Recent Advances in Charm Physics

June 20, 2002 Alex SmithUniversity of Minnesota

Recent Advances in Charm Physics

• Why charm physics?• Searches for new physics using D meson decays

– Mixing– CP violation

• Measurements which provide input to QCD– Decay processes

• Charm semileptonic decays

• Lifetimes

– Production mechanisms

• What to expect from future experiments• Conclusions

Alex SmithUniversity of Minnesota

Physics in CollisionsJune 20-22, 2002


Why Charm?

• Searches for new physics:

• D mixing

• CP violation

• Measurements which guide QCD

• Necessary in order to extract standard model parameters

• Form factors and decay constants -> B decay CKM elements

• Final state interactions, resonances in multi-body decays

• Lifetimes, masses, branching fractions

• Charmonium production mechanisms

• Spectroscopy of light mesons/glueball candidates

• Dalitz plot fits of D meson decays (see talk by Brian Meadows)

• J/ radiative decays (see talk by Shen Xiaoyan)

Charm contributes to a variety of important topics in HEP…Charm contributes to a variety of important topics in HEP…


sPrediction and Motivation :Mixing 00 DD xx mixing: mixing: Channel for new physics…Channel for new physics…

yy

yy (long-range) mixing: SM background… (long-range) mixing: SM background…

xx

Standard model prediction:Standard model prediction:

2y

Mx

2221

mix6

mix

3

where,10

10,

yxRR

yx

……although long-distance contributions although long-distance contributions could increase thesecould increase these

* New physics will enhance * New physics will enhance xx but not but not yy

* CP * CP violation in mixing would violation in mixing would be a smoking gun for new be a smoking gun for new physicsphysics

1)1) All mixing contributions doubly All mixing contributions doubly Cabibbo suppressedCabibbo suppressed- Factor of tan- Factor of tan44cc in rate in rate

2)2) Further GIM suppression of Further GIM suppression of xx possiblepossible

Two types of mixing:Two types of mixing:


Mixing 00 DD

tDD etyxtyRRtr

2

mixing

2241

ceinterferenDCS

Mixing is not the only way toMixing is not the only way toget to “wrong sign” hadronicget to “wrong sign” hadronicstates…states…

Need to fit Need to fit proper decay timeproper decay time in order to in order to distinguish mixing (both distinguish mixing (both xx and and yy) from doubly ) from doubly Cabibbo-suppressed (DCS) decays…Cabibbo-suppressed (DCS) decays…

Complication:Complication: phase phase difference, difference, KK, between, between

CFCF and and DCSDCS amplitudes can amplitudes can lead to observable quantities lead to observable quantities x’x’ and and y’, y’, related to related to xx and and yy by a by a rotation rotation

0D

0DdoublydoublyCabibboCabibbosuppressedsuppressed((RRDD))

mixingmixing((xx22+y+y22))

CabibboCabibboFavoredFavored (CF)(CF)

““Wrong sign”Wrong sign”

K

Notation:Notation: “right-signed” (RS)“right-signed” (RS) => Cabibbo-favored decays => Cabibbo-favored decays ““wrong-signed” (WS)wrong-signed” (WS) => Mixing or doubly Cabibbo-suppressed decays => Mixing or doubly Cabibbo-suppressed decays

Look for mixing in “wrong signed” (WS) decays of Look for mixing in “wrong signed” (WS) decays of DD00……


Current Status of D0-D0 Mixing

““Typical” non-SM predictions (many higher and lower, however)Typical” non-SM predictions (many higher and lower, however)

““Typical” upper SM predictionsTypical” upper SM predictions

- Current measurements cutting into range of some non-SM predictions Current measurements cutting into range of some non-SM predictions - Much room for improvement before we hit SM backgroundMuch room for improvement before we hit SM background

KD0

0

0 ,

D

KKD

(*)0 KD

xx

yy


KDRyx D0 from and ,

11613527

8.44 7.97.8

RS

WS

N

N

C.L. %95@

%69.0%24.0

%2.0%2.5

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DR

y

x

• Currently, best constraints come from this mode Currently, best constraints come from this mode if assumptions if assumptions about strong phaseabout strong phase are madeare made

• Unknown strong phase difference weakens these limitsUnknown strong phase difference weakens these limits• CLEO measurement remains the strongest constraint on xCLEO measurement remains the strongest constraint on x


KDRyx D0 from and , ,

C.L. %95@

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x

19536760

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RS

WS

N

N

xx

yy

FOCUS FOCUS x-x-yy limit limit

CLEO limit (still CLEO limit (still best constraint best constraint on on xx))


31082960

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WS

N

N

KDRWS0 from

54120

210

RS

WS

N

N

%02.004.038.0 WSR %03.0~03.038.0 WSR

RS

WSRWS

• Belle and BaBar have new WS rate measurementsBelle and BaBar have new WS rate measurements


WSR RateSign Wrong theof tsMeasuremen

RRWSWS in in DD00->K->K++

%03.038.00 KDRWS

RRWSWS in multi-body hadronic modes in multi-body hadronic modes

%04.041.0

%07.043.012.011.0

0

11.010.0

00

KDR

KDR

WS

WS

• Belle and BaBar – Significant improvements in RWS

– x’ and y’ proper time fits soon!

• Information in multi-body modes not yet fully exploited– x, y, CP violation

• Situation more complicated• Dalitz plot fits of RS and WS required

to get limits on x, y, CPV• Need lots of statistics

00 KD


000 From KDK

05.005.006.0

000000

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LS

LS

KDKD

KDKDA

• Measurement of ratio of D0 rates into K0L0 and K0

S0 can be used to disentangle the CF and DCS amplitudes:

• K0L content of K0 and K0 is equal

• K0L content of K0 and K0 is opposite in sign to K0

S

• Get DCS rate from interference between the two

000

000

:CF

:DCS

KD

KD

Very important measurement!Very important measurement!Uncertainty still too large to limit Uncertainty still too large to limit KK, but more data on the way…, but more data on the way…

First measurement!First measurement!


0000 using mixing for Searches SKDDD

• Measure x and y rather than x’2 and y’

• RS and WS occupy the SAME Dalitz plot:

• Simultaneous measurement of relative strong phase between CF and DCS

• Only mode with sensitivity to sign of x!• Doubly-Cabibbo-suppressed modes

• y sensitivity comparable to CP eigenstate (eg., D0->K+K-) analyses

• Better scaling of sensitivity to x with int. luminosity than D0->K+- analysis

• Complicated Dalitz plot and proper time fit required

xx

yy


D0->K0spipi CLEO 00 oft Measuremen CLEO SKD

73529900 SKDN

• Time-independent Dalitz fit so far…

• Rich resonance structure– , K*-, …– Interference effects

• Fit results shown in projections

fitfitdatadata


00 oft Measuremen CLEO SKD

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KPhase convention:Phase convention:

Final fit with intermediate states:Final fit with intermediate states:

Right signRight sign

First measurement of strong phase difference between CF and DCS!First measurement of strong phase difference between CF and DCS!

0143* K

%2.03.06.0*0 KDRWS

Wrong signWrong sign

(Breit-Wigner resonance line shape)(Breit-Wigner resonance line shape)


00SKD

15,753 events!15,753 events!• CLEO will have CLEO will have RRDD, , xx, , yy, and , and AACPCP

measurements very soonmeasurements very soon

• BaBar analysis is in progressBaBar analysis is in progress

• Difficult analysisDifficult analysis

• Many systematic uncertainties will Many systematic uncertainties will scale with statisticsscale with statistics


00 and from oft Measuremen DKKDyCP

CPCP

CPCPy2

1

0

0

KKD

KDyCP

yy can be determined by measuring the lifetime difference between can be determined by measuring the lifetime difference between DD00 decays to decays to CPCP-even and -even and CPCP-odd final states:-odd final states:

Experimentally, it is easier to measure the lifetime difference of a Experimentally, it is easier to measure the lifetime difference of a CPCP-even decay -even decay relative to the non-relative to the non-CPCP final state final state DD00->K->K--+ + (assumes no(assumes no CP CP violation): violation):

These were some of the first These were some of the first DD mixing results to come out of the mixing results to come out of the BB factories factories

Many systematic errors will cancel in the ratio Many systematic errors will cancel in the ratio



KKD0 KD0

• Technique, resolution, and systematics are quite different at fixed target experiments (FOCUS, E791) and e+e- (Belle, BaBar, CLEO)

fs 40: F.T.

fs 160:

t

tee



yyCPCP from from DD00->K->K++KK--//++

%7.00.1 CPy

• FOCUS measurement is high relative to both CLEO and FOCUS D0->K+- limits– Unknown strong phase

difference

• New BaBar and Belle measurements pull yCP back towards D0->K+- limits

xx

yy

0

0 ,

D

KKD


Measurements of the Mixing Rate Using Wrong Sign Semileptonic D0 Decays

• Sensitive to mixing only (no DCS decays):

• Will need separate measurement of y if that turns out to be larger or comparable to x

• Measurements from– E791 (D0->Kl): – CLEO (D0->K*l):

• Sensitivity estimate from FOCUS• B factories should have results soon• Accessible to future experiments

– Hadron machines• Lepton helps triggering

– CLEO-c• Opposite side tag

2221

mix yxR

xx

yy

(*)0 KD


Three Types of CP Violation

f D0 D0 D0 D0

f

Df

2D

f

2

2 2

f

f f D0 D0 D0 D0

D0

f

2D0

2

+ +

Mixing (AM)

Interference between mixing and decay ()

Decay (AD)

|Af| |Af |


Searches for CP Violation• Ingredients for observing non-standard

model physics through CPV in D decays– Decay amplitude with contributions from at

least two diagrams with different weak phases

– Non-negligible strong phase shift• Likely to be non-zero in charm decays,

since SU(3) flavor symmetry is badly violated

• SM predictions:– O(10-3) or below in SCS modes:

• Due to interference of tree and penguin amplitudes

– No SM CPV in DCS and CF modes• Any observation is new physics

• Non-SM predictions:– Up to O(10-2)

%57.148.00 KKDACP

%6.21.20 DACP

%1.12.0 KKDACP

% 1600sin

% 123

% 116380mixing

1617decay

A

A(DCS) 0 KD


Charm Semileptonic Decay Rates and Form Factors

• Measurements of charm semileptonic branching fractions and form factors can be used to improve estimates of corresponding quantities in the B sector

– Leads to improved estimates of |Vub| and |Vcb|

• Several experiments are working on other semileptonic modes:– D0->llKl– Ds->l

02.062.0

0*

KD

KDR

New FOCUS result is a dramatic improvement (tiny backgrounds)!

(FOCUS also sees first evidence for an S-wave component)

0*KD


Motivation to Measure Charmed Particle Lifetimes

Non-perturbative QCD effects are important in weak decays of charmed particlesNon-perturbative QCD effects are important in weak decays of charmed particles

ExternalExternalSpectatorSpectator

InternalInternalSpectatorSpectator W ExchangeW Exchange W AnnihilationW Annihilation

Color-suppressedColor-suppressedHelicity and WavefunctionHelicity and Wavefunction

SuppressedSuppressed

Which processes are important in charmed meson and baryon decays?Which processes are important in charmed meson and baryon decays?

Challenge for theory is to Challenge for theory is to reproduce the observed lifetime reproduce the observed lifetime hierarchy in charmed baryons hierarchy in charmed baryons and mesonsand mesons


D Meson Lifetimes

Large observed ratioLarge observed ratio

is understood to be due to is understood to be due to destructive interference in destructive interference in diagrams contributing only to diagrams contributing only to DD++ decays decays

5.20

D

D

5.96.495 sD

9.67.1042 D

D

0D

sD

New precise measurements of New precise measurements of ((DD00) ) and and ((DD++) from FOCUS) from FOCUS

5.15.4100 D


Charmed Baryon Lifetimes

0c

c

c

fs 422 2019average

c

fs 3200average c

fs 106 98

0average

c

• Unlike charmed mesons, decays ofUnlike charmed mesons, decays of charmed baryons charmed baryons are not color or are not color or helicity suppressedhelicity suppressed

– W-exchange diagrams may be W-exchange diagrams may be importantimportant


Charmed Particle Lifetimes• Theory now describes most of the observed lifetime hierarchy

• Still some notable discrepancies with theory, however:

• Further measurements will help guide theory– New and more precise lifetimes

– Further analyses of charmed hadron decays (like c+)

– Tuning with data will yield better theoretical tools

2~

theory

experiment :

c

c


XJee / :Production CharmoniumPrompt

:VG 6.10at n expectatio NRQCD es

DominantDominant DominantDominantat at pp** endpoint endpoint

OO(10%)(10%) SmallSmall

• Tevatron Run 1A: CDF and D0 observe O(10-100) surplus in charmonium production cross section above NRQCD predictions– Something is missing in the model. Color-octet? Gluon splitting?

• Can test NRQCD using e+e- collisions at lower energies


XJee / :Production CharmoniumPrompt

PRL PRL 8888, 052001, (2002), 052001, (2002)

• Some NRQCD calculations predict Some NRQCD calculations predict a large yield in the endpoint region a large yield in the endpoint region due to due to color-octet color-octet ee++ee--J/J/gg

– This was not observed!This was not observed!• By comparing on/off resonance:By comparing on/off resonance:

• Cross sections for 2.0 GeV/c< Cross sections for 2.0 GeV/c< pp** < < pp**

maxmax::

ee++ee--J/J/gg

not observed innot observed in

endpoint regionendpoint region

C.L. %[email protected]/4 4 XJS B

pb 09.067.02

pb 09.004.005.1/09.011.0

XSee

XJee


XccJee / :Production CharmoniumPrompt

6.7

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Clear thresholdClear thresholdAt 2*mAt 2*mcc

J/J/SideSidebandband


XDJee (*)/ :Production CharmoniumPrompt

ee++ee--J/J/DD*+*+XX ee++ee--J/J/DD00XX

• Use Use DD*+*+->D->D00++, D, D00->K->K, KK, K, KK, K, , KKss

00, K, K00

signif. 3.5

5.10/ 6.30.3

*

XDJN signif. 7.3

9.14/ 4.57.4

0

XDJN

• Use Use DD00->K->K, KK , KK modesmodes


ccJee / :Production CharmoniumPrompt

Use JETSET rates to convert (e+e-J/D(*)X) to (e+e-J/cc)

Compare with measured (e+e-J/X):

Recall that prediction was only O(0.1)!

12.059.0

/

/ 15.013.0

XJee

ccJee


The Near Future in Charm Physics• DD00 mixing: mixing:

– New measurements ofNew measurements of x’x’ and and y’y’ from Belle and BaBar using from Belle and BaBar using DD00->K->K++- -

– KK from Belle by measuring different from Belle by measuring different D->KD->K isospin states isospin states • Can getCan get x x and and yy from from DD00->K->K++--

– Time-dependent Time-dependent CPCP asymmetry measurements in asymmetry measurements in DD00->K->K++KK--, , ++--

– Dalitz analyses:Dalitz analyses:• DD00->K->Kss

00++-- – Best sensitivity to Best sensitivity to xx with with BB factory samples (including its sign) factory samples (including its sign)– RS and WS interfere since they have the same final stateRS and WS interfere since they have the same final state– CLEO will have mixing/CLEO will have mixing/CPVCPV limits soon limits soon– Babar is working on this mode with 3X the CLEO statisticsBabar is working on this mode with 3X the CLEO statistics

• QCD input from charmQCD input from charm– Necessary ingredient to improve measurements of standard model Necessary ingredient to improve measurements of standard model

parametersparameters– Semileptonic branching ratios and form factors (several new FOCUS results Semileptonic branching ratios and form factors (several new FOCUS results

imminent)imminent)– ffDD and and ffDsDs measurements (Belle, BaBar) measurements (Belle, BaBar)– More lifetime measurements and spectroscopy at B factoriesMore lifetime measurements and spectroscopy at B factories– Further understanding of charmonium production puzzleFurther understanding of charmonium production puzzle


The Near Future in Charm Physics: D Mixing

• Does not include B factory results, for Does not include B factory results, for which sensitivity estimates have not which sensitivity estimates have not been shown:been shown:

• D0->K0s+-

• D0->K+- • D0->K*+l-

• Can expect great improvement when Can expect great improvement when these measurements are addedthese measurements are added

xx

yy

KD0

0

0 ,

D

KKD

(*)0 KD

00SKD


Future Experiments in Charm Physics• e+e- machines:

– Belle, BaBar--- running– CLEO-c: 2003 : L~(1-4)x1032/cm2s– BESIII: 2005-6 : L~1033/cm2s– Clean environment– Easy triggering– Lower cross section than in hadronic collisions

• Hadron machines: – CDF, D0, BTeV , LHCb, Compass, Hera-b– Difficult triggering on hadronic final states– Large cross section for charm (also 10X that for b’s)


CLEO-c Experiment• 2003: 3 fb-1 at (3770)

– L~3.6x1032/cm2s– 30M events, 6M tagged D decays– 310 times MARK III

• 2004: 3 fb-1 at ~sqrt(s)=4100 MeV– L~3.0x1032/cm2s

– 1.5M Ds pairs, 0.3M tagged Ds decays

– 480X MARK III, 130X BESII

• 2005: 1 fb-1 at the J/(3100)– L~1.0x1032/cm2s– 1 billion J/ decays– 170 times MARK III, 20X BESII


CLEO-c ExperimentCLEO-c reach for some key measurements…CLEO-c reach for some key measurements…

• Absolute branching fractions

• Semileptonic form factors

• D mixing searches

• CP violation searches

• Rare D decays

D

D

sD

%18%3%4.1

%25%105%32

%7%53%7.0

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none%2010%3.2

Presentfb 400

BaBar

fb 4-2

c-CLEOMeas.

1-1-

DBR

DBR

KDBR

f

f

s

D

D

s


Future Charm Physics at Hadron Machines• CDF

– Up to 107 D0->K– => ~15,000 WS D0->K+

• Assumes current trigger rate holds up

• Assumes same RS/WS efficiency ratio as B factories

– CPV reach of 10-3?

• LHCb – Trigger not optimal for charm

• BTeV– Up to 108 D0->K– => ~150,000 WS D0->K+

• Many assumptions in this number

– CPV reach down to 10-4?


Summary and Outlook• Many exciting new results from existing data

– Including many other important results I did not have time to cover

• Several new results expected within a year or less– B factories:

• Data is coming in fast• Eagerly awaiting results from analyses in progress

– CDF:• SVX triggers are taking charm!• Great potential if charm stays within the trigger bandwidth budget

• Future experiments– Funding decision soon on CLEO-c, first data in 2003– Many uncertainties in charm physics potential at hadron machines,

however:• Potential for huge gains in sensitivity• Preliminary Run II CDF charm plots show that it can be done!• BTeV trigger should be quite good for charm

• We can look forward to great advances in charm physics which will improve our understanding of the standard model and beyond

Documents

Recent Advances in Charm Physics