New Results on Heavy Flavor Baryons Charm 2006

Charm2006Beijing 6 June 2006

Jim Russ - Carnegie Mellon 1

New Results on Heavy Flavor BaryonsNew Results on Heavy Flavor BaryonsCharm 2006Charm 2006

Outline– Qqq Masses and Lifetimes – theoretical issues and new

resultsc mass shift

b lifetimeCharm baryon lifetime systematics –new data

– Qqq Decay and Excitation Properties b Branching Ratios

More New c states c Branching Ratio Measurements

– QQq States – an update– Conclusions



A Weighty Matter - What is the A Weighty Matter - What is the cc Mass? Mass?

PDG value static for a decade, dominated by CLEO and NA32 results

New results from BaBar and Selex with much smaller errors pull mass 1.5 MeV/c2 higher

Important information for any future studies of c c resonant production at e+e- machines.



Qqq Baryon Lifetime IssuesQqq Baryon Lifetime Issues

• HQET [ (1 /mQ)2 suppression of non-spectator effects] all B-hadron lifetimes should be very similar. (b

0 )/(d0 ) is well below prediction in LEP, CDF

Run I data.

• Charm baryon lifetime hierarchy predicted from quark models already in 1984-86. HQET agrees.

• Data match HQET except for c+. The ratio (c

+ )/ (c0 ) is

off by the same factor as the lifetime. Problem for HQET: lifetime ratios vary as (1 /mQ)3 while the lifetime itself varies like (1 /mQ)2 .



Selected Lifetime RatiosSelected Lifetime Ratios

PDG 2005 lifetimes

Theory Data(PDG05)

B+/ B0 1.06 1.086 0.017

bB0 0.9-1.0 0.797

c+/ c

+ 1.5 2.2

c+/ c

0 2.7 2.9

Model calculations describe lifetime systematics well, with two conspicuous problems.



New New bb0 0 Results from CDF Results from CDF

CDF and D0 measure lifetime using b

0 J First results using fully-reconstructed decays.

New CDF measurement (1 fb-1): = 1.59 (stat)(syst) ps

0 lifetime agrees well with PDG: 1.524 ps

Ratio to 0 Js minimizes systematics:

b / = 1.037



Restoration of Order in HQET?Restoration of Order in HQET?Bigi and Uraltsev: ‘natural’ range of b / is 0.94 - competing effects from positive and negative interference.

Models enhanced sub-leading terms in 1/mb matrix element expansion faster decay rate. Predictions for b / range from 0.86 to 0.90 in these models.

With this new result, are we back to the basic model for b decays?



One Disagreement gone – what about One Disagreement gone – what about cc++??

c+)/ c

+) ~ 1.5 in models c

+) ~ 300 fs

CLEO: c+) = 503 fs (250

evts)FOCUS: c

+) = 439 fs (532 evts)

New SELEX Result

SELEX: c+) = 419 fs (301

evts)Excellent agreement with FOCUS

Problem with c+) is not experiment !

SELEX Preliminary

c+)

301 evts



ccooLifetimeLifetime

FOCUS (180 GeV beam): 59 evts in 2 modes

stat)syst) fs

Using PDG c+ lifetime, the lifetime ratio becomes

(c+)/ c

0)= 2.81 compared with the model prediction of 2.7

SELEX(600 GeV - beam): 76 evts in 2 modes

stat)syst) fs

Recent Results from FOCUS, SELEX

signal backgnds for 2 modes



Branching Ratio MeasurementsBranching Ratio MeasurementsLifetimes are inclusive calculations. What about BRs, where W-scattering and Pauli Interference terms are important, as in the c

0 system studied in great detail recently by BaBar and Belle

Tevatron, e+ e- B-factories producing new b- and c-baryon branching ratio measurements. Theoretical predictions for some baryon modes

now available from Soft Collinear Effective Theories (SCET).

c0Spectator + Pauli c

0WS + Pauli



New New bb Branching Ratio Measurements Branching Ratio Measurements

CDF: BR for single-pion emission in Bo and b decays – test of SCET. Note complex background for b. Limiting error comes from the BR for c pK- + , not statistics!

bc+-BoD+ -) = 3.3 0.3(stat) 0.4(sys) 1.1(frag+BR)

while SCET (Leibovich, Ligeti, Stewart and Wise) predicted 1.7 We wish we knew the c pK-+ BR better.



More SCET TestsMore SCET TestsSCET + HQET + 1/Nc predicts b semileptonic decays dominated by c

+ ground state (6%) + p-wave excitations (2-3% for each state) and predicts that c modes are suppressed.

Predictbc+bc

+-New CDF measurements of these quantities.

Good news for theory: CDF measurement bc

+bc+-stat) 1.2(sys)

1.2(BR)And not so good news – CDF has first measurements of semileptonic decays to excited charm baryon states. Four different channels measured :

bc+(2593)bc

+… not ½ .

bc++ bc

+same order.



BELLE and BABAR BELLE and BABAR cc00 Studies Studies

BABAR

c0c

0

(stat) (syst)

CLEO(92)

(stat) (syst)Körner and Kramer (92) quark model

0.32 (WS / Spectator)

BELLE

c0KSc

0

(stat) (syst) [1st]Zenczykowski (94) quark model + CA

0.28 (WS + Internal W)/Spectator

Quark Models do pretty well. How can we move beyond them?

For charm SCET arguments break down. Excellent new data on branching ratios is compared to venerable quark models.



BaBar BaBar cc00 Studies Studies

BaBar reports a lovely c primarily in the two-body decay channel. They report at 90% C.L.This is a surprising result.

For the spin-1/2 charm baryons c

+ and c

+ the 3 relative

branching ratios are of order 3.3!

CLEO and E687(photoproduction) had also reported only an upper limit for Is there something unusual about the spin-3/2 decay mechanism?



Charm Baryon Spectroscopy – from Charm Baryon Spectroscopy – from harmonic oscillator to the latticeharmonic oscillator to the lattice

• State of the art in spectroscopy still based on Copley, Isgur and Karl from 1979 – valence quarks in harmonic oscillator potential. Model has huge number of states, but only a few are seen.

• New lattice calculation program underway (LHPC, Colin Morningstar) – aims to compute excitation spectra for normal and charmed baryons with dynamic pions as light as 300 MeV. – expect first results in 2007.

• Meanwhile, Belle and Babar report new c and c states.



Belle Data Show New Belle Data Show New cc State State

c+ +

Reflection from c+(2880)

Quark model calculations predict width ~ 15 MeV/c2

Experimental width ~ 70 MeV/c2

Mixing with other states? nearby c1 ?

Quark model candidate state: c2 D-wave excitation c+ -

c0 c

+ c++



New New cc++ from BaBar from BaBar

BaBar data show known narrow c(2880) and new c (2940) state, both in pDo (new decay mode for c(2880) ).

New state 6 MeV below pD*o threshold, one pion mass above Belle c(2800) state.

No trace of either state in CDF data with comparable mass resolution.



Spectroscopy ConclusionsSpectroscopy ConclusionsQuark model spectroscopy accomodates the observed c

+ , c states with

reasonable accuracy. Width predictions generally not good. Fixing quantum numbers is hard. without a model as a guide.

• The 2880 decays both to pDo and c2940 goes only to pDo .

• Lattice gauge calculations are starting to treat low-lying states with almost-physical pions. Data have fascinating regularities as a challenge for theory.

CLEO BELLEBaBar



Now QQq Baryons Now QQq Baryons

Phys Rev Lett 89 (2002)112001

First QQq candidate comes from baryon beam expt:

• (ccd)+c+ K- Cabibbo-favored spectator

mode

•state seen from p but not

• not seen in FOCUS photoproduction expt

• lifetime is very short – disagrees with extrapolation from single charm

Production cross section is a sizeable fraction of c

+ production – consistent with intrinsic charm model.



A Different A Different cccc++ Decay Mode Decay Mode

cc+ pD+K-is another ccd

all-charged decay mode.

• Have automatic background check with pD-K+

• Event-mixed background (grn) gives absolutely-normalized description of bkg .

• Wrong-sign pD-K+ are featureless at same level as combinatoric.



Combine Combine cccc++ Mass Distributions Mass Distributions

Phys. Lett. B628,18 (2005)Gaussian with width fixed from MC fitted to pD+K-data to fix mass: 3518 MeV/c2 .

Combine with 3519 MeV/c2 from other mode:

m(cc+) = 3518.7 MeV/c2

.(pD+K-)/c+K-



Also a Also a cccc++++ Excited State Candidate Excited State Candidate

Look at Q=2 candidates in c+ K-

final state from - beam. No new cuts.

See broad structure at 3780 MeV/ c2 – wider than resolution – either has natural width or two states

• Combinatoric background from event mixing describes high-mass side of plot

• fitted background under peak compares well with event-mixed level.

• Have one (or maybe HQET pair of) ccu excited state(s).



BaBar and Belle Null Searches for BaBar and Belle Null Searches for cccc+,+++,++

BaBar sample: 600,000 c+ pK-with PID (DIRC)

BaBar finds no hint of a signal in any double-charm state from continuum annihilation at 10.58 GeV/c and sets a 95% C.L upper limit corresponding to 7% of the production of singly-charmed c

0 -

Belle (Preliminary!) also finds no cc

+ but they report two new c

+ states at 2980 and 3077 MeV/c2 from the search.

higher mass state is narrow. Lattice, where are you?

cx(2980)+

cx(3077)+



ConclusionsConclusions• Belle and Babar continue CLEO tradition of charmed baryon spectroscopy. New c

+ states not seen in hadron experiments,e.g., CDF.

• CDF has new b0 measurements in fully-reconstructed modes. CDF

lifetime result removes conflict with HQET/1/mQ expansion. Await b

0,- , b- measurements for further tests of lifetimes and SL decay

widths .

• Charm baryon lifetimes agree well with model calculations except for the c

+ . Experiments agree well. Theory???

• New c+ , c

0,+,++ , c+ states from BaBar and Belle challenge lattice

spectroscopy to predict sparse charm baryon mass population.

• SELEX double charm baryons are statistically significant, limited signal populations. Production definitely baryon-baryon – not seen in photoproduction. Intrinsic charm?



And WishesAnd Wishes• Many Qqq baryon studies hinge on knowing the BR for c pK-

+. I wish for e+e- running at 2mc to nail the BRs.

• Experiment continues to add new Qqq states. I wish for high statistics samples of B decays to c-baryons for JP analysis. Belle has made a start.

• Collider experiments are starting precision tests of SCET and factorization for baryons as well as mesons. I wish for continued developments in theory and data. I hope for the b-c baryon soon to be seen at the Tevatron.

• Double charm studies are still active and point to purely hadron-hadron production. I wish there were future hadron experiments to pursue such issues in flavor physics. (maybe LHCb)

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New Results on Heavy Flavor Baryons Charm 2006

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