Wednesday, 7 May 2014

Pheno 2014 Liveblog: Day Two Session 4

The last set of parallel talks.  I'm in B Physics 2 and BSM, for reasons that are probably apparent to anyone who knows me.

4:30 pm: Mass and Lifetime Measurements of Heavy Flavour Hadrons, Adrian Pritchard

An LHCb experimental talk.  A number of b-meson measurements that resolve a CDF-D0 discrepancy.

Measurements of charm mesons, point to X(3872) being a tetraquark/molecule.

B oscillations;

There's a lot of results here and not much in the way of structure, that I can see.

4:45 pm: Physics with b-Baryons at LHCb, James McCarthy

b-Baryons relatively unexplored in heavy flavour physics.  Possess intrinsic spin, which also makes them interesting.  Observation of decays and measurements of branching fractions.  Also asymmetries, with the usual nice property that some errors cancel.

5:00 pm: Isospin Violation in the Yield of S-Wave Heavy Meson Pairs Near Threshold, Xin Li

Non-perturbative result to all order in couplings and mass splitting.  Also reveals correlations between different isospin channels.  Considering Z mesons, objects near b thresholds that might be tetraquarks.

Looking at ratio of production of charged vs neutral meson pairs.  Equals 1 if isospin is exact.  Leading order terms previously known.  However, it depends on momentum: of the charged or the neutral mesons?

Use small-radius QCD approximation for meson wavefunctions.  Final result then depends on this extra parameter, but only weakly.  Result in I=1 channel depends on I=0 parameters.

5:15 pm: Electroweak Penguin Decays to Leptons at LHC, Peter Griffith

Another LHCb experimental talk.  Which is odd to see it come now, so the previous theory talk was between two experimental ones!

Looking at FCNC decays.  Particular focus on B to Kμμ decays.  These results, of course, agree with the SM and are tight constraints on NP.  Some anomalies for K*, BRs slightly below the SM predictions.

5:30 pm: A Swarm of Bs, Jared Evans

A gap in existing LHC coverage: easy to cover, easy for models to live there.

All-hadronic final states, with no MET or leptons and many b-jets.  Easy to construct models with ~6 b jets, e.g. Stealth SUSY, RPV SUSY or b'.

Example model: MFV RPV SUSY, signal bbbbbbjj.  No current limits; a 2-b tag search nearly sets limits.  So 3 tags would likely set limits; 5 certainly would.  But it hasn't been done yet.  Simulation shows ~ 5 events; signals in the 10s for stop mass less than 700 GeV.

This is good for exclusion, but definite uncertainty on backgrounds.  So backgrounds set conservatively by assuming no background; still very strong.

For discovery, use jet ensemble method (CMS).  Use all possible combinations of jets and compute jet mass and summed pt; for resonances, latter is large.  Has been used in prior studies, so does work.

5:45 pm: Difficult BSM Signatures at the LHC, Matthew Buckley

Super-razor: look for electroweak production.

Most searches look for some mass-difference variable to distinguish from background.  If this is small/close to mW, holes open up in parameter space.

Improvement on razor method from CMS.  Attempt to reconstruct general SUSY-like event.  Impossible event-by-event, what about statistically?  Idea is to reconstruct parent frames by "inspired guesses".  Key assumption: visible and invisible invariant masses roughly equal.

This is fine, part of so far, except when spectrum is squeezed.  Assumption breaks down.  This is clued in when the parent rest frame has visible particles not very aligned.

Searches improved, but problems with triggering.  Trigger on super-razor variables?

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