119107849
Bose symmetry interference effects of 4 pi final states
We analyze the relative branching ratios of 4 pi final states pi(+)pi(-)pi(+)pi(-), pi(+)pi(-)pi(0)pi(0), and pi(0)pi(0)pi(0)pi(0), from various resonances with J(PC) = 0(++), 0(-+), 2(++). We find that in some cases the interference effects due to Bose symmetry make their ratios obviously different from the naive counting values without these effects. The results allow an accurate estimate of the 4 pi branching ratios of relevant resonances when only one (or two) modes are measured in a given experiment.
119179797
Searching for high speed long-lived charged massive particles at the LHC
The conventional way to search for long-lived CHArged Massive Particles (CHAMPs) is to identify slow (small β) tracks using delayed time of flight and high ionization energy loss. But at the 7–14 TeV center of mass energy of the LHC, a CHAMP may be highly boosted (high β) and therefore look more like a minimum ionizing particle, while for high momentum muons (≳500 GeV/c) the radiative effect dominates energy deposition. This suggests a new strategy to search for CHAMPs at the LHC. Using energy deposition from different detector components, we construct a boosted decision tree discriminant to separate high momentum CHAMPs from high momentum muons. This method increases substantially the CHAMP discovery potential and it can be used to distinguish possible di-CHAMP or CHAMP–muon resonance models from di-muon resonance models. We illustrate the new method using a mGMSB model and a recently proposed di-CHAMP model and we give updated CHAMP mass limits for these two models using the results from a recent CDF CHAMP search.
120267358
The UV‐Cutoff Effects on the Chiral Critical Surface in Hot and Dense QCD
The search of the QCD critical point is one of the interesting issues both in theoretical and experimental particle physics. In this article, we use the Nambu Jona‐Lasinio model to study the UV‐cutoff effects on the critical surface which may play a crucial role to the possible existence/non‐existence of the critical point. Then we compare the indications between the results obtained through our effective approach and the lattice QCD simulations.
15400749
A critical cosmological constant from millimeter extra dimensions
We consider `brane universe' scenarios with standard-model fields localized on a 3-brane in 6 spacetime dimensions. We show that if the spacetime is rotationally symmetric about the brane, local quantities in the bulk are insensitive to the couplings on the brane. This potentially allows compactifications where the effective 4-dimensional cosmological constant is independent of the couplings on the 3-brane. We consider several possible singularity-free compactification mechanisms, and find that they do not maintain this property. We also find solutions with naked spacetime singularities, and we speculate that new short-distance physics can become important near the singularities and allow a compactification with the desired properties. The picture that emerges is that standard-model loop contributions to the effective 4-dimensional cosmological constant can be cut off at distances shorter than the compactification scale. At shorter distance scales, renormalization effects due to standard-model fields renormalize the 3-brane tension, which changes a deficit angle in the transverse space without affecting local quantities in the bulk. For a compactification scale of order 10−2 mm, this gives a standard-model contribution to the cosmological constant in the range favored by cosmology.
119449850
Shear viscosity to entropy density ratio of QCD below the deconfinement temperature
Abstract Using chiral perturbation theory we investigate the QCD shear viscosity ( η ) to entropy density ( s ) ratio below the deconfinement temperature ( ∼ 170 MeV ) with zero baryon number density. It is found that η / s of QCD is monotonically decreasing in temperature ( T ) and reaches 0.6 with estimated ∼ 50 % uncertainty at T = 120 MeV . A naive extrapolation of the leading order result shows that η / s reaches the 1 / 4 π minimum bound proposed by Kovtun, Son, and Starinets using string theory methods at T ∼ 200 MeV . This suggests a phase transition or cross over might occur at T ≲ 200 MeV in order for the bound to remain valid. Also, it is natural for η / s to stay close to the minimum bound around the phase transition temperature as was recently found in heavy ion collisions.
122417032
Hypernucleus physics at RHIC
Abstract We report recent progress in hypernucleus studies measured by the STAR collaboration at the Relativistic Heavy Ion Collider. We show a preliminary hypertriton measurement from our current event sample and discuss the next step for this project.
118576689
{pi}{pi} scattering in twisted mass chiral perturbation theory
In this report we describe both I=2 and I=0 {pi}{pi} scattering for twisted mass lattice QCD utilizing twisted mass chiral perturbation theory at next-to-leading order. Focusing on the lattice spacing (b) corrections, we demonstrate that in the exotic I=2, I{sub 3}={+-}2 channels ({pi}{sup {+-}}{pi}{sup {+-}}), the leading scaling violations of {pi}{pi} scattering at maximal twist begin at O(m{sub {pi}}{sup 2}b{sup 2}). This is not the case in any other isospin channel, for which the scaling violations at maximal twist begin at O(b{sup 2}). Furthermore, we demonstrate the existence of a mixing between the I=2, I{sub 3}=0 and I=0 scattering channels due to the breaking of isospin symmetry by the twisted mass term. The mixing term, although formally next-to-leading order, is relatively large, thus necessitating the use of a coupled channel analysis. We argue that this mixing likely renders the computation of the I=0 channel impractical with twisted mass lattice QCD.