A.M. Halling

Dalitz plot analysis of the decay D+ ---> K- pi+ pi+ and indication of a low-mass scalar K pi resonance

We study the Dalitz plot of the decay D^+ -->K^- pi^+ pi^+ with a sample of 15090 events from Fermilab experiment E791. Modeling the decay amplitude as the coherent sum of known K pi resonances and a uniform nonresonant term, we do not obtain an acceptable fit. If we allow the mass and width of the K^*_0(1430) to float, we obtain values consistent with those from PDG but the chi^2 per degree of freedom of the fit is still unsatisfactory. A good fit is found when we allow for the presence of an additional scalar resonance, with mass 797 +/- 19 +/- 43 MeV/c^2 and width 410 +/- 43 +/- 87 MeV/c^2. The mass and width of the K^*_0(1430) become 1459 +/- 7 +/- 5 MeV/c^2 and 175 +/- 12 +/- 12 MeV/c^2, respectively. Our results provide new information on the scalar sector in hadron spectroscopy.

Observation of color-transparency in diffractive dissociation of pions

We have studied the diffractive dissociation into dijets of 500 GeV/c pions scattering coherently from carbon and platinum targets. Extrapolating to asymptotically high energies (where t(min)-->0), we find that when the per-nucleus cross section for this process is parametrized as sigma = sigma0Aalpha, alpha has values near 1.6, the exact result depending on jet transverse momentum. These values are in agreement with those predicted by theoretical calculations of color-transparency.

Asymmetries between the production of D+ and D− mesons from 500 GeV/c π−-nucleus interactions as a function of xF and pt2

Abstract We present measurements of the production of Ds− mesons relative to Ds+ mesons as functions of xF and of pt2 for a sample of 2445 Ds decays to φπ. The Ds mesons were produced in Fermilab experiment E791 with 500 GeV/c π− mesons incident on one platinum and four carbon foil targets. The acceptance-corrected integrated asymmetry in the xF range −0.1 to 0.5 for Ds± mesons is 0.032 ± 0.022 ± 0.022, consistent with no net asymmetry. We compare the results as functions of xF and pt2 to predictions and to the large production asymmetry observed for D± mesons in the same experiment. These comparisons support the hypothesis that production asymmetries come from the fragmentation process and not from the charm quark production itself.

MEASUREMENTS OF LIFETIMES AND A LIMIT ON THE LIFETIME DIFFERENCE IN THE NEUTRAL D-MESON SYSTEM

Using the large hadroproduced charm sample collected in experiment E791 at Fermilab, we report the first directly measured constraint on the decay-width difference Delta Gamma for the mass eigenstates of the D0-D0bar system. We obtain our result from lifetime measurements of the decays D0 -->K-pi+ and D0 -->K-K+, under the assumption of CP invariance, which implies that the CP eigenstates and the mass eigenstates are the same. The lifetime of D0 -->K-K+ (the CP-even final state is \tau_KK = 0.410 +/- 0.011 +/- 0.006 ps, and the lifetime of D0 -->K-pi+ (an equal mixture of CP-odd and CP-even final states is tau_Kpi = 0.413 +/- 0.003 +/- 0.004 ps. The decay-width difference is Delta Gamma = 2(Gamma_KK - Gamma_Kpi) = 0.04 +/- 0.14 +/- 0.05 ps^-1. We relate these measurements to measurements of mixing in the neutral D-meson system.

Search for D0 - anti-D0 mixing in semileptonic decay modes

We report the result of a search for D0 - D0_bar mixing in the data from hadroproduction experiment E791 at Fermilab. We use the D* tag and semileptonic decay vertices of D0 to look for wrong-sign decays with mixing time dependence.

Search for rare and forbidden dilepton decays of the D+, Ds+, and D0 charmed mesons

Abstract We report the results of a search for flavor-changing neutral current, lepton-flavor violating, and lepton-number violating decays of D + , D s + , and D 0 mesons (and their antiparticles) into modes containing muons and electrons. Using data from Fermilab charm hadroproduction experiment E791, we examine the π ll and K ll decay modes of D + and D s + and the l + l − decay modes of D 0 . No evidence for any of these decays is found. Therefore, we present branching-fraction upper limits at 90% confidence level for the 24 decay modes examined. Eight of these modes have no previously reported limits, and fourteen are reported with significant improvements over previously published results.

Search for CP violation in charged D meson decays

Abstract We report results of a search for CP violation in the singly Cabibbo-suppressed decays D + → K − K + π + , φπ + , K ∗ (892) 0 K + , and π − π + π + based on data from the charm hadroproduction experiment E791 at Fermilab. We search for a difference in the D + and D − decay rates for each of the final states. No evidence for a difference is seen. The decay rate asymmetry parameters ( A CP ), defined as the difference in the D + and D − decay rates divided by the sum of the decay rates, are measured to be: A CP ( KKπ ) = −0.014±0.029, A CP ( φπ ) = −0.028±0.036, A CP (K ∗ (892)K) = −0.010±0.050 and A CP ( πππ ) = −0.017±0.042.We report results of a search for CP violation in the singly Cabibbosuppressed decays D → KKπ, φπ, K(892)0K+, and πππ based on data from the charm hadroproduction experiment E791 at Fermilab. We search for a difference in the D and D decay rates for each of the final states. No evidence for a difference is seen. The decay rate asymmetry parameters (ACP ), defined as the difference in the D + and D decay rates divided by the sum of the decay rates, are measured to be: ACP (KKπ) = −0.014 ± 0.029, ACP (φπ) = −0.028 ± 0.036, ACP (K(892)K) = −0.010 ± 0.050, and ACP (πππ) = −0.017 ± 0.042. PACS numbers: 11.30.Er, 12.15.Ji, 13.25.Ft, 14.40.Lb Typeset using REVTEX

Search for rare and forbidden charm meson decays D0 ---> V lepton+ lepton- and h h lepton-lepton

We report results of a search for flavor-changing neutral current (FCNC), lepton flavor, and lepton-number violating decays of the D0 (and its antiparticle) into three and four bodies. Using data from Fermilab charm hadroproduction experiment E791, we examine modes with two leptons (muons or electrons) and a rho(0), K( *0), or straight phi vector meson or a nonresonant pi(pi), Kpi, or KK pair of pseudoscalar mesons. No evidence for any of these decays is found. Therefore, we present branching-fraction upper limits at 90% confidence level for the 27 decay modes examined (18 new).

Asymmetries between the production of

This paper presents measurements of the production of Ds- mesons relative to Ds+ mesons as functions of x_F and square of p_t for a sample of 2445 Ds decays to phi pi. The Ds mesons were produced in Fermilab experiment E791 with 500 GeV/c pi- mesons incident on one platinum and four carbon foil targets. The acceptance-corrected integrated asymmetry in the x_F range -0.1 to 0.5 for Ds+- mesons is 0.032 +- 0.022 +- 0.022, consistent with no net asymmetry. The results, as functions of x_F and square of p_t, are compared to predictions and to the large production asymmetry observed for D+- mesons in the same experiment. These comparisons support the hypothesis that production asymmetries come from the fragmentation process and not from the charm quark production itself.

D_s^-

Using the large hadroproduced charm sample collected in experiment E791 at Fermilab, we have measured ratios of branching fractions for the two-body singly-Cabibbo-suppressed charged decays of the D0: (D0 -> KK)/(D0 -> Kpi) = 0.109 +- 0.003 +- 0.003, (D0 -> pipi)/(D0 -> Kpi) = 0.040 +- 0.002 +- 0.003, and (D0 -> KK)/(D0 -> pipi) = 2.75 +- 0.15 +- 0.16. We have looked for differences in the decay rates of D0 and D0bar to the CP eigenstates K+K- and pi+pi-, and have measured the CP asymmetry parameters A_CP(K+K-) = -0.010 +- 0.049 +- 0.012 and A_CP(pi+pi-) = -0.049 +- 0.078 +- 0.030, both consistent with zero.