125960882
Measurement of Drell-Yan cross sections and flavor asymmetry in the nucleon sea
Measurements of Drell-Yan cross sections from the bombardment of liquid deuterium and hydrogen with an 800 GeV proton beam are reported. The relative cross section (σpd/2σpp) directly probes the ratio of anti-down (d) to anti-up (ū) quarks in the nucleon sea, while absolute measurement of the deuterium cross section constrain d+ū. Results are compared with previous experiments and next-to-leading order calculations based on current sets of parton distribution functions.
121866403
GENERATION OF ULTRA-SHORT ELECTRON BUNCHES FOR LIGHT SOURCE RESEARCH
An S-band thermionic 1.5-cell rf gun injector system is being built at NSRRC for Taiwan Photon Source (TPS) booster. At optimized field ratio, an electron beam with linear energy chirp can be generated by the rf gun. The beam is then compressed by an alpha magnet such that ultra-short electron bunches at femto-second bunch length can be obtained. Particle dynamics has been studied for an rf gun with nose cone at the cathode, simulation results show that 74 pC bunches at about 97 fs is achievable. Some of the critical components such as the rf gun and alpha magnet have been fabricated and being tested in house. Experiments for intense coherent THz radiations and tunable femto-second X-ray from ultra-short bunches are being proposed as future applications.
18308235
Search for new particles in hadronic events with isolated photons
Abstract A search for the neutral Higgs boson in the processes e + e − → Z → H 0 γ → q q γ and e + e − → Z → Z ∗ H 0 → q q γγ has been performed using 2.8 million hadronic Z decays collected with the L3 detector at LEP from 1991 through 1994. No evidence for these processes has been observed. Upper limits at 95% confidence level for the corresponding cross sections have been set and the results have been compared with theoretical predictions beyond the Standard Model.
17067286
Hard Photodisintegration of a Proton Pair
We present the first study of high energy photodisintegration of proton-pairs through the gamma + 3He -> p+p+n channel. Photon energies from 0.8 to 4.7 GeV were used in kinematics corresponding to a proton pair with high relative momentum and a neutron nearly at rest. An s^{-11} scaling of the cross section was observed, as predicted by the constituent counting rule. The onset of the scaling is at a higher energy and the cross section is significantly lower then for pn pair photodisintegration. For photon energies below the scaling region, the scaled cross section was found to present a strong energy-dependent structure not observed in deuteron photodisintegration.
14695790
String Gas Cosmology and Non-Gaussianities
Recently it has been shown that string gas cosmology, an alternative model of the very early universe which does not involve a period of cosmological inflation, can give rise to an almost scale invariant spectrum of metric perturbations. Here we calculate the non-Gaussianities of the spectrum of cosmological fluctuations in string gas cosmology, and find that these non-Gaussianities depend linearly on the wave number and that their amplitude depends sensitively on the string scale. If the string scale is at the TeV scale, string gas cosmology could lead to observable non-Gaussianities, if it is close to the Planck scale, then the non-Gaussianities on current cosmological scales are negligible.
124435122
Projectile fragmentation reactions of Ar-40 at 57 MeV/nucleon
The projectile fragmentation reactions of Ar-40 at 57 MeV/nucleon on Be-9 and Ta-181 targets have been studied by the Radioactive Ion Beam Line in Lanzhou (RIBLL) at the Heavy-Ion Research Facility in Lanzhou (HIRFL). The momentum distributions of fragments have been measured and the competition between different mechanisms are observed. The production cross sections have been obtained and compared with the empirical parametrization of fragmentation cross section (EPAX), abrasion-ablation (AA), and heavy-ion phase space exploration (HIPSE) models, and the target dependence of fragment cross sections has also been discussed
118426546
Transverse-Momentum Resummation for Gauge Boson Pair Production at the Hadron Collider
We perform the transverse-momentum resummation for $W^{+}W^{-}$, $ZZ$, and $W^{\pm}Z$ pair productions at the next-to-next-to-leading logarithmic accuracy using soft-collinear effective theory for $\sqrt{S}=8 \text{TeV}$ and $\sqrt{S}=14 \text{TeV}$ at the LHC, respectively. Especially, this is the first calculation of $W^{\pm}Z$ transverse-momentum resummation. We also include the non-perturbative effects and discussions on the PDF uncertainties. Comparing with the next-to-leading logarithmic results, the next-to-next-to-leading logarithmic resummation can reduce the dependence of the transverse-momentum distribution on the factorization scales significantly. Finally, we find that our numerical results are consistent with data measured by CMS collaboration for the $ZZ$ production, which have been only reported by the LHC experiments for the unfolded transverse-momentum distribution of the gauge boson pair production so far, within theoretical and experimental uncertainties.