Simulations of LBNF/DUNE Muon Monitors Jeremy Lopez University of Colorado 23 January 2017
Muon Monitoring Basics More Absorber Alcoves/Stations Horns Decay Pipe Target Neutrino Pion Muon Station 1 ND Hall ● Muons + neutrinos produced in hadron decays ● Muon decays can produce more neutrinos ● Want to measure muons in alcove(s) downstream of absorber ● Typical rate of ~10 7 -10 8 muons / cm 2 / spill – Need to handle large signals ● Almost no protons, but large neutron flux – need detectors that will survive for long periods of time 1/23/17 Muon Monitoring 2
Muon Monitoring at NuMI ● This past year: ● Component failure caused upstream end of Horn 1 to be misaligned vertically by 3- 4 mm ● Was not discovered for quite some time ● Large enough to affect on-axis flux J. Hylen ● Can muon monitors find this? With sufficient manpower and good enough precision, yes. NuMI systems not quite up to task 1/23/17 Muon Monitoring 3
NuMI Muon Monitor Data MM1 Total Signal MM3 Total Signal MM1 signal decreases from October 2015 to mid-Jan. 2016, then is fairly flat MM3 signal increases from October 2015 to mid-Jan. 2016, then is fairly flat G. Brunetti https://indico.fnal.gov/conferenceDisplay.py?confId=11797 1/23/17 Muon Monitoring 4
NuMI Muon Monitor Data Position [cm] Position [cm] Position [cm] Position [cm] G. Brunetti https://indico.fnal.gov/co nferenceDisplay.py? confId=11797 1/23/17 Muon Monitoring 5
Muon Monitors for LBNF/DUNE Absorber hall & muon alcove (not to scale) ~2 m ~3.7 m iron iron pion neutrino muon Hadron absorber Station 1: Ionization Shielding & additional stations: detector array, Cherenkov Ionization detectors, stopped detector muon counters, etc ● Have several detector stations where we can measure muons ● Several detector types to measure both the spatial distribution and energy distribution of muons 1/23/17 Muon Monitoring 6
Hadron Absorber Reference Design ● Several features that may affect muon measurements – Spoiler + mask & sculpting: provide voids where muons can decay – Mask & sculpting: highly non-uniform absorber profile even near beam center – Core size: muons beyond ~60 cm from beam center travel through much more material ● These will (1) shape the signal, so the profile shape may tell us mostly about the absorber geometry, and (2) bias the signals toward the nominal beam center, so that the measured centroid or peak is always at or near the same position 1/23/17 Muon Monitoring 7
Beam Simulations ● 10 9 POT per data set ● 90 GeV proton beam, 1.6 mm beam width ● Using NuMI-style target (rectangular fins, 10 mm wide), 2 m long – Few, if any, protons hit absorber ● 3-horn optimized beamline geometry (see BOTF report) ● Exact numbers will change as beamline design is refined & finalized 1/23/17 Muon Monitoring 8
Hadron Absorber in Simulation ● Reference design Steel – Engineered for reference beam – Reference beam: 15% of protons hit absorber – Optimized beam & long target: almost no protons hit absorber Aluminum – May be able to simplify with optimized beamline Cartoon – Not to scale ● Simplified geometry: – No spoiler – No mask – No sculpting of aluminum layers Air – Wider aluminum core (1.52 m square to 2.8 m) – Much more uniform, but need to see what can be done given safety and cost constraints Cartoon – Not to scale 1/23/17 Muon Monitoring 9
What Do We Measure? Reference Absorber Simplified Absorber Y [cm] Y [cm] X [cm] X [cm] Ionization Signal Ionization Signal X Profile, X Profile, |y|<7.5 cm |y|<7.5 cm All profiles in this talk: For ionization detector just downstream of absorber, perpendicular to beam Typically: Sample every 25 cm or so (~ every 5 points in these plots) 1/23/17 Muon Monitoring 10
What Do We Measure? Initial energies of muons found in alcove Muons just downstream of absorber r < 20 cm Neutrinos associated with muons found in alcove with r<1 m from beam center ● Exponential-like distribution of muon energies in alcoves ● Initial energies above 5 GeV ● Same hadrons give neutrinos with E above 3 GeV 1/23/17 Muon Monitoring 11
Altered Beam Conditions Simulated Change Type Amount Beam X 1 mm Changes considered will generally generate deviations Beam Y 2 mm in ND total flux of 1-5% Beam Width 100 micron DocDB-1486 Horn Current 3 kA (1%) Target Density 5% More details in muon monitor Horn A X (shift) 1 mm tech notes. Horn A Y (shift) 2 mm Horn A X (tilt) 2.5 mm Horn A Y (tilt) 2.5 mm Horn B X (shift) 2.5 mm Horn B Y (shift) 2.5 mm Horn B X (tilt) 2.5 mm Horn B Y (tilt) 2.5 mm 1/23/17 Muon Monitoring 12
Changes in the Neutrino Flux at Near Detector Beam X Shift Horn A x Shift Target Density Reduction Horn A y Tilt 1/23/17 Muon Monitoring 13
Beam Shifted in X Simplified Absorber Reference Absorber Centroid: 0.04 cm Peak clearly shifted Centroid: -0.61 cm Gaus. Mean: -0.47 cm Gaus. Mean: -1.58 cm Peak at 0 Ion. Det. Signal Ion. Det. Signal Normal beam Normal beam Beam Shifted by +1 mm Beam Shifted by +1 mm Altered Beam / Nominal Beam Some asymmetry present Very clear asymmetry Ratio, Ratio, Ref. Abs. Simp. Abs. For reference absorber, still peaks at nominal beam center ● Would need to look for a small asymmetry – Simple absorber shows a much larger shift in the profile shape ● 1/23/17 Muon Monitoring 14
Horn A Shifted in Y Centroid: 3.04 cm Centroid: 2.61 cm Ref. Abs. Simp. Abs. Gaus. Mean: 5.15 cm Gaus. Mean: 3.16 cm Ion. Det. Signal Ion. Det. Signal Normal beam Normal beam Horn A Shifted by +2 mm Horn A Shifted by +2 mm Simp. Abs. Ref. Abs. Ratio Ratio ● Similar to beam shift: Hard to find changes in a fit, centroid, peak, etc for the reference absorber, but an asymmetry still present 1/23/17 Muon Monitoring 15
Target Density Reduction Reference Absorber ● At E=90 GeV, the total Ion. Det. Signal signal does not change much for the reference Normal beam absorber Target dens. reduced by 5% ● No significant change in shape Muons just downstream of Absorber, r<20 cm ● Large increase in muon flux at high energies ● Slight decrease at low energies Ratio = (fluence in altered beam)/(fluence in normal beam) 1/23/17 Muon Monitoring 16
More Ref. Abs. Ref. Abs. Horn A y Shift Horn A y Tilt (US end +2.5 mm in y, DS end -2.5 mm in y) Reduction in total flux Shape changes at max near 5 GeV ● Measurements of the flux in a narrow energy band are likely more useful than threshold measurements 1/23/17 Muon Monitoring 17
Preliminary Requirements for Physics Monitoring ● To help identify beam problems, we'll want to monitor: – Mean position stability to ~1-2 cm precision – ~5 GeV muon flux stability to 2% precision – ~8 GeV muon flux stability to 4% precision – Total muon signal stability to 1-2% precision (within 2 m x 2 m square around nominal beam center) 1/23/17 Muon Monitoring 18
Conclusions (1) ● Reference absorber design suppresses changes in the beam position – Beam profile driven by absorber geometry not beam physics – Standard statistics such as centroid, peak position, Gaussian fit mean, etc are not very meaningful – Can still look for asymmetries but would be more difficult and harder to interpret 1/23/17 Muon Monitoring 19
Conclusions (2) ● Muon spectrum measurements very important for measuring beam problems – Should measure the muon flux at least around 0, 5, and 8+ GeV – Measurements in narrow ranges with specialized spectrum- sensitive detectors (stopped muon counters, Cherenkove detectors) also useful – Exact amounts of shielding for an alcove would need some optimization (have simulated flux just downstream of absorber, not at different stations with different amounts of shielding) ● For 5 GeV, need ~3.7 m of iron shielding, 2 m more for 8 GeV ● Also possible that the reference absorber will create challenges for flux measurements 1/23/17 Muon Monitoring 20
Backup 1/23/17 Muon Monitoring 21
10% increase in flux In some energy bins between 2015 and 2016 Rui Chen NuMIX-doc 127 1/23/17 Muon Monitoring 22
Ionization Detectors ● Create an array of detectors to sample ionizing particles ● Measure the transverse beam profile ● Can extract information such as: – Overall signal intensity – Peak position/signal centroid (i.e. direction) – Width – Timing (with solid state detectors) ● Monitoring: Look for changes (event to event or long term trends) in signals Possible technologies: Example beam profile Ion chambers Place detectors at ~25 cm intervals Solid state (diamond, silicon) Secondary emission detectors (for very high flux) 1/23/17 Muon Monitoring 23
Threshold Cherenkov Detectors ● Gas density determines Cherenkov threshold ● Fast signals, measures ● If left alone: Monitor flux for some particular subset of muon kinematics ● Can also scan over gas density, detector angle to constrain the muon spectrum at many different points with a single detector 1/23/17 Muon Monitoring 24
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