Studies of the muon transfer process in a mixture of hydrogen and higher Z gas with FAMU

Transcription

1 Studies of the muon transfer process in a mixture of hydrogen and higher Z gas with FAMU the path towards the precision spectroscopic measurement of the hyperfine splitting (hfs) in the 1S state of muonic hydrogen E hfs(μ -p)1s Emiliano Mocchiutti and Andrea Vacchi on behalf of the FAMU Collaboration International Conference on Precision Physics and Fundamental Physical Constants (FFK-2017) Warsaw, May 2017

2 PAMELA FAMU Collaboration meetings INFN Trieste: V. Bonvicini, E. Furlanetto, E. Mocchiutti, C. Pizzolotto, A. Rachevsky, L. Stoychev, A. Vacchi (also Università di Udine), E. Vallazza, G. Zampa, Elettra- Sincrotrone: M. Danailov, A. Demidovich, ICTP: J. Niemela, K.S. Gadedjisso-Tossou INFN Bologna: L. Andreani, G. Baldazzi, G. Campana, I. D'Antone, M. Furini, F. Fuschino, A. Gabrielli, C. Labanti, A. Margotti, M. Marisaldi, S. Meneghini, G. Morgante, L. P. Rignanese, P. L. Rossi, M. Zuffa INFN Milano Bicocca: A. Baccolo, R. Benocci, R. Bertoni, M. Bonesini, T. Cervi, F. Chignoli, M. Clemenza, A. Curioni, V. Maggi, R. Mazza, M. Moretti, M. Nastasi, E. Previtali, R. Ramponi (also Politecnico Milano CNR) INFN Pavia: A. De Bari, C. De Vecchi, A. Menegolli, M. Rossella, R. Nardò, A. Tomaselli INFN Roma3: L. Colace, M. De Vincenzi, A. Iaciofano, L. Tortora, F. Somma INFN Seconda Università di Napoli: L. Gianfrani, L. Moretti INFN GSSI: D. Guffanti, RIKEN-RAL: K. Ishida INP, Polish Academy of Sciences: A. Adamczak INRNE, Bulgarian Academy of Sciences: D. Bakalov, M. Stoilov, P. Danev 2

3 Outline Introduction The FAMU experiment Beam test at RAL (2014/2016) Spectral lines measurements Muonic transfer rate measurements Present status and future measurements Summary 3

4 Introduction 4

5 Fundamental physics Study of the properties of the proton u 2010: first measurement of the proton radius from muonic hydrogen. 2017: the proton radius puzzle persists... u d Muonic hydrogen transitions ~7 σ Electron transitions or electron scattering 5

6 FAMU: HFS of µ - p ground level 1) scattering: electron experiments 2) scattering: elastic muon-proton 3) spectroscopy: electronic atoms and ions 4) spectroscopy: exotic atoms HFS of muonic hydrogen ground level 6

7 FAMU: a worthwhile challenge First measurement of the HFS of (μ - p) 1S New and different measurement respect to PSI results Better estimate of Zemach radius Different systematics respect previous experiments Laser developement Muon transfer studies hyperfine structure 7

8 A long time ago in a lab far, far away... 8

9 HFS of (μ - p) 1S : a ~25 years old idea 9

10 HFS of (μ - p) 1S : a ~25 years old idea o(mev) 300K, 10 atm, H2 pressurized target µp E k1 µp high intensity muon beam µ µp* µp E k2 µp Au layers laser 183 mev collision with H2 molecules: de-excitation and Ek gain E k2 > E k1 time distribution of delayed X-rays changes 10

11 HFS of (μ - p) 1S : a ~25 years old idea o(mev) 300K, 10 atm, H2 pressurized target µp E k1 µp high intensity muon beam µ µp* µp E k2 µp laser how to efficiently illuminate the gas? laser 183 mev collision with H2 molecules: de-excitation and Ek gain E k2 > E k1 time distribution of delayed X-rays changes 11

12 HFS of (μ - p) 1S : a ~25 years old idea o(mev) 300K, 10 atm, H2 pressurized target µp E k1 µp high intensity muon beam µ µp* µp E k2 µp laser how to efficiently illuminate the gas? laser 183 mev collision with H2 molecules: de-excitation and Ek gain E k2 > E k1 time distribution of delayed X-rays changes 12

13 HFS of (μ - p) 1S : a ~25 years old idea o(mev) 300K, 10 atm, H2 pressurized target µp E k1 µp high intensity muon beam µ µp* µp E k2 µp laser how to efficiently illuminate the gas? laser 183 mev collision with H2 molecules: de-excitation and Ek gain E k2 > E k1 time distribution of delayed X-rays changes 13

14 The FAMU experiment Fisica Atomi MUonici (Physics with muonic atoms) 14

15 FAMU: μ - p spectroscopy Usual spectroscopy flow: 1) create muonic hydrogen 2) laser excitation 3) count triplets repeat varying laser energy ( E) to find resonance value. How is it possible to distinguish HFS excited states? Hyperfine splitting of (μ - p) 1S ~183 mev... 15

16 μ - transfer rate to high-z atoms is energy dependent Usual spectroscopy flow: 1) create muonic hydrogen 2) laser excitation 3) count triplets repeat varying laser energy ( E) to find resonance value. How is it possible to distinguish HFS excited states? Hyperfine splitting of (μ - p) 1S ~183 mev... Key point: The muon transfer rate to higher-z atoms in collisions is (kinetic) energy dependent at epithermal energies (~100/200 mev) 16

17 μ - transfer rate to high-z atoms is energy dependent Key point: The muon transfer rate to higher-z atoms in collisions is (kinetic) energy dependent at epithermal energies (~100/200 mev) H. Schneuwly, Z. Phys. C - Particles and Fields 56, 280 (1992). R. Jacot-Guillarmod, Muon transfer from thermalized muonic hydrogen isotopes Phys. Rev. A51, 2179 ~1995. F. Mulhauser and H. Schneuwly, J. Phys. B 26, 4307 ~1993. L. Schellenberg, P. Baeriswyl, R. Jacot-Guillarmod, B. Mis- chler, F. Mulhauser, C. Piller, and L. A. Schaller, in Muonic Atoms and Molecules, edited by L. A. Schaller and C. Petitjean ~Birkhaüser-Verlag, Basel, 1993, p R. Jacot-Guillarmod, F. Bienz, M. Boschung, C. Piller, L. A. Schaller, L. Schellenberg, H. Schneuwly, W. Reichart, and G. Torelli, Phys. Rev. A 38, 6151 ~1988. A. Werthmüller, A. Adamczak, R. Jacot-Guillarmod, F. Mulhauser, C. Piller, L. A. Schaller, L. Schellenberg, H. Schneu- wly, Y.-A. Thalmann, and S. Tresch, Hyperfine Interact. 103, 147~1996. A. Werthmüller et. al. Energy dependence of the charge exchange reaction from muonic hydrogen to oxygen ; Hyperfine Interactions 116 (1998)

18 FAMU workflow: μ - p generation 1. Create muonic hydrogen and wait for thermalization 18

19 FAMU workflow: laser flash 2. Laser! at resonance (λ 0 ~6.8µ) spin state of µ - p from 1 1 S 0 to 1 3 S 1, spin is flipped: µ p( ) µ p( ) ; 3. µ - p (1 3 S 1 ) de-excitation and acceleration, µ p( ) hits a H atom and is depolarized back to µ p( ) and accelerated by ~120 mev ; 19

20 FAMU workflow: µ transfer 4. µ - are transferred to heavier gas with energy-dependent rate; 20

21 FAMU: principle of operation 1. Create muonic hydrogen and wait for thermalization 2. Laser! at resonance (λ 0 ~6.8µ) spin state of µ - p from 1 1 S 0 to 1 3 S 1, spin is flipped: µ p( ) µ p( ) ; 3. µ - p (1 3 S 1 ) de-excitation and acceleration, µ p( ) hits a H atom and is depolarized back to µ p( ) and accelerated by ~120 mev ; 4. µ - are transferred to heavier gas with energy-dependent rate; 5. λ 0 resonance is determined by the maximizing the time distribution of µ - transferred events. 21

22 FAMU: principle of operation 1. Create muonic hydrogen and wait for thermalization 2. Laser! at resonance (λ 0 ~6.8µ) spin state of µ - p from 1 1 S 0 to 1 3 S 1, spin is flipped: µ p( ) µ p( ) ; 3. µ - p (1 3 S 1 ) de-excitation and acceleration, µ p( ) hits a H atom and is depolarized back to µ p( ) and accelerated by ~120 mev ; 4. µ - are transferred to heavier gas with energy-dependent rate; 5. λ 0 resonance is determined by the maximizing the time distribution of µ - transferred events. Ingredients needed: - high intensity muon beam 22

23 FAMU: principle of operation 1. Create muonic hydrogen and wait for thermalization 2. Laser! at resonance (λ 0 ~6.8µ) spin state of µ - p from 1 1 S 0 to 1 3 S 1, spin is flipped: µ p( ) µ p( ) ; 3. µ - p (1 3 S 1 ) de-excitation and acceleration, µ p( ) hits a H atom and is depolarized back to µ p( ) and accelerated by ~120 mev ; 4. µ - are transferred to heavier gas with energy-dependent rate; 5. λ 0 resonance is determined by the maximizing the time distribution of µ - transferred events. Ingredients needed: - high intensity muon beam - proper gas mixture and target 23

24 FAMU: principle of operation 1. Create muonic hydrogen and wait for thermalization 2. Laser! at resonance (λ 0 ~6.8µ) spin state of µ - p from 1 1 S 0 to 1 3 S 1, spin is flipped: µ p( ) µ p( ) ; 3. µ - p (1 3 S 1 ) de-excitation and acceleration, µ p( ) hits a H atom and is depolarized back to µ p( ) and accelerated by ~120 mev ; 4. µ - are transferred to heavier gas with energy-dependent rate; 5. λ 0 resonance is determined by the maximizing the time distribution of µ - transferred events. Ingredients needed: - high intensity muon beam - proper gas mixture and target - innovative high energy and fine-tunable laser 24

25 FAMU: principle of operation 1. Create muonic hydrogen and wait for thermalization 2. Laser! at resonance (λ 0 ~6.8µ) spin state of µ - p from 1 1 S 0 to 1 3 S 1, spin is flipped: µ p( ) µ p( ) ; 3. µ - p (1 3 S 1 ) de-excitation and acceleration, µ p( ) hits a H atom and is depolarized back to µ p( ) and accelerated by ~120 mev ; 4. µ - are transferred to heavier gas with energy-dependent rate; 5. λ 0 resonance is determined by the maximizing the time distribution of µ - transferred events. Ingredients needed: - high intensity muon beam - proper gas mixture and target - innovative high energy and fine-tunable laser - best X-rays detectors (fast and accurate) 25

26 Three phases project 2014 Study the muon beam, test target and detectors, measure transfer rate constant conditions of PTV) 26

27 Three phases project Find the best gas mixture, temperature and pressure in order to observe neatly and measure the transfer rate energy dependence, no laser Study the muon beam, test target and detectors, measure transfer rate constant conditions of PTV) 27

28 Three phases project 2018 Full working setup with laser, determination of proton Zemach radius (target on beam in 2017) Find the best gas mixture, temperature and pressure in order to observe neatly and measure the transfer rate energy dependence, no laser Study the muon beam, test target and detectors, measure transfer rate constant conditions of PTV) 28

29 Study of beam and transfer rate 29

30 Phases 1 and 2 Beam characteristics 30

31 Phases 1 and 2 X-rays signals 31

32 Phases 1 and 2 Target, gas purity and gas operations 32

33 Phases 1 and 2 Observation of delayed X-rays, first time measurement of transfer rate as function of temperature 33

34 RIKEN RAL muon facility Rutherford Appleton Laboratory Oxfordshire UK UK - Didcot The highest pulsed muon beam facility in the world! 34

35 High intensity muon beam UK - Didcot Tunable momentum: MeV/c Flux µ - : 7 x 10 4 muons/s Double pulsed beam 20 ms (50 Hz) 20 ms (50 Hz) 35

36 Hodoscope for beam shape monitoring Final version: two planes (X and Y) of 32 scintillating fibers 1 x 1 mm 2 square section SiPM reading with fast electronics 3D printed supports hodoscope in the 2016 setup 36

37 Hodoscope: PORT1 commissioning 2017 data at PORT1: tuning magnets currents to change beam shape with millimetric resolution 37

38 Hodoscope: PORT1 commissioning immagini commissioning 2017 data at PORT1: tuning magnets currents to change beam shape with millimetric resolution 38

39 Hodoscope: PORT1 commissioning 2017 data at PORT1: tuning magnets currents to change beam shape with millimetric resolution 39

40 Target: a challenge itself 2015 target: detectors and beam test and validation ~12 cm ~26 cm 2016 target: cryogenic target, transfer rate measurement 2018 target: cryogenic target + optical path and cavity, Zemach radius measurement 40

41 Target: a necessary trade-off Main requirements: - Operating temperature range: 40 K T 325 K - Temperature control for measurement runs at fixed T steps from 300 K to 50K - constant density, H 2 charge pressure at room T is ~40 atm - International safety certification (Directive 97/23/CE PED) - Minimize walls and windows thickness - Target shape and dimensions to maximize muon stop in gas to minimize distance gas detectors to be compliant to allowable volume at Riken Port - H 2 compatible... and, of course, all the above within time and cost constraints! 41

42 Best solution Target= Inner vessel with high P gas (44 bar) - Al alloy 6082 T6 cylinder D = 60 mm and L = 400 mm, inner volume of 1.08 l - Internally Ni/Au plated (L = 280 mm) - Cylinder side wall thickness = 3.5 mm - Wrapped in 20 layers of MLI - Front window D= 30 mm 2.85 mm thick - Three discs of mm Al foil for window radiative shield - 304L SS gas charging tube - 304L SS cooler cold-end support - G10 mechanical strut - Two Cu straps for cooling Vacuum vessel = outer cylinder (P atm) - Al6060 D=130 mm, 2 mm thick walls - 30mm between inner/outer walls - Flanged Al window 0.8 mm thick - Pumping valve & harness feed-tru s 42

43 Target in lab 43

44 Target on beam line µ 44

45 Thermal cycles 2016 N 2 (100% ) H 2 O 2 (0.05%) H 2 (100%) H 2 Ar (1%) H 2 O 2 (1%) H 2 CO 2 (0.3%) N 2 (100%) H 2 O 2 (0.3%) H 2 Ar (0.3%) H 2 CH 4 (0.3%) Cold Head Target Heater % Setpoint 21/02/ /02/ days: Feb 2016 measurements run 45

46 Target cryo performances: T control steps 2017 on beam: lowest temperature target cold head 46

47 Detectors: suited for time-resolved X-ray spectroscopy Germanium HPGe: low energy X-rays spectroscopy ORTEC GLP: Energy Range: kev Crystal Diameter: 11 mm Crystal Length: 7 mm Beryllium Window: mm Resolution Warrented (FWHM): - at 5.9 kev is 195 ev (T sh 6 μs) - at 122 kev is 495 ev (T sh 6 μs) ORTEC GMX: Energy Range: kev Crystal Diameter: 55 mm Crystal Length: 50 mm Beryllium Window: 0.5 mm Resolution Warrented (FWHM): - at 5.9 kev is 600 ev (T sh 6 μs) - at 122 kev is 800 ev (T sh 6 μs) 47

48 Detectors: suited for time-resolved X-ray spectroscopy Lanthanum bromide scintillating crystals [LaBr 3 (Ce)]: fast timing X-rays detectors Eight cylindrical 1 inch diameter 1 inch long LaBr 3 (5%Ce) crystals read by PMTs. Fast electronics and fast digital processing signal available Lab test 48

49 Star-shaped support for detectors 49

50 2016: experimental setup µ 50

51 2016: experimental setup LaBr µ 51

52 2016: experimental setup LaBr µ HPGe 52

53 Spectral lines measurements 53

54 Germanium detectors: excellent energy resolution Pure H 2 target in aluminium container H 2 + (4% w/v)co 2 gas mixture in aluminium container 54

55 LaBr 3 (5%Ce) scintillating crystals H 2 + (4% w/v)co 2 gas mixture in aluminium container 55

56 LaBr 3 (5%Ce) scintillating crystals H 2 + (4% w/v)co 2 gas mixture in aluminium container 56

57 Muonic transfer rate measurement 57

58 Time spectrum: peaks and tails 20 ms (50 Hz) 320 ns Detected time spectrum 70 ns 70 ns 58

59 Peaks: prompt emission of X-rays Detected time spectrum 40 atm) Prompt emission: X-rays from µ capture, e - from µ decay 59

60 Tails: (bounded) muon live time Detected time spectrum 40 atm) Delayed emission: delayed X-rays from µ transfer, e - from µ decay, bremsstrahlung γ (everywhere) 60

61 2016: transfer rate measurement Steps: 1) fix a target temperature (i.e. mean kinetic energy of gas constant) 2) produce µp and wait for thermalization 3) study time evolution of Oxygen X-rays 4) repeat with different temperature 61

62 Steps: 2016: transfer rate measurement 1) fix a target temperature (i.e. mean kinetic energy of gas constant) 2) produce µp and wait for thermalization 3) study time evolution of Oxygen X-rays 4) repeat with different temperature three hours 62

63 Steps: 2016: transfer rate measurement 1) fix a target temperature (i.e. mean kinetic energy of gas constant) 2) produce µp and wait for thermalization 3) study time evolution of Oxygen X-rays 4) repeat with different temperature Delayed emission: delayed X-rays from µ transfer 63

64 2016: transfer rate measurement 3) study time evolution of Oxygen X-rays time bin 1 time bin 4 time bin 12 T = 300 K 64

65 2016: transfer rate measurement PSI FAMU 65

66 2016: transfer rate measurement PSI FAMU 66

67 FAMU journey, ok and on time Up to now: 1) Double pulsed muon beam ok for the project 2) Confirmed high purity of the gas target 3) Excellent detection of X-rays and transition lines 4) Excellent time resolution 5) Observation of muon transfer to higher Z charged nuclei 6) Transfer rate measured as function of T for different nuclei 67

68 Present status and future measurements 68

69 Innovative powerful laser Tunable pulsed IR laser at λ = 6.8 µm 2.5 mj direct difference frequency generation non-oxide non linear crystals single-mode Nd:YAG laser + tunable Cr:forsterite laser Wavelength λ = 6780 nm THz Line width: λ = 0.07 nm 456 MHz Tunability range: nm 39 GHz Repetition rate: 25 Hz 69

70 Ready in a couple of months 70

71 Ready in a couple of months 71

72 Multipass cavity and new target 1. Preliminar optical simulation of multipass optical cavity (MPOC) in MatLab environment; 2. Complete Design of MPOC with Zemax OpticStudio; 3. Fabrication and optical characterization of MPOC by means a QCL at 6.7 µm. loss factor: 15x10-4 per reflection light travels ~16 m before loosing a factor 1/e >700 reflections 2016 target adapted to include optical path and cavity 8 new LaBr detectors 72

73 Transfer rate up to 120 mev ~100 K ~300 K 73

74 Transfer rate up to 120 mev ~100 K ~300 K µp energy after laser pulse 74

75 Study of best setup to maximize signal 75

76 From data analysis: Measurement plan about 10 muon transferred events were observed per second per detector: with 16 detectors ~ events/(3 hours) are expected. From simulations: laser shot: ~6% event excess, i.e. about 10 5 events/(3 hours), enough statistics at a given fixed laser frequency. 6 hours = one step (0.1 nm) half signal (laser), half background (no laser) Rough scan: 420 hours to acquire 70 different laser frequencies. Fine scan around resonance peak: 180 hours, 30 different laser frequencies. Total time (with setup and preparation): ~40 days 76

77 Summary FAMU: investigation of the proton radius puzzle with HFS of (µ - p) 1S An exciting journey: started 25 years ago most intense pulsed beam in the world best detectors for energy and time observation first time measurement of the muon transfer rate to Oxygen innovative and powerful laser system Looking forward to perform the final measurement! 77

78 Summary FAMU: investigation of the proton radius puzzle with HFS of (µ - p) 1S An exciting journey: started 25 years ago most intense pulsed beam in the world best detectors for energy and time observation first time measurement of the muon transfer rate to Oxygen innovative and powerful laser system Looking forward to perform the final measurement! 78