Milene Calvetti

We report the observation of four electron-positron pairs and one muon pair which have the signature of a two-body decay of a particle of mass ∼ 95 GeV/c2. These events fit well the hypothesis that they are produced by the process p̄+ p→Z0+X(with Z0→ ℓ++ ℓ−), where Z0 is the Intermediate Vector Boson postulated by the electroweak theories as the mediator of weak neutral currents.

We have measured transverse momentum spectra up to 10 GeV/c for charged particles produced centrally in proton-antiproton collisions at 540 GeV in the centre of mass at the CERN collider. Our results are compared with data at ISR energies and with the predictions of a QCD model. The charged particle spectrum shows a clear dependence on charged track multiplicity.

A sample of 1.69×107 fully reconstructed π0→γe+e− decay candidates collected by the NA48/2 experiment at CERN in 2003–2004 is analyzed to search for the dark photon (A′) production in the π0→γA′ decay followed by the prompt A′→e+e− decay. No signal is observed, and an exclusion region in the plane of the dark photon mass mA′ and mixing parameter ε2 is established. The obtained upper limits on ε2 are more stringent than the previous limits in the mass range 9MeV/c2<mA′<70MeV/c2. The NA48/2 sensitivity to the dark photon production in the K±→π±A′ decay is also evaluated.

The NA48 experiment at CERN has performed a new measurement of direct CP violation, based on data taken in 1997 by simultaneously collecting KL and KS decays into π0π0 and π+π−. The result for the CP violating parameter Re(ε′/ε) is (18.5±4.5(stat)±5.8(syst))×10−4.

The double ratio R of the relative decay rates of the short- and long-lived neutral kaons into two charged and two neutral pions was measured to be 0.980±0.004±0.005. The deviation of R from the CP violation in the transition of the CP-odd K2 into two pions with ϵ′/ϵ=(3.3 ± 1.1)×10−3.

A new measurement of the ratio of the CP-violating amplitudes for KL → 2π0 and KL → π+π− is reported. The measured value for R = ∣η00/η+-∣2 is 0.9878±0.0026±0.0030, where the first error is the statistical uncertainty and the second is the estimate of the systematic uncertainty. This gives a value for the parameter describing direct CP violation: Re ϵ'/ϵ = (2.0 ± 0.7) × 10−3.

The direct CP violation parameter Re(epsilon'/epsilon) has been measured from the decay rates of neutral kaons into two pions using the NA48 detector at the CERN SPS. The 2001 running period was devoted to collecting additional data under varied conditions compared to earlier years (1997-99). The new data yield the result: Re(epsilon'/epsilon) = (13.7 +/- 3.1) times 10^{-4}. Combining this result with that published from the 1997, 98 and 99 data, an overall value of Re(epsilon'/epsilon) = (14.7 +/- 2.2) times 10^{-4} is obtained from the NA48 experiment.

We report the observation of five events in which a missing transverse energy larger than 40 GeV is associated with a narrow hadronic jet and of two similar events with a neutral electromagnetic cluster (either one or more closely spaced photons). We cannot find an explanation for such events in terms of backgrounds or within the expectations of the Standard Model.

A clear signal is observed for the production of an isolated large-transverse-momentum lepton in association with two or three centrally produced jets. The two-jet events cluster around the W± mass, indicating a novel decay of the Intermediate Vector Boson. The rate and features of these events are not consistent with expectations of known quark decays (charm, bottom). They are, however, in agreement with the process W→ tb followed by t → bℓv, where t is the sixth quark (top) of the weak Cabibbo current. If this is indeed so, the bounds on the mass of the top quark are 30 GeV/c2 < mt <550 GeV/c2.

A sample of 52 Intermediate Vector Boson decays in the (vee) channel is described. They were produced at the CERN SPS Collider for an integrated luminosity of 0.136 pb−1. Both production and decay properties fit well with expectations from the Standard Model of weak interactions. An improved value for the W mass is given and compared with the previously published value for the Z0 mass.

With a segmented total absorption calorimeter of large acceptance, we have measured the total transverse energy spectrum for pp̄ collisions at s12 = 540 GeV up to ΣET= 130 GeV in the pseudo-rapidity range |η|< 1.5. Using two different algorithms, we have looked for localized depositions of transverse energy (jets). For ΣET > 40 GeV, the fraction of events with two jets increases with ΣET; this event structure is dominant for ΣET > 100 GeV. We measure the inclusive jet cross section up to ET(jet) = 60 GeV and the two-jets mass distribution to 120 GeV/c2. The measured cross sections are compatible with the predictions of hard scattering models based on QCD.

We report the results from a study of a partial sample of ∼2.3×107 K±→π±π0π0 decays recorded by the NA48/2 experiment at the CERN SPS, showing an anomaly in the π0π0 invariant mass (M00) distribution in the region around M00=2m+, where m+ is the charged pion mass. This anomaly, never observed in previous experiments, can be interpreted as an effect due mainly to the final state charge exchange scattering process π+π−→π0π0 in K±→π±π+π− decay [N. Cabibbo, Phys. Rev. Lett. 93 (2004) 121801]. It provides a precise determination of a0−a2, the difference between the ππ scattering lengths in the isospin I=0 and I=2 states. A best fit to a rescattering model [N. Cabibbo, G. Isidori, JHEP 0503 (2005) 21] corrected for isospin symmetry breaking gives (a0−a2)m+=0.268±0.010(stat)±0.004(syst), with additional external uncertainties of ±0.013 from branching ratio and theoretical uncertainties. If the correlation between a0 and a2 predicted by chiral symmetry is taken into account, this result becomes (a0−a2)m+=0.264±0.006(stat)±0.004(syst)±0.013(ext).

We present a detailed study of hadronic jets obtained in a data sample taken in the UA1 detector with a localized transverse energy trigger. We discuss the average shape of jets in terms of energy and charged particle content, and compare this to data generated in Monte Carlo programs. We further extend the previously reported inclusive jet cross section to the region of ET = 100 GeV. A comparison with theoretical models of cross sections for events with more than two jets is also given.

The phases of the CP-violating amplitudes in K0→π+π− and K0→2π0 decays, φ+−=46.9°±2.2° and φ00=47.1°±2.8°, have been measured in the same experiment, and a direct comparison gives the phase difference φ00−φ+−=0.2°±2.9°. This result leads to an upper limit on possible CPT violation in the K0 mass matrix, of |(mK0−mK0)/mK0|<5×10−18 at the 95% confidence level and is the most stringent test of the equality of particle and antiparticle masses.

The two-jet cross section measured in the UA1 apparatus at the CERN pp Collider has been analysed in terms of the centre-of-mass scattering angle θ and the scaled longitudinal parton momenta x1 and x2. The angular distribution dσ/d cos σ rises rapidly as cos → 1, independent of x2 and x2, as expected in vector gluon theories (QCD). The differential cross section in x1 and x2 is consistent with factorization and provides a measurement of the proton structure function F(x) = G(x) + 49[Q(x) + Q(x)] at values of the four-momentum transfer squared, -t̂ ≈ 2000 GeV2. Over the range x = 0.10−0.80 the structure function shows an exponential x dependence and may be parametrized by the form F(x) = 6.2 exp (−9.5x).

We report results from the analysis of the $\mbox {$\mathrm {K}^{\pm}$}\rightarrow \pi^{+} \pi^{-} \mathrm{e}^{\pm} \nu$ ( $\mbox {$\mathrm {K}_{\mathrm {e}4}$}$ ) decay by the NA48/2 collaboration at the CERN SPS, based on the total statistics of 1.13 million decays collected in 2003–2004. The hadronic form factors in the S- and P-wave and their variation with energy are obtained. The phase difference between the S- and P-wave states of the ππ system is accurately measured and allows a precise determination of $\mbox {$a_{0}^{0}$}$ and $\mbox {$a_{0}^{2}$}$ , the I = 0 and I = 2 S-wave ππ scattering lengths: $\mbox {$a_{0}^{0}$}= 0.2220 \pm 0.0128 \mbox {$\mathrm {_{stat}}$}\pm 0.0050 \mbox {$\mathrm {_{syst}}$}\pm 0.0037\mbox {$\mathrm {_{th}}$},\mbox {$a_{0}^{2}$}= -0.0432 \pm 0.0086 \mbox {$\mathrm {_{stat}}$}\pm 0.0034 \mbox {$\mathrm {_{syst}}$}\pm 0.0028\mbox {$\mathrm {_{th}}$}$ . Combination of this result with the other NA48/2 measurement obtained in the study of $\mbox {$\mbox {$\mathrm {K}^{\pm}$}\rightarrow \mbox {$\pi ^{0}$}\mbox {$\pi ^{0}$}\mbox {$\scriptstyle \pi ^{\pm }$}$}$ decays brings an improved determination of $\mbox {$a_{0}^{0}$}$ and the first precise experimental measurement of $\mbox {$a_{0}^{2}$}$ , providing a stringent test of Chiral Perturbation Theory predictions and lattice QCD calculations. Using constraints based on analyticity and chiral symmetry, even more precise values are obtained: $\mbox {$a_{0}^{0}$}=0.2196 \pm 0.0028\mbox {$\mathrm {_{stat}}$}\pm 0.0020 \mbox {$\mathrm {_{syst}}$}$ and $\mbox {$a_{0}^{2}$}= -0.0444 \pm 0.0007 \mbox {$\mathrm {_{stat}}$}\pm 0.0005 \mbox {$\mathrm {_{syst}}$}\pm 0.0008 \mbox {$\mathrm {_{ChPT}}$}$ .

We report results from a new measurement of the Ke4 decay K±→π+π-e±ν by the NA48/2 collaboration at the CERN SPS, based on a partial sample of more than 670 000 Ke4 decays in both charged modes collected in 2003. The form factors of the hadronic current (F,G,H) and ππ phase difference (δ=δs-δp) have been measured in ten independent bins of the ππ mass spectrum to investigate their variation. A sizeable acceptance at large ππ mass, a low background and a very good resolution contribute to an improved experimental accuracy, a factor two better than in the previous measurement, when extracting the ππ scattering lengths a0 0 and a0 2. Under the assumption of isospin symmetry and using numerical solutions of the Roy equations, the following values are obtained in the plane (a0 0,a0 2): a0 0=0.233±0.016stat±0.007syst,a0 2=-0.0471±0.011stat±0.004syst. The presence of potentially large isospin effects is also considered and will allow comparison with precise predictions from Chiral Perturbation Theory.

Track information from the central detector in the UA1 experiment at the CERN proton-antiproton collider (√s = 540 GeV) is used to determine the charged particle multiplicity distribution for the pseudorapidity range ∣η∣ < 1.3. The mean value for this multiplicity per unit of η is 3.9 ± 0.3 for events having at least one track in this range. Data from the central electromagnetic and hadron calorimeters are used to examine the correlation between the transverse energy measured in the collisions and the multiplicity in the central region.

Proton-antiproton elastic scattering at CM energy 540 GeV has been studied in the t-range 0.04 < −t < 0.45 GeV2. The data are well fitted by the form exp (bt) with b = 17.1 ± 1.0 GeV−2 for |t| = 0.04 − 0.18 GeVsu2 and b = 13.7 ± 0.2 ± 0.2 GeV−2 for |t| = 0.21−0.45 GeV2. A luminosity measurement combined with the optical theorem gives σtot = 67.6 ± 5.9 ± 2.7 mb and σe1/σtot = 0.209 ± 0.018 ± 0.008.

A measurement of the direct CP violating charge asymmetries of the Dalitz plot linear slopes Ag=(g+-g-)/(g++g-) in K±→π±π+π- and K±→π±π0π0 decays by the NA48/2 experiment at CERN SPS is presented. A new technique of asymmetry measurement involving simultaneous K+ and K- beams and a large data sample collected allowed a result of an unprecedented precision. The charge asymmetries were measured to be Ac g=(-1.5±2.2)×10-4 with 3.11×109K±→π±π+π- decays, and An g=(1.8±1.8)×10-4 with 9.13×107K±→π±π0π0 decays. The precision of the results is limited mainly by the size of the data sample.

Results on charged particle production in pp̄ collision at s12 = 540 GeV are presented. The data were obtained at the CERN pp̄ collider using the UA1 detector, operated without magnetic field. The central particle density is 3.3 + - 0.2 per unit o pseudo-rapidity for non-diffractive events. KNO scaling of the multiplicity distributions withresults from ISR energies is observed.

We report the results from a study of the full sample of ∼6.031×107 K ±→π ± π 0 π 0 decays recorded by the NA48/2 experiment at the CERN SPS. As first observed in this experiment, the π 0 π 0 invariant mass (M 00) distribution shows a cusp-like anomaly in the region around M 00=2m +, where m + is the charged pion mass. This anomaly has been interpreted as an effect due mainly to the final state charge exchange scattering process π + π −→π 0 π 0 in K ±→π ± π + π − decay. Fits to the M 00 distribution using two different theoretical formulations provide the presently most precise determination of a 0−a 2, the difference between the π π S-wave scattering lengths in the isospin I=0 and I=2 states. Higher-order π π rescattering terms, included in the two formulations, allow also an independent, though less precise, determination of a 2.

A sample of 3120 K±→π±μ+μ− decay candidates with (3.3±0.7)% background contamination has been collected by the NA48/2 experiment at the CERN SPS, allowing a detailed study of the decay properties. The branching ratio was measured to be BR=(9.62±0.25)×10−8. The form factor W(z), where z=(Mμμ/MK)2, was parameterized according to several models. In particular, the slope of the linear form factor W(z)=W0(1+δz) was measured to be δ=3.11±0.57. Upper limits of 2.9×10−2 and 2.3×10−2 on possible charge asymmetry and forward–backward asymmetry were established at 90% CL. An upper limit BR(K±→π∓μ±μ±)<1.1×10−9 was established at 90% CL for the rate of the lepton number violating decay.

Results are presented on two-jet and three-jet cross sections, measured in the UA1 experiment at the CERN Super Proton Synchrotron (SPS) pp̄ Collider, at the highest available subprocess cms energies (ŝ>150 GeV). Precise measurements of the two-jet angular distribution are consistent with previous results but show significant scale-breaking effects. The three-jet Dalitz plot and the three-jet angular distributions show evidence for final- and initial-state bremsstrahlung processes, in agreement with the leading-order QCD predictions. A comparison of the yield of wide-angle three-jet events with the yield of two-jet events at smaller scattering angles gives for the strong interaction coupling constant: αs(K3JK2J)=0.16±0.02±0.03 at Q2≈4000 GeV2, where the factor K3JK2J may plausibly be assumed to be close to unity.

The K0 beam and detector used for a high-precision measurement of the CP-violation parameter ϵ′ at the CERN Super Proton Synchrotron (SPS) are described. The beam provides KL and KS alternately through a common decay region. The detection of the decays is based on wire chambers and calorimeters without employing a magnet. The trigger and readout system achieve a high selectively for the suppressed, CP-violating, two-pion decays of the KL by incorporation of hard-wired processors. The readout is based on Fastbus for maximum data rates.

A sample of 7253 $K^\pm\toπ^\pm e^+e^-(γ)$ decay candidates with 1.0% background contamination has been collected by the NA48/2 experiment at the CERN SPS, allowing a precise measurement of the decay properties. The branching ratio in the full kinematic range was measured to be ${\rm BR}=(3.11\pm0.12)\times 10^{-7}$, where the uncertainty includes also the model dependence. The shape of the form factor $W(z)$, where $z=(M_{ee}/M_K)^2$, was parameterized according to several models, and, in particular, the slope $δ$ of the linear form factor $W(z)=W_0(1+δz)$ was determined to be $δ=2.32\pm0.18$. A possible CP violating asymmetry of $K^+$ and $K^-$ decay widths was investigated, and a conservative upper limit of $2.1\times 10^{-2}$ at 90% CL was established.

Muons of high transverse momentum pμT have been observed in the large drift chambers surrounding the UA1 detector at the CERN 540 GeV pp̄ collider. For an integrated luminosity of 108 nb−1, 14 isolated muons have been found with pT > 15 GeV/c. They are correlated with a large imbalance in total transverse energy, and show a kinematic behaviour consistent with the muonic decay of the Intermediate Vector Boson W± of weak interactions. The partial cross section is in agreement with previous measurements for electronic decays and with muon-electron universality. The W mass is determined to be mW = 81+6−7 GeV/c2.

The construction of a large (25 m3, 23 000 wires) drift chamber assembly with image readout to be used at the CERN p-p collider facility is reported. In this contribution the emphasis is mainly directed towards the mechanical and electrostatic design and on the implementation of the various control procedures.

The decay mode KL→π0γγ has been observed with a signal of 21 events and an expected background of 1.5±0.9 events. A branching ratio for decays with invariant γγ masses above 280 MeV of (2.1±0.6)×10−6 is calculated. This result is compared with the values estimated from theoretical models and has implications for the CP conserving contribution to KL→π0e+e− decay.

The electronics systems for the readout of a large drift chamber (25 m3, 6110 sense wires) with image readout, to be used at the CERN p-p collider, is described. The system uses a flash analog-to-digital converter and is able to measure directly the drift time, the charge division, and the energy losses for many tracks on each wire. The results obtained with chamber and electronics prototypes are reported.

The NA48/2 experiment at CERN collected a large sample of charged kaon decays to final states with multiple charged particles in 2003–2004. A new upper limit on the rate of the lepton number violating decay K±→π∓μ±μ± is reported: B(K±→π∓μ±μ±)<8.6×10−11 at 90% CL. Searches for two-body resonances X in K±→πμμ decays (such as heavy neutral leptons N4 and inflatons χ) are also presented. In the absence of signals, upper limits are set on the products of branching fractions B(K±→μ±N4)B(N4→πμ) and B(K±→π±X)B(X→μ+μ−) for ranges of assumed resonance masses and lifetimes. The limits are in the (10−11,10−9) range for resonance lifetimes below 100 ps.

The NA48 collaboration is preparing a new experiment at CERN aiming to study CP violation in the K0-K0 system with an accuracy of 2 × 10−4 in the parameter Re(ϵ′/ϵ). Decays in two π0's will be recorded by a quasi-homogeneous liquid krypton calorimeter. A liquid krypton calorimeter has been chosen to combine good energy, position and time resolution with precise charge calibration and long-term stability. The prototype calorimeter incorporating the final design of the electrode read-out structure is presented in this paper. An energy resolution of ≃3.5%√E with a constant term smaller than 0.5% has been obtained. The time resolution was found to be better than 300 ps above 15 GeV.

The decay rate of KL→π0γγ has been measured with the NA48 detector at the CERN SPS. A total of 2558 KL→π0γγ candidates have been observed with a residual background of 3.2%. The branching ratio is determined to be (1.36±0.03(stat)±0.03(syst)±0.03(norm))×10−6 and the vector coupling constant av=−0.46±0.03(stat)±0.04(syst). This result suggests that the CP-violation effects are dominating in the KL→π0e+e− decay. An upper limit for the KL→π0γγ decay rate in the two photon mass region mγγ<mπ0 is also given.

A search for the decay KS→π0e+e− has been made by the NA48/1 experiment at the CERN SPS accelerator. Using data collected during 89 days in 2002 with a high-intensity KS beam, 7 events were found with a background of 0.15 events. The branching fraction BR(KS→π0e+e−,mee>0.165 GeV/c2)=(3.0+1.5−1.2(stat)±0.2(syst))×10−9 has been measured. Using a vector matrix element and a form factor equal to one, the measurement gives BR(KS→π0e+e−)=(5.8+2.9−2.4)×10−9.

The decay rates of KL → 2γ and KS → 2γ have been measured at the CERN SPS. The results are Γ(KL→2γ)/χ(KL→2π0)=0.632±0.004±0.008 and Γ(KS→2γ)/Γ(KL→2γ)=2.3 ±1.0±0.4. This is the first observation of KS→2γ decays.

A large sample of Dalitz decays, KL→e+e−γ, has been observed. The branching ratio is Γ(KL→e+e−γ)Γ(KL →all)=(9.2±0.5±0.5)×10−6 in good agreement with theoretical predictions. We observe an enhancement at high masses in the distribution of the invariant electron-positron pair mass, compared to the distribution expected from QED. This excess is interpreted as being due to virtual mesons contributing to the photon propagator.

We report the observation of five muonic Z0 decays. The mass and cross section times branching ratio is consistent with the previous measurements of Z0→e+e−. Three of the muonic decays have unexpected features. One event is of the type Z0→μ+μ−γ. Two of the Z0→μ+μ− decays are accommpanied by several (>4) energetic (ET > 10 GeV) jets which are difficult to explain within the framework of standard QCD corrections.

A search for events having the characteristics of cosmic ray Centauros has been made in 540 GeV centre of mass proton-antiproton collisions, using information on charged particle multiplicities and transverse momenta from our central detector image chamber, together with energy deposition in our calorimeters. No such events were found in 48 000 low bias events.

A sample of two-jet events from the UA1 experiment at the CERN pp̄ Collider has been used to study the fragmentation of high-energy quark and gluon jets into charged hadrons. Compared with lower-energy jets observed in e+e− and pp collisions, the fragmentation function measured in the present experiment is softer (i.e. peaked to smaller values of z) and the mean internal transverse momentum is larger, mainly because of the effects of the QCD scaling violations. Using our knowledge of the quark and gluon structure functions in the proton, together with the QCD matrix elements, a statistical separation of quark and gluon jets is achieved within the present experiment. The fragmentation function for the gluon jets is found to be softer, and the angular spread of the fragmentation products larger, than is the case for quark jets.

This Letter reports on a new high precision measurement of the form factors of the KL→π±μ∓νμ decay. The data sample of about 2.3×106 events was recorded in 1999 by the NA48 experiment at CERN. Studying the Dalitz plot density we measured a linear, λ+′=(20.5±2.2stat±2.4syst)×10−3, and a quadratic, λ+″=(2.6±0.9stat±1.0syst)×10−3 term in the power expansion of the vector form factor. No evidence was found for a second order term for the scalar form factor; the linear slope was determined to be λ0=(9.5±1.1stat±0.8syst)×10−3. Using a linear fit our results were: λ+=(26.7±0.6stat±0.8syst)×10−3 and λ0=(11.7±0.7stat±1.0syst)×10−3. A pole fit of the form factors yields: mV=(905±9stat±17syst)MeV/c2 and mS=(1400±46stat±53syst)MeV/c2.

A search for the decay KS→π0μ+μ− has been made by the NA48/1 Collaboration at the CERN SPS accelerator. The data were collected during 2002 with a high-intensity KS beam. Six events were found with a background expectation of 0.22−0.11+0.18 events. Using a vector matrix element and unit form factor, the measured branching ratio is B(KS→π0μ+μ−)=[2.9−1.2+1.5(stat)±0.2(syst)]×10−9.

Inclusive fragmentation of jets into charged particles has been studied in the UA1 experiment at the CERN Super Proton Synchrotron (SPS) pp̄ Collider at s = 540 GeV for jets having a transverse energy above 30 GeV. The observed fragmentation function is very similar to that seen in e+e−jets and is therefore indicative of similar hadronization processes for gluons and quarks. Scaling with the energy of the jet is valid to a good approximation, although slight deviations are suggested by the data. The average transverse momentum with respect to the jet axis for jets with ET > 30 GeV is 600 MeV/c for particles having z > 0.1 and increases slowly with the jet energy.

A bstract The NA48/2 experiment at CERN reports the first observation of the K ± → π 0 π 0 μ ± ν decay based on a sample of 2437 candidates with 15% background contamination collected in 2003–2004. The decay branching ratio in the kinematic region of the squared dilepton mass above 0.03 GeV 2 / c 4 is measured to be (0.65 ± 0.03) × 10 − 6 . The extrapolation to the full kinematic space, using a specific model, is found to be (3.45 ± 0.16) × 10 − 6 , in agreement with chiral perturbation theory predictions.

The full data set of the experiment NA31 at CERN has been used to analyse the decay mode KL→π0γγ. A signal of 63 events has been observed with an estimated background of 6.0±1.7 events, corresponding to a branching ratio of (1.7±0.3)×10−6 consistent with our previous result based on partial statistics. The invariant mass spectrum of the two photons is found to be consistent with chiral perturbation theory, and the decay is dominated by the J = 0 two photon state.

We report evidence for the production of the charged D∗ mesons in pp̄ collisions at s = 540 GeV. The search was confined to the charged particle fragments of hadronic jets, which are expected to be predominantly gluon jets in this experiment. The fragmentation function and production rate for D∗ in jets of average transverse momentum of 28 GeV/c are given.

3roton-antiproton elastic scattering at cm energy 540 GeV has been studied in the t range 0.14 ⩽ −t ⩽ 0.26 GeV2. The data is well fitted by an exponential form exp(bt) with b = 13.3 ± 1.5 GeV−2.

In events at centre of mass energy 540 GeV from the CERN pp collider, we have found clear evidence for correlations in rapidity and azimuthal angle between high transverse momentum charged particles. These correlations increase with transverse momentum and are much stronger than the general two-particle correlations in minimum bias events. By analogy to ISR results, a qualitative interpretation in terms of hard scattering and fragmentation of partons is discussed.

Antiprotons have been stored in the ICE Storage Ring and held for 85h with the help of stochastic cooling. We set a limit of at least 32 h for the antiproton lifetime (in its rest frame).

We report on the measurement of the direct emission (DE) and interference (INT) terms of the K\pm -> \pi\pm\pi^0 g decay by the NA48/2 experiment at the CERN SPS. From the data collected during 2003 and 2004 about 600k such decay candidates have been selected. The relative amounts of DE and INT with respect to the internal bremsstrahlung (IB) contribution have been measured in the range 0<T*\pi<80 MeV: Frac_{DE} (0<T*\pi<80 MeV) = (3.32\pm 0.15_{stat} \pm 0.14_{sys})x10^{-2} Frac_{INT} (0<T*\pi<80 MeV) = (- 2.35\pm 0.35_{stat} \pm 0.39_{sys})x10^{-2}, where T*pi is the kinetic energy of the charged pion in the kaon rest frame. This is the first observation of an interference term in T*\pi decays. In addition, a limit on the CP violating asymmetry in the K^+ and K^- branching ratios for this channel has been determined to be less than 1.5x10^{-3} at 90% confidence level.

New measurements of the $\eta$ and $K^0$ masses have been performed using decays to 3$\pi^0$ with the NA48 detector at the CERN SPS. Using symmetric decays to reduce systematic effects, the results $M(\eta) = 547.843\pm0.051$ MeV/c$^2$ and $M(K^0) = 497.625\pm0.031$ MeV/c$^2$ were obtained.

A search for the decay KL→π0e+e− has been performed at the CERN SPS. One candidate event has been found, compatible with an expected background of 1.5 events. The corresponding upper limit for the branching ration is Γ(KL→π0e+e−)Γ(KL → all)<4×10−8 with 90% confidence.

From 56 days of data taking in 2002, the NA48/1 experiment observed 6316 Ξ0→Σ+e−ν¯e candidates (with the subsequent Σ+→pπ0 decay) and 555 Ξ0¯→Σ+¯e+νe candidates with background contamination of 215±44 and 136±8 events, respectively. From these samples, the branching ratios BR(Ξ0→Σ+e−ν¯e)=(2.51±0.03stat±0.09syst)×10−4 and BR(Ξ0¯→Σ+¯e+νe)=(2.55±0.14stat±0.10syst)×10−4 were measured allowing the determination of the CKM matrix element |Vus|=0.209−0.028+0.023. Using the Particle Data Group average for |Vus| obtained in semileptonic kaon decays, we measured the ratio g1/f1=1.20±0.05 of the axial-vector to vector form factors.

We present experimental evidence for a resonant behaviour of the hadron production from e+e− annihilations at the e+e− storage ring ADONE. A Breit-Wigner fit to the enhancement present between 1800 and 1850 MeV gives the following parameters M = 1812−13+7 MeV, Γ = 34−15+21 MeV.

The construction and the operation of a large-area transition radiation detector (TRD) for the NA31 experiment at CERN are described. The TRD incorporates several novel features for stabilizing the detector response. The density of the gas mixture (xenon+helium+methane) in the detection chambers is matched to the carbon dioxide gas in the surrounding radiators by tuning the helium concentration to avoid a hydrostatic pressure difference, which would deform the chamber walls. The chamber pressure is continuously regulated by computer control to maintain it to within 1 μbar of the radiator pressure. The gas gain of each of the four chambers is regulated to better than 0.2% by changing the high voltage under computer control, using the pulse-height spectra of 16 109Ca sources mounted on the chambers. The results of performance studies are described. The detector has a pion efficiency of 98.7% with an electron rejection of a factor of 10.

We report the observation of 21 dimuon events at the CERN pp Collider with the UA1 detector. The events range in invariant dimuon mass from 2 to 22 GeV / c2. The properties of these events are given. The bulk of the events are consistent with heavy-flavour production (mainly bb) with a few candidates for Drell-Yan production. There remain a few events which are difficult to interpret in terms of these processes, in particular two events with isolated, like-sign muons.

The KS→γγ decay rate has been measured with the NA48 detector using a high intensity short neutral beam from the CERN SPS. The measured branching ratio BR(KS→γγ)=(2.78±0.06stat±0.04syst)×10−6, obtained from 7461±172 KS→γγ events, is significantly higher than the O(p4) prediction of chiral perturbation theory. Using a KL beam the ratio Γ(KL→γγ)Γ(KL→π0π0π0)=(2.81±0.01stat±0.02syst)×10−3 has been measured.

Abstract We report here on a semi-automatic system for the control and measurement of the wire tension in a large detector (23 000 wires) to be used by the UA1 Collaboration in an experiment at the CERN p p collider. The method consists in feeding an alternating current of variable frequency to the wire in the presence of a small magnetic field. The wire resonance frequency, which is simply related to the mechanical tension, is found by requiring a 90° phase shift between the driving current and the oscillation of the wire. The control procedure is computer controlled and can be applied to any large system of wire chambers where a precise (

Measured ratios of decay rates for ${\mathcal{R}}_{K e 3 / K2\pi}$ , ${\mathcal{R}}_{K \mu3 / K2\pi}$ and ${\mathcal{R}}_{K \mu3 / Ke3}$ are presented. These measurements are based on K± decays collected in a dedicated run in 2003 by the NA48/2 experiment at CERN. The results obtained are ${\mathcal{R}}_{K e 3 / K2\pi} = 0.2496\pm0.0009 ({\text{stat}})\pm0.0004 ({\text{syst}})$ and ${\mathcal{R}}_{K \mu3 / K2\pi} = 0.1637\pm0.0006 ({\text{stat}})\pm0.0003 ({\text{syst}})$ . Using the PDG average for the K±→π±π0 normalisation mode, both values are found to be larger than the current values given by the particle data book and lead to a larger magnitude of the |Vus| CKM element than previously accepted. When combined with the latest particle data book value of |Vud|, the result is in agreement with unitarity of the CKM matrix. In addition, a new measured value of ${\mathcal{R}}_{K \mu3 / Ke3} = 0.656\pm0.003({\text{stat}})\pm0.001({\text{syst}})$ is compared to the semi-empirical predictions based on the latest form factor measurements.

The NA48/2 experiment at CERN collected two data samples with minimum bias trigger conditions in 2003 and 2004. A measurement of the rate and dynamic properties of the rare decay K±→π±γγ from these data sets based on 149 decay candidates with an estimated background of 15.5±0.7 events is reported. The model-independent branching ratio in the kinematic range z=(mγγ/mK)2>0.2 is measured to be BMI(z>0.2)=(0.877±0.089)×10−6, and the branching ratio in the full kinematic range assuming a particular Chiral Perturbation Theory description to be B(Kπγγ)=(0.910±0.075)×10−6.

Abstract Large apecture forward spectrometers with planar geometry perpendicular to the beam line are the natural detectors to accomodate the expected forward peaking of Beauty particle production at high energy hadron colliders. We have designed, built and tested a prototype planar silicon strip vertex detector for triggering such a spectrometer system. The test system consisted of 43 000 channels, configured in six planes, each with four quadrants, perpendicular to the beam line and installed inside the SPS-collider vacuum pipe at the center of an interaction region. Events recorded with the rf shield of the silicon system 1.5 mm from the circulating beams show negligible event-unrelated background.

The Central Detector of the UA1 experiment at the CERN proton-antiproton Collider underwent a first physics run at the end of 1981. The detector consists of a large drift chamber assembly (25 m3, ~ 6000 sense wires). An electronics readout with multi-hit capability simultaneously digitizes the time and the analog information used for charge division and energy measurement. The initial performance of the readout and control system will also be presented. The detector was tested in two cosmic-ray runs, and is now fully operational for the second physics run; this started at the beginning of October 1982.

The distribution of the K±→π±π+π− decays in the Dalitz plot has been measured by the NA48/2 experiment at the CERN SPS with a sample of 4.71×108 fully reconstructed events. With the standard Particle Data Group parameterization the following values of the slope parameters were obtained: g=(−21.134±0.017)%, h=(1.848±0.040)%, k=(−0.463±0.014)%. The quality and statistical accuracy of the data have allowed an improvement in precision by more than an order of magnitude, and are such as to warrant a more elaborate theoretical treatment, including pion–pion rescattering, which is in preparation.

Using the full data set of the NA48/2 experiment, the decay K+- -> pi+- e+ e- gamma is observed for the first time, selecting 120 candidates with 7.3 +- 1.7 estimated background events. With K+- -> pi+- pi0D as normalisation channel, the branching ratio is determined in a model-independent way to be Br(K+- -> pi+- e+ e- gamma, m_eegamma > 260 MeV/c^2) = (1.19 +- 0.12_stat +- 0.04_syst) x 10^-8. This measured value and the spectrum of the e+ e- gamma invariant mass allow a comparison with predictions of Chiral Perturbation Theory.

As first observed by the NA48/2 experiment at the CERN SPS, the π0π0 invariant mass (M00) distribution from K±→π±π0π0 decay shows a cusp-like anomaly at M00=2m+, where m+ is the charged pion mass. An analysis to extract the ππ scattering lengths in the isospin I=0 and I=2 states, a0 and a2, respectively, has been recently reported. In the present work the Dalitz plot of this decay is fitted to a new empirical parameterization suitable for practical purposes, such as Monte Carlo simulations of K±→π±π0π0 decays.

The NA48/2 experiment at CERN reports the first observation of the K±→π±π0e+e− decay from an exposure of 1.7×1011 charged kaon decays recorded in 2003–2004. A sample of 4919 candidates with 4.9% background contamination allows the determination of the branching ratio in the full kinematic region, BR(K±→π±π0e+e−)=(4.24±0.14)×10−6. The study of the kinematic space shows evidence for a structure dependent contribution in agreement with predictions based on chiral perturbation theory. Several P- and CP-violating asymmetries are also evaluated.

Prototype test results are reported from the NA48 KS tagging system. Thin scintillator foils were arranged as two staircases intersecting in space. A geometric alignment to 0.4 mrad, a light yield of 300–400 photoelectrons and a time resolution of 70–90 ps with conventional TDCs were achieved. A FADC system operating at 450 megasamples/s performed at 50 ps intrinsic time resolution. Overlapping pulses could be resolved down to 7 ns.

We have searched for the sequence of decays KL0→π0H0 and H0→e+e− at the CERN Super Proton Synchrotron (SPS), and have allowed for a non-zero H0 lifetime. Three candidates have been seen, consistent with an expected background of 3.3. Limits on the branching ratio product in the range 10−8–10−7 are presented as a function of the mass and lifetime of the H0. These can be used to restrict the neutral Higgs of the minimal standard model.

Using data taken during the year 2000 with the NA48 detector at the CERN SPS, a search for the CP violating decay K_S -> 3 pi0 has been performed. From a fit to the lifetime distribution of about 4.9 million reconstructed K0/K0bar -> 3 pi0 decays, the CP violating amplitude eta_000 = A(K_S -> 3 pi0)/A(K_L -> 3 pi0) has been found to be Re(eta_000) = -0.002 +- 0.011 +- 0.015 and Im(eta_000) = -0.003 +- 0.013 +- 0.017. This corresponds to an upper limit on the branching fraction of Br(K_S -> 3 pi0) < 7.4 x 10^-7 at 90% confidence level. The result is used to improve knowledge of Re(epsilon) and the CPT violating quantity Im(delta) via the Bell-Steinberger relation.

We report a measurement of the direct CP violation asymmetry parameter $A_g$ in charged kaon decays $K^\pm\to\pi^\pm\pi^+\pi^-$ by the NA48/2 experiment at the CERN SPS. The experiment has been designed not to be limited by systematics in the asymmetry measurement. Using $1.67\times 10^9$ such decays collected during the 2003 run, the charge asymmetry in the Dalitz plot linear slope parameter $g$ has been measured to be $A_g=(1.7\pm2.9)\times 10^{-4}$. The precision of the result is limited by the statistics used.

The decay asymmetries of the weak radiative hyperon decays Ξ0→Λγ and Ξ0→Σ0γ have been measured with high precision using data of the NA48/1 experiment at CERN. From about 52 000 Ξ0→Λγ and 15 000 Ξ0→Σ0γ decays, we obtain for the decay asymmetries αΞ0→Λγ=−0.704±0.019stat±0.064syst and αΞ0→Σ0γ=−0.729±0.030stat±0.076syst, respectively. These results are in good agreement with previous experiments, but more precise.

Abstract Two events with the characteristic of the decay K L O → e + e − e − have been observed with a negligible expected background from which a branching ratio of (4±3)×10 −8 is derived. This result is consistent with values estimated from theoretical models based on the double internal conventional of the decay K L O → γγ .

Abstract The total cross section for electron-positron annihilation into three or more hadrons has been measured for centre of mass energies between 1.4 and 2.0 GeV. The data were obtained at ADONE by the BB experiment.

In data taken with the NA48 experiment at the CERN SPS in 1999, 730 candidates of the weak radiative hyperon decay Ξ0→Λγ have been found with an estimated background of 58±8 events. From these events the Ξ0→Λγ decay asymmetry has been determined to α(Ξ0→Λγ)=−0.78±0.18stat±0.06syst, which is the first evidence of a decay asymmetry in Ξ0→Λγ. The branching fraction of the decay has been measured to be Br(Ξ0→Λγ)=(1.16±0.05stat±0.06syst)×10−3.

A sample of 65210 K ± → π 0 π 0 e ± ν (K e4 00 ) decay candidates with 1% background contamination has been collected in 2003-2004 by the NA48/2 collaboration at the CERN SPS. A study of the differential rate provides the first measurement of the hadronic form factor variation in the plane (M 2 , M 2 ) and brings evidence for a cusp-like structure in the distribution of the squared π 0 π 0 invariant mass around $$ 4{m}_{\pi^{+}}^2 $$ . Exploiting a model independent description of this form factor, the branching ratio, inclusive of radiative decays, is obtained using the K ± → π 0 π 0 π ± decay mode as normalization. It is measured to be BR(K e4 00 ) = (2.552 ± 0.010stat ± 0.010syst ± 0.032ext) × 10−5, which improves the current world average precision by an order of magnitude while the 1.4% relative precision is dominated by the external uncertainty from the normalization mode. A comparison with the properties of the corresponding mode involving a π + π − pair (K e4 + − ) is also presented.

A measurement of the KS lifetime is presented using data recorded by the NA48 experiment at the CERN-SPS during 1998 and 1999. The KS lifetime is derived from the ratio of decay time distributions in simultaneous, collinear KS and KL beams, giving a result which is approximately independent of the detector acceptance and with reduced systematic errors. The result obtained is τS=(0.89598±0.00048±0.00051)×10−10 s, where the first error is statistical and the second systematic.

A search for the decay KS→π0e+e− has been made using the NA48 detector at the CERN SPS. Using data collected in 1999 during a 40-hour run with a high-intensity KS beam, an upper limit for the branching fraction B(KS→π0e+e−)<1.4×10−7 at 90% confidence level has been obtained.

Data from NA31 experiment at CERN have been used to measure the decay KS → γγ. From 69 candidate events of the type K0 → γγ, 52 events can be attributed to KL → γγ and one event is expected from background processes. The ratio of the relative decay widths R = Γ(KS → γγ)Γ(KL → γγ) is measured to be R = 2.2 ± 1.0(stat.) ± 0.3(syst.) ± 0.2(ext.) where the external systematic error is due to the experimental uncertainty in the branching ratio of the decay KL → γγ. This translates into a branching ratio of BR(KS → γγ) = (2.2 ± 1.1) × 10−6. If these data are combined with the published data from an earlier data taking period with the same experiment, the ratio R is determined to be R = 2.35 ± 0.75(stat.) ± 0.4(syst.) + 7.5 · (1 − BR(KL → γγ)5.86 × 10−4) where the last term accounts for the dependence on the measured KL → γγ branching ratio. The corresponding branching ratio for KS → γγ is BR(KS → γγ) = (2.4 ± 0.9) × 10−6. The measurement is a sensitive test of chiral perturbation theory and in good agreement with theoretical predictions.

The decay rate of the neutral K meson KL→e+e−γ has been measured with the NA48 detector at the CERN SPS. A total of 6864 events has been observed with an estimated background of 10 events. The branching ratio is Γ(KL→e+e−γ)/Γ(KL→all) = (1.06±0.02stat±0.02sys±0.04calc)×10−5. The parameter αK∗ describing the relative strength of the two contributing amplitudes to this decay through intermediate pseudoscalar or vector mesons was measured to be αK∗=−0.36±0.06stat±0.02sys.

We present the first observation of the decay KS→π+π−e+e− based upon the data collected in 1998 by the NA48 experiment at CERN. We have identified a clean sample of 56 events with negligible background contamination. Using KL→π+π−π0D decays as normalization sample, the branching ratio is measured to be BR(KS→π+π−e+e−)=[4.5±0.7(stat)±0.4(syst)]×10−5. This result is in good agreement with the theoretical expectations from the mechanism of inner bremsstrahlung.

Results are presented of the search for an antiproton decay into an electron and a neutral pion. Using a stacking scheme based on stochastic cooling an average of 7000 antiprotons was accumulated and stored in the ICE ring for 10 days. No experimental evidence for such an antiproton decay was found. The following lower limit for the antiproton lifetime has been established in the antiproton rest frame: τ > BR × 1700 h at 90% confidence level (CL), where BR is the branching ratio for this decay channel.

Using the NA48 detector at the CERN SPS, 31 KS->pi0 gamma gamma candidates with an estimated background of 13.7 +- 3.2 events have been observed. This first observation leads to a branching ratio of BR(KS->pi0 gamma gamma) = (4.9 +- 1.6(stat) +- 0.9(syst)) x 10^-8 in agreement with Chiral Perturbation theory predictions.

A search for the decay KS→π0γγ has been made using the NA48 detector at the CERN SPS. Using data collected in 1999 during a 40-hour run with a high-intensity KS beam, an upper limit for the branching ratio BR(KS→π0γγ,z⩾0.2)<3.3×10−7 has been obtained at 90% confidence level, where z=mγγ2/mK02.

The NA48 Collaboration has measured the amplitude of the CP-conserving component of the decay KS0→π+π−π0 relative to KL0→π+π−π0. For the characteristic parameter λ, the values Reλ=0.038±0.010 and Imλ=−0.013±0.007 have been extracted. These values agree with earlier measurements and with theoretical predictions from chiral perturbation theory.

We present a measurement of the relative branching ratio of the decay K0→π±e±νγ (Ke3γ) with respect to K0→π±e±ν (Ke3+Ke3γ) decay. The result is based on observation of 19 000 Ke3γ and 5.6×106 Ke3 decays. The value of the branching ratio is Br(Ke3γ0,Eγ*>30MeV, θeγ*>20°)/Br(Ke30)=(0.964±0.008−0.009+0.011)%. This result agrees with theoretical predictions but is at variance with a recently published result.

The decay rate of KS→πeν relative to the rate of KL→πeν has been measured by the NA48 Collaboration in a neutral kaon beam originating from 400 GeV proton-Be interactions at the CERN SPS. The result is 0.993±0.026stat±0.022syst, compatible with 1 in agreement with the Standard Model prediction at tree level. It implies BR(KS→πeν)=(7.05±0.18stat±0.16syst)×10−4.

The KS→π+π−e+e− decay mode was investigated using the data collected in 2002 by the NA48/1 Collaboration. With about 23 k KS→π+π−e+e− events and 59 k KL→π+π−πD0 normalization decays, the KS→π+π−e+e− branching ratio relative to the KL→π+π−πD0 one was determined to be BR(KS→π+π−e+e−)/BR(KL→π+π−πD0)=(3.28±0.06stat±0.04syst)×10−2. This result was used to set the upper limit |gE1/gBR|<3.0 at 90% CL on the presence, in the decay amplitude, of an E1 direct emission (gE1) term relative to the dominant inner bremsstrahlung (gBR) term. The CP-violating asymmetry Aϕ in the sinϕcosϕ distribution of KS→π+π−e+e− events, where ϕ is the angle between the π+π− and the e+e− decay planes in the kaon centre of mass, was found to be Aϕ=(−0.4±0.8)%, consistent with zero. These results are in good agreement with a description of the KS→π+π−e+e− decay amplitude dominated by the CP-even inner bremsstrahlung process.

Abstract A sample of more than one million K ± → π + π − e ± ν ( K e 4 ) decay candidates with less than one percent background contamination has been collected by the NA48/2 experiment at the CERN SPS in 2003–2004, allowing a detailed study of the decay properties. The branching ratio, inclusive of K e 4 γ decays, is measured to be BR ( K e 4 ) = ( 4.257 ± 0.016 exp ± 0.031 ext ) × 10 − 5 with a total relative error of 0.8 % . This measurement complements the study of S- and P-wave hadronic form factors by assigning absolute values to the relative hadronic form factors obtained earlier in a simultaneous analysis of the ππ scattering lengths conducted on the same data sample. The overall form factor normalization f s = 5.705 ± 0.017 exp ± 0.031 ext is obtained with a total relative precision of 0.6 % .

From the 2002 data taking with a neutral kaon beam extracted from the CERN-SPS, the NA48/1 experiment observed 97 $\Xi^{0}\rightarrow \Sigma^{+} \mu^{-} \bar{\nu}_{\mu}$ candidates with a background contamination of $30.8 \pm 4.2$ events. From this sample, the BR($\Xi^{0}\rightarrow \Sigma^{+} \mu^{-} \bar{\nu}_{\mu}$) is measured to be $(2.17 \pm 0.32_{\mathrm{stat}}\pm 0.17_{\mathrm{syst}})\times10^{-6}$.

The CP-violation experiment NA48 at CERN aims at measuring direct CP-violation in the decays of neutral kaons into π+π− and π0π0. The experiment uses simultaneous, almost collinear beams of neutral KL0 and KS0 mesons, which are produced on two different targets. KS0 events are “tagged” by measuring the times of the protons that fly towards the KS0 production target. In order to sustain the high rate of 107 protons/s in this beam without suffering from too many pile-up events, the detector consists of 24 separate scintillators (12 horizontal and 12 vertical), each of which sees only a small fraction of the beam. Their signals are digitized by specially developed 1 GHz FADCs. The exact time of a pulse is established offline by a fit procedure. The detector and its electronics have been successfully used during test beams in 1994–1996 and during the first physics run of NA48 in 1997. The inefficiency of the detector has been measured to 2×10−4. Sources of background have been identified to allow for off-line correction. The mechanical setup of the detector, the 1 GHz FADC and results from the test and data runs are presented.

The decay rate of the long-lived neutral K meson into the e+e−e+e− final state has been measured with the NA48 detector at the CERN SPS. Using data collected in 1998 and 1999, a total of 200 events has been observed with negligible background. This observation corresponds to a branching ratio of Br(KL→e+e−e+e−)=(3.30±0.24stat±0.23syst±0.10norm)×10−8.

Abstract We report the results from a study of a partial sample of ∼ 2.3 × 10 7 K ± → π ± π 0 π 0 decays recorded by the NA48/2 experiment at the CERN SPS, showing an anomaly in the π 0 π 0 invariant mass ( M 00 ) distribution in the region around M 00 = 2 m + , where m + is the charged pion mass. This anomaly, never observed in previous experiments, can be interpreted as an effect due mainly to the final state charge exchange scattering process π + π − → π 0 π 0 in K ± → π ± π + π − decay [N. Cabibbo, Phys. Rev. Lett. 93 (2004) 121801]. It provides a precise determination of a 0 − a 2 , the difference between the ππ scattering lengths in the isospin I = 0 and I = 2 states. A best fit to a rescattering model [N. Cabibbo, G. Isidori, JHEP 0503 (2005) 21] corrected for isospin symmetry breaking gives ( a 0 − a 2 ) m + = 0.268 ± 0.010 ( stat ) ± 0.004 ( syst ) , with additional external uncertainties of ±0.013 from branching ratio and theoretical uncertainties. If the correlation between a 0 and a 2 predicted by chiral symmetry is taken into account, this result becomes ( a 0 − a 2 ) m + = 0.264 ± 0.006 ( stat ) ± 0.004 ( syst ) ± 0.013 ( ext ) .

Data from the NA31 experiment at CERN have been used for a search for the decay mode KL → π0π0γ. After all cuts, three events remain in the signal region with an estimated background of 2.2 ± 0.9 events. The upper limit for the branching ratio of KL → π0π0γ is 5.6 × 10−6 at the 90% confidence level.

The decay rate of KS → γγ has been measured with the NA48 detector at the CERN SPS. A total of 149 KS → γγ events have been observed. The branching ratio is determined to be (2.58±0.36(stat)±0.22(sys))×10−6.

The NA48/2 experiment at CERN reports the first observation of the $K^{\pm} \rightarrow \pi^{0} \pi^{0} \mu^{\pm} \nu$ decay based on a sample of 2437 candidates with 15% background contamination collected in 2003--2004. The decay branching ratio in the kinematic region of the squared dilepton mass above $0.03$~GeV$^2/c^4$ is measured to be $(0.65 \pm 0.03) \times 10^{-6}$. The extrapolation to the full kinematic space, using a specific model, is found to be $(3.45 \pm 0.16) \times 10^{-6}$, in agreement with chiral perturbation theory predictions.

The concept of KS proton tagging and first prototype test results are reported from the NA48 experiment. Thin scintillator foils were arranged as two staircases intersecting in space. A geometric alignment to 0.4 mrad, a light yield of 300–400 photoelectrons and a time resolution of 70–90 ps with conventional TDCs were achieved. A FADC system operating at 450 megasamples/s performed at 50 ps intrinsic time resolution. Overlapping pulses could be resolved down to 7 ns.

The KL→π±π0e∓νe(ν̄e) decay was investigated with the NA48 detector at CERN SPS using a beam of long-lived neutral kaons. The branching ratio Br(KL→π±π0e∓νe(ν̄e))=(5.21±0.07stat±0.09syst)×10−5 was fixed from a sample of 5464 events with 62 background events. The form factors f̄s, f̄p, λg and h̄ were found to be in agreement with previous measurements but with higher accuracy. The coupling parameter of the chiral Lagrangian L3=(−4.1±0.2)×10−3 was evaluated from the data.

We report results of a search for narrow resonances in e+e− annihilation at center-of-mass energies between 1.85 and 3.1 GeV performed with the KEDR detector at the VEPP-4M e+e− collider. The upper limit on the leptonic width of a narrow resonance ΓeeR⋅Br(R→hadr)<120 eV has been obtained (at 90% C.L.).

(l) J . J . AUBERT, U. BECKER, J . P . BIGGS, J . BURGER, M. CHEN, G. EVERHART, P . GOLDHAGEN, J . LEONQ, T. Me CORRISTON, T. G. RHOADES, M. •OHDE, S. C. C. TING, SAW LAN WU a n d Y. Y. LEE: Iok~8. Rev. Lett., 33, 1404 (1974). (l) J . E . AUGUSTIN, A. ~ . BOYARSKI, M. BREIDENBACH, 1~. BULOS, J . T. DAKIN, G. J . FELDMAN, G. E. FISCHER, D. FRYBERGER, G. HANSON, B. JEAN-1VIARIE, R . 1~. LARSEN, V. LUTH, H . L. LYNCH, D. LYON, C. C. ~r J . ~r PATERSON, ~[. L. PERL, B. RICHTER, P . RAPIDIS, R . F. SCHWITTERS, W. ~ . TANENBAUM, F. VANN~rCCI, G. S. ABRAMS, D. BRIGGS, W . CHINOWSKY, C. ]~. I~RIEDBERG, G. GOLDHABER, R . J . •OLLEBEEK, J . A. I~ADYK, B. LULU, F. PIERRE, G. H. TRILLING, J . 8. WHITAKER, J. Wiss and J. E. ZIPSE: IOh~8. ReV. Let t . , 33, 1406 (1974). (3) C. ]3ACCI, R . BALDINI-CELIO, M. BERNA.RDINI, G. CAPOI~, l~. DEL FABBRO, 1VL GRILLI, E. IAROCCI, L. H . JONES, M. LOCCI, C. MENCUCCINI, G. P . ~URTAS, G. PENSO, G. SALVINI, ~r SPINETTI, M. SPA~O, B. STELLA, V. VALENTE, B. BARTOLI, D. BISELLO, B. ESPOSITO, F. FELICETrI, P . ~ONACELLI, M. NIGRO, L. PAOLUZI, I . PERUZZI, G. PIANO ~ORTARI, 1~. PICCOLO, F. ~ONGA, F. SEBASTIA~I, L. TRASATTI, F. VANOLI, G. BARBARINO, G. BARBIELLINI, C. BEMPORAD, R . BIANCASTELLI, M. CASTELLANO, F. CEVENII~I, ~[. CALVETTI, F. COSTANTINI, P . LARICCIA, P . PARASCANDOLO, 8. PATRICELLI, E. BASSI, C. SPENCER, L. TORTORA, U. TROYA a n d S. VITALE: Phys. Rev. Left., 33, 1408 (1974).

Simplified Template Cross Sections (STXS) have been adopted by the LHC experiments as a common framework for Higgs measurements. Their purpose is to reduce the theoretical uncertainties that are directly folded into the measurements as much as possible, while at the same time allowing for the combination of the measurements between different decay channels as well as between experiments. We report the complete, revised definition of the STXS kinematic bins (stage 1.1), which are to be used for the upcoming measurements by the ATLAS and CMS experiments using the full LHC Run 2 datasets. The main focus is on the three dominant Higgs production processes, namely gluon-fusion, vector-boson fusion, and in association with a vector boson. We also comment briefly on the treatment of other production modes.