Crisis in Semileptonic Heavy Meson Decays in Semileptonic Heavy Meson Decays W.Johns Nuclear and Particle Physics Seminar Vanderbilt University, Sept. 6, 2004 What constitutes a “crisis”

Crisis in Semileptonic Heavy Meson Decays

W.JohnsNuclear and Particle Physics SeminarVanderbilt University, Sept. 6, 2004

What constitutes a “crisis” in physics

- A friend who needs help?- An unexpected result? (this can be a good

kind of crisis to have)- Contradictory results?- An unexplainable result?- All of the above- None of the above(In this talk, we may see hints of the 1st four…)

In 2002 FOCUS published a result…• But it sort of disagreed with a result that

was published at almost the same time• But FOCUS found something in the decay

that other experiments only saw hints of• So FOCUS took a little more time in

publishing everything about this decay• But the difference remained…• And there were other things that were

interesting

What is a particle decay?A transition of a particle from one (initial) state to another (final) state (consisting of more particles) – as described by Fermi’s Golden Rule:

=

SpacePhase

ElementMatrix

CouplingUniversal

RateTransition

But a particle lifetime is governed by theTotal Transition Rate which includes all possible states (i.e. we don’t get different lifetimes for the same initial particle by measuring different final states unless very special physics is involved)

Another way to look at this:• Even though different initial states

(particles) can have different lifetimes, decay rates for individual transitions can be almost the same if the physics (matrix element) and the phase space (“Q”) are similar!

≠→

≈→

CALifetimeYZAC

CLifetimeYXC

ALifetimeZXA ~,~%%

A powerful check for states with great similarities

A simple case• Semileptonic Pseudoscalar Meson decay- Hadronic current tends to be simpler and

quasi-free of final state interactions

νµπ )(0 −−→− eorK

This is actually a combo:

)(2

10 dduu +=π

So we only get half…

Strong Force included asA form factor

Weak current is well understood fromthings like muon decay

Other quark in the decay acts as a “Spectator”

Similar Decay to compare: νµπ )(0 −−+→ eorK

At 1st glance, form factorlooks the same

But in the bottom line, we’vechanged a d for a u

We actually observe the neutral kaon as an admixture of particle and anti-particle. With long and sort lifetimes.

Lets do a comparison

‘stable’stable2200~026.051.812.4Lifetime(ns)

~00.511106135140498494Mass(MeV)

νe+µ+π0π+K0longK

+/-

MeVMKMMeVMKM L 358)()(359)()( 00 =±−=−± ππ

µνµπ

µνµπ

27.3,87.4))(0%(

19.27,81.38))(%( 0

eeorK

eeorKL

=±±→

=±±→±

m

Notice % electron modes > % muon modes-Muons eat Q (expect muons~2/3 electron modes)-and effects proportional to M(lepton)2 (few percent effect)

End up with….

01.067.0)(%)(%

01.070.0)(%)(%

0

0

±=

±=

+

+

eKK

eKK

L

L

µ

µ

06.097.0)8.51)(069.0(

)08958.0)(81.38()(%

)(%

022.0994.0)(%

)(%)2/1(

016.0953.0)(%

)(%)2/1(

0

0

0

0

±==

±=+

±=+

+

+

nsns

LeKSeK

LK

KLeK

eK

S

L

L

L

τ

τ

τµ

τµ

τ

τ

This better be close to 1!

Experiment “Theory”

0.67

0.67

0.97

0.97

This is complicated stuff• Lots of model corrections on the order of 1%• Used to find Vus CKM angle (Part of the coupling)• Discrepancy appears to be in neutral kaon• Combine carefully with other: Vud Vub ...Get

Expect:

)2004(0015.09967.0)2004()2002(0019.09957.0)2002(

1|||||| 222

±=±=

=++

EstimatesPDGEstimatesPDG

VVV ubusud

Find a greater than 2 sigma discrepancy!

Other Heavy Mesons decay too

))/(21(5HeavyLightHeavye MMM −∝Γ

Approximately

MevMM lightHeavy 5~~ δδAnd (at most!)

Expect differences to get smaller for similar light/heavy ratio with increasingly heavier mesons when we change an up for a down quark

00.1))(/)((

01.1))(/)((50

50

=

=+

+

BMBM

DMDM AndExpect 0.1),(/),(

01.1),(/),(0

0

=ΓΓ

=ΓΓ+

+

µµ

µµ

eBeB

eDeD

996.0)(/)(97.098.0)(/)(

=ΓΓ−=ΓΓ

eBBeDD

µµ

And the case is fine for B’s

15.008.1),(/),(0 ±=ΓΓ + µµ eBeB

But Charm mesons are interesting!

38.00.1)(/)(

06.089.0)(/)( 00

±=ΓΓ

±=ΓΓ++ eDD

eDD

µ

µ

Another >2 sigma effect!

Errors are too big to tell

31.087.0)(/)(

11.074.0)(/)(0

0

±=ΓΓ

±=ΓΓ+

+

µµ DD

eDeD

How do we increase our Charm?• Where’s the biggest error coming from?

psD

KD

eKD

5.13.410)(

17.019.3)%(

18.058.3)%(

0

0

0

±=

±=+−→

±=+−→

τ

νµ

ν

fsD

KD

eKD

71040)(

5.20.7)0%(

9.07.6)0%(

±=

±=+→

±=+→

+

+

+

τ

νµ

νBestCandidates!

Is there anything else that helps?• Charm and Beauty mesons have a lot more

mass than kaons, so there are more decay possibilities

• In fact, earlier models predicted that:

)*()( νν eKDKeD →Γ≈→Γ

Lowest excited Kaon state

-But Experiments throughout the 90’s were seeing

5.0)()*(

≈→Γ

→Γνν

KeDeKD

So in 2002, a new measurement:

• Got me pretty excited• And a friend of mine got pretty excited because

if you compared his measurement to theirs:

07.006.099.00%

*%±±=

+→

+→+

+

ν

ν

eKD

eKD

12.023.1*%

*%±=

+→

+→+

+

ν

νµ

eKD

KD And 0.95 was expected

And I was especially excited…• Since I was working on a measurement of:

• And about half of the previous experiments that compared rates from D+ and D0 just assumed:

))(())((

),)(())((

00

*00*

νµνµ

νµνµ

+−→Γ=+→Γ

+−→Γ=+→Γ

+

+

eorKDeorKD

oreorKDeorKD

νµ

νµ+→

+→+

+

0

0*

%

%

KD

KD

Including me in my thesis ….(This is a crisis!)

So how do you measure this?

• Since the shorter lived neutral kaon and the excited neutral kaon decay into 2 charged tracks at a very predictable rate, the systematic errors, which are prevalent when comparing decays with different track multiplicities or decays containing reconstructed neutrals in only one state, will tend to be smaller… Blah blah blah

You try to pick decays which have similar topologies and compare them

Because Experiments are Complex

Big

And did I mention Complex?

So you need to simulate the detector response

Signature of Charm Mesons

Beam

Target

Hits in detector planesfrom the tracks

Primary Interaction in Target make tracks

Since the D meson is moving very nearly the speed of light, a 1 pslifetime becomes ~1 cm of travel

ConnectThe Dots!

And you can do lots with tracks

νµπ ++ → ),( KD

L/σ – Lσp

σs ISO1 – CL DK’s in prim

DCL – CL of DK vertex

Vertexing “cuts”:

ISO2 – No Xtra trks in DK OOM – No DK’s in stuff

Use Magnets Measure Momentum

Signature of other particles

Particles moving faster thanc/n in a gas, make a “shock Wave” of light (Mass sensitive)

(assuming n(λ) is ~constant)

Cherenkov Detectors

Muon Detectors

Muons have a much higher chance of penetrating material thanpaons, pions, electrons…

GAS

Stuff

Form invariant Quantities (Mass)

Estimate Backgrounds

The K*

Since Ks decays into2 pions, this is the massof the 2 pions and a muon

(Interesting since K* can decay into a Kshort and a neutral pion as well as a charged kaon and a charged pion

And be especially careful!• The K* has a lifetime < 10-20s• But the Kshort has a lifetime of 90 ps

Only a fraction of the Kshorts decay in the same area as the D meson

But that fraction is in a VERY well understood part of the detector….

Because the super strength of FOCUS is the measurement of short lifetimes

FOCUSLifetimesComparisonFrom ICHEP04 talkby Ian Shipsey

But to be sure, you vary lots of things, and see the effect on the ratio

So you can compare with confidence

030.0043.0594.00

0*

±±=→

→++

++

νµ

νµ

KD

KD

Final FOCUS(04) Result:

Old Thesis Paper:

11.062.0)(

)(0

0*

±=−→Γ

→Γ+

++

νµ

νµ

KD

KD

Looks like ratio is closer to 0.5 again

And Compare to Models etc.Models cluster around the data results

13.002.1)(/)(

15.015.1)(/)(

22.042.1)(/)(

0

0

±=ΓΓ

±=ΓΓ

±=ΓΓ

+

+

++

eDD

DD

eDD

µ

µµ

µ

New result agrees with neutral D meson

That measurement that got everything started, wasn’t really a measurement!

In terms of our original interest

)(µ+ΓD)(eD+Γ)(0 µDΓ)(0 eDΓ

Errors grow since these comparisons tend to be indirect This is the odd

man out now

And the conclusion of the analysis

• The ratio of the K*/K ratio is indeed closer to ½ than 1 (evidence is overwhelming now)

• Charged D meson rate into a kaon and andelectron is probably underestimated

• Some other conclusions ancillary to this talk(It’s in PLB 598, pg 33-41)

And then the Results started to come in from the summer conferences (and preprints)

I’m happiest about this one• At ICHEP04 in Beijing (Jiangchuan Chen)

And here’s where they all fall.)(µ+ΓD)(eD+Γ)(0 µDΓ)(0 eDΓ

BES

CLEO-c

BES(in PLB)

(Prel)

(Prel)

And you might be interested to know

)0029.0666.0(0026.06640.0)(%)(%

0

0

±=±= predneweK

K

L

L µ

0019.09982.0|||||| 222 ±=++ ubusud VVV

Which gives:

KTeV has done a measurement

And the new CLEO-c measurements give:

09.059.00

*0

±=−→

−→+

+

ν

ν

eKD

eKD

And now we are beginning to really measure the Matrix Element

DPF04 Talk by Lorenzo Agostino

Round up and the future>For now this charm decay crisis looks solved(electron mode for the charged D appears low)• The ratio of K*/K is grounded around 0.6• Interest in these decays is accelerating!

(Big e+/e- samples are finally appearing)Hmmmmm…. Couplings measured in a few years!• There’s actually more FOCUS data sitting around,

and with a lot of work, the muon sample could double, and we could do e’s and maybe measure that swell matrix element…

Lot of references used in this talkThe Particle Data Group tables and summaries (2000-2004)The ICHEP04 talks of Ian Shipsey and Jiangchuan ChenThe DPF04 talk of Lorenzo AgostinoAll the references in PLB 598, pg 33-41The Klong papers hep-ex 0406001 v1 & 0406003 v1I’m sure to have missed a couple…

And special thanks to:University of Colorado and Vanderbilt for supporting the sabbatical during which this work was performed

(And Cynthia for projector help)

Differences in the K* analysisFOCUS

Other Experiment

Semileptonic Charm Decays

022

222

2

cossin4

sin})cos1()cos1{(

coscos

Γ+

−Γ−++Γ+

∝Γ

V

V

V ddd

θθ

θθθ

θθ

l

ll

l

(D decay, No form factors, V decays to spin 0 particles)

Neutrino is left handed

Prefers W spin along muon,e

V products spinless

Prefer LZ=0

Form Factors

Scalar Resonance? CP?

More than just CKM measurement tools…

FOCUS saw discrepancies in the data

−−−−

++

∝Γ

−

2

20

2

2

2

5

)(sincos2

)()cos1(sin

)()cos1(sin

coscos

0*

0*

0*

qHB

qHBe

qHBe

ddddqdmd

KV

Ki

V

Ki

V

Vk

l

l

l

l

θθ

θθ

θθ

χθθ

χ

χ

π

Phys.Lett.B535:43-51, 2002hep-ex/0203031

νµ++ → 0*KD

Yield 31,254

DataMC

Focus “K*” signal

matches model

-15% F-B asymmetry!

FOCUS added a term, things got better

+−−−−

++

∝Γ

−

2

20

2

2

2

5

)()(cossin2

)(sin)cos1(

)(sin)cos1(

coscos

0*

0*

0*

qHAeB

qHBe

qHBe

ddddqdmd

iKV

Ki

V

Ki

V

Vk

δ

χ

χ

π

θθ

θθ

θθ

χθθ

l

l

l

l

L=0 ansatz

Signal Events weightedby avg(cosθV):

No added term

Here we are taking a background from the datawhere events likely had anextra track and comparing it to a background dominated by K*munu. (Which happens for sure when the signal is very clean)

The tighter you cut, the less statistics you have.But it’s worse here since the data based background has a small component of signal in it: we’ve correlated the signal and background in a bad way!

But you can get the same sort of background from the simulation. Since the majority of unmodelledjunk occurs at low separation (l/sigma) we expect agreement to be better at higher separation.

Except in the simulation, we know when the signal is leaking into the background, so we can remove it a-priori, and the error “bonus” goes away!

Matrix Element Parameterization

2

Evolution of the strong current

Assuming a massive propagator