High-resolution Photon Spectrometer Research Articles

Temporal X-ray Reconstruction using Temporal and Spectral Measurements at LCLS

Transverse deflecting structures (TDSs) are widely used in accelerator physics to measure the longitudinal density of particle bunches. When used in combination with a dispersive section, the whole longitudinal phase space density can be imaged. At the Linac Coherent Light Source (LCLS), the installation of such a device downstream of the undulators enables the reconstruction of the X-ray temporal intensity profile by comparing longitudinal phase space distributions with lasing on and lasing off. However, the resolution of this TDS is limited to around 1 fs rms (root mean square), and therefore, it is not possible to resolve single self-amplified spontaneous emission (SASE) spikes within an X-ray photon pulse. By combining the power spectrum from a high resolution photon spectrometer and the temporal structure from the TDS, the overall resolution is enhanced, thus allowing the observation of temporal, single SASE spikes. The combined data from the spectrometer and the TDS is analysed using an iterative algorithm to obtain the actual intensity profile. In this paper, we present some improvements to the reconstruction algorithm as well as real data taken at LCLS.

Temporal X-ray reconstruction using temporal and spectral measurements

Transverse deflecting structures (TDS) are widely used in accelerator physics to measure the longitudinal density of particle bunches. When used in combination with a dispersive section, the whole longitudinal phase space density can be imaged. At the Linac Coherent Light Source (LCLS), the installation of such a device downstream of the undulators enables the reconstruction of the X-ray temporal intensity profile by comparing longitudinal phase space distributions with lasing on and lasing off [1]. However, the resolution of this TDS is limited to around 1 fs rms (root mean square), and therefore, in most cases, it is not possible to resolve single self-amplified spontaneous emission (SASE) spikes within one photon pulse.By combining the intensity spectrum from a high resolution photon spectrometer [2] and the temporal structure from the TDS, the overall resolution is enhanced, thus allowing the observation of temporal, single SASE spikes. The combined data from the spectrometer and the TDS is analyzed using an iterative algorithm to obtain the actual intensity profile.In this paper, we present the reconstruction algorithm as well as analyzed data obtained from simulations which shows the reliability of this method. Real data will be published at a later stage.

Potential physics measurement with ALICE electromagnetic calorimeters

We present the two electromagnetic calorimeters of the ALICE (A Large Ion Collider Experiment) experiment at LHC (Large Hadron Collider). One is the high-resolution PHOton Spectrometer (PHOS) made of lead tungsten crystals and the other is the ElectroMagnetic Calorimeter (EMCal), a Lead-Scintillator sampling calorimeter. They are dedicated to the measurement and identification of direct photons, light neutral mesons such as π 0 , η and ω ( 782 ) , and jets emitted in proton-proton and heavy-ion collisions at the LHC energies. The PHOS is capable of precisely detecting photons with momentum range between 0.1 GeV/c and 100 GeV/c and the EMCal can extend the prompt photon and light neutral meson momentum measurement beyond 200 GeV/c. The objective of the study is to explore the physics of strongly interacting QCD matter under extreme conditions of energy density.

ALICE-PHOS: acceptance and efficiency correction factors p−p→π 0+X at 10 TeV

In ultra-relativistic Heavy-Ion Collisions (HIC), the properties of the quark gluon plasma (QGP) can be explored, in particular, via measurements of neutral pions. The π0 is an important probe for both proton and heavy ion physics. In the former case, π0 production provides an important mean of testing pQCD as well as useful data to constrain current and future theoretical models. In the latter case, π0 measurements will serve as a baseline for exploring the nature of the HIC hard scattering. In the ALICE experiment, π0 mesons are identified as they decay into two photons (π0→γγ) using the high-resolution photon spectrometer (PHOS). PHOS will measure π0 transverse momentum over a wide range, from hundreds of MeV/c to several tens of GeV/c. An estimation of π0 production cross-section in proton–proton collisions is calculated in a next-to-leading order (NLO) approximation and first presented. The π0 geometrical acceptance and the identification efficiency along with the analysis on the invariant mass are the two important correction factors for obtaining a realistic π0 spectrum discussed in this paper.

Effects of photon collimators on the spectral distribution of bremsstrahlung radiation between 20 and 35 MeV

The relative effects of photon collimators on the spectral distribution of bremsstrahlung radiation in the energy range 20–35 MeV have been measured using a high resolution photon spectrometer.

Branching Ratio of theγRays from the 184.6-keV State inZn67

Using a high-resolution photon spectrometer, the relative intensity of the 91.3- and 93.3-keV $\ensuremath{\gamma}$ rays from the decay of ${\mathrm{Ga}}^{67}$ has been measured as $\frac{{I}_{\ensuremath{\gamma}}(91.3)}{{I}_{\ensuremath{\gamma}}(93.3)}=(8.5\ifmmode\pm\else\textpm\fi{}0.8)%$. From this result, the branching ratio of the transitions depopulating the 184.6-keV state of ${\mathrm{Zn}}^{67}$ was deduced as $\frac{I(91.3)}{I(184.6)}=\frac{3.5}{24.2}$. The internal conversion coefficients for the nearly pure $M1$ 91.3-keV transition are given. Several apparent discrepancies in the literature are discussed.