A Study of B→c$\bar{c}$γK in the BaBar Experiment

Abstract

The BABAR Collaboration is a high energy physics experiment located at the Stanford Linear Accelerator Center. The primary goal of the experiment is to study charge and parity violation in the B-meson sector, however the copious production of B mesons decaying to other final states allows for a wide-ranging physics program. In particular, one can access the charmonium system via colour-suppressed b → c decays of the type B → ccK.This thesis presents a study of B → ccγK decays where cc includes J/ψ and ψ(2S), and K includes K ± , K 0 S and K * (892). The particular emphasis is on a search for the radiative decays X(3872) → J/ψ γ and X(3872) → ψ(2S)γ. The X(3872) state is a recently-discovered resonance of undetermined quark composition, speculatively a conventional charmonium state or exotic four-quark di-meson molecule. This research is also sensitive to the well-known radiative charmonium decays B → χ c1,2 K, which are used as verification for the analysis technique.This dissertation sets the best B → χ c1 K branching fraction measurements to date, and sees the first evidence for factorization-suppressed B 0 → χ c2 K * 0 decay at a level of 3.6σ. It also provides evidence for X(3872) → J/ψγ and X(3872) → ψ(2S)γ with 3.6σ and 3.3σ significance, respectively.The product of branching fractions B(B ± → X(3872)K ± ) · B(X(3872) → J/ψγ) = (2.8 ± 0.8(stat.) ± 0.2(syst.)) × 10 −6 and B(B ± → X(3872)K ± ) · B(X(3872) → ψ(2S)γ) = (9.5 ± 2.7(stat.) ± 0.9(syst.)) × 10 −6 are measured.These results improve upon previous X(3872) → J/ψ γ measurements, and represent the first evidence for X(3872) → ψ(2S)γ.

Dynamics of hadronic molecule in one-boson exchange approach and possible heavy flavor molecules

“…To identify this state with Xð3872Þ, the mixing between this D " D Ã = " DD Ã molecule and the conventional charmonium state should be further considered to be consistent with the recent experimental data on Xð3872Þ ! c ð2SÞ [27]. For the BB Ã system, the PV systems with C ¼ B ¼ 1 and C ¼ ÀB ¼ 1, near threshold molecular states may exist.…”

“…Since unexpectedly large branch ratio of Xð3872Þ ! c ð2SÞ recently was reported [27], we have to take into account the mixing between the 1 þþ D " D Ã = " DD Ã molecule and the conventional charmonium state in order to identify this state with Xð3872Þ. This is outside the range of the present work.…”

Production of theX(3872)at the Tevatron and the LHC

“…The quantum numbers of the Xð3872Þ are 1 þþ , which follows from (i) the observation of its decay into J=c , which implies that it is even under charge conjugation [10,11], (ii) analyses of the momentum distributions from its decay into J=c þ À , which imply that its spin and parity are 1 þ or 2 À [7,12], (iii) either the observation of its decays into D 0 " D 0 0 [13], which disfavors 2 À because of angularmomentum suppression, or the observation of its decay into c ð2SÞ [14], which disfavors 2 À because of multipole suppression. The most recent measurements of the mass of the Xð3872Þ in the J=c þ À decay mode [8,15,16] imply that its energy relative to the D Ã0 " D 0 threshold is…”

Quark structure of theX(3872)andχb(3P)resonances

“…The nature of the X(3872) meson, discovered by Belle in B meson decay [1] and then confirmed by CDF [2], D0 [3] and BABAR [4], is still unknown. There are two possible interpretations for this resonance: a weakly bound meson-meson molecule [5][6][7][8][9] or a charmonium state [10][11][12][13][14][15][16], both with 1 ++ quantum numbers. Indeed, recently the new results from the LHCb collaboration [17] have ruled out the 2 −+ hypothesis [18] and therefore only the 1 ++ one remains.…”

“…The second possibility is to interpret the X(3872) as a DD * meson-meson molecule with 1 ++ quantum numbers [5][6][7][8][9]. According to Refs.…”