• Energy Research

Parton energy loss in the quark-gluon plasma (QGP) is studied with a measurement of photon-tagged jet production in 1.7 nb$^{-1}$ of Pb+Pb data and 260 pb$^{-1}$ of $pp$ data, both at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV, with the ATLAS detector. The process $pp \to \gamma$+jet+$X$ and its analogue in Pb+Pb collisions is measured in events containing an isolated photon with transverse momentum ($p_\mathrm{T}$) above $50$ GeV and reported as a function of jet $p_\mathrm{T}$. This selection results in a sample of jets with a steeply falling $p_\mathrm{T}$ distribution that are mostly initiated by the showering of quarks. The $pp$ and Pb+Pb measurements are used to report the nuclear modification factor, $R_\mathrm{AA}$, and the fractional energy loss, $S_\mathrm{loss}$, for photon-tagged jets. In addition, the results are compared with the analogous ones for inclusive jets, which have a significantly smaller quark-initiated fraction. The $R_\mathrm{AA}$ and $S_\mathrm{loss}$ values are found to be significantly different between those for photon-tagged jets and inclusive jets, demonstrating that energy loss in the QGP is sensitive to the colour-charge of the initiating parton. The results are also compared with a variety of theoretical models of colour-charge-dependent energy loss. Physics letters / B 846, 138154 - (2023). doi:10.1016/j.physletb.2023.138154 Published by North-Holland Publ., Amsterdam

The PICASSO project is a cold dark matter (CDM) search experiment relying on the superheated droplet technique. The detectors use superheated freon liquid droplets (active material) dispersed and trapped in a polymerized gel. This detection technique is based on the phase transition of superheated droplets at about room temperature and ambient pressure. The phase transition is induced by nuclear recoils when an atomic nucleus in the droplets interacts with incoming subatomic particles. This includes CDM particles candidate as the neutralino (a yet-to-discover particle predicted in extensions of the Standard Model of particle physics). Simulations performed to understand the detector response to neutrons and alpha particles are presented along with corresponding data obtained at the Montreal Laboratory. 13 pages, 4 figures. To appear in the Proceedings of the 14th International Conference on Solid State Dosimetry, June 27 - July 2 2004, Yale University, New Haven, CT, USA

AbstractA dedicated sample of Large Hadron Collider proton-proton collision data at centre-of-mass energy$$ \sqrt{s} $$s= 8 TeV is used to study inclusive single diffractive dissociation,pp → X p. The intact final-state proton is reconstructed in the ATLAS ALFA forward spectrometer, while charged particles from the dissociated systemXare measured in the central detector components. The fiducial range of the measurement is−4.0<log10ξ < −1.6 and 0.016< |t| <0.43 GeV2, whereξis the proton fractional energy loss andtis the squared four-momentum transfer. The total cross section integrated across the fiducial range is 1.59±0.13 mb. Cross sections are also measured differentially as functions ofξ,t, and ∆η, a variable that characterises the rapidity gap separating the proton and the systemX. The data are consistent with an exponentialtdependence, dσ/dt ∝eBtwith slope parameterB= 7.65±0.34 GeV−2. Interpreted in the framework of triple Regge phenomenology, theξdependence leads to a pomeron intercept ofα(0) = 1.07±0.09.