Matthew Jones Purdue University ICHEP 2020 1 July 29 2020 Mu2e Conversion Physics Motivation Charged lepton flavor violation is allowed in the standard model and in many models of new physics ID: 1040132
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1. The Mu2e Experiment: Beam Delivery and ExtinctionMatthew JonesPurdue UniversityICHEP 20201July 29, 2020
2. Mu2e Conversion: Physics MotivationCharged lepton flavor violation is allowed in the standard model and in many models of new physicsPredicted branching fraction:Observation would be a clear indication of physics beyond the standard model July 29, 2020ICHEP 20202
3. Searches for Charged Lepton Flavor ViolationSearches for , , July 29, 2020ICHEP 20203 Free 2-body decayMuonic atom90% C.L. LimitsBernstein and Cooper, Phys. Rep. 532: 27 (2013).
4. The Mu2e ExperimentStopping Target(aluminum foils)Detector SolenoidTransport SolenoidProton beamProduction SolenoidProduction TargetTrackerCalorimeterJuly 29, 2020ICHEP 20204Not shown here: Cosmic Ray Veto, beam extinction monitor, stopping target monitor
5. Experimental SensitivityPulsed beam experiment: protons-on-targetMuons transported to aluminum stopping targetSpecially designed tracker detects 105 MeV conversion electrons July 29, 2020ICHEP 20205
6. Pulsed Beam StructureRadiative pion capture is a potentially limiting source of backgroundPions arriving at the stopping target are in-time with the arrival of muonsJuly 29, 2020ICHEP 20206Critical parameter: beam extinction between proton pulses
7. Beam Delivery And ExtinctionJuly 29, 2020ICHEP 20207“Batches” of 8 GeV protons are injected into the Recycler RingDivided into 8 “bunches”: protons longBunches are extracted one at a time into the Delivery Ring period of circulationNatural extinction is only “Resonant” extraction removes protons on each orbit
8. Beam Extraction in Delivery RingJuly 29, 2020ICHEP 2020Unstable beam motion created by operating close to the resonant tune with significant sextupole field strengthSeparatrix defines the boundary between stable and unstable motionRate at which beam migrates to unstable orbit is modulated by injecting RF noiseExtracted pulse intensity controlled by spill monitor and a feedback system8
9. Delivery Ring Beam Extraction July 29, 2020ICHEP 20209Cathode (-100 kV)Cathode (-100 kV)Electro-static SeptumESS 2Red line is foil planeBeam between foil plane and cathode is kicked horizontally into extraction channelBeam on the other side of the foil plane sees zero fieldQuadQuadLambertsonHoriz. focus quadVert. focus quadFurther deflection of extracted beam into extraction channelLambertson Magnetic SeptumTwo channels Top channel is field freeBottom channel contains dipole field that kicks the beam vertically upwardElectro-static SeptumESS 1
10. Beam Line ExtinctionRequired extinction of beam on target is Natural extinction of extracted beam is only A magnet is used to deflect out-of-time beam:The kicker magnet needs to be pulsed every Impossible with present technologyInstead, use a system of resonant magnets (“AC dipole”) July 29, 2020ICHEP 202010
11. AC Dipole DesignJuly 29, 2020ICHEP 202011AC Dipole excited with a superposition of two harmonics: 300 kHz and 4.5 MHzTested with ½-meter and 1-meter prototypesTwo identical 3-meter vacuum vessels with individually powered 1-meter elements
12. Expected PerformanceNatural extinction from delivery ring:In-time beam transmission:Beam-line extinction:Total extinction:Satisfies extinction requirement of July 29, 2020ICHEP 202012
13. Measuring the ExtinctionRelevant parameter to measure is the extinction on beam-on-targetContinuously monitor particle production:July 29, 2020ICHEP 202013Proton beamParticles from targetCollimatorsPermanent dipole
14. Extinction Monitor SystemJuly 29, 2020ICHEP 202014High efficiency tracking of charged particles using ATLAS IBL silicon pixel sensors and FE-I4b readout chipsTotal of 8 pixel planes – permanent dipole magnet deflects low-energy secondary particles
15. Extinction Monitor SystemJuly 29, 2020ICHEP 202015Acceptance calculated to be tracks per proton-on-targetExpect tracks at nominal pulse intensityEvent reconstruction relies on pattern recognition and track countingTrigger scintillators fully efficient for any out-of-time track (numerator)Count the number of in-time tracks on the time scale of hours (denominator)Place limit on observed extinction of
16. Resonant Extraction Feedback Systems Extracted pulse intensity measured using wall-current monitorIntensity of beam-on-target measured directly with extinction monitor systemDigital feedback provided by optical linkJuly 29, 2020ICHEP 202016Rate at which beam in delivery ring migrates to extraction orbit modulated by injecting RF noise
17. Status and Schedule*Extinction monitor hardware ready for test beamTesting of electrostatic septum and AC Dipole is progressingAccelerator and beamline construction expected to be completed in 2021Beam to diagnostic absorber in early 2021Commissioning of beam delivery, extinction, and feedback systems in 2022Production, transport, and detector solenoid installation in 2022Expected project completion date in 2023July 29, 2020ICHEP 202017*Taking into account the known COVID-19 related delays so far
18. SummarySensitivity of future searches for charged lepton flavor violation rely critically on accelerator performanceBeam delivery requirements are challenging but achievableProcurement of the components needed for extraction, extinction, and monitoring are on trackRobust system for extinction monitoring has been designed – ready for test beamWe hope to show results next year at ICHEP2021!July 29, 2020ICHEP 202018