L. Pontecorvo1 The Muon New Small Wheels INFN CSN L. Pontecorvo

L. Pontecorvo2 Introduction The New Small Wheel is the major phase-1 upgrade item of the Muon spectrometer. Upgrade needed for high luminosity beyond the design luminosity L1 rate: many fakes, limited p T resolution. Use Inner Wheel to form a segment to confirm trigger, fast detectors Muon tracking: performance deterioration due to high bkg in small wheels. Use rate tolerant, high resolution detectors It is called Small… but is not so small

L. Pontecorvo3 ?, IR 4x, bunch spacing 25 ns ~20-25 fb -1 ~ fb -1 ~350 fb -1, bunch spacing 25 ns, bunch spacing 50 ns Go to design energy, nominal luminosity Injector and LHC Phase-1 upgrade to full design luminosity HL-LHC Phase-2 upgrade, IR, crab cavities? √ s=14 TeV, L=5x10 34 cm -2 s -1, luminosity levelling √ s=14 TeV, L~2x10 34 cm -2 s -1, bunch spacing 25 ns √ s=13~14 TeV, L~1x10 34 cm -2 s -1, bunch spacing 25 ns √ s=7~8 TeV, L=6x10 33 cm -2 s -1, bunch spacing 50 ns  LHC startup, √ s = 900 GeV LHC Timeline

L. Pontecorvo4 The ATLAS Muon Spectrometer SMALL WHELL (SW) Tracking: MDT-CSC Drift tubes at high pressure Cathode Strip Chambers TGC: second coordinate Big WHELL (BW) Tracking: MDT Triggering: TGC Thin Gap wire chambers  =2.7  =1  =2  =1.4 EI EM EO

L. Pontecorvo5 Motivation for upgrade Cavern background Muon spectrometer designed for luminosity 1x10 34 with safety margin of x5 with respect to the background estimate (>10 years ago) Cavern Background 7 TeV and up to L=2x10 33 Quite good agreement between Data and new MC Simulation (FLUGG) both on absolute number and shape. Ratio Data (MDT)/FLUGG

L. Pontecorvo6 Motivation for upgrade Cavern background Main uncertainties for the extrapolation to higher luminosities: Different Center of Mass Energy (about x1.3 for 14 TeV) Different Beam Pipe In Al Beam Pipe will be installed (about 30% reduction of Cavern Background) Improvement in shielding and changes in machine parameters

L. Pontecorvo7 Motivation of upgrade Measured and scaled cavern background in the EI (small wheel) MDT rate limit 1x10 34 is OK, but no margin any more at higher lumi Cavern background Bkg rate estimate for 14 TeV L=3x10 34 L=2x10 34 L=1x10 34 ATLAS simulation

Effect of Cavern Background on MDTs MDT efficiency drops very fast with tube rate (red points) For L= 2x10 34 >300 KHz /tube-> Eff< 70% Resolution degraded due to Space charge effects

L. Pontecorvo9 Motivation of upgrade MU20 vs  2010/2011 data ~ 6-7x higher rate in Endcap wrt Barrel 50 ns bunch spacing Muon L1 issue Unexpected L1 high rate observed in the muon endcap region Fake triggers due to particles not coming from the IP L1 endcap (TGC) is based on track angle at EM (Big wheel) Barrel End Cap

L. Pontecorvo10 Motivation of upgrade What are the origin of fake triggers ? Tracks not having hits in Inner layers E.G. Protons generated in the EC Toroids TOF measurement with MDT EM and EO Slow particles ! FLUGG MC birth position of protons FLUGG MC  DATA

L. Pontecorvo11 Rate reduction with NSW Rate reduction due to New Small Wheel studied with MDT Data. Pt distribution for different cuts including SW info Rate reduction using info from SW NSW is vital for running at high luminosity

L. Pontecorvo12 New Small Wheels are designed to Kill the fake triggers by requiring IP pointing segment in EI (small wheel) Improve Pt resolution in Phase 2 Provide precision tracking that works up to the ultimate luminosity 5-7x10 34, with some safety margin Trigger rate reduction studied using data ~ 1/6 in 1.3<  <2.5

L. Pontecorvo13 New small wheel Requirements Provide on line reconstruction of track segments with 1 mrad accuracy. Trigger formed with coincidence of track segment from the Big Wheel BC Identification (fast detectors) High angular resolution needed to improve the trigger threshold sharpness Robust trigger against unexpected backgrounds Precision tracking to preserve position and angular resolution as good even at ultimate high luminosity, including phase-2. Cavern background foreseen in the hottest region up to 14 KHz/cm 2 Large number of high resolution space points (100  m ) High rate capability and High efficiency

L. Pontecorvo14 New small wheel: R&D phase Technologies Large R&Ds program to develop detectors for NSW small tubefine strip TGCLarge Micromegas 15 mm tube : much shorter drift time. works at x7 rate fine strip analog readout. position resolution <100  m Used for precision tracking and L1 trigger. Success of resistive anode ensuring stability against sparks. Used for precision tracking and L1 trigger. Thin gap, multi-gap RPC were also proposed for trigger Excellent time resolution but moderate space resolution

L. Pontecorvo15 sMDT 15 mm tube : much shorter drift time. works at x7 rate Mature technology But.. Resolution: degradation for very high background: marginal in the inner ring of the NSW Efficiency: For inner ring efficiencies per plane :70-80% Very good and safe solution for larger radii but at the limit in the inner ring

L. Pontecorvo16 TGC Proven technology Very high rate capability due to lower resistivity cathode > 20 KHz/cm 2 Tested up to 6 C/cm of accumulated charge Good time resolution for Bunch ID Good spatial resolution with TOT read-out about 100  m Very easy read-out segmentation: Strip plane 3 mm pitch for bending coordinate Wires on second coordinate Pads for triggering pourposes

L. Pontecorvo17 Micromegas High rate tolerance good spatial resolution good two track separation But there were/are issues Vulnerability to spark Large detector (2x1 m2) never built Now with good prospect resistive MM (innovation by ATLAS) bulk technology (industrial PCB technology) Becoming a very robust detector Additional good things possibility of track vector reconstruction (  TPC) simple concept of L1 trigger segment complementary to TGC sensitivity to cavern background : ~ 1/3 of MDT result from test chamber in ATLAS cavern (prelim.) Gain vs rate

L. Pontecorvo18 Phase-1 upgrade : Technology choice Summer 2011 formed a panel of ATLAS non-muon people. A. Romaniuk, F. Lanni, P. Farthuat, N. Kostantinidis, M. Nessi 2 days workshop held in Le Brassus in January to summarize the status of the R&D End of February 2 possible schemes suggested by the panel and Muon/NSW management: Split Solution: Tracking with Micromegas in inner ring and sMDT in the outer part Triggering with TGC Homogeneous solution: Both triggering and tracking with Micromegas and TGC over the full Small wheel area with large redundancy on both functions Muon week March. NSW workshop on 20 th, Muon IB on 22 nd. Proposed baseline : Homogeneous solution, TGC + MM Now in the process of endorsement in the Muon community

L. Pontecorvo19 Baseline layout sTGC Micromegas 4 layers each Both detectors do trigger and tracking TGC primarily trigger, MM primarily tracking Total 16 measurements (3d) along a track Very robust, flexible to cope with unexpected Common FE chip : 1 st prototype test soon

L. Pontecorvo20 Read-out: Strips, pads, wire groups – ~385,000 channels 3.2mm strips 16 sectors per wheel each wheel: 8 layers, in two quadruplets wire groups (not used in trigger, but read out on L1A) R = 3.64m, Δz = 30cm TGC basics numbers

L. Pontecorvo21 Micromegas basics numbers Total number of MM planes: 1024 Total number of chambers: sectors per wheel each wheel: 8 layers, in two quadruplets Read-out: 2 Coordinates per plane – ~2 M channels 0.5 mm strips

L. Pontecorvo22 At each BC, find local tracks that point to the Big Wheel to corroborate its coincidences. Pointing to < 1mrad precision is required. This precision is attained by finding the centroid of 3 to 5 3.2mm strips in each layer From the 8 centroids extrapolate to the Big Wheel Use pad tower coincidence to choose relevant strips BEFORE reading them out to the track finder – Reduces bandwidth – Reduces amount of centroid and track finding logic Pad trigger selects a band of strips under row of logical pads sTGC quadruplet TGC Trigger concept Measured centroids

L. Pontecorvo23 Critical milestones for the baseline Short term (end of this year) Proof of  TPC operation with resolution of 100 mm (MM) Proof of feasibility of Large chambers (MM) Proof of robustness against sparks (MM) Proof of internal alignment concepts (MM and TGC) Demonstration of Trigger concept with Test Beam Data. (TGC) Progress report on construction and industrialization (MM and TGC)

commissioning installation JD-nSW integration removal old nSW assembly + system tests integration and commissioning at CERN chambers / electr. construction module 0 qualified in beams Module 0 construction approval/organize resources TDR Design & gen R&D support structure construction Time line An idea to see if all fit L. Pontecorvo Full commissioning on surface

L. Pontecorvo25 ATLAS approval - Schedule, time line Consolidate consensus in the muon system, define critical milestones, IB endorsement Complete NSW TP (internal) kick off meetings Form consortia to work on NSW CB approval iMoU LHCC, RRB …. Real work !

L. Pontecorvo26 Interesse Italiano NSW Project: Forte interesse di gruppi italiani espresso per: La tecnologia Micromegas : Costruzione, quality control, commissioning Lo studio e la realizzazione di algoritmi di trigger e relativa elettronica

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