Nucl. Instrum. Meth. A

The first combined test of an electromagnetic liquid argon accordion calorimeter and a hadronic scintillating-tile calorimeter was carried out at the CERN SPS. These devices are prototypes of the barrel calorimeter of the future ATLAS experiment at the LHC. The energy resolution of pions in the energy range from 20 to 300 GeV at an incident angle θ of about 11° is well-described by the expression σ E = (( 46.5 ± 6.0% √E+(1.2±0.3)% ) ⊕ (3.2±0.4) GeV E . Shower profiles, shower leakage, and the angular resolution of hadronic showers were also studied.

Phys.Lett.B

A search with the DELPHI detector at LEP for excited leptons ( e ∗ , μ ∗ , τ ∗ and ν ∗ ) decaying through γ, W or Z transitions is reported. The data used correspond to an integrated luminosity of 10 pb −1 at an e + e − centre-of-mass energy of 161 GeV. The search for pair produced excited leptons established the limits m e ∗ > 79.6 GeV /c 2 , m μ ∗ > 79.6 GeV /c 2 , m τ ∗ > 79.4 GeV /c 2 and m ν ∗ > 56.4 GeV /c 2 at 95% confidence level, assuming that the SU(2) and U(1) couplings of excited leptons are in the same ratio as for normal leptons and considering both left and right-handed components. Limits corresponding to other assumptions are also given. The search for single excited lepton production established upper limits on the ratio λ m ℓ ∗ of the coupling of the excited lepton to its mass.

Z.Phys.C

We calculate cross-sections for neutral current deep inelastic scattering at HERA with photon tagging. Both the exact lowest-order cross-section and a leading logarithmic approximation of next-order corrections are calculated. The latter amounts to less than 20% in a large kinematical range. The integrations are performed numerically but without relying on Monte Carlo methods.

Mod. Phys. Lett. A

We analyze constraints on the parameters of the R-parity violating supersymmetry which can be extracted from non-observation of the neutrinoless nuclear double beta decay ($0\nu\beta\beta$) at a given half-life lower bound. Our analysis covers a large class of phenomenologically viable R-parity violating SUSY models. We introduce special characteristics: the SUSY sensitivity of a $\beta\beta$ decaying isotope and the SUSY reach of a $0\nu\beta\beta$ experiment. The former provides a physical criterion for a selection of the most promising isotopes for SUSY searches and the latter gives a measure of success for a $0\nu\beta\beta$ experiment in exploring the R-parity violating SUSY parameter space. On this basis we discuss prospects for exploration of supersymmetry in various $0\nu\beta\beta$ experiments.

Z. Phys. C

From data recorded by DELPHI between 1991 and 1994, which corresponds to 3.2 million hadronic Z0 decays, a measurement of the $⩈erline {{⊼ B}_d^0}$ meson lifetime, based on the inclusive reconstruction of 3520 ± 150 semileptonic decays of the type $⩈erline {{⊼ B}_d^0}⌝ghtarrow {⊼ D}^{⇒t +}{⊼ ⩼ X} ⫑l ⩈erline {v_{⫑l}},$ has been performed. The result is: $∢u ⩈erline {({⊼ B_d^0})}=1.532 pm 0.041(stat.) pm 0.040(syst.)ps.$. The contribution to the systematic uncertainty which depends on external errors is ±0.015.

Z.Phys.C

A search for lepton flavour number violating Z0 decays in the channels Z0 → μτ, Z0 → eτ, Z0 → eμ, using the DELPHI detector with data collected during the 1991–94 LEP runs, is described. No signal was found. Upper limits at 95% confidence level for the respective branching fractions of 1.2 × 10−5, 2.2 × 10−5, and 0.25 × 10−5, were obtained.

Z. Phys. C

Inclusive charged particle and event shape distributions are measured using 321 hadronic events collected with the DELPHI experiment at LEP at effective centre of mass energies of 130 to 136 GeV. These distributions are presented and compared to data at lower energies, in particular to the precise Z data. Fragmentation models describe the observed changes of the distributions well. The energy dependence of the means of the event shape variables can also be described using second order QCD plus power terms. A method independent of fragmentation model corrections is used to determine αs from the energy dependence of the mean thrust and heavy jet mass. It is measured to be: $$←pha _s(133 {⤪ GeV})={0.116}pm {0.007}_{exp-0.004theo}^{+0.005}$$ from the high energy data.

Phys. Lett. B

An upper limit for BR ( Z 0 → 3 g ) is obtained from a correlation method, which distinguishes statistically between quark and gluon jets by using the difference in their charged particle multiplicity distributions. From the sample of threefold symmetric three-jet events collected by the DELPHI experiment at LEP during 1991–1994, the 95% confidence level upper limit is deduced to be: BR ( Z 0 → 3 g ) ≤ 1.6 × 10 −2 for the JADE and BR ( Z 0 → 3 g ) ≤ 1.5 × 10 −2 for the DURHAM jet-finder.

Phys. Lett. B

The production of antiprotons in $pp$ collisions is investigated close to threshold where experimental data about the total cross section are not available. We analyze the latter reaction within the LUND string model for inclusive $\bar{p}$ production and within the framework of a one-boson exchange model for the exclusive reaction $pp \rightarrow ppp\bar{p}$. The application of our new results to the analysis of subthreshold antiproton production in $d + p$ and $d + d$ collisions shows cross sections that are much lower than expected before. Nevertheless, the comparison of experimental $\bar{p}$ differential cross sections from $d +p$ and $d + d$ is expected to provide valuable information about a nonnucleonic component in the deuteron wavefunction.

Z. Phys. C

The energy loss spectrum of 150 GeV muons has been measured with a prototype of the ATLAS hadron calorimeter in the H8 beam of the CERN SPS. The differential probability dP/dv per radiation length of a fractional energy loss v = ΔEμ/Eμ has been measured in the range v = 0.01 ÷ 0.95; it is compared with the theoretical predictions for energy losses due to bremsstrahlung and production of electron—positron pairs or of energetic knock-on electrons. The integrated probability \(\int_{0.01}^{0.95}({\rm d}P/{\rm d}v){\rm d}v\) is (1.610 ± 0.015stat ± 0.105syst) · 10−3 in agreement with the theoretical predictions 1.556 · 10−3 and 1.619 · 10−3. Agreement with theory is also found in two intervals of v where production of electron-positron pairs and knock-on electrons dominates. In the region of bremsstrahlung dominance (v = 0.12 ÷ 0.95) the measured integrated probability (1.160 ± 0.040stat ± 0.075syst) · 10−4 is in agreement with the theoretical value of 1.185 · 10−4, obtained using the Petrukhin and Shestakov description of the bremsstrahlung process. The same result is about 3.6 standard deviations (defined as the quadratic sum of statistical and systematic errors) lower than the theoretical prediction of 1.472 · 10−4, obtained using Tsai’s description of bremsstrahlung.

Phys. Rev. D

We address the question of how light can be the lightest supersymmetric particle neutralino to be a reliable cold dark matter (CDM) particle candidate. To this end we have performed a combined analysis of the parameter space of the Minimal Supersymmetric Standard Model (MSSM) taking into account cosmological and accelerator constraints including those from the radiative $b\rightarrow s\gamma$ decay. Appropriate grand unification (GUT) scenarios were considered. We have found that the relaxation of gaugino mass unification is sufficient to obtain a phenomenologically and cosmologically viable solution of the MSSM with the neutralino as light as 3GeV. We have found good prospects for direct detection of these superlight CDM neutralinos via elastic scattering off various nuclei in the forthcoming experiments with low-threshold DM detectors. In a certain sense, these experiments can probe the gaugino mass unification giving constraints on the possible GUT scenarios within the MSSM.

JETP Lett.

It is shown that the calculation of the Mott corrections to the Bethe-Bloch formula can be reduced to summation of a series whose terms are bilinear in the Mott partial amplitudes.

Z. Phys. C

Event shape and charged particle inclusive distributions are measured using 750000 decays of the Z to hadrons from the DELPHI detector at LEP. These precise data allow a decisive confrontation with models of the hadronization process. Improved tunings of the JETSET, ARIADNE and HERWIG parton shower models and the JETSET matrix element model are obtained by fitting the models to these DELPHI data as well as to identified particle distributions from all LEP experiments. The description of the data distributions by the models is critically reviewed with special importance attributed to identified particles.

Z.Phys.C

Results are presented of a search for pair production of heavy objects decaying into four hadronic jets, as expected for example from associated or pair production of MSSM Higgs bosons, hA or H+H−, using a data sample of 5.9pb−1 of e+e− collisions at $sqrt{s}=130-136 {⤪ GeV}$ collected with the DELPHI detector at LEP in November 1995. The data and expectations from standard processes agree after four-jet selections. An analysis based on b-tagging finds no hA candidate with high mass. A study optimized to search for H+H−events with mass in the 40–50 GeV/c2 range also finds no candidate. Finally a comparison is made with a recent ALEPH analysis which found an excess of four-jet events with high multiplicity and high mass. Such a signal is not observed in the DELPHI data, although a slight excess in the mass region around 105 GeV/c2 is seen.

Nucl.Instrum.Meth.A

Using matrices of lead tungstate crystals, energy resolutions better than 0.6% at 100 GeV have been achieved in the test beam in 1995. It has been demonstrated that a lead tungstate electromagnetic calorimeter read out by avalanche photodiodes can consistently achieve the excellent energy resolutions necessary to justify its construction in the CMS detector. The performance achieved has been understood in terms of the properties of the crystals and photodetectors.

Phys.Lett.B

Using data accumulated by DELPHI during the November 1995 LEP run at 130–136 GeV, searchs have been made for events with jets or leptons in conjunction with missing momentum. The results are interpreted in terms of limits on the production of neutralinos, scalar leptons, and scalar quarks.

Nucl. Instrum. Meth. A

We present the results of measurements of the light yield dependencies for the plastic scintillators on magnetic field value and orientation. The magnetic field value was changed from 0 up to 3.8 T. Scintillators were irradiated by electrons ( 137 Cs and 207 Bi) and by alpha-particles ( 241 Am). The detected light spectra in the electron irradiating cases show two dependencies: the first one is dependence on the magnetic field value only and the second-light output is dependent on the magnetic field orientation when the radioactive source is outside of the scintillator. The value and behavior of the first dependence agree with data published earlier.

Z. Phys. A

We performed a combined analysis of the parameter space of the Minimal Supersymmetric Standard Model (MSSM) taking into account cosmological and accelerator constraints including those from the radiative $b\rightarrow s\gamma$ decay measured by the CLEO collaboration. Special attention is paid to the event rate, $R$, of direct dark matter neutralino detection. We have found domains of the parameter space with $R\simeq 5-10$events/kg/day. This would be within the reach of current dark matter experiments. The $b\rightarrow s\gamma$ data do not essentially reduce these large event rate domains of the MSSM parameter space.

Phys.Lett.B

A search for pair production of the lightest chargino at s =130.4 and 136.3 GeV has been carried out using the data sample corresponding to the 5.92 pb −1 recorded by the DELPHI detector during the high energy run of LEP in the last period of 1995. The theoretical reference model has been the Minimal Supersymmetric Standard Model with R-parity conservation. The three topologies expected for the decay of a pair of charginos, namely two acoplanar leptons plus missing energy (ℓℓ), two jets and an isolated lepton plus missing energy ( jj ℓ) and missing energy in a hadronic environment ( s ), were investigated. No evidence of a signal was found. Lower mass limits were derived for various scenarios, including the case of a low mass difference between the chargino and the neutralino and of a light sneutrino. The mass limits range between 56.3 GeV/c 2 and the kinematic limit.

Z. Phys. C

A search for high mass photon pairs from the processes\(e^ +e^ -\to \ell ^ +\ell ^ -\gamma \gamma \),\(e^ +e^ -\to q\bar q\gamma \gamma \) and\(e^ +e^ -\to \nu \bar \nu \gamma \gamma \) with the DELPHI detector at LEP I is reported. From a data sample containing 3.5 million hadronic Z0 decays, collected by DELPHI during the years 1991 to 1994, 79 events with two charged leptons and two isolated photons were selected with photon pair masses above 10 GeV/c2, where 76±6 events were predicted from standard sources. In the same data sample, no\(\nu \bar \nu \gamma \gamma \) candidates were found and no accumulation of events was visible forγγ masses above 10 GeV/c2 in the\(q\bar q\gamma \gamma \) channel. Upper limits at 95% confidence level on the Z0 branching ratios for the three different channels were extracted from the data. In the mass regionmγγ>30 GeV/c2 the limits obtained are between 3×10−6 and 4×10−6.

Z.Phys.C

The inclusive production of the neutral vector mesons K*0(892) and ϕ(1020), and of the tensor meson ${⤪ K}_{2}^{⇒t 0}(1430)$, in hadronic decays of the Z has been measured by the DELPHI detector at LEP. The average production rates per hadronic Z decay have been determined to be 0.77 ± 0.08 K*0(892), 0.104 ± 0.008 ϕ(1020) and ${⤪ K}_{2}^{⇒t 0}(1430)$. The ratio of the tensor-to-vector meson production yields, $«ngle {⤪ K}_{2}^{⇒t 0}(1430)»ngle$, is smaller than the 〈f2(1270)〉/〈ρ0(770)〉 and $«ngle f_{2}^{⌕ime}(1525)»ngle$ ratios measured by DELPHI. The production rates and differential cross sections are compared with the predictions of JETSET 7.4 tuned to the DELPHI data and of HERWIG 5.8. The K*0(892) and ϕ(1020) data are compatible with model predictions, but a large disagreement is observed for the ${⤪ K}_{2}^{⇒t 0}(1430)$.

Phys.Lett.B

This letter reports the results of the measurement of single photon production in the reaction e + e − → γ + invisible particles at centre-of-mass energies s =130 and 136 GeV and an integrated luminosity of 5.83 pb −1 , collected with the DELPHI detector at LEP. The signal is compatible with the prediction of the Standard Model for the process e + e − → ν ν γ , and the number of neutrino families has been determined to be N ν = 3.1 ± 0.6. Limits have been derived on anomalous neutral gauge boson couplings and on compositeness in the framework of a specific model.

Phys.Lett.B

During the last 1995 data acquisition period at LEP, the DELPHI experiment collected an integrated luminosity of 5.9 pb −1 at centre-of-mass energies of 130 GeV and 136 GeV. Radiative leptonic events ( e , μ, τ) with high energy photons were studied and compared to Standard Model predictions. The data were used to search for charged excited leptons decaying through an electromagnetic transition. No significant signal was found. From the search for pair produced excited leptons, the limits m e ∗ > 62.5 GeV /c 2 , m μ ∗ > 62.6 GeV /c 2 and m τ ∗ > 62.2 GeV /c 2 at 95% confidence level were established. For single excited lepton production, upper limits on the ratio λ m l ∗ of the coupling of the excited charged lepton to its mass were derived.

Z. Phys. C

Rare decays of beauty particles were studied in several charmless modes using the data collected with the DELPHI detector at LEP from 1991 to 1994. These decays are mediated by both tree levelb→u and one-loop penguinb→s, d transitions. Evidence for charmlessB decays was obtained in two body hadronic modes. The branching ratios ofBd,s0 toπ+π− orK+π− andBu− toρ0π− orK*0π− were found to be (2.8−1.0+1.5±0.2)×10−5 and (1.7−0.8+1.2±0.2)×10−4 respectively. The fraction of these decays with a charged kaon in the final state that is not from the spectators quark, was measured to be 0.58±0.18. Upper limits were set at 90% confidence level on the branching ratios for three and four body charmless hadronic decays in the range of (1–3)×10−4, for inclusive radiativeb→sγ decays at 5.4×10−4, for the exclusive radiative decaysBd0→K*(892)0γ andBs0→φ(1020)γ at 2.1×10−4 and 7.0×10−4 respectively, and for dineutrino decays\(b \to s\nu \bar \nu \), in the exclusive channels\(B_d^0\to K^* (892)^0 \nu \bar \nu \) and\(B_s^0\to \phi (1020)\nu \bar \nu \) at 1.0×10−3 and 5.4×10−3 respectively. The limits on dineutrino decays constrain theories with a newU(1) gauge boson coupling predominantly to the third family of fermions.

Phys.Lett.B

The first measurement of like-sign charged kaon correlations in hadronic decays of the Z 0 is presented, based on data collected by the DELPHI detector. The charged kaons are identified by means of ring imaging Cherenkov detectors. A significant enhancement at small values of the four-momentum difference is observed in the ratio of like-sign to unlike-sign KK pairs and in the ratio of like-sign pairs to a simulated reference sample. An update of the measurement of K s 0 K s 0 interference is also presented. An enhancement is found in the production of pairs of K s 0 of similar momenta, as compared with a simulated reference sample. The measured Bose-Einstein correlation parameters λ and r are similar for charged and neutral kaon pairs. The value of the Bose-Einstein correlation strength λ is consistent with unity.