MIRA/LOOK Exhibition

This exhibition produced for the Wistariahurst Museum in Holyoke and displayed in September and October of 2008, highlights community planning and design initiatives that promote cultural expression and community visions for Holyoke. The designs were created by Professor Joseph Krupczynski and students from the Architecture + Design program at the University of Massachusetts Amherst

MIRA/LOOK Exhibition

This exhibition produced for the Wistariahurst Museum in Holyoke and displayed in September and October of 2008, highlights community planning and design initiatives that promote cultural expression and community visions for Holyoke. The designs were created by Professor Joseph Krupczynski and students from the Architecture + Design program at the University of Massachusetts Amherst

Multiplicity dependence of light (anti-)nuclei production in p–Pb collisions at sNN=5.02 TeV

The measurement of the deuteron and anti-deuteron production in the rapidity range −1 < y < 0 as a function of transverse momentum and event multiplicity in p–Pb collisions at √sNN = 5.02 TeV is presented. (Anti-)deuterons are identified via their specific energy loss dE/dx and via their time-of- flight. Their production in p–Pb collisions is compared to pp and Pb–Pb collisions and is discussed within the context of thermal and coalescence models. The ratio of integrated yields of deuterons to protons (d/p) shows a significant increase as a function of the charged-particle multiplicity of the event starting from values similar to those observed in pp collisions at low multiplicities and approaching those observed in Pb–Pb collisions at high multiplicities. The mean transverse particle momenta are extracted from the deuteron spectra and the values are similar to those obtained for p and particles. Thus, deuteron spectra do not follow mass ordering. This behaviour is in contrast to the trend observed for non-composite particles in p–Pb collisions. In addition, the production of the rare 3He and 3He nuclei has been studied. The spectrum corresponding to all non-single diffractive p-Pb collisions is obtained in the rapidity window −1 < y < 0 and the pT-integrated yield dN/dy is extracted. It is found that the yields of protons, deuterons, and 3He, normalised by the spin degeneracy factor, follow an exponential decrease with mass number

Measurement of prompt D0^{0}, D+^{+}, D∗+^{*+}, and DS+ {\mathrm{D}}_{\mathrm{S}}^{+} production in p–Pb collisions at sNN \sqrt{{\mathrm{s}}_{\mathrm{NN}}} = 5.02 TeV

International audienceThe measurement of the production of prompt D$^{0}$, D$^{+}$, D$^{*+}$, and ${\mathrm{D}}_{\mathrm{S}}^{+}$ mesons in proton–lead (p–Pb) collisions at the centre-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV, with an integrated luminosity of 292 ± 11 μb$^{−1}$, are reported. Differential production cross sections are measured at mid-rapidity (−0.96 < y$_{cms}$< 0.04) as a function of transverse momentum (p$_{T}$) in the intervals 0 < p$_{T}$< 36 GeV/c for D$^{0}$, 1 < p$_{T}$< 36 GeV/c for D$^{+}$ and D$^{*+}$, and 2 < p$_{T}$< 24 GeV/c for D$^{+}$ mesons. For each species, the nuclear modification factor R$_{pPb}$ is calculated as a function of p$_{T}$ using a proton-proton (pp) ref- erence measured at the same collision energy. The results are compatible with unity in the whole p$_{T}$ range. The average of the non-strange D mesons R$_{pPb}$ is compared with theoretical model predictions that include initial-state effects and parton transport model predictions. The p$_{T}$ dependence of the D$^{0}$, D$^{+}$, and D$^{*+}$ nuclear modification factors is also reported in the interval 1 < p$_{T}$< 36 GeV/c as a function of the collision centrality, and the central-to-peripheral ratios are computed from the D-meson yields measured in different centrality classes. The results are further compared with charged-particle measurements and a similar trend is observed in all the centrality classes. The ratios of the p$_{T}$-differential cross sections of D$^{0}$, D$^{+}$, D$^{*+}$, and ${\mathrm{D}}_{\mathrm{S}}^{+}$ mesons are also reported. The ${\mathrm{D}}_{\mathrm{S}}^{+}$ and D$^{+}$ yields are compared as a function of the charged-particle multiplicity for several p$_{T}$ intervals. No modification in the relative abundances of the four species is observed with respect to pp collisions within the statistical and systematic uncertainties

Azimuthal correlations of prompt D mesons with charged particles in pp and p–Pb collisions at sNN\sqrt{s_{NN}} = 5.02 TeV

International audienceThe measurement of the azimuthal-correlation function of prompt D mesons with charged particles in pp collisions at $\sqrt{s} =5.02\ \hbox {TeV}$ and p–Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02\ \hbox {TeV}$ with the ALICE detector at the LHC is reported. The $\mathrm{D}^{0}$, $\mathrm{D}^{+}$, and $\mathrm{D}^{*+}$ mesons, together with their charge conjugates, were reconstructed at midrapidity in the transverse momentum interval $3 0.3\ \hbox {GeV}/c$ and pseudorapidity $|\eta | < 0.8$. The properties of the correlation peaks appearing in the near- and away-side regions (for $\Delta \varphi \approx 0$ and $\Delta \varphi \approx \pi$, respectively) were extracted via a fit to the azimuthal correlation functions. The shape of the correlation functions and the near- and away-side peak features are found to be consistent in pp and p–Pb collisions, showing no modifications due to nuclear effects within uncertainties. The results are compared with predictions from Monte Carlo simulations performed with the PYTHIA, POWHEG+PYTHIA, HERWIG, and EPOS 3 event generators

Longitudinal and azimuthal evolution of two-particle transverse momentum correlations in Pb-Pb collisions at sNN=2.76TeV\sqrt{s_{\rm{NN}}} = 2.76 TeV

This paper presents the first measurements of the charge independent (CI) and charge dependent (CD) two-particle transverse momentum correlators G2CI and G2CD in Pb–Pb collisions at sNN=2.76TeV by the ALICE collaboration. The two-particle transverse momentum correlator G2 was introduced as a measure of the momentum current transfer between neighboring system cells. The correlators are measured as a function of pair separation in pseudorapidity (Δ η ) and azimuth (Δ φ ) and as a function of collision centrality. From peripheral to central collisions, the correlator G2CI exhibits a longitudinal broadening while undergoing a monotonic azimuthal narrowing. By contrast, G2CD exhibits a narrowing along both dimensions. These features are not reproduced by models such as HIJING and AMPT. However, the observed narrowing of the correlators from peripheral to central collisions is expected to result from the stronger transverse flow profiles produced in more central collisions and the longitudinal broadening is predicted to be sensitive to momentum currents and the shear viscosity per unit of entropy density η/s of the matter produced in the collisions. The observed broadening is found to be consistent with the hypothesized lower bound of η/s and is in qualitative agreement with values obtained from anisotropic flow measurements.This paper presents the first measurements of the charge independent (CI) and charge dependent (CD) two-particle transverse momentum correlators $G_{2}^{\rm CI}$ and $G_{2}^{\rm CD}$ in Pb--Pb collisions at \sqrt{s_{\text{NN}}} = 2.76\;\text{\TeVe} by the ALICE collaboration. The two-particle transverse momentum correlator $G_{2}$ was introduced as a measure of the momentum current transfer between neighbouring system cells. The correlators are measured as a function of pair separation in pseudorapidity ($\Delta \eta$) and azimuth ($\Delta \varphi$) and as a function of collision centrality. From peripheral to central collisions, the correlator $G_{2}^{\rm CI}$ exhibits a longitudinal broadening while undergoing a monotonic azimuthal narrowing. By contrast, $G_{2}^{\rm CD}$ exhibits a narrowing along both dimensions. These features are not reproduced by models such as HIJING and AMPT. However, the observed narrowing of the correlators from peripheral to central collisions is expected to result from the stronger transverse flow profiles produced in more central collisions and the longitudinal broadening is predicted to be sensitive to momentum currents and the shear viscosity per unit of entropy density $\eta/s$ of the matter produced in the collisions. The observed broadening is found to be consistent with the hypothesized lower bound of $\eta/s$ and is in qualitative agreement with values obtained from anisotropic flow measurements

Λ3H^3_\Lambda\mathrm{H} and Λˉ3H‾^3_{\bar{\Lambda}}\mathrm{\overline{H}} lifetime measurement in Pb-Pb collisions at sNN=\sqrt{s_{\mathrm{NN}}} = 5.02 TeV via two-body decay

International audienceAn improved value for the lifetime of the (anti-)hypertriton has been obtained using the data sample of Pb–Pb collisions at sNN=5.02 TeV collected by the ALICE experiment at the LHC. The (anti-)hypertriton has been reconstructed via its charged two-body mesonic decay channel and the lifetime has been determined from an exponential fit to the d N /d( ct ) spectrum. The measured value, τ=242−38+34 (stat.) ± 17 (syst.) ps, is compatible with representative theoretical predictions, thus contributing to the solution of the longstanding hypertriton lifetime puzzle

Evidence of rescattering effect in Pb-Pb collisions at the LHC through production of K∗(892)0\rm{K}^{*}(892)^{0} and ϕ(1020)\phi(1020) mesons

Measurements of K$^*$(892)$^0$ and ϕ(1020) resonance production in Pb–Pb and pp collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with the ALICE detector at the Large Hadron Collider are reported. The resonances are measured at midrapidity (|y| < 0.5) via their hadronic decay channels and the transverse momentum ($p_{\rm T}$) distributions are obtained for various collision centrality classes up to $p_{\rm T}$ = 20 GeV/c . The $p_{\rm T}$-integrated yield ratio K$^*$(892)$^0$/K in Pb–Pb collisions shows significant suppression relative to pp collisions and decreases towards more central collisions. In contrast, the ϕ(1020)/K ratio does not show any suppression. Furthermore, the measured K$^*$(892)$^0$/K ratio in central Pb–Pb collisions is significantly suppressed with respect to the expectations based on a thermal model calculation, while the ϕ(1020)/K ratio agrees with the model prediction. These measurements are an experimental demonstration of rescattering of K$^*$(892)$^0$ decay products in the hadronic phase of the collisions. The K$^*$(892)$^0$/K yield ratios in Pb–Pb and pp collisions are used to estimate the time duration between chemical and kinetic freeze-out, which is found to be ∼ 4–7 fm/c for central collisions. The $p_{\rm T}$-differential ratios of K$^*$(892)$^0$/K, ϕ(1020)/K, K$^*$(892)$^0$/ π , ϕ(1020)/π , p/K$^*$(892)$^0$ and p/ϕ(1020) are also presented for Pb–Pb and pp collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. These ratios show that the rescattering effect is predominantly a low-$p_{\rm T}$ phenomenon

Exploration of jet substructure using iterative declustering in pp and Pb–Pb collisions at LHC energies

The ALICE collaboration at the CERN LHC reports novel measurements of jet substructure in pp collisions at $\sqrt{s}$= 7 TeV and central Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV. Jet substructure of track-based jets is explored via iterative declustering and grooming techniques. We present the measurement of the momentum sharing of two-prong substructure exposed via grooming, the $z_{\rm{g}}$, and its dependence on the opening angle, in both pp and Pb-Pb collisions. We also present the first measurement of the distribution of the number of branches obtained in the iterative declustering of the jet, which is interpreted as the number of its hard splittings. In Pb-Pb collisions, we observe a suppression of symmetric splittings at large opening angles and an enhancement of splittings at small opening angles relative to pp collisions, with no significant modification of the number of splittings. The results are compared to predictions from various Monte Carlo event generators to test the role of important concepts in the evolution of the jet in the medium such as color coherence