Search for the decayD0→γγand measurement of the branching fraction forD0→π0π0

Abstract

We search for the rare decay of the D 0 meson to two photons, D 0 → γγ, and present a measurement of the branching fraction for a D 0 meson decaying to two neutral pions, B(D 0 → π 0 π 0 ). The data sample analyzed corresponds to an integrated luminosity of 470.5 fb −1 collected by the BABAR detector at the PEP-II asymmetric-energy e + e − collider at SLAC. We place an upper limit on the branching fraction, B(D 0 → γγ) < 2.2 × 10 −6 , at 90% confidence level. This limit improves on the existing limit by an order of magnitude. We also find B(D 0 → π 0 π 0 ) = (8.4 ± 0.1 ± 0.4 ± 0.3) × 10 −4 .PACS numbers: 12.15. Mm, 13.25.Ft, 14.40.Lb, 14.70.Bh I. I. INTRODUCTIONIn the Standard Model (SM) flavor-changing neutral currents (FCNC) are forbidden at tree level [1]. These decays are allowed at higher order and have been measured in the K and B meson systems [2]. In the charm sector, however, the small mass difference between downtype quarks of the first two families translates to a large suppression at the loop level from the GIM mechanism [1]. To date, measurements of radiative decays of charm mesons are consistent with results of theoretical calculations that include both short-distance and long-distance * Now at Temple University, Philadelphia, Pennsylvania 19122, USA † Also with Università di Perugia, Dipartimento di Fisica, Perugia, Italy ‡ Now at University of South Alabama, Mobile, Alabama 36688, USA § Also with Università di Sassari, Sassari, Italy contributions and predict decay rates several orders of magnitude below the sensitivity of current experiments [3][4][5][6][7][8]. While these rates are small, it has been postulated that new physics (NP) processes can lead to significant enhancements [9].In this paper we report results of a search for the FCNC decay of the neutral D meson into two photons. The only previous study was conducted by the CLEO collaboration using 13.8 fb A separate calculation using heavy quark effective theory combined with chiral perturbation theory (HQχPT) [12] reveals a similar dominance of long-distance over shortdistance (SD) effects, with the SD branching ratio esti-4 mated to be [11]In the context of the Minimal Supersymmetric Standard Model, gluino exchange can enhance the SM rate by up to a factor of 200 [9]. The large number of charm decays in the BABAR dataset provide the opportunity to study this enhancement. A 200-fold increased rate would result in approximately 1370 events in the BABAR dataset (470.5 fb −1 ) with only six events predicted from the theoretical SM branching fraction (3.5 × 10 −8 , as determined in the VMD calculation.) A summary of the relevant branching fractions is shown in Table I.In this paper we also report a new measurement of the branching fraction for the decay D 0 → π 0 π 0 , which is the dominant background in the D 0 → γγ analysis. II. II. THE BABAR DETECTOR AND DATASETThis analysis is based on a data sample corresponding to an integrated luminosity of 470.5 fb −1 collected by the BABAR detector at the SLAC PEP-II e + e − asymmetricenergy collid...

Search for $D^0\toγγ$ and improved measurement of the branching fraction for $D^0 \to π^0π^0$

“…Using 2.92 fb −1 of e + e − annihilation data collected at √ s = 3.773 GeV with the BESIII detector, we have searched for the FCNC decay D 0 → γγ and observe no significant signal. We set an upper limit B(D 0 → γγ) < 3.8 × 10 −6 at the 90% CL, which is consistent with the upper limit previously set by the BABAR Collaboration [7] and with the SM prediction. Ours is the first experimental study of this decay using data at open-charm threshold.…”

“…The previous experimental studies of D 0 → γγ were performed by the CLEO and BABAR experiments using data samples collected at the Υ(4S) peak [7,8]. With an integrated luminosity of 470.5 fb −1 , corresponding to more than 250 million D 0 mesons based on the quoted number of reconstructed D 0 → π 0 π 0 candidates, its efficiency, and the measured B(D 0 → π 0 π 0 ) in Ref.…”

“…With an integrated luminosity of 470.5 fb −1 , corresponding to more than 250 million D 0 mesons based on the quoted number of reconstructed D 0 → π 0 π 0 candidates, its efficiency, and the measured B(D 0 → π 0 π 0 ) in Ref. [7], BABAR set an upper limit at 90% confidence level (CL) on the D 0 → γγ branching fraction of 2.2 × 10 −6 which is the most stringent limit to date.…”

Heavy QCD Axion at Belle II: Displaced and Prompt Signals

“…The background estimate must take into account the m γγ resolution of the signal peak. For prompt axion decays, the relevant resolution ranges from σ mγγ ≈ 11 MeV for m γγ ≈ 540 MeV [61] to σ mγγ ≈ 35 MeV for m γγ ≈ 1860 MeV [62].…”

Search for CPV in D0 decays to radiative and hadronic decays at Belle

“…The best upper limit to date was set by BaBar at B(D 0 → γγ) < 2.2 × 10 −6 (90% C.L.) [9]. The decay D 0 → γγ represents a good probe for NP, as the SM prediction for the branching fraction, which is of the order of 10 −8 , can be enhanced by several orders of magnitude by NP contributions.…”