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A Road to W/Z Separation at ILC

A Road to W/Z Separation at ILC. (From a hadron collider perspective) Hadron collider experiments do not have very sophisticated hadron calorimeters. Granularity is rather coarse in h,f . Few (if any) depth segments. Jet energy resolution is not very good, in general.

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A Road to W/Z Separation at ILC

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  1. A Road to W/Z Separation at ILC (From a hadron collider perspective) Hadron collider experiments do not have very sophisticated hadron calorimeters. Granularity is rather coarse in h,f. Few (if any) depth segments. Jet energy resolution is not very good, in general. The physics potential (jet-jet mass resolution) is not, in general, limited by the detector performance, but rather by physics and environmental effects: jet definition, gluon radiation, underlying event fluctuations.. Will not the same effects limit the physics potential at the ILC???

  2. Here (and later): WW and ZZ @ 500 GeV, jet clustering at the particles level Various versions of JADE and Durham jet algorithms. Particles taken as massless or pions or real massed used. Detectable differences in jet-jet mass resolution, but W and Z peaks well separated. Cone in h,f space, R=1. Left: Jet energy/direction only. Right: Jet mass calculated from the ‘cells’ hit.

  3. Environment in e+e- collider is very different from that at the hadron collider • Every particle assigned to some jet • No underlying event It appears that W/Z separation is in principle possible, given ‘good enough’ detector.

  4. Jet Energy Smearing: Take 1 • Take jets a massless objects, E=p, smear the energy with A/sqrt(E) and recalculate jet-jet masses • Plots are for A=0, 20%, 40%, 60%, 80% • Severe degradation of jet-jet mass even for A=0. Jet masses are important for jet-jet mass resolution • Correct procedure is to smear the observed energy deposits, cluster, etc.. In the meantime, though..

  5. Jet Energy Smearing, Take 2 • Smear the jet energy • Rescale the jet mass by Esmared/Etrue Rough impression about the stochastic term: • 0.2 – excellent • 0.4 – quite good • 0.6 – not so good • 0.8 - hopeless

  6. Jet Composition Well known fact: • 60% charged particles • 28% photons • 10 % neutral hadrons (neutrons and K0’s) Caveats: exact proportions may vary: • Jet type • Jet finding algorithm

  7. Temptation (a.k.a. PFA) Measure different components of the jet with different sub-detectors best suited for this component: • Charged particles – tracking – Dp < 10-4p • Photons – EM calorimeter - DE = 0.15*sqrt(E) • Neutral hadrons – hadron calorimeter - DE = A*sqrt(E) Hadron calorimeter design specification: how important A is? How small can it be? Cost vs complexity vs physics tradeoffs?

  8. perfect Tracking EM A=0.4 A=1.2 A=0.8 How Good Had Calorimeter ? • A = 0.4 – 0.8 quite acceptable • Note: hadron calorimeter may be the dominant contribution to the resolution, provided that it can be used to measure ‘neutrals only’

  9. Of all desired features of the hadron calorimeter the most important one is the ability to measure neutral hadrons without ‘contamination’ from charged hadrons • What features of the calorimeter are important? • What are the unavoidable limitations due to jets natural distributions and hadron showers sizes in matter?

  10. Jet Particles Distribution about the Jet Axis Dq • Hadron-physics measures Dh,Df are not useful in e+e- environment • Although some of jet particles may be surprisingly far from the jet axis (~p), most of them are within a tight cone (especially high energy ones) Dh DR Df

  11. Where are the ‘Other’ (i.e. Not-jet) Particles with Respect to Jet Axis ? • An indication of back-to-back jets, but • Fairly uniform population in the detector, including high energy ‘foreign’ particles close to the jet axis

  12. Jet Particles In the Hadron Calorimeterr A typical distance between hadrons at the front face of the hadron calorimeter is ~10-20 cm The detector challenge is to separate the hadronic showers

  13. Hadron Calorimeter • (How) Can one separate energy depositions of different hadrons? • What features of passive/active medium is the most important? Toy-tool: • homogenous hadron calorimeter • Variable sampling frequency • Variable absorber material • Variable active detector (scintilator vs RPC) • Variable call granularity

  14. RPC vs Solid Scintillator: Sensitivity to low Energy Neutrons 10 GeV pions RPC: Smaller showers Fewer hits Scintilator: Wider showers More hits

  15. RPC Gallery • Relatively clean environment at the expense of the energy resolution (fewer hits) • Treatment of the disconnected (topologically) energy deposits likely to be the principal challenge

  16. Scintilator: ‘Cleaning Up’ ? • It is possible (but not proven) that the abundance of hits (contributing to the energy resolution) is detrimental to the PF algorithm and that a better jet energy resolution would be accomplished by reducing the sensitivity to slow neutrons • Slow neutrons rattle around for a long time. Timing cut? • Slow neutrons kick slower yet protons. Energy threshold? • Can such a cleanup be used in stages: pattern recognition/energy measurement?

  17. Timing cut? < 1 nsec < 10 nsec < 100 nsec > 100 nsec

  18. Pulse Height Cut? Ph > 0.5 mip

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