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Register a new userProduction of Exotic Hadrons in $poverline{p}$ Collisions at 1.96 TeV at D0
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Peter H. Garbincius
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D0 presents results on the hadronic production of $X(3872)$, $psi(2S)$, $Z_c^pm(3900)$, and the inclusive production of pentaquarks $P_c rightarrow J/psi p$.
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Prompt and nonprompt productions of exotic multiquark states are studied using the $sim$10.4 fb$^{-1}$ data sample collected by the D0 experiment in Tevatron $pbar{p}$ collisions at $sqrt{s}$ = 1.96 TeV. The recent D0 results on the prompt and nonprompt production of the $X(3872)$ and $Z_c^+(3900)$ states and the $P_c$ pentaquarks at the 4450 MeV region are reported. Signals corresponding to these states are found in the nonprompt production, whereas only the $X(3872)$ state is seen in the prompt production. The ratio of prompt to nonprompt $X(3872)$ production is about three times larger in the D0 measurement than that obtained by the ATLAS experiment at 8 TeV. Theoretically, the production, formation, coalescence, and disassociation processes are expected to be quite different for conventional mesons with a spatial size of (0.4-0.8) fm, compact multiquark states such as tetraquarks with a size of a few fm, and spatially extended molecular states with a size of (4-10) fm. They can be differently affected in prompt hadron-hadron collisions where there are many additional particles emitted from the interaction point. Consequently, the prompt to nonprompt production ratio of spatially extended exotic states can be suppressed at LHC comparing with the Tevatron conditions, because of large difference in the hadron-hadron collisions particle multiplicity. The prompt production studies provide an opportunity to better understand the nature of exotic states.
We have observed exclusive gammagamma production in proton-antiproton collisions at sqrt{s}=1.96 TeV, using data from 1.11 pm 0.07 fb^{-1} integrated luminosity taken by the Run II Collider Detector at Fermilab. We selected events with two electromagnetic showers, each with transverse energy E_T > 2.5 GeV and pseudorapidity |eta| < 1.0, with no other particles detected in -7.4 < eta < +7.4. The two showers have similar E_T and azimuthal angle separation Deltaphi sim pi; 34 events have two charged particle tracks, consistent with the QED process p bar{p} to p + e^+e^- + bar{p} by two-photon exchange, while 43 events have no charged tracks. The number of these events that are exclusive pi^0pi^0 is consistent with zero and is < 15 at 95% C.L. The cross section for pbar{p} to p+gammagamma+bar{p} with |eta(gamma)| < 1.0 and E_T(gamma) > 2.5$ GeV is 2.48^{+0.40}_{-0.35}(stat)^{+0.40}_{-0.51}(syst) pb.
We present various properties of the production of the $X(3872)$ and $psi(2S)$ states based on 10.4 fb$^{-1}$ collected by D0 experiment in Tevatron $p bar p$ collisions at $sqrt{s}$ = 1.96 TeV. For both states, we measure the nonprompt fraction $f_{NP}$ of the inclusive production rate due to decays of $b$-flavored hadrons. We find the $f_{NP}$ values systematically below those obtained at the LHC. The $f_{NP}$ fraction for $psi(2S)$ increases with transverse momentum whereas for the X(3872) it is constant within large uncertainties, in agreement with the LHC results. The ratio of prompt to nonprompt $psi(2S)$ production, $(1 - f_{NP}) / f_{NP}$, decreases only slightly going from the Tevatron to the LHC, but for the $X(3872)$ this ratio decreases by a factor of about 3. We test the soft-pion signature of the $X(3872)$ modeled as a weakly-bound charm-meson pair by studying the production of the $X(3872)$ as a function of the kinetic energy of the $X(3872)$ and the pion in the $X(3872)pi$ center-of-mass frame. For a subsample consistent with prompt production, the results are incompatible with a strong enhancement in the production of the $X(3872)$ at small kinetic energy of the $X(3872)$ and the $pi$ in the $X(3872)pi$ center-of-mass frame expected for the $X$+soft-pion production mechanism. For events consistent with being due to decays of $b$ hadrons, there is no significant evidence for the soft-pion effect but its presence at the level expected for the binding energy of 0.17 MeV and the momentum scale $Lambda=M(pi)$ is not ruled out.
We describe a measurement of the ratio of the cross sections times branching fractions of the $B_c^+$ meson in the decay mode $B_c^+ rightarrow J/psi mu u$ to the $B^+$ meson in the decay mode $B^+ rightarrow J/psi K^+$ in proton-antiproton collisions at center-of-mass energy $sqrt{s}=1.96$ TeV. The measurement is based on the complete CDF Run II data set, which comes from an integrated luminosity of $8.7,{rm fb}^{-1}$. The ratio of the production cross sections times branching fractions for $B_c^+$ and $B_c^+$ mesons with momentum transverse to the beam greater than $6~textrm{GeV}/c$ and rapidity magnitude smaller than 0.6 is $0.211pm 0.012~mbox{(stat)}^{+0.021}_{-0.020}~mbox{(syst)}$. Using the known $B^+ rightarrow J/psi K^+$ branching fraction, the known $B^+$ production cross section, and a selection of the predicted $B_c^+ rightarrow J/psi mu u$ branching fractions, the range for the total $B_c^+$ production cross section is estimated.
We measure exclusive $pi^+pi^-$ production in proton-antiproton collisions at center-of-mass energies $sqrt{s}$ = 0.9 and 1.96 TeV in the Collider Detector at Fermilab. We select events with two oppositely charged particles, assumed to be pions, with pseudorapidity $|eta| < 1.3$ and with no other particles detected in $|eta| < 5.9$. We require the $pi^+pi^-$ system to have rapidity $|y|<$ 1.0. The production mechanism of these events is expected to be dominated by double pomeron exchange, which constrains the quantum numbers of the central state. The data are potentially valuable for isoscalar meson spectroscopy and for understanding the pomeron in a region of transition between nonperturbative and perturbative quantum chromodynamics. The data extend up to dipion mass $M(pi^+pi^-)$ = 5000 MeV/$c^2$ and show resonance structures attributed to $f_0$ and $f_2(1270)$ mesons. From the $pi^+pi^-$ and $K^+K^-$ spectra, we place upper limits on exclusive $chi_{c0}(3415)$ production.
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