The MUSE Experiment at PSI

Transcription

1 International Workshop on Precision Physics of Simple Atomic Systems (PSAS2016) Jerusalem, Israel, May 22-27, The MUSE Experiment at PSI Michael Kohl <kohlm@jlab.org> * Hampton University, Hampton, VA Jefferson Laboratory, Newport News, VA * Supported by DOE awards DE-SC and DE-SC

2 MUSE: MUon Scattering Experiment at PSI 2 Appollo and the nine muses

3 MUSE: MUon Scattering Experiment at PSI Motivation Proposed experiment Muon beamline Detector Expected sensitivity Status & Schedule 3 NY Times, July 12,

4 The proton radius puzzle in the media 4 R. Pohl et al., Nature 466, (2010)

5 The proton radius puzzle in the media July 2010 January

6 The proton radius puzzle in the media 6 April 2013

7 The proton radius puzzle in the media 7 July 2013

8 The proton radius puzzle in the media January

9 The proton radius puzzle in the media January

10 The proton radius puzzle 10 >7σ (4%) discrepancy between muonic and electronic measurements High-profile articles in Nature, NYTimes, etc. Puzzle unresolved, possibly New Physics Muonic R p = 0.84 fm Electronic R p = 0.88 fm Spectroscopy Scattering R P = (67) fm R P = 0.875(10) fm R P = (51) fm R P = (39) fm

11 The proton radius puzzle 11 The proton rms charge radius measured with electrons: ± fm (CODATA2010+Zhan et al.) muons: ± fm R. Pohl et al., Nature 466, 213 (2010) A. Antognini et al., Science 339, 417 (2013) Proton charge radius (fm)

12 The proton radius puzzle 12 The proton rms charge radius measured with electrons: ± fm (CODATA2010+Zhan et al.) muons: ± fm R. Pohl et al., Nature 466, 213 (2010) A. Antognini et al., Science 339, 417 (2013) Belushkin, Hammer, Meissner PRC 75, (2007) Lorenz, Hammer, Meissner EPJ A 48, 151 (2012) Proton charge radius (fm)

13 The proton radius puzzle 13 The proton rms charge radius measured with electrons: ± fm (CODATA2014) muons: ± fm 5.6 σ R. Pohl et al., Nature 466, 213 (2010) A. Antognini et al., Science 339, 417 (2013) Belushkin, Hammer, Meissner PRC 75, (2007) Lorenz, Hammer, Meissner EPJ A 48, 151 (2012) Proton charge radius (fm)

14 Possible resolutions to the puzzle 14 The ep (scattering) results are wrong Fit procedures not good enough Q 2 not low enough, structures in the form factors The ep (spectroscopy) results are wrong Accuracy of individual Lamb shift measurements? Rydberg constant could be off by 5 sigma The µp (spectroscopy) result is wrong Discussion about theory and proton structure for extracting the proton radius from muonic Lamb shift measurement Proton structure issues in theory Off-shell proton in two-photon exchange leading to enhanced effects differing between µ and e Hadronic effects different for µp and ep: e.g. proton polarizability (effect m l4 ) Physics beyond Standard Model differentiating µ and e Lepton universality violation, light massive gauge boson Constraints on new physics e.g. from kaon decays

15 New measurements are on their way 15 Additional measurements needed / in preparation Spectroscopy with µd, µhe, and regular H; Rydberg constant ep-, ed-scattering (PRad at Jlab, ISR-ep and ed elastic at MAMI; MESA) µ ± p- and e ± p-scattering in direct comparison at PSI (MUSE) Searches for lepton universality violating light bosons (e.g. kaon decays such as TREK/E36 at J-PARC) r p (fm) ep µp Spectroscopy ± ± Scattering ± 0.060??? Need more precision for extraction from scattering More insights from comparison of ep and µp scattering

16 Mainz ep scattering at low Q2 MAMI A1 J. Bernauer et al. PRL105 (2010) Rosenbluth separation at low Q2 Precise charge and magnetic rms radii: RE = ± fm RM = 0.777± fm 16

17 Proton radius from Mainz A1 data 17 GE(Q 2 ) = 1 - Q 2 r 2 / Low Q 2 J. Bernauer et al., PRL105 (2010) Left: world + Mainz fit; Middle: Mainz raw data; Right rebinned GE Large difference in slope between r = 0.84 and 0.88 fm Floating normalization, higher-order Q 2 terms present Controversies about radius extraction dependence on fit model Need yet higher precision

18 The PRad proton radius proposal (JLAB) 18 Low intensity beam in Hall Jlab into windowless gas target Scattered ep and Moller electrons into HYCAL at 0 o Lower Q 2 than Mainz. Very forward angle, insensitive to 2γ, GM Conditionally approved by PAC38 (Aug 2011): ``Testing of this result is among the most timely and important measurements in physics. Approved by PAC39 (June 2012), graded A Scheduled to run in Hall B in May-June 2016 (just started)

19 Initial state radiation (ISR) at MAMI 19 Radiative tail dominated by coherent sum of two Bethe-Heitler diagrams 2 Q Reconstruct 2 2 Q Vertex + = In data ISR can not be distinguished from FSR Combining data and simulation, ISR and form factor can be extracted Q 2 (Reconstructed) > Q 2 (Vertex for ISR) Idea behind new MAMI experiment to extract G p E at lowest Q 2 ~ 10-4 (GeV/c) 2 Method tested at higher Q 2 Data taken in 2014, under analysis

20 Search for a new particle in K + µ + ν e + e - 20 QED background: K + µ + ν e + e - Γ(K + µ + ν ee) ~ 2.5 x 10-5 Expect stopped K + in E36 250k QED evts or ~1000 / MeV Signal: K + µ + ν Α, Α e + e - C. Carlson, B. Rislow, hep-ph/ Phys. Rev. D89, (2014) same background! Dark photon model (universal coupling) Γ(K + µ + ν Α ) ~ 10-9 Batell model (univ.-violating, right-handed muons) Γ(K + µ + ν Α ) ~ B. Batell, D. McKeen, and M. Pospelov, PRL107, (2011),

21 Search for a new particle in K + µ + ν e + e - 21 QED background: K + µ + ν e + e - Γ(K + µ + ν ee) ~ 2.5 x 10-5 Expect stopped K + in E36 250k QED evts or ~1000 / MeV Signal: K + µ + ν Α, Α e + e - C. Carlson, B. Rislow, hep-ph/ Phys. Rev. D89, (2014) same background! Carlson&Rislow model (universality-violating, fine tuned); Γ(K + µ + ν Α ) ~ HUGE signals predicted, J-PARC TREK/E36 stringent test

22 Motivation for µp scattering 22 Electronic hydrogen Spectroscopy Muonic hydrogen ± ± ± Electron scattering ± Scattering Muon scattering???

23 Lepton scattering and charge radius 23 Lepton scattering from a nucleon: Vertex currents: µ ±, e ± F 1, F 2 are the Dirac and Pauli form factors Sachs form factors: Derivative in Q 2 0 limit: Fourier transform (in the Breit frame) gives spatial charge and magnetization distributions Expect identical result for ep and µp scattering

24 Lepton scattering and charge radius 24 Lepton scattering from a nucleon: Vertex currents: µ ±, e ± F 1, F 2 are the Dirac and Pauli form factors Sachs form factors: Derivative in Q 2 0 limit: Fourier transform (in the Breit frame) gives spatial charge and magnetization distributions Expect identical result for ep and µp scattering

25 e-µ universality in lepton scattering s-1970s: several experiments tested e-µ universality in scattering Elastic µp scattering: Ellsworth et al., Phys. Rev. 165 (1968) Elastic µp: Kostoulas et al., PRL 32 (1974) no difference 1/Λ 2 = ± GeV -2 Data ~ 15% low DIS µp scattering: Entenberg et al., PRL 32 (1974) σµp/σep 1.0 ± 0.04 (±8.6% systematics) e-c, and µ-c are in agreement Constraints are not very good

26 e-µ universality in lepton scattering s-1970s: several experiments tested e-µ universality in scattering Elastic µp scattering: Ellsworth et al., Phys. Rev. 165 (1968) Elastic µp: Kostoulas et al., PRL 32 (1974) no difference 1/Λ 2 = ± GeV -2 Data ~ 15% low DIS µp scattering: Entenberg et al., PRL 32 (1974) σµp/σep 1.0 ± 0.04 (±8.6% systematics) e-c, and µ-c are in agreement Constraints are not very good

27 Two-photon exchange tests in µp-elastic 27 L. Camilleri et al., PRL23, 149 (1969) No evidence for two-photon exchange effects Constraints are not very good Rosenbluth plots linear

28 MUon Scattering Experiment (MUSE) at PSI Use the world s most powerful low-energy separated e/π/µ beam for a direct test if µp and ep scattering are different: to higher precision than previously in the low Q2 region, similar to Mainz (Bernauer) and JLab (Zhan) for sensitivity to radius measure both µ±p and e±p for direct comparison and a robust, convincing result depending on the results, 2nd generation experiments (lower Q2, µ±n,d,he, higher Q2,...) might be desirable 28

29 MUon Scattering Experiment (MUSE) at PSI Use the world s most powerful low-energy separated e/π/µ beam for a direct test if µp and ep scattering are different: Simultaneous, separated beam of (e+/π+/µ+) or (e-/π-/µ-) on liquid H2 target Separation by time of flight Measure absolute cross sections for ep and µp If radii differ by 4%, then form factor slope by 8%, x-section slope by 16% Measure e+/µ+, e-/µ- ratios to cancel certain systematics Directly disentangle effects from two-photon exchange (TPE) in e+/e-, µ+/µ Multiple beam momenta MeV/c to separate GE and GM (Rosenbluth) 29

30 πm1 / MUSE beamline 30 LH 2 target Intermediate Focus Dispersion 7cm/% π, µ, e πm1: MeV/c Momentum selective RF+TOF separated π, µ, e Limited beam flux (5 MHz) Large angle, non-magnetic detectors to detect leptons Secondary beam Tracking of beam particles to target Mixed beam Identification of beam particle in trigger protons

31 MUSE experiment layout 31 Beam particle tracking Liquid hydrogen target Scattered lepton detection Measure e ± p and µ ± p elastic scattering p = 115, 153, 210 MeV/c Θ = 20 o to 100 o Q 2 = (GeV/c) 2 ε = Challenges Secondary beam with π background Non-magnetic spectrometer Background from Møller scattering and muon decay in flight

32 Separation of e, π, µ by RF time 32 Requirement: particle separation in time for PID 50 MHz RF 20 ns between bunches Timing of particles in target region wrt electron (β = 1) Minimum time separation of particles in target region p = 115, 153, and 210 MeV/c

33 Beamline and target considerations 33 Target: 4 cm LH2, thickness constrained by effects of multiple scattering p= 115 MeV/c % change in cross section for θ ms = 10 mr Target thickness giving θ ms = 10 mr Limits acceptance to > 20 o Limits target thickness to 0.3 g/cm 2 Fast TOF counters in beamline (for RF time) and scattered particle detector (for TOF) for trigger, PID, background suppression

34 Background considerations 34 Requirement: low backgrounds or background rejection Scattering from electrons: Muons from π decays π, µ 210 MeV/c π µν Møller/Bhabha 153 MeV/c π µν Recoil e's 115 MeV/c π µν π, µ at forward angles e-,e+ <10 MeV above 15 o Recoil e's low momentum Will have π RF time (3 orders of magnitude suppression) Track will not point back to the target Suppression of µ eνν background with offline time-of-flight (8-20 σ) Suppression of Møller/Bhabha background with beam scintillator anticoincidence

35 Scattered particle considerations 35 Large angle, very low energy Møller / Bhabha e s lose large fraction of energy in target Recoil protons E loss so large that all except forward angle recoil protons stopped in target All the low-energy electron and proton backgrounds are ranged out in the first scintillator layer

36 Beamline instrumentation 36 Beamline Elements: e/π/µ separated in,me Thin Scintillators GEM chambers target Beam Scintillator Thin scintillators with SiPM+CFD readout (PSI/Rutgers/TAU): Fast timing (~60ps): beam TOF (RF time), scattered particle TOF Flux, PID, Trigger, TOF, momentum GEM telescope (Hampton University) Incident track angle to ~0.5 mr intrinsic; <5 mr mult.sc. Third GEM to reject ghost tracks Existing chambers from OLYMPUS 3 GEMs 10x10 cm 2 from OLYMPUS@DESY 36

37 Target and veto 37 Low-power liquid hydrogen target (GWU) Advanced conceptual design Geant4 implementation Veto scintillators (USC): Annullar veto ring defines accepted beam aperture, smaller than transverse target cell diameter (6 cm)

38 Main detector instrumentation 38 University of South Carolina: 2 planes of scintillators (CLAS12 design) 94 bars (2 sides + beam) High precision (~50ps) timing PID and trigger, background rejection HUJI & Temple: Straw Tube Tracker (STT), ~3000 straws Determine scattered particle trajectory Existing PANDA design 140 µm resol. Thin walls (25µm), overpressured (2 bar) Directly coupled to fast readout boards

39 Trigger and DAQ 39 GWU, Montgomery College & Rutgers: FPGA design for beam PID (TRB or v1495) Beam scintillator + beam RF beam PID Count particles and reject pions e or µ beam part. + scattered part. + no veto Custom signal splitters FPGAs as front end discriminator/amplifier, custom designed TDCs (PADIWA/TRB3) High channel density (192ch/board) VME QDCs (MESYTEC)

40 Mechanical assembly 40 T. O Connor (ANL) Rotating table Retractable beam tracker Dedicated alignment procedures

41 MUSE test beamtimes MUSE Test Runs to characterize pim1 beam to test detector prototypes (scintillators, Cerenkov, straw tubes) to study and optimize GEM performance Oct 2012 May 2013 July 2013 Oct 2013 (Cosmics) Dec 2013 June 2014 Dec 2014 Feb 2015 (Cosmics) June-July 2015 Dec 2015 May 2016 Representation from 13 institutions 12th run scheduled for June-July 2016

42 First beam tests 42 e + µ + π + e - Time of flight relative to RF time (Fall 2012) µ - π - Beam spot with GEM May 23, 2013

43 Composition of the πm1 secondary beam 43 Beam test result from December 2013

44 3D beam tomography 44

45 Simulations (S. Strauch, USC) 45 Particle vertex and scattering-angle reconstruction meet MUSE requirements Background from target walls and windows can be cleanly eliminated or subtracted ee ep

46 Simulations (S. Strauch, USC) 46 Muon decay-in-flight background can be removed with time-of-flight measurements Møller/Bhabha scattering events can be efficiently suppressed with event-veto from the beamline monitor detector

47 Projected sensitivity for MUSE 47 Cross sections to <1% stat. for backward µ, <<1% for e and forward µ Absolute 2%, point-to-point relative uncertainties few x10-3 Individual radius extractions from e ±, µ ± each to 0.01 fm

48 Projected sensitivity for MUSE 48 Cross sections to <1% stat. for backward µ, <<1% for e and forward µ Absolute 2%, point-to-point relative uncertainties few x10-3 Individual radius extractions from e ±, µ ± each to 0.01 fm Compare e ± xsecs and µ ± xsecs for TPE. Charge-average to eliminate TPE. From e/µ xsec ratios: extract e-µ radius difference with minimal truncation error to fm or ~8σ (1st-order fits) If no difference, extract radius to fm (2nd-order fit)

49 Projected sensitivity for MUSE 49 Charge radius extraction limited by systematics, fit uncertainties Many uncertainties are common to all extractions in the experiments: Cancel in e+/e-, µ+/µ-, and µ/e comparisons R e -R µ = 0.034±0.006 fm (5.6σ), MUSE: δr = fm (7.6σ) MUSE suited to verify 5.6σ effect (CODATA2014) with even higher significance

50 MUSE activities and status 50 Proton puzzle alive and well in 2016 MUSE first proposed in 2012 R&D program with NSF, BSF, and DOE support since mid 2014 Test beamtimes in June, July and December 2015 Mini-workshop with PSI PAC subcommittee in July 2015 Technical design report November 2015 Collaborative funding proposal at NSF in Nov NSF mid-scale NSF technical review February 2016 four main charges to be addressed PSI PAC February 2016 Restructuring in February 2016: New project management (R. Gilman); E. Downie, G. Ron, S. Strauch (spokespeople) Target conceptual design March 2016 MOU with PSI April 2016 Test beamtime to demonstrate STT performance May 2016 Project management review May 2016 Funding for construction hoped/expected to begin in fall 2016 Construct and commission MUSE experiment Data taking 2x 6 months in

51 MUon Scattering Experiment MUSE MUSE collaborators from 24 institutions in 5 countries: A. Afanasev, A. Akmal, J. Arrington, H. Atac, C. Ayerbe-Gayoso, F. Benmokhtar, N. Benmouna, J. Bernauer, A. Blomberg, E. Brash, W.J. Briscoe, E. Cline, D. Cohen, E.O. Cohen, K. Deiters, J. Diefenbach, B. Dongwi, E.J. Downie, L. El Fassi, S. Gilad, R. Gilman, K. Gnanvo, R. Gothe, D. Higinbotham, Y. Ilieva, L. Li, M. Jones, N. Kalantarians, M. Kohl, G. Kumbartzki, J. Lichtenstadt, W. Lin, A. Liyanage, N. Liyanage, Z.-E. Meziani, P. Monaghan, K.E. Mesick, P. Moran, J. Nazeer, C. Perdrisat, E. Piasetzsky, V. Punjabi, R. Ransome, D. Reggiani, P.E. Reimer, A. Richter, G. Ron, T. Rostomyan, A. Sarty, Y. Shamai, N. Sparveris, S. Strauch, V. Sulkosky, A.S. Tadepalli, M. Taragin, and L. Weinstein George Washington University, Montgomery College, Argonne National Lab, Temple University, College of William & Mary, Duquesne University, Massachusetts Institute of Technology, Christopher Newport University, Rutgers University, Hebrew University of Jerusalem,,Tel Aviv University, Paul Scherrer Institut, Johannes Gutenberg-Universität, Hampton University, University of Virginia, University of South Carolina, Jefferson Lab, Los Alamos National Laboratory, Norfolk State University, Technical University of Darmstadt, St. Mary s University, Soreq Nuclear Research Center, Ieizmann Institute, Old Dominion University

52 MUon Scattering Experiment MUSE 52 Proton Radius Puzzle still unresolved ~6 years later MUSE Experiment at PSI Measure µp and ep scattering and compare µ+/e+ and µ-/e- directly Measure e+/e- and µ+/µ- to study/constrain TPE effects Technical Challenges PID, timing, background rejection, momentum and flux determination Timeline Initial proposal February 2012 Technical review July 2012 First beam tests in fall 2012 PAC-approved in January 2013 Further beam tests 2x yearly in summer and fall Funding & construction Production running (2x 6 months)

53 Backup 53

54 PSI muonic hydrogen measurements 54 R. Pohl et al., Nature 466, (2010): 2S 2P Lamb shift ΔE(meV) = (49) rp rp 3 rp = ± fm Possible issues: atomic theory & proton structure UPDATE: A. Antognini et al., Science 339, 417 (2013): 2S 2P Lamb + 2S-HFS ΔE L (mev) = (15) (10)rp (20) TPE rp = ± fm

55 JLAB ep scattering at low Q 2 55 Hall A PR07-004, PR (PAC31/33) Recoil polarization, completed 2008 Polarized target, completed 2012 BLAST (polarized target) C. Crawford et al., PRL98 (2007) X. Zhan, E LEDEX update Phys. Lett. B 705 (2011) 59 2-sigma difference lower than BLAST Charge and magnetic rms radii: R E = ± fm R M = ± fm

56 TREK (E36) at J-PARC 56 Measurement of Γ(K + e + ν)/γ(k + µ + ν) and Search for heavy sterile neutrinos using the TREK detector system Official website: Data taking completed in 2015

57 Carbon radius and e-µ universality C radius determinations from ec scattering, µc scattering, and µc atoms agree Cardman et al. ec: ± fm Offermann et al. ec: ± fm Schaller et al. µc X rays: ± fm Ruckstuhl et al. µc X rays: ± fm Sanford et al. µc elastic: fm If carbon is right e s and µ s are the same If hydrogen is right e s and µ s are different If both are right - opposite effects for proton and neutron canceling in carbon? Investigate µd, µhe Muonic H + eh/d isotope shift r d = (22) fm (A. Antognini et al.) ed elastic scattering: r d = 2.130(10) fm Muonic D consistent (preliminary, unpublished, large polarizability correction)