Choong Sun Kim (C.S. Kim)

Department of Physics, Yonsei University, Korea

FORWARD-BACKWARD ASYMMETRY OF TOP QUARKIN UNPARTICLE PHYSICS

ICPP-ISTANBUL II

2nd International Conference on Particle Physics

Outline

Motivation Observation at Tevatron Phenomenon & History over Q-FBA Possible Models & Mechanisms Our results in Unparticle Physics Summary

1. Observations at TevatronD PRL100, 142002 (2008)

Process: p pbar → t tbar + X;

the first measurement of the

integrated forward-backward (FB) charge asymmetry

D Observable:

Nf(b): number of events with a positive (negative) Δy

y = yt – ytbar , y: rapidity

f bFB

f b

N NA

N N

Observations at TevatronCDF: PRL101, 202001 (2008)

CDF observable:

With 1.9 fb−1

With 3.2 fb-1

cos cos

cos co

0

0 0s

0

pp frame:ppFB

N Q N QA

N Q N Q

0 0

0 0

tt frame:ttFB

N Q N QA

N

y

Q

y

y yQ N

1

2 2ˆ

cos2 tanh

1 4 / ( )4

ttt t

t t

y y ym s m

0.08

0.24 0.1

17

4

0.ppFB

ttFBA

A

0.193 0.065 0.024ppFBA

If CP is invariant,

2. PhenomenonAsymmetry

Integral charge asymmetry

Ni (j): # of particle i observed in

the direction of particle j

Forward-backward asymmetry

( )

( )t

Ctt

tN p N pA

N p N p

( )

( )t

Bt

Ft

t pN p NA

p pN N

( )t t C FBN pp N A A

History over Heavy Quark FBA1. Brown et al, PRL43(1979)1069; FBA of c-quak production in analogy to QED.

2. [1] F. Halzen, P. Hoyer, C.S. Kim, PLB195(1987)74; FBA of b,t-quark in QCD from (i) radiative corrections to q-qbar annihilation, (ii) interference between different contributions to qg t+tbar+q, (and its CP conj.)

~~~ no more progress about 10 years

3. [2] J.H. Kuhn, G. Rodrigo, PRL81(1998)49; detailed QCD calculation

4. [3] O. Antunano, J.H. Kuhn, G. Rodrigo, PRD77(2008)014003; FBA of t-quak within the SM = 0.050 +- 0.015

5. D0 and CDF measured FBA ~ 20% Now so many works beyond the SM

SM prediction Kuhn& Rodrigo PRD59(99); Antunano etal PRD77(08);

Leading order (d): charge asymmetry vanishes

Next-to-leading order: nonzero AC will be induced by the interference between (a) and (b) and the

interference between (c) and (d)

Since the measurements of D and CDF have 2 deviation from the SM, the observed large FBA strongly

indicate the new Physics

( )0.051(6)

( )t

Ct

t

t

N y N yA

N y N y

0.193 0.065 0.024CD

ppFB F

A

3. Models by s-channelFerrario & Rodrigo PRD80(09); Frampton etal, arXiv:0911.2955

Axigluon: Color-octet gauge bosons (AGs) that couple to quarks with a

nonvanishing axial-vector couplings It could be generated by symmetry

breaking from SU(3)R SU(3)L to

SU(3)C

AG could be as heavy as TeV

ˆcosc

Models by s-channelDjouadi Moreau, Richard,Singh, arXiv:0906.0604

KK excitations of gluons in warped extra dimensional models The couplings of KK to quarks have the axial-vector component At

FB|RS ~ few %

12ˆ KK KK KKD s M i M

Models by t-channelJung, Murayama, Pierce, Wells, arXiv:0907.4112

. .Z X RL g uZ hP ct

• New Z’ gauge boson

• Nonuniversal Z’ model

Models by t-channelCheung,Keung, Yuan PLB682(09); Barger, Keung, Yu:

arXiv:1002.1048

2 ˆ(1 cos )

2ts

t m

Model-independent approach D.W. Jung, P. Ko, J.S. Lee, S.H. Nam, arXiv:0912.1105

Effective interactions

SUSY R-parity violation by J. Chao, Z. Heng, L. Wu and J.M. Yang, arXiv:0912.1447

Diquark models Shu, Tait, Wang :0911.3237, Arhrib, Benbrik,Chen:0911.4875,

Dorsner etal :0912.0972

Diquark is the particle that couples to quarks by qaT C qb Hab ,

where a, b are the color indices

The possible representations under SU(3)CSU(2)LU(1)Y :

(6, 3)1/3 , (6,1) 4/3,1/3,-2/3 ,

(3, 3)-1/3 ,, (3,1)2/3,-1/3,-4/3

We would like to pay attention to (3,1,-4/3) and (6,1,4/3)

The relevant interac-tions

The corresponding Feynman diagram

3 6 63 ,ij ji ij jifff f

4. Unparticle Physics, s-channel C.H. Chen, Gorazd Cvetic, C.S Kim, PLB694(2011)393

A stuff dictated by scale invariance, proposed by Georgi

Here, we considered colored unparticle, in which the effective interactions to quarks are proposed to be

Due to nonintegral scale dimension and no mass scale in the propagator, it will be interesting to see the unparticle effects

on the top-quark FBA

Phys.Rev.Lett.98:221601,2007Phys.Lett.B650:275-278,2007

1 5(1

)qA

q a aV Ud

U

L qq T O

Cacciapaglia, Marandella, Terning, JHEP0801:070,2008

1/ ,q d qU g VorA

with

Then,

Scattering amplitude combined with the SM becomes

Spin and color averaged amplitude-square is

3 physical observables are:

3 independent parameters: ( , ) first we set 2 remaining dimensionless parameters are from assuming flavor blind (colored) unparticle and finally the scale dimension i.e. the flavor-blind and chirality-independent couplings

Experimental numerical constraints:

M. Cacciari et al., JHEP 0809, 127 (2008); N. Kidonakis and R. Vogt, Phys. Rev. D 78, 074005 (2008); S. Moch and P. Uwer, Phys. Rev. D 78, 034003 (2008)

d_U=1.28+-0.22, lambda=2.05+-0.45

Phys.Rev.Lett.102:222003,2009 (CDF).

For detailed analysis, cosider Mtt-restricted FBA,

5. Summary An unexpected large FBA of top-quark is observed by D and

CDF: strongly indicate the new physics effects (NLO effects). Various possible solutions to the “anomaly” are proposed, like

axigluon, KK excitations of gluon, Z’, W’, colored scalars, etc

We investigated whether colored flavor-conserving unparticle can explain the measured FBA of ttbar production at Tevatron. With a natural assumption of quark flavor-blind and chirality- independent unparticle, UP contribution can explain the deviation.

Thank you for your attention