The large iron structure, serving as the flux return, is segmented with graded thickness (2÷10 cm plates) and instrumented with Resistive Plate Counters (RPC).

This fine segmentation permits muon identification at low momentum muons and KL detection.

The Muon and Neutral Hadron DetectorThe Muon and Neutral Hadron Detector INFN - Bari, INFN - Frascati, INFN - Genova, LLNL, INFN - Bari, INFN - Frascati, INFN - Genova, LLNL,

INFN - Napoli, University of Praire View, University of WinsconsinINFN - Napoli, University of Praire View, University of Winsconsin

Instrumented Flux Return (IFR)Instrumented Flux Return (IFR)

Pions

p (GeV)

log 10

(L/

L)

Muons

Pions

Hadron DiscriminationHadron Discrimination

Hadrons and muons have different interactions in the Fe absorbers:

• hadrons are stopped earlier than muons

• hadrons may produce showers

• hadrons may decay

Track finding is quite straight forward since the average occupancy is rather low

• using appropriate algorithms IFR reconstruction produces

• 1D clusters (one or more adjacent strips hit on the same readout plane of a single layer),

• 2D clusters (two or more 1D clusters on different layers),

• cluster are then associated with charged tracks in the drift chamber and clusters in the calorimeter

Discriminating variables separate muons from pions. They depend on the detailed pattern of the IFR clusters (for example the penetration depth in the iron of the track, the transverse size of the cluster, the missed planes along the track etc).

To combine the rejection power of all the considered variables, a likelihood ratio criterion is applied.

The IFR muon identification capabilities decrease at low momenta (charged tracks with p< 400 MeV/c do not reach the IFR because of the effect of the magnetic field and energy loss in the inner detectors).

Last layer hit for cosmics muonsLast layer hit for cosmics muons Last layer hit for muons Last layer hit for muons (Monte Carlo)(Monte Carlo)

Likelihood ratio of the Likelihood ratio of the on on hypothesis hypothesis

Muons

Muon identification Muon identification efficiency (Barrel)efficiency (Barrel)

p (GeV)

p(GeV)

(rad)

Rms = 0.09 rad

Expected efficiency as a function of momentum and polarExpected efficiency as a function of momentum and polarangle resolution for Kangle resolution for KLL from Monte Carlo simulation from Monte Carlo simulation

Neutral Hadron DetectionNeutral Hadron Detection• IFR is also able to detect neutral hadrons. In particular it allows the study of B decay

channels involving a KL , which have opposite asymmetry respect to a KS.

• A KL “candidate” is tagged as a 3D cluster (containing at least 4 hit layers or 3 layers and an EMC cluster) that is not associated to any track in the Drift Chamber .

• IFR measures the direction of the cluster with a good resolution ; the KL energy is not measured.

KKL L detection efficienciesdetection efficiencies• Since detection efficiency cannot be reliably estimated for low momentum KL,

calibration with data are needed.• Calibration channels are:

• KL, from inclusive production and decay

• radiative production e + e- • KL, from D* decays.

BBJ/J/ K KL L event selectionevent selection• Look for J/ l+l- decays

• Look for a KL in the opposite direction in the xy plane (cut=400mrd)

• Derive KL momentum from:

M2 = mK

2 + m2 + 2 (EK E - pK p cos

A di-muon event from colliding beamsA di-muon event from colliding beams