Muon g 2 in 10 (ish) minutes 11 June 2019 New Perspectives 2019 - PowerPoint PPT Presentation

Muon g – 2 in 10 (ish) minutes 11 June 2019 New Perspectives 2019 Jason Hempstead (on behalf of the Muon g – 2 collaboration)

Outline • The physics of g μ – 2 – Magnetic dipole moments – Standard model calculation – Past experiments • Fermilab E989 – Experimental technique – Current status 2 11 June 2019 Jason Hempstead | New Perspectives 2019

Outline • The physics of g μ – 2 – Magnetic dipole moments – Standard model calculation – Past experiments • Fermilab E989 – Experimental technique – Current status 3 11 June 2019 Jason Hempstead | New Perspectives 2019

Magnetic dipole moment Applied • Spin will precess about an external field magnetic field – At a rate dependent on the size of the magnetic moment Spin 𝜈 " • Dirac calculated g = 2 – Later, Schwinger calculated a correction due to a photon loop in the vertex 𝛿 • Define the “magnetic anomaly” – this is what we are measuring 𝜈 " 4 11 June 2019 Jason Hempstead | New Perspectives 2019

Standard model calculation • Value of 𝑏 % sensitive to all particles – New physics would show up in difference between SM calculation and measurement • Calculation split into 4 categories, organized by what particles are loopy: – QED • Leptons and photons – Hadronic • Vacuum polarization (HVP) • Light-by-light (HLbL) – Weak • Higgs, Z, W 5 11 June 2019 Jason Hempstead | New Perspectives 2019

Brookhaven (BNL) E821 measurement • Results of most recent measurement at Brookhaven E821 hint at something unknown… 3.7 σ 6 11 June 2019 Jason Hempstead | New Perspectives 2019

Outline • The physics of g μ – 2 – Magnetic dipole moments – Standard model calculation – Past experiments • Fermilab E989 – Experimental technique – Current status 7 11 June 2019 Jason Hempstead | New Perspectives 2019

To resolve this… 8 11 June 2019 Jason Hempstead | New Perspectives 2019

Fermilab E989 • 4x the precision of BNL – 540 parts per billion (ppb) à 140 ppb • 100 ppb statistical uncertainty – ≈ 10 )) collected positrons – Roughly 21x the statistics taken at BNL 3.7 σ 7.0 σ • 100 ppb systematic uncertainty – 70 ppb for magnetic field measurement – 70 ppb for spin precession frequency 9 11 June 2019 Jason Hempstead | New Perspectives 2019

Measuring 𝒃 𝝂 with a storage ring • Inject polarized muons into highly uniform 1.45 T field – High energy positrons preferentially emitted in direction of spin ≈ 0 for motion transverse to magnetic field ≈ 0 for muons at “magic” momentum Momentum vector 3.1 GeV / c or 𝛿 = 29.3 Spin vector 10 11 June 2019 Jason Hempstead | New Perspectives 2019

Measuring 𝒃 𝝂 with a storage ring • Inject polarized muons into highly uniform 1.45 T field – High energy positrons preferentially emitted in direction of spin • Record data in 700 μ s “fills” – 10 (boosted) lifetimes of muon precession data • Magnetic field measured in terms of the Larmor Momentum vector precession frequency of the free proton, 𝜕 2 Spin vector 11 11 June 2019 Jason Hempstead | New Perspectives 2019

Getting a number for g μ – 2 • Combination of constants measured very well 12 11 June 2019 Jason Hempstead | New Perspectives 2019

Fermilab Muon g – 2 (E989) Protons and 8 GeV 3.1GeV protons Protons and Target muons separated protons and pions polarized muons 13 11 June 2019 Jason Hempstead | New Perspectives 2019

Understanding injection • Beam entrance counters: – T0 • Scintillating paddle coupled to 2 PMTs • Provides absolute injection time – Inflector Beam Monitoring System (IBMS) • Series of 3 detectors along beam path • Scintillating fibers coupled to silicon photomultipliers (SiPMs) • Spatial profile of beam 14 11 June 2019 Jason Hempstead | New Perspectives 2019

Storing muons to watch them precess • Superconducting inflector – Cancels out magnetic field to allow injection μ + 15 11 June 2019 Jason Hempstead | New Perspectives 2019

Storing muons to watch them precess • Superconducting inflector – Cancels out magnetic field to allow injection • Magnetic kickers – Deflect muons onto the proper orbit μ + 16 11 June 2019 Jason Hempstead | New Perspectives 2019

Storing muons to watch them precess • Superconducting inflector – Cancels out magnetic field to allow injection • Magnetic kickers – Deflect muons onto the proper orbit • Electrostatic quadrupoles μ + – Provide vertical focusing μ + Cross-section of storage region 17 11 June 2019 Jason Hempstead | New Perspectives 2019

Measuring the magnetic field ( 𝝏 𝒒 ) • Nuclear magnetic resonance (NMR) probes (x17) on a trolley to survey the muon storage region periodically – When no beam present – Measures Larmor precession of the protons in petroleum jelly samples • 378 additional probes outside the storage region to monitor continuously • Very well understood water sample to calibrate the trolley probes 18 11 June 2019 Jason Hempstead | New Perspectives 2019

Measuring the magnetic field ( 𝝏 𝒒 ) • Nuclear magnetic resonance (NMR) probes (x17) on a trolley to survey the muon storage region periodically – When no beam present – Measures Larmor precession of the protons in petroleum jelly samples • 378 additional probes outside the storage region to monitor continuously • Very well understood water sample to calibrate the trolley probes 19 11 June 2019 Jason Hempstead | New Perspectives 2019

Measuring beam distribution • 2 stations of straw tracking detectors – Extrapolate positron tracks to decay position • Provide information about location of beam – 𝜕 2 → 6 𝜕 2 G. Lukicov. High precision track-based alignment of the tracking detector of the g-2 experiment (poster). Fermilab Users Meeting 2019. 20 11 June 2019 Jason Hempstead | New Perspectives 2019

Measuring beam distribution • 2 stations of straw tracking detectors – Extrapolate positron tracks to decay position • Provide information about location of beam – 𝜕 2 → 6 𝜕 2 G. Lukicov. High precision track-based alignment of the tracking detector of the g-2 experiment (poster). Fermilab Users Meeting 2019. 21 11 June 2019 Jason Hempstead | New Perspectives 2019

Measuring the precession frequency ( 𝝏 𝒃 ) • Use electromagnetic calorimeters – 24 equally spaced around ring – Each is a 9x6 grid of lead fluoride (PbF 2 ) Decay positron curling inward from the crystals read out individually by SiPMs muon storage orbit to strike a calorimeter J. Hempstead. Preparing the Muon g – 2 calorimeters for Run 2 (poster). Fermilab Users Meeting 2019. 22 11 June 2019 Jason Hempstead | New Perspectives 2019

Measuring the precession frequency ( 𝝏 𝒃 ) • Use electromagnetic calorimeters – 24 equally spaced around ring – Each is a 9x6 grid of lead fluoride (PbF 2 ) crystals read out individually by SiPMs • 𝜕 7 = 𝜕 8 − 𝜕 : is imprinted in the number of positrons in a given direction N hits over threshold vs. time after injection c c 2 2 / ndf / ndf 2544 / 2472 2544 / 2472 – Cut on positron energy 5 N over threshold / 149.2 ns 10 Prob Prob 0.1526 0.1526 ± ± N N 6.118e+04 6.118e+04 2.786e+01 2.786e+01 0 0 t t ± ± 64.32 64.32 0.02 0.02 ± ± A A 0.356 0.356 0.000 0.000 f f - - ± ± 2.148 2.148 0.002 0.002 - - ± ± R R 24.01 24.01 11.04 11.04 • Fit using 4 10 M. Bhattacharya. Pileup Systematic Studies in the Fermilab 30 40 50 60 70 80 90 100 µ Time after injection [ s] Muon g-2 Experiment. New Perspectives 2019. 23 11 June 2019 Jason Hempstead | New Perspectives 2019

Laser system • Track and correct gain of individual channels in calorimeters • Timing alignment of individual channels – Synchronization laser pulse at the beginning of every fill 24 11 June 2019 Jason Hempstead | New Perspectives 2019

Current status • Run 1 analysis underway – About 1.4x the statistics of the E821 result (in 𝜕 7 fit) – Magnetic field uniformity about 2x better 60 hours Vertical (cm) R-R 0 (cm) 25 11 June 2019 Jason Hempstead | New Perspectives 2019

Current status • Run 1 analysis underway – About 1.4x the statistics of the E821 result (in 𝜕 7 fit) – Magnetic field uniformity about 2x better • Run 2 in progress – Currently collected ~1.8x the statistics of E821 – Improved stability of run conditions S. Ganguly. Muon g-2: Measuring the anomalous magnetic dipole moment of a muon to high precision. Fermilab Users Meeting 2019. 26 11 June 2019 Jason Hempstead | New Perspectives 2019

Thanks! 27 11 June 2019 Jason Hempstead | New Perspectives 2019

Back-up 28 11 June 2019 Jason Hempstead | New Perspectives 2019