Measurement of sigma chi c2 B(chi c2-->J/psi gamma)/sigma chi c1 B(chi c1 -->J/psi gamma) in pp collisions at square root s=1.96 TeV

We measure the ratio of cross section times branching fraction, Rp=sigma chi c2 B(chi c2-->J/psi gamma)/sigma chi c1 B(chi c1-->J/psi gamma), in 1.1 fb(-1) of pp collisions at square root s=1.96 TeV. This measurement covers the kinematic range pT(J/psi)>4.0 GeV/c, |eta(J/psi)<1.0, and pT(gamma)>1.0 GeV/c. For events due to prompt processes, we find Rp=0.395+/-0.016(stat)+/-0.015(syst). This result represents a significant improvement in precision over previous measurements of prompt chi c1,2 hadro production.     

Observation of B --> phiK and B --> phiK*

We have studied two-body charmless hadronic decays of B mesons into the final states straight phiK and phiK(*). Using 9.7 million B&Bmacr; pairs collected with the CLEO II detector, we observe the decays B- --> phiK- and B0--> phiK(*0) with the following branching fractions: B(B--->phiK-) = (5.5(+2.1)(-1.8)+/-0.6)x10(-6) and B(B0--> phiK(*0)) = (11.5(+4.5+1.8)(-3.7-1.7))x10(-6). We also see evidence for the decays B0-->phiK0 and B---> phiK(*-). However, since the statistical significance is not overwhelming for these modes, we determine upper limits of <12.3x10(-6) and <22.5x10(-6) ( 90% confidence level), respectively.     

Real radiation at next-to-next-to-leading order in QCD: e+e- --> 2 jets through O(alpha2s)

We present a calculation of the differential two-jet cross section in e(+)e(-) annihilation through next-to-next-to-leading order (NNLO) in the strong coupling constant alpha(s). The calculation is performed using a new method for dealing with real radiation suggested recently by us. For the first time, the two-jet event rate is computed directly, without any reference to the inclusive cross section e(+)e(-)-->hadrons. We also calculate the energy distribution of the leading jet in e(+)e(-)-->2 jets and find significant modifications of the shape of this distribution at NNLO.     

Dynamic stabilization in 1sigma(u)-->1pi(g) excited nitrogen clusters

High-resolution 1s near-edge spectra of molecular nitrogen and variable size nitrogen clusters obtained using monochromatic synchrotron radiation from the high brilliance BESSY-II storage ring facility are reported. The vibrationally resolved 1sigma(u)-->1pi(g) core-to-valence excitation band of clusters shows a distinct redshift of 6+/-1 meV relative to the isolated molecule, but the vibrational structure and linewidths are essentially unchanged. This shift is assigned to dynamic stabilization of 1sigma(u)-->1pi(g) excited molecules in clusters, arising from the dynamic dipole moment generated by core-hole localization in the low-symmetry cluster field. This leads to changes in intermolecular interactions compared to the ground-state cluster. Such spectral shifts are expected to occur generally in molecular clusters and in the corresponding condensed phase.     

Measurement of the ratio of inclusive cross sections sigma(pp --> Z + b jet)/sigma(pp --> Z + jet) at square root(s) = 1.96 TeV

Using the data collected with the D0 detector at square root(s) = 1.96 TeV, for integrated luminosities of about 180 pb(-1), we have measured the ratio of inclusive cross sections for pp --> Z + b jet to pp --> Z + jet production. The inclusive Z + b-jet reaction is an important background to searches for the Higgs boson in associated ZH production at the Fermilab Tevatron collider. Our measurement is the first of its kind, and relies on the Z --> e+ e- and Z --> mu+ mu- modes. The combined measurement of the ratio yields 0.021+/-0.005 for hadronic jets with transverse momenta pT > 20 GeV/c and pseudorapidities absolute value(eta) < 2.5, consistent with next-to-leading-order predictions of the standard model.     

Lineshape studies of the 1s yellow exciton in Cu2O by resonance Raman scattering

The enhancement of the cross section for Raman scattering has been measured near resonance with the 1S yellow exciton in Cu₂O $\text{(}\text{v}{}_{\mathrm{1SY}}\text{? 16,399 cm}{}^{-1}\text{)}$. The shape of the enhancement is shown to be Lorentzian to beyond 10 halfwidths from the peak. From the temperature dependence of the width of the enhancement profile, we extract separately the rates for exciton- acoustic phonon scattering, γ_sc(T), and for non-radiative decay, γ_nr, of this exciton state. We find γ_nr = 2.4 × 10¹⁰sec^-1 and γ_sc(T=5.4K) = 0.85 × 10¹⁰sec^-1.     

Q2 Dependence of quadrupole strength in the gamma*p --> Delta(+)(1232) --> p pi(0) transition

Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual tensor forces between quarks or distortions from the pion cloud. Sensitivity to quark versus pion degrees of freedom occurs through the Q2 dependence of the magnetic (M1+), electric (E1+), and scalar (S1+) multipoles in the gamma*p-->Delta(+)-->p pi(0) transition. We report new experimental values for the ratios E(1+)/M(1+) and S(1+)/M(1+) over the range Q2 = 0.4-1.8 GeV2, extracted from precision p(e,e(')p)pi(0) data using a truncated multipole expansion. Results are best described by recent unitary models in which the pion cloud plays a dominant role.