Development of a robust continuum fighting technique for Belle II - PowerPoint PPT Presentation

Development of a robust continuum fighting technique for Belle II Gagan Mohanty TIFR, Mumbai DHEP Seminar February Belle II General Meeting 2, 2012 @ Bad Aibling, Munich July 22-26,2012

What is the fuss about?  Belle II aims to precisely examine the whole pattern of CP violation and to search for several SM-suppressed decays in the B meson system in its pursuit for the holy-grail of new physics beyond the SM uds:cc:bb = 2.1:1.3:1.1  Most dominant background is from e + e − → qq (q = u,d,s,c) continuum events – roughly ¼ times BF(B→X) at the Υ(4S) resonance 2

What is the current baseline?  We mostly make use of the difference in event topology to distinguish spherical BB events from the jet-like continuum background  Typical event-shape variables used are: 3

Add B-decay variables to the list  Further discrimination is provided by the fact that in one side we have a B decay while prompt, continuum events on the other side  Two variables of interest:  Distance along the z -axis between the reconstructed B vertex and that of rest-of-the-event “recoil B”  Product of flavor tagging output and quality factor (q.r)  Colour legends are swapped between two plots (in the left plot signal is blue and continuum is red while in the right plot it is other way around) 4

Let’s look at q.r in some detail  The philosophy behind flavor tagging is to distinguish between B 0 vs. B 0 ; not really optimized to separate continuum from B-decay events 5

What do we plan to do?  The plan is to go behind each and every variable we think can provide useful discrimination against the continuum background  Some variables we have thought about are  The number of kaons (they are expected to be produced in “pairs” for  The number of kaons (they are expected to be produced in “pairs” for the continuum background, especially for e + e − → ss events)  Energy spectra of leptons (in BB events they mostly originate from a semi-leptonic decay and are expected to have higher momentum than that in continuum)  Momentum of the daughter pions (they are relatively softer if their mother is a D * meson inside the charm continuum) 6

One typical variable  Plots below show energy distributions for leptons (electrons/muons in the top/bottom row) from e + e − → uu, dd, ss (left), cc (middle) and a typical BB event (right) 7

Closing remarks  We have just started this project few months back, actually due credit to Bruce Yabsley as the original proposer  Need to put some more effort V.Gaur and another student would spend some time with this project  Hope to have some more news by the November B2GM Thanks for your kind attention 8