arXiv subjects

F. Balestra

Publications and source records attributed to F. Balestra.

64 records · Page 4Linked to original sources

arXiv2010

Indication of a deeply bound compact K-pp state formed in the pp -> p Lambda K+ reaction at 2.85 GeV

We have analyzed data of the DISTO experiment on the exclusive pp -> p Lambda K+ reaction at 2.85 GeV to search for a strongly bound compact K-pp (= X) state to be formed in the pp -> K+ + X reaction. The observed spectra of the K+ missing-mass and the p Lambda invariant-mass with high transverse momenta of p and K+ revealed a broad distinct peak with a mass M_X = 2265 +- 2 (stat) +- 5 (syst) MeV/c2 and a width Gamma_X = 118 +- 8 (stat) +- 10 (syst) MeV.

nucl-ex↗

arXiv2009

DISTO data on Kpp

The data from the DISTO Collaboration on the exclusive pp -> p K+ Lambda production acquired at T_p = 2.85 GeV have been re-analysed in order to search for a deeply bound K- pp (= X) state, to be formed in the binary process pp -> K+ X. The preliminary spectra of the DeltaM_{K+} missing-mass and of the M_{p Lambda} invariant-mass show, for large transverse-momenta of protons and kaons, a distinct broad peak with a mass M_X = 2265 +- 2 MeV/c^2 and a width Gamma_X = 118 +- 8 MeV/c^2.

hep-ex↗

arXiv2009

Collins and Sivers asymmetries for pions and kaons in muon-deuteron DIS

The measurements of the Collins and Sivers asymmetries of identified hadrons produced in deep-inelastic scattering of 160 GeV/c muons on a transversely polarised 6LiD target at COMPASS are presented. The results for charged pions and charged and neutral kaons correspond to all data available, which were collected from 2002 to 2004. For all final state particles both the Collins and Sivers asymmetries turn out to be small, compatible with zero within the statistical errors, in line with the previously published results for not identified charged hadrons, and with the expected cancellation between the u- and d-quark contributions.

hep-ex↗

arXiv2006

On the muon neutrino mass

During the runs of the PS 179 experiment at LEAR of CERN, we photographed an event of antiproton-Ne absorption, with a complete pi+ -> mu+ ->e+ chain. From the vertex of the reaction a very slow energy pi+ was emitted. The pi+ decays into a mu+ and subsequently the mu+ decays into a positron. At the first decay vertex a muon neutrino was emitted and at the second decay vertex an electron neutrino and a muon antineutrino. Measuring the pion and muon tracks and applying the momentum and energy conservation and using a classical statistical interval estimator, we obtained an experimental upper limit for the muon neutrino mass: m_nu < 2.2 MeV at a 90% confidence level. A statistical analysis has been performed of the factors contributing to the square value of the neutrino mass limit.

nucl-ex↗

arXiv2006

Resonant behaviour in double charge exchange reaction of π^+ mesons on the nuclear photoemulsion

The invariant mass spectra of the $ppπ^-$ and $pp$ systems produced in the double charge exchange (DCX) of positively charged pions on photoemulsion are analysed. A pronounced peak is observed in the $ppπ^-$ invariant mass spectrum, while the $M_{pp}$ spectrum exhibits a strong Migdal-Watson effect of the proton-proton final state interaction. These findings are in favor of the $NN$-decoupled $NNπ$ pseudoscalar resonance with T=0 called $d'$.

hep-ph↗

arXiv2002

Rho^0 meson production in the pp ->pppi+pi- reaction at 3.67 GeV/c

Total and differential cross sections for the exclusive reaction pp->pp rho^0 observed via the pi+pi- decay channel have been measured at beam momentum=3.67 GeV/c. The observed total meson production cross section is determined to be 23.4 +- 0.8 +-8 microb and is significantly lower than typical cross sections used in model calculations for heavy ion collisions. The differential cross sections measured indicate a strong anisotropy cos^2(theta^{CM}) in the rho^0 meson production.

hep-ex↗

arXiv2000

$ϕ$ and $ω$ Meson Production in pp Reactions at $p_{lab}$=3.67 GeV/c

The exclusive production cross sections for $ω$ and $ϕ$ mesons have been measured in proton-proton reactions at $p_{lab}=3.67$ GeV/c. The observed $ϕ/ω$ cross section ratio is $(3.8\pm0.2^{+1.2}_{-0.9})\times 10^{-3}$. After phase space corrections, this ratio is enhanced by about an order of magnitude relative to naive predictions based upon the Okubo-Zweig-Iizuka (OZI) rule, in comparison to an enhancement by a factor $\sim 3$ previously observed at higher beam momenta. The modest increase of this enhancement near the production threshold is compared to the much larger increase of the $ϕ/ω$ ratio observed in specific channels of $\bar pp$ annihilation experiments. Furthermore, differential cross section results are also presented which indicate that although the $ϕ$ meson is predominantly produced from a $^3P_1$ proton-proton entrance channel, other partial waves contribute significantly to the production mechanism at this beam momentum.

nucl-ex↗

arXiv2000

Production of $η\prime$ Mesons in the $pp \to ppη\prime$ Reaction at 3.67 GeV/c

The ratio of the total exclusive production cross sections for $η\prime$ and $η$ mesons has been measured in the $pp$ reaction at $p_{beam}=3.67$ GeV/c. The observed $η\prime/η$ ratio is $(0.83\pm{0.11}^{+0.23}_{-0.18})\times 10^{-2}$ from which the exclusive $η\prime$ meson production cross section is determined to be $(1.12\pm{0.15}^{+0.42}_{-0.31})μb$. Differential cross section distributions have been measured. Their shape is consistent with isotropic $η\prime$ meson production.

nucl-ex↗

arXiv1999

K$^-$ Meson Production in the Proton-Proton Reaction at 3.67 GeV/c

The total cross section of the reaction $pp\to ppK^+K^-$ has been determined for proton--proton reactions with $p_{beam}=3.67 GeV/c$. This represents the first cross section measurement of the $pp \to ppK^-K^+$ channel near threshold, and is equivalent to the inclusive $pp\to ppK^-X$ cross section at this beam momentum. The cross section determined at this beam momentum is about a factor 20 lower than that for inclusive $pp\to ppK^+X$ meson production at the same CM energy above the corresponding threshold. This large difference in the $K^+$ and $K^-$ meson inclusive production cross sections in proton-proton reactions is in strong contrast to cross sections measured in sub-threshold heavy ion collisions, which are similar in magnitude at the same energy per nucleon below the respective thresholds.

nucl-ex↗

arXiv1999

Spin Transfer in Exclusive Lambda Production from pp Collisions at 3.67 GeV/c

We report the first polarization transfer measurements for exclusive hyperon production reactions. The normal spin transfer coefficient DNN for pp -> p K+ Lambda is large and negative for forward Lambda production at a beam momentum of 3.67 GeV/c, a result qualitatively consistent with expectations for a mechanism dominated by kaon-exchange and rescattering. The sign of DNN is opposite to that observed in the fragmentation regime for inclusive Lambda production at much higher energies.

nucl-ex↗