Transcript Document 7274944

Physics of Charged Higgs Boson(s) at the LHC
Marian Zdražil
Friday Physics Seminar
January 28, 2005
Outline:
 Introduction
 MSSM
 Charged Higgs Production and Decays
 M(H±) < 170 GeV
 ttbar  bWbH±  blνbτν (TDR)
 ttbar  bWbH±  bqqbτν (new)
 ttbar  bWbH±  blνcs
 M(H±) > 180 GeV
 gb  tH±, H±  tb,t  blν (TDR)
 gb  tH±, H±  τν, tbqq (new)
 gg  tbH±  tbtb
 Properties – mass and tanβ determination
 Summary
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Introduction
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MSSM Higgs(es)
 Complex analyses; 5 Higgses: F = h0, H0, A0, H;
 At tree level, all masses and couplings depend on only two parameters;
traditionally taken to be MA and tanb (Born level, mh<MZ)
 2 complex Higgs doublets  8 d.o.f.  3 eaten by massive vector bosons
W±/Z  5 physical Higgs fields
 For tanβ > 1. A, H, H± couples dominantly to the heaviest lepton (τ) and to the
heaviest down type quark (b)
 Radiative corrections from loop containing top quarks & SUSY particles are
substantial  searches are affected
MH±2 = MA2 + MW2
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MSSM Higgs Discovery modes
 Large variety of observation modes
 if SUSY particles heavy
 SM-like:
h  gg, bb; H  4l
 MSSM-specific: A/H  mm, tt, tt ; H  hh, A  Zh; H  tn
 if SUSY particles accessible:
 H/A  c20 c20  4l + missing Energy
 h produced in cascade decays (e.g. c20  h c10)
 H± decays into lightest chargino c1± and neutralino c10 or
decays to sleptons would dominate when kinematically
allowed
 Studies performed in two steps:
i. SUSY particles are heavy: no contribution to Higgs
production/decay  decays only into SM particles possible
ii. SUSY particles contribute in production/decays
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Charged Higgs Production and Decays (i)
 Charged Higgs bosons have masses that are almost degenerate
with the masses of H- and A-bosons. Only a few production
mechanisms are possible (assuming a heavy SUSY spectrum):
MH < 170 GeV/c2
ppbar  ttbar production (gg fusion process ~90%)
σ(tt incl.) ~ 833 pb  over 8M events in ∫L dt = 10 fb-1
~ 320 pb (leptons)
 t H± b decays:
 Charged Higgs searches might be performed in this channel up to
kinematic limit imposed by top quark mass
 BR is large at SMALL and LARGE tanβ (for a given MH) but it has a
pronounced minimum at tanβ ~ √mtop / mb ~ 7.5
BR(tH±b) ~ mt2 cotan2β + mb2 tan2β
the depth and an exact position is sensitive to QCD corrections to the
running b-quark mass
 H± decay channels:
H±  τν (BR~100%)
STUDIED:
H±  cs
(low tanβ non-negligible)
3-body off-shell decays:
H±  h°W*, H±  AW*
and H±  bt*  bbW
(150 GeV < H± < 180 GeV)
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Charged Higgs Production and Decays (ii)
If MSSM Charged
Higgs exists, the ttbar
production cross-section
will be reduced to
~240 pb, ~130 pb for
Higgs masses 110 GeV,
130 GeV respectively
(tanβ~1.5). That could
be a hint that there is a
Charged Higgs boson !
Signal rates are only 1.7
pb, 0.7 pb respectively.
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Charged Higgs Production and Decays (iii)
MH > 180 GeV/c2
 above tb threshold
Produced by gluon-gluon and gluon-b fusion
or by other b-quark initiated processes:
FINAL STATE:
gg  H± tb : 2 top quarks and 2 b-quarks
gb  H± t : 2 top quarks and a b-quark
( possibility to reconstruct top-quark pairs )
COMMON CHARACTERISTICS: multi b-jet
final states with at least one top-quark
DECAY CHANNELS:
tanβ > 10 (high) : H±  tb and H±  τν
BR(tb)~80%,
BR(τν)~20%
tanβ < 1.5 (low) : H±  tb only !
BR~100%
tanβ
MH
[GeV]
1.5
10.
30.
200
3.4
0.4
1.6
250
2.0
0.18
1.2
300
1.2
0.14
1.0
400
0.6
0.08
0.4
Production cross-section
[pb] for bg  H±t
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Charged Higgs Production and Decays (iv)
Recent progress on understanding
how to generate signal…
(2  2) = gb  tH+
(2  3) = gg  tbH+
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M(H±) < 170 GeV
(below mtop-mb)
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tt  bWbH±  blνbτν
“Leptonic channel” (D. Cavalli et al., ATL-PHYS-94-53):
tH+b; H+tn; thadrons n;
t  leptons
IDEA:
Enhanced tau-lepton rate in ttbar decays
 mass of H± cannot be directly reconstructed because several
neutrinos are produced in the final state
 Excellent τ-ID is a must !
 Measurement of significance of the event excess with an
isolated τ with respect to rate foreseen by SM universality
SIGNAL:
BACKGROUNDS:
intrinsic
Due to fake tau’s
W+jets, bbbarμ10 jets
tt  bWbH±  blνbτν (cont’d)
EVENT SELECTION:
 one isolated high-pT lepton within by t-lepton within |η|<2.5
! TRIGGER ! This lepton originates from semi-leptonic decays of the second top quark
 one identified tau-lepton (EXCELLENT tau-id needed)
 at least 3 jets wit pT > 20 GeV and |η|<2.5
 2 b-tags !
 also ΔΦ cut (mainly to remove bbbar, W+jets bgnd)
Reduction of the bgnd from W+jets and bbbar production to the level below ttbar level.
Tau-ID trivia:
TDR 9.1.5, also see Marjorie’s talk
 Narrow calorimeter clusters  well collimated
jets as compared to QCD jets
 ~78% of hadronic τ-decays has exactly one
charged track
 Soft leptons (direction of the lepton ~ tau)
Trigger: combination of LVL1
multi-jet trigger, ETmiss + tau, ETmiss+jet
Trigger: hadronic tau-trigger
LVL1 Calo + LVL2 EM iso + LVL3 Pxl iso
LVL1: 90% for signal and 6kHz QCD bgd
LVL2+LVL3: 40% for signal and e(QCD)=10-3
further improvement with using tracking at LVL3 possible
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tt  bWbH±  blνbτν (cont’d)
The single-prong, e.g. t  ± (12.5%), hadronic t decays from H±tn are
harder than the ones produced in W±tn decays due to spin
configuration (very useful against bgnds: ttbar, Wt, W+jets and QCD)
This effect is very useful for larger Higgs masses.
The cuts select mainly the right-handed
tau-leptons from charged Higgs decay
with respect to W-decay because the
products are harder in pT.
Significance of the H± signal:
R-handed
L-handed
Significance = excess of tau’s produced / error (stat.  syst.)
# of events observed from MSSM production of
(one or more) Higgs bosons and of WW pairs
+
# of events from SM WW pair production
(using universality from W e/μ mode.
Includes error from fake
tau’s in MSSM and SM
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tt  bWbH±  blνbτν : Results
In 30 fb-1, mH = 130 GeV,
tanβ = 5., the excess of
τ-leptons is 1,200; 2,500
τ-leptons come from Wdecays and 3,400 are
fake τ-leptons
mH± (GeV) 110 130 150
σxBR(pb)
23.3
13.1
4.8
Signal
3,050
1,550
380
Background
7,020
7,170
9,120
Syst. err.
233
234
290
Significance
13.1
6.6
1.3
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tt  bWbH±  bqq‘bτν
Catherine Biscarat, Mireia Dosil,
 “Hadronic channel”
ATL-PHYS-2003-038
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- Signal σ ~ 12.6 pb, tanβ = 30, M(H) = 127 GeV/c
- in this channel, it is possible to reconstruct Higgs
mass out of the transverse mass distribution,
because two FS neutrino are in the same hemisphere
- Counting experiment - # of events after the final cut
compared with the null hypothesis (bgnd only)
- statistical significance = S / √B
BACKGROUNDS:
CUTS:
 2 b-jets
 2 light-jets (from W decays)
 1 tau-jet (hadronic tau decay)
1.
tt  bWbW  bqq‘bτν σxBR = 57.2 pb
2.
QCD bgnd: topology very different (huge σ ~ 55 mb)
3.
Z/γ and W bgnd: large combined σ ~ 17 nb, W/Z
produced tau-jets in their decays
 large MET
 single-prong tau-decay story
for W and charged Higgs
Again: Excellent tau-ID +
good MET measurement
• (Jet+Etmiss) OR (t+Etmiss) trigger
• Top mass reconstruction (|mjjb-mtop| < 40 GeV)
• Higgs mass can be reconstructed by means of
MT
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tt  bWbH±  bqq‘bτν (cont’d)
MT cut and pTt cuts very effective against irreducible background
MT = 2 pTt ETmiss (1 - cos(  ( pTt , ETmiss )))
MT distribution for SM kinematically constrained to be below mW
ATLAS all MSSM Higgses (10 fb-1)
Now covered
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tt  bWbH±  blνbcs
• Searches performed in a low tanβ region
• Higgs masses between 110 and 150 GeV
• Extraction of the peak in mjj distribution
seems to be difficult
Kétévi Assamagan
ATL-PHYS-99-013
H±  cs
• ttbar events are required to have:
• one isolated high-pT lepton within
tracker acceptance, it actually
triggers the experiment
• two b-tagged jets with pT > 15 GeV,
|η| < 2.5, VETO on an additional jet
• at least two non-b central jets within
|η| < 2.0 for the H±  cs reconstruction
• VETO on any extra jet above 15 GeV
in the central region.
The peak sits on a tail of the Wjj distribution
from ttbar events which decay mainly via a Wb.
mH = 130 GeV
tanβ = 1.5
∫Ldt = 30 fb-1
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M(H±) > 180 GeV
(above mtop+mb)
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gb  tH±, H±  tb, t  blν
H+  tb
Kétévi Assamagan
EVENT SELECTION:
 one isolated high-pT lepton within by t-lepton within |η|<2.5 ! TRIGGER !
 three b-tagged jets with pT > 30 GeV, |η| < 2.5 and a VETO on additional jet
 at least two non-b jets for the Wjj reconstruction of the other top quark
 both top-quark masses reconstructed inside a window
 one of the top-quarks to be matched with the remaining b-jet for the
reconstruction of the peak in the mbb distribution from H± tb decay
ATL-PHYS-99-013
Advantage:
BR~80%
Disadvantage:
Large irreducible
background
At the beginning: S/B ~ 1:100
3 b-tagged jets: S/B ~ 1:20
Acceptance: 2.5% (5.1%) for mH=200(500) GeV
After the selection: 70% ttb events, 30% ttj events
comparable results to ttH, Hbb
Wjj resolution ~12.5 GeV
tjjb resolution ~10.0 GeV
ATLAS
The mass resolution is not as good as it
might be expected from the
reconstruction of other multi-jet
resonance channels.
If only the true H±tb combinations
were taken  the resolution would be
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σH ~ 17 GeV
gb  tH±, H±  τν, t  bqq‘
H+  tn
EVENT SELECTION:
Kétévi Assamagan et al.
 one hadronic t-jet, pT > 30 GeV, within |η|<2.5
ATL-PHYS-2000-031
 at least three not-τ jets, pT > 30 GeV, one of these jets must be a
b-tagged jet with |ηb| < 2.5
BGNDS:
 W from associated top quark is reconstructed and |mjjb-mtop| < 25 GeV
QCD, W+jets, single-top production,
 raise the pT(tau) cut to more than 100 GeV – ’polarization story’, W needs a
Wtb, ttbar (Wjj, other Wτν)
boost, charged Higgs does not
Almost free of irreducible bgnds !!!
 to optimize the S/B ratio, missing pT > 100 GeV (MT calculation)
mH± can be extracted from MT distribution with
likelihood method: overall precision from 1.3%
at mH±=226 GeV to 3.1% at mH±=511 GeV
for 100 fb-1
ATLAS
improvement in the signal to bgnd ratio
wrt H+tb channel (large combinatorial bgnds)
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MSSM Higgs Discovery Potential (i)
Assuming SUSY particles are heavy
5s contours
 Plane fully covered with 30 fb-1
 2 or more Higgses observable
in large fraction of plane
 disentangle SM / MSSM
Main channels:
h  gg, tth  ttbb
MA > 100 GeV any tanb
A/H  tt, mm
large tanb
H  tn, tb
MA < 130 GeV any tanb
MA>180 GeV large/small tanb
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MSSM Higgs Discovery Potential (ii)
Large fraction of plane explored already after ~ one year
5s contours
In the intemediate tanβ
region only the
SM-like h0 is observable
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Properties
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H± Mass and tanβ Determination
Charged Higgs: parameter measurements
mass determination
From transverse mass in H  τν case
From invariant mass in H  tb case
Precision dominated by statistics.
Method: maximum likelihood or fit of signal+bgnd
Systematics: bgnd rate, bgnd shape and energy
scale
ATLAS analysis
tanβ determination
Can be determined from rates only.
σxBR ~ tan2 β for large tanβ
Precision limited by uncertainties in
luminosity and systematics.
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Summary
 Most of MSSM parameter space
covered with little luminosity (10 fb-1)
 Sensitivity to heavy MSSM Higgs
dominated by τ in FS
 Little sensitivity to “intermediate
region” in tanβ with SM decays
 SUSY decays (?)
 H±tn (mH±>mtop): covers the discovery
potential in the high tanb range
 H±tn (mH±<mtop): the hadronic channel
(Wqq’) fills the ‘hole’ around tanb10
already after the 1st year (10 fb-1)
Charged Higgs 5σ contour with 30 fb-1
goal is to extend coverage
for intermediate tanβ
Coverage established so far...
…but more ideas on the way…
* gg 
tbH+,
H±SUSY
for moderate tanβ
* even studies of H± and extra dimensions
CMS is looking at it…
tanβ=5
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Additional slides…
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Observability of MSSM Higgses
5 s contours
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3
2
1
Higgs
Higgs
Higgs
Higgs
observable
observable
observable
observable
Here only SM-like h0
We may be unlucky, that even
if we do find a light Higgs, we
will not be able to tell if it is
SM or MSSM
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Coverage…
Coverage established so far......
but more ideas on the way....
* gg  tbH+ , H+  SUSY for moderate tan b
* gluinos/squarks  χχ +X  H+( tn) + X
seems promising for moderate tan b
* even studies of H+ and extra dimensions
CMS is looking at it…
goal is to extend coverage
for intermediate tanβ
tan b =5
tan b =40
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