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.
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.
A sample of 7253 K±→π±e+e−(γ) decay candidates with 1.0% background contamination has been collected by the NA48/2 experiment at the CERN SPS, which allowed a precise measurement of the decay ...properties. The branching ratio in the full kinematic range was measured to be BR=(3.11±0.12)×10−7, where the uncertainty includes also the model dependence. The shape of the form factor W(z), where z=(Mee/MK)2, was parameterized according to several models, and, in particular, the slope δ of the linear form factor W(z)=W0(1+δz) was determined to be δ=2.32±0.18. A possible CP violating asymmetry of K+ and K− decay widths was investigated, and a conservative upper limit of 2.1×10−2 at 90% CL was established.
New measurement of the K±→π±μ+μ− decay Kalmus, G.; Lazzeroni, C.; Munday, D.J. ...
Physics letters. B,
02/2011, Letnik:
697, Številka:
2
Journal Article
Recenzirano
Odprti dostop
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.
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 precision test of lepton flavour universality has been performed by measuring the ratio RK of kaon leptonic decay rates K+→e+ν and K+→μ+ν in a sample of 59 813 reconstructed K+→e+ν candidates with ...(8.71±0.24)% background contamination. The result RK=(2.487±0.013)×10−5 is in agreement with the Standard Model expectation.
The NA62 experiment collected a large sample of charged kaon decays in 2007 with a highly efficient trigger for decays into electrons. A measurement of the π0 electromagnetic transition form factor ...slope parameter from 1.11×106 fully reconstructed K±→π±πD0, πD0→e+e−γ events is reported. The measured value a=(3.68±0.57)×10−2 is in good agreement with theoretical expectations and previous measurements, and represents the most precise experimental determination of the slope in the time-like momentum transfer region.
Dwarf galaxies are widely believed to be among the best targets for indirect dark matter searches using high-energy gamma rays and indeed gamma-ray emission from these objects has long been a subject ...of detailed study for ground-based atmospheric Cherenkov telescopes. Here, we update current exclusion limits obtained on the closest dwarf, the Sagittarius dwarf galaxy, in light of recent realistic dark matter halo models. The constraints on the velocity-weighted annihilation cross-section of the dark matter particle are of a few 10 super(-23) cm super(3) s super(-1) in the TeV energy range for a 50 hr exposure. The limits are extrapolated to the sensitivities of future Cherenkov Telescope Arrays. For 200 hr of observation time, the sensitivity at the 95% confidence level reaches 10 super(-25) cm super(3) s super(-1). Possible astrophysical backgrounds from gamma-ray sources dissembled in the Sagittarius dwarf are studied. It is shown that with long enough observation times, gamma-ray background from millisecond pulsars in a globular cluster contained within the Sagittarius dwarf may limit the sensitivity to dark matter annihilations.
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