The Hoyle state plays a crucial role in the helium burning of stars that have reached the red giant stage. The close proximity of this state to the triple-alpha threshold is needed for the production of carbon, oxygen, and other elements necessary for life. We investigate whether this life-essential condition is robust or delicately fine-tuned by measuring its dependence on the fundamental constants of nature, specifically the light quark mass and the strength of the electromagnetic interaction. We show that there exist strong correlations between the alpha-particle binding energy and the various energies relevant to the triple-alpha process. We derive limits on the variation of these fundamental parameters from the requirement that sufficient amounts of carbon and oxygen be generated in stars. We also discuss the implications of our results for an anthropic view of the Universe.

The MuCap experiment at the Paul Scherrer Institute has measured the rate ${\Lambda }_S$ of muon capture from the singlet state of the muonic hydrogen atom to a precision of 1%. A muon beam was stopped in a time projection chamber filled with 10-bar, ultrapure hydrogen gas. Cylindrical wire chambers and a segmented scintillator barrel detected electrons from muon decay. ${\Lambda }_S$ is determined from the difference between the ${\mu }^{-}$ disappearance rate in hydrogen and the free muon decay rate. The result is based on the analysis of $1.2\times {10}^{10}$ ${\mu }^{-}$ decays, from which we extract the capture rate ${\Lambda }_S=(714.9\pm {5.4}_{\mathrm{stat}}\pm {5.1}_{\mathrm{syst}}){\mathrm{s}}^{-1}$ and derive the proton’s pseudoscalar coupling $g_P(q_0^2=-0.88m_{\mu }^2)=8.06\pm 0.55$.

In this Letter we report the first results on ${\pi }^{\pm }$, $K^{\pm }$, $p$, and $\overline{p}$ production at midrapidity ($|y|<0.5$) in central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$, measured by the ALICE experiment at the LHC. The $p_{\mathrm{T}}$ distributions and yields are compared to previous results at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ and expectations from hydrodynamic and thermal models. The spectral shapes indicate a strong increase of the radial flow velocity with $\sqrt{s_{\mathrm{NN}}}$, which in hydrodynamic models is expected as a consequence of the increasing particle density. While the $K/\pi$ ratio is in line with predictions from the thermal model, the $p/\pi$ ratio is found to be lower by a factor of about 1.5. This deviation from thermal model expectations is still to be understood.

The excited state of the ${}^{12}\mathrm{C}$ nucleus known as the “Hoyle state” constitutes one of the most interesting, difficult, and timely challenges in nuclear physics, as it plays a key role in the production of carbon via fusion of three alpha particles in red giant stars. In this Letter, we present ab initio lattice calculations which unravel the structure of the Hoyle state, along with evidence for a low-lying spin-2 rotational excitation. For the ${}^{12}\mathrm{C}$ ground state and the first excited spin-2 state, we find a compact triangular configuration of alpha clusters. For the Hoyle state and the second excited spin-2 state, we find a “bent-arm” or obtuse triangular configuration of alpha clusters. We also calculate the electromagnetic transition rates between the low-lying states of ${}^{12}\mathrm{C}$.

The suppression of the individual ${\rm Y}(nS)$ states in PbPb collisions with respect to their yields in $pp$ data has been measured. The PbPb and $pp$ data sets used in the analysis correspond to integrated luminosities of $150\mu {\mathrm{b}}^{-1}$ and $230{\mathrm{nb}}^{-1}$, respectively, collected in 2011 by the CMS experiment at the LHC, at a center-of-mass energy per nucleon pair of 2.76 TeV. The ${\rm Y}(nS)$ yields are measured from the dimuon invariant mass spectra. The suppression of the ${\rm Y}(nS)$ yields in PbPb relative to the yields in $pp$, scaled by the number of nucleon-nucleon collisions, $R_{AA}$, is measured as a function of the collision centrality. Integrated over centrality, the $R_{AA}$ values are $0.56\pm 0.08(\mathrm{stat})\pm 0.07(\mathrm{syst})$, $0.12\pm 0.04(\mathrm{stat})\pm 0.02(\mathrm{syst})$, and lower than 0.10 (at 95% confidence level), for the ${\rm Y}(1S)$, ${\rm Y}(2S)$, and ${\rm Y}(3S)$ states, respectively. The results demonstrate the sequential suppression of the ${\rm Y}(nS)$ states in PbPb collisions at LHC energies.

We introduce a novel photon production mechanism stemming from the conformal anomaly of $\mathrm{QCD}\times \mathrm{QED}$ and the existence of strong (electro)magnetic fields in heavy ion collisions. Using the hydrodynamical description of the bulk modes of QCD plasma, we show that this mechanism leads to the photon production yield that is comparable to the yield from conventional sources. This mechanism also provides a significant positive contribution to the azimuthal anisotropy of photons, $v_2$, as well as to the radial “flow.” We compare our results to the data from the PHENIX Collaboration.

Classical novae are important contributors to the abundances of key isotopes, such as the radioactive ${}^{18}\mathrm{F}$, whose observation by satellite missions could provide constraints on nucleosynthesis models in novae. The ${}^{17}\mathrm{O}(p,\gamma ){}^{18}\mathrm{F}$ reaction plays a critical role in the synthesis of both oxygen and fluorine isotopes, but its reaction rate is not well determined because of the lack of experimental data at energies relevant to novae explosions. In this study, the reaction cross section has been measured directly for the first time in a wide energy range $E_{\mathrm{c}.\mathrm{m}.}\simeq 200–370\mathrm{keV}$ appropriate to hydrogen burning in classical novae. In addition, the $E_{\mathrm{c}.\mathrm{m}.}=183\mathrm{keV}$ resonance strength, $\omega \gamma =1.67\pm 0.12\mu \mathrm{eV}$, has been measured with the highest precision to date. The uncertainty on the ${}^{17}\mathrm{O}(p,\gamma ){}^{18}\mathrm{F}$ reaction rate has been reduced by a factor of 4, thus leading to firmer constraints on accurate models of novae nucleosynthesis.

Two years after the discovery of element 117, we undertook a second campaign using the ${}^{249}\mathrm{Bk}+{}^{48}\mathrm{Ca}$ reaction for further investigations of the production and decay properties of the isotopes of element 117 on a larger number of events. The experiments were started in the end of April 2012 and are still under way. This Letter presents the results obtained in 1200 hours of an experimental run with the beam dose of ${}^{48}\mathrm{Ca}$ of about $1.5\times {10}^{19}$ particles. The ${}^{249}\mathrm{Bk}$ target was irradiated at two energies of ${}^{48}\mathrm{Ca}$ that correspond to the maximum probability of the reaction channels with evaporation of three and four neutrons from the excited ${}^{297}117$. In this experiment, two decay chains of ${}^{294}117$ ($3n$) and five decay chains of ${}^{293}117$ ($4n$) were detected. In the course of the long-term work, ${}^{249}\mathrm{Cf}$—the product of decay of ${}^{249}\mathrm{Bk}$ (330 d)—is being accumulated in the target. Consequently, in the present experiment, we also detected a single decay of the known isotope ${}^{294}118$ that was produced during 2002–2005 in the reaction ${}^{249}\mathrm{Cf}({}^{48}\mathrm{Ca},3n){}^{294}118$. The obtained results are compared with the data from previous experiments. The experiments are carried out in the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, using the heavy-ion cyclotron U400.

The passage of muons through matter is dominated by the Coulomb interaction with electrons and nuclei. The interaction with the electrons leads to continuous energy loss and stopping of the muons. The interaction with nuclei leads to angle “diffusion.” Two muon-imaging methods that use flux attenuation and multiple Coulomb scattering of cosmic-ray muons are being studied as tools for diagnosing the damaged cores of the Fukushima reactors. Here, we compare these two methods. We conclude that the scattering method can provide detailed information about the core. Attenuation has low contrast and little sensitivity to the core.

The transverse energy ($E_{\mathrm{T}}$) in Pb-Pb collisions at 2.76 TeV nucleon-nucleon center-of-mass energy ($\sqrt{s_{\mathrm{NN}}}$) has been measured over a broad range of pseudorapidity ($\eta$) and collision centrality by using the CMS detector at the LHC. The transverse energy density per unit pseudorapidity ($d{E}_{\mathrm{T}}/d\eta$) increases faster with collision energy than the charged particle multiplicity. This implies that the mean energy per particle is increasing with collision energy. At all pseudorapidities, the transverse energy per participating nucleon increases with the centrality of the collision. The ratio of transverse energy per unit pseudorapidity in peripheral to central collisions varies significantly as the pseudorapidity increases from $\eta =0$ to $|\eta |=5.0$. For the 5% most central collisions, the energy density per unit volume is estimated to be about $14\mathrm{GeV}/{\mathrm{fm}}^3$ at a time of $1\mathrm{fm}/c$ after the collision. This is about 100 times larger than normal nuclear matter density and a factor of 2.6 times higher than the energy density reported at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ at the Relativistic Heavy Ion Collider.

We report on a search for neutrinoless double-beta decay of ${}^{136}\mathrm{Xe}$ with EXO-200. No signal is observed for an exposure of 32.5 kg yr, with a background of $\sim 1.5\times {10}^{-3}{\mathrm{kg}}^{-1}{\mathrm{yr}}^{-1}{\mathrm{keV}}^{-1}$ in the $\pm 1\sigma$ region of interest. This sets a lower limit on the half-life of the neutrinoless double-beta decay $T_{1/2}^{0\nu \beta \beta }({}^{136}\mathrm{Xe})>1.6\times {10}^{25}\mathrm{yr}$ (90% C.L.), corresponding to effective Majorana masses of less than 140–380 meV, depending on the matrix element calculation.

The rotational band structure of the $Z=104$ nucleus ${}^{256}\mathrm{Rf}$ has been observed up to a tentative spin of $20\hslash$ using state-of-the-art $\gamma$-ray spectroscopic techniques. This represents the first such measurement in a superheavy nucleus whose stability is entirely derived from the shell-correction energy. The observed rotational properties are compared to those of neighboring nuclei and it is shown that the kinematic and dynamic moments of inertia are sensitive to the underlying single-particle shell structure and the specific location of high-$j$ orbitals. The moments of inertia therefore provide a sensitive test of shell structure and pairing in superheavy nuclei which is essential to ensure the validity of contemporary nuclear models in this mass region. The data obtained show that there is no deformed shell gap at $Z=104$, which is predicted in a number of current self-consistent mean-field models.

Charge correlations in lattice gauge calculations suggest that up, down, and strange charges move independently in the quark-gluon plasma, and that the density of such charges is similar to what is expected from simple thermal arguments. Here, we show how specific elements of the charge-charge correlation matrix in the quark-gluon plasma survive hadronization and become manifest in final-state charge-charge correlation measurements.

The current evaluation of the triple-$\alpha$ reaction rate assumes that the $\alpha$ decay of the 7.65 MeV, $0^{+}$ state in ${}^{12}\mathrm{C}$, commonly known as the Hoyle state, proceeds sequentially via the ground state of ${}^8\mathrm{Be}$. This assumption is challenged by the recent identification of two direct $\alpha$-decay branches with a combined branching ratio of $17(5)\%$. If correct, this would imply a corresponding reduction in the triple-$\alpha$ reaction rate with important astrophysical consequences. We have used the ${}^{11}\mathrm{B}({}^3\mathrm{He},d)$ reaction to populate the Hoyle state and measured the decay to three $\alpha$ particles in complete kinematics. We find no evidence for direct $\alpha$-decay branches, and hence our data do not support a revision of the triple-$\alpha$ reaction rate. We obtain an upper limit of $5\times {10}^{-3}$ on the direct $\alpha$ decay of the Hoyle state at $95\%$ C.L., which is 1 order of magnitude better than a previous upper limit.

We report on the first experimental study of quadrupole collectivity in the very neutron-rich nuclei ${}^{47,48}\mathrm{Ar}$ using intermediate-energy Coulomb excitation. These nuclei are located along the path from doubly magic Ca to collective S and Si isotopes, a critical region of shell evolution and structural change. The deduced $B(E2)$ transition strengths are confronted with large-scale shell-model calculations in the sdpf shell using the state-of-the-art SDPF-Uand EPQQM effective interactions. The comparison between experiment and theory indicates that a shell-model description of Ar isotopes around $N=28$ remains a challenge.

We report the first measurement of the parity-violating asymmetry $A_{\mathrm{PV}}$ in the elastic scattering of polarized electrons from ${}^{208}\mathrm{Pb}$. $A_{\mathrm{PV}}$ is sensitive to the radius of the neutron distribution ($R_n$). The result $A_{\mathrm{PV}}=0.656\pm 0.060(\mathrm{stat})\pm 0.014(\mathrm{syst})\mathrm{ppm}$ corresponds to a difference between the radii of the neutron and proton distributions $R_n-R_p={0.33}_{-0.18}^{+0.16}\mathrm{fm}$ and provides the first electroweak observation of the neutron skin which is expected in a heavy, neutron-rich nucleus.

We report on the first observation of dineutron emission in the decay of ${}^{16}\mathrm{Be}$. A single-proton knockout reaction from a $53\mathrm{MeV}/\mathrm{u}$ ${}^{17}\mathrm{B}$ beam was used to populate the ground state of ${}^{16}\mathrm{Be}$. ${}^{16}\mathrm{Be}$ is bound with respect to the emission of one neutron and unbound to two-neutron emission. The dineutron character of the decay is evidenced by a small emission angle between the two neutrons. The two-neutron separation energy of ${}^{16}\mathrm{Be}$ was measured to be 1.35(10) MeV, in good agreement with shell model calculations, using standard interactions for this mass region.

The first direct mass measurement of ${}^6\mathrm{He}$ has been performed with the TITAN Penning trap mass spectrometer at the ISAC facility. In addition, the mass of ${}^8\mathrm{He}$ was determined with improved precision over our previous measurement. The obtained masses are $m({}^6\mathrm{He})=6.018885883(57)\mathrm{u}$ and $m({}^8\mathrm{He})=8.03393444(11)\mathrm{u}$. The ${}^6\mathrm{He}$ value shows a deviation from the literature of $4\sigma$. With these new mass values and the previously measured atomic isotope shifts we obtain charge radii of 2.060(8) and 1.959(16) fm for ${}^6\mathrm{He}$ and ${}^8\mathrm{He}$, respectively. We present a detailed comparison to nuclear theory for ${}^6\mathrm{He}$, including new hyperspherical harmonics results. A correlation plot of the point-proton radius with the two-neutron separation energy demonstrates clearly the importance of three-nucleon forces.

Charge radii of all magnesium isotopes in the $sd$ shell have been measured, revealing evolution of the nuclear shape throughout two prominent regions of assumed deformation centered on ${}^{24}\mathrm{Mg}$ and ${}^{32}\mathrm{Mg}$. A striking correspondence is found between the nuclear charge radius and the neutron shell structure. The importance of cluster configurations towards $N=8$ and collectivity near $N=20$ is discussed in the framework of the fermionic molecular dynamics model. These essential results have been made possible by the first application of laser-induced nuclear orientation for isotope shift measurements.

Evidence for the neutron-rich hypernucleus ${}_{\Lambda }{}^6\mathrm{H}$ is presented from the FINUDA experiment at $\mathrm{DA}\Phi \mathrm{NE}$, Frascati, studying $({\pi }^{+},{\pi }^{-})$ pairs in coincidence from the $K_{\mathrm{stop}}^{-}+{}^6\mathrm{Li}\to {}_{\Lambda }{}^6\mathrm{H}+{\pi }^{+}$ production reaction followed by ${}_{\Lambda }{}^6\mathrm{H}\to {}^6\mathrm{He}+{\pi }^{-}$ weak decay. The production rate of ${}_{\Lambda }{}^6\mathrm{H}$ undergoing this two-body ${\pi }^{-}$ decay is determined to be $(2.9\pm 2.0)\times {10}^{-6}/K_{\mathrm{stop}}^{-}$. Its binding energy, evaluated jointly from production and decay, is $B_{\Lambda }({}_{\Lambda }{}^6\mathrm{H})=(4.0\pm 1.1)\mathrm{MeV}$ with respect to ${}^5\mathrm{H}+\Lambda$. A systematic difference of $(0.98\pm 0.74)\mathrm{MeV}$ between $B_{\Lambda }$ values derived separately from decay and from production is tentatively assigned to the ${}_{\Lambda }{}^6\mathrm{H}$ $0_{\mathrm{g}.\mathrm{s}.}^{+}\to 1^{+}$ excitation.