Give time resolution of order 1 ns.

Avalanche mode:
The number of secondary electron-ion pairs is proportional to the number of primary electrons (so, Q∝dE/dx)

Streamer mode:
It's the most used in HEP. Higher voltages. The incident particle causes a discharge. No sensitivity to energy.
A quencher gas is added to the detector gas to control and localize the discharge.

Gas mixture for the streamer mode:

• Detector main gas: noble gases are the best, since they require the lowest electric field for discharge (argon is the cheapest and ionizes easily)
• Quencher: polyatomic gas (e.g. methane), since they absorb the radiated photons and dissipate their energy through dissociation and elastic collisions

RPCs in CMS

The electric field inside a RPC is uniform. Electrons made free by the ionizing particle near the cathode generate a larger number of secondary electrons (exponential multiplication). The detected signal is the cumulalive effect of all the avalanches. A proper threshold setting allows the detection of a signal dominated by the electrons generated near the cathode. The threshold setting determines to a large extent the time delay of the pulse, the time resolution and also the efficiency.