29
Charmed Ba ryons Char med Baryons Hai-Yang Cheng Academia Sinica, Taipei Spectroscopy Strong & EM decays Charm 2007, Cornell, August 5-8, 2007

Charmed Baryons

  • Upload
    corbin

  • View
    73

  • Download
    0

Embed Size (px)

DESCRIPTION

Charmed Baryons. Charmed Baryons. Hai-Yang Cheng Academia Sinica, Taipei Spectroscopy Strong & EM decays. Charm 2007, Cornell, August 5-8, 2007. Spectroscopy. In SU(3) representation, diquark = 3  3 = 3 +6 - PowerPoint PPT Presentation

Citation preview

Page 1: Charmed Baryons

Charmed Baryons Charmed Baryons

Hai-Yang Cheng Academia Sinica, Taipei

Spectroscopy Strong & EM decays

Charm 2007, Cornell, August 5-8, 2007

Page 2: Charmed Baryons

2

Spectroscopy

Many new resonances observed:

Ground state: c

*(2770) with mass = 2768.33.0 MeV (BaBar)

Orbitally excited p-wave states: L=1

e.g. c(2593), c(2625), … etc. (CLEO)

Positive parity excitations: L=2,1,0

e.g. JP[c(2880)]=5/2+ (Belle)

In SU(3) representation, diquark = 33 = 3+6

3: c+,c

+,c0, all decay weakly

6: c0,’+

c,’0c,c

++,+,0 only c0 decays weakly

c*0,*+

c,*0c,c

*++,+,0 S=0 S=1

Page 3: Charmed Baryons

3

Orbitally excited charmed baryon states

L½+L¸=Ll (not L½+L¸=L !)

Two possible p-wave states (L+L=1):

1. L½=1, L¸=0; antisymmetric under q1q2

2. L½=0, L¸=1; symmetric under q1q2

Jl=Sl+Ll, J=Sc+Jl

symmetric

antisymmetric

(denoted by a tilde)

¤cJ ` (JP )

In HQ limit, Jl & Sc are separately conserved

Page 4: Charmed Baryons

4

First positive parity excitations (L+L=2):

1. L½=2, L¸=0; L½=0, L¸=2 symmetric under q1q2; Ll=2

2. L½=L¸=1 antisymmetric under q1q2; Ll=2,1,0

Page 5: Charmed Baryons

5

½-

½-

½-

3/2-

3/2-

Only the parity of c & c(2880) has been measured

3/2-

3/2-

3/2-

3/2-

Page 6: Charmed Baryons

6

c(2595), c(2625) → c1(1/2-,3/2-)

c1(1/2-)![c]S, c1(3/2-)![¤c¼¼]P, [c]D

⇒ ¤c(2625) is narrower than ¤c(2595)

c0→[c]S, c1→[c]

P, c2→[

c]D

Since c(2880) observed in c spectrum has a width 65 MeV, and (c0→c) 405 MeV from HHChPT ⇒ c(2880) is most likely to be a c2(3/2-)

c(2800): c2(3/2-), c1(3/2-), c0(1/2-)

Antitriplet charmed baryons:

½+ (c, c+, c

0)

½- (c(2595)+, c(2790)+, c(2790)0)

3/2- (c(2625)+, c(2815)+, c(2815)0)

c(2790), c(2815) → c1(1/2-,3/2-)

Page 7: Charmed Baryons

7

c(2880): first positive parity excited charmed baryon

Candidates for spin-5/2 states:

2/5~

,2/5~

,2/5~

,2/5~

,2/5 ''3

''2

'222 ccccc

45.142.02

7

))2880((

))2880((

2

7

)][)2/5(~

(

)][)2/5(~

(5

*5

2

*2

cc

cc

Dcc

Dcc

p

p

23.029.05

4

))2880((

))2880((

5

4

)][)2/5((

)][)2/5((7

*7

2

*2

cc

cc

Fcc

Fcc

p

p

36.029.04

5

))2880((

))2880((

4

5

)][)2/5(~

(

)][)2/5(~

(7

*7

3

*''3

cc

cc

Fcc

Fcc

p

p

)%4.61.24())2880((

))2880(( 1.15.4

*

cc

cc ⇒ parity assignment for c(2880)

Angular analysis of c(2880)→ cby Belle ⇒ J=5/2 is preferred

JP=5/2- is

disfavored

However, c2(5/2+) can decay into c* in a P-wave

robust prediction

c(2880) could be an admixture of 2/5~

& 2/5 ''32 cc

HQS

Chua,HYC (’07)

Page 8: Charmed Baryons

8

Remarks:

Based on the diquark idea, JP[c(2880)]=5/2+ has been predicted by

Wilczek and Selem before Belle experiment

Peking group (Zhu et al., hep-ph/0704.0075) has studied the strong

decays of charmed baryons using 3P0 model

⇒ Since c(2880) decays into D0p, it cannot be a radial excitation

⇒ c(2880) is a pure state

c2(5/2+) leads to too large ratio of c*/c for L=0, L=2,

and too large width ( 78 MeV) for L=2, L=0

2/5~ ''

3c

2/5~ ''

3c

An issue about mass: According to QM, m[c2(5/2+)] 2910MeV,

The mass of is even higher

Page 9: Charmed Baryons

9

Other even-parity excitated states ?

c(2765): even-parity orbital excitation ½+, supported by

QM (Capstick, Isgur ‘86) & Skyrme model (Oh & Park ‘96)

radial excitation 2½+ (Ebert, Faustov, Galkin ‘07)

c(2940): 3/2+, 5/2-, can be tested by measuring the ratio c*/c

m(D*0)+m(p)=2945 MeV ⇒ a D*0p molecular ½- state for

c(2940) with binding energy 5 MeV ? (X.G. He et al.)

first radial excitation of c with JP=3/2+ (Ebert et al.)

M(c)-M(c) 180200 MeV for JP= ½+, ½-,3/2-

⇒ c(2980) & c(3077) considered as counterparts of c(2765) & c(2880)

c(2980): ½+, or 2½+

c(3077): 5/2+,

c(3055): ? c(3123): ?

c(2980) is broader than c(3077); both are above D threshold

or c(2765)

Page 10: Charmed Baryons

10

½+,2½+

3/2+,5/2-

5/2+

5/2+

½+,2½+ ½+,2½+

Page 11: Charmed Baryons

11

5/2+

3/2-

3/2+1/2+

c c c c

1/2+5/2+

Page 12: Charmed Baryons

12

An ideal place for testing heavy quark symmetry and chiral symmetry: heavy hadron chiral perturbation theory (HHChPT)

Strong decays of s-wave charmed baryons are governed by two couplings g1 & g2. While info on g1 is absent due to the lack of c

*→c, g2 is fixed to be 0.61±0.04 by the measured rate of c

++→c++

(in units of MeV)

Wise; Yan et al.; Burdman, Donoghue (’92)

(c*) 7(c), though they have same widths in HQ limit

Page 13: Charmed Baryons

13

S-wave (D-wave) transitions between s-wave and p-wave baryons are described by six couplings h2,…,h7 (eight couplings h8,…,h15)

Pirjol, Yan (’97)

h2

h10

h10 &

h8=h

10

1308.010.010

114.0102.02 MeV 10)86.0( ,437.0

hh Chau, HYC

Page 14: Charmed Baryons

14

Strong decays of p-wave charmed baryons

⇒ isospin violation: c+0 2 c

0+ , c00 c+- as 0 is lighter than

Strong decays of c(2593) are near threshold⇒ sensitive to masses

(c0(1/2-)→c) 405 MeV

Page 15: Charmed Baryons

15

Electromagnetic decays

cccccc

cccc

cccc

BB

BB

BB

*''**6

*6

'**3

*6

'36

, , :

, :

, :

suitable framework: HHChPT+ QM (Yan et al. ’94)

(in units

of keV)

It will be very difficult to measure EM decay rates

Page 16: Charmed Baryons

16

Other topics:

Hadronic weak decays of c+,c

+,c0,c

0

Charm-flavor-conserving weak decays

Lifetime differences

Semileptonic decays

Weak radiative decays

discussed in back-up slides

See review article on charmed baryons in Tau-Charm

Physics Book at BESIII. Hope it will be posted on archive soon

Page 17: Charmed Baryons

17

Conclusions

HQS & S can be nicely tested in charmed baryon sector.

Strong couplings g2, h2 & h10 are updated

Many orbitally excited charmed baryons have been observed

Some form multiplets

c(2880) is a first even-parity excited state. It could an

admixture of 2/5~

& 2/5 ''32 cc

We need more strong decay measurements to pin down spin-

parity assignment

Page 18: Charmed Baryons

18

Back-up Slides

Page 19: Charmed Baryons

19

Lifetimes

c+ 44226

c+ 2006

c0 112+13

-10

c0 6912

10-15s

...)(192

)(33

22

03

52

cc

CKMcF

c m

A

m

AAV

mGfB

D+ 10407

Ds+ 5007

D0 410.11.5

heavy quark expansion:

Pauli interference & W-exchange are 1/mc3

corrections, enhanced by p.s. enhancement factor of 162

c decay W-exchange

destructive P.I.

constructive P.I.

Page 20: Charmed Baryons

20

Dec Ann Int(-)

Int(+) Semi-inclusive

(10-13s) Expt

c+ 1 s2 1 c2 small P.I. 3.68 4.420.26

c+ 1 c2 1 s2 2.64 2.000.06

c0 1 1 1 1 small P.I. 1.93 1.12+0.13

-0.10

c0 1 6s2 10/3c2 large P.I. 1.71 0.690.12

s=sinC, c=cosC

Lifetime hierarchy (c+)>(c

+)>(c0)>(c

0) is qualitatively understandable, but not quantitatively.

It has been claimed that lifetimes can be accommodated (except c

+) provided that hybrid renormalization is employed and replacement of fD by FD is made (Shifman, Blok, Guberina, Bigi…..)

It is difficult to explain (c+)/(c

+)=2.210.15

1/mc expansion is not well convergent and sensible

Page 21: Charmed Baryons

21

Hadronic weak decays

Complications:

Baryons are made of three quarks

Factorization approximation generally doesn’t work

W-exchange is not subject to helicity & color suppression

Current algebra is no longer applicable as the outgoing meson is

far from being “soft”. Also this soft-meson technique is not

applicable to vector meson production

Page 22: Charmed Baryons

22

Hadronic weak decays

Diagrammatic scheme (Chau, HYC, Tseng ‘96)

Two distinct internal W emission diagrams, three different W exchange diagrams

Need information of decay asymmetry to extract s-wave and p-wave amplitudes separately

Page 23: Charmed Baryons

23

Dynamical model calculation

pole model:

Consider low-lying pole contributions:

s-wave is governed by ½- resonances

p-wave is dominated by ½+ ground-state baryons

Relativistic QM: Korner, Kramer, Ivanov,…

iffi uBAuiPBBM )()( 5

Page 24: Charmed Baryons

24

BRs of Cabibbo-allowed decays

W-exchange plays an essential role

Page 25: Charmed Baryons

25

Decay asymmetry for Cabibbo-allowed decays

??

Longitudinal pol. of daughter baryon from unpol. parent baryon

⇒ information on the relative sign between s- and p-waves

Page 26: Charmed Baryons

26

Decay modes that proceed through factorizable diagrams

c+→ p ⇒ |a2|=0.600.10, close to c2

1/Nc is also applicable to charmed baryon sector

c0→-+ ⇒ a1

c0→*0K0 ⇒ a2

Page 27: Charmed Baryons

27

Charm-flavor-conserving weak decays:

Light quarks undergo weak transitions, while c quark behaves as a “spectator” e.g. cc, c’c

Br(c0c

+-) = 2.9 10-4

Br(c+c

+0) = 6.7 10-4

Br(c0’+

c-)= 4.5 10-6

should be readily accessible soon

Page 28: Charmed Baryons

28

Semileptonic decays

Semileptonic rate depends on Bc→B form factors

|→ NRQM | RQM LFQM QSR QSR

in units of 1010s-1

Six form factors are reduced to two in mQ limit

Page 29: Charmed Baryons

29

Weak radiative decays

Charm-flavor-changing

c+→+, c

0→0

Charm-flavor-conserving

c→c, c→c

i) e.m. penguin cu

ii) emission from external quark in W-exchange

emission from W boson in W-exchange

0.86 ,106.3)(

0.86 ,109.4)(500

5

c

c

Br

Br