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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
