CERN Accelerating science

Components of a ``traditional'' particle physics experiment. Each particle type has its own signature in the detector. For example, if a particle is detected only in the electromagnetic calorimeter, it is fairly certain that it is a photon.

Comparison of the relative energy resolutions (as given by Eq.~\ref{eq:cal}) of the different EM calorimeters (left image) and hadronic calorimeters (right image) at the LHC experiments. The values of the parameters $a$, $b$ and $c$ were in all cases determined by fits to the data from beam tests and are given in the descriptions of the different experiments in Sects. \ref{sec:atlascms}, \ref{sec:alice} and \ref{sec:lhcb}. In case of the ATLAS and CMS hadronic calorimeters the resolutions of the whole systems combining EM and hadronic calorimeters are shown.

Comparison of the relative energy resolutions (as given by Eq.~\ref{eq:cal}) of the different EM calorimeters (left image) and hadronic calorimeters (right image) at the LHC experiments. The values of the parameters $a$, $b$ and $c$ were in all cases determined by fits to the data from beam tests and are given in the descriptions of the different experiments in Sects. \ref{sec:atlascms}, \ref{sec:alice} and \ref{sec:lhcb}. In case of the ATLAS and CMS hadronic calorimeters the resolutions of the whole systems combining EM and hadronic calorimeters are shown.

{\it Armenteros-Podolanski plot} from the ALICE experiment using data from $\sqrt{s}=900$\,GeV proton collisions. The different V$_0$ particles can be separated using the kinematics of their decay products. The orientation of the decay is described with respect to the momentum vector of the $V_0$. $p^\pm_L$ are the longitudinal momenta of the positively and negatively charged decay products with respect to the V$_0$ particle's direction. $q_T$ represents the transverse component of the momentum of the positive decay product.

Demonstration of the power of PID by mass determination, using the example of the $\phi \rightarrow$\ K$^+$K$^-$ decay measured with the LHCb RICH system (preliminary data from $\sqrt{s}=900$\,GeV p--p collisions~\cite{lhcbmoriond}). The left image shows the invariant mass obtained from all combinations of pairs of tracks without PID. The right image shows how the $\phi$ meson signal appears when tracks can be identified as kaons.

Approximate minimum detector length required to achieve a K/$\pi$ separation of $n_\sigma\geq 3\,\sigma$ with three different PID techniques. For the energy loss technique we assume a gaseous detector. For the TOF technique, the detector length represents the particle flight path over which the time-of-flight is measured. For the Cherenkov technique only the radiator thickness is given. The thicknesses of an expansion gap and of the readout chambers have to be added.

Perspective view of the ATLAS detector~\cite{atlas}. The dimensions are 25\,m in height and 44\,m in length, the overall weight of the detector is approximately 7000 tonnes.

Perspective view of the CMS detector~\cite{cms}. The dimensions are 14.6\,m in height and 21.6\,m in length. The overall weight is approximately 12\,500 tonnes.

Perspective view of the ALICE detector~\cite{alice}. The dimensions are 16\,m in height and 26\,m in length. The overall weight is approximately 10\,000 tonnes.

Schematic view of the LHCb detector~\cite{lhcb}.

Typical curves of the ionization signal as a function of particle momentum for a number of known charged particles. A parameterization like the one suggested in Ref.~\cite{blumrolandi} was used to calculate the curves.

Typical separation power achievable with ionization measurements in a gaseous detector. The ionization curves from Fig.~\ref{fig:aleph} were used together with an assumed energy resolution of 5\%.

3D view of the TPC field cage~\cite{tpcnim}. The high voltage electrode is located at the center of the 5\,m long drift volume. The two endplates are divided into 18 sectors holding two readout chambers each.

Measured ionization signals of charged particles as a function of the track rigidity (particle momentum divided by charge number). $11\times 10^{6}$ events from a data sample recorded with $\sqrt{s}=7$\,TeV p--p collisions provided by the LHC were analysed. The lines correspond to a parameterization of the Bethe-Bloch curve as described in Ref.~\cite{blumrolandi}. Also heavier nuclei like deuterons and tritium and their anti-particles are found.

Distribution of the difference between the measured ionization signals and the one expected for Kaons for a momentum slice of 50\,MeV/c width. The lines are fits, indicating that a sum of four Gaussians represents well the data. The peak centered at zero reflects the abundance of kaons, the other peaks represent other particle species.

Particle separation with TOF measurements for three different system time resolutions ($\sigma_{TOF}=60$, 80 and 100\,ps) and for a track length $L=3.5$\,m. Infinitely good precisions on momentum and track length measurements are assumed.

Cross-section of an ALICE MRPC~\cite{alice}.

TOF measurements with a cosmic data sample from the year 2009. Since the start and stop time were both measured with the ALICE TOF, the resolution of a single time measurement is obtained from the histogram by dividing its width by $\sqrt{2}$. The resulting resolution of 88.5\,ps corresponds to $\sigma_{t_1}$ from Eq.~\ref{eq:tofressum}.

Velocity $\beta=v/c$ as measured with the ALICE TOF detector as a function of the particle momentum $p$ multiplied with the particle charge number $Z$ for a data sample taken with $\sqrt{s}=7$\,TeV collisions provided by the LHC in the year 2010. No data is available for momenta $\lesssim$300\,MeV/c, since these particles do not reach the detector due to the curvature of their tracks in the magnetic field.

Histogram of the TOF signal for a given momentum window of 100\,MeV/c width. The data sample was recorded with $\sqrt{s}=900$\,GeV p--p collisions provided by the LHC. The lines are fits to the data, indicating that a sum of three Gaussians well represents the data.

Demonstration of ALICE's PID capabilities by combining the ionization measurements in the TPC and the mass calculated using the TOF signal. Electrons, pions, kaons and protons are clearly visible in a wide momentum range. The data sample was recorded with $\sqrt{s}=900$\,GeV p--p collisions provided by the LHC.

Schematic drawing of a TOF counter based on a MCP-PMT~\cite{richtof2}. The MCP-PMT actually detects Cherenkov photons emitted in the quartz glass entrance window and has a very good time resolution.

Left image: schematic layout of an ALICE HMPID module, showing radiator, expansion gap and photon detector~\cite{alice}. Right image: example ring as seen by the HMPID. The ring has a radius of the order 10\,cm, but its shape is distorted due to the impact angle of the particle.

Left image: schematic layout of an ALICE HMPID module, showing radiator, expansion gap and photon detector~\cite{alice}. Right image: example ring as seen by the HMPID. The ring has a radius of the order 10\,cm, but its shape is distorted due to the impact angle of the particle.

Dependence of the Cherenkov angle measured by the ALICE HMPID on the particle momentum. The lines are the theoretical curves calculated using Eq.~\ref{eq:cangle} with the refractive index $n=1.3$. No data is available for momenta below about 600\,MeV/c, because only particles with higher momenta reach the detector.

Left image: schematic layout of the LHCb RICH1 detector. The acceptance of $\pm 250$mrad is indicated. Right image: schematic view of an HPD of the LHCb RICH system. Both figures are taken from Ref.~\cite{lhcb}.

Left image: schematic layout of the LHCb RICH1 detector. The acceptance of $\pm 250$mrad is indicated. Right image: schematic view of an HPD of the LHCb RICH system. Both figures are taken from Ref.~\cite{lhcb}.

Cherenkov angles as a function of momentum for different particle species and for the three different values of the refractive index $n$ corresponding to the three radiator materials used in the LHCb RICH setup.

Typical, simulated LHCb event in the RICH1 detector~\cite{lhcb}. The data from the two photodetector planes are drawn in the upper and lower halves.

Particle separation achievable with Cherenkov angle measurements for the three different radiator materials used in the LHCb RICH detectors. As Cherenkov angular resolutions the expected values from Tab.~\ref{tab:lhcbrich} were used.

Schematic view of a proximity-focusing RICH with an inhomogeneous aerogel radiator in the focusing configuration. Cherenkov photons from the different radiator layers overlap, thus minimising the error in the angular resolution due to the uncertainly in the emission point~\cite{aero3}.

Schematic side view of a TOP counter~\cite{top1}. Cherenkov photons are guided to the photon detector by total internal reflections. The difference in the propagation time for two particle types (here kaons and pions) is due to the emission angle of the Cherenkov radiation and can be used to enhance PID information.

Schematic view of the AMS\,02 spectrometer~\cite{ams}.