21999175
Beam-energy dependence of charge separation along the magnetic field in Au+Au collisions at RHIC.
Local parity-odd domains are theorized to form inside a quark-gluon plasma which has been produced in high-energy heavy-ion collisions. The local parity-odd domains manifest themselves as charge separation along the magnetic field axis via the chiral magnetic effect. The experimental observation of charge separation has previously been reported for heavy-ion collisions at the top RHIC energies. In this Letter, we present the results of the beam-energy dependence of the charge correlations in Au+Au collisions at midrapidity for center-of-mass energies of 7.7, 11.5, 19.6, 27, 39, and 62.4 GeV from the STAR experiment. After background subtraction, the signal gradually reduces with decreased beam energy and tends to vanish by 7.7 GeV. This implies the dominance of hadronic interactions over partonic ones at lower collision energies.
118405509
ABC Effect in Basic Double-Pionic Fusion --- Observation of a new resonance?
P. Adlarson, C. Adolph, W. Augustyniak, V. Baru, 5 M. Bashkanov, F.S. Bergmann, M. Berłowski, H. Bhatt, K.–T. Brinkmann, M. Büscher, 11 H. Calén, H. Clement, D. Coderre, 11, 12 E. Czerwiński, ∗ E. Doroshkevich, C. Ekström, R. Engels, 11 W. Erven, 11 W. Eyrich, P. Fedorets, 5 K. Föhl, K. Fransson, F. Goldenbaum, 11 P. Goslawski, K. Grigoryev, 11, 17 V. Grishina, C.–O. Gullström, J. Hampe, 11, 18 C. Hanhart, 11, 19 L. Heijkenskjöld, V. Hejny, 11 F. Hinterberger, M. Hodana, 11, 13 B. Höistad, M. Jacewicz, M. Janusz, A. Jany, B.R. Jany, L. Jarczyk, J. Jaus, T. Johansson, B. Kamys, G. Kemmerling, 11 O. Khakimova, A. Khoukaz, S. Kistryn, J. Klaja, 11, 13 H. Kleines, 11 B. Kłos, F. Kren, W. Krzemień, P. Kulessa, S. Kullander, A. Kupść, K. Lalwani, B. Lorentz, 11 A. Magiera, R. Maier, 11 P. Marciniewski, B. Mariański, M. Mikirtychiants, 11, 17 P. Moskal, H.–P. Morsch, B.K. Nandi, H. Ohm, 11 A. Passfeld, C. Pauly, 11, † E. Perez del Rio, Y. Petukhov, N. Piskunov, P. Pluciński, P. Podkopał, A. Povtoreyko, D. Prasuhn, 11 A. Pricking, 10 K. Pysz, T. Rausmann, C.F. Redmer, J. Ritman, 11, 12 A. Roy, R.J.M.Y. Ruber, Z. Rudy, S. Schadmand, 11 A. Schmidt, W. Schroeder, T. Sefzick, 11 V. Serdyuk, 11, 24 N. Shah, M. Siemaszko, R. Siudak, T. Skorodko, M. Skurzok, J. Smyrski, V. Sopov, R. Stassen, 11 J. Stepaniak, G. Sterzenbach, 11 H. Stockhorst, 11 H. Ströher, 11 A. Szczurek, A. Täschner, T. Tolba, 11 A. Trzciński, R. Varma, P. Vlasov, G.J. Wagner, W. Węglorz, A. Winnemöller, A. Wirzba, 11, 19 M. Wolke, A. Wrońska, P. Wüstner, 11 P. Wurm, 11 L. Yurev, 11, 24 J. Zabierowski, M.J. Zieliński, W. Zipper, J. Złomańczuk, and P. Żuprański
27276714
Precision Measurement of the Longitudinal Double-Spin Asymmetry for Inclusive Jet Production in Polarized Proton Collisions at sqrt[s]=200  GeV.
We report a new measurement of the midrapidity inclusive jet longitudinal double-spin asymmetry, A_{LL}, in polarized pp collisions at center-of-mass energy sqrt[s]=200  GeV. The STAR data place stringent constraints on polarized parton distribution functions extracted at next-to-leading order from global analyses of inclusive deep-inelastic scattering (DIS), semi-inclusive DIS, and RHIC pp data. The measured asymmetries provide evidence at the 3σ level for positive gluon polarization in the Bjorken-x region x>0.05.
123105671
Radio pulses and the detection of large air showers
123142973
Elliptic flow of non-photonic electrons in Au+Au collisions at $\sqrt{s_{\rm NN}} = $ 200, 62.4 and 39 GeV
We present the measurements of elliptic flow ($v_2$) of non-photonic electrons (NPE) by the STAR experiment using 2- and 4-particle correlations, $v_2${2} and $v_2${4}, and the event plane method in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV, and $v_2${2} at 62.4 and 39 GeV. $v_2${2} and $v_2${4} are non-zero at low and intermediate transverse momentum ($p_T$) at 200 GeV, and $v_2${2} is consistent with zero at low $p_T$ at other energies. For Au+Au collisions at $p_T<1$ GeV/c, there is a statistically significant difference between $v_2${2} at 200 GeV and $v_2${2} at the two lower beam energies.
119232438
Study of hyperon-hyperon correlations and search for $H$-dibaryon using STAR detector at RHIC
High yield of strange particle production per central collision in nucleus-nucleus collisions at RHIC and high statistics data set from STAR experiment allow us to measure \Lambda\Lambda correlations. The \Lambda\Lambda correlation measurement is also closely related to a possible six-quark state H-dibaryon, which is yet to be observed experimentally. The first measurement of \Lambda\Lambda correlations in Au+Au collisions for \sqrt{s_{NN}}= 39, 62.4 and 200 GeV and search for H-dibaryon with its weak decay \Lambda p\pi in Au+Au collisions for \sqrt{s_{NN}}= 200 GeV using the STAR experiment at RHIC are presented here.
118394634
Light Dark Matter and the Electroweak Phase Transition in the NMSSM
We analyze the stability of the vacuum and the electroweak phase transition in the NMSSM close to the Peccei-Quinn symmetry limit. This limit contains light Dark Matter (DM) particles with a mass signicantly smaller than the weak scale and also light CP-even and CP-odd Higgs bosons. Such light particles lead to a consistent relic density and facilitate a large spin-independent direct DM detection cross section, that may accommodate the recently reported signatures at the DAMA and CoGeNT experiments. Studying the one-loop eective potential at nite temperature, we show that when the lightest CP-even Higgs mass is of the order of a few GeV, the electroweak phase transition tends to become rst order and strong. The inverse relationship between the direct-detection cross-section and the lightest CP-even Higgs mass implies that a cross-section of the order of 10 41 cm 2 is correlated with a strong rst order phase transition.
118570168
SUSY-Breaking Parameters from RG Invariants at the LHC
We study Renormalization Group invariant (RGI) quantities in the Minimal Supersymmetric Standard Model and show that they are a powerful and simple instrument for testing high scale models of supersymmetry (SUSY)-breaking. For illustration, we analyze the frameworks of minimal and general gauge mediated (MGM and GGM) SUSY-breaking, with additional arbitrary soft Higgs mass parameters at the messenger scale. We show that if a gaugino and two first generation sfermion soft masses are determined at the LHC, the RGIs lead to MGM sum rules that yield accurate predictions for the other gaugino and first generation soft masses. RGIs can also be used to reconstruct the fundamental MGM parameters (including the messenger scale), calculate the hypercharge D-term, and find relationships among the third generation and Higgs soft masses. We then study the extent to which measurements of the full first generation spectrum at the LHC may distinguish different SUSY-breaking scenarios. In the case of MGM, although most deviations violate the sum rules by more than estimated experimental errors, we find a 1-parameter family of GGM models that satisfy the constraints and produce the same first generation spectrum. The GGM-MGM degeneracy is lifted by differences in the third generation masses and the messenger scales. ∗http://theory.fnal.gov ar X iv :1 01 1. 49 58 v2 [ he pph ] 1 0 M ar 2 01 1
12291219
A Heavy Higgs and a Light Sneutrino NLSP in the MSSM with Enhanced SU(2) D-terms
The Minimal Supersymmetric extension of the Standard Model provides a solution to the hierarchy problem and leads to the presence of a light Higgs. A Higgs boson with mass above the present experimental bound may only be obtained for relatively heavy third generation squarks, requiring a precise, somewhat unnatural balance between different contributions to the effective Higgs mass parameter. It was recently noticed that somewhat heavier Higgs bosons, which are naturally beyond the LEP bound, may be obtained by enhanced weak SU(2) Dterms. Such contributions appear in models with an enhanced electroweak gauge symmetry, provided the supersymmetry breaking masses associated with the scalars responsible for the breakdown of the enhanced gauge symmetry group to the Standard Model one, are larger than the enhanced symmetry breaking scale. In this article we emphasize that the enhanced SU(2) D-terms will not only raise the Higgs boson mass but also affect the spectrum of the nonstandard Higgs bosons, sleptons and squarks, which therefore provide a natural contribution to the T parameter, compensating for the negative one coming from the heavy Higgs boson. The sleptons and non-standard Higgs bosons of these models, in particular, may act in a way similar to the so-called inert Higgs doublet. The phenomenological properties of these models are emphasized and possible cosmological implications as well as collider signatures are described.
118481994
Vacuum stability and Higgs diphoton decays in the MSSM
A bstractCurrent Higgs data at the Large Hadron Collider is compatible with a SM signal at the 2σ level, but the central value of the signal strength in the diphoton channel is enhanced with respect to the SM expectation. If the enhancement resides in the diphoton partial decay width, the data could be accommodated in the Minimally Super-symmetric Standard Model (MSSM) with highly mixed light staus. We revisit the issue of vacuum instability induced by large mixing in the stau sector, including effects of a radiatively-corrected tau Yukawa coupling. Further, we emphasize the importance of taking into account the tan β dependence in the stability bound. While the metastability of the Universe constrains the possible enhancement in the Higgs to diphoton decay width in the light stau scenario, an increase of the order of 50% can be achieved in the region of large tan β. Larger enhancements may be obtained, but would require values of tan β associated with non-perturbative values of the tau Yukawa coupling at scales below the GUT scale, thereby implying the presence of new physics beyond the MSSM.
15534390
Gravitons and dark matter in universal extra dimensions
Models of universal extra dimensions (UED) at the TeV scale lead to the presence of Kaluza Klein (KK) excitations of the ordinary fermions and bosons of the standard model that may be observed at hadron and lepton colliders. A conserved discrete symmetry, KK-parity, ensures the stability of the lightest KK particle (LKP), which, if neutral, becomes a good dark matter particle. It has been recently shown that for a certain range of masses of the LKP a relic density consistent with the experimentally observed one may be obtained. These works, however, ignore the impact of KK graviton production at early times. Whether the G{sup 1} is the LKP or not, the G{sup n} tower thus produced can decay to the LKP, and depending on the reheating temperature, may lead to a modification of the relic density. In this article, we show that this effect may lead to a relevant modification of the range of KK masses consistent with the observed relic density. Additionally, if evidence for UED is observed experimentally, we find a stringent upper limit on the reheating temperature depending on the mass of the LKP observed.