beach2002

Slide1: 

Charm Semileptonic Decays New Results from FOCUS Angel M. López University of Puerto Rico (Mayaguez) Representing FOCUS Outline Interference in D+  Kpmn BR D+  K*mn/K2p BR Ds+  fmn/fp BEACH2002 June 27, 2002 - Vancouver

New results on D+  Kpmn: 

21,370 events New results on D+  Kpmn Right Sign Wrong Sign Data Fit charm bkg Our Kp spectrum (like everyone else’s) looks like 100% K*(890). This has been “known” for about 20 years. MKp (GeV/c2) events RS-WS backgrounds are pretty small But a funny thing happened when we tried to measure the form factor ratios by fitting the angular distributions ... WS-subtracted

Five observables are studied: 

Five observables are studied MKp MW2  q2  t A 4-body decay requires 5 kinematic variables: Three angles and two masses. right-handed m+ left-handed m+ (“mass terms”) H0(q2), H+(q2), H-(q2) are helicity-basis form factors computable by LGT Wigner D-matrices Two amplitude sums over W polarization

An unexpected asymmetry in the K* decay: 

An unexpected asymmetry in the K* decay dataMC Yield 31,254 We noticed a forward-backward asymmetry in cosqV below the K* pole, but almost none above the pole. Could it be QM interference? HUGE asymmetry!

Simplest approach — Try an interfering spin-0 amplitude: 

Simplest approach — Try an interfering spin-0 amplitude We simply add a new constant amplitude : A exp(id) in the place where the K* couples to a helicity=0 W+ with amplitude H0. (plus mass terms) A exp(id) will produce 3 interference terms

Since A << B, interference will dominate..: 

Since A << B, interference will dominate.. Ignoring the “mass terms”, If we average over acoplanarity we only get the first term This is the term that created our forward-backward asymmetry! If our model is right: The asymmetry will have a particular mass dependence: The asymmetry should be proportional to sin2ql The asymmetry should have a q2 dependence given by q2 H02(q2)

Studies of the acoplanarity-averaged interference: 

Studies of the acoplanarity-averaged interference Extract this interference term by weighting data by cosqV. Since all other c-averaged terms in the decay intensity are constant or cos2qv , they do not contribute. We begin with the mass dependence: Our weighted mass distribution.. A=0 0.36 exp(ip/4) ..looks just like the calculation.. Efficiency correction is small A constant 450 phase works great... ...but a broad resonance is fine as well.

Dependence of asymmetry on cosql: 

Dependence of asymmetry on cosql We plot the asymmetry versus cos ql and expect a parabola in cos2 ql since sin2 ql = (1 - cos2 ql) 0.36 exp(ip/4) A=0 Looks  - (1 - cos2 ql). Some modulation due to efficiency and resolution

q2 dependence of asymmetry: 

q2 dependence of asymmetry 0.36 exp(ip/4) A=0 Below the pole

Acoplanarity dependent interference terms: 

Acoplanarity dependent interference terms The interference adds two new terms to the acoplanarity dependence. Without s-wave interference, the acoplanarity terms are even in c: Only cos c and cos 2c dependencies are present The interference produces sin c terms which break c to -c symmetry

The loss of c to -c symmetry is seen in the data.: 

The loss of c to -c symmetry is seen in the data. Same sign (incorrect) convention used for D+ and D- Can be mistaken for CP violation! Opposite sign (correct) convention used for D+ versus D- When sign of c is handled properly, the D+ and D- acoplanarity distributions become consistent.

The correct acoplanarity convention: 

The correct acoplanarity convention The sine of the acoplanarity is a product of five vectors. Under CP, D+ => D-. We want c to have the same value for CP transformed states but the formula above changes sign when all 5 vectors reverse. Thus we must take the opposite sign for D+ versus D- decays. counter clockwise about 

The model is not a unique solution. A broad resonant amplitude also works well.: 

The model is not a unique solution. A broad resonant amplitude also works well. We can mimic the cosV dependence for a constant amplitude using a BW put in with a relatively real phase. For example use a wide width (400 MeV) and center it above the K* pole (1.1 GeV). cos qV term

But surely an effect this large must have been observed before?: 

But surely an effect this large must have been observed before? Although the interference significantly distorts the decay intensity.... ...the interference is nearly invisible in the Kp mass plot.

New results on D+  K*ln/ K2p branching ratio: 

New results on D+  K*ln/ K2p branching ratio — RS — WS With tighter cuts FOCUS total signal

This rate is very much an open experimental and theoretical question.: 

This rate is very much an open experimental and theoretical question. The recent CLEO num-bers are higher than previous measurements. G(K*l n)/G(Kpp)

Fitted Mass Histograms for the FOCUS DataSamples with baseline + out-of-material + secondary vertex isolation cuts.: 

Fitted Mass Histograms for the FOCUS Data Samples with baseline + out-of-material + secondary vertex isolation cuts. K*mn after subtracting wrong-sign and charm background (from MC). Backgrounds are well understood! For the Kpp normalization channel it is sufficient to fit a Gaussian peak over a polynomial background.

The FOCUS Result: 

The FOCUS Result We multiply muon results by 1.05 to compare to electron results. Our number is 1.59 standard deviations below CLEO and 2.1 standard deviations above E691. G(K*l n)/G(Kpp) muons electrons This result takes into consideration the interference phenomenon which affects the reconstruction efficiency.

New FOCUS Ds+  fmn/fp Branching Ratio: 

New FOCUS Ds+  fmn/fp Branching Ratio — data — charm background MC Once we demand a decay out of the target segments, the backgrounds are matched by our Monte Carlo. This is a “c,cbar” MC exclud-ing events that contain a fmn decay.

Comparison of Results: 

Comparison of Results FOCUS value is 0.54  0.033  0.048. There is very good agreement among experiments.

Summary: 

Summary (1) S-wave interference in D+  Kpmn of form The new amplitude is small: 7% of BW peak amplitude in the H0 part.  6% of all Kpmn over the full Kp range (2) D+  K*mn/K2p Branching Ratio New FOCUS value is 0.602  0.010  0.021 (1.57s lower than CLEO) (3) Ds+ fmn/fp Branching Ratio New FOCUS value is 0.54  0.033  0.048

Many interesting FOCUS results are on the way: 

Many interesting FOCUS results are on the way (1) rv and r2 form factor measurements for K*mn and fmn (2) f(q2) measurement for D0  Kmn (3) Cabibbo suppressed ratios: D+ rmn/K*mn & D0 pmn/Kmn There are probably still many surprises (such as the interference in Kpmn) to be discovered in charm and beauty physics even in places where we least expect it.