The hadronic tau decay of a heavy charged Higgs in models with singlet neutrino in large extra dimensions

11 Pages·0.64 MB·

by  Ketevi A. Assamagan

The hadronic τ decay of a heavy charged Higgs
in models with singlet neutrino in large extra dimensions
2
0
0 K´et´evi Adikl`e Assamagan
2

n
Department of Physics, BrookhavenNational Laboratory
a
J Upton, NY 11973 USA

5
1
Aldo Deandrea

2
v
Institut de Physique Nucl´eaire, Universit´e de Lyon I
6
4 rue E. Fermi, F-69622 Villeurbanne Cedex, France
5
2
1
1
1
0
/
h Abstract
p
p- We study the LHC sensitivity to the charged Higgs discovery in the channel H− τ−ν
→ L
e in models with a singlet neutrino in large extra dimensions. The observation of such a
h signalwouldprovideadistinctive evidence forthese models sinceinthe standardtwo Higgs
v: doublet model type II, H− τ−ν is completely suppressed.
→ L
i
X
r
a
PACS: 11.10.Kk, 14.80.Cp, 12.60.Jv
LYCEN-2001-77
November 2001
The hadronic τ decay of a heavy charged Higgs
in models with singlet neutrino in large extra dimensions
K´et´evi A. Assamagan∗
Department of Physics, Brookhaven National Laboratory, Upton, NY 11973 USA
Aldo Deandrea†
Institut de Physique Nucl´eaire, Universit´e Lyon I,
4 rue E. Fermi, F-69622 Villeurbanne Cedex, France
(Dated: November,2001)
WestudytheLHCsensitivitytothechargedHiggsdiscoveryinthechannelH− τ−ν inmodels
→ L
with a singlet neutrino in large extra dimensions. The observation of such a signal would provide
a distinctive evidence for these models since in the standard two Higgs doublet model type II,
H− τ−ν is completely suppressed.
→ L
PACSnumbers: 1.10.Kk,14.80.Cp,12.60.Jv
I. INTRODUCTION couple to the SM states on the brane as right handed
neutrinoswithsmallcouplings–theYukawacouplingsof
the bulk fields aresuppressedby the volumeof the extra
The possibility that our world has more than four
dimensions. The interactions between the bulk neutrino
space–time dimensions has been considered long time
and the wall fields generate Dirac mass terms between
ago [1]. More recently phenomenological studies based
the wall fields and all the Kaluza-Klein modes of the
on simplified models have brought new insight on how
bulk neutrino. As long as this mass is less than 1/R,
extra dimensions may show up in present and future ex-
theKaluza-Kleinmodesareunaffectedwhileforthezero
perimentalsetups. LocalizationofStandardModel(SM)
mode, the interaction generates a Dirac neutrino mass
degrees of freedom on a (3+1)–dimensional wall or 3–
suppressed by the size of the extra dimensions:
brane explains why low energy physics is effectively four
dimensional [2]. In models where extra dimensions open
λ M
up at the TeV scale, small neutrino masses can be gen- m = ∗ v (2)
D
erated without implementing the seesaw mechanism [3]. √2MPl
Thesemodelspostulatetheexistenceofδ additionalspa-
whereλis adimensionlessconstantandv the Higgsvac-
tialdimensionsofsizeRwheregravityandperhapsother
uum expectation value (VEV), v 246 GeV. The mix-
fields freely propagate while the SM degrees of freedom ≃
ing between the lightest neutrino with mass m and the
areconfinedto(3+1)-dimensionalwall(4D)ofthehigher D
heavierneutrinos introduces a correctionN to the Dirac
dimensional space. The idea that our world could be a
mass such that the physical neutrino mass m is [3]:
topologicaldefectofahigher–dimensionaltheory[4]finds ν
a natural environment in string theory [5].
m
D
The true scale of gravity,or fundamental Planck scale mν = , (3)
N
M , of the (4+δ)D space time is related to the reduced
∗
4D Planck scale MPl, as: where
MP2l =RδM∗δ+2 , (1) |~n|<M∗R m R 2
D
N 1+ , (4)
where MPl = 2.4 1018 GeV is related to the usual ≃ X~n (cid:18) ~n (cid:19)
×
Planckmass1.2 1019 GeV=√8πM . Sincenoexper-
Pl
imental deviatio×ns from Newtonian gravity are observed ~n is a vector with δ integer components counting the
atdistancesabove0.2mm[6],theextradimensionsmust number of states and the summation is taken over the
beatthesub-millimeterlevelwithM∗ aslowasfewTeV Kaluza-Klein states up the fundamental scale M∗. The
and δ 2. sum over the different Kaluza-Klein states can be ap-
The≥righthandedneutrinocanbe interpretedasasin- proximately replaced by a continuous integration. The
gletwith no quantumnumbers to constrainit to the SM following formula can be used:
brane and thus, it can propagate into the extra dimen-
sions just like gravity [7]. Such singlet states in the bulk |~n|<M∗R ~n2 M∗
f S Rδ dxxδ−1f(x2), (5)
(cid:18)R2(cid:19)−→ δ Z
X~n 0
∗Electronicaddress: [email protected] wheref is afunction of~n2/R2 andSδ =2πδ/2/Γ(δ/2)is
†Electronicaddress: [email protected] thesurfaceofaunitradiussphereinδ dimensions. After
2
summing over Kaluza-Klein states up to the cut-off M ,
∗
assuming δ =2:
6
m 2 M 2 2πδ/2 1
D Pl
N 1+ . (6)
≃ (cid:18)M (cid:19) (cid:18) M (cid:19) Γ(δ/2)δ 2
∗ ∗
−
As shown in Table I, small neutrino masses, m , can
ν
be obtained consistent with atmospheric neutrino oscil-
lations [8].
The framework of singlet neutrino in large extra
dimensions must satisfy some phenomenological con-
straints: for δ =2, the mixing between the lightest state
and the higher Kaluza-Klein excitations can be of O(1)
andthereforeproblematicsinceinsuchacasem <1/R
D
is no longer valid. In addition, due to such a large mix- FIG. 1: The charged production at the LHC through the
ing, this scenario might run into problem with nucle- 2 3process,gg tbH±andthe2 2process,gb tH±.
→ → → →
osynthesis [2, 3, 7] (we consider δ > 2 in this analy- The inclusive cross section is the sum of both contributions
afterthesubtractionofthecommonterms. Intheframework
sis). Finally, too much energy could be dissipated into
of large extra dimensions with singlet neutrino in the bulk,
the bulk neutrino modes, leading to an unacceptable ex-
therearenoadditionalHiggsbosons. Thus,thechargedHiggs
pansion rate of the universe if m2 10−3 (eV)2 and
D ≥ productions are thesame as in the 2HDM-II.
1/R 10 keV [2, 11] (we confine this analysis to the
≤
parameter space where this constraint is satisfied).
ThespectrumofmanyextensionsoftheSMincludesa
chargedHiggsstate. We considerasaprototypeofthese
2HDM-II, the polarization asymmetry would be 1.0.
models the 2-Higgs Doublet Model of type II (2HDM- −
In this framework of large extra dimensions, the polar-
II),wheretheHiggsdoubletwithhypercharge 1/2cou-
ization asymmetry could also be 1.0 if the left handed
−
ples only to right–handed up–type quarks and neutrinos −
τ component of the decay (9) is completely suppressed.
whereas the +1/2 doublet couples only to right–handed In such a case, the decay of H− would be similar to
charged leptons and down–type quarks; an example is
the 2HDM-II case but possibly with a different phase
the Minimal Supersymmetric Standard Model (MSSM).
space since the neutrino contains some admixture of the
InthefollowingwewillcontinuetousetheVEVv 246
Kaluza-Klein modes.
≃
GeV as in formula (2). Its meaning in terms of v (VEV
1 The singlet neutrino may not necessarily propagate
of the +1/2 doublet) and v (VEV of the 1/2 doublet)
2 − into the δ-extra dimensional space. It is possible to pos-
is the usual one:
tulatethatthesingletneutrinopropagateintoasubsetδ
ν
√v2 =qv12+v22 tanβ = vv21 (7) (cδaνse≤thδe)foofrmthaeliδsmadfdorititohneaglesnpeartaitailodnimofesnmsiaolnlsD,iirnacwnheicuh-
trinomassesismerelyageneralizationofthe caseδ =δ
H− decays to the right handed τ− through the τ ν
discussed above [2].
Yukawa coupling:
The charged Higgs decay to right handed τ, H−
H− →τR−ν¯. (8) τInR−tν¯hihsapvaepbeer,enweexdtisecnussivsetlhyesptuodssiiebdiliftoyrttohoebLseHrCve[H9,−10→].
TheH−decaytolefthandedτ−iscompletelysuppressed τ−ψ at the LHC above the top-quark mass. Table→I
L
in MSSM. However, in the scenario of singlet neutrino shows the parameters selected for the current analysis.
in large extra dimensions, H− can decay to both right The cases where the asymmetry is +1 are discussed in
handedandlefthandedτ− dependingontheparameters details. We assume a heavy SUSY spectrum with max-
M∗, mD, δ, mH± and tanβ: imal mixing. The present analysis is conducted in the
framework of PYTHIA6.1 [12] and ATLFAST [13], and
H− τ−ν¯+τ−ψ, (9)
→ R L the Higgs masses and couplings are calculated to 1-loop
where ψ is a bulk neutrino and ν is dominantly a light with FeynHiggsFast [14].
neutrino with a small admixture of the Kaluza-Klein
modes of the order mR/n. The measurement of the
| |
polarization asymmetry, II. H± PRODUCTION AND DECAYS
Γ(H− τ−ψ) Γ(H− τ−ν¯)
A= Γ(H− →τL−ψ)−+Γ(H− →τR−ν¯), (10) In this framework, no additional Higgs bosons are
→ L → R needed. As a result, the charged Higgs productions are
can be used to distinguish between the ordinary 2HDM- thesameasinthe2HDM-II,showninFig.1. Weconsider
II and the scenario of singlet neutrino in large extra di- the2 2productionprocesswherethechargedHiggsis
mensions – depending on the parameters – since in the produ→ced with a top-quark, gb tH±. Further, we re-
→
3
TABLEI:Theparametersusedinthecurrentanalysis ofthesignal withthecorrespondingpolarization asymmetry.
Ingeneral,H−woulddecaytoτ−andτ−,H− τ−ν¯+τ−ψ,dependingontheasymmetry. ForthedecayH− τ−ν¯
L R → R L → R
(asin MSSM),theasymmetry is 1and thiscase isalready studiedfor theLHC[9, 10]. Thesignal tobestudiedis
H− τ−ψ. −
→ L
M∗ (TeV) δν δ mD (eV) mH± (GeV) tanβ Asymmetry mν (eV)
Signal-1 2 4 4 3.0 219.9 30 1 0.5 10−3
∼
Signal-2 20 3 3 145.0 365.4 45 1 0.05
∼
Signal-3 1 5 6 5.0 506.2 4 1 0.05
∼
Signal-4 100 6 6 0.005 250.2 35 1 0.005
∼−
Signal-5 10 4 5 0.1 350.0 20 1 0.04
∼−
Signal-6 50 5 5 0.04 450.0 25 1 0.04
∼−
quirethehadronicdecayofthetop-quark,t Wb jjb For the H− decay to the right handed τ, we have [16]
→ →
and the charged Higgs decay to τ-leptons. The studies
Γ (H− τ−ν¯)
reported in [9, 10] were carried out in MSSM where, as → R ≃
previously stated, the H− would decay to right handed Γ(H− τ−ν¯) [1+f(mD,M∗,δ)] (14)
τ-leptons: H− τ−ν¯. In the scenario of large extra → R MSSM N2
→ R (cid:2) (cid:3)
dimensions, the τ decay of charged Higgs would contain and the normalization factor N is given by Equa-
both left and right handed τ-leptons depending on the tion (6) and the function f(m ,M ,δ) is (for δ =2):
D ∗
asymmetry: H− τ−ν¯+τ−ψ. The right handed com- 6
ponent, H− τ−→ν¯,Ris similLar to the MSSM case up to f(m ,M ,δ) = m2D mHδ−2 MPl 2 2πδ/2
some phase s→pacRe factors, in which case the details of D ∗ M∗δ (cid:18) M∗ (cid:19) Γ(δ/2)
the analysis would not differ from [9, 10]. The objec- 1 2 1
+ . (15)
tive of the current work is to study the LHC sensitivity × (cid:18)δ 2 − δ δ+2(cid:19)
to the left handed component, H− τ−ψ. The detec- −
→ L One can generalize these formulas for a singlet neutrino
tion of such a signal could provide a distinctive evidence
in a smaller number of extra dimensions δ <δ than the
for models such as large extra dimensions with singlet ν
extra dimensions available to gravity [3]. Assuming that
neutrino in the bulk. However, further measurements –
all the extra dimensions are of the same size R, one has
of the rate and the polarization asymmetry – would be
to replace in formulas (6) and (11–15):
necessary to identity the actual scenario that is realized.
The major backgrounds are the single top production M 2 M 2(δν/δ)
Pl Pl
gb Wt, and tt¯production with one W+ jj and the δ δν (16)
oth→er W− τ−ν¯. Depending on the polar→izationasym- → (cid:18) M∗ (cid:19) →(cid:18) M∗ (cid:19)
metry (see→EquLation 10), H− τ−ν¯ will contribute as The more general case of a non–symmetric internal δ–
→ R dimensional manifold is given in [3].
an additional background. In Table II, we list the rates
for the signal and for the backgrounds. For the phe- Depending on the parameters M∗, mD, δ, mH± and
tanβ,theτν decayofthechargedHiggscanbeenhanced
nomenological analysis, it is convenient to express the
or suppressed compared to the MSSM case. In Fig. 2
partial widths in terms of inclusive formulas, where the
and Fig. 3, we show few cases of how the other decays
contributionsofthe Kaluza-Kleinmodes aresummedup
of the charged Higgs are affected in this framework; for
to the kinematical limit m m as the τ mass can
ψ H
≤ the chosen values of M and δ, the decay branchings are
be neglected. The partial width of the Higgs decays ∗
similar to MSSM for small values of m while at larger
to τν depends of the parameters M∗, mD, δ, mH± and D
m , the τν decay mode becomes strongly enhanced, es-
tanβ [16]: D
peciallyatlowtanβ. InFig.4,we showthe polarization
Γ(H− →τL−ψ)≃ m8Hπ± (cid:16)mvD(cid:17)2 taχnδ2β (mH±R)δ, (11) afosrymdimffeerternytavsalauefusnocftmionDoafntdhetacnhβa:rgfeodrsHmigagllsmmDas,sriagnhdt
handed τ’s are produced, except at low tanβ while the
where (mH±R)δ is the number of Kaluza-Klein modes asymmetry increases with m (see Equation 11). For
D
lighter than the charged Higgs mass and χ includes the
δ very large values of M and small m , we recover the
∗ D
phase space integral:
MSSM case as shown in Fig. 5 irrespective of the values
of δ considered.
2πδ/2 1 2 1
χ + . (12) In general, H− τ−ψ + τ−ν¯ with the asymmetry
δ ≃ Γ(δ/2) (cid:18)δ − δ+2 δ+4(cid:19) → L R
between -1 and 1. However, the study of H− τ−ν¯
→ R
Using the relation (1), has been carried out in detail and reported elsewhere [9,
10]. Therefore, in the current study, we consider the
(mH±R)δ =(cid:18)mMH±(cid:19)δ×(cid:18)MMPl(cid:19)2. (13) pasayrmammeetterrys isshoownen,iin.e.T,aHb−le I aτn−dψT.able II for which the
∗ ∗ → L
4
TABLE II: The expected rates (σ BR), for the signal gb tH± with H− τ−ν¯+τ−ψ and
t jjb, and for the backgrounds:×Wt and tt¯with W− →τ−ν¯ and W+ →jj. RWe assLume an
in→clusive tt¯production cross section of 590 pb. Other cros→s seLctions are tak→en from PYTHIA 6.1
with CTEQ5L parton distribution function. See Table I for the parameters used for Signal-1,
Signal-2 and Signal-3. In the last columns, we compare the H± τν branching ratios in this
→
model to thecorresponding MSSMbranching ratios from HDECAY [15].
Process σ BR (pb) BR(H± τν+τψ) MSSM: BR(H± τν)
× → →
Signal-1 1.56 0.73 0.37
Signal-2 0.15 1.0 0.15
Signal-3 0.04 1.0 0.01
tt¯ 84.11
gb Wt(pT >30 GeV) 47.56
→
FIG. 2: Charged Higgs decays in models with a singlet neu- FIG. 3: Charged Higgs decays in models with a singlet neu-
trino in large extra dimensions for M∗ =2 104 GeV, δ=3 trino in large extra dimensions for M∗ =2 104 GeV, δ=3
× ×
and tanβ = 1.5. For small values of mD, we see similar de- and tanβ = 45. The dependence in mD is similar to the
cay branchings as in MSSM. As mD gets larger, H± τν situation of Fig. 2.
→
becomes dominant below and above thetop-quarkmass.
comefromthechargedHiggsdecay,H− τ−ν¯,whilein
→ R
III. ANALYSIS the backgrounds, left handed τ−’s come from the decay
L
of the W−( τ−ν¯). Since the charged Higgs is a scalar
The polarization of the τ-lepton is included in this and the W−→aLvector, the polarization of the τ results
analysis through TAUOLA [17]. We consider the in a strongerτ-jet in the MSSM signalthan in the back-
hadronic one-prong decays of the τ-lepton since these groundsforτ− π−ν andlongitudinalρanda1[10,18].
→
are believed to carry a better imprint of the τ- Thestudiesreportedin [9,10]takeadvantageofthispo-
polarization [18]: larization effect in suppressing the backgrounds further
bydemandingthatthechargedtrackcarriesasignificant
τ− π−ν (11.1%) (17) part of the τ-jet energy:
→
τ− → ρ−(→π−π0)ν (25.2%) (18) pπ/Eτ−jet >80%. (20)
τ− a−( π−π0π0)ν (9.0%) (19)
→ 1 →
For the signal in MSSM, this requirement would retain
In Fig. 6, we show the effects of the τ polarization in only the π and half of the longitudinal ρ and a con-
1
the signal and the backgrounds in the case of one-prong tributions while eliminating the transverse components
τ− π−ν. For the signal in MSSM, right handed τ−’s along with the other half of the longitudinal contribu-
→ R
5
FIG. 4: The polarization asymmetry as a function of mH±, FIG.6: Polarizationofthedecayτ fromH± inMSSMandin
for various values of tanβ and mD. For small values of mD, models with a singlet neutrino in large extra dimensions. In
thedecayτ− arerighthanded(exceptforsmalltanβ values) thelattercase,bothleftandrighthandedτ’scanbeproduced
while left handed τ−’s are produced as mD gets larger. with some polarization asymmetry. In the backgrounds, the
τ comes from thedecay of theW±. Thesignal to bestudied
is in the box — the polarization of the decay τ in this signal
isthesameasinthebackground. Thus,τ polarizationeffects
wouldnothelpinsuppressingthebackgroundsbuttheymay
help distinguish between the2HDM and other models.
tions as can be seen from Fig. 7. However, this require-
mentwouldsuppressmuchofthe backgrounds,shownin
Fig. 8. In the framework of large extra dimensions, we
are interested in H− τ−ψ where, as shown in Fig. 6,
→ L
thepolarizationoftheτ-leptonwouldbe identicaltothe
backgroundcasebutoppositetotheMSSMcase. There-
fore, the requirement (20) would not help in suppressing
the backgrounds, as can be seen from Fig. 8 and Fig. 9.
Nevertheless, there are still some differences in the kine-
matics which can help reduce the background level, and
we discuss the details of the analysis as follow:
(a) Search for one-prong hadronic τ decays with one τ-
jet, pτ > 30 GeV and ητ 2.5, at least three
T | | ≤
jet
non τ jets with p > 30 GeV. One of these jets
T
mustbeab-taggedjetwith ηb <2.5. Further,we
| |
apply a b-jet veto by requiring only a single b-jet
with η 2.0 and p > 50 GeV. We assume a τ-
T
| | ≤
jet identification efficiency of 30% and a b-tagging
FIG. 5: The polarization asymmetry and the H± τν efficiency of 50%, for an integrated luminosity of
→
branching ratio for two values of (M∗, mD) and δ = 4, 5 100 fb−1. We further assume a multi-jet trigger
and 6. For very large M∗ and small mD, we recovery the with a high level τ trigger.
MSSMcase, i.e., anasymmetryof 1(righthandedτ−) and
−
MSSM branchingratios (bottom plots). (b) The W from the associated top-quark is recon-
structed and the candidates satisfying m
jj
| −
m 25 GeV are retained (and their four-
W
| ≤
momenta are renormalized to the W mass) for the
6
gb→tH-, H-→t -n--, t -→ 1-prong, t→jjb gb→tH-, H-→t -y , t -→ 1-prong, t→jjb
R R L L
n 35 35 n 120
Bi Bi 120
ents / 2350 2350 ents / 100 100
Ev 20 20 Ev 80 80
60
15 15 60
10 10 40 40
5 5 20 20
0 0 0 0
-0.5 0 0.5 1 1.5 -0.5 0 0.5 1 1.5 -0.5 0 0.5 1 1.5 -0.5 0 0.5 1 1.5
14 50
180
60
12 40 160
10 50 140
30 40 120
8
100
6 20 30 80
4 20 60
10 40
2 10 20
0 0 0 0
-0.5 0 0.5 1 1.5 -0.5 0 0.5 1 1.5 -0.5 0 0.5 1 1.5 -0.5 0 0.5 1 1.5
pp/Et-jet pp/Et-jet
FIG.7: Theoneprongdecaysoftheτ-leptonfromthesignal FIG.9: Theoneprongdecaysoftheτ-leptonfromthesignal
in MSSM: H− τ−ν¯. We plot the ratio of the momentum in models with a singlet neutrino in large extra dimensions
carried by the c→hargRed track to the τ-jet energy. This ratio with a polarization asymmetry of 1: H− τ−ψ. (The τ−
peaks near 1 for τ πν and near 0 and 1 for longitudinal fromH− decaysare100%lefthanded). Th→esitLuationisthus
→
ρ and a1. For transverse ρ and a1, this ratio peaks in the similar to thebackgrounds butopposite to signal in MSSM.
middle.
reconstruction of the top-quark: this is done by
tt-+Wt backgrounds,W-→tL-n--,tL-→1-prong, W+→jj minimizing the variable χ2 = (mjjb −mt)2. We
n 4000 take m =80.14 GeV and m =175 GeV. Subse-
Bi W t
ents / 33050000 56000000 aqrueenrteltya,intheedefvoernftusrtshateirsfayninagly|smisj.jb−mt|<25GeV
v
E 2500 4000
2000 (c) Weraisethecutonpτ,i.e.,pτ >100GeV.Tosatisfy
3000 T T
1500 thispτ cut,theτ jetfromthebackgroundsneedsa
2000 T
1000 large p boost from the W boson. This will result
T
500 1000 in a smaller opening angle, ∆φ, between the decay
0 0
-0.5 0 0.5 1 1.5 -0.5 0 0.5 1 1.5 productsτν. ∆φistheazimuthalopeninganglebe-
4500
tweenthe τ jetandthe missingtransversemomen-
4000 10000
tum. In the signal H± τν, the τ jet will require
3500
3000 8000 little or no boost at all→to satisfy this high pτ cut.
T
2500 6000 This explains the backward peak in the ∆φ distri-
2000 butionforthe signalasshowninFigures10and11
1500 4000
– this backwardpeak in ∆φis more pronouncedas
1000
2000
500 the Higgs mass increases. Similarly, the missing
0 0 transverse momentum p and the transverse mo-
-0.5 0 0.5 1 1.5 -0.5 0 0.5 p1p/Et-j1et.5 mentum ofthe τ-jet are6 iTncreasinglyharderforthe
signal as the Higgs mass increases as seen in Fig-
ures10and11. Becauseoftheneutrinointhefinal
FIG. 8: The one prong decays of the τ-lepton from the tt¯
andWtbackgrounds: W− τ−ν. Herethesituationshould state, only the transverse mass
→ R
be reversed and it is for the ρ and a1. For τ πν, the
rjeattiloabsheloiunlgdcprietaekrianeianrA0T; tLhFeApSeTa:kanejeatri1sclaobmeelsedf→raomτ-tjehtebτy- mT =q2pτT 6pT [1−cos(∆φ)] (21)
requiring the hadronic decay products to carry a significant can be reconstructed. In the backgrounds, the
fraction (>0.9) of the τ-jet energy within a jet cone (∆R< transverse mass has an upper bound at the W−
0.3). For τ πν, these criteria would select charged pions mass (W− τ−ν) while in the signal, it is con-
with this rat→io near 1. strained by→the charged Higgs mass (H− τ−ν).
→
However, due to the experimental resolution of
7
H-→t -y (m = 219.9 GeV, tanb =30), W-→t -n-- H-→t -y (m = 365.4 GeV, tanb =45), W-→t -n--
L H+ L L H+ L
Bin 104 Bin 104
nts / 103 103 nts / 103 103
Eve 102 102 Eve 102 102
10 10 10 10
1 1
1 1
-1 -1
-1 10 -1 10
10 10
0 200 400 0 200 400 0 200 400 0 200 400
pmiss (GeV) pt (GeV) pmiss (GeV) pt (GeV)
T T T T
40 40
35 35
102 30 102 30
25 25
20 20
15 15
10 10 10 10
5 5
0 0
0 1 2 3 100 150 200 250 0 1 2 3 100 200 300 400
Df (pt,pmiss) rad. m (GeV) Df (pt,pmiss) rad. m (GeV)
T T T T T T
FIG. 10: The reconstructions of pmiss, the τ-jet transverse FIG. 11: The reconstructions of pmiss, the τ-jet transverse
T T
momentum, pτ−jet (top plots), the azimuthal opening angle momentum, pτ−jet (top plots), the azimuthal opening angle
T T
between pmiss and pτ−jet and the transverse charged Higgs between pmiss and pτ−jet and the transverse charged Higgs
T T T T
2m0a0ssGe(bVo,tttaonmβp=lot3s0))faonrdtthheesbiganckagl,roHun−ds→W−τL−ψ τ(−mν¯A. I=n m35a0ssGe(Vbo,tttaonmβ =plo4t5s))afnodrtthheebasicgkngarlo,uHnd−sW→− τL−ψτ−,ν¯(.mpAmis=s
→ L → L T
the signal, the transverse mass is bound from above by the andpτ−jetareharderinthesignalparticularlyathigherHiggs
T
charged Higgs mass while in thebackgrounds, thetransverse mass,andtheopeningangle∆φ(pτ−jet,pmiss)peaksforward
T T
mass is constrained by the W mass. However, due to the in the backgroundsand backward in the signal.
Emiss resolution, we see a “leak” intothe signal region.
T
Emiss, the m distribution for the backgrounds
T T the charged track should help determine whether
showsa“leak”intothesignalregionascanbeseen
the scenario is MSSM or not.
in Figures 10 and 11.
(d) To optimize the signal-to-backgroundratiosandthe
signal significances, we apply a cut on the missing The maineffects responsibleforthe suppressionofthe
transverse momentum: p >100 GeV. backgrounds are: the azimuthal opening angle — be-
T
6 tweentheτ-jetandthemissingtransversemomentum—
(e) Afinalcutof∆φ>1.0radisappliedandtheresults whichpeaksforwardinthebackgrounds(W± τν)and
→
are shown in Fig. 12 and used for the calculation backward in the signal (H± τψ); and the difference
→
of the signal-to-background ratios and the signal in the kinematic bounds on the transverse mass — this
significances shown in Table III. The reconstruc- bound is at the W-mass in the backgrounds whereas in
tionofthe transversemass,showninFig.12isnot the signal, the bound is at the chargedHiggs mass. The
enough to distinguish between the MSSM and the overall efficiencies of the kinematic cuts (c), (d) and (e)
singletneutrinoinlargeextradimensions. Thedif- might change as a result of the event by event difference
ferences in these two scenarios are best seen in the in the neutrino mass m leading to an overall change in
ψ
distribution of pπ/Eτ−jet, the fraction of the en- thesignal-to-backgroundratiosandsignalsignificancesof
ergy carried by the charged track which is shown Table III but the results of Figures 12, 13 and 14 would
in Figures 13 and 14. In MSSM, this distribu- not be affected because these results rely on the differ-
tion peaks near 0 and 1 while in H− τ−ψ from ences in the τ-polarization and in the kinematic bounds
→ L
largeextradimensionsandinthebackgrounds,this onthe transversemass,irrespectiveofthe neutrinomass
distribution peaks in the center. The backgrounds m . In Table III, we present results for 3 different val-
ψ
are relatively very small, and as concluded in [9] ues of the number of extra dimensions. With different
and [10], the discovery reach is limited by the sig- mass distributions of m depending on the number of
ψ
nalsizeitself. Thereforetheobservationofasignal extra dimensions, the overallefficiencies for the cuts (c),
in the transverse mass distribution and in the dis- (d) and(e)mightchangedifferently for eachofthe cases
tribution of the fraction of the energy carried by presented in Table III.
8
TABLE III: The expected signal-to-background ratios and signifi-
cancescalculatedaftercut(e)foranintegratedluminosityof100fb−1
(one experiment). See Table I for the parameters used for Signal-1,
Signal-2 and Signal-3. In all the cases considered, the signal can be
observed at the LHC with significances in excess of 5-σ at high lumi-
nosity.
Signal-1 Signal-2 Signal-3
Signal events 41 215 16
tt¯ 7 7 7
Wt 3 3 3
Total background 10 10 10
S/B 4.1 21.5 1.6
S/√B 13.0 68.0 5.1
H-→t -n--, H-→t -y and W-→t -n-- M = 2 103 GeV, d = 4, m =3 eV, m = 219.9 GeV, tanb = 30
R L L * D H-
GeV 3.5 2.5 0.02 2.25
Events / 5 2.235 1.25 Events / 2
1.75
1.5
1
1 1.5
0.5
0.5
1.25
0 0
100 200 300 400 500 100 200 300 400 500
2.25 8
2 1
7
1.75
6
1.5 0.75
5
1.25
1 4 0.5
0.75 3
0.5 2 0.25
0.25 1
0 0 0
100 200 300 400 500 100 200 300 400 500 0 0.2 0.4 0.6 0.8 1 1.2
m (GeV) pp/Et-jet
T
FIG. 12: The reconstructions of the transverse mass for the FIG. 13: The distribution of the ratio of the charged pion
signal in MSSM, thesignal in models with a singlet neutrino track momentum in one prong τ decay to the τ-jet energy
inlargeextradimensionsandforthebackgrounds,foraninte- for mA = 200 GeV, tanβ = 30, M∗ = 2 TeV, δ = 4 and
grated luminosity of 100 fb−1. In general, an MSSMcharged mν = 0.510−3 eV. In the case shown here, the polarization
Higgs can be discovered at the LHC depending on mA and asymmetryis 1( 100%lefthandedτ−). Weseethediffer-
∼ ∼
tanβ. In the models with a singlet neutrino in large extra ence between MSSM and large extradimensions with singlet
dimensions, thesignal can also bediscovered at theLHCde- neutrinoin thebulk. InFig. 14, thedifferencebetween these
pending on the parameters M∗, δ, mD, mA and tanβ. The two models is more pronounced due to the more significant
observation of the signal in the transverse mass distribution signals.
would not be sufficient to identify themodel: the τ polariza-
tion effects must be explored further.
In these models, the right handed neutrino can freely
propagate into the extra dimensions because it has no
IV. CONCLUSIONS quantum numbers to constrain it to the SM brane. The
interactionsbetweenthebulk neutrinoandtheSMfields
Large extra dimensions models with TeV scale quan- on the brane can generate Dirac neutrino masses con-
tum gravity assume the existence of additional dimen- sistent with the atmospheric neutrino oscillations with-
sions where gravity – and possibly other fields – propa- out implementing the seesaw mechanism. There are no
gate. The size of the extra dimensions are constrained additional Higgs bosons required in these models. The
to the sub-millimeter level since no experimental devia- charged Higgs productions are therefore the same as in
tions from the Newtonian gravity has been observed at the 2HDM.
distances larger than 0.2 millimeter. ThechargedHiggscandecaytoboththerightandthe
∼
9
require the hadronic decay of the associated top-quark:
M* = 2 104 GeV, d = 3, mD=145 eV, mH- = 365.4 GeV, tanb = 45 t jjb. The major backgrounds considered are the
02 7 sin→gle top-quark production, gb tW± and the tt¯pro-
nts / 0. duction with one W+ → jj and→the other W− → τL−ν¯.
ve 6 We include the τ polarization in the analysis and select
E
one-prong hadronic τ decays since these events carry a
5 betterimprintoftheτ polarization. Due totheneutrino
in the final state, only the transversemass canbe recon-
structed. In the backgrounds, the transverse mass has
4
an upper bound at the W mass while in the signal, the
bound is at the charged Higgs mass. As a result, above
3
theWthreshold,thebackgroundisrelativelyverysmall.
Thus, the discoveryreachofthe chargedHiggs in the τν
2 channel is limited by the signal size itself.
Themassoftheneutrinoψwouldbedifferentonevent
1 byeventbasis. Consequently,the efficienciesofthe kine-
matic cuts would somewhat be different. However,main
resultsofthe currentanalysisderivefromthe differences
0
0 0.2 0.4 0.6 0.8 1 1.2
pp/Et-jet inthe polarizationsoftheτ-lepton andin the transverse
mass bounds, and would not be significantly affected by
the neutrino mass effect.
FIG. 14: The distribution of the ratio of the charged pion
Although the observation of a signal in the transverse
track momentum in one prong τ decay to the τ-jet energy
mass distribution can be used to claim discovery of the
for mA = 350 GeV, tanβ = 45, M∗ = 20 TeV, δ = 3 and
charged Higgs, it is insufficient to pin down the scenario
mν =0.05 eV.In the2HDM-II,this ratio would peak near 0
thatisrealized. Additionally,byreconstructingthefrac-
and1asshownwhileinothermodels,theactualdistribution
of this ratio would depend on the polarization asymmetry tion of the energy carried by the charged track in the
sincebothleft and righthandedτ’swould contribute. Inthe one-prong τ decay, it is possible to claim whether the
case shown, the asymmetry is 1 and the ratio peaks near scenariois the ordinary2HDM or not. The further mea-
∼
thecenter of the distribution. surementofthe polarizationasymmetrymight providea
distinctive evidence for models with singlet neutrino in
large extra dimensions.
left handed τ-leptons, H− τ−ν¯+τ−ψ whereas in the
→ R L
2HDM-II such as MSSM, only the right handed τ decay
of the H− is possible through the τ Yukawa coupling: Acknowledgments
H− τ−ν¯. The τ decay of the charged Higgs has been
→ R
studied in details for ATLAS and CMS. In the current K.A.AssamaganexpressesgratitudetoK.Agashefor
study,wefocusontheobservabilityofH− τ−ψ atthe fruitfuldiscussions. Thisworkwaspartiallyperformedat
→ L
LHC for Higgs masses larger than the top-quark mass. the Les Houches Workshop: “Physics at TeV Colliders”
ThechargedHiggsisgeneratedthroughthe2 2pro- 21 May – 1 June 2001. We thank the organizers for the
cess, gb tH± — where H− τ−ν¯+τ−ψ —→and we invitation.
→ → R L
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