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.
We report results from a new measurement of the K
e4
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 K
e4
decays in both charged ...modes collected in 2003. The form factors of the hadronic current (F,G,H) and ππ phase difference (δ=δ
s
-δ
p
) 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 a
0
0
and a
0
2
. Under the assumption of isospin symmetry and using numerical solutions of the Roy equations, the following values are obtained in the plane (a
0
0
,a
0
2
): a
0
0
=0.233±0.016stat±0.007syst,a
0
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.
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.
A drift chamber with a new type of straws for operation in vacuum Azorskiy, N.; Glonti, L.; Gusakov, Yu ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2016, Volume:
824
Journal Article
Peer reviewed
A 2150×2150mm2 registration area drift chamber capable of working in vacuum is presented. Thin-wall tubes (straws) of a new type are used in the chamber. A large share of these 9.80mm diameter drift ...tubes are made in Dubna from metalized 36µm Mylar film welded along the generatrix using an ultrasonic welding machine created at JINR. The main features of the chamber and some characteristics of the drift tubes are described. Four such chambers with the X, Y, U, V coordinates each, containing 7168 straws in total, are designed and produced at JINR and CERN. They are installed in the vacuum volume of the NA62 setup in order to study the ultra-rare decay K+→π+vv¯ and to search for and study rare meson decays. In autumn 2014 the chambers were used for the first time for the data taking in the experimental run of the NA62 at CERN׳s SPS.
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 9 MeV/c2<mA′<70 MeV/c2. The NA48/2 sensitivity to the dark photon production in the K±→π±A′ decay is also evaluated.
A device for fabricating thin-wall (straw) drift tubes using polyethylene terephthalate film 36 μm thick by ultrasonic welding is described together with the technique for controlling their quality. ...The joint width amounts to 0.4–1.0 mm. The joint breaking strength is 31.9 kg/mm
2
. The argon leakage from a tube of volume 188.6 cm
3
under a pressure gradient of 1.0 atm does not exceed 0.3 × 10
–3
cm
3
/min, which is mainly related to the absence of metallization in the joint vicinity. The high strength, the low tensile creep due to the absence of glued layers, the small value of gas leakage makes the new tubes capable of reliable and long-term operation in vacuum, which is confirmed by the operation of 7168 straw tubes for two years in the NA62 experiment.
A search for heavy neutral lepton (N) production in K+→e+N decays using the data sample collected by the NA62 experiment at CERN in 2017–2018 is reported. Upper limits of the extended neutrino mixing ...matrix element |Ue4|2 are established at the level of 10−9 over most of the accessible heavy neutral lepton mass range 144–462 MeV/c2, with the assumption that the lifetime exceeds 50 ns. These limits improve significantly upon those of previous production and decay searches. The |Ue4|2 range favoured by Big Bang Nucleosynthesis is excluded up to a mass of about 340 MeV/c2.
The NA62 experiment at CERN reports searches for K+→μ+N and K+→μ+νX decays, where N and X are massive invisible particles, using the 2016–2018 data set. The N particle is assumed to be a heavy ...neutral lepton, and the results are expressed as upper limits of O(10−8) of the neutrino mixing parameter |Uμ4|2 for N masses in the range 200–384 MeV/c2 and lifetime exceeding 50 ns. The X particle is considered a scalar or vector hidden sector mediator decaying to an invisible final state, and upper limits of the decay branching fraction for X masses in the range 10–370 MeV/c2 are reported for the first time, ranging from O(10−5) to O(10−7). An improved upper limit of 1.0×10−6 is established at 90% CL on the K+→μ+ννν¯ branching fraction.
A search for heavy neutral lepton production in K+ decays using a data sample collected with a minimum bias trigger by the NA62 experiment at CERN in 2015 is reported. Upper limits at the 10−7 to ...10−6 level are established on the elements of the extended neutrino mixing matrix |Ue4|2 and |Uμ4|2 for heavy neutral lepton mass in the ranges 170–448 MeV/c2 and 250–373 MeV/c2, respectively. This improves on the previous limits from HNL production searches over the whole mass range considered for |Ue4|2, and above 300 MeV/c2 for |Uμ4|2.
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