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					   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
        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  identification
  • Good jet and missing ET resolution
  • Precise muon ID & reconstruction




EPS03 Meeting, 17 July 2003, Aachen   A/H and A/H at LHC,   S.Arcelli         2
                              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
EPS03 Meeting, 17 July 2003, Aachen   A/H and A/H at LHC,   S.Arcelli        3
                                          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 ID+reconstruction (>90%)
   and invariant mass resolution s(M )= 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 tan

 Feasibility studies:

 ATLAS: ATLAS physics TDR

 CMS: CMS-NOTE-98-039, and full simulation+realistic reconstruction study,
      results presented in this talk (CMS preliminary)
          (L. Bellucci, “MSSM Neutral Higgs Bosons Search with CMS in the  channel”,
            PHD Dissertation, Universita’degli Studi di Firenze)
EPS03 Meeting, 17 July 2003, Aachen      A/H and A/H at LHC,   S.Arcelli           4
                                 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.

EPS03 Meeting, 17 July 2003, Aachen          A/H and A/H at LHC,   S.Arcelli               5
                                                                        CMS preliminary
   Di-muon system:
                                                                MA= 150 GeV
                                                                  tan= 30
                                                                GH,A ~ 3 GeV
• Two isolated muons with PT >10 GeV,
  efficiency ~ 87 %
• Mass resolution ~1.5 %, GH,A ~ O(1-10 GeV)
  depending on MA,tan

               CMS preliminary
       MA= 150 GeV
        tan= 30
                                                                                      M(GeV)

                                                  •With cuts on the di-muon system alone,
                                                   5s signal observable only with integrated
                                                   luminosity >100 fb-1
                              L= 20 fb-1
                                                  •b-tagging allows to substantially improve
                                                   the S/B ratio! 

                                      M(GeV)
EPS03 Meeting, 17 July 2003, Aachen        A/H and A/H at LHC,   S.Arcelli           6
                                                                         CMS preliminary
     B-Tagging:                                                                     MA= 150 GeV
                                                                                     tan= 30

 b-jets from associated production are soft,
 low efficiency for jet reconstruction
(typical efficiency for 1 jet ID+b-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%,
                           N. Of secondary vertices        factor ~10 rejection on Z/g*

  EPS03 Meeting, 17 July 2003, Aachen       A/H and A/H at LHC,   S.Arcelli                 7
                      Top Rejection:

                      b tagging not effective against top background, which contains 2 hard central
                      jets from b’s ; use a jet veto and require small missing ET:
Probability/dET jet




                               CMS Preliminary
                                                                                       • No jet with ET>30 GeV
                                                                                       • ETmiss < 40 GeV

                                                                                                CMS Preliminary




                                                                      Events/dET jet
                                                      jet ET(GeV)


                      Top background suppressed
                      by factor ~ 20,  signal ~ 70%                                                         Missing ET(GeV)


                EPS03 Meeting, 17 July 2003, Aachen           A/H and A/H at LHC,          S.Arcelli                8
                               CMS preliminary
Events/GeV



                       S / (S+B) ~ 7              MA= 150 GeV           • Final selection efficiency ~ 22%
                                                    tan= 30
                                                                         ~ independent on the Higgs mass.
                           L= 20 fb-1

                                                                         • Fitting with a gaussian (for signal)
                                                                         + exponential (for background):

                                                                           Mean = 150.7±0.6 GeV
                                                                           Width = 3.7±0.7 GeV

                                                       M (GeV)

              With full di-muon mass resolution/calibration this channel should allow for :

               • Precise measurement of A/H mass, expect dM/M~0.2 % for L=60 fb-1

               • For tan>20, 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
                                                                                                 M (GeV)
             EPS03 Meeting, 17 July 2003, Aachen         A/H and A/H at LHC,   S.Arcelli            9
                                     A/H, 5s discovery reach

                   CMS preliminary
tan




                                                                                     ATLAS




                                                MA (GeV)
• Substantial portion of the MA-tan 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)
       EPS03 Meeting, 17 July 2003, Aachen   A/H and A/H at LHC,   S.Arcelli      10
                                      A/H
Observation of atmosferic - 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, study done by ATLAS.
(ATLAS-COM-PHYS-2002-031)

Two different (Type III) 2-Higgs doublet models (a,b) were considered:




                                                        BR
BR(A/H ) = k2  (2m/m) BR(HSM  )

• kdepends on LFV coupling l ,a,
  and widths GHSM,GA/HModel a,b

• BR(A/H ) 1% -0.1 % for k = 1

                                                                              MH (GeV)
EPS03 Meeting, 17 July 2003, Aachen   A/H and A/H at LHC,   S.Arcelli          11
Search performed using hadronic and e tau decays. Background expected from
Z/g* , tt, WW,WZ production and W+jets (hadronic channel):

• Jet veto against W+jets, 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 W+jets background



                          , ETmiss
                                                  • High pT ,isolated , muon harder than tau
         Df(,)                hadron (tau jet), decay product with large opening angle in
                                   electron         transverse plane (2-body decay).
                                                • Tau higly boosted, require Etmiss collinear
                                                  to visible tau decay product and pT >50 GeV
                                                 pT = pT-jet,e + ETmiss (p can also be derived)

EPS03 Meeting, 17 July 2003, Aachen         A/H and A/H at LHC,   S.Arcelli          12
                      A/H, jet +                A/H, e
Events/ 2 GeV


                                   MA= 130 GeV                MA= 130 GeV               Signal in 30 fb-1
                                    tan= 45                   tan= 45
                                     K=1                      K=1                 MA=130 GeV, tan=30,
                                                                                           k = 1
                                     L= 30 fb-1                L= 30 fb-1
                                                                                       Significance>5 up to
                                                                                         MA  150 GeV

                                       M (GeV)                  M (GeV)


                 •Comparable significance in jet +, e

                 •Analysis efficiently differentiates A/H
                                                                               L= 30 fb-1
                  and A/H (A/H  ),
                  separation depends on on l ,a,



                                                                                                  M (GeV)
                EPS03 Meeting, 17 July 2003, Aachen    A/H and A/H at LHC,   S.Arcelli              13
k
                                                             •5s bounds on k range from 0.2 o 1
                                                             depending on tan 

                                                             •95% C.L. exclusion limits for k  1
                                                             can be set with very low integrated
                                                             luminosities (< 10 fb-1)


                                                 MH (GeV)
                                       Limits on l depend on the Model:
l




                                                                      • Range 10-2 –1 in lexplored
                                                                        with L=100 fb-1

                                                                      • About 10-100 better reach than
                                                                        current limits from g-2 data,
                                                                       ~10 times better than Tevatron


 EPS03 Meeting, 17 July 2003, Aachen            A/H and A/H at LHC,   S.Arcelli          14
                                      Conclusions
Despite low BR~2x10-4, 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  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 tan
●   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 tan, E.Boss, A.Djouadi, A.Nikitenko, hep-ph/0307079)


Within the framework of 2HDM models, the search for A/H 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
EPS03 Meeting, 17 July 2003, Aachen      A/H and A/H at LHC,   S.Arcelli          15

				
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