A measurement of the $Z(\rightarrow\mu^+\mu^-)$+jet production cross-section in $pp$ collisions at a centre-of-mass energy $\sqrt{s} = 7$ TeV is presented. The analysis is based on an integrated luminosity of $1.0\,\text{fb}^{-1}$ recorded by the LHCb experiment. Results are shown with two jet transverse momentum thresholds, 10 and 20 GeV, for both the overall cross-section within the fiducial volume, and for six differential cross-section measurements. The fiducial volume requires that both the jet and the muons from the Z boson decay are produced in the forward direction ($2.0<\eta<4.5$). The results show good agreement with theoretical predictions at the second-order expansion in the coupling of the strong interaction.
The $Z$+jet cross-section at Born level in $pp$ collisions at $\sqrt{s}=7$ TeV. The first uncertainty is statistical, the second is systematic and the third is the uncertainty due to the luminosity determination.
The cross-section ratio $\sigma(Z+\mathrm{jet})/\sigma(Z)$ at Born level in $pp$ collisions at $\sqrt{s}=7$ TeV. The first uncertainty is statistical, the second is systematic and the third is the uncertainty due to the luminosity determination.
Differential cross-section for $Z$+jet in the leading jet $p_T$, for $p_{T}^{\mathrm{jet}} > 10$ GeV/$c$. These results are not corrected for FSR from the final state muons from the $Z$ boson decay.
Data have been taken at the φ energy with the same large solid angle detector which has been used for the measurement of the ϱ and ω production by e + e − annihilations. From the φ → K o L K o S π + φ − excitation curve we have deduced the φ width Γ φ = (3.81 ± 0.37) MeV and the cross-section σ e + e − → K o L K o S = (1.48±0.08±0.12) μ b. (the quoted errors are respectively statistical and systematical.)
EXPERIMENTAL CROSS SECTION INCLUDING RADIATIVE EFFECTS.
FITTED CROSS SECTION AT PHI PEAK, RADIATIVELY CORRECTED.
The results of the first experiment performed at DCI in e + e − annihilations in the c.m. energy range 1.350–2.125 GeV region are presented. The cross sections of various multipion channels are extracted. Significant structure appears in some specific channels. A relatively narrow resonance around 1.660 GeV decaying into 3 π 's is found. Charged and neutral multiplicities, and also the ratio R are given.
PEAK CROSS SECTION FROM FIT WITH BREIT-WIGNER RESONANCE PLUS CONSTANT BACKGROUND TO ISOSCALAR JPC = 1-- STRUCTURE OF MASS 1652 +- 17 MEV AND WIDTH OF 42 +- 17 MEV.
R VALUE SEEMS CONSTANT OVER THIS ENERGY RANGE.
The production of multipion events by e + e − annihilation has been measured at centre of mass energies 915,990 and 1076 MeV. Both channels e + e − → π + π − π o and e + e − → π + π − π + π − have been analysed. An energy threshold effect analysed. An energy threshold effect around 919 MeV ( m ω + m π o ) has been evidenced for the π + π − π o π o channel and the cross section is consistent with the quasi two-body process e + e − → ωπ o . The cross section for π + π − π + π − is lower by an order of magnitude and increases with the energy.
SYSTEMATIC ERROR INCLUDED. RADIATIVE EFFECT (<15 PCT) INCLUDED.
MULTIHADRON PRODUCTION CROSS SECTION DEDUCED AS SUM OF FOUR PION CHANNELS.
The radiative decay models of the φ-meson have been studied: e + e − → φ → ηγ →3 γ ; e + e − → φ → π o γ →3 γ . Cross sections σ φ → ηγ →3 γ and σ φ → π o γ →3 γ have been measured at five energies in the φ-meson energy region and clearly show the φ-resonance in the ηγ → 3 γ mode as well as in the π o γ → 3 γ mode. From a Breit-Wigner fit to the experimental data the values of the branching ratios are deduced: B φ → ηγ = (1.5 ± 0.4) × 10 −2 ; B φ → π o γ = (1.4 ± 0.5) × 10 −3 .
REMOVING RADIATIVE CORRECTIONS, THE PHI PEAK CROSS SECTIONS ARE 66 NB +- 25 PCT <ETA GAMMA> AND 6.5 NB +- 30 PCT <PI0 GAMMA>.
The cross section e + e − → π + π − π o has been measured in the φ energy region and at three other energies (915, 990, 1076 MeV) chosen outside the ω and φ resonances. In the same experiment the energy position and the width of the φ resonance have been determined from the φ →K S o K L o channel. It is found that the magnitude and energy dependence of the experimental cross section are well described by coherent production of ω and φ in the whole energy range 770 to 1076 MeV. Our data clearly show an interference effect which corresponds to an opposite sign between the two products g γω g ω →3 π and g γφ g φ →3 π of the coupling constants.
EXPERIMENTAL CROSS SECTIONS - RADIATIVE CORRECTIONS CAN BE SIGNIFICANT.
A large solid angle detector has been used to observe π + π − π o events produced at the φ energy by electron-positron collisions in the Orsay storage ring. Fitting our data with a Breit and Wigner curve, with a fixed width Γ = (3.8±0.4) MeV coming from K O S K O L analysis, we deduce σ e + e − → π + π − π O = (0.70±0.13) μ bat 2 E = Mφ . Using our measurements on the other φ decay modes we deduce ( φ → π + π − π o )/( φ → K o S K o L ) = 0.47±0.06 and ( φ → η o γ )/( φ → K o S K o L ) = 0.077±0.022. Assuming ( φ → K + K − )/( φ → K o S K o L ) = 1.60, we derive σ TOT = (4.7±0.4) μ b, Γ e + e − = (1.27±0.11 keV and g 2 o /4 π = 14.3±1.3 (without finite width correction). Furthermore (from the observation of the ππγ coplanar events) we put an upper limit to the mode e + e − → φ π + π − γ , Γ ( φ → π + π − γ ) ⩽ 0.007 Γ ( φ → Total ) with 90% C.L.
EXPERIMENTAL CROSS SECTIONS INCLUDING RADIATIVE EFFECTS.
FITTED PARTIAL AND TOTAL CROSS SECTION AT PHI PEAK, RADIATIVELY CORRECTED.
A large solid angle detector has been used to observe π + π − π 0 events produced, at the ω energy, by electron-positron collisions in the ORSAY storage ring. From the ω excitation curve we have deduced: σ ( e + e − → ω 3 π ) = (180 ± 0.20) μ b, Γ = (9.1 ± 0.8) MeV and with B( ω → π + π − π 0 ) = 0.898 ± 0.045 we have calculated Γ e + e − = (0.76 ± 0. 08) keV and g 2 ω 4π = 18.4 ± 1.8 .
EXPERIMENTAL CROSS SECTION INCLUDING RADIATIVE EFFECTS.
FITTED CROSS SECTION AT OMEGA PEAK, RADIATIVELY CORRECTED.
A large solid angle detector has been used to observe two body events produced by electron-positron collisions in the Orsay storage ring. From the π + π − excitation curve in the ϱ region we have deduced the amplitude and the phase of the ω-ϱ interference, and the ϱ resonance paramaters: M ϱ = (775.4±7.3) MeV, Γ ϱ = (149.6 ± 23.2) MeV, √ B ( ω → π + π − ) = 0.19 ± 0.05, φ = (85.7 ± 15.3) 0 , σ ( e + e − → ϱ ) = (1.00 ± 0.13) μ b at S = M ϱ 2 , B ( ϱ → e + e − = (4.1 ± 0.5) × 10 −5 , Γ ( ϱ → e + e − ) = (6.1 ± 0.7) keV, ( g ϱ 2 /4 π ) = 2.26 ± 0.25, ( g ϱππ 2 /4 π ) = 2.84 ± 0.50.
STATISTICAL ERRORS ONLY. CROSS SECTION AT RHO0 PEAK IS 1.00 +- 0.13 MUB FROM FIT.
None
No description provided.
The e + e − → π + π − cross section has been measured from about 280 events (an order of magnitude more than the previous world statistics) in the energy interval 1.35 ⩽ s ⩽ 2.4 GeV with the DM2 detector at DCI. The pion squared form factor | F π | 2 shows a deep minimum around 1.6 GeV/ c 2 and is better fit under the hypothesis of two ϱ-like resonance ⋍0.25 GeV/ c 2 wide with 1.42 and 1.77 GeV/ c 2 masses.
Statistical errors only.
Data were taken at the energy 2 E = 990 MeV to search for multibody events, with the same large solid angle detector which has been used for the measurement of the ϱ , ω and φ production by e + e − annilations. Assuming a π + π − π 0 π 0 production by the quasi two-body process e + e − → ϱ → ωπ 0 we give the correspondi ng cross section σ (e + e − → π + π − π 0 π 0 ) = (1.1 ± 0.5) 10 −32 cm 2 . Since no events with 3 and 4 charged pions have been observed σ (e + e − → π + π − π 0 π − ) ⩽ 1.5 × 10 −33 cm 2 .
RATIO TO MUON PAIR PRODUCTION CALCULATED FROM CROSS SECTION. INCLUDING SYSTEMATIC ERRORS.
None
No description provided.
The cross sections fore+e−→π+π−π0 ande+e−→ωπ+π− have been measured in the 1.35 ≦\(\sqrt s \) ≦2.4 GeV range from 1900 nb−1 collected by DM2 at DCI. The second process proceeds via a resonant state at ≈- 1660 MeV/c2, ≈- 280 MeV/c2 wide. The first one is larger than a VDM extrapolation from the ω-ϕ peaks and, although does not show any clear structure, is compatible with the presence of the above resonance.
No description provided.
No description provided.
The\(e^ +e^ -\to K_s^0 K^ \pm\pi ^ \mp\) andK+K−π0 cross sections have been measured in the energy interval\(1350 \leqq \sqrt s\leqq 2400\) with the DM2 detector at DCI. The\(K_s^0 K^ \pm\pi ^ \mp\) cross section shows the contribution of an isoscalar vector meson at ≈1650 MeV/c2 in agreement with a previous experiment. The low statisticsK+K−π0 measurement is consistent with the above result.
The K0S K+- PI-+ cross section.
The K+ K- PI0 cross section.
Search for baryon pairs production ine+e− annihilation at\(\sqrt s= 2386 MeV\) is reported. The data relate to a luminosity of 161 nb−1 collected by the DM2 experiment at DCI, the Orsay colliding ring. First measurements of directe+e− annihilation into\(\Lambda \bar \Lambda \) and ofe+e−→\(p\bar p\) at this energy are presented. First observation of a goode+e−→\(n\bar n\) candidate is reported and upper limits are given fore+e−→\(n\bar n, \Lambda \bar \sum ^0+ c.c.\) and\(\Sigma ^0 \bar \Sigma ^0 \).
No description provided.
No description provided.
No description provided.
The e + e − → p p cross section has been measured in the energy interval (1975 ⩽ 2 E ⩽ 2250) MeV for |cos θ | < 0.7. The measurement is based on ∼ 100 events, thus improving by a factor 3 on the previous existing statistics in this energy interval. The form factor | G | 2 is given as a function of energy under the assumption | G E | = | G M |. We also give the first measurement of the differential cross section, averaged over the energy interval, and estimate the ratio G M |/| G E | from it.
No description provided.
No description provided.
No description provided.
The e + e − → ηπ + π − reaction has been measured in the center of mass energy interval 1350–2400 MeV by the magnetic detector DM2 at the Orsay storage ring DCI. Under the hypothesis of only one large resonance the cross section is not fit in a satisfactory way. The branching ratio τ − → η − π 0 ν τ =(0.13 ± 0.02)% is deduced via CVC from the above measurement.
No description provided.
This paper presents experimental results on π + π − production threshold from the collision of quasi-real photons. The data, obtained at the e + e − collider DCI, are a combination of the results from the DM1 and DM2 experiments. Using the e + e − and π + π − production for normalization and cross-checks, we observe a pion pair yield at low invariant mass ( W < 500 MeV/ c 2 ) which is approximately twice the one expected from Born terms.
Data read from graph.
Data read from graph.
None
ASSUMING ABS(GE)=ABS(GM).
No description provided.
No description provided.
Thee+e−→K+K− cross section has been measured from about 750 events in the energy interval\(1350 \leqq \sqrt s\leqq 2400 MeV\) with the DM2 detector at DCI. TheK± form factor |FF±| cannot be explained by the ρ, ω, ϕ and ρ′(1600). An additional resonant amplitude at 1650 MeV has to be added as suggested by a previous experiment.
No description provided.
No description provided.
Measurements of the Xi- and anti-Xi+ masses, mass differences, lifetimes and lifetime differences are presented. The anti-Xi+ sample used is much larger than those used previously for such measurements. In addition, the Xi production rates in Z -> b anti-b and Z -> q anti-q events are compared and the position xi* of the maximum of the xi distribution in Z -> q anti-q events is measured.
Corrected LN(1/X) distribution for (XI- + XIBAR+) production.
Measured and extrapoplated production rates.
Extrapolated production rate in b-bbar events.
The production of two high-p_T jets in the interactions of quasi-real photons in e+e- collisions at sqrt{s_ee} from 189 GeV to 209 GeV is studied with data corresponding to an integrated e+e- luminosity of 550 pb^{-1}. The jets reconstructed by the k_T cluster algorithm are defined within the pseudo-rapidity range -1 < eta < 1 and with jet transverse momentum, p_T, above 3 GeV/c. The differential di-jet cross-section is measured as a function of the mean transverse momentum ptmean of the jets and is compared to perturbative QCD calculations.
Total cross section for dijet production. Errors are combined statistics and systematics.
Measured dijet production cross section as a function of the mean jet transverse momentum. Errors include both statistics and systematics.
Measured dijet production cross section as a function of jet pseudorapiditydifference. Errors include both statistics and systematics.
The nature of b-quark jet hadronisation has been investigated using data taken at the Z peak by the DELPHI detector at LEP. Two complementary methods are used to reconstruct the energy of weakly decaying b-hadrons, E^weak_B. The average value of x^weak_B = E^weak_B/E_beam is measured to be 0.699 +/- 0.011. The resulting x^weak_B distribution is then analysed in the framework of two choices for the perturbative contribution (parton shower and Next to Leading Log QCD calculation) in order to extract measurements of the non-perturbative contribution to be used in studies of b-hadron production in other experimental environments than LEP. In the parton shower framework, data favour the Lund model ansatz and corresponding values of its parameters have been determined within PYTHIA~6.156 from DELPHI data: a= 1.84^{+0.23}_{-0.21} and b=0.642^{+0.073}_{-0.063} GeV^-2, with a correlation factor rho = 92.2%. Combining the data on the b-quark fragmentation distributions with those obtained at the Z peak by ALEPH, OPAL and SLD, the average value of x^weak_B is found to be 0.7092 +/- 0.0025 and the non-perturbative fragmentation component is extracted. Using the combined distribution, a better determination of the Lund parameters is also obtained: a= 1.48^{+0.11}_{-0.10} and b=0.509^{+0.024}_{-0.023} GeV^-2, with a correlation factor rho = 92.6%.
The combined unfolded and weighted results, per bin, for $f(x^{\rm weak}_{\rm B})$. Quoted uncertainties have been scaled by 1.31.
The average value of the $x^{\rm weak}_{\rm B}$ distribution.
Infrared and collinear safe event shape distributions and their mean values are determined in e+e- collisions at centre-of-mass energies between 45 and 202 GeV. A phenomenological analysis based on power correction models including hadron mass effects for both differential distributions and mean values is presented. Using power corrections, alpha_s is extracted from the mean values and shapes. In an alternative approach, renormalisation group invariance (RGI) is used as an explicit constraint, leading to a consistent description of mean values without the need for sizeable power corrections. The QCD beta-function is precisely measured using this approach. From the DELPHI data on Thrust, including data from low energy experiments, one finds beta_0 = 7.86 +/- 0.32 for the one loop coefficient of the beta-function or, assuming QCD, n_f = 4.75 +/- 0.44 for the number of active flavours. These values agree well with the QCD expectation of beta_0=7.67 and n_f=5. A direct measurement of the full logarithmic energy slope excludes light gluinos with a mass below 5 GeV.
1-THRUST distribution.
THRUST-MAJOR distribution.
THRUST-MINOR distribution.
Tau-pair production in the process e+e- -> e+e-tau+tau- was studied using data collected by the DELPHI experiment at LEP2 during the years 1997 - 2000. The corresponding integrated luminosity is 650 pb^{-1}. The values of the cross-section obtained are found to be in agreement with QED predictions. Limits on the anomalous magnetic and electric dipole moments of the tau lepton are deduced.
The measured cross sections for the individual samples divided into years and the overall average value.
This paper presents DELPHI measurements and interpretations of cross-sections, forward-backward asymmetries, and angular distributions, for the e+e- -> ffbar process for centre-of-mass energies above the Z resonance, from sqrt(s) ~ 130 - 207 GeV at the LEP collider. The measurements are consistent with the predictions of the Standard Model and are used to study a variety of models including the S-Matrix ansatz for e+e- -> ffbar scattering and several models which include physics beyond the Standard Model: the exchange of Z' bosons, contact interactions between fermions, the exchange of gravitons in large extra dimensions and the exchange of sneutrino in R-parity violating supersymmetry.
Measured cross sections and forward-backward asymmetries for non-radiative E+ E- --> E+ E- events.
Differential cross sections for non-radiative E+ E- --> E+ E- events at centre of mass energy 189 GeV.
Differential cross sections for non-radiative E+ E- --> E+ E- events at centre of mass energy 192 GeV.
A study of the inclusive charged hadron production in two-photon collisions is described. The data were collected with the DELPHI detector at LEP II. Results on the inclusive single-particle p_T distribution and the differential charged hadrons dsigma/dp_T cross-section are presented and compared to the predictions of perturbative NLO QCD calculations and to published results.
Differential inclusive DSIG/DPT distribution of charged particles produced in GAMMA* GAMMA* interaction with two pseudorapidity cut offs.
These final results on e+e- -> W+W- production cross-section measurements at LEP2 use data collected by the DELPHI detector at centre-of-mass energies up to 209 GeV. Measurements of total cross-sections, W angular differential distributions and decay branching fractions, and the value of the CKM element |V_{cs}| are compared to the expectations of the Standard Model. These results supersede all values previously published by DELPHI.
W pair production cross section for the fully hadronic channel.
W pair production cross section for the semi-leptonic decay channel.
W pair production cross section for the fully leptonic decay channel.
Double-tagged interactions of photons with virtualities Q^2 between 10 GeV^2 and 200 GeV^2 are studied with the data collected by DELPHI at LEPII from 1998 to 2000, corresponding to an integrated luminosity of 550 pb^{-1}. The gam* gam* -> mu+mu- data agree with QED predictions. The cross-section of the reaction gam* gam* -> hadrons is measured and compared to the LO and NLO BFKL calculations.
Measured cross section for the process E+ E- --> E+ E- HADRONS.
Measured cross section for the process GAMMA* GAMMA* --> HADRONS.
Differential cross section for GAMMA* GAMMA* --> MU+ MU-.
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.
No description provided.
No description provided.
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.
SIG with C=HPC and C=FEMC correpond to the events in the barrel and forwardregion, respectively.
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 ${⤪ K}_{2}^{⇒t 0}(1430)$.
SIG in (1/SIG) is the total hadronic cross section. The statistical and systematic errors are combined quadratically.
SIG in (1/SIG) is the total hadronic cross section. The erros are statistical ones. The cross sections SIG(C=A), SIG(C=B), and SIG(C=C) obtained with A) both kaons identified, B) at least one kaon identified, and C) without requiring kaon identification.
SIG in (1/SIG) is the total hadronic cross section. The statistical and systematic erros are combined quadratically. For 0.05<X<0.2 the resulting cross s ection was taken by averaging the results with both identified kaons and with at least one identified kaon, for 0.2<X<1 the results obtained without particle id entification.
The inclusive production of the f ′ 2 (1525) in hadronic Z 0 decays has been studied in data collected by the DELPHI detector at LEP. The Ring Imaging Cherenkov detectors were important tools in the identification of the decay f ′ 2 (1525) → K + K − . The average number of f ′ 2 (1525) produced per hadronic Z decay, 〈f′ 2 〉 = 0.020 ± 0.005 (stat) ± 0.006 (syst), and the momentum distribution of the f ′ 2 (1525) have both been measured. The mass and width of the f ′ 2 (1525) are found to be 〈M f′ 2 〉 = 1535 ± 5 (stat) ± 4 (syst) MeV/c 2 , (T f′ 2 ;) = 60 ± 20 (stat) ± 19 (syst) MeV/c 2
SIG in (1/SIG) is the total hadronic cross section.
No description provided.
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.
Transverse momentum PTIN w.r.t. the Thrust axis. For the first table Thrust axis definition is from seen charged particles corrected to final state particles. For the second table Thrust axis definition is from seen charged plus neutral particles corrected to final state charged plus neutral particles.
Transverse momentum PTOUT w.r.t. the Thrust axis. For the first table Thrust axis definition is from seen charged particles corrected to final state particles. For the second table Thrust axis definition is from seen charged plus neutral particles corrected to final state charged plus neutral particles.
Transverse momentum PTIN w.r.t. the Sphericity axis. For the first table Sphericity axis definition is from seen charged particles corrected to final state particles. For the second table Sphericity axis definition is from seen charged plus neutral particles corrected to final state charged plus neutral particles.
No description provided.
From the data collected by DELPHI at LEP in autumn 1995, the multiplicity of charged particles at a hadronic energy of 130 GeV has been measured to be 〈 n ch 〉 = 23.84 ± 0.51 (stat) ± 0.52 (syst). When compared to lower energy data, the value measured is consistent with the evolution predicted by QCD with corrections at next-to-leading order, for a value α s (130 GeV) = 0.105 ± 0.003 (stat) ± 0.008 (syst).
No description provided.
Statistical error only.
No description provided.
No description provided.
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.
mean values for event shape variables.
Integral of event shape distribution over the specified interval.
Integral of event shape distribution over the specified interval.
A sample of about 1.4 million hadronic Z decays, selected among the data recorded by the DELPHI detector at LEP during 1994, was used to measure for the first time the momentum spectra of K + , K 0 , p , Λ and their antiparticles in gluon and quark jets. As observed for inclusive charged particles, the production spectra of identified particles were found to be softer in gluon jets than in quark jets, with a higher total multiplicity.
Y events.
Mercedes events.
A measurement of the Δ ++ (1232) inclusive production in hadronic decays of the Z at LEP is presented, based on 1.3 million hadronic events collected by the DELPHI detector in the 1994 LEP running period. The DELPHI ring imaging Cherenkov counters are used for identifying hadrons. The average Δ ++ (1232) multiplicity per hadronic event is 0.079 ± 0.015 which is more than a factor of two below the JETSET, HERWIG and UCLA model predictions. It agrees with a recently proposed universal mass dependence of particle production rates in e + e − annihilations.
Differential DELTA(1232)++ cross section. Errors are combined statistics and systematics.
Mean multiplicities. Extrapolation to full x range using a combination of JETSET, HERWIG and UCLA models. The second systematic error comes from the uncertainty in the extrapolation.
Three jet events arising from decays of the Z boson, collected by the DELPHI detector, were used to measure differences in quark and gluon fragmentation. Gluon jets were anti-tagged by identifying b quark jets. Unbiased quark jets came from events with two jets plus one photon. Quark and gluon jet properties in different energy ranges were compared for the first time within the same detector. Quark and gluon jets of nearly the same energy in symmetric three jet event topologies were also compared. Using three independent methods, the average value of the ratio of the mean charged multiplicities of gluon and quark jets is $$< r >=1.241 pm 0.015 (stat.)pm 0.025 (syst.).$$ Gluon jets are broader and produce fragments with a softer energy spectrum than quark jets of equivalent energy. The string effect has been observed in fully symmetric three jet events. The measured ratio Rγ of the charged particle flow in the qq̅ inter-jet region of the qq̅g and qq̅γ samples agrees with the perturbative QCD expectation. The dependence of the mean charged multiplicity on the hadronic center-of-mass energy was analysed in photon plus n-jet events. The value for αs(MZ) determined from these data using a QCD prediction with corrections at leading and next-to-leading order is $$←pha_s(M_Z)=0.116pm 0.003 (stat.)pm 03009 (syst.).$$
No description provided.
Durham and JADE algoritms were used.
A sample of 25000 Z 0 → τ + τ − events collected by the DELPHI experiment at LEP in 1991 and 1992 is used to measure the leptonic branching fractions of the τ lepton. The results are B(τ → eν ν ) = (17.51 ± 0.39) % and B(τ → μν ν ) = (17.02 ± 0.31) %. The ratio of the muon and electron couplings to the weak charged current is measured to be g μ g e = 1.000 ± 0.013 , satisfying e-μ universality. The leptonic branching fraction corrected to the value for a massless lepton, assuming e-μ universality, is found to be B(τ → lν ν ) = (17.50 ± 0.25) %.
Axis error includes +- 0.23/0.23 contribution (Data statistics).
Axis error includes +- 0.19/0.19 contribution (Data statistics).
Combined from the two branching fractions above. E-MU universality assumed.
Data are presented on the reaction e+e− → γ + no other detected particle at centre-of-mass energies of 89.48, 91.26 and 93.08 GeV. The cross-section for this reaction is related directly to the number of light neutrino generations which couple to the Z° boson, and to several other possible phenomena such as the production of excited neutrinos, the production of any invisible ‘X’ particle, and the magnetic moment of the tau neutrino. Based on the observed number of single photon events, the number of light neutrinos that couple to the Z° is measured to be Nv = 2.89 ± 0.38. No evidence is found for anomalous production of energetic single photons, and upper limits at 95% confidence level are determined for excited neutrino production (BR < 4 − 8 × 10−6 depending on its mass), production of an invisible ‘X’ particle (σ, < 0.1 pb for masses below 60 GeV), and the magnetic moment of the tau neutrino (< 5.1 × 10-6 μB).
No description provided.
Limit on an anomalous magnetic moment for tau-neutrino from '1GAMMA + nothing' events. Magnetic moment in Bohr magnetons.
Here UNSPEC is invisible particle.
In a sample of 3.02 million hadronic Z 0 decays collected by the DELPHI detector, 270 J ψ → ℓ + ℓ − candidates have been selected. A search for fully reconstructed B c ± mesons has yielded one B c ± → J ψ π ± candidate, no B c ± → J ψ ℓ ± ν ℓ candidates, and one B c ± → J ψ , π + π − π ± candidate, consistent with expected background in each channel. The following 90% confidence level upper limits are determined: Br(Z 0 → B c ± X) × Br(B c ± → J ψ π ± ) < (1.05 to 0.84) × 10 −4 and Br(Z 0 → B c ± X) × Br(B c ± → J ψ ℓ ± ν ℓ ) < (5.8 to 5.0) × 10 −5 , where the ranges quoted correspond to the range of predicted B c ± lifetimes from 0.4 to 1.4 ps, and Br(Z 0 → B c ± X) × Br(B c ± → J ψ π + π − π ± ) < 1.75 × 10 −4 , constant over the range of predicted B c ± lifetimes.
B/C life-time equals (0.4 to 1.4) ps.
The hadronic fragmentation functions of the various quark flavours and of gluons are measured in a study of the inclusive hadron production from Z 0 decays with the DELPHI detector and are compared with the fragmentation functions measured elsewhere at energies between 14 GeV and 91 GeV. A large scaling violation is observed, which is used to extract the strong coupling constant from a fit using a numerical integration of the second order DGLAP evolution equations. The result is α s ( M Z ) = 0.124 −0.007 +0.006 (exp) ± 0.009(theory) where the first error represents the experimental uncertainty and the second error is due to the factorization and renormalization scale dependence.
SIG(Q=BQ, Q=CQ, Q=UDS) corresponds to BQ, CQ, and U,D,S quarks fragmentation into charged hadron.
alpha_s was evaluated from the scaling violation of the fragmentation func tions. The data from other experiments are used for the fitting procedure.
An analysis is presented of inclusive π0 production in Z0 decays measured with the DELPHI detector. At low energies, π0 decays are reconstructed by using pairs of converted photons and combinations of converted photons and photons reconstructed in the barrel electromagnetic calorimeter (HPC). At high energies (up to $x_p={2cdot p≪/{sqrt s}=0.75}$) the excellent granularity of the HPC is exploited to search for two-photon substructures in single showers. The inclusive differential cross section is measured as a function of energy for qq̅ and bb̅ events. The number of π0’s per hadronic Z0 event is $N(≪^0)/Z_{had} ^0=9.2pm 0.2({⤪ stat})pm 1.0 ({⤪ syst})$ and for bb̅ events the number of π0’s is ${⤪ N}(≪^0)/{⤪ b⋏r b}=10.1pm 0.4({⤪ stat})pm 1.1 ({⤪ syst})$. The ratio of the number of π0’s in bb̅ events to hadronic Z0 events is less affected by the systematic errors and is found to be 1.09 ±0.05 ±0.01. The measured π0 cross sections are compared with the predictions of different parton shower models. For hadronic events, the peak position in the $xi_{⤪ p}={⤪ ln}(1/{⤪ x_p})$ distribution is $xi_p^{⋆ar}=3.90_{-0.14}^{+0.24}.$ The average number of π0’s from the decay of primary B hadrons is found to be N(B → π0X)/B hadron = 2.78 ± 0.15(stat) ± 0.60(syst).
Differential cross section for all events.
Mean PI0 multiplicity extrapolated below 0.011 with JETSET 7.3.
Differential cross section for the enriched (b bbar) data set.
A search has been made for direct production of heavy quarkonium states in more than 3 million hadronic Z0 decays in the 1991–1994 DELPHI data. Prompt J/ψ, ψ(2S) and Υ candidates have been searched for through their leptonic decay modes using criteria based on the kinematics and decay vertex positions. New upperlimits are set at the 90% confidence level for Br(Z0 → (QQ) X)/Br (Z0 → hadrons) for various strong production mechanisms of J/ψ and Υ these range down to 0.9 × 10−4. The limits are set in the presence of a small excess (∼ 1% statistical probability of a background fluctuation) in the sum of candidates from prompt J/ψ, ψ(2S), Υ(1S),Υ(2S) and Υ(3S) relative to the estimated background.
The analysis of hadrons (from X) provides to distinguish of the various decay modes of Z-boson (see text).
No description provided.
No description provided.
Low x domain.
In 1996 LEP ran at a centre-of-mass energy of 161 GeV, just above the threshold of W-pair production. DELPHI accumulated data corresponding to an integrated luminosity of 9.93 pb −1 , and observed 29 events that are considered as candidates for W-pair production. From these, a cross-section for the doubly resonant e + e − → WW process of 3.67 −0.85 +0.97 ± 0.19 pb has been measured. Within the Standard Model, this cross-section corresponds to a mass of the W-boson of 80.40 ± 0.44 (stat.) ± 0.09 (syst.) ± 0.03 (LEP) GeV/ c 2 . Alternatively, if m W is held fixed at its current value determined by other experiments, the observed cross-section is used to obtain limits on trilinear WWV (V ≡ γ, Z) couplings.
No description provided.
Forum