Lessons from PHOBOS

In June 2005 the PHOBOS Collaboration completed data taking at RHIC. In five years of operation PHOBOS recorded information for Au+Au at $\sqrt{s_{NN}}$ = 19.6, 62.4, 130, and 200 GeV, Cu+Cu at 22.4, 62.4 and 200 GeV, d+Au at 201 GeV, and p+p at 200 and 410 GeV, altogether more than one billion collisions. Using these data we have studied the energy and centrality dependence of the global properties of charged particle production over essentially the full 4$\pi$ solid angle and (for pions near mid rapidity) charged particle spectra down to transverse momenta below 30 MeV/c. We have also studied correlations of particles separated in pseudorapidity by up to 6 units. We find that the global properties of heavy ion collisions can be described in terms of a small number of simple dependencies on energy and centrality, and that there are strong correlations between the produced particles. To date no single model has been proposed which describes this rich phenomenology. In this talk I summarize what the data is explicitly telling us.Comment: 8 pages, 15 figure

Extended Longitudinal Scaling: direct evidence of saturation

Multiparticle production of charged particles at high energies exhibit the phenomenon of Limiting Fragmentation. Furthermore, the region in rapidity over which the production of particles appears to be independent of energy, increases with energy. It is argued that this phenomenon, known as Extended Longitudinal Scaling, is a direct manifestation of some kind of saturation, akin to that in the Color Glass Condensate picture of particle production.Comment: 10 pages, 10 figures, Invited paper presented at The Glasma Workshop, BNL, May 201

Trends in multiparticle production and some "predictions" for pp and PbPb collisions at LHC

Based on trends seen at lower energies we "predict" the multiplicities and pseudorapidity distributions of particle density and elliptic flow that will be seen in PbPb and pp collisions at the LHC. We argue that, if these predictions turn out to be correct, either these quantities are insensitive to the state of matter created in high energy heavy ion collisions or the observed simplicity and universality of the data must be telling us something profound about the mechanism of particle production, which to this date is not well understood.Comment: Invited Talk at SQM2007 Conferenc

Strangeness enhancement at LHC

We study production of strangeness in the hot QGP fireball in conditions achieved at LHC, and use these results to obtain soft (strange) hadron multiplicities. We compare the chemical equilibrium and non-equilibrium conditions and identify characteristic experimental observables.Comment: Presented at SQM07, to appear in JPG special issue. One table with prediction

Particle production at very low and intermediate transverse momenta in d+Au and Au+Au collisions

The transverse momentum spectra of identified charged particles have been measured at very low and intermediate transverse momenta in Au+Au collisions at sqrt(s_NN) = 62.4 GeV and d+Au collisions at sqrt(s_NN) = 200 GeV using the PHOBOS detector at RHIC. New results on charged particle production at very low p_T in central Au+Au collisions at sqrt(s_{NN) = 200 GeV in the centrality intervals 0-6% and 6-15% are presented. A comparison of the PHOBOS low-p_T data with predictions of a recent optical model is shown. The shapes of m_T spectra for d+Au and Au+Au collisions are compared.Comment: Presented at the 18th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions, Quark Matter 2005, Budapest, Hungary, Aug. 4-9, 200

Molecular and Behavioral Analysis of \u3cem\u3eDrosophila\u3c/em\u3e Circadian Photoreception and Circadian Thermoreception: A Dissertation

Circadian clocks are biological timekeepers that help maintain an organism’s behavior and physiological state optimally timed to the Earth’s day/night cycle. To do this, these internal pacemakers must accurately keep track of time. Equally importantly, they must be able to adjust their oscillations in response to external time cues to remain properly synchronized with the environment, and correctly anticipate environmental changes. When the internal clock is offset from its surrounding day/night cycle, clinically relevant disruptions develop, ranging from inconveniences such as jet-lag to more severe problems such as sleep disorders or mood disorders. In this work, I have used the fruit fly, Drosophila melanogaster, as a model organism to investigate how light and temperature can synchronize circadian systems. My initial studies centered on an intracellular photoreceptor, CRYPTOCHROME (CRY). CRY is a blue light photoreceptor previously identified as a major component of the primary light-input pathway into the Drosophila circadian clock. We used molecular techniques to show that after light-activation, CRY binds to the key circadian molecule TIMELESS (TIM). This interaction irreversibly targets TIM, but not CRY, for degradation. Further studies characterizing a newly isolated cry mutant, crym, showed that the carboxyl-terminus of CRY is not necessary for CRY’s ability to impart photic information to the molecular clock. Instead, the C-terminus appears to be necessary for normal CRY stability and protein-protein interactions. Thus, we conclude that in contrast to previous reports on CRYs of other species, where the C-terminal domain was required for transduction of photic information, the C-terminus of DrosophilaCRY has a purely modulatory function. During the second part of my dissertation work, I focused my studies on circadian thermoreception. While the effects of light in synchronization of the Drosophilaclock to environmental cycles have been extensively characterized, significantly less is known about temperature input pathways into the circadian pacemaker. I have used two approaches to look at how temperature affects the circadian system. First, I conducted a series of behavioral analyses looking at how locomotor rhythms can be phase-shifted in response to temperature cycles. By examining the behavior of genetically ablated flies, we determined that the well-characterized neurons controlling morning and evening surges of activity during light/dark cycles are also implicated in morning and evening behaviors under temperature cycles. However, we also find evidence of cells that contribute to modulating afternoon and evening behavior specifically under temperature cycles. These data contribute to a growing number of studies in the field suggesting that pacemaker cells may play different roles under various environmental conditions. Additionally, we provide data showing that intercellular communication plays an important role in regulating circadian response to temperature cycles. When the morning oscillator is absent or attenuated, the evening cells respond abnormally quickly to temperature cycles. My work thus provides information on the roles of different cell groups during temperature cycles, and suggests that beyond simply synchronizing individual oscillating cells, intercellular network activity may also have a role in modulating proper response to environmental time cues. Finally, I present some preliminary work looking at effects of temperature on known circadian molecules. Using a combination of in vivo and cell culture techniques, I have found that TIM protein levels decrease at higher temperatures. My cell culture data suggest that this is a proteasome-independent degradation event. As TIM is also a key molecule in the light-input pathway, the stability of TIM proteins may be a key point of integration for light and temperature input pathways. While additional research needs to be conducted to confirm these effects in vivoin wild-type flies, these preliminary results identify a possible avenue for further study. Taken together, my work has contributed new data on both molecular and neuronal substrates involved in processing light and temperature inputs into the Drosophila circadian clock

Bulk hadron production at high rapidities

Recent experimental observations on the `bulk' features of particle production at high (pseudo)rapidities will be reviewed. This kinematic region is of interest mostly because of its relevance to the theoretical description of initial state effects of nuclei at ultra-relativistic energies. Measurements of the charged hadron multiplicity density as well as the pseudorapidity dependence of the elliptic and directed flow exhibit a remarkable scaling property as a function of collision energy. This scaling seems to hold for pions and even photons and J/Psi-s, but is violated for protons. The special role of baryons will be discussed using selected results on nuclear transparency and baryon stopping.Comment: 10 pages, 8 figures. Prepared for the Proceedings of the Quark Matter 2005 Conferenc

3D Jet Tomography of Twisted Strongly Coupled Quark Gluon Plasmas

The triangular enhancement of the rapidity distribution of hadrons produced in p+A reactions relative to p+p is a leading order in A^{1/3}/log(s) violation of longitudinal boost invariance at high energies. In A+A reactions this leads to a trapezoidal enhancement of the local rapidity density of produced gluons. The local rapidity gradient is proportional to the local participant number asymmetry, and leads to an effective rotation in the reaction plane. We propose that three dimensional jet tomography, correlating the long range rapidity and azimuthal dependences of the nuclear modification factor, R_{AA}(\eta,\phi,p_\perp; b>0), can be used to look for this intrinsic longitudinal boost violating structure of $A+A$ collisions to image the produced twisted strongly coupled quark gluon plasma (sQGP). In addition to dipole and elliptic azimuthal moments of R_{AA}, a significant high p_\perp octupole moment is predicted away from midrapidity. The azimuthal angles of maximal opacity and hence minima of R_{AA} are rotated away from the normal to the reaction plane by an `Octupole Twist' angle, \theta_3(\eta), at forward rapidities.Comment: 10 Pages, 16 Figures, RevTex, Replaced with Peer reviewed verion for PR