Scaling and thermal equilibrium of hadrons fromZ 0 decays

An analysis of secondary hadrons fromZ ⁰ (91) decays of the LEP experiments indicates that the scaling of distributions implies the same temperatureT=0.261 GeV for all the secondaries. The multiplicities ofZ ⁰,K ⁰, ,..., and computed with their quark contents and the sameT agree with the data. The ratio of to the phase-space covered by the rapidity distribution, depends only on the energy, , fore ⁺ e ^– annihilations and collisions as well.     

Measurement ofR and determination of the charged-particle multiplicity ine+e? annihilation at 13-113-113-1around 10 GeV

We have measured theR value in non-resonante ⁺ e ^– annihilation using the ARGUS detector at the storage ring DORIS II. At a centre-of-mass energy GeV the ratio of the hadronic cross-section to the -pair cross section in lowest order QED has been determined to beR=3.46±0.03±0.13. In addition, we have measured the charged-particle multiplicities in non-resonant hadron production at GeV just below theB threshold and in (4S) resonance decays. For the average charged-particle multiplicities in continuum events and (4S)B decays we obtain n>_cont=8.35±0.02±0.20 and n>_(4s)=10.81±0.05±0.23.Supported by the German Bundesministerium für Forschung und Technologie, Contract no. 054DO51P     

Slepton and squark production and decay inep collisions at the LHC

We present a detailed study of and and the subsequent decays of , , and at the LHC . We explore the relevant supersymmetry parameter range. We calculate the cross sections as well as the rates for interesting signatures such as the production of one or two leptons on the lepton side.     

Mass dependent αs evolution and the light gluino existence

There is an intriguing discrepancy between values measured directly at the CERNZ ₀-factory and low-energy (at few GeV) measurements transformed toQ=M _z0 by a massless QCD evolution relation. There exists and attempt to reconcile this discrepancy by introducing a light gluinog in the MSSM. We study in detail the influence of heavy thresholds on evolution. First, we construct the exact explicit solution to the mass-dependent two-loop RG equation for the running . This solution describes heavy thresholds smoothly. Second, we use this solution to recalculate a new values corresponding to low-energy input data. Our analysis demonstrates that usingmass-dependent RG procedure generally produces corrections of two types: Asymptotic correction due to effective shift of threshold position; Local threshold correction only for the case when input experiment lies in the close vicinity of heavy particle threshold:Q _expt -M _h . Both effects result in the effective shift of the values of the order of 10^–3. However, the second one could be enhanced when the gluino mass is close to a heavy quark mass. For such a case the sum effect could be important for the discussion of the light gluino existence as it further changes theg mass.Work supported in part by INTAS-93-1180     

From the deuteron to deusons,an analysis of deuteronlike meson-meson bound states

A systematic study of possible deuteronlike twomeson bound states,deusons, is presented. Previous arguments that many such bound states may exist are elaborated with detailed arguments and numerical calculations including, in particular, the tensor potential. This tensor potential which is crucial for the deuteron binding is shown to be very important also in the mesonic case. Especially, in the pseudoscalar³ P ₀ pseudoscalar-vector and vector-vector channels the important observation is made that the centrifugal barrier from theP-wave can be overcome by the 1/r ² and 1/r ³ terms of the tensor potential. In the heavy meson sector one-pion exchange alone is strong enough to form at least deuteronlike and composites bound by approximately 50 MeV. Composites of and states bound by pion exchange alone are expected near the thresholds, while in the light meson sector one generally needs some additional short range attraction to form bound states. The quantum numbers of these states areI=0, andJ ^PC=0^–+, 1⁺⁺ for the states andI=0,J ^PC=0⁺⁺, O^–+, 1^+– and 2⁺⁺ for the composites. In the states: ^b (10545), _b1(10562) are predicted and in , one finds the states: ^b (10590), _bQ (10582),h _b(10608), _b2(10602). Near the threshold the states: ^c (3870), _c0(3870) are predicted, and near the threshold one finds the states: _b0(4015), ^c (4015),h _c(4015), _c2(4015). Within the light meson sector pion exchange gives strong attraction for and systems with quantum numbers where the best non- candidates exist, although pion exchange alone is not strong enough to support such bound states. Thus, although one cannot conclude with certainty it to be the case, this fact does favour the picture that the (1440) and thef ₁ (1420) are mainly composites and thef ₀(1710) mainly a bound state, while thef ₀(1515) andf ₂(1520) could be predominantly composites. If the predicted and states are found, these would support this interpretation of the light states. In channels with exotic flavour orCP quantum numbers pion exchange is generally repulsive or quite weak. Therefore one does not expect that such deuteronlike bound states exist, althoughB*B* may be an exception.     

Understanding the scalar mesonq\bar q nonet

It is shown that one can fit the available data on thea _o(980),f _o(1300) andK _o ^* (1430) mesons as a distorted 0⁺⁺ nonet using very few (5–6) parameters and an improved version of the unitarized quark model. This includes all light two-pseudoscalar thresholds, constraints from Adler zeroes, flavour symmetric couplings, unitarity and physically acceptable analyticity. The parameters include a bare or mass, an over-all coupling constant, a cutoff and a strange quark mass of 100 MeV, which is in accord with expectations from the quark model. It is found that in particular for thea ₀(980) andf ₀(980) the component, in the wave function is large, i.e., for a large fraction of the time the state is transformed into a virtual pair. This component, together with a similar component of for thea ₀(980), and , and components for thef ₀(980), causes the substantial shift to a lower mass than what is naively expected from the component alone. Mass, width and mixing parameters, including sheet and pole positions, of the four resonances are given, with a detailed pedagogical discussion of their meaning.     

O $$(\bar \Lambda /m_c )$$ effects in tests of factorization hypothesis for heavy-hadron nonleptonic decays

In the framework of the heavy-quark effective theory, theO ( O(_QCD)) corrections are estimated in the test of factorization hypothesis forB-meson nonleptonic decays proposed by Bjorken. Similar calculations are also carried out for _b nonleptonic decays. The effects of these corrections on the estimate of theD _s -meson decay constant are discussed.     

Measurement of the forward-backward asymmetry of charm and bottom quarks at theZ pole usingD*± mesons

The forward-backward asymmetries for the processes and at theZ resonance are measured using identifiedD ^*± mesons. In 905,000 selected hadronic events, taken in 1991 and 1992 with the DEL-PHI detector at LEP, 4757D ^*+D ⁰⁺ decays are reconstructed. Thec andb quark forward-backward asymmetries are determined to be:

Aspects of χ and ψ production in polarized proton-proton collisions

Several topics of relevance to low transverse momentum and _1,2(c ) production in polarized proton-proton collisions are discussed. The leadingO( _S ³ ) contributions to the lowp _{T 1} production cross-sections viagg, qg, andq initial states are calculated as well as the corresponding spin-spin asymmetries. We find that ₁ production increases relative to direct and ₂ production, providing up to 25% of the observablee ^* e ^– pairs arising from decays inpp collisions at s=500 GeV. The spin-dependence of ₁ production, however, is much smaller than for either direct or ₂ production and so will likely be far less useful than either process in probing the polarized gluon structure function of the proton. A subset of theO( _S ³ ) radiative corrections to ₂ production involving initial state quarks are also performed and compared to leading ordergg₂ predictions.     

Search for muon to electron neutrino oscillations

A search for _e and oscillations has been carried out with the CHARM II detector exposed to the CERN wide band neutrino beam. The data were collected over five years, alternating beams mainly composed of muon-neutrinos and muon-antineutrinos. The number of interactions of _e and observed is comparable with the number of events expected from flux calculations. For large squared mass differences the upper limits obtained on the mixing angle aresin ²2 < 9.4=" ·=">^–3 for oscillating to _e andsin ²2 < 4.8=" ·=">^–3 for to , at the 90% confidence level. Combining neutrino and antineutrino data the upper limit is 5.6 · 10^–3.On leave of absence from ITEP (Moscow)     

A measurement of the forward-backward asymmetry of e+e?→bb by applying a jet charge algorithm to lifetime tagged events

The forward-backward asymmetry of has been measured using approximately 2.15 million hadronicZ ⁰ decays collected at the LEP e⁺e^– collider with the OPAL detector. A lifetime tag technique was used to select an enriched event sample. The measurement of the asymmetry was then performed using a jet charge algorithm to determine the direction of the primary quark. Values of:

CP violation in charmlessB 0 decays: A coupled channel approach

We consider the CP-violating asymmetry betweenB ⁰f and f in the case thatf is a CP-eigenstate containing no charmed quarks. The asymmetry is assumed to arise as a result of mixing with other channelsf having the same quantum numbers but containing ac pair. Inelastic unitarity is implemented by means of the K-Matrix formalism, in which the constraints of CPT are manifestly satisfied. The formalism is applied to a hypothetical two-channel problemB ⁰M ,M , and then to a realistic four-channel situationB ^{0 + –}, ^{0 0},D ⁺ D ^–,D ^{0 0}. Asymmetries and branching ratios are estimated for the decaysB ^{0 + –}, ^{0 0}.     

On the asymptotics of nodes ofL 2-solutions of Schrödinger equations in dimensions ≧ 3

Let _R = ⁿ B _R, wheren3 andB _R={x ⁿ :|x|R}. We investigate the asymptotics of real valued solutions L ²( _R ) of the Schrödinger equation (–+V–E)=0, whereE<0>V(x)0 for |x|: LetD denote an unbounded nodal domain of (i.e. a component of _R {x:(x)=0}), and letS(r)={yS ^n–1:ryD} withS ^n–1 the unit sphere in ⁿ . Under suitable assumptions onV it is shown that for some >0,

Is the channelH \to b\bar b observable at LHC?

A detailed study of associated Standard Model Higgs production (WH and ) at the LHC (or a possible upgraded Tevatron collider), where the Higgs boson decays to pairs, is reported for 80m _H <120 gev.=" even=" for=">b-tagging performances of the detector, the signal cannot be cleanly extracted from the background. For an integrated luminosity of 10⁴ pb ^–1 andm _H =100 GeV, one can expect at best 110 reconstructed decays fromWH production, above a resonant background of 150WZ events and a non-resonant background of 4800 events, and 100 reconstructed pairs (of which 50 from decay) from production, above a background of 4000 events. The main difficulty in extracting these two channels is in the expected low signal rate after reconstruction, the need for accurate control of all the background sources and for extremely goodb-tagging performance. Nevertheless, for a few years of running at a luminosity of 10³³ cm^–2s^–1, channel may be the best way to probe the region 80m _H <100>     

Lepton flavor violating <Emphasis Type="Italic">Z</Emphasis>-decays in supersymmetric seesaw model

In the supersymmetric seesaw model, large flavor mixings of sleptons induce the lepton flavor violating (LFV) interactions ( ), which give rise to various LFV processes. In this work we examine the LFV decays . Subject to the constraints from the existing neutrino oscillation data and the experimental bounds on the decays , these LFV Z-decays are found to be sizable, and among them the largest-rate channel can occur with a branching ratio of 10^-8 and may be accessible at the LHC or GigaZ experiment.Received: 1 September 2003, Published online: 20 November 2003     

The droplet in the tube: A case of phase transition in the canonical ensemble

We consider the 2-dimensional Ising model with ferromagnetic nearest neighbour interaction at inverse temperature. LetS _N = _t be the total magnetization inside anN×N square box, ^per be the Gibbs state in with periodic b.c., andm() be the spontaneous magnetization. We show the existence of the limit

Diffractive production of ρ-mesons and of ρπ-systems by neutrinos and antineutrinos on protons

Evidence is presented for diffractive production of -mesons and of -systems invp and chargedcurrent interactions. In the (anti-)neutrino energy range 10 GeVE _v <60 gev=" the=" cross=" sections=" for=" diffractive="> and diffractive production are found to be (0.64±0.14 (stat.)±0.08 (syst.))% and (0.28±0.08 (stat.)±0.04 (syst.))% of the charged-current cross section. The diffractive signal is consistent with being entirely due to diffractivea ₁ production. However, the data cannot distinguish between diffractivea ₁ and diffractive nonresonant production. The experimental distributions ofW, Q ²,x _Bj andy _Bj for diffractive and events are consistent with model predictions.     

Study of B c → D π in the perturbative QCD approach

We investigate the branching ratios and direct CP-asymmetries of the and decays in the PQCD approach. All the diagrams with emission topology or annihilation topology are calculated strictly. A branching ratio of 10^-6 and 10^-7 for and decay is predicted, respectively. Because of the different weak phase and strong phase from penguin operator and two kinds of tree operator contributions, we predict a possible large direct CP-violation: and when γ = 55°, which can be tested in the coming LHC. PACS: 13.25.Hw, 12.38.Bx     

Detecting metastable staus and gravitinos at the ILC

A study of various SUSY scenarios is presented in which the lightest supersymmetric particle is the gravitino and the next-to-lightest supersymmetric particle is a scalar tau with lifetimes ranging from seconds to years. Gravitinos are interesting dark matter candidates which can be produced in decays of heavier sparticles at the International Linear Collider (ILC), but remain undetected in direct searches of astrophysical experiments. We investigate the detection and measurement of metastable staus, which may be copiously produced at the ILC either directly or via cascade decays. A proper choice of the experimental conditions will allow one to collect large samples of s coming to rest in the calorimeters of the ILC detector and to study the subsequent decays . Detailed simulations show that the properties of the stau and the gravitino, such as mass and lifetime and mass, can be accurately determined at a future ILC and may provide direct access to the gravitational coupling, respectively Planck scale.