# Presentation: 498607

## Higgs Physics at the LHC

- Marcela Carena
- Theoretical Physics Department
- Fermilab
- Pascos 2006,
- The Ohio State University Columbus, OH
-  September 10-15, 2006

## Outline

- Testing the Standard Model Higgs boson
-         -- production channels, cross section measurements,
-             mass measurements, determination of Higgs couplings
- The MSSM Higgs Bosons
-       -- the impact of radiative corrections on the various SM-like Higgs
-          search channels, and on the                   and                channels
-       -- tan beta measurements
- B and Higgs Physics at the Tevatron and LHC
-    -- the impact of rare decays:
-        on direct Non-Standard  Model Higgs searches

##                     In the Standard Model:  The Higgs Mechanism

-                     _In the Standard Model_:  The Higgs Mechanism
- a self interacting complex scalar doublet with no trivial quantum numbers under SU(2)L x U(1)Y

##              Discovering the Higgs will put the final piece

-              **Discovering the Higgs will put the final piece**
**                          ****of the Standard Model in place**

**but will present big mysteries of its own!**

-    First evidence of EWSB ==> masses of gauge bosons
-    Measuring the WWH and ZZ H couplings is essential to identify the Higgs as the
-    agent of EWSB: without a v.e.v, no such trilinear coupling at tree level
-     ==> we need to detect the Higgs in association with gauge bosons
-  The other particle whose mass is related to the source of EWSB is the top quark
-     -- If there were other particles (Higgs) responsible for the top mass, their v.e.v. will be small
-    (not responsible for W,Z masses)  ==> their couplings to the top would need to be too strong --
-    ==> if the theory remains perturbative, the top mass will mainly come from a
-           Higgs with SM-like couplings to W and Z

## The first step is discovery:  

**Observe one Higgs boson or more. **
_**Next Step: determine its basic properties**_** :**
**mass, spin, total width, CP quantum numbers; couplings to boson and fermions, Higgs self couplings and reconstruct Higgs potential, observe rare decay modes**
_**Use precision measurement of basic properties to learn about basic model of nature**_:  Is this scalar a Higgs boson? Disentangle between SM , the MSSM, other non-minimal Higgs sector?  Investigate CP viol., beyond the SM , via effects in the Higgs sector; Higgs mixings in ED,
- ...
**Both the LHC and the ILC will be crucial in establishing **
** ****the nature of the EWSB mechanism**

## Direct Higgs search at LEP

Constraints on        from precision tests of the SM
    (accuracy at the per mille level) from CERN, Fermilab, SLAC

- _Constraints on        from precision tests of the SM_
-     (accuracy at the per mille level) from CERN, Fermilab, SLAC

- final LEP result, 2003

- Although the Higgs boson has not been seen and its mass is unknown, it enters via loop corrections in electroweak observables: particle masses, decay rates, etc

- All electroweak parameters have at most logarithmic dependence on
- However, preferred value of          can be determined

**To avoid a light Higgs Boson, must have new phenomena below 1 TeV**

## SM Higgs production processes at hadron colliders

-      Crucial to compute production cross sections with high
-       accuracy to obtain information from data  about ratio of
-       decay widths and eventually couplings and total width
- Much progress recently in computing
-  NLO and NNLO QCD corrections
-  http://maltoni.home.cern.ch/maltoni/TeV4LHC/SM.html

## Search Channels  for the SM Higgs at the LHC

-  **Low mass range** mH < 200 GeV

|         Production
DECAY | Inclusive | VBF | WH/ZH | ttH |
| --- | --- | --- | --- | --- |
| H → γγ | YES | YES | YES | YES |
| H → bb |  |  | YES | YES |
| H → ττ |  | YES |  |  |
| H → WW* | YES | YES | YES |  |
| H → ZZ*, Z l+l- | YES |  |  |  |

-  **Intermediate mass range**
- 200 GeV < mH< 700 GeV
- Inclusive H ==>ZZ-->4l

-  **Large mass range**:  mH> 700 GeV
-   VBF with  H ==>WW==>lv jj
-                               ZZ ==>ll vv

- Nikitenko, ICHEP06

- With K factors

## Slide 9

## The LHC potential

- _Total sensitivity combining all channels_
- _ __plus two experiments_

- 5     discovery possible over the entire SM Higgs mass range of interest with 5 fb-1 (?)

-   ==> For mH~120 GeV combination of many
- different channels necessary, hence, requires
- a good understanding of the detectors.
-   ==> The Tevatron may explore such region

**Higgs mass resolution**:  0.1 to 1%, combining most channels for 300 fb-1 and both experiments, using H-->ZZ--> 4l or H-->gamma gamma
**Total Width resolution**: 5-8 %  for mH > 300 GeV, ATLAS 300 fb-1, H-->ZZ--> 4l

## Measuring Higgs Couplings at LHC

-                                                     of decay widths             assumptions
-                                                   ratios of couplings

_**Measuring Higgs Couplings at LHC**_

**Measuring  HWW and HZZ couplings of order one (SM-like) will be evidence of  a Higgs responsible for the EWSB**
**      ****==> WW fusion most relevant channel**

- LHC rates for partonic processes are given by

- Precision of 10-40% for
- ==> 5-20% in the couplings

- Duehrssen, Heinemeyer, Logan
- Rainwater, Weiglein, Zeppenfeld

## The Higgs Sector in Minimal Supersymmetric Standard Model

-   ==> lightest (SM-like) Higgs                , others heavy and roughly degenerate

- Since the up and down sectors are diagonalized independently, the Higgs
- interactions remain flavor diagonal at tree level.

- _The Higgs Sector in Minimal Supersymmetric Standard Model_
-  2 Higgs SU(2) doublets      and      : after Higgs Mechanism
-                              2 CP-even   h, H  with mixing angle
-                           1 CP-odd    A      and a charged pair
- All Higgs masses and couplings given in terms of 2  parameters        and

- At tree level, one Higgs doublet couples only  to down quarks and the other couples
-  to up quarks only

- Couplings to gauge bosons
-        and fermions
-      (SM normalized)

## Radiative Corrections to Higgs Boson Masses 

- Important quantum corrections due to incomplete cancellation of particles and
- superparticles in the loops

** **        **enhancement  **
** ****log sensitivity to stop masses**
** ****depend. on stop mass mixing**

**After 2 -loop corrections****    ****stringent test of the MSSM**

- Main effects:  stops;
- and sbottoms at large tan beta

## Radiative Corrections to the Higgs Couplings

- 1  Through radiative corrections to the CP-even Higgs mass matrix           , which defines the mixing angle

- The off diagonal elements are prop. to

- Important effects of rad. correc. on          or            depending on the sign of
- and the magnitude of
- ===> govern couplings of Higgs to fermions
- ===> via rad. correc. to                  and                 governs couplings to vector bosons
- When off-diagonal elements vanish,  possible for small mA and large tan beta
- ===> either         or           vanish  ===> strong
- suppression of the SM-like Higgs boson coupling to bottom-quarks and tau-leptons

- M.C. Mrenna, Wagner

## 2)          enhanced loop corrections to neutral Higgs-fermion couplings

**2)          enhanced loop corrections to neutral Higgs-fermion couplings**

- Dependence
- on SUSY
- parameters

**  **_**In terms of the quark mass eigenstates   **_

-   R diagonal

- Dedes , Pilaftsis

## Flavor Conserving Higgs-fermion couplings

-  In terms of h,H and A:
- Hence:

- M.C. Mrenna, Wagner

## How can different SUSY Benchmark Scenarios impact LHC Searches?

**How can different SUSY Benchmark Scenarios impact LHC Searches?**

- First, full simulation analysis of qqH, H->->l+jet
- Nikitenko, ICHEP 06

- The mhmax scenario:
- -- Maximizes mh and allows conservative tan beta bounds
- --                   enhanced due to                       factor for low mA and intermediate
-       and large tan beta   (analogous for H if small mA)
-  ==> strong suppression of

- Optimized ==>NN with kinematics and  isolation as input

- The No-Mixing scenario:     Xt=0
- ==> similar behavior for Higgs couplings
- to tau leptons, bottom quarks and photons

**Discovery reach for SM-like MSSM Higgs**

## The small            (rad.correc.    ) scenario:

==>                    importantly suppressed  for large tan beta and small mA,
                             and in different ways due to         corrections

         hence,            channel enhanced with respect to SM

- ==>                    importantly suppressed  for large tan beta and small mA,
-                              and in different ways due to         corrections
-          hence,            channel enhanced with respect to SM

- Prospects for SM–like Higgs searches at LHC: small              scenario

- --  Complementarity in coverage
- --   One can see a SM-like Higgs in the     channel and not in the       channelr

- M.C., Mrenna, Wagner
- M.C.,  Menon. Wagner

## Non-Standard Higgs Production at the Tevatron and LHC

**      **Enhanced couplings to b quarks  and tau-leptons
-       Considering value of running bottom mass and 3 quark colors

- There is a strong dependence on the SUSY parameters in the bb search channel. This dependence is much weaker in the tau-tau channel

## H/A  Higgs searches at the LHC

_**Searches for Non-Standard Neutral Higgs bosons at the LHC**_

- Robustness of results under variations of SUSY space ==>handle on tan beta

- M.C, Heinemeyer, Wagner, Weiglein

- Kinnunen et al.

## Similarly to the neutral Higgs case,  there are tan beta enhanced loop corrections which depend on SUSY parameters

- Charged Higgs searches at the LHC

- Much more robust under radiative corrections
- Including variation due to charged Higgs
- decay into SUSY particles for small mu

- M.C., Heinemeyer, Wagner, Weiglein

## B and Higgs Physics at the Tevatron and the LHC  explore complementary regions of SUSY parameter space

**Important Flavor Changing effects:** 1)  tree level ==> charged Higgs induced via
- 2) tan beta enhanced loop corrections both in the neutral and charged Higgs sectors
-                ==> model dependent ==> assume Minimal Flavor Violation
- A) **Bs mixing**:                                                   and  SM CKM fit
- Due to correlation between Bs mixing and                         ==> if A/H at the reach of LHC
-  then largest contribution to          due to new physics at most a few ps-1
- B)                          :   ==> SM rate of order 10-9 at the reach of LHC with about 10fb-1,
- but important SUSY corrections can enhanced it by 2 orders of magnitude
- C)                          :
-            :  good agreement with SM ==>
-  SUSY contributions from chargino-stop and charged Higgs-top loops need to partially cancel

- important constraint from recent measurement at Belle

## Large to moderate values of Xt  ==> SM like Higgs heavier than 120 GeV

_**Large to moderate values of X**__**t**_  ==> SM like Higgs heavier than 120 GeV

**    **

- Experimental bound ==> small

- M. C. et al. hep-ph/0603106 and in preparation

-  Sizeable LR stop mixing <==> small/moderate mu
-              ==> **B searches more powerful than Non-SM like Higgs searches**
** ****SM-like Higgs:  coverage with 30fb****-1**** but needs both**

##   Small Xt , sizeable      ==>  No mixing scenario

**  ****Small X****t ****, sizeable      ==>  No mixing scenario**

- Interesting region since light SM-like Higgs lighter than 125 GeV
**No constraints from**
- Mild constraints from

-    Important constraint from recent measurement of

- M.C., Menon, Wagner

- --  small stop mixing (Xt≈0) and large Higgsino mass parameter mu
-  ==> good for the Tevatron ==> has sensitivity to discover all 3 MSSM neutral Higgs bosons
- -- SM-like Higgs at the LHC: needs di-tau and di-photon channels to discover (30 fb-1)

## Conclusions

- SM Higgs observable in multiple channels at the LHC
- Information on Higgs couplings with 5--20% accuracy with 300 fb-1 of data
- SUSY SM-like Higgs  ==> strong variation in the discovery reach depending on
-                            SUSY parameter space via radiative corrections
- Other MSSM Higgs bosons ==> Need sizeable         enhancement for  discovery
-                                                        robust results under variation of SUSY space
-                                                                      moderate sensitivity to tan beta

-     The Non-Standard MSSM Higgs searches at the LHC can be strongly constrained
-      by B physics measurements depending on the SUSY parameter space.

-                              EXTRAS

##  What is the origin of Mass of the Fundamental Particles ?orThe mystery of Electroweak Symmetry Breaking (EWSB)

- There is a Dark Field that fills all the Universe
-          -- it does not disturb gravity and electromagnetism but it renders
-              the weak force short ranged
-          -- it slows down the fundamental particles from the speed of light

- We know that the electromagnetic and weak
-   forces are unified ==> electroweak theory
-             what breaks the symmetry
-                 ==> the Dark Field
-      We know EWSB occurs at the TeV scale
-  New phenomena associated to the Dark field
-       should lie in the TeV range or below
-                  within LHC/ILC reach

- HERA ep collider

## MSSM Higgs 

- Charged Higgs

- SM-like Higgs

_**Present Status of MSSM Higgs searches**_95%C.L. limits

- main decay mode

## Direct Higgs Searches at the Tevatron 

**Tevatron  can search for a **
**Higgs in parts**** of the mass range preferred by precision data **

- Quite challenging! Evidence of a signal
- will mean that the Higgs has strong
-     (SM-like) couplings to W and Z

**  ****A large region of the full MSSM **
**parameter space can be proved!**

- Heavy neutral MSSM Higgs searches

## Higgs Search Potential at the LHC

**If the SM Higgs exists:**
**It will be discovered at LHC !**

-  LHC can search for a Higgs via many
-   channels, already in the first few years

-  Many SUSY Higgs production and
-   decay processes accessible with full
-   LHC potential

-  Still regions where only a SM-like   Higgs is visible

- ATLAS and CMS with 300fb-1

## Slide 31

## Absolute normalization of the HWW coupling fromVBF with H-->WW   

- Absolute normalization of the HWW coupling fromVBF with H-->WW

## Mass and Width Resolution

- Analysis of indirect widths** **for mass range below 200 GeV**:****  **
**        ****10-20% precision**

**MSSM Higgs****                        ********m/m**** (%)      300 fb****-1**
**h, A, H ********                                     ****0.1********0.4**
**H ******** 4 ********                                            ****0.1********0.4**
**H/A ******** ********0.1-1.5**
**h ******** bb                                                ****1********2**
****** ****hh ******** bb ********1-2**
****** ****Zh ******** bb ********                                ****1********2**
**H/A ******** ********1-10**

##   What can we learn from Bs-mixing?

- Upper bound on NP from CDF ==>

- _How strong is the bound on_                            ?

-   For natural values of mA< 1000 GeV ==> largest contributions at most a few ps-1

- A/H at the reach of the Tevatron or  the LHC
-   strong constraints on

## Slide 35

##  Tevatron and LHC searches at small/moderate Xt  and large mu

-   H/A Higgs reach is marginal at the Tevatron, unless                            observed as well
-   A relatively large region of SUSY parameter space can be probed at the LHC even for           relatively “low” luminosities

- --  increasing the stop mixing for sizeable mu
-      ==>  Tevatron A/H searches become marginal, excellent region for  LHC
- --  for SM-like Higgs  similar situation as the small               scenario