arXiv subjects

S. E. Vigdor

Publications and source records attributed to S. E. Vigdor.

12 recordsLinked to original sources

arXiv2012

Formation of the $S=-1$ resonance X(2265) in the reaction $pp -> X + K^+$ at 2.50 and 2.85 GeV

Analyzing DISTO data of $pp -> p Lambda K^+$ at $T_p = 2.50$ and 2.85 GeV to populate a previously reported X(2265) resonance with $M_X = 2267$ MeV/$c^2$ and $Gamma_X = 118$ MeV at 2.85 GeV, we found that the production of X(2265) at 2.50 GeV is much less than that at 2.85 GeV (less than 10%), though it is expected from a kinematical consideration to be produced as much as 33% of that at 2.85 GeV. The small population of X(2265) at 2.50 GeV is consistent with the very weak production of Lambda (1405) at the same incident energy toward its production threshold, thus indicating that Lambda (1405) plays an important role as a doorway state for the formation of X(2265).

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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.

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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.

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arXiv2006

Measurement of the Absolute Differential Cross Section for np Elastic Scattering at 194 MeV

A tagged medium-energy neutron beam has been used in a precise measurement of the absolute differential cross section for np back-scattering. The results resolve significant discrepancies within the np database concerning the angular dependence in this regime. The experiment has determined the absolute normalization with 1.5% uncertainty, suitable to verify constraints of supposedly comparable precision that arise from the rest of the database in partial wave analyses. The analysis procedures, especially those associated with evaluation of systematic errors in the experiment, are described in detail so that systematic uncertainties may be included in a reasonable way in subsequent partial wave analysis fits incorporating the present results.

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arXiv2004

Measurement of the Absolute np Scattering Differential Cross Section at 194 MeV

We describe a double-scattering experiment with a novel tagged neutron beam to measure differential cross sections for np back-scattering to better than 2% absolute precision. The measurement focuses on angles and energies where the cross section magnitude and angle-dependence constrain the charged pion-nucleon coupling constant, but existing data show serious discrepancies among themselves and with energy-dependent partial wave analyses (PWA). The present results are in good accord with the PWA, but deviate systematically from other recent measurements.

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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.

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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.

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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.

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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.

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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.

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arXiv1999

The RHIC Spin Program: Snapshots of Progress

I review progress toward the experimental study of polarized proton collisions at RHIC, at center-of-mass energies of several hundred GeV. The tools under development for these experiments are summarized, with emphasis on the complementarity for the spin program of the two major detectors, PHENIX and STAR. The proposed research program includes measurements of the spin structure of hadrons, tests of QCD predictions for spin observables, and polarization searches for interactions beyond the Standard Model. I argue, in particular, that RHIC should provide the best determination of the gluonic contribution to proton spin foreseen for the coming decade.

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arXiv1998

Roper excitation in $\vec{p}+α\to \vec{p}+α+X$ reactions

We calculate differential cross sections and the spin transfer coefficient $D_{nn}$ in the $\vec{p}+α\to \vec{p}+α+π^0$ reaction for proton bombarding energies from 1 to 10 GeV and $π^0 - p$ invariant masses spanning the region of the N$^*$(1440) Roper resonance. Two processes -- $Δ$ excitation in the $α$-particle and Roper excitation in the proton -- are included in an effective reaction model which was shown previously to reproduce existing inclusive spectra. The present calculations demonstrate that these two contributions can be clearly distinguished via $D_{nn}$, even under kinematic conditions where cross sections alone exhibit no clear peak structure due to the excitation of the Roper.

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