesh the circuit size boardof detector area technology detectors a fabrication made and by robustness. the industry,manufacturing consequently Going of with PCB to low boards, cost very nowadays large limited to area, a this maximum width method of is 602.2 limited cm. by the The industrial resistive-strip spark protection scheme In order to detect minimumgain, ionizing particles of with the high order efficiency, the of MM 10 operate at quite large 2015 JINST 10 C02026 6 10 . The × 4 m thick µ 10 × 2 . 1 ∼ – 5 – : The monitored HV and currents as a function of the mesh HV under neutron irradiation gas mixtures. 2 /s, on the chambers. Both chambers were operated with the same electronics and the same 2 Figure4 (from [10]) shows the monitored high-voltage (HV) and the currents for both cham- 200 nA for a mesh HV of 590 V, corresponding to an effective gas gain of few high current points inFollowing these figure4 tests,(right panel) all correspond furtherresistive strips. to developments for the the currents ATLAS during upgrade HV were ramp done up. on3 MM with Further improvements towards large areaWhilst Micromegas the for problem ATLAS of sparking has been resolved,to a move number of towards remaining issues the had to constructionthem, be of addressed the the need large to areaPCB overcome MM manufacturing the (see for limitation section the2.1). in NSWthe the While ATLAS readout upgrade. in dimensions PCB, the imposed in Among bulk by thecontaining MM the proposed the the cathode scheme metallic bulk plane. mesh of technique is This large of thus integrated forms area not into depending the MM, on drift the its gap, dimensions. mesh whichmesh” In is is figure5 technique, integrated separatedthe is sketch from in of shown. the the the readoutwith MM panel PCB, The the assembly with drift figure the and “floating is readout astrips panels on schematic in the open drawing readout (left) of panels, and the abetween closed mesh the single (right) support mesh MM position. pillars and are plane On the deposited. assembly photo-imageable top resistive The strips. of coverlay pillars the Are to define resistive produced the the by distance mesh PCB, laminating is exposing, two integrated layers and of in developing 64 thesurrounding the the drift pattern drift panel. stiffening of panel. the It The pillars. is coupling of first the The stretched drift and panel to then the glued readout on panel requires the aluminum frame bers for the same neutron irradiationchamber exposure the for mesh different HV mesh broke HV downwith settings. as the soon In resistive-strip as the protection the non-resistive no neutron∼ HV beam breakdown was switched was on. observed and For the the detector current did not exceed n/cm Ar:CO Figure 4 for a non-resistive MM (left) andthe the points resistive MM the (right) current. [10]. The continuous line shows the HV, protection with a 5.5 MeVThe neutron resistive beam MM and at a the MM without Demokritos resistive National strips Laboratory were exposed in to Athens neutrons flux [10]. up to 1.5 2015 JINST 10 C02026 – 6 – : Schematics of a single MM plane assembly. Left: the drift panel (top) and the readout m over lengths of meters. µ In the process of optimizing the design and ease the construction, and following the results of 50 Figure 5 panel (bottom) are shown inglued open on position. an aluminum The frame mesh (thepanel. is mesh an frame). element Right: integrated the in drift the panel drift is coupled panel, up to thevery readout high mechanical accuracy to positionAs the shown mesh in on figure5, top of whenthe the closed, pillars. pillars the and For mesh-frame in ATLAS, should the contact reach with required∼ them. a precision in position the just machining below of the all top the of frames is attests the on level prototypes, of the high–voltage (HV)applying scheme negative has HV also on been the revised andadopted mesh improved. in and Instead MM), keeping of the the mesh resistiveSuch strips has been at a grounded ground scheme and potential has positive (asconsidered HV several usually scheme was advantages. applied of figure5 to Itwhere the simplifiesbe having resistive an strips. an the issue) insulation detector and between allows construction for the an (especially mesha easy segmentation and in implementation on the of the the readout a frame boards). segmentation would of Atvoltage the the and HV, same if time, allows desired it (through for decouples the a driftexample lower and the voltage the amplification on HV the distributions drift intests electrode figure2 that for itand the provides figure3). same a drift morea Most stable field higher importantly, detector (compare gas it performance for gain. was allowing forand observed This operation from the of can the resistive be detectors strips. explained at strips, by contrary the All to better field the electrostatic configuration linesthe configuration where insulator. end between the In on mesh resistive the strips the eventowing are of strips to at a the and the spark spark, is the same not constrained mesh ground on locally. stays potential the at as ground insulator potential between and the the 4 field perturbation Layout and construction of Micromegas forThe the design New and Small the Wheel constructionstudies procedures of for panels the construction NSWsurements with Micromegas, of extensive are deformations prototyping the in and result comparisonmodels. tests, of with and detailed (and In with of each the a sector,sides support the campaign of of) MM of a mechanical are mea- central simulations arranged supportules in frame. (quadruplets). two Each wedges There wedge (see are is figure1) four radially mounted segmented types on into of the two MM two MM quadruplets 4-layers (basically mod- different in dimensions) 2015 JINST 10 C02026 strips stereo ( ◦ 5 . 1 ± onto two stiffening panels with an aluminum 1 – 7 – 600 mm), and the segmentation was chosen with boards < planes) for the measurement of the precision coordinate X . 2 strips or eta ) while the two r/o planes of the second panel are tilted by η m for the panels in the large (small) sectors. One central double sided panel and µ m). In each gas gap the mesh separates the drift and amplification gaps, of 5 mm and 128 : Sketch of the assembly of a quadruplet. Left: the five panels before assembly (see µ planes) for the measurement of the second coordinate (azimuthal). The pitch of the strips At the time of this paper, the complete design and technical drawings are being finalized for The sketch of the main components of a quadruplet is shown in figure6. The readout (r/o) The strips are on either sides of the stiff panel resulting in opposite field configuration. UV 1 m, respectively. µ (pseudorapidity or is 450 (425) the construction of the finalinto full-size prototypes series of production each in moduleone type mid-2015. (Modules-0) of before the In entering modules figure7 (LM1)Ita is also shown. preliminary shows technical The the drawing drawing segmentationthe on (3D of standard the industrial model) the left PCB of shows PCB processing an boards ( overview (per of plane). the 5 The panels. segmentation is imposed by two external panels sustaining thecoupled to stainless the steel two mesh, r/o panels (alsothe to referred form relative the to alignment four as between gas drift gaps. thethan In panels) readout 30 the are planes assembly then the must panels be are screwed controlled and with high precision (better honeycomb internal structure (r/obases panels). of the One trapezoid of ( them is equipped with strips parallel to the about 450 mm wide. Thefor active the area of innermost one modules detection (SM1LM2). plane and will LM1) On be and composed the by by contrarysegmented, 5 3 the it readout PCB mesh, PCBs is for connected a the to outermost single the modules piece drift (SM2 with panels and chamber (not dimensions, visible so in that the the figure) module is has not essentially no planes are disposed in a “back-to-back” configuration description in the text); Right:of the the assembled eta quadruplet. and stereo In strips the is insert, shown. a All sketch dimensions of are the not to orientation scale. arranged on the various sectorslarge of sectors, the NSW: and LM1 SM1 (lower andwith radius) dimensions SM2 and between for LM2 2 and the (larger 3 radius) small m for sectors. the All quadruplets have trapezoidal shapes Figure 6 2015 JINST 10 C02026 2 – 8 – , basically with the same structure as foreseen for the NSW upgrade. This 2 : Preliminary technical drawing of the Micromegas quadruplet LM1. 0.5 m ) have been built at CERN [9]. A step forward in the prototyping towards the 2 × 2 m Figure 7 × and provide the second coordinate. In the central panel of the figure, a photo of the readout m and comprise a total of 4096 strips. In two of the four planes the strips are inclined by ◦ In figure8 a picture of the detector is shown together with some of its components. The µ 5 At the time this paper is published, the schedule is such that the MMSW is foreseen to be installed (in Summer . 2 1 2015) first in a different position induring the the Endcap first part shutdown of when the accessibility Muon allows. Spectrometer and eventually moved in the Small Wheel is the first examplesize of prototype a also multilayer provided input MM forsection, chamber the and is design ever essential of built. to the establish final theprototype The modules procedures (MicroMegas for just construction for the reported the of construction in Small and this the Wheel) assembly.Strip previous medium- The was Chamber MMSW designed (CSC) to fit detector thechambers installed in dimension left in of of half the figure1). a The present Cathode facing goal Small is a to Wheel CSC install the in chamber, MMSW hence ATLAS intoSmall (copper in Wheel. the ATLAS This the experiment colored will in location allow 2014, the where integrationand the of to a NSW new evaluate detector the will into detector eventually the response ATLAS replace Muon under Spectrometer, the realistic current conditions during the 2015–2016detector LHC has run. been realizedmesh using from the the readout resistive-strip structure. technology415 The and four readout decoupling planes the are amplification segmented into strips with a pitch of final configuration was done in thedimensions summer 1.2 2014 with the construction of the first quadruplet, with ± PCB is shown where thea layer polyimide of film resistive (Kapton) strips thata is is microscopic visible. picture then of press-glued The the totop, resistive resistive the respectively). strips pattern readout are As are PCB. can deposited also A be on shown seen magnified in from picture the these and figure pictures (right the bottom pattern and is right designed with resistive strips dead area in the junctionof between figure7 shows two a PCBs detail (only ofcooling one the (light missing assembled brown) module strip). and along gas with Theof (dark some the drawing brown) front of distribution on end the pipes the boards services. are (green right In visible rectangles). particular, as well as4.1 the envelopes Construction of the firstBefore four plane starting Micromegas the prototype construction of(up the to Modules-0 1 several large size single plane MM prototypes 2015 JINST 10 C02026 10 × the gas ii) screen printing i) m on a small MM µ (88:10:2) gas mixture [13]. 10 H 4 :iC 4 m insulating Kapton foil by sputtering, µ a too fine granularity (small pitch size) would i) – 9 – m operated with a Ar:CF 30%) of the resistivity. The foils produced so far with this µ carbon sputtering and liftoff method, a new technique, developed < ii) (93:7) mixture, already available in ATLAS to operate the MDT chambers, was 2 : The Micromegas prototype for the Small Wheel (MMSW). Left: the first MM quadruplet m strip-pitch has been adopted, resulting in about 2M channels for the full NSW system, µ Results presented in the following sections are mostly based on tests performed in the summer Currently two techniques of resistive foils production are under evaluation: Nevertheless a few points must be considered: 400 of 2012 at the H6 beam line at the Super Proton Synchrotron (SPS) at CERN on small size (10 demonstrated to fulfill the requirements of∼ the NSW. Concerning the readout strips,a the large, choice but of still a reasonable, number. prototype with a strip pitch of 250 result in a huge numbermixture of must electronic be channels safe in from ATLAS, theThe with point reuse associated of of cost view an issues; of existing ageingto (as gas minimize a mixture the general in rule costs. the eco-gasesof Muon must the After Spectrometer be Ar:CO having used). is tried also highly several desirable of in the order most popular gas mixtures, the choice Figure 8 built so far. Center: The readout board. Right: magnified views of the resistive0.3 pattern. mm wide withof staggered an interconnections optimization every from 10 theresistivity, simple mm. independent pattern of with Such the parallel a distance strips,broken configuration lines. along which is guarantees the a the strips. homogeneous result Moreover it is essentially insensitive to which is a standard technique toyears deposit tested resistive on paste, large used surfaces; for small prototypes and in the recent A result by far exceeding the requirements of the ATLAS upgrade. in the context of MM detectors forThe the ATLAS resistive upgrade, to foils produce for MPGD the resistive electrodeslayer MMSW [12]. have (sub-micrometer been thickness) produced is withresulting the deposited sputtering in on technique. a a The 50 good carbon technique, uniformity are extremely ( robust with respect to mechanical and chemical damage. 5 Performance of the Micromegas with highThe energy performance particle of MM beams have been extensivelyity studied in since 2009. the First beginning of results the have MAMMA demonstrated activ- a spatial resolution as good as 40 2015 JINST 10 C02026 m in diameter, with pitch µ 2 assuming the same resolution √ software inefficiency (1.9%), in case no clusters on the chambers. Up to eight resistive MM test iii) 2 – 10 – 2 cm ∼ (93:7) gas mixture and an electrical drift field of 600 V/cm TPC) mode [19]. Measuring the arrival time of the ionized 2 µ the cluster charge-centroid method cannot guarantee the desired ◦ cluster inefficiency (1.3%), if no clusters (with minimum 2 hits) are ii) m/ns and converting the measured time to the position from which the drift µ from the expected impact point (black histogram). A global inefficiency in the σ gas mixture (93:7) with different values of the drift and amplification electrical fields. 2 hardware inefficiency, accounting for a total of 0.2%, in case no hits at all are found in i) m/ns, and an amplification voltage HV=500 V. µ m was obtained with an average cluster size of 3.2 strips. The data acquisition system was based on the Scalable Readout System (SRS) [15] developed An example of such a distribution is shown in figure9–left panel. A spatialThe resolution distribution of of about local inefficiencies has also been studied from the extrapolation of recon- The SPS H6 beam line provides a 120 GeV/c pions beam, with a particle rate between 5 and , a readout plane with 0.4 mm strip pitch, and a drift gap of 5 mm. The chambers were operated ) prototypes. The results presented here summarize and update previous studies], [14 as a result µ 2 2 by the RD51 Collaboration [16].ASIC The [17]. front-end electronics was The basedtrigger APV25 on and will the tracking 128 not primitives channel for be both APV25 produced employed the in MM in its and second the sTGC prototype will NSW. version. be The the front-end VMM [18], ASIC currently providing5.1 being the Spatial resolution for perpendicular tracksIn and case efficiencies of perpendicularthe tracks, charge-weighted a positions of good the estimate detectortracks hit was of estimated clusters. the by The the spatial spatial differencebers. resolution resolution of the for can The cluster perpendicular standard be centroid deviation measurements obtained from of the from pairs gaussian of fit MM cham- is divided by Results are reported for chambersof operated 47 at 600 V/cm electrical drift field, with a drift velocity with Ar:CO 73 structed particle tracks to the chamber underoccur study. at As shown regular in figure9–right intervals, panel, clearly inefficiencies corresponding to the pillars (300 chambers (T1–T8) were aligned alongcm the beam line. All chambers had an active area of 10x10 for the two chambers. spacing of 2.5 mm) sustaining thesidered: mesh. Three different definitions ofthe chamber efficiencies (red have histogram); been con- reconstructed in the chamber (blue histogram); of improved tuning of algorithms and a re-analysis of the data. 30 kHz and transverse dimensions of range 1 to 2% ismust consistent be with noted the that in partially case deadover of more area inclined strips. due tracks to the the inefficiencies are presence reduced of since the the pillars. signals5.2 spread It also Spatial resolution for inclined tracks.For impact The angles micro-TPC greater method than 10 cm are found within 5 resolution. One possibility ismicro-Time-Projection-Chamber to ( exploit singleelectrons strip with time a information time toionization resolution operate process. of the With a MM the few in Ar:CO the nanoseconds the drift velocity allows is reconstructing 47 the position of the 2015 JINST 10 C02026 TPC µ TPC) applied in the µ ” corresponding to the segment hal f x – 11 – . The effect has been understood to be due to the ◦ TPC track from data. µ with respect to (the normal to) the MM chamber is shown. . The simulations are in very good agreement with the data. ◦ ◦ TPC concept as well as an example of a track reconstruction within the drift gap of a µ TPC method has been successfully applied in many test-beam data. However, a sizable : Left: Illustration of the micro-Time Projection Chamber concept ( µ : Left: Distribution of the difference between charge weighted cluster centroids recon- The The peak of thecapacitive induction distribution of is the signal at on neighboring aboutthe strips (the 23 major first and role) last strips and incentral it the panel cluster of is playing figure well 11 the reproduced measuredinclinations and by simulated of reconstructed simulations angles the are (LTSpice, reported beam, ANSOFT for up different Maxwell). to 40 In the segments, for a beam angle of 20 angular bias is observed incan the reconstructed be values seen of the in segment figure angles.11. This systematic In effect the left panel the angular distribution of the reconstructed electrons originate, it isfigure possible10 tothe reconstruct the segment of the track insidefit at the half-gap, drift where the gap. interpolated position In estimate minimizes the error. test chamber, are shown. The best position measurement is at “ MM drift gap. Right: Reconstruction of a Figure 10 Figure 9 structed in the test chambersThe peak T3 structure and is T4; clearly Right: duethree definitions to Inefficiencies of the the from pillars inefficiencies. full as discussed tracking in reconstruction. the text. The text also describes the 2015 JINST 10 C02026 . ◦ TPC µ ). The ◦ –32 ◦ TPC method alone µ TPC method without and with µ TPC method is observed. The bias µ – 12 – TPC spatial resolution is observed. µ m or better in the full angular interval of the NSW (8 TPC methods can be adopted to further improve the resolution (as TPC method reaches best performance for larger angles. Combina- µ µ TPC reconstruction the effect is a tilt of the original track towards µ µ : The left plot shows the reconstruction of the track angle for an incident beam at 20 In figure 12 the results of the resolutions obtained with the segment reconstruction. A correction procedure,induced based charge on the (based identification on of theand/or the charge last strip ratios) signals strips and by in subsequent thethe weighting cluster angle has or bias been suppression and implemented. of an improvement the After in first correction, the a significant reductioncorrection of are summarized (open redrection and has full larger effects red at data small angles. points,guarantees With respectively). a such resolution a As correction, of expected the 100 the usespatial of cor- resolutions the have also been measured usingwith the blue cluster symbols centroid method. in Results the(small are figure. cluster reported size) As while the expected, thetion of cluster the centroid cluster behaves centroid and bettershown at in small [2, 14]) angles 6 Conclusions After six years of intensive R&D onments ATLAS Micromegas, have major been breakthroughs achieved. and These many efforts improve- madeof it possible the for technologies the for Micromegas to the be NSW.out, approved Further design, as developments one construction, and operations, optimizations and onwill analysis) several allow have aspects for made (lay- a the safe MM operation a2018/19 of mature and ATLAS beyond technology. with for This high the performance high after luminosity their era planned of installation the in LHC following the 2023/24 upgrades. Figure 11 A systematic bias in theto reconstruction larger of angles the decreases angle with with thedue the track to angle the (central capacitive panel). induction Thesketch on effect, on the understood the to first right be and explains mainly last the strips, mechanism as is reported well in reproduced the by text. simulations. The A sketch of theof mechanism figure assumed11. to betheir Induced responsible neighbors, signals of and in the in thelarger the bias, first angles. is and Recent developments shown last of the in strips algorithms the of have improved right a the performance panel cluster of the have same arrival times of 2015 JINST 10 C02026 JINST (1996) 29. , , 2008 A 376 , CERN-LHCC-2013-006 (2013). Nucl. Instrum. Meth. , Micromegas: A High granularity position ), as well as at the definition of the procedures for 2 – 13 – 2–3 m ∼ The ATLAS Experiment at the CERN Large Hadron Collider New Small Wheel Technical Design Report Research and Development in Micromegas Detector for the ATLAS Upgrade : MicroMegas spatial resolution summary as a function of the track angle. S08003. Figure 12 3 sensitive gaseous detector for high particle flux environments CERN-THESIS-2014-148 (2014). In the last two years the efforts have been aimed at the definition and finalization of the layout [2] ATLAS collaboration, [1] The ATLAS collaboration, [3] Y. Giomataris, P. Rebourgeard, J.P. Robert and G. Charpak, [4] G. Iakovidis, and design of large MM quadrupletsthe ( construction and the designwith of activities of the construction and necessary tests tooling. ofa a series huge This of effort activity prototypes has (mechanical has made and always operational). theproduction run Such project, phase started in with more parallel than the six nextfull years milestone size ago, prototypes. being to be the ready construction now in to 2015 enter in of the the Modules-0, final Acknowledgments The author would liketheir to incredible thank contribution over all the theMicromegas past technology. six colleagues More years recently of the to Collaboration the the hasproject, grown developments MAMMA more to and include, than ATLAS breakthroughs on 20 R&D the of Institutes. Micromegas program the Thanksthe to for initial the huge concept effort evolved of to physicists, enter engineers, the and phase technicians, of construction. 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