HEP2003, 17/07/2003E.Radicioni2 The physics is straightforward … But its application in a real accelerator string is a matter of a delicate balance of many parameters. Build a prototype cooling channel and evelop a beam diagnostic able to prove that it works Ionization Cooling: Theory and Practice ….maybe…
HEP2003, 17/07/2003E.Radicioni3 Motivations About 20% of the cost of a Neutrino Factory is determined by the muon cooling: the neutrino flux ultimately available for physics strongly depends on how many muons can make it in the muon accelerator section Quantitative evaluation of cost trade-off between cooling and acceleration cost optimization of a Neutrino Factory The physics is known, but the demonstration in practice still has to be done Design, build and operate a section of cooling channel capable to operate at the desired performances Place it in a muon beam and measure its performances in a variety of operating modes Show that the design tools agree with the experiment Calibrate the simulations to make more safe to extrapolate from the prototype cooling channel to the real one.
HEP2003, 17/07/2003E.Radicioni6 Quantities to be measured in a cooling experiment GOAL: measure emittance reduction and transmission of the cooling channel Check the equilibrium-emittance condition Need to count particles (of a give type) and to measure track parameters cooling effect at nominal input emittance : ~10% Particle losses
HEP2003, 17/07/2003E.Radicioni7 MICE setup: cooling + diagnostics Cools and measures about 100 muons/s
HEP2003, 17/07/2003E.Radicioni8 Measured quantities Complete determination of a particle beam implies measuring Number and type of particles x, y, t x’=dx/dz=Px/Pz, y’=dy/dz=Py/Pz, t’=dt/dz=E/Pz All these quantities must be measured IN and OUT of the cooling channel When such parameters are known, the 6D emittance, as well as the 4D emittance ( ε ), can be determined completely. For a sample of N particles, one can determine the following statistical quantities: Averages,,,, etc. Variances 2 xy, … and Covariance Matrix C xy,.. Single-particle measurement of ε in and ε out ?
HEP2003, 17/07/2003E.Radicioni9 Required precision and error sources Measurements 10% emittance reduction measured to 1% absolute errors <0.1% Statistical Take 10 6 muons to reduce statistical error to 10 -3 on Systematic Description of apparatus: Detectors themselves must not spoil measurements by MCS Magnitude (and phase) of magnetic and RF fields Thickness/density of absorber, windows, etc. Alignment Beam energy scale Simulation of MCS and dE/dx Systematic differences between spectrometers: Efficiency, noise differences Mis-alignment/mis-match Different fields Transport: wrong particles with different kinematics will spoil the measurements Muon in … muon out / and /e rejection at < 1% level
HEP2003, 17/07/2003E.Radicioni10 Particle-by-particle diagnostic? Tag and identify incoming and outgoing particles this helps in reducing the systematic error: pion and electron contamination can spoil the measurement. This is only possible in single-particle mode. Correlations between phase space parameters can be easily measured It is possible to study the effect of different beam parameters: Energy Transverse momentum Input emittance RF phase … Any desired input beam condition can be reconstructed from the data sample by cutting/slicing the population of observed particles
HEP2003, 17/07/2003E.Radicioni11 Detectors /trackers: baseline 0.34 X 0 per plane No active electronics / HV close to liquid H 2 350 m staggered fibers, 3 projections Key element for small X 0 : VLPC readout, high quantum efficiency Very good timing (background rejection) Modular construction Possibility of multiplexing to reduce cost (related to background issues)
HEP2003, 17/07/2003E.Radicioni12 Detectors /trackers: alternative Low X 0 gas (0.15% X 0 ) Many points per track High precision tracking Potential cost saving Large integration time Effect of X-rays on GEMs
HEP2003, 17/07/2003E.Radicioni13 Backgrounds on the trackers Dark currents due to electron field emission from the cavity surfaces Electrons are stopped in the absorbers X-rays with wide spectrum (brehmstrahlung) will convert in the detector Quantify the problem on sample cavity and simulate the detectors in a flux of X-rays. Fibers are OK (small integration time) but there might be a cost issue (possibility of multiplexing) TPG is very light (less conversions) but integration time is much larger. Occupancy is the main issue.
HEP2003, 17/07/2003E.Radicioni14 Approach to construction
HEP2003, 17/07/2003E.Radicioni15 Challenges High-gradient RF cavities in solenoidal fields Operating liquid H 2 absorbers with thin windows and complying with safety regulations Integration of cooling channel components For cost reasons, only a small section of the cooling channel: Emittance reduction will be about 10% need to measure emittance reduction at the level of 10 -3 Particle detectors will have to be operated in a harsh environment (RF and X-ray from dark current in RF cavities) An accelerator physicist AND a particle physicist challenge!
HEP2003, 17/07/2003E.Radicioni16 Detectors /upstream particle ID and timing Time of flight system: 10 m flight path TOF scintillator hodoscopes with 70 ps time resolution Yields / separation better than 1% at 300 MeV/c
HEP2003, 17/07/2003E.Radicioni17 Fiber tracker performance (p T ) = 110 keV (p T /p z ) ~ 0.06% (E/p z ) ~ 0.06% Resolution better than 10% of widths at eq. emittance
HEP2003, 17/07/2003E.Radicioni18 Detectors /downstream PID and timing 0.5% of decay in flight. Large bias if a forward-decay e is kept as Two systems are foreseen to get to eliminate electrons below 10 -3 : Electromagnetic Calorimeter (mip = em shower 27 MeV, use also z profile) Aerogel Cherenkov ( n=1.02, blind, threshold well above beam momentum ) Positive Identification of a particle in the calorimeter consistent with a muon AND no electron signal in the Cherenkov