Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 47
Filtrar
Más filtros

Bases de datos
País/Región como asunto
Tipo del documento
Intervalo de año de publicación
1.
Phys Rev Lett ; 130(3): 031901, 2023 Jan 20.
Artículo en Inglés | MEDLINE | ID: mdl-36763394

RESUMEN

We present the study of B[over ¯]^{0}→Σ_{c}(2455)^{0,++}π^{±}p[over ¯] decays based on 772×10^{6} BB[over ¯] events collected with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. The Σ_{c}(2455)^{0,++} candidates are reconstructed via their decay to Λ_{c}^{+}π^{∓} and Λ_{c}^{+} decays to pK^{-}π^{+}, pK_{S}^{0}, and Λπ^{+} final states. The corresponding branching fractions are measured to be B(B[over ¯]^{0}→Σ_{c}(2455)^{0}π^{+}p[over ¯])=(1.09±0.06±0.07)×10^{-4} and B(B[over ¯]^{0}→Σ_{c}(2455)^{++}π^{-}p[over ¯])=(1.84±0.11±0.12)×10^{-4}, which are consistent with the world average values with improved precision. A new structure is found in the M_{Σ_{c}(2455)^{0,++}π^{±}} spectrum with a significance of 4.2σ including systematic uncertainty. The structure is possibly an excited Λ_{c}^{+} and is tentatively named Λ_{c}(2910)^{+}. Its mass and width are measured to be (2913.8±5.6±3.8) MeV/c^{2} and (51.8±20.0±18.8) MeV, respectively. The products of branching fractions for the Λ_{c}(2910)^{+} are measured to be B(B[over ¯]^{0}→Λ_{c}(2910)^{+}p[over ¯])×B(Λ_{c}(2910)^{+}→Σ_{c}(2455)^{0}π^{+})=(9.5±3.6±1.6)×10^{-6} and B(B[over ¯]^{0}→Λ_{c}(2910)^{+}p[over ¯])×B(Λ_{c}(2910)^{+}→Σ_{c}(2455)^{++}π^{-})=(1.24±0.35±0.10)×10^{-5}. Here, the first and second uncertainties are statistical and systematic, respectively.

2.
Phys Rev Lett ; 131(2): 021801, 2023 Jul 14.
Artículo en Inglés | MEDLINE | ID: mdl-37505960

RESUMEN

We report the first measurement of the Michel parameter ξ^{'} in the τ^{-}→µ^{-}ν[over ¯]_{µ}ν_{τ} decay with a new method proposed just recently. The measurement is based on the reconstruction of the τ^{-}→µ^{-}ν[over ¯]_{µ}ν_{τ} events with subsequent muon decay in flight in the Belle central drift chamber. The analyzed data sample of 988 fb^{-1} collected by the Belle detector corresponds to approximately 912×10^{6} τ^{+}τ^{-} pairs. We measure ξ^{'}=0.22±0.94(stat)±0.42(syst), which is in agreement with the standard model prediction of ξ^{'}=1. Statistical uncertainty dominates in this study, being a limiting factor, while systematic uncertainty is well under control. Our analysis proved the practicability of this promising method and its prospects for further precise measurement in future experiments.

3.
Phys Rev Lett ; 130(15): 151903, 2023 Apr 14.
Artículo en Inglés | MEDLINE | ID: mdl-37115880

RESUMEN

Using the data sample of 980 fb^{-1} collected with the Belle detector operating at the KEKB asymmetric-energy e^{+}e^{-} collider, we present the results of an investigation of the Λπ^{+} and Λπ^{-} invariant mass distributions looking for substructure in the decay Λ_{c}^{+}→Λπ^{+}π^{+}π^{-}. We find a significant signal in each mass distribution. When interpreted as resonances, we find for the Λπ^{+} (Λπ^{-}) combination a mass of 1434.3±0.6(stat)±0.9(syst) MeV/c^{2} [1438.5±0.9(stat)±2.5(syst) MeV/c^{2}], an intrinsic width of 11.5±2.8(stat)±5.3(syst) MeV/c^{2} [33.0±7.5(stat)±23.6(syst) MeV/c^{2}] with a significance of 7.5σ (6.2σ). As these two signals are very close to the K[over ¯]N threshold, we also investigate the possibility of a K[over ¯]N cusp, and find that we cannot discriminate between these two interpretations due to the limited size of the data sample.

4.
Phys Rev Lett ; 130(18): 181804, 2023 May 05.
Artículo en Inglés | MEDLINE | ID: mdl-37204904

RESUMEN

We study B^{+}→π^{+}π^{0}π^{0} using 711 fb^{-1} of data collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. We measure an inclusive branching fraction of (19.0±1.5±1.4)×10^{-6} and an inclusive CP asymmetry of (9.2±6.8±0.7)%, where the first uncertainties are statistical and the second are systematic, and a B^{+}→ρ(770)^{+}π^{0} branching fraction of (11.2±1.1±0.9_{-1.6}^{+0.8})×10^{-6}, where the third uncertainty is due to possible interference with B^{+}→ρ(1450)^{+}π^{0}. We present the first observation of a structure around 1 GeV/c^{2} in the π^{0}π^{0} mass spectrum, with a significance of 6.4σ, and measure a branching fraction to be (6.9±0.9±0.6)×10^{-6}. We also report a measurement of local CP asymmetry in this structure.

5.
Phys Rev Lett ; 131(21): 211801, 2023 Nov 24.
Artículo en Inglés | MEDLINE | ID: mdl-38072600

RESUMEN

The first simultaneous determination of the absolute value of the Cabibbo-Kobayashi-Maskawa matrix element V_{ub} using inclusive and exclusive decays is performed with the full Belle data set at the ϒ(4S) resonance, corresponding to an integrated luminosity of 711 fb^{-1}. We analyze collision events in which one B meson is fully reconstructed in hadronic modes. This allows for the reconstruction of the hadronic X_{u} system of the semileptonic b→uℓν[over ¯]_{ℓ} decay. We separate exclusive B→πℓν[over ¯]_{ℓ} decays from other inclusive B→X_{u}ℓν[over ¯]_{ℓ} and backgrounds with a two-dimensional fit that utilizes the number of charged pions in the X_{u} system and the four-momentum transfer q^{2} between the B and X_{u} systems. Combining our measurement with information from lattice QCD and QCD calculations of the inclusive partial rate as well as external experimental information on the shape of the B→πℓν[over ¯]_{ℓ} form factor, we determine |V_{ub}^{excl}|=(3.78±0.23±0.16±0.14)×10^{-3} and |V_{ub}^{incl}|=(3.88±0.20±0.31±0.09)×10^{-3}, respectively, with the uncertainties being the statistical error, systematic errors, and theory errors. The ratio of |V_{ub}^{excl}|/|V_{ub}^{incl}|=0.97±0.12 is compatible with unity.

6.
Phys Rev Lett ; 128(14): 142005, 2022 Apr 08.
Artículo en Inglés | MEDLINE | ID: mdl-35476485

RESUMEN

The measurement of two-particle angular correlation functions in high-multiplicity e^{+}e^{-} collisions at sqrt[s]=10.52 GeV is reported. In this study, the 89.5 fb^{-1} of hadronic e^{+}e^{-} annihilation data collected by the Belle detector at KEKB are used. Two-particle angular correlation functions are measured in the full relative azimuthal angle (Δϕ) and three units of pseudorapidity (Δη), defined by either the electron beam axis or the event-shape thrust axis, and are studied as a function of charged-particle multiplicity. The measurement in the thrust axis analysis, with mostly outgoing quark pairs determining the reference axis, is sensitive to the region of additional soft gluon emissions. No significant anisotropic collective behavior is observed with either coordinate analyses. Near-side jet correlations appear to be absent in the thrust axis analysis. The measurements are compared to predictions from various event generators and are expected to provide new constraints to the phenomenological models in the low-energy regime.

7.
Phys Rev Lett ; 127(26): 261801, 2021 Dec 24.
Artículo en Inglés | MEDLINE | ID: mdl-35029480

RESUMEN

The first measurements of differential branching fractions of inclusive semileptonic B→X_{u}ℓ^{+}ν_{ℓ} decays are performed using the full Belle data set of 711 fb^{-1} of integrated luminosity at the ϒ(4S) resonance and for ℓ=e, µ. With the availability of these measurements, new avenues for future shape-function model-independent determinations of the Cabibbo-Kobayashi-Maskawa matrix element |V_{ub}| can be pursued to gain new insights in the existing tension with respect to exclusive determinations. The differential branching fractions are reported as a function of the lepton energy, the four-momentum-transfer squared, light-cone momenta, the hadronic mass, and the hadronic mass squared. They are obtained by subtracting the backgrounds from semileptonic B→X_{c}ℓ^{+}ν_{ℓ} decays and other processes, and corrected for resolution and acceptance effects.

8.
Phys Rev Lett ; 122(1): 011801, 2019 Jan 11.
Artículo en Inglés | MEDLINE | ID: mdl-31012694

RESUMEN

We report on the first Belle search for a light CP-odd Higgs boson, A^{0}, that decays into low mass dark matter, χ, in final states with a single photon and missing energy. We search for events produced via the dipion transition ϒ(2S)→ϒ(1S)π^{+}π^{-}, followed by the on-shell process ϒ(1S)→γA^{0} with A^{0}→χχ, or by the off-shell process ϒ(1S)→γχχ. Utilizing a data sample of 157.3×10^{6} ϒ(2S) decays, we find no evidence for a signal. We set limits on the branching fractions of such processes in the mass ranges M_{A^{0}}<8.97 GeV/c^{2} and M_{χ}<4.44 GeV/c^{2}. We then use the limits on the off-shell process to set competitive limits on WIMP-nucleon scattering in the WIMP mass range below 5 GeV/c^{2}.

9.
Phys Rev Lett ; 122(4): 042001, 2019 Feb 01.
Artículo en Inglés | MEDLINE | ID: mdl-30768311

RESUMEN

We report the first observation of the spontaneous polarization of Λ and Λ[over ¯] hyperons transverse to the production plane in e^{+}e^{-} annihilation, which is attributed to the effect arising from a polarizing fragmentation function. For inclusive Λ/Λ[over ¯] production, we also report results with subtracted feed-down contributions from Σ^{0} and charm. This measurement uses a dataset of 800.4 fb^{-1} collected by the Belle experiment at or near a center-of-mass energy of 10.58 GeV. We observe a significant polarization that rises with the fractional energy carried by the Λ/Λ[over ¯] hyperon.

10.
Phys Rev Lett ; 121(23): 232001, 2018 Dec 07.
Artículo en Inglés | MEDLINE | ID: mdl-30576207

RESUMEN

We report the observation of ϒ(2S)→γη_{b}(1S) decay based on an analysis of the inclusive photon spectrum of 24.7 fb^{-1} of e^{+}e^{-} collisions at the ϒ(2S) center-of-mass energy collected with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. We measure a branching fraction of B[ϒ(2S)→γη_{b}(1S)]=(6.1_{-0.7-0.6}^{+0.6+0.9})×10^{-4} and derive an η_{b}(1S) mass of 9394.8_{-3.1-2.7}^{+2.7+4.5} MeV/c^{2}, where the uncertainties are statistical and systematic, respectively. The significance of our measurement is greater than 7 standard deviations, constituting the first observation of this decay mode.

11.
Phys Rev Lett ; 118(21): 211801, 2017 May 26.
Artículo en Inglés | MEDLINE | ID: mdl-28598663

RESUMEN

We report the first measurement of the τ lepton polarization P_{τ}(D^{*}) in the decay B[over ¯]→D^{*}τ^{-}ν[over ¯]_{τ} as well as a new measurement of the ratio of the branching fractions R(D^{*})=B(B[over ¯]→D^{*}τ^{-}ν[over ¯]_{τ})/B(B[over ¯]→D^{*}ℓ^{-}ν[over ¯]_{ℓ}), where ℓ^{-} denotes an electron or a muon, and the τ is reconstructed in the modes τ^{-}→π^{-}ν_{τ} and τ^{-}→ρ^{-}ν_{τ}. We use the full data sample of 772×10^{6} BB[over ¯] pairs recorded with the Belle detector at the KEKB electron-positron collider. Our results, P_{τ}(D^{*})=-0.38±0.51(stat)_{-0.16}^{+0.21}(syst) and R(D^{*})=0.270±0.035(stat)_{-0.025}^{+0.028}(syst), are consistent with the theoretical predictions of the standard model.

12.
Phys Rev Lett ; 118(11): 111801, 2017 Mar 17.
Artículo en Inglés | MEDLINE | ID: mdl-28368653

RESUMEN

We present a measurement of angular observables and a test of lepton flavor universality in the B→K^{*}ℓ^{+}ℓ^{-} decay, where ℓ is either e or µ. The analysis is performed on a data sample corresponding to an integrated luminosity of 711 fb^{-1} containing 772×10^{6} BB[over ¯] pairs, collected at the ϒ(4S) resonance with the Belle detector at the asymmetric-energy e^{+}e^{-} collider KEKB. The result is consistent with standard model (SM) expectations, where the largest discrepancy from a SM prediction is observed in the muon modes with a local significance of 2.6σ.

13.
Phys Rev Lett ; 115(22): 221803, 2015 Nov 27.
Artículo en Inglés | MEDLINE | ID: mdl-26650291

RESUMEN

We report the first observation of the decays B^{0}→pΛ[over ¯]D^{(*)-}. The data sample of 711 fb^{-1} used in this analysis corresponds to 772×10^{6} BB[over ¯] pairs, collected at the ϒ(4S) resonance by the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. We observe 19.8σ and 10.8σ excesses of events for the two decay modes and measure the branching fractions of B^{0}→pΛ[over ¯]D^{-} and B^{0}→pΛ[over ¯]D^{*-} to be (25.1±2.6±3.5)×10^{-6} and (33.6±6.3±4.4)×10^{-6}, respectively, where the first uncertainties are statistical and the second are systematic. These results are not compatible with the predictions based on the generalized factorization approach. In addition, a threshold enhancement in the dibaryon (pΛ[over ¯]) system is observed, consistent with that observed in similar B decays.

14.
Phys Rev Lett ; 114(15): 151601, 2015 Apr 17.
Artículo en Inglés | MEDLINE | ID: mdl-25933306

RESUMEN

We report the measurement of the direct CP asymmetry in the radiative B¯â†’X(s+dγ) decay using a data sample of (772 ± 11)×10(6) BB[over ¯] pairs collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. The CP asymmetry is measured as a function of the photon energy threshold. For Eγ*≥2.1 GeV, where Eγ* is the photon energy in the center-of-mass frame, we obtain A(CP)(B¯â†’X(s+dγ))=(2.2±3.9±0.9)%, consistent with the standard model prediction.

15.
Phys Rev Lett ; 110(13): 131801, 2013 Mar 29.
Artículo en Inglés | MEDLINE | ID: mdl-23581309

RESUMEN

We measure the branching fraction of B- → τ- ν(τ) using the full Υ(4S) data sample containing 772×10(6) BB pairs collected with the Belle detector at the KEKB asymmetric-energy e+ e- collider. Events with BB pairs are tagged by reconstructing one of the B mesons decaying into hadronic final states, and B- → τ- ν(τ) candidates are detected in the recoil. We find evidence for B- → τ- ν(τ) with a significance of 3.0 standard deviations including systematic errors and measure a branching fraction B(B- → τ- ν(τ))=[0.72(-0.25)(+0.27)(stat)±0.11(syst)]×10(-4).


Asunto(s)
Partículas Elementales , Física Nuclear/métodos , Teoría Cuántica
16.
Phys Rev Lett ; 111(11): 112001, 2013 Sep 13.
Artículo en Inglés | MEDLINE | ID: mdl-24074074

RESUMEN

We search for bottomonium states in Υ(2S) → (bb)γ decays with an integrated luminosity of 24.7 fb(-1) recorded at the Υ(2S) resonance with the Belle detector at KEK, containing (157.8±3.6)×10(6) Υ(2S) events. The (bb) system is reconstructed in 26 exclusive hadronic final states composed of charged pions, kaons, protons, and K(S)(0) mesons. We find no evidence for the state recently observed around 9975 MeV (X(bb)) in an analysis based on a data sample of 9.3×10(6) Υ(2S) events collected with the CLEO III detector. We set a 90% confidence level upper limit on the branching fraction B[Υ(2S) → X(bb)γ] × ∑(i)B[X(bb) → h(i)] < 4.9×10(-6), summed over the exclusive hadronic final states employed in our analysis. This result is an order of magnitude smaller than the measurement reported with CLEO data. We also set an upper limit for the ηb(1S) state of B[Υ(2S) → ηb(1S)γ] × ∑(i)B[ηb(1S) → h(i)] < 3.7×10(-6).


Asunto(s)
Interacciones de Partículas Elementales , Modelos Teóricos , Física Nuclear/métodos , Método de Montecarlo
17.
Transplant Cell Ther ; 29(1): 27-33, 2023 01.
Artículo en Inglés | MEDLINE | ID: mdl-36241147

RESUMEN

Although it has been shown that the production of functional chimeric antigen receptor T cells is feasible in patients with B-cell malignancies, it is currently unclear whether sufficient amounts of functional autologous CAR T cells can be generated from patients with autoimmune diseases. Intrinsic T-cell abnormalities and T-cell-targeted immune suppression in patients with autoimmunity may hamper the retrieval of sufficient T cells and their transduction and expansion into CAR T cells. Patients with active systemic lupus erythematosus (SLE) underwent leukapheresis after tapering glucocorticoids and stopping T-cell-suppressive drugs. This material was used as source for manufacturing anti-CD19 CAR T-cell products (CAR) in clinical scale. Cells were transduced with a lentiviral anti-CD19 CAR vector and expanded under good manufacturing practice (GMP) conditions using a closed, semi-automatic system. Functionality of these CAR T cells derived from autoimmune patient cells was tested in vitro. Six SLE patients were analyzed. Leukapheresis could be successfully performed in all patients yielding sufficient T-cell numbers for clinical scale CAR T-cell production. In addition, CAR T cells showed high expansion rates and viability, leading to CAR T cells in sufficient doses and quality for clinical use. CAR T cells from all patients showed specific cytotoxicity against CD19+ cell lines in vitro. GMP grade generation of CD19 CAR T-cell products suitable for clinical use is feasible in patients with autoimmune disease.


Asunto(s)
Lupus Eritematoso Sistémico , Receptores Quiméricos de Antígenos , Humanos , Linfocitos T , Línea Celular , Linfocitos B , Lupus Eritematoso Sistémico/terapia
18.
J Neuroimmunol ; 61(1): 97-104, 1995 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-7560019

RESUMEN

The effect of an endogenous opiate, beta-endorphin, on the replication of HIV was investigated in brain perivascular microglia. Beta-endorphin enhanced the synthesis of p-24 antigen and transactivation of HIV promoter. Dialysed culture supernatants of endorphin-treated microglia re-activated latent HIV infection. These culture supernatants showed elevated levels of interleukin-1 beta, IL-6 and tumor necrosis factor alpha. Sub-optimal concentration of beta-endorphin potentiated GP-120-induced synthesis of these cytokines. Nalaxone reversed beta-endorphin-induced, but not GP-120-induced, cytokine production and enhanced HIV replication. These results suggest that endogenous opiates may contribute to the progression of AIDS dementia complex.


Asunto(s)
VIH/crecimiento & desarrollo , Microglía/microbiología , Replicación Viral/efectos de los fármacos , betaendorfina/farmacología , Citocinas/biosíntesis , VIH/patogenicidad , Duplicado del Terminal Largo de VIH , Humanos , Técnicas In Vitro , Naloxona/farmacología , Antagonistas de Narcóticos/farmacología , Activación Transcripcional , Latencia del Virus
19.
Fertil Steril ; 27(9): 1009-23, 1976 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-964392

RESUMEN

Sixty gravidas 8 to 20 menstrual weeks' gestation were studied to evaluate (1) the efficacy of intramuscularly administered 15(S)-15-methyl prostaglandin F2alpha tromethamine (15(S)-Me-PGF2alpha) as an abortifacient; (2) the effectiveness of prochlorperazine and Lomotil for attenuation of vomiting and diarrhea; and (3) the practicability of augmenting this prostaglandin dose schedule with intracervical laminaria tents. Group I subjects received 250 mug of 15(S)-Me-PGF2alpha intramuscularly every 2 hours for the initial 24 hours and 500 mug for the next 24-hour period. Group II received the same dose schedule of prostaglandin and prearranged doses of prochlorperazine and Lomotil. Group III received the same dose schedule of prostaglandin after intracervical laminaria tents had been inserted, and prochlorperazine and Lomotil were administered by the prearranged dose schedule. It appears that (1) the 15(S)-Me-PGF2alpha was effective in inducing abortion; (2) a significant decrease in body temperature occurred; (3) the abortifacient effectiveness of this prostaglandin dose schedule was not altered by the regimen of prochlorperazine and Lomotil; (4) only diarrhea was significantly attenuated with the regimen of prochlorperazine and Lomotil; and (5) laminaria augmentation was not useful.


Asunto(s)
Aborto Inducido/métodos , Prostaglandinas F Sintéticas , Adolescente , Adulto , Presión Sanguínea/efectos de los fármacos , Temperatura Corporal/efectos de los fármacos , Cuello del Útero , Diarrea/inducido químicamente , Difenoxilato/uso terapéutico , Evaluación de Medicamentos , Femenino , Humanos , Inyecciones Intramusculares , Embarazo , Proclorperazina/uso terapéutico , Prostaglandinas F/administración & dosificación , Prostaglandinas F/efectos adversos , Prostaglandinas F/farmacología , Trometamina/administración & dosificación , Trometamina/efectos adversos , Trometamina/farmacología , Contracción Uterina/efectos de los fármacos , Vómitos/inducido químicamente
20.
Fertil Steril ; 26(4): 369-79, 1975 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-1116632

RESUMEN

PIP: Due to the need for an effective and safe parental administration technique, 2 intramuscular dose schedules of prostaglandin 15(S)ME2 were evaluated for practicability. 30 physically healthy women, ranging in age from 18-42 years, who were 8-22 menstrual weeks' gestation, had abortions at the Clinical Research Unit of the University of North Carolina Memorial Hospital. The women were treated according to 1 or 2 intramuscular prostaglandin (PG) 15(S)ME2 dose schdules. The 20 subjects in group 1 received 5 mc of PG 15(S)ME2 initially and at 4-hour intervals until abortion of the fetus or for a maximum of 48 hours. The 10 subjects in group 2 received 10 mc of PG 15(S)ME2 initially and at 8-hour intervals until abortion of the fetus or for a maximum of 48 hours. Subjects were monitored for signs of PG 15(S)ME2 toxicity and uterine contractions. 6 subjects from each group were continuously monitored in duplicate for intra-amniotic pressure by the open-end catheter technique. 4 criteria of abortifacient efficacy were used to compare the 2 dose schedules: the proportion of subjects aborting within the initial 24 hours, the proportion of subjects aborting within 48 hours, the mean abortion time of those subjects who aborted, and the cumulative abortion rate. Within 24 hours of the initial injection, 13 of the 20 group 1 subjects and only 2 of the 10 group 2 subjects aborted. Within 48 hours, 17 of the group 1 and 5 of the group 2 subjects aborted. The differences in the cumulative abortion rates between the 2 groups were significant at 24 and at 48 hours. Since constant monitoring of intrauterine pressure showed no significant differences in the mean frequency, intensity, tonus, or total uterine activity between the 2 groups or between subjects who aborted or failed to abort, it seems doubtful that constant intra-amniotic pressure monitoring will be useful in further defining the most practicable dose schedule.^ieng


Asunto(s)
Abortivos/administración & dosificación , Aborto Inducido/métodos , Prostaglandinas/administración & dosificación , Aborto Inducido/efectos adversos , Adolescente , Adulto , Amnios , Endometritis/etiología , Ésteres , Femenino , Fiebre/etiología , Humanos , Inyecciones Intramusculares , Metilación , Paridad , Embarazo , Presión , Prostaglandinas/efectos adversos , Prostaglandinas/toxicidad , Factores de Tiempo , Cateterismo Urinario , Urticaria/inducido químicamente
SELECCIÓN DE REFERENCIAS
DETALLE DE LA BÚSQUEDA