Jet properties in pp and its modification in nuclear matter
Abstract
Jets are manifestation of hard scatterings of partons and its understanding in pp involves the partondistribution functions, the QCD-hard scattering processes and the long distance fragmentation phenomena.Therefore, jets can be used to study the parton level kinematics. Intrinsic transverse momentumof partons and the subsequent gluon radiations prior to hard scatterings [1], give rise to acoplanarityof dijets, depending on the Q2 of hard scatterings and the center of mass energy of collisions. Multiplescatterings of the hard scattered partons in cold nuclear matter may incorporate a modi cation of jetstructure.Two quantities commonly used to characterize the properties of jets are (i) jt, the transverse momentumof the jet fragments relative to the jet axis and (ii) kt, the transverse component of the momentumof the hard scattered partons. A measurement of the jet parameters, phj2t i and phk2t i [2] at STAR inpp collisions at ps = 62.4, 200 and 500 GeV using di-hadron correlation techniques is presented in widekinematics rage. 0 (Et = 6.5 to 18.5 GeV) and charged tracks (pt = 3.0-8.5 GeV/c) are used as triggerparticles in this analysis. A comparison of the jet parameters for pp and dAu (at various centralities) atps = 200 GeV will be presented.References[1] R.P Feynman, R.D. Field, and G.C. Fox, Phys. Rev. D18 3320(1978).[2] S.S. Adler et al., Phys. Rev. D74 072002(2006).
Observation of Collective Lamb Shift in Single-Photon Superradiance
Abstract
In 1955 Willis Lamb received the noble prize, for the experimental observation of the ‘Lamb-shift’, a tiny energy shift of the bound atomic levels due to the interaction of the electron with virtual photons, which is at the heart of quantum electrodynamics and subsequent quantum field theories. However, Lamb shift was observed only for atomic gases. Although predicted about 35 years ago, the ‘collective lamb shift’ in real solid state samples was not observed, because (1) the atom-atom interaction masks the observable shift, ((2) the sample should be optically thin upon absorption and optically thick upon emission – such a sample was not realized in practice. We have overcome these problems by embedding a 57Fe (14.4 keV nuclear resonance) probe layer at the centre of a planar wave guide and exciting the 57Fe nuclei to a superradiant state by 14.4 keV single-photon pulsed-synchrotron radiation at a grazing incidence geometry (at the 1st wave guide mode of the cavity). Finally, by using the (coherent elastic) nuclear resonant scattering combined with Doppler energy analysis, we have measured, for the first time, the collective Lamb shift and the single-photon superradiance of 57Fe nuclei in two wave guide samples with 0.6 nm and 1.2 nm thickness of the 57Fe layer, respectively [1]. The details will be presented. Our observation and experimental method opens a new field for the study of light-mater interaction and the study of the Lamb shift and superradiance in quantum optics.[1] R. Röhlsberger, K. Schlage, B. Sahoo, S. Couet and R. Rüffer, Science, 328 (2010) 1248.
