Emittance Reduction Measurement Results of simulations Beam requirements

Emittance Reduction Measurement Results of simulations, Beam requirements Patrick Janot, CERN EP OUTLINE • (Obsolete) Experimental Layout: Detectors and Cooling Channel • Fast Simulation: What’s simulated and what is not ? • Emittance Reduction measurement: Principle and Design • Emittance Reduction measurement: Results and Optimization • Pion Rejection and Beam Requirements • Electron Identification • Perspectives and Outlook Workshop on MICE 25 -27 Oct. 2001 Beam Emittance Reduction Measurements 1

(Obsolete) Experimental Layout (I) Pb, 0. 1 X 0 Pb, 4 X 0 10 m About 5% of the muons arrive here 88 MHz Channel with or without cooling B = 5 T, R = 15 cm, L = 15 m Measure x, y px, py, pz Measure t, x, y For pion rejection Workshop on MICE 25 -27 Oct. 2001 Determine, with many ’s: • Initial RMS 6 D-Emittance i • Final RMS 6 D-Emittance f • Emittance Reduction R Beam Emittance Reduction Measurements 2

(Obsolete) Experimental Layout (II) Initial Beam: • Negligible transverse dimensions • <p. T> = 3 Me. V/c; • <pz> = 290 Me. V/c, Spread 10%; After diffusion on Pb: • Transverse dimensions: 15 cm RMS • <p. T> = 30 Me. V/c; • <pz> = 260 Me. V/c, Spread 10%; The beam must “fill” entirely the solenoid acceptance to allow the 6 D-emittance to be conserved without cooling in the channel Workshop on MICE 25 -27 Oct. 2001 10, 000 Muons Beam Emittance Reduction Measurements 3

Fast Simulation: What’s in ? q Particle transport in magnetic field and in RF; q Multiple Scattering in matter; q Energy Loss (average and Landau fluctuations) in matter; q Bremsstrahlung in matter; q Beam contamination with pions, pion decay in flight; q Muon decay in flight (with any polarization), electron transport; q Poor-Man Cooling Simulation (only Bz and EZ) to quantify particle and correlation losses with cooling; q Gaussian errors on measured quantities (x, y, t). Workshop on MICE 25 -27 Oct. 2001 Beam Emittance Reduction Measurements 4

Fast Simulation: What’s not in ? q Imperfections of magnetic fields; heating at solenoid exits; (A full simulation would be needed here… Volunteers needed! Might be the source of important systematic biasses and uncertainties) q Dead channels; (Act as a global ineffiency, mostly irrelevant if independent of muon initial momentum and direction; to be checked) q Misalignment of detector elements; (Easy to align in absence of background with a few thousand muons; To be done in practice. ) q Background of any origin (RF, beam, …) (Could well spoil the measurement. Need redundancy in case…) q…? Workshop on MICE 25 -27 Oct. 2001 Beam Emittance Reduction Measurements 5

Emittance Measurement: Principle (I) Need to determine, for each muon, x, y, t, and x’, y’, t’ (=px/pz, py/pz, E/pz) at entrance and exit of the cooling channel: Solenoid, B = 5 T, R = 15 cm, L > 3 d (to keep B uniform on the plates) z d T. O. F. Measure t With st 70 ps Workshop on MICE 25 -27 Oct. 2001 Note: To avoid heating exit of the solenoid due to radial fields, the cooling channel has to either start with the same solenoid, or be matched to it as well as Possible. d Three plates of, e. g. , three layers of sc. fibres (diameter 0. 5 mm) Measure x 1, y 1, x 2, y 2, x 3, y 3 with precision 0. 5 mm/ 12 Extrapolate x, y, t, px, py, pz, at entrance of the channel. Make it symmetric at exit. Beam Emittance Reduction Measurements 6

Emittance Measurement: Principle (II) In the transverse view, determine a circle from the three measured points: x 2 , y 2 Df 12 Df 23 C x 1, y 1 R x 3 , y 3 Ø Compute the transverse momentum from the circle radius: p. T = 0. 3 B R px = p. T sinf py = -p. T cosf Ø Compute the longitudinal momentum from the number of turns p. Z = 0. 3 B d / Df 12 = 0. 3 B d / Df 23 = 0. 3 B 2 d / Df 13 (provides constraints for alignment) d = pz/E c. Dt RDf 12 = p. T/E c. Dt Ø Adjust d to make 1/3 of a turn between pz/d = p. T/ RDf 12 two plates (d = 40 cm for B = 5 T and p. Z = 260 Me. V/c) on average Ø Determine E from (p 2 + m 2)1/2 Workshop on MICE 25 -27 Oct. 2001 Beam Emittance Reduction Measurements 7

Emittance Measurement: Improvement (I) q The previous (minimal) design leads to reconstruction ambiguities for particle which make a full turn between the two plates (only two points to determine a circle) q It also leads to reconstruction efficiencies and momentum resolutions dependent on the longitudinal momentum, which bias the emittance measurements. Solution: Add one plate, make the plates not equidistant z 30 cm 35 cm 40 cm (optimal for 5 T) To find p. T and p. Z, minimize: Workshop on MICE 25 -27 Oct. 2001 Beam Emittance Reduction Measurements 8

Emittance Measurement: Improvement (II)? q The previous design is optimal for muons between 150 and 450 Me. V/c (or any dynamic range [x, 3 x]. q Decay electrons have a momentum spectrum centred a smaller values and some of them may make many turns between plates. The reconstructed momentum is between 150 and 450 Me. V anyway. Very low momentum electrons cannot be rejected later on… 5 cm z 30 cm 35 cm 40 cm q Possible cure: Add a fifth plate close to the fourth one in the exit diagnostic device. First try in the simulation (yesterday) looks not too good, but the reconstruction needs to be tuned to this new configuration. (The rest of the presentation uses the design with four plates. ) Workshop on MICE 25 -27 Oct. 2001 Beam Emittance Reduction Measurements 9

Emittance Measurement: Results (I) Resolution on p. T: • Same for all particles; (4 plates) • s(p. T) 0. 8 Me. V/c. Resolution on p. Z: • Strong dependence on p. T; • Varies from 1 to 50 Me. V/c. 10, 000 muons Workshop on MICE 25 -27 Oct. 2001 20% Beam Emittance Reduction Measurements 10

Emittance Measurement: Results (II) Transverse Emittance Resolution ( p. T /p. Z ) s(p. T/p. Z) 2. 5% Workshop on MICE 25 -27 Oct. 2001 Longitudinal Emittance Resolution ( E/p. Z) s(E/p. Z) 0. 25% Beam Emittance Reduction Measurements 11

Emittance Measurement: Results (III) 1 mes in Cooling channel without cooling No contamination, no decay out With 1000 samples of 1000 accepted muons each: mes out Generated Measured in out Ratio meas/gen Workshop on MICE 25 -27 Oct. 2001 4 0. 5% 0. 6% with 1000 Beam Emittance Reduction Measurements 12

Emittance Reduction: Results (IV) R = out/ in Generated Each entry is the ratio of emittances (out/in) from a sample of 1000 muons. Biases and resolutions are determined from this kind of plots in the following. RGEN, 1. (No cooling) Measured RMEAS, (1. + )2 Bias 1% (No cooling) Workshop on MICE 25 -27 Oct. 2001 A 0. 9% measurement with 1000 single ’s (corresponding to • 25, 000 single ’s produced • 70, 000 “bunches” sent) Note: is purely instrumental (mostly due to multiple scatt. in the detectors). It can be predicted and corrected for, if not too large. Beam Emittance Reduction Measurements 13

Emittance Reduction: Optimization (I) (1000 ’s, No cooling, Perfect /e Identification) Optimization with respect to the distance between the 1 st and the last plates 6 D reduction: Resolution 6 D reduction: Bias 4 D reduction: Resolution 4 D reduction: Bias No clear minimum, but the resolution and bias on the long. emittance reduction become (slightly) worse when the average muon cannot do a full turn between 1 st and last plates… (possibly alleviated with reconstruction tuning ? ) Workshop on MICE 25 -27 Oct. 2001 Beam Emittance Reduction Measurements 14

Emittance Reduction: Optimization (II) (1000 ’s, No cooling, Perfect /e Identification) Optimization with respect to the scintillating fibre diameter Measured Perfect detectors 6 D bias 6 D resolution 4 D bias 4 D resolution The smaller the better… Keeping the 6 D bias and resolution at the % level requires a diameter of 0. 5 mm. Still acceptable with 1 mm, though. (2% bias, 1. 2% resolution) Workshop on MICE 25 -27 Oct. 2001 Beam Emittance Reduction Measurements 15

Emittance Reduction: Optimization (III) (1000 ’s, No cooling, Perfect /e Identification) Optimization with respect to the TOF resolution q Almost irrelevant (between 0 and 500 ps) for the emittance measurement: no effect on the transverse emittance, and marginal effect on the 6 D emittance (resolution 0. 9% 1. 1%); q Quite useful to determine the timing with respect to the RF, so as to select those muons in phase with the accelerating 1/10 th of a period (i. e. , 1. 1 ns for 88 MHz and 0. 5 ns for 200 MHz). The resolution ought to be 10% of it, i. e. , 100 ps for 88 MHz and 50 ps for 200 MHz. q Essential to identify pions at the entrance of the channel: Indeed the presence of pions in the muon sample would spoil the longitudinal. emittance measurement (E is not properly determined for pions, and part of these pions decay in the cooling channel). Workshop on MICE 25 -27 Oct. 2001 Beam Emittance Reduction Measurements 16

Pion Rejection: Principle -34 Me. V ( ) -31 Me. V ( ) z 1 z 0 Beam 10 metres z 0. 1 X 0 (Pb) Measure t 0 4 X 0 (Pb) Measure x 0, y 0 1. 11 for ’s 1. 06 for ’s Measure x 1, y 1 (p = 290 Mev/c) Measure t 1 Compare with With st = 70 ps 1. 08 for ’s and ’s Measured in solenoid Workshop on MICE 25 -27 Oct. 2001 Cut Beam Emittance Reduction Measurements 17

Pion Rejection: Optimization (I) (1000 ’s, No cooling, Perfect e Identification) Optimization with respect to the TOF resolution Ø Assume an initial beam formed with 50% muons and 50% pions (same momentum spectrum) Remaining pion fraction Ø Vary the T. O. F. resolution Ø Apply the previous pion cut (E/p)/(E /p) < 1. 00 and check the remaining pion fraction in a 10, 000 muon sample. Because of the beam momentum spread and of the additional spread introduced by the 4 X 0 Pb plate, the / separation does not improve for a resolution better than 100 -150 ps (for a path length of 10 m) Workshop on MICE 25 -27 Oct. 2001 Beam Emittance Reduction Measurements 18

Pion Rejection: Optimization (II) (1000 ’s, No cooling, Perfect e Identification) Beam Purity Requirement (confirmed with cooling) Measured Perfect detectors 6 D bias 4 D bias 6 D resolution 4 D resolution Need to keep the pion contamination below 0. 1% (resp 0. 5%) to have a negligible effect on the 6 D (resp. 4 D) emittance reduction resolution and bias. It corresponds to a beam contamination smaller than 10% (50%) when entering the experiment. Workshop on MICE 25 -27 Oct. 2001 Beam Emittance Reduction Measurements 19

Pion Rejection: Optimization (III) (1000 ’s, Perfect e Identification) Beam Purity Requirement with Cooling 1) 6 D-Cooling and Resolution Pion cut at 1. 00 Pion cut at 0. 99 (Four 88 MHZ cavities) 2) Statistical significance with 1000 ’s 6 D Cooling No Effect Resolution Workshop on MICE 25 -27 Oct. 2001 (in the beam) Beam Emittance Reduction Measurements 20

Pion Rejection: Optimization (IV) (1000 ’s, Perfect e Identification) Beam Purity Requirement with Cooling 1) Transverse-Cooling and Resolution Pion cut at 1. 00 Pion cut at 0. 99 (Four 88 MHZ cavities) 2) Statistical significance with 1000 ’s 4 D Cooling No Effect Resolution Workshop on MICE 25 -27 Oct. 2001 (in the beam) Beam Emittance Reduction Measurements 21

Poor-Man Electron Identification (I) q At the end of the cooling channel, a few electrons from muon decays (up to 0. 4% of the particles for a 15 m-long channel) are detected in the diagnostic device. q These electrons have very different momenta and directions from the parent muons, and they spoil the measurement of the RMS emittance (6 D and 4 D) q About 80% of them can be rejected with kinematics, without effect on muons Poor fits for electrons (Brems) e Large p. Z difference (pin-pout) e Workshop on MICE 25 -27 Oct. 2001 Beam Emittance Reduction Measurements 22

Poor-Man Electron Identification (II) (1000 ’s, with cooling, 0 to 20 RF cavities) 1) 6 D-Cooling and Resolution • Generated • Measured, perfect e-Id • Measured, poor man e-Id 2) Statistical significance with 1000 ’s Remaining electron fraction 3 10 -4 6 10 -4 8 10 -4 6 D Cooling Resolution Workshop on MICE 25 -27 Oct. 2001 Need better e-Id to get back to the red curve! • Cerenkov detector (1/1000) • El’mgt calorimeter (? ) Beam Emittance Reduction Measurements 23

Poor-Man Electron Identification (III) (1000 ’s, with cooling, 0 to 20 RF cavities) 1) Transverse Cooling and Resolution • Generated • Measured, perfect e-Id • Measured, poor man e-Id 2) Statistical significance with 1000 ’s Remaining electron fraction 3 10 -4 6 10 -4 8 10 -4 4 D Cooling Resolution Workshop on MICE 25 -27 Oct. 2001 No need for more e Id For the transverse cooling measurement Beam Emittance Reduction Measurements 24

Perspectives and Outlook q A 1% measurement of 6 D cooling and a 0. 5% measurement of transverse cooling can be achieved with 1, 000 detected muons (i. e. , 100, 000 muon bunches) and reasonable detectors (typical transverse size 30 cm): Ø Three time measurements with a 50 -100 ps precision Ø Two 1. 5 to 2 m long, 5 T solenoids Ø Ten (twelve? ) 0. 5 mm diameter scintillating fibre plates (three layers each) Ø One Cerenkov detector and/or one electromagnetic calorimeter (10 X 0 Pb) q However, some systematic effects have to be addressed with a detailed full simulation (to be written) to make this estimate rock-solid Ø Effect of magnetic field (longitudinal and radial) imperfections Ø Effect of background (any) Ø Effect of dead channels and misalignment q Other possibilities should be studied to evaluate their potential/feasibility Ø Thin silicon detectors instead of scintillating fibres ? Ø Detector design with a 200 MHz cooling channel ? Workshop on MICE 25 -27 Oct. 2001 Beam Emittance Reduction Measurements 25