B Physics at D

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B Physics at DØ
Recently approvedresults
Tamsin Edwards
b quark - the second heaviest quark
B hadrons - particles containing a b quark
Observation of X(3872) ? J/? pp-
Events where X(3872) is central

• meson - a particle made of a quark and
  anti-quark
• baryon - a particle made of three quarks
• hadron - a group name for mesons baryons

Can we observe this new particle discovered by
Belle in 2003?
Compare to the ?(2S)

• the mass is close

• it can decay to the same set of particles J/? p
  p -

X(3872) unknown
X any set of particles
Measurement of rate of semileptonic B decays to
narrow D mesons
Measure the mass difference ?M M(J/? p p -)
- M(J/?)
- smaller experimental uncertainty than just
M(J/? p p -)
Can we isolate B hadrons decaying to orbitally
excited D mesons?
?M 0.7749 0.0031 (stat.) 0.0030 (syst.)
GeV/c2
- narrow refers to the width of the mass peak
Compare other properties of X(3872) and ?(2S)
Measure the rate for B hadrons to decay to these
particles
- similar, within uncertainties
Measurement of Lifetime Ratio for Neutral and
Charged B mesons

• pseudorapidity (?) - a measure of the angle
  of the particle direction with respect to the
  beam
• lifetime - the length of time before a particle
  decays (follows an exponential distribution)

? D- p
Rate 0.280 0.021 (stat.) 0.088 (syst.)
Which generally lives longer charged or neutral
B mesons?
Much recent progress in theoretical predictions
for pattern of lifetimes in B hadrons
charged B, B-
A cascade of decays
Example of the way large samples of specific B
hadronsamples are found for use in mixing and
lifetime studies
Measure ratio of lifetimes of two types of B
mesons
peaks are very close measure the two together
New analysis method with potential for reduced
experimental uncertainty
work backwards from final particles
charged B mesons generally live longer
Theory predicts this to be around 1.03 -1.07
Sensitivity analysis of the rare decay Bs0 ?µµ-
What is the lowest rate of this rare decay that
we can exclude (or observe if it is there)?
Decay rate is sensitive to theoretical
predictions beyond the Standard Model
Expected upper limit (95 confidence level)
blind analysis box covering signal region has
not yet been removed
Determine if either oscillated before decay using
charge of the two muons

• same sign one B hadron oscillated
• opposite sign both or neither oscillated

For N(Bs)

• measure number of B

Oscillation frequency
?m 0.506 0.055 (stat.) 0.049 (syst.) ps-1
- predict number of Bs using ratio of Bs to
B production
very slow lifetime of Bd is about 1.5 ps
Gearing up for studying the faster oscillating Bs
system
- current limits say that Bs oscillates at least
30 times faster than B0 (and Bs lifetime is
similar to B0)