Table Of ContentSUSY Higgs boson flavor-changing neutral currents at the LHC
6
0 Santi B´ejarab, Jaume Guaschc, Joan Sola`cb∗
0
2 aGrup de F´ısica Teo`rica, Universitat Aut`onoma de Barcelona, E-08193,Bellaterra, Barcelona,
n Catalonia, Spain
a
J bInstitut de F´ısica d’Altes Energies, Universitat Aut`onoma de Barcelona,E-08193,Bellaterra,
0 Barcelona,Catalonia, Spain
3
cHEP Group, Departament d’Estructura i Constituents de la Mat`eria, Universitat de Barcelona,
2 Diagonal 647, E-08028 Barcelona,Catalonia, Spain
v
1 UAB-FT-597, UB-ECM-PF-06/03, hep-ph/0601191
9
We compute and analyze the Flavor-Changing Neutral Current (FCNC) interactions of Minimal Supersym-
1 metric Standard Model Higgs bosons (h ≡ h0, H0, A0) with heavy quarks (top and bottom), focusing on
1
the strongly-interacting sector. We correlate the Higgs bosons production cross-section at the LHC with the
0
FCNC decay branching ratios and find the maximum allowed values of the production rates, σ(pp → h →
6
0 qq′) ≡ σ(pp → h) × B(h → qq′) (qq′ ≡ tc or bs) after taking into account limits from low energy data
/ on flavor-changing interactions. We single out the top quark channel, with a maximum production rate of
h σmax(pp→h→tc)≃10−3−10−2pb, as themost promising FCNC channel tobe detected at theLHC.
p
-
p
e 1. Introduction the SM. In the SM the FCNC effects are com-
h
pletelyabsentatthetree-level. Atoneloop,how-
:
v The possibility that Nature hides the last pos- ever,theyarepossible,butthenthecontributions
i sible symmetry of the S-matrix, Supersymmetry
X fromthenewparticlesenteronequalfootingwith
(SUSY),intheformofabrokensymmetryofthe
thosefromSMparticles. Incertainregionsofthe
r
a fundamental interactions is one of the most in- parameterspacethenewphysicaleffectsmaywell
triguing puzzles over the last 30 years of high
dominate the SM contributions. This is particu-
energy physics. SUSY offers a most tantalizing
larly so when the SM one-loop effects turn out
paradigm to unify Particle Physics interactions
to be highly suppressed. In such situations the
with Gravity, and it might even provide a clue
sole observation of these FCNC processes would
to a more fundamental superstring unification of
be instant evidence of new physics. An example
all interactions. As such SUSY will be scruti-
of this kind of appealing scenarios occurs within
nized in great detail at the LHC. It also offers
the FCNC physics of the SM Higgs boson (HSM)
a possible solution to the longstanding natural-
interactionswithquarks. Forexample,theFCNC
ness problem in the Higgs sector of the SM [1].
vertexHSMtcmaylead(atoneloop)tosuchrare
If SUSY is realized around the TeV scale, the
decaysast→HSMc orHSM →tc,depending on
LHC experiments shall be able to directly pro-
the mass of HSM. Both of these modes are ex-
duce the SUSY particles for masses smaller than
tremely suppressed at one loop, with branching
a few TeV [2]. Among the many strategies de- ratios of order 10−14 or less [3,4], hence 10 or-
visedtohuntforSUSY,Flavor-ChangingNeutral
dersofmagnitudebelowothermoreconventional
Currents (FCNC) offer perhaps a unique labora-
(and relatively well measured) FCNC processes
tory to seek for the new signs of physics beyond
like b→sγ [5].
The MinimalSupersymmetricStandardModel
∗Contribution to the proceedings of 7th International
(MSSM) introduces new sources of FCNC inter-
Symposium on Radiative Corrections, Shonan Village,
actions mediated by the strongly-interacting sec-
Japan,October2-7,2005
1
2 Santi B´ejar, Jaume Guasch, Joan Sola`
tor1. They are produced by the misalignment relevant channels: Γ(h → ff¯,ZZ,W+W−,gg).
of the quark mass matrix with the squark mass The off-shell decays Γ(h → ZZ∗,W±W∓∗) have
matrix, and the main parameter characterizing also been included. This is necessary to consis-
these interactionsis the non-flavor-diagonalterm tently compute the total decay width of Γ(h0 →
in the squark-mass-matrix, which we parame- X) in regions of the parameter space where the
terize in the standard fashion [8] as (M2) = maximization of the cross-section (1) is obtained
ij
δ m˜ m˜ (i 6= j), m˜ being the flavor-diagonal at the expense of greatly diminishing the partial
ij i j i
mass-term of the i-flavor squark. Since there are decay widths of the two-body process h0 → b¯b
squarks of different chiralities, there are different (due to dramatic quantum effects that may re-
δ parameters for the different chirality mixings. duce the CP-even mixing angle α to small val-
ij
In this work we will assume flavor-mixing only ues [13]). The one-loop decay rate Γ(h → gg)
among the Left-Chiral squarks, since these mix- has been taken from [14] and the off-shell decay
ing terms are expected to be the largest ones by partial widths have been recomputed explicitly.
Renormalization Group analysis [9]. The MSSM Higgs boson production cross-
Some work in relation with the MSSM Higgs sections have been computed using the programs
bosons FCNCs has already been performed [4,7, HIGLU 2.101 and PPHTT 1.1 [14,15]. These
10,11]. In this work we compute and analyze programs include the following channels: gluon-
the production of any MSSM Higgs boson (h = gluonfusion,andassociatedproductionwithtop-
h0,H0,A0) atthe LHC, followedby the one-loop and bottom-quarks. We have used the leading
FCNC decay h → bs or h → tc, and we find order approximation for all channels. The QCD
the maximum production rates of the combined renormalizationscaleissettothedefaultvaluefor
cross-section: each program. We have used the set of CTEQ4L
PDF [16].
σ(pp→h→qq′) ≡ σ(pp→hX)B(h→qq′)
For the constraints on the FCNC parameters,
B(h→qq′) ≡ Γ(h→qq¯′+q¯q′) (1) we use B(b → sγ) = (2.1−4.5)×10−4 as the
iΓ(h→Xi) experimentally allowed range within three stan-
P
darddeviations[5]. We alsorequirethatthe sign
qq′ being a pair of heavy quarks (qq′ ≡ bs or
of the b → sγ amplitude is the same as in the
tc), taking into account the restrictions from the
SM [17]2.
experimentaldeterminationofB(b→sγ)[5]. For
Running quark masses (m (Q)) and strong
othersignalsofSUSYFCNCattheLHC,without q
coupling constants (α (Q)) are used throughout,
Higgs bosons couplings see Ref. [6]. s
withtherenormalizationscalesettothedecaying
Higgs boson mass in the decay processes.
2. Computation setup
Given this setup, we have performed a Monte-
In this section we give a summarized explana- Carlo maximization [18] of the cross-section (1)
tion of the computation. For further details see overthe MSSMparameterspace,keepingthe pa-
Refs. [4,11]. rameter tanβ fixed, and under the simplification
We include the full one-loop SUSY-QCD con- that the squark and gluino soft-SUSY-breaking
tributions to the FCNC partial decay widths parameter masses are at the same scale:
Γ(h→qq′) in the observable (1).
The Higgs sector parameters (masses and CP- md˜L =md˜R =mu˜R =mg˜ ≡MSUSY . (2)
evenmixingangleα)havebeentreatedusingthe
Although we have performed a full one-loop
leading m and m tanβ approximation to the
t b
computation, involving the exact diagonalization
one-loop result [12].
ofthe6×6squarkmassmatrix,itisenlightening
TheHiggsbosonstotaldecaywidthsΓ(h→X)
tolookattheapproximateleadingexpressionsto
are computed at leading order, including all the
1For a brief description of these interactions see e.g. 2Thisconstraintautomaticallyexcludesthefine-tuned re-
Ref.[6],fordetailssee[7]. gionsofRef.[4].
SUSY Higgs boson flavor-changingneutral currents at the LHC 3
0.004 h H0 h0 A0
0.0035 B(h→bs) 9.1×10−4 3.1×10−3 9.1×10−4
Γ(h→X) 11.2GeV 1.4×10−3GeV 11.3GeV
0.003
δ23 10−0.43 10−0.8 10−0.43
0.0025
Β(H0−> q q’) MSUSY 1000GeV 975GeV 1000GeV
0.002 Β(h0−> q q’) A −1500GeV −1500GeV −1500GeV
Β(A0−> q q’) b
0.0015 µ −460GeV −1000GeV −460GeV
0.001 B(b→sγ) 4.49×10−4 4.48×10−4 4.49×10−4
Table 1
0.0005
MaximumvaluesofB(h→bs)andcorresponding
0100 150 200 250 300 SUSYparametersformA0 =200GeV,tanβ =50.
mA0
discuss first the general trend, which is valid for
Figure 1. The maximum value ofB(h→bs) as a
allstudiedprocesses: themaximumisattainedat
function of mA0, for tanβ =50. largeMSUSY andmoderateδ23. The SUSY-QCD
contributiontob→sγ(3)decreaseswithMSUSY,
therefore to keep B(b→sγ) in the allowedrange
understand the qualitative trend of the results. when MSUSY is small, it has to be compensated
The SUSY-QCD contribution to the b→sγ am- with a low value of δ23, providing a small FCNC
plitude can be approximated to: effectivecoupling(4). Ontheotherhand,atlarge
m (µ−A tanβ) MSUSY the second factor in eq. (3) decreases, al-
ASQCD(b→sγ)∼δ23 b M2 b , (3) lowingalargervalueofδ23. Thus,the firstfactor
SUSY in eq. (4) grows, but the second factor in eq. (4)
whereasthe MSSM Higgs bosons FCNC effective stays fixed (provided that |µ| ∼ MSUSY), overall
couplings behave as: providing a larger value of the effective coupling.
On the other hand, a too large value of δ23 has
ghqq¯′ ∼δ23M−Sµ2UmSgY˜ csoins((ββ1−−ααeeffff)) (((HAh000))) . (4) tinob(3e)c,opmropveonksiantgedabryedauscmtiaolnlvinalu(4e)o.fI|nµ|t/hMeSeUnSdY,
the balance of the various interactions involved
produces the results of Table 1.
The different structure of the amplitudes in
The maximum value of the branching ratio for
eqs. (3) and (4), will permit to obtain and ap-
the lightest Higgs boson channel is obtained in
preciable FCNC Higgs boson decay rate, while
the prediction for B(b→sγ) stays inside the ex- the small αeff scenario [13]. In this scenario the
couplingofbottomquarkstoh0isextremelysup-
perimentally allowed range.
pressed. The large value of B(h0 → bs) is ob-
tained because the total decay width Γ(h0 →X)
3. Bottom-strange channel
in the denominator of (1) tends to zero (Ta-
For the analysis of the bottom-strange pro- ble 1), andnot because a largeFCNC partialde-
duction channel, we study first the Higgs boson cay width in its numerator [4].
branching ratio (1). Figure 1 shows the maxi- The leading production channel of h0 at the
mum value of B(h → bs) as a function of the LHC at high tanβ is the associated production
pseudoscalarHiggsbosonmassmA0. We observe with bottom quarks, and therefore the h0 pro-
thatfairlylargevalues ofB(h0 →bs)∼0.3%are duction will be suppressed when B(h0 → bs) is
obtained. Table 1 shows the actual values of the enhanced. Wehavetoperformacombinedanaly-
maximum branching ratios, and the parameters sis of the full process (1) to obtain the maximum
that provide them for each Higgs boson. Let us productionrateofFCNCHiggsbosonsmeditated
4 Santi B´ejar, Jaume Guasch, Joan Sola`
10 106 h H0 h0 A0
σ(pp -> H0 -> b s) σ(pp→h→bs) 0.45pb 0.34pb 0.37pb
1 σ(pp -> h0 -> b s) 105 events/100fb−1 4.5×104 3.4×104 3.7×104
σ(pp -> A0 -> b s) B(h→bs) 9.3×10−4 2.1×10−4 8.9×10−4
10-1 tanβ = 50 104-1b Γ(h→X) 10.9GeV 1.00GeV 11.3GeV
σ[pb]10-2 103 vents/100f mδ23q˜ 91900−G0.e6V2 61700−G1.e3V2 91900−G0.e4V4
e
A −2750GeV −1960GeV −2860GeV
b
µ −720GeV −990GeV −460GeV
10-3 102
B(b→sγ) 4.50×10−4 4.47×10−4 4.39×10−4
Table 2
10-40 200 400 600 800 100100 Maximum value of σ(pp→h→bs) at the LHC,
mA0 [GeV] for mA0 = 200GeV and tanβ = 50. Shown are
also the corresponding values of B(h → bs) and
of the total width of the Higgs bosons, together
Figure2. MaximumSUSY-QCDcontributionsto with the values of the SUSY parameters.
σ(pp→h→bs)asafunctionofmA0,tanβ =50.
here3. From Table 3 we would expect some 300
events/100fb−1 at the LHC. However, the maxi-
events at the LHC. Figure 2 and Table 2 show
mum is attained at low tanβ, and we have fixed
the result of the maximization of the production
a moderate value of tanβ = 5. By taking lower
cross-section (1). The central column of Table 2
values of tanβ we find that the number of events
shows that when performing the combined maxi-
mizationΓ(h0 →X)hasamuchlargervalue,and growsfast[11],e.g. upto∼(500,900,2000)ifwe
would have chosen tanβ = (4,3,2) respectively.
therefore the maximum of the combined cross-
Due to the single top quark signature the detec-
sectionis notobtainedinthe small αeff scenario.
tionofthischannelshouldbefeasibleattheLHC.
The number of expected events at the LHC is
around50,000events/100fb−1. Whileitisalarge
number,thehugeb-quarkbackgroundattheLHC 5. Conclusions
will mostlikely preventits detection. Note, how-
WehaveperformedacomputationofHiggsbo-
ever, that the maximum FCNC branching ratios
sonmediatedFCNC eventsatthe LHC.Alterna-
are around10−4–10−3, whichis atthe same level
tive effects of SUSY FCNC have been considered
that the already measured B(b→sγ).
in Ref. [6]. Note from eq. (4) that the present
effects, though smaller than the latter, do not
4. Top-charm channel decouple with MSUSY = mg˜ = |µ|. The maxi-
mum expected branchingratio for thebs channel
Theresultsofthenumericalscanforthischan- is large, and we expect a maximum of ∼ 50,000
nel are similar to the bs channel, so we will focus events/100fb−1inthischannelattheLHC,which
mainly on the differences. Figure 3 shows the mightbe difficult to detectdue to the hugeback-
maximum value of the production cross-section ground. Forthetcchannelweexpectamaximum
σ(pp → h → tc) as a function of mA0, while of σmax(pp → h → tc) ≃ 10−3−10−2pb, which
Table 3 shows the actual value of the maximum, meansseveralthousandeventsper100fb−1atthe
together with the SUSY parametersthat provide
them, for mA0 = 300GeV. Only the heavy neu- t3oRtehcealclotrhraetspthoendδiinjgpapraarmameteetresrsininthteheupd-oswecnt-osrecatroerrbeylatthede
tralHiggsbosonscontributetothischannel. The
Cabibbo-Kobayashi-Maskawamatrix,seee.g.[8],andare
general trend explained in section 3 is also valid thereforeconstrainedbyB(b→sγ).
SUSY Higgs boson flavor-changingneutral currents at the LHC 5
10-2 103 h H0 A0
σ(pp→h→tc) 2.4×10−3pb 5.8×10−4pb
events/100fb−1 240 58
10-3 102
B(h→tc) 1.9×10−3 5.7×10−4
-1b Γ(h→X) 0.41GeV 0.39GeV
σ[pb]10-4 10 vents/100f mδ23q˜ 81800−G0.e1V0 81500−G0.e1V3
e
A −2590GeV 2410GeV
t
10-5 σ(pp -> H0 -> t c) 1 µ −700GeV −930GeV
σ(pp -> A0 -> t c) B(b→sγ) 4.13×10−4 4.47×10−4
tanβ = 5 Table 3
10-60 200 40m0A0 [GeV60]0 800 100100-1 As in Table 2, but for σ(pp → h → tc), mA0 =
300GeV and tanβ =5.
Figure3. MaximumSUSY-QCDcontributionsto
σ(pp→h→tc) as a function of mA0, tanβ=5. 5. S.Eidelmanetal., Phys.Lett.B592,1(2004).
6. J. Guasch, W. Hollik, S. Pen˜aranda, J. Sola`,
these proceedings, hep-ph/0601218.
7. J.Guasch,J.Sola`,Nucl.Phys.B562,3(1999),
LHC. Due to the single top quark signature they hep-ph/9906268.
should be easier to detect than the bs channel, 8. F. Gabbiani et al., Nucl. Phys.
providingthe key to a new door to study physics B477, 321 (1996), hep-ph/9604387;
beyondthe StandardModel. It is now anexperi- M. Misiak, S. Pokorski, J. Rosiek,
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and prove that these events can be effectively be eds.A.J.Buras,M.Lindner,hep-ph/9703442.
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Acknowledgements The work of SB has been 10. J. Guasch, proc. of QEMSSM, 256, ed. J.
supported by CICYT (FPA2002-00648), by the Sola`, hep-ph/9710267; J. Guasch, J. Sola`,
EU (HPRN-CT-2000-00152), and by DURSI proc. of LCWS 99, 196, eds. E. Ferna´ndez,
(2001SGR-00188); JG by a Ramon y Cajal con- A. Pacheco, hep-ph/9909503; S. B´ejar,
tract from MEC (Spain); JG and JS in part by J. Guasch, J. Sola`, proc. of RADCOR 2000,
MEC and FEDER (2004-04582-C02-01) and by hep-ph/0101294;A.M.Curiel,M.J.Herrero,
DURSI (2005SGR00564). D. Temes, Phys. Rev. D67, 075008 (2003),
hep-ph/0210335; D. A. Demir, Phys. Lett.
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