Aart Heijboer 1 July 7, nikhef colloquium mixing at CDF Aart Heijboer University of Pennsylvania/CDF Outline for today Introduction and motivation The measurement Collecting the signal Measuring the decay time Flavour tagging Results Eat a herring Bram's Defense Down hill from there Measurement of the Bs-Bsbar Oscillation Frequency hep-ex/ submitted to PRL Aart Heijboer 2 July 7, nikhef colloquium Flavor Oscillations B s and B s mesons can transform into each other. They form a single QM system: M11=M22 (cpt) in the simplest case (CP), M and gamma are real. Then ML= M11-M12, MH=M22+M12 M H = M + M/2 M L = M - M/2 M = 2M 12 b s t W s b _ t W _ _ BsBs BsBs H not diagonal B and B are not mass eigenstates the mass eigenstates are: _ V ts The Schrodinger equation: : Aart Heijboer 3 July 7, nikhef colloquium Pmt e BBP P e BBP mix t umix t cos / / Oscillation probability as function of time life time oscillation frequency = M [ 1 ps -1 ~ 7 x eV (~1.5x m b ) ] Solving the time dependent SE b s t W s b _ t W _ _ BsBs BsBs Because of a coupling between the two states, we get: two separate mass eigenstates oscillation between B s and B s We have seen that before Aart Heijboer 4 July 7, nikhef colloquium test Energy eigenstates (normal modes) time Classical analogon By measuring the frequency, we are measuring the strength of the coupling Aart Heijboer 5 July 7, nikhef colloquium Motivation New physics is constrained by testing prediction of SM... in particular: test unitarity of the CKM matrix pretty well known not wel known and interesting To get at V td : measure m d (B d oscillations) hard to calculate (lattice QCD). uncertainty: 10% 1.21 0.05 q=s or d If we measure m s, we can form the ratio which allows for much more accurate measurement of V ts /V td (hep-lat/ ) b s t s b t BsBs BsBs V ts Aart Heijboer 6 July 7, nikhef colloquium Motivation 2005 Limit on m s was already helping to measure CKM matrix... Plot Combines many different measurements to constrain and . Check that all measurements are consistent: i.e. that CKM matrix is unitary. V td =A 3 (1- -i ) Turn the argument around: standard model prediction: Go measure if SM is right. If the answer is no..... Aart Heijboer 7 July 7, nikhef colloquium Motivation: new physics New particles can enhance the B s B s transition harnik et al. hep-ph/ supersymmetry with large mixing between squarks m s is sensitive to new physics Phys.Lett.B596: ,2004 Z' Aart Heijboer 8 July 7, nikhef colloquium =1.54 ps m d =0.5 ps -1 B s vs B d BdBd =1.41 ps m s =~20 ps -1 BsBs d =0.18 can measur e m d by measuring == 1 1+ ( m) fraction of mixed events s =1/2 O(10 -3 ) no information on m s in need to resolve oscillation need good time resolution now: Bd mixing fully resolved Bd mixing first observed by measuring d (UA1, ARGUS 1987) mt PP PP A mixumix mixumix cos asymmetry Aart Heijboer 9 July 7, nikhef colloquium Amplitude scan Experimental effects dampen the asymmetry A is known as the Amplitude: the size of the asymmetry, corrected for detector effects. A=1 means mixing A=0 means data is compatible with no mixing knowledge about detector is put into likelihood, to 'correct' for damping of the asymmetry Aart Heijboer 10 July 7, nikhef colloquium What we know already all data before 2004 LEP + SLD World average before Tevatron run II Amplitude scan: fix m s and measure the amplitude of the corresponding frequency component (Fourier) Recent D0 result 17 < ms look for displaced tracks Trigger on events with two displaced (d>120 m) tracks d very fast reconstruction of silicon data at L2 (20 s latency) by dedicated hardware: SVT cdf d ( ) Displaced track trigger Aart Heijboer 18 July 7, nikhef colloquium Hadronic signals low background under the B s peak P T (B s ) 'perfectly' measured mixing fit in range > 5.3 GeV to remove partially reconstructed 'satellites' high statistics 'light B' samples: B + D 0 (26 k events) B 0 D- (22 k events) Aart Heijboer 19 July 7, nikhef colloquium Semileptonic signals ~ Bs l D s signal events (and ~1M in B 0 /B + ) missing particles ( ): no B-mass peak, but mass of lepton+D s gives discriminating power. Aart Heijboer 20 July 7, nikhef colloquium Proper decay time and resolution Aart Heijboer 21 July 7, nikhef colloquium Sources of uncertainty: L xy Lxy is biased because of the SVT trigger how to measure (L xy ) contributions from primary and secondary vertex improved recently by using EBE primary P T Negligible uncertainty in hadronic Important for semileptonic (missing momentum) Only have lepton and D s Determine k P T (l+D)/P T (B) from MC Proper time reconstruction: hadronic Hadronic: ct 0 : ~ 30 m (100 fs) p /p < 1% Semileptonic ct 0 : ~ 50 m (167 fs) p /p ~ 15% (K factor) Bs/BsBs/Bs L xy piece of cake! Aart Heijboer 22 July 7, nikhef colloquium Sources of uncertainty: L xy Lxy is biased because of the SVT trigger how to measure (L xy ) contributions from primary and secondary vertex improved recently by using EBE primary P T Negligible uncertainty in hadronic Important for semileptonic (missing momentum) Only have lepton and D s Determine k P T (l+D)/P T (B) from MC Proper time: Semileptonic Hadronic: ct 0 : ~ 30 m (100 fs) p /p < 1% Semileptonic ct 0 : ~ 50 m (167 fs) p /p ~ 15% (K factor) Bs/BsBs/Bs L xy k-factor obtained from Monte Carlo Take advantage of variation in k-factor distribution with l D s mass. (high m lDs means small missing p T ) can not measure p T for semileptonic correct for missing p T on average Aart Heijboer 23 July 7, nikhef colloquium Proper time reconstruction Displaced track trigger sculpts proper decay length distribution Modeled by efficiency function (t) Derived from MC Not crucial for mixing measurement, but important for lifetimes Aart Heijboer 24 July 7, nikhef colloquium Lifetime measurement (hadronic) N Aart Heijboer 25 July 7, nikhef colloquium Proper time resolution Effect of non-zero ct error asymmetry: attenuation of the oscillation Smearing of decay time causes attenuation of asymmetry signal: Have to know ct to measure the mixing amplitude How to measure ct ? 2 2 )( t t m eD Aart Heijboer 26 July 7, nikhef colloquium Measuring the proper time resolution Cannot measure the ct resolution directly on data (no prompt peak in the B s signal due to trigger) Solution: construct events that look like a B but are known to come from the PV.. real D some pion from the underlying event (i.e. from PV) True must be zero; compare error with predicted error from the vertex fit. And study dependence on kinematic variables, isolation, 2 of fit etc.. Aart Heijboer 27 July 7, nikhef colloquium proper time resolution Aart Heijboer 28 July 7, nikhef colloquium 3) Flavour tagging Aart Heijboer 29 July 7, nikhef colloquium Flavour tagging Bs/BsBs/Bs LxyLxy We need to know the flavor of the B s at production. Opposite side tag: look at the decay products of the other b quark in the event: Leptons charge of the b-'jet' the two b quarks fragment independently: can calibrate opposite side taggers with B d & B u other B often outside acceptance Same side tag: look at particles produced in B meson formation (K in case of Bs) Very powerful (high acceptance) but cannot calibrate on B d & B u Need to rely on MC need to identify Kaons K e/ Aart Heijboer 30 July 7, nikhef colloquium A tagger is characterized by : efficiency D: dilution = 1-2 x mistag rate (large dilution is good) Dampens asymmetry: Figure of merit: D 2 x D We must know what D is to measure A D pi D 2 from lepton taggers measured on B 0 and B + in this sample: 4.5% ! (compare with 1.5 for other samples) Aart Heijboer 60 July 7, nikhef colloquium The Future Many improvements on the way: more data factor 2-3 more already collected Tevatron Luminosity going up Same Side Kaon tagging Additional trigger paths Use satellites in hadronic modes Improve ct resolution Reoptimize event selection (NN) D 2 = 5% & improve ct) by 10% D 2 = 3.5% D 2 = 1.55% Mode Yield events in total Aart Heijboer 61 July 7, nikhef colloquium