# Presentation: 702662

## Physics of Charged Higgs Boson(s) at the LHC

**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

**Marian Zdražil**
**Friday Physics Seminar**
**January 28, 2005**

## Introduction

## MSSM Higgs(es)

- Complex analyses; 5 Higgses:  h0, H0, A0, H;
- At tree level, all masses and couplings depend on only two parameters; traditionally taken to be MA and tan**(Born level, m****h****<M****Z****)**
- 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

## MSSM Higgs Discovery modes

- Large variety of observation modes
**if SUSY particles heavy**
- SM-like:**         **h  bb; H   4
- MSSM-specific:** **A/H  , , tt ; H  hh, A  Zh; H  
**if SUSY particles accessible:**
- H/A  20 20  4+ missing Energy
- h produced in cascade decays (e.g. 20  h 10)
- H± decays into lightest chargino ± and neutralino 10 or decays to sleptons would dominate when kinematically allowed
- Studies performed in two steps:
- SUSY particles are heavy: no contribution to Higgs production/decay  decays only into SM particles possible
- SUSY particles contribute in production/decays

## 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

- σ(tt incl.) ~ 833 pb  over 8M events in ∫L dt = 10 fb-1
-                        ~ 320 pb (leptons)

- ppbar  ttbar production (gg fusion process ~90%)

- 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%)     H±  h°W*, H±  AW*
-         H±  cs                      and H±  bt*  bbW
-                        (low tanβ non-negligible)             (150 GeV < H± < 180 GeV)

- STUDIED:

- 3-body off-shell decays:

## Charged Higgs Production and Decays (ii)

**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.

## Charged Higgs Production and Decays (iii)

- MH > 180 GeV/c2

-   above tb threshold

- tanβ > 10 (high)  : H±  tb and H±  τν
-                             BR(tb)~80%,
-                             BR(τν)~20%
- tanβ < 1.5  (low) :  H±  tb only !
-                             BR~100%

- 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:

| 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 |

-   MH
- [GeV]

- 1.5

- 10.

- 30.

- tanβ

- Production cross-section [pb] for bg   H±t

## Charged Higgs Production and Decays (iv)

- Recent progress on understanding
- how to generate signal...

**(2**** ******** ****2) = gb**** ******** ****tH****+**** **
**(2**** ******** ****3) = gg**** ******** ****tbH****+**

## M(H±) < 170 GeV(below mtop-mb)

##  tt  bWbH±  blνbτν

_**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

**“****Leptonic channel” (D. Cavalli et al., ATL-PHYS-94-53):**
**t********H+b; H+********; ********hadrons ********; **

- BACKGROUNDS:

- intrinsic

- Due to fake tau’s

- W+jets, bbbarμ jets

- SIGNAL:

##  tt  bWbH±  blνbτν (cont’d)

-  one isolated high-pT lepton within by 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.**

- EVENT SELECTION:

- Tau-ID trivia:

-  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)

- TDR 9.1.5, also see Marjorie’s talk

_**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

**    ****Trigger:**  **combination of LVL1**
** ****multi-jet trigger, E****T****miss**** + tau, E****T****miss****+jet**

##  tt  bWbH±  blνbτν (cont’d)

**The single-prong, e.g. ******** ******** ********± ****(12.5%), hadronic ******** decays from H±************ are  **
**harder than the ones produced in W****±************ decays due to spin **
**configuration (very useful against bgnds: ttbar, Wt, W+jets and QCD)**

**R-handed**

**L-handed**

- 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:

**    ****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**

- This effect is very useful for larger Higgs masses.

##  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 W-decays 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 |

## “Hadronic channel” 
    - Signal σ ~ 12.6 pb, tanβ = 30, M(H) = 127 GeV/c2 
    - 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

-     - Signal σ ~ 12.6 pb, tanβ = 30, M(H) = 127 GeV/c2
-     - 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

** ****tt ******** bWbH****±**** ******** bqq‘b****τν**

- BACKGROUNDS:

- CUTS:

-  2 b-jets
-  2 light-jets (from W decays)
-  1 tau-jet (hadronic tau decay)
-  large MET
-  single-prong tau-decay story
-    for W and charged Higgs

- tt  bWbW  bqq‘bτν  σxBR = 57.2 pb
- QCD bgnd:  topology very different (huge σ ~ 55 mb)
- Z/γ and W bgnd:  large combined σ ~ 17 nb, W/Z produced tau-jets in their decays

- Again: Excellent tau-ID + good MET measurement

** ****(Jet+E****tmiss****) OR (********+E****tmiss****) trigger**
** ****Top mass reconstruction (|m****jjb****-m****top****| < 40 GeV)**
** ****Higgs mass can be reconstructed by means of M****T**

**Catherine Biscarat, Mireia Dosil, **
**     ****ATL-PHYS-2003-038**

##  tt  bWbH±  bqq‘bτν (cont’d)

**M****T**** cut and p****T******** cuts very effective against irreducible background**
**M****T**** distribution for SM kinematically constrained to be below m****W**

##  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
-  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.

-    mH = 130 GeV
-      tanβ = 1.5
-   ∫Ldt = 30 fb-1

- The peak sits on a tail of the Wjj distribution from ttbar events which decay mainly via a Wb.

**Kétévi Assamagan **
**ATL-PHYS-99-013**

**H****±**** ******** cs**

## M(H±) > 180 GeV(above mtop+mb)

## gb  tH±, H±  tb, t  blν

**H****+ ******** tb**

- ATLAS

**gb ******** tH****±****, H****± ******** ****tb****, t ******** bl****ν**

-  one isolated high-pT lepton within by 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

- EVENT SELECTION:

**Kétévi Assamagan **
**ATL-PHYS-99-013**

**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 **
**σ****H ****~ 17 GeV**

**At the beginning: S/B ~ 1:100**
**3 b-tagged jets:  S/B ~ 1:20**
**Acceptance: 2.5% (5.1%) for m****H****=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**

_**Advantage:**_
**BR~80%**
_**Disadvantage:**_
**Large irreducible**
**background**

## gb  tH±, H±  τν, t  bqq‘

**H****+ ******** ******

- ATLAS

**m****H±**** can be extracted from M****T**** distribution with**
**likelihood method: overall precision from 1.3% **
**at ****m****H±****=226 GeV to 3.1% at m****H±****=511 GeV **
**for 100 fb****-1**** **

**gb ******** tH****±****, H****± ******** ****τν****, t ******** bqq‘**

**Kétévi Assamagan et al.**
**ATL-PHYS-2000-031**

**EVENT SELECTION:**

-  one hadronic jet, pT > 30 GeV, within |η|<2.5
-  at least three not-τ jets, pT > 30 GeV, one of these jets must be a
-     b-tagged jet with |ηb| < 2.5
-  W from associated top quark is reconstructed and |mjjb-mtop| < 25 GeV
-  raise the pT(tau) cut to more than 100 GeV – ’polarization story’, W needs a
-     boost, charged Higgs does not
-  to optimize the S/B ratio, missing pT > 100 GeV (MT calculation)

**BGNDS:**

**QCD, W+jets, single-top production,**
**Wtb, ttbar (W********jj, other W********τν****)**
**Almost free of irreducible bgnds !!!**

## MSSM Higgs Discovery Potential (i)

- Assuming SUSY particles are heavy

- 5 contours

-  Plane fully **covered** with 30 fb-1
-  2 or more Higgses observable in large fraction of plane
-  **disentangle SM / MSSM**

- _Main channels:_
- h  , tth  ttbb    MA > 100 GeV any tan
- A/H  large tan
- H  , tb               MA < 130 GeV any tan
- MA>180 GeV large/small tan

## MSSM Higgs Discovery Potential (ii)

- 5 contours

- Large fraction of plane explored already after ~ one year

- In the intemediate tanβ region only the
- SM-like h0 is observable

## Properties

## H± Mass and tanβ Determination

**mass determination**

**tan****β**** 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

- Can be determined from rates only.
- σxBR ~  tan2 β  for large tanβ
- Precision limited by uncertainties in luminosity and systematics.

**ATLAS analysis**

**H****±**** Mass and tan****β**** Determination**

## 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± (mH±>mtop): covers the discovery potential in the high tan range
- H± (mH±<mtop): the hadronic channel (Wqq’) fills the ‘hole’ around tan10 already after the 1st year (10 fb-1)

**Charged Higgs 5****σ**** contour with 30 fb****-1**

**goal is to extend coverage**
**for intermediate tan****β**

**Coverage ****established**** so far...**
**      ...****but more ideas on the way...**

***  ****gg ******** tbH****+****, H****±********SUSY for moderate tan****β**
***  even studies of H****±**** and extra dimensions**

**CMS is looking at it****...**

**tan****β****=5**

## Additional slides...

## Observability of MSSM Higgses

**5**** ********contours**

- 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**

## 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**

- tan =5

- tan =40

**goal is to extend coverage**
**for intermediate tan****β**

**CMS is looking at it****...**