Higgs working group status report F'Cerutti and G'Unal on behalf of the Higgswg

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Higgs working group status reportF.Cerutti and
G.Unal on behalf of the Higgs-wg

• Update since ATHENS physics workshop
• SM discovery revisited Old channels and new
  ideas
• Higgs properties (spin, couplings,
  self-coupling)te
• SUSY Higgs
• Getting ready for real data analysis
• Plans for Rome Physics Workshop
• Conclusions

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Disclaimer

• Many activities and people involved over the last
  year
• since ATHENS 9 meetings with more than 80
  presentations
• Not everything can be covered in this talk
  limited to few more recent items/developments
• For complete list of recent notes and summary of
  current activities, analysis status see Higgs-wg
  web page (maintained by G.Unal)
• http//atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/HIGG
  S/higgs.html

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SM Higgs

• TDR discovery channels mainly inclusive
  searches - look for mass peak over (unknown)
  continuous background (design robust analyses)
• ttH with H-gt bb
• H-gt g g
• H-gt Z Z -gt 4 leptons
• H-gt W W -gt lnln
• EW Production mechanism reduces QCD background
  (tt, WWj, Zj) Vector Boson Fusion VBF
• H-gt W W -gt ln ln (-gt ln jj)
• H-gt t t -gt lnn lnn and -gt lnn hn

Discovery potential Scientific Note
2003-024 Bonn, Cracow, KEK, Mainz, Montreal,
Pisa, Sheffield, Tokio, Wisconsin
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ttH, H-gtbb

• Revisited recently by J.Cammin-Bonn SN 2003-024
• Discovery potential similar to TDR loss due to
  better bkg. estimate recovered by improved
  Likelihood method used in mass reconstruction
• Studies on background normalization,
  extrapolation
• Use of mass sideband (very challenging)
• Bkg. from ttjj events (reverse b tagging) mass
  shape correction from MC
• Other ttH channels
• H-gttt (Zivkovic,Tanaka)
• H-gtWW (Leveque,Tanaka)
• not discovery channels but useful for coupling
  measurements

(30 fb-1)
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H-gt ZZ-gt 4 leptons

• One of the most investigated channel
• 4 m Cosenza, Frascati, Saclay, MPI, Dubna,
  Wisconsin, Athens, Thessaloniki
• 4 electrons Wisconsin, Weizmann
• 2e-2m Wisconsin
• 2e-2t Weizmann (hopeless at low mass)
• Important progress
• Analyses revised with full simulation DC1
• Use of multivariate techniques (NN and
  likelihood) in parallel to TDR cuts for reducible
  and irreducible bkg rejection (Cosenza-Frascati,
  Wisconsin)
• Study of NLO/LO k-factors vs cuts for sign
  irr. Bkg (Wisconsin)
• Study of bkg control samples and systematics
  (Cosenza-Frascati)
• Relaxed iso-cut analysis 3 iso-lep 1
  Loose-iso-lep (Wisconsin)
• Impact of noise and pileup on muon isolation
  investigated with full simulation negligible at
  low-luminosity (Dubna ATL-COM-PHYS-2004-037)

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H-gt ZZ-gt 4 m

• Mass resolution and selection efficiency studied
  with DC1 data deterioration with respect to TDR
  (both m-standalone and m-combined)
• Some efficiency loss attributed to detector
  change (services in m-spectrometer) some to
  software problems
• TDR performance reproduced also thanks to
  multivariate techniques a part for MH180-200
  GeV opening of ZZ on-shell background (probably
  not correctly taken into account correctly in TDR
  ?)

H-gt4m x 4
E.Meoni et al. ATLAS-PHYS-COM 2004-040
R.Nicolaidou et al.- Saclay
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H-gt ZZ-gt 4e

• Analyses performed on DC1 samples e-calibration
  (strong contribution of Wisconsin group) and
  e-isolation studied
• TDR results reproduced a part for 180 GeV ! (as
  for 4 muons)

M.Riveline E.Gross Weizmann
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H-gt ZZ-gt 4e and 2e2m

• Proposed by Wisconsin looser lepton-isolation (1
  loose isolation required for 1 out of 4 leptons)
  slight improvement in significance 10 at the
  price of having a reducible background (Zbb) at
  similar level than the irreducible one

B.Mellado et al. Wisconsin ATL-COM-PHYS-2004-042
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H-gt g g

• Full simulated gg from DC1 used to check mass
  resolution performance Tartarelli-Carminati
  (Milan) also by Escalier (Paris) and Fang
  (Wisconsin)
• Mass resolution 5-10 worse than in TDR (more
  material IDmore conversions) Still g-conversion
  identification from MC truth instead than from ID
  recon
• Study of reducible background with full
  simulation using DC1 QCD samples Escalier,
  Loureiro(Wisconsin), Unal (LAL)
• Study of NLO prediction for signal and
  irreducible background B.Mellado(Wisconsin),
  Unal, Escalier, Laforge
• From inclusive to H n-jets analyses Mellado,
  Unal, Minagawa, Kanzaki (KEK), Escalier, Laforge

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H-gt g g from DC1

• Background from fake photons reevaluated using
  inclusive DC1 QCD-jj samples
• Rejection similar to TDR studies (Wielers)
• q-Jets less rejected than g-Jets (harder
  fragmentation function)
• TDR estimate of gjet Bkg. was underestimated
  factor 2-3
• Reducible B mostly q-jet for this process while
  rejection parameterized on QDC-jj sample
  dominated by g-jet !
• To finalize this study
• Tighter isolation cuts at low luminosity
• Reconstruction of conversions with the tracker

G.Unal
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H -gt gg NLO studies

• Irreducible background exists at NLO (caveat
  LO and NLO not well defined for gg)
• TDR computation LO cross-section for signal,
  BornBox production of gg (x1.5 to account for
  Bremsthralung contribution)
• NLO computation NLO cross-section for signal,
  NLO contribution for gg Box at NLO

Irreducible bkg.
Born
LO
NLO
Box
(30 fb-1)
MH120 GeV L30fb-1
Significant uncertainty on MC background
predictions Background will be known much better
with the data !
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H -gt gg From inclusive to H jets ?

• Studies based on NLO MC
• Comparison of gg1 jet with inclusive gg channel
  (old idea used by CMS, no conclusion in TDR
  because of lack of NLO computations)
  (Mellado,Unal)
• Use other variables than Mgg to discriminate
  Signal and Background, for instance Pt gg
  (Escalier,Laforge)
• Better S/B can be achieved

• VBF H-gtgg channel investigated much better S/B
  but less statistical sensitivity (50
  inclusive)
• Mellado et al.-Wisconsin ATL-PHYS-2003-036
• Minagawa, Kanzaki Tokyo-KEK
• VBF and inclusive channels can be combined

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H-gt W W

• Inclusive channel used in TDR counting
  experiment with small shape difference Signal vs
  Background
• VBF production better significance -gt reach
  lower Higgs masses (down to 120 GeV
• Recent developments
• NLO computation for S and B (mostly WW, tt) for
  inclusive TDR channel (M.Duehrssen-Freiburg)
• Shape of WW background at NLO shape of
  SignalBackground at LO (MH170 GeV) !
• Study of VBF analysis re-optimization with
  multivariate techniques NN (improvement 30-40
  on significance) and NLO bkg. Estimate (Cranmer
  et al. - Wisconsin). Includes studies on bkg.
  control samples
• New idea Combine WW0 jet (TDR), WW2jets
  (VBF) and WW1 jet (one jet forward) Quayle
  et al. - Wisconsin. Statistical sensitivity looks
  promising.

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VBF H-gt t t

• Key Issue here is Z-gttt mass tails need to study
  on full simulation
• VBF analysis of DC1 fully simulated events
  started K.Cranmer-Wisconsin and
  I.Rottlaender-Bonn Problems with PT-miss
  calibration
• Recent development (Mellado et al.Wisconsin
  ATL-PHS-COM 2004-023)
• H -gt tt 1 jet , jet in intermediate h region
• Expected to be less sensitive to detector
  systematics/calibration
• intermediate jet tagging hJgt1
• more relaxed jet veto in central region 30
  GeV
• Statistical sensitivity good from fast simulation
  
• Need higher order QCD correction for Bkg estimate
  and control samples from data (study started by
  Wisconsin)
• Strong correlation with VBF channel combination
  difficult ? Choose one of the two (But VBF
  important for coupling measurement) ?

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Higgs properties

• Scientific note on H spin/parity measurement for
  M(H)gt200 GeV from H-gt ZZ -gt 4-leptons SN 2003-025
  (Buszello et al.)
• At low-mass studies started measure CP in tth
  h-gtbb (Hockeppel Bonn) or in tth h-gtgg
  (McGarvie -Royal Holloway)
• Measurement of ratios of couplings. Use all
  channels available. New study completed by
  M.Duehrssen ATL-PHYS 2003-030
• Update on H self-coupling (Dhahloff-Freiburg)
  disagreement on tt bkg. with previous studies
  (F.Mazzucato Geneva)

some (moderate) assumptions no significant
contributions in loop from new particles and
light quarks, only one Higgs boson
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SUSY Higgs
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CP SUSY Higgs

• New scenarios with CP violating SUSY couplings
  investigated
• Couplings to SM particles are changed (production
  and decay)
• Particularly challenging scenario suggested by
  theorist (Carena et al) H1 decouples from gauge
  bosons Very light H1 escapes LEP searches
• Most of the parameter space covered with existing
  searches
• Some holes left at very low MH1 under
  investigation recovered with specific topologies
  like H -gt WH1 ?

Preliminary
M.Schumacher - Bonn
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Charged Higgs in the transition region

• Study of charged Higgs in the transition region
  MHMtop performed K.Assamagan et al.
• Preliminary study has been performed with fast
  simulation and is reported in ATL-COM-PHYS-2004-00
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• Look for gg-gtbtH with H -gt tn 2-gt3 process
  with correct treatment of transition region (from
  on-shell to off-shell t) HERWIG version 6.4
• Gap in transition region covered

Preliminary
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Getting ready for real data

• More details see report to Physics
  commissioning meeting July 2004 (FC)
• First step Detector performance and calibration
  
• e/m/t/g identification and measurement
• jet reconstruction (forward tagging jets
  Zjet statistics will be limiting),
• PT-miss calibration
• ? performance groups
• Second step estimate of background from
  data/control samples
• Bkg estimate easy in principle for some
  inclusive channels (gg, 4-leptons)
• More involved for more exclusive channels (like
  VBF WW, tt)
• Bkg. Normalization measure of SM processes
  (ttnj, Wnj, Znj, WWnj, ggnJ with n0,1,2,)
  ? SM, QCD and top groups
• Clear strategies on extrapolation from control
  samples to signal region
• Higgs could be discovered (statistically) with
  10 fb-1 crucial to have detector
  calibration/performance and SM background
  understanding with first collected samples (we
  have 1 concurrent exp.)

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Participation to DC2

• Higgs working group has requested SB samples for
  first DC2 phase and beyond work organized by
  B.Mellado-Wisconsin
• http//www-wisconsin.cern.ch/bmellado/MC/
• Larger samples (mainly background) will be needed
  to finalize some analyses
• Validation of generators/ATLFAST for signal
  performed
• First look at DC2 fully simulated/reconstructed
  events still long way to go for FULL DC2
  validation

S.Paganis - Wisconsin Very first look !
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Plans for Rome physics workshop

• Complete DC1 based re-analysis of gg and 4-lepton
  channels write SN notes with updated results
• Finalize systematic studies of VBF tt and WW
  channels including impact of full simulation
  background systematics included based on control
  samples studies
• Consistent update of SM discovery sensitivity
• DC2 based analyses for Rome ? Difficult to get
  final results probably validation and some
  particular cross-checks (NLO samples, initial
  detector layout)
• Measurement of some of the Higgs properties in
  the low mass region (CP, spin, self-coupling) to
  be revisited
• Finalize updates on some MSSM channels

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Conclusions (1)

• Quite impressive amount of work performed in the
  Higgs working group since ATHENS
• Improvement in understanding of signal and bkg
  processes (MC_at_NLO, RESBOS, K-factors)
• Intensive use of DC1 data
• Validation of full simulation
• Impact of detector layout change
• More realistic performance taken into account
• Studies on control samples to estimate bkg. Size
  and uncertainty started in many channels
• Complementing TDR inclusive channels with more
  exclusive ones (in addtion to VBF WW and tt)
• H-gtgg1 jet, VBF H-gtgg
• H-gttt 1jet
• H-gtWW 0,1,2 jets

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Conclusions (2)

• Problematic issues
• Full simulation with calibrated objects needed
  to finalize realistic analyses PT-miss
  calibration, forward jet calibration,.
• Interaction between performance/sub-detector
  experts and Higgs wg very important November
  Physics Week is a very good opportunity/idea
• Validation of full simulation/reconstruction
  still an issue
• Some DC1 problems survived in DC2 production ?
• DC2 validation difficult issue many things
  changed at the same time

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Other developments/ongoing works not covered here

• VBF H-gtZZ-gtqqll large mass K.Cranmer et al.
  Wisconsin, Weizmann
• Update of VFB H-gtWW for masses 150-300 GeV
  K.Cranmer et al. Wisconsin
• ttH with H-gttt L.Zivkovic et al - Weizmann,
  R.Tanaka - Okayama
• h0-gta1a1-gtbbtt in NMSSM S.Baffioni-LAL
• MSSM H/A -gt tt -gt ll nnnn T.Szymocha et al. -
  Cracow
• WH, ZH with H-gtbb J.Vossebeld et al. - Liverpool
• ttH with H-gt invisible B. Kersevan - D.Schroff
  - Freiburg
• H -gt WH with H-gtbb B.Mohn et al. - Bergen,
  Uppsala
• tt -gt WbHb X.Portell et al. - IFAE
• Studies of NLO corrections to VBF cross section
  R.Mazini-Toronto
• ZH with Z-gtnn and H-gtgg G.Azuelos et al. -
  Montreal
• MSSM h-gtmm for Mh100 GeV S.Gentile et al -
  Rome/Fascati
• Impact of PDF uncertainty on H production Paris,
  Montpellier
• Trigger efficiency for H -gt4e - V.Perez-Real-Bern
• t-ID algorithm in fast simulation L.Zivkovic
  and E.Gross
• Almost all the studies documented in ATLAS notes

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Spare slides
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Introduction (1)

• SM Higgs focus on low mass region- 115-250 GeV
  TDR discovery channels mainly inclusive
  searches - look for mass peak over (unknown)
  continuous background (Design robust analyses)
• ttH with H-gt bb
• H-gt g g
• H-gt Z Z -gt 4 leptons
• H-gt W W -gt lnln
• EW Production mechanism strongly reduces QCD
  background (tt, WWj, Zj) Vector Boson Fusion VBF
  entered in the game
• H-gt W W -gt ln ln (-gt ln jj)
• H-gt t t -gt lnn lnn and -gt lnn hn
• (H-gt g g)

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Introduction (2)

• Comments on VBF
• Improvement in difficult region 120 GeV
• Important contribution to coupling measurements
  more channels available at each mass (redundancy)
  
• Larger S/B w.r.t. inclusive channels
• Involves difficult detector aspects forward
  jet calibration, central jet veto, PT-miss
• Control samples to estimate the background from
  the data (counting experiments)
• Opened Issues on SM Discovery Potential
• non-VBF channels are from TDR Change in
  detector performance/layout ?
• LO Cross-section used for H production
  (conservative) NLO computations/generators for
  S and B ?
• Only some aspects (forward jet tagging, jet
  veto) studied with full simulation Need to fully
  validate VBF results with up to date full
  simulation

VBF Discovery potential VBF Scientific Note
2003-024 Bonn, Cracow, KEK, Mainz, Montreal,
Pisa, Sheffield, Tokio, Wisconsin
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H-gt g g from DC1
Tratarelli-Carminati

• Mass reconstruction studied on DC1 samples
  special corrections/calibration
• Still g-conversion identification from MC truth
  instead than from ID recon.
• Mass resolution 5-10 worse than in TDR
• (more material IDmore conversions)

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From inclusive gg to gg jet(s) exclusive final
states Clear trend in S/B. S/sqrt(B) precise
predictions difficult
G. Unal
For VBF H-gtgg studies from Wisconsin
ATL-PHYS-2003-036 and Minagawa VBF and inclusive
can be combined
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t-identification

• Crucial for several channels VBF H-gttt, ttH with
  H-gttt, MSSM H/A-gttt with different pt and event
  topologies
• t-id with full simulation (-gt detector
  performance group)
• D.Cavalli, M.Heldman standard tau
  identification optimization with full simulation
• Alternatives t-id algorithm E.Richter-Waas
  (track based), J.Tanaka
• Problems with t-ID in fast simulation standard
  ATLFAST parameterization is not working at low-Pt
  and has a strong process-dependence (L.Zivkovic
  and E.Gross)
• Attempt to perform an event by event t-ID in
  ATLFAST (Weizmann) using fast-shower variables
  (Mainz)
• Not yet satisfactory results obtained with both
  approaches work in progress
• All channels containing taus studied with fast
  simulation ONLY must be validated with full
  simulation

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Example tt 1 jet B.Mellado et al. Wisconsin
(Atlfast)
5 sigma for MH120 GeV for 30 fb-1
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MSSM Higgs

• New scan for typical scenarios performed by
  M.Schumacher
• Atlas note on the way

tt reach for (30 fb-1)
(300 fb-1)
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Trigger issues

• Study of impact of new HLT menu on Higgs channels
  performed in collaboration with HLT-TDAQ group
• http//cerutti.home.cern.ch/cerutti/new_trigger_me
  nu.html
• Inclusive approach is in general good no need of
  more exclusive triggers
• Most problematic channels
• bbh/A with h/A-gtbb (MSSM)
• VBF H-gtbb (SM couplings)
• VBF H-gt Invisible
• Possible solutions for 4-b channels under study
  J.Kanzaki and I.Vivarelli b-tag at LVL-2 with
  looser PT-jet
• Trigger efficiency for H -gt 4e channels studied -
  V.Perez-Real-Bern no significant loss between
  LVL1 and offline recon.