Two recent exotic results from Fermilab
& New light particles
( HyperCP events & D0 anomaly )
吳世哲 (Sechul
(S h l Oh,
Oh 오세철)
Academia Sinica
with Jusak Tandean
arXiv:1008.2153 (to appear in PLB)
JHEP 1001, 022 (2010);
Journal Club, NCTS, December 21, 2010
Outline
The HyperCP events
E pe iments HyperCP
Experiments:
H pe CP (Fermilab)
(Fe milab) , KTeV (Fermilab)
(Fe milab) , Belle (KEK)
data
Theoretical interpretations: a new light particle
Implications to B decay processes
Th D0 anomalous
l
lik
i dimuon
di
h
t
The
like-sign
charge
asymmetry
Experimental data from D0 (Fermilab)
Theory: a model-independent approach with a light spin-1 particle
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The HyperCP events
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Introduction
The detection of a new particle having a sub-GeV mass would likely
hint at the presence of physics beyond the SM.
This possibility has been raised recently by the observation of
three events for the rare decay mode
Σ+ Æ p μ+ μ-
with dimuon invariant masses narrowly clustered around 214.3 MeV
by the HyperCP Collaboration a few years ago.
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HyperCP data (Fermilab)
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(1/4)
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HyperCP data (Fermilab)
FCNC
(2/4)
internal conversion
SM
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Digression: History of β decay
n Æ p
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e-
(1/3)
_
νe
Rare B decays with HyperCP particle
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Digression: History of β decay
n Æ p
e-
_
ν?e
(2/3)
Î 2 body decay ?
?
Continuous energy spectrum
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Rare B decays with HyperCP particle
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Digression: History of β decay
n Æ p
e-
_
νe
(3/3)
Î 3 body decay !
Continuous energy spectrum
Î 3 body decay
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Rare B decays with HyperCP particle
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What if an opposite situation happens?
( i.e.,, 3 bodyy decayy ?? Î No,, 2 bodyy decayy !! )
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HyperCP data (Fermilab)
(3/4)
Æ 3-body
decay type
213.7, 214.3, 214.7 MeV/c2
Æ within 1 MeV/c2 !!
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HyperCP data (Fermilab)
(4/4)
The dimuon mass distribution for Σ+ Æ p μ+ μ- decay is expected
to be broad (Å 3-body decays).
Assuming a “3-body decay,” the probability that the three events have
the same dimuon mass (within 1 MeV/c2) is less than 1% !!
Î The unexpectedly narrow dimuon mass distribution may suggest
a two-body decay:
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Possible new particle (X0) interpretations
(1/2)
In the spinless case, X0 could be
g
Sgoldstino
in SUSY models
D.S. Gorbunov and V.A. Rubakov (2006)
CP-odd Higgs
gg boson in the next-to-minimal SUSY SM
(NMSSM)
X.G. He,, J. Tandean and G. Valencia ((2007))
In the spin-1 case, one possible candidate for X0 is
Gauge (U) boson of an extra U(1) gauge group in some extensions
of the SM
C.H. Chen, C.Q. Geng, and C.W. Kao (2008);
M. Pospelov
p
((2008);
); M. Reece and L.T. Wang
g (2009)
(
)
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Possible new particle (X0) interpretations
(2/2)
The presence of X0 in Σ+ Æ p μ+ μ- implies that it also contributes
to other ||ΔS|| = 1 transitions:
K Æ π μ+ μ- .
g,
e.g.,
X0
( Spin 0 case )
s
d
The “scalar part” of the s-d-X coupling is already constrained by
small
K Æ π μ μ data to be negligibly small.
The “pseudoscalar
pseudoscalar part
part” of the ss-d-X
d X coupling can be probed by
K Æ π π μ μ measurements.
Î KTeV experiment
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KTeV data (Fermilab)
arXiv:0911.4516
He, Tandean, Valencia
The scenario in which X has spin 0 and its ss-d-X
d X pseudoscalar coupling
is “real” is disfavored.
Î But, the case where the s-d-X
s d X psedoscalar coupling is
almost “purely imaginary” is still allowed.
The scenario in which X has spin 1 is not yet strongly challenged by
the KTeV data.
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Belle data (KEK)
PRL 105, 091801 (2010)
This results rule out some of “sgoldstino” scenario.
scenario
Î The Belle result also restricts the spinless X0 scenario.
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Focus on B decays
Various B meson decay processes can be used to search
for the hypothetical new particle X0.
Î B decays become important to probe the X0 .
Consider the contributions of X with “spin 1.”
C.H. Chen & C.Q. Geng (2007)
Adopt a model-independent approach.
Our assumptions are
Assume that X has both “vector”
vector and “axial-vector”
axial vector couplings to
b-d & b-s.
X does not interact strongly and decays inside the detector
with
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Effective Lagrangian with a Light X0
Assuming that X has spin 1 & does not carry electric or color charge,
the Lagrangian describing the effective b-q-X couplings (q = d, s) is
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B0 - bar B0 mixing
(1/3)
It is characterized by the physical mass difference
between the heavy and light mass-eigenstates in the
b
q
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X0
(q = d, s)
system.
q
b
19
B0 - bar B0 mixing
(2/3)
(1) q = d
(2) q = s
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B0 - bar B0 mixing
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(3/3)
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Inclusive decay b Æ q X
X0
b
q =d, s
Decay rate:
Branching ratio:
BaBar data:
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B Æ P X decays
(1/2)
X0
B
b
d, s
q
q
P, S
Decay amplitude & rate:
the vector coupling only!
the axial-vector coupling only!
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B Æ P X decays
(2/2)
Exp. data:
most stringent
constraints !
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B Æ V X decays
X0
B
b
d s
d,
q
q
V, A
Belle data:
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Combining B Æ PX & V X decays
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Our predictions: B Æ P X decays
Using gVd bounds:
Using gVs bounds:
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Our predictions: B Æ V X decays
Using gVd & gAd bounds:
Using gVs & gAs bounds:
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Our predictions: B Æ S X &
AX
B Æ SX
In contrast to the B Æ P X case,
case gAq is the only relevant coupling !
B Æ AX
In contrast to the B Æ V X case, the gVq term in the longitudinal
component H0 is dominant.
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Summary
The possibility that X has spin 1 is not well challenged by experiment
y
yet.
Various B meson decay processes can be used to search for the
hypothetical new particle X0.
Î The B Æ M X branching ratios are predicted to reach
the 10-7 level, which is comparable to the upper limits (~ 10-8)
for
o the branching
ba
g ratios
a o of
o B Æ ρ0 X,, K*0 X
recently measured by Belle.
We would like to encourage our experimental colleagues to make more
e g at Belle II and LHCb experiments.
experiments
efforts to search for the X0, e.g.,
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The D0 anomaly
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D0 Anomaly
(1/2)
X
B
B q0
B q0
X
‹
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D0 Anomaly
(2/2)
‹
‹
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Partial List of References (appeared in 2010)
~ 70 papers so far
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Theory
(1/2)
‹
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Theory
(2/2)
‹
Im
‹ Experimental values
New
Physics
Re
‹ SM predictions
Lenz, Nieste;
Kubo,, Lenz
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Effective Lagrangian with a Light X0
‹ Assuming that X has spin 1 & does not carry electric or color charge,
the Lagrangian describing the effective b-q-X couplings (q = d, s) is
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B0 - bar B0 mixing: Ms12
(1/3)
‹ It is characterized by the physical mass difference
between the heavy and light mass-eigenstates in the
(q = d, s)
system.
SM:
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B0 - bar B0 mixing: Ms12
X contribution:
b
X0
q
(2/3)
q
b
dominant if mX << mb
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B0 - bar B0 mixing: Ms12
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(3/3)
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B0 - bar B0 mixing: Γs12
(1/3)
‹
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B0 - bar B0 mixing: Γs12
(2/3)
‹
b
b
s
s
X0
Bs
s
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s
If mX < mb , mX can be produced
as a “physical particle” !
( cf. heavy Z’ )
s
Bs
s
b
b
42
B0 - bar B0 mixing: Γs12
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(3/3)
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Theory
(1/2)
‹
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asls, exp, (ΔΜsexp ΔΓsexp ), Γ(b->sX)
m X =0.5
=0 5 GeV
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m X =2 GeV
m X =4 GeV
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|Γs12 / Γs12,SM|,
sin φs
m X =4 GeV
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asls, exp, (ΔΜsexp ΔΓsexp ), Γ(b->sX)
m X =0.5 GeV
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m X =2 GeV
m X =4 GeV
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Summary
‹ We have investigated the possibility that the D0 anomaly arises
from the contribution of a light spin-1 particle to the Bs mixing.
‹ In contrast to a heavy Z’ particle, X can be produced as a physical
particle
ti l in
i Bs decay,
d
and
d so it affects
ff t nott only
l Ms12 , but
b t also
l
Γs12.
‹ Under constraints from available experimental data, the effect of X
can increase |Γs12| to become a few times larger than its SM value,
and enlarge the size of sinφs by a factor of a few hundred.
Î Can explain the D0 anomaly.
Î But, mX ~ 0.2 GeV is unlikely allowed.
Thank you!
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