<<O>>  Difference Topic AlgoritmoParticleFlowEnLaZonaHaciaDelante (r1.4 - 23 Dec 2008 - Main.iglesias)

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## 4. Algoritmo Particle Flow en la zona hacia delante

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As you know, The majority of the interesting physics processes at the Linear Collider involves multi-jet final states. One of the goals of the Linear Collider detector performance is to be able to separate W and Z boson in their hadronic decay modes.

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In order to achieve this goal, the jet energy resolution of detectors (sigma E/E) is required to be as good as:
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In order to achieve this goal, the jet energy resolution of detectors (σE/E) is required to be as good as:

This is a factor two better than the best energy resolution achieved at LEP.

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#### 4.a.ii.Porque es interesante la zona hacia delante?

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An application of the capability to distinguish between W and Z jets are the gauge boson pair production (e+e- WW, e+e-  ZZ). The gauge boson are typically very low angle emited (see Marcel’s talk).
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An application of the capability to distinguish between W and Z jets are the gauge boson pair production (e+e- → WW, e+e- → ZZ). The gauge boson are typically very low angle emited (see Marcel’s talk in 8th SiLC Meeting).

The events for the ZZ production process are generated as:

The W pair production is generated as:

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If only leptonic decays of W and Z bosons are considered, the polar angle distribution of e- and e+ from both processes is extremely peaked in the forward direction. At Ecm=500 GeV? two thirds of e- are emitted with < 30o or > 150o. At larger energy the tendency for e- to be emitted in the very forward direction becomes even more pronounced. The polar angle distribution of muons and -leptons is more central but still a considerable fraction is to be reconstructed in the forward detector: for the ZZ events, (~60 %).

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Therefore, these processes form a very strong physics case for a low-angle reconstruction with great precision. So, where Particle Flow is really usefull for improvement the enegy resolution is in the Forward Region

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Therefore, these processes form a very strong physics case for a low-angle reconstruction with great precision. So, we can say that where Particle Flow is really usefull for improvement the enegy resolution is in the Forward Region.

#### 4.a.iii.Problemas en la zona hacia delante en ILD

Our area of study will be: theta 30-10 degrees, so the jets will pass throught:
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Some problem that we can find in the forward region are:

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• Noise occupancy due to pair production which affect track reconstrucion,
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• Noise occupancy due to pair production which affect track reconstrucion: When the two bunches of the ILC collide, the electrons are disturbed by the electromagnetic field of the incoming bunch. Under this influence, the electrons radiate photons (an effect known as beamstrahlung). The produced photons may convert into pairs of an electron and a positron through one of the processes whose diagrams are depicted in the figure below:

The large majority is soft and/or emitted at low angle and are trapped in the “accumulation zone”.

• Less favourable orientation of the magnetic field,
• the amount of material along the particle trajectory,
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• the degradation of the electromagnetic resolution due to the TPC EndPlate? (Which difficult the identification of e- and photons)…
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• Abundant low momentum tracks: Tracks below a given pT curl up and “loop” through the detector, leaving through the endcap. For a Bfield of 4 Tesla and a radius of over 1.5 m, pT = 0.3 B R = nearly 2 GeV?. A challenge for reconstruction due to Multiple Scattering

• the degradation of the electromagnetic resolution due to the TPC EndPlate (Which difficult the identification of e- and photons)…

For the aplication of the Particle Flow algorithm, we also will have the problem to extrapolate track from TPC to ECAL matching TPC hits with ECAL cluster using information from  the Endcap Tracker Disks (between TPC end-plate and the face of ECAL endcap)as well as take into account the energy loss in TPC endplate

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