The 750 GeV diphoton excess at the LHC and dark matter constraints

Yoshitaro Takaesu

di-photon excessATLAS-CONF-2015-081EXO-15-004-pas

Selection cuts

Signal region: m�� > 200 GeV

At least 2 isolated photons are required with the following cuts

�(m��) � 5 GeV

(EBEB)

m�� > 320 GeV (EBEE)

EBEB EBEE

Signal region: m�� > 500 GeV

ATLAS-CONF-2015-081

EXO-15-004-pas

ATLAS-CONF-2015-081

EXO-15-004-pas

m�� = 750GeV

m�� = 760GeV

3.6(2.0)� NWA3.9(2.3)� 45 GeV width

compatible with 8TeV data within 1.4�

(RSG,� � 0.1 GeV)2.6(1.2)�

(Breit-Wigner+res., )1% < �/m < 10%

1512.05777 (lines added)

data -BG

1512.05777 (lines added)

8TeV results

1504.05511

1506.02301

8TeV results

8+13 TeVcombined

8TeV + 14TeV ATLAS + CMS

combined analysis1512.05777

Fitting to combined data

Fit Breit-Wigner distribution to the (observed - BG) data

3 fitting parameters: • mass • width

mS

�S

Data set

No strong preference btw. Large width and Narrow width

�2 =?

�2SM � �2(40GeV) = 13

8TeV di-photon (ATLAS+CMS) 95%CL exclusion region

fit

fit

68%

95%

Broad width?

Simple effective model for the 750 GeV excess

Assumptions• The excess is due to a SM-singlet scalar • CP conservation for the lagrangian • higgs portal coupling is suppressed

1512.06787

* Phenomenology for the LHC excess is almost the same for . m� � mV

Couplings to EW gauge bosonsL0+ � �

��kAAAµ�Aµ� + kZZZµ�Zµ� + kAZAµ�Zµ� + k2

�W+

µ�W+µ� + W�µ�W�µ�

��

1. k1 = 0 case

�ZZ �k2

ZZ

k2AA

��� � 10 ��� �WW � k22

k2AA

��� � 20 �����Z �k2

AZ

k2AA

��� � 10 ���

Constrained by di-boson searches

2. k2 = 0 case�ZZ � 0.1 ��� ��Z � ��� �WW � 0 weakly Constrained

k1 > k2 would be needed

1512.06787

(NWA)(We only consider )

�(pp� �� ��) � �2

8m�spp

�gg���

��Lgg(m�, spp)

��/m� < 10%

�(pp� �� ��) � �gg���

��� k2

3k21

k23 + �k2

1�(pp� �� ��) � k2

3k22

k23 + �k2

2

�� � 45 GeV realization is non-trivial !k1 � O(1)@ � = 1TeV

k1 ���ff�1

4�Y 2NcNfI�� (e.g. k1 is induced via VL quark loop)

� �Br(�� ��) = 5� 20 fb

Invisible decay of phi for the Large width ?

Assuming the invisible Br ~1, k1 ~ O(0.01), k3 ~ O(0.01) may be possible for .�� � 45 GeV

However, k1 < 0.1 is excluded by 8TeV mono-jet search.

k1 ~ O(0.1) is favored.* non-zero k2 may soften the lower bound on k1 unless excluded by diboson searches.

invisible decay into DM ?

Anyway, it is interesting to see the possibility

Simple effective model for the 750 GeV scalar with DMAssumptions

• DM only couples to the scalar via the renormalizable interaction • Z2 symmetry for the DM

�2�2* terms are not considered in this paper

Parameter scan

m� = 750GeV� = 1TeV

� � Br(�� ��) = 5� 20 fb

LHC Run-I bounds ZZ, WW, ZA, di-jet, monojet

�� > 75 GeV �� > 75 GeV

�� > 75 GeV

Parameter scan

m� = 750GeV� = 1TeV

� � Br(�� ��) = 5� 20 fb

LHC Run-I bounds ZZ, WW, ZA, di-jet, monojet

m� = m�/2 m� = m�

resonance ��� ��m� = m�/2 m� = m�

resonance ��� ��

Large �inv

Small�inv

gamma-ray line constraintsgamma-ray line search put strong constraint on DM models

Large width 750 GeV scalarwith the DM is almost excludedin the simple model.

* Annihilation cross section of the Majorana DM with the CP-even mediator is velocity-suppressed.

dwarf and pbar/p constraints

cosmic-ray propagarion models DR-2 (diffusion re-acceleration) DC (diffusion convection)

Less constrained

Direct detection constraintsXENON1T will investigate most of the models with Large width scalar

* scattering cross section of the Majorana DM with the CP-odd mediator is spin dependent and momentum suppressed.

Summary plot

* Black circle shows the viable point for the 750 GeV scalar with the DM model

fermionic DM with CP-even scalar is the most viable model for the DM explanation of the Large width of the 750 GeV scalar

XENON 1T will testify it! (If this excess remains…)