|M.Sc Student||Kadosh Avihay|
|Subject||Two-Photon Exclusive Decays of d0 Mesons|
|Department||Department of Physics||Supervisors||Professor Emeritus Michael Gronau|
|Professor Emeritus Paul Singer (Deceased)|
The investigation of flavor changing weak radiative transitions of charmed
mesons has emerged
during the past few years as a rather fruitful field of research both
theoretically. There is already a measurement by CLEO of the exclusive decay
D0 → φγ,
BR(D0 → φγ) = (2.5+0.7-0.6)*10-5, and
only an upper bound on the D0 → K* γ mode,
BR(D0 → K* γ) < 7.5 *10-5.
These measurements confirm within the existing accuracy the Standard model(SM). In particular, taking into account that the short distance(SD) contributions for such decays are exceedingly small comparing to the long distance(LD), due to strong GIM cancellation and small CKM matrix elements and using a hybrid model which combines HQET and chiral lagrangians the authors of  find the SM theoretical prediction to be BR(D0 → φγ) = 0.4 − 1.9*10-5 The two photon decays of D mesons are also of considerable interest since their measurement will probably be possible in a few years most likely in CLEO.
In this work we present a model for the first calculation of the exclusive decays of the the D meson into one pseudoscalar(P) and two photons based on the model described in  and focusing on the modes D0 → ηγγ D0 → η’γγ and D0 → ¯K 0γγ.
The calculation includes only the LD contributions since in these decays the SD contributions are suppressed as well, due to the same reasons mentioned above and as will be further explained in the body of the work. However, since the uncertainty in the results was significantly reduced(also for the predictions of ), due to new experimental data which helped us to determine with better accuracy some parameters in the effective lagrangians used in the calculation, large deviations of the measured branching fractions from our predictions, which are on the O(10−7) range, might offer some opportunities to look for new physics. In particular to explain an enhancement in the SD process of relevance c → uγγ.