Madrid

1
A/H??? and A/H??? decays at the LHC
Silvia Arcelli Univ. of Bologna and INFN for the
ATLAS and CMS Collaborations

• Outline of the talk
• The LHC and ATLAS,CMS
• MSSM A/H Higgs production
• A/H???
• A/H???
• Conclusions

Covering Abstracts Abs 674 Search for A/H???
with CMS Abs
421 Studies of Lepton Flavor Violation with
ATLAS
HEP2003 Europhysics Conference Aachen, Germany,
17-23 July 2003
2
The LHC and ATLAS,CMS detectors

• pp at 14 TeV, collision rate 40 MHz , with a
  design luminosity L 1034 cm-2 s-1.
• First physics run planned for Aug 2007 at L 2
  x1033 cm-2 s-1
• ATLAS and CMS detectors equipped with high
  precision tracking systems,
• high resolution ECAL and hermetic calorimetry ,
  large acceptance muon
• spectrometers to ensure

• Efficient b-tagging and t identification
• Good jet and missing ET resolution
• Precise muon ID reconstruction

3
MSSM A/H Production

• Predominantly via gluon fusion
• and bbA/H associated production
• bbA/H production and decays to down
• type fermions dominant at high tan?
• A/H degenerate over most MA-tan? plane

• Golden channel at LHC is A/H??? (BR 10), but
  other rare/non-standard decays
• can be effective probes of the MSSM Higgs
  sector and of physics beyond the SM
• A/H??? very small branching ratio (3 10-4)
  but very clean signature
• A/H??? search for LFV effects involving the 2nd
  and 3rd generation

4
A/H???

• Decay hardly observable at LHC in case of SM
  Higgs (s,vLHC), but low branching ratio is
  compensated by the cross-section enhancement in
  the MSSM
• Although BR(A/H???)/BR(A/H???) 2 10-3 ,
  discovery potential
• in ?? channel enhanced by very efficient muon
  IDreconstruction (gt90)
• and invariant mass resolution s(Mmm ) 1-2 ,
  10 times better than in ??
• Excellent di-muon mass resolution allows for a
  precise measurement of
• the Higgs mass and a direct measurement of the
  Higgs width for high tanb
• Feasibility studies
• ATLAS ATLAS physics TDR
• CMS CMS-NOTE-98-039, and full
  simulationrealistic reconstruction study,
• results presented in this talk (CMS
  preliminary)
• (L. Bellucci, MSSM Neutral Higgs
  Bosons Search with CMS in the mm channel,
• PHD Dissertation,
  Universitadegli Studi di Firenze)
  

5
bbA/H?bb?? in CMS

• bbA/H associated production channel, assuming low
  luminosity conditions. Search strategy based on
  clean signature from
• high Pt, isolated muons
• Sharp di-muon mass peak
• b-tag of the associated production

Main Background processes
Drell-Yan production Z/g???
top pair production tt?????bb
bbZ/g ? bb?? ( 2 of inclusive
Drell-Yan )
other potential backgrounds like bb,cc, WW,ZZ ?
??X negligible.
6
CMS preliminary
Di-muon system
MA 150 GeV tanb 30 GH,A 3 GeV

• Two isolated muons with PT gt10 GeV,
• efficiency 87
• Mass resolution 1.5 , GH,A O(1-10 GeV)
• depending on MA,tan?

CMS preliminary
MA 150 GeV tanb 30
M??(GeV)

• With cuts on the di-muon system alone,
• 5s signal observable only with integrated
• luminosity gt100 fb-1
• b-tagging allows to substantially improve
• the S/B ratio! ?

L 20 fb-1
M??(GeV)
7
CMS preliminary
B-Tagging
MA 150 GeV tanb 30
b-jets from associated production are soft, low
efficiency for jet reconstruction (typical
efficiency for ?1 jet IDb-tag 20)
CMS preliminary
B-jet ET(GeV)

• Event b-tag used, relaying on a
• combination of different variables
• Number of secondary vertices
• 2,3-d track impact parameter
• impact parameter significance
• ? b-tag 40,
• factor 10 rejection on Z/g

N. Of secondary vertices
8
Top Rejection
b tagging not effective against top background,
which contains 2 hard central jets from bs
use a jet veto and require small missing ET
CMS Preliminary

• No jet with ETgt30 GeV
• ETmiss lt 40 GeV

Probability/dET jet
CMS Preliminary
Events/dET jet
jet ET(GeV)
Top background suppressed by factor 20, ?
signal 70
Missing ET(GeV)
9
CMS preliminary

• Final selection efficiency 22
• independent on the Higgs mass.
• Fitting with a gaussian (for signal)
• exponential (for background)
• Mean 150.70.6 GeV
• Width 3.70.7 GeV

MA 150 GeV tanb 30
S /? (SB) 7
Events/GeV
L 20 fb-1
Mmm (GeV)
With full di-muon mass resolution/calibration
this channel should allow for

• Precise measurement of A/H mass, expect dM/M0.2
  for L60 fb-1
• For tanbgt20, where the natural Higgs width
  dominates over the detector
• resolution, can directly measure GA/H and
  have an independent constraint
• on tan? in addition to that from event rates

Mmm (GeV)
10
A/H???, 5s discovery reach
CMS preliminary
tanb
ATLAS
MA (GeV)

• Substantial portion of the MA-tanb plane covered
  already with 20 fb-1. Comparable
• results obtained in ATLAS TDR study
• Same strategy can be extended to h/A search for
  MA 105-125 GeV (h,A degenerate),
• requires maximal luminosities
• (recent studies by ATLAS, ATL- PHYS- 2002- 021,
  ATL- PHYS- 2003- 013)

11
A/H?t?

• Observation of atmosferic nm-nt neutrino
  oscillations with maximal mixing and implies
  lepton number non-conservation ? expect LFV
  decays
• One possibility to search for LFV effects at the
  LHC
• is the decay A/H??m, study done by ATLAS.
• (ATLAS-COM-PHYS-2002-031)
• Two different (Type III) 2-Higgs doublet models
  (a,b) were considered
• BR(A/H ?t?) k2 tm (2mm/mt) BR(HSM ? tt)
• ktmdepends on LFV coupling l tm,a,b
• and widths GHSM,GA/HModel a,b
• BR(A/H ?t?) 1 -0.1 for kmt 1

BR
MH (GeV)
12
Search performed using hadronic and enn tau
decays. Background expected from Z/g , tt,
WW,WZ production and Wjets (hadronic channel)

• Jet veto against Wjets, b-jet veto against tt
• (gluon fusion production is considered)
• In hadronic channel select 1-prong decays
• (collimated jet with single energetic hadron)
• to suppres Wjets background

n, ETmiss

• High pT ,isolated m, muon harder than tau
• decay product with large opening angle in
• transverse plane (2-body decay).
• Tau higly boosted, require Etmiss collinear
• to visible tau decay product and pTt gt50 GeV
• pTt pTt-jet,e ETmiss (pt can also be
  derived)

Df(m,t)
hadron (tau jet), electron
m
13
A/H???, ??jet ?
A/H???, ??e?n
Signal in 30 fb-1 MA130 GeV,
tanb30, kmt 1 Significancegt5 up to
MA ? 150 GeV
MA 130 GeV tanb 45 Ktm1
MA 130 GeV tanb 45 Ktm1
Events/ 2 GeV
L 30 fb-1
L 30 fb-1
Mtm (GeV)
Mtm (GeV)

• Comparable significance in ??jet ?, e?n
• Analysis efficiently differentiates A/H??m
• and A/H??? (A/H ??? ?mnn?),
• separation depends on on l tm,a,b

L 30 fb-1
Mtm (GeV)
14
kmt

• 5s bounds on kmt range from 0.2 to 1 depending
  on tan b
• 95 C.L. exclusion limits for kmt ? 1 can be set
  with very low integrated luminosities (lt 10 fb-1)

MH (GeV)
Limits on lmt depend on the Model
ltm

• Range 10-2 1 in ltmexplored
• with L100 fb-1
• About 10-100 better reach than
• current limits from g-2 data,
• 10 times better than Tevatron

15
Conclusions

• Despite low BR2x10-4, A/H??? is a quite powerful
  channel for the detection and the study of the
  MSSM heavy neutral Higgs bosons
• Complements golden channel A/H ?tt in A/H
  discovery.
• Allows for a precise measurement of Higgs mass
  and provides the unique
• possibility to directly measure the A/H
  natural width at high tanb
• May allow to disentangle all neutral Higgs
  states in regions where h,H,A are
• non-degenerate, possibility under
  investigation ( Intense-Coupling Regime,
• MA 130 GeV, high tanb, E.Boss, A.Djouadi,
  A.Nikitenko, hep-ph/0307079)
• Within the framework of 2HDM models, the search
  for A/H??t decays at the LHC will allow to test
  Lepton Flavour Violation with a much better
  sensitivity compared to current constraints from
  muon g-2 data, and to the bounds achievable
• at the Tevatron in the same search channel.

Many thanks to my colleagues in CMS and ATLAS for
providing material and help in preparing this
talk, in particular K.Assamagan, R.Kinnunen,
S.Nikitenko, M.Vos