2005-6-20c.h. chang, itp, as beijing1 chao-hsi chang ( 张肇西 zhao-xizhang) zhangzx@itp.ac.cn...

2005-6-20 C.H. Chang, ITP, AS Beijing 1

Chao-Hsi Chang ( 张肇西 Zhao-XiZhang) zhangzx@itp.ac.cn

I.T.P., Chinese Academy of Sciences 1. Introduction (the meson Bc & it

s mass)2. Decay (lifetime, …)3. Production (Tevatron vs LHC)4. Outlook

Production and decay of the meson Bc

—— A brief review of theoretical studies ——

(Based on the collaboration with Y.-Q. Chen, X.-Q. Li, C.-D. Lu, C.-F. Qiao, G.-L. Wang, J.-X. Wang, X.-G. Wu, et al)

2005-6-20 C.H. Chang, ITP, AS Beijing 2

1. Introduction (the meson Bc & its mass)

Of the six quarks u c t u c t d s b - u, d, s, light - c, b, t , heavy (top lifetime τ too short to form hadrons) Bc: double heavy-flavor mesons (unique in SM)

(weak decay only)

Very similar to, and very different from, hidden flavored heavy quarkonium J/ψ, ηc, …,Υ,ηb…. Good and new object for tests of PM, NRQCD, Lattice results etc.

2005-6-20 C.H. Chang, ITP, AS Beijing 3

1. Introduction (the meson Bc & its mass)

Bc mass : Lattice QCD : I.F. Allison et al, PRL 94 172001.

PM: Y.Q. Chen &Y.P. Kuang, PRD 46, 1165; Eichten & C.Quigg, PRD 49, 5845;….:

A. Kronfeld’s talk

2005-6-20 C.H. Chang, ITP, AS Beijing 4

1. Introduction (the meson Bc & its mass)

Theoretical estimate & LEP-I (ALAPH, PLB 402, 213; DELPHI PLB 398, 207): experimental studies of Bc can be carry out at Tevatron and LHC only!

Theoretical estimate at Z resonance (LEP-I) :

OPAL result PLB 420, 157:

The “early” day’s results

2005-6-20 C.H. Chang, ITP, AS Beijing 5

1. Introduction (the meson Bc & its mass)

• CDF discovery (1998 Observation) PRD 58, 112004

- 110 Pb-1 data ECM=1.8 TeV RunI Bc± J/(+-) ±

- The only previous evidence by CDF RunI

• CDF new Observation hep-ex/0505076

Bc± J/(+-) ± - 360 Pb-1 data ECM=1.96 TeV, RunIImBc=6287.0±4.8(stat)±1.1(syst) MeV/c2, 18.9±5.7 events

• D0 new Observation ICHEP-04 & Fermilab 4539-CONF

- 200 Pb-1 data ECM=1.96 TeV, RunII Bc± J/(+-) ±

Mass: 5.95 ± 0.34 GeV/c2

Events: 95 ± 12±11 +0.14

-0.13

Lifetime: 0.448 +0.123 ± 0.121 ps-0.096

- Br~2.4% + trilepton final state + easy to trigger

Note: even Br(Bc± J/(+-) ± )/Br(Bc± J/(+-) ± ) not available !

Present experimental status:

2005-6-20 C.H. Chang, ITP, AS Beijing 6

2. Decay

Bc lifetime: weak decay only (no strong &EM direct decay) according to spectator model and B & D mesons’ lifetime and annihilation: one may estimate More careful estimate:

vertex detector is useful in observation

Decay: Pure (radiative) leptonic Semoleptonic Nonleptonic

2005-6-20 C.H. Chang, ITP, AS Beijing 7

2. Decay

:

:

Bc lifetime (non-spectator effects involved)

: :

( )

In comparison with D & B mesons (input), we obtain:

2005-6-20 C.H. Chang, ITP, AS Beijing 8

2. Decay• Pure leptonic (radiative) decay (about measurement of the decay constant fBc):

Pure leptonic (tree) decay: (chiral suppression)

Radiative leptonic decay (decay constant):(escaped from chiral suppression)

QED corrections (one-loop):

2005-6-20 C.H. Chang, ITP, AS Beijing 9

2. DecayRadiative leptonic decay (QED correction to the tree level) in total:

Photon spectrum:

It is quite difficult for hadronic expt. to measure the decay constant!

2005-6-20 C.H. Chang, ITP, AS Beijing 10

2. Decay• Leptonic decay with light hadrons (color-singlet vs color-octet):

Color-singlet:

Short distance:

Long distance:

Charge lepton spectrum:

In the decay

2005-6-20 C.H. Chang, ITP, AS Beijing 11

2. DecayColor-octet:

P-wave (color-octet)

S-wave(color-octet)

Color-singlet

Near the endpoint of the charged lepton in the decay to observe the color-octet components!

Charged lepton spectrum:

2005-6-20 C.H. Chang, ITP, AS Beijing 12

2. Decay

• Semileptonic decays :

Transitions (decays with great momentum recoil)

The key factor:

2005-6-20 C.H. Chang, ITP, AS Beijing 13

2. Decay

Mandelstam formulation (or say composite quantum field theory) to

deal with the recoil effects in transitions:

The ‘wave function’ of bound state equation:

To cover a great range of momentum transfer (recoil), BS equation seems to be one of good choices for the problem.

2005-6-20 C.H. Chang, ITP, AS Beijing 14

2. Decay

Carry out the contour integrations & :

2005-6-20 C.H. Chang, ITP, AS Beijing 15

2. Decay

The semileptonic decays (S-wave) :

One I-W function

2005-6-20 C.H. Chang, ITP, AS Beijing 16

2. Decay

The semileptonic decays (P-wave or ) :

Two I-W functions

Recoil one

Normal one

Spectrum of charged lepton in the decays:

2005-6-20 C.H. Chang, ITP, AS Beijing 17

2. Decay

Nonleptonic decays (S-wave product): EFT+Factorrization

2005-6-20 C.H. Chang, ITP, AS Beijing 18

2. DecayNonleptonic decays (P-wave product or ):

2005-6-20 C.H. Chang, ITP, AS Beijing 19

2. Decay

•The lifetime is ‘quite long’ that the vertices of production and decay can be measured by vertex detector experimentally• Sizable decay channels are rich• The branch ratio of the decay to is quite great (form factors)• The branch ratio of decay to or is very large• Study two flavor ‘simultaneously’ (Vcb & Vcs)• Radiative pure leptonic decays escape from chiral suppression, but to measure the decay constant is still difficult • The color-octet component might be observable through • …….

2005-6-20 C.H. Chang, ITP, AS Beijing 20

3. Production (Tevatron & LHC)

Gluon-gluon fusion mechanism dominant

36 Feynman diagrams for complete calculations

‘Complete LO computation’: information about the accompany quark-jets is kept

QCD factorization:

Subprocess:

2005-6-20 C.H. Chang, ITP, AS Beijing 21

3. Production (Tevatron & LHC)

The lowest order calculations: uncertainties from

The cross-section at LHC is greater than that at Tevatron

S-wave state production

2005-6-20 C.H. Chang, ITP, AS Beijing 22

3. Production (Tevatron & LHC)

LHC

Tevatron

Uncertainty from mC

2005-6-20 C.H. Chang, ITP, AS Beijing 23

3. Production (Tevatron & LHC)

and

Uncertainty

from PDFs

2005-6-20 C.H. Chang, ITP, AS Beijing 24

3. Production (Tevatron & LHC)

Uncertainties: quite great; sensitive to Q2, mc . High order calculation can suppress them but it is too complicated.

Uncertainty from

2005-6-20 C.H. Chang, ITP, AS Beijing 25

3. Production (Tevatron & LHC)P-wave excited state productionTo match the wave functions correctly (special attention on the spin structure), we start with the Mandelstam formulation on BS solution:

2005-6-20 C.H. Chang, ITP, AS Beijing 26

3. Production (Tevatron & LHC)

1P1

3P1 3P23P0

3P0

3P1

1P1

3P2

LHC TEVATRON

P-wave production ( color-singlet)

To see the contributions to Bc

& the P-wave characters

2005-6-20 C.H. Chang, ITP, AS Beijing 27

| |2| |2 | |2

3. Production (Tevatron & LHC)

Color octet may be comparable with that of color singlet

Color-singlet (P-wave) M.E.

Color-octet (S-wave) M.E.

Scaling rule of NRQCD:

2005-6-20 C.H. Chang, ITP, AS Beijing 28

3. Production (Tevatron & LHC)

LHC

Tevatron

Color-octet 1S0

Color-octet 3S1

Color-singlet 3P2

Color-singlet 1P1

Color-singlet 3P0

Color-singlet 3P1

P-wave production color-singlet vs color-octetColor-octet

2005-6-20 C.H. Chang, ITP, AS Beijing 29

• The cross section of Bc at LHC is greater than that at Tevatron by one and more order of magnitude• The uncertainties are quite big for LO PQCD• The cross section is at the order 10-3 (less) of B meson production

3. Production (Tevatron & LHC)

Experimental needs of the M.C. generator:Difficulties of the experiments in Hadronic Collider

High efficiency for the generator

Generator: BCVEGPY1.0 (S-wave, helicity techniques )

BCVEGPY2.0 (S,P-wave, Color-octet,…& Mixture)

Signals for feasibility studies

CPC Lib. & hppt://www.itp.ac.cn/~zhangzx/

2005-6-20 C.H. Chang, ITP, AS Beijing 30

3. Production (Tevatron & LHC)

(ours)another

The generator is tested by comparing with PYTHIA

The generator is proved to be suitable for the original purpose.

2005-6-20 C.H. Chang, ITP, AS Beijing 31

3. Production (Tevatron & LHC)

- Bc Bs + h+ + X?

beam beam※PV

Bc: 140m

6.4GeV?

Bs: 438m

5.4GeV Oscilla.

h+: , ,,e() tracks: pT~100-500MeV,too soft, off-line only

※Ds- : 147m

1.968GeV

※K

0*

-

K+

K-

(36%)

(8%)

(3.3%)

(100%)

- Bc Bs associated h+ (as a tag for Bs).

- Br[ BcBs +h+ +X ] as Bs CP violation source ? Bc decay vertex is crucial .

To be a possible source for tagged Bs (at LHC) ?

2005-6-20 C.H. Chang, ITP, AS Beijing 32

3. Production (Tevatron & LHC)

beam beam

-

※PV

Bc: 140m

6.4GeV

Bs: 438m

5.4GeV

oscillati

on

h+: , ,,e() tracks: pT~100-500MeV,too soft, off-line only

※Ds- : 147m

1.968GeV

※K

0*

K+

K-

(36%)

(13%)

(3.3%)

(100%)

※

b-jet(B0,B+)

(pT>1)

Br~10%!

- Bs decay: the Bc decay vertex might be fixed with soft h+ tracks, Br increases by 50%The from the other side b-quark fragmentation Muon + opposite 2nd VTX (on Ds)

under feasibility investigation !

2005-6-20 C.H. Chang, ITP, AS Beijing 33

4. Outlook

• Experimental studies on Bc meson have been started at Tevatron

already, and fresh results will be issued ‘from time to time’.• The production cross-section at LHC is greater than that at

Tevatron, so further experimental studies at LHC can be expected.• Some model predictions will be tested.• Theoretical estimates are requested to decrease the uncertainties

and to increase the precision with data being accumulated.• Bc studies may solve some puzzles relating to charmonium

e.g. the observation may clarify up some of contents

in , in meson there are more charm quarks than in meson.

and some ‘unexpected things’ might be found.• ……

2005-6-20 C.H. Chang, ITP, AS Beijing 34

Thanks