Measurement of emittance in the Muon Ionization Cooling Experiment

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1 Measurement of emittance in the Muon Ionization Cooling Experiment François Drielsma on behalf of the MICE collaboration University of Geneva August 26, 216 François Drielsma (UniGe) Emittance in MICE August 26, / 24

The Muon Ionization Cooling Experiment (MICE) The need for MICE Ionization cooling is the only viable technique to reduce the emittance of a muon beam within their lifetime ( 2.

2 The Muon Ionization Cooling Experiment (MICE) The need for MICE Ionization cooling is the only viable technique to reduce the emittance of a muon beam within their lifetime ( 2.2 µs) Cooled muons are essential to achieve the luminosity required by future muon facilities such as a Neutrino Factory or a Muon Collider MICE physics program Demonstrate the feasibility of ionization cooling Study and validate the cooling equation Energy loss and scattering of muons (material physics) François Drielsma (UniGe) Emittance in MICE August 26, / 24

Principle of ionization cooling Muon cooling can be characterised by the rate of change of the normalised emittance (phase space occupied by the beam), approximated by dε N ds ε N β 2 E µ de µ ds + β

3 Principle of ionization cooling Muon cooling can be characterised by the rate of change of the normalised emittance (phase space occupied by the beam), approximated by dε N ds ε N β 2 E µ de µ ds + β (.14) 2 2β 3 ; (1) E µ m µ X Energy loss, de µ /ds, reduces both p L and p T Scattering heats the beam as 1/X, must maximize X RF cavities restore p L only The absorber must be placed at a focus for best cooling performance François Drielsma (UniGe) Emittance in MICE August 26, / 24

4 MICE beam line François Drielsma (UniGe) Emittance in MICE August 26, / 24

5 MICE beam line François Drielsma (UniGe) Emittance in MICE August 26, / 24

6 Experimental apparatus at present (Step IV) All the detectors are in and working Three time-of-flight detector stations Two Cherenkov counters and a downstream calorimetry module Two scintillating-fibre trackers Part of the cooling channel (no RF yet) Two Spectrometer Solenoids (SS), each composed of 5 coils An Absorber Focus Coil (AFC) module, made of 2 coils MICE Muon Beam (MMB) Time-of-flight hodoscope 1 (ToF ) Variable thickness high-z diffuser Upstream spectrometer module Absorber/focus-coil module Downstream spectrometer module 7th February 215 Electron Muon Ranger (EMR) MICE Cherenkov counters (CKOV) ToF 1 Liquid-hydrogen absorber Scintillating-fibre trackers Pre-shower (KL) ToF 2 François Drielsma (UniGe) Emittance in MICE August 26, / 24

7 Single-particle experiment MICE is a single-particle experiment, i.e. There is no beam as such going down the beam line, particles go down the beam line one by one (f 2 khz for 1 ms every second) At each DAQ cycle, a single particle track is recorded Particle tracks are bunched at the analysis level to create an ensemble of which to compute the emittance First direct measurement of emittance of muon beams by a scintillating fibre-tracker François Drielsma (UniGe) Emittance in MICE August 26, / 24

8 Definition The emittance represents the volume occupied by the beam in phase-space. In 2D it is a simple ellipse. The 4D normalised RMS transverse emittance is defined as ɛ n = 1 m µ 4 det Σ (2) with m µ the muon mass and Σ the covariance matrix, i.e. σ xx σ xpx σ xy σ xpy Σ = σ pxx σ pxpx σ pxy σ pxpy σ yx σ ypx σ yy σ ypy (3) σ pyx σ pypx σ pyy σ pypy with σ αβ = αβ α β the covariance of α and β. François Drielsma (UniGe) Emittance in MICE August 26, / 24

9 MICE Scintillating-Fibre trackers Two SciFi trackers (US and DS), 5 stations per tracker, 3 planes per station, 214 fibres per plane Measured tracker resolution (cosmics): σx, σy = 467 ± 2 µm Franc ois Drielsma (UniGe) Emittance in MICE August 26, / 24

10 Tracker momentum reconstruction In a uniform solenoid magnetic field, a particle follows a helical path x = ρ cos (qbt/m) y = ρ sin (qbt/m) ρ = p T /qb (4) z = p L t/m Each tracker samples the helix in 5 points (x i, y i ) A circle fit in the (x, y) yields the radius ρ and hence p T The gradient of the arc-length, ds/dz, yields p L Resolutions from MC: σ pl 1.3 MeV/c, σ pt 4 MeV/c y x 2πp L /qb ρ x z François Drielsma (UniGe) Emittance in MICE August 26, / 24

11 Run 7469 In October 215, the upstream spectrometer was powered for the first time at its designed current. Run 7469 was taken that day: 2 MeV/c positive muon input beam 7 minutes of data taking 1976 good muon tracks acquired This run was used to characterise the MICE muon beam and validate the tracker reconstruction. Results follow. François Drielsma (UniGe) Emittance in MICE August 26, / 24

12 Event selection Selection criteria applied to clean up the beam Reject time-of-flights below threshold (e + ) Keep only particles that hit every TOF and tracker stations Remove particles that scraped the apparatus (magnet bore, diffuser) Time of flight (ns) MICE Preliminary ISIS Cycle 215/ P at Tracker (MeV/c) 12 Figure: time of flight between the first and second TOF stations as a function of the reconstructed total momentum tracker A single curve signifies a single particle species: muons. François Drielsma (UniGe) Emittance in MICE August 26, / 24

13 Position at the tracker reference plane The reference plane corresponds to the tracker station closest to the absorber The position distribution is the result of as many helical fits as particles The fiducial surface of each tracker plane is 3 mm in diameter y (mm) 15 MICE Preliminary ISIS Cycle 215/ x (mm) Visual representation of one of the covariance matrix elements, σ 2 xy François Drielsma (UniGe) Emittance in MICE August 26, / 24

14 2D beam ellipses Another two plots of the elements σ 2 xp x and σ 2 yp y of the covariance matrix Similar distribution in the two 2D subspaces In an uncoupled phase space, these would represent the horizontal and vertical 2D emittance of the beam, respectively Px (MeV/c) 1 MICE Preliminary ISIS Cycle 215/ Py (MeV/c) 1 MICE Preliminary ISIS Cycle 215/ x (mm) y (mm) François Drielsma (UniGe) Emittance in MICE August 26, / 24

15 Beam dispersion The second bending magnet (D2) has a large acceptance Large momentum spread and dispersion in the beam Mean position of the beam proportional to momentum/bending radius Need to bin the sample in p z to remove chromatic effects Pz (MeV/c) 3 MICE Preliminary ISIS Cycle 215/ Radius of beam centre (mm) 65 MICE Preliminary ISIS Cycle 215/ x (mm) <Pz> (MeV/c) François Drielsma (UniGe) Emittance in MICE August 26, / 24

16 Comparaison with Monte Carlo End-to-end Monte Carlo Pion production, target Transport with G4BL Custom MICE Analysis User Software MC Good agreement Accurately reproduces the tracker beam profiles (xp x, yp y ) Tool for systematic analysis Provides understanding of the beam dispersion Px (MeV/c) Py (MeV/c) 1 MICE Preliminary ISIS Cycle 215/ x (mm) 1 MICE Preliminary ISIS Cycle 215/ y (mm) Px (MeV/c) Py (MeV/c) 1 MICE Preliminary Simulation x (mm) 1 MICE Preliminary Simulation y (mm) François Drielsma (UniGe) Emittance in MICE August 26, / 24

17 ISIS Cycle 215/2 ISIS Cycle 215/2 ISIS Cycle 215/2 ISIS Cycle 215/2 ISIS Cycle 215/2 ISIS Cycle 215/2 Poincaré sections of the covariance matrix in data x p x y p y σ 2 xx Px (MeV/c) 1 MICE Preliminary y (mm) MICE Preliminary Py (MeV/c) 1 MICE Preliminary x x (mm) x (mm) x (mm) Px (MeV/c) 1 MICE Preliminary Py (MeV/c) 1 MICE Preliminary σ 2 p xp x px y (mm) Px (MeV/c) Figure: Visual representation of the off-diagonal elements of the covariance matrix used to compute the emittance σ 2 yy Py (MeV/c) 1 MICE Preliminary y y (mm) François Drielsma (UniGe) Emittance in MICE August 26, / 24

18 First direct measurement of emittance with MICE trackers Transverse normalised emittance (mm) 4.2 MICE Preliminary ISIS Cycle 215/ <Pz> (MeV/c) François Drielsma (UniGe) Emittance in MICE August 26, / 24

Latest MICE field-on data taking In July 216, great progress was made with the cooling channel operation Both spectrometers ECE coil triples were powered at 14 A, which corresponds to 2 T in each

19 Latest MICE field-on data taking In July 216, great progress was made with the cooling channel operation Both spectrometers ECE coil triples were powered at 14 A, which corresponds to 2 T in each tracker The focus coil was powered at 5 A together with the spectrometers A 3 mm-14 MeV/c input beam was used, empty absorber module First look at muons that made it through the entire MICE channel First focus coil transfer matrix measurements François Drielsma (UniGe) Emittance in MICE August 26, / 24

Beam profiles up and downstream the focus coil In two hours of data taking (run 8155 on July 27th 216) Upwards of 8 muon and pion tracks were recorded going through the entire MICE step IV

20 Beam profiles up and downstream the focus coil In two hours of data taking (run 8155 on July 27th 216) Upwards of 8 muon and pion tracks were recorded going through the entire MICE step IV magnet channel Both trackers were successful in the reconstruction of helical tracks at half the nominal spectrometer field TKD TKU François Drielsma (UniGe) Emittance in MICE August 26, / 24

21 Cooling in MICE Step IV The MICE collaboration intends to measure emittance change for 3 1 mm tunable emittance (tuned with the diffuser) 14, 2 and 24 MeV/c mean momentum Lithium hydride absorber (LiH) and liquid hydrogen (LH2) Two types of lattices: solenoid and flip mode A first cooling measurement is soon to be made in MICE Step IV Whole cooling channel will be powered in September, empty absorber The lithium hydride absorber will go in before the end of 216 The liquid hydrogen absorber will go in this winter François Drielsma (UniGe) Emittance in MICE August 26, / 24

22 Simulated emittance change 2 MeV/c sol. 2 MeV/c flip François Drielsma (UniGe) Emittance in MICE August 26, / 24

Alternative: Kernel Density Estimation method A Kernel Density Estimator (KDE) is a nonparametric PDF defined as f( r) = 1 h d N N ( ) r ri K h i=1 (5) with h an arbitrary bandwidth, K the

23 Alternative: Kernel Density Estimation method A Kernel Density Estimator (KDE) is a nonparametric PDF defined as f( r) = 1 h d N N ( ) r ri K h i=1 (5) with h an arbitrary bandwidth, K the kernel, a normalised dimension d Normal distribution. This allows to compute contours and see changes in the phase space density François Drielsma (UniGe) Emittance in MICE August 26, / 24

24 Conclusions The first direct measurement of emittance with the MICE trackers The trackers and PID detectors are fully operational The emittance was measured and chromatic effects were understood A technique paper is in preparation First emittance change measurement to come in the near future MICE will observe transverse muon beam emittance reduction The first set of LiH data will be taken in 216 More to come! Transverse normalised emittance (mm) 4.2 MICE Preliminary ISIS Cycle 215/ <Pz> (MeV/c) François Drielsma (UniGe) Emittance in MICE August 26, / 24

Emittance Measurement in the Muon Ionization Cooling Experiment

Emittance Measurement in the Muon Ionization Cooling Experiment Department of Physics, Imperial College London E-mail: v.blackmore@imperial.ac.uk The Muon Ionization Cooling Experiment (MICE) collaboration