Form factor of Higgs boson?

Transcription

1 1/15 Form factor of Higgs boson? Susumu Oda Kyushu University I have thought about this Higgs boson form factor after I talked to Yamazaki san in March.

2 2/15 Is the observed Higgs boson an elementary particle or a composite particle? Indirect study would be the measurement of its couplings and mass. Direct study would be the measurement of its spatial size, I think. We think that elementary particles are point like particle and they don t have finite size.

3 3/15 Form factor, F, of proton. Mott scattering is electron scattering including its spin. Form factor,, is the Fourier transformation of the charge distribution,. is three momentum transfer.

4 4/15 Form factors of electron, proton and nucleus Form factors of pointlike particles don t depend on. Figures are taken from Particles and Nuclei, Povh, Rith, Scholz, Zetsche

5 5/15 Form factor of charged pion * * q is now four momentum transfer. a) is e scattering and q 2 <0. Virtual photon is space like. Transfers momentum b) is + production by e + e collision and q 2 >0. Virtual photon is time like. Transfers energy t q 2 <0 Space like e scattering Shown in previous pages ep Deep Inelastic Scattering is space like, Q 2 = q 2 >0 q 2 >0 Time like + production Figures are taken from L.G. Landsberg, Physics Reports 128 (1985) 301.

6 6/15 Form factor of neutral particles by Dalitz decay * * A, B and P are neutral particles. Dalitz decay (=internal conversion, decay into virtual photon) is sensitive to the form factor. ll q 2 >0 and time like. q 2 is ll. BR( 0 )=98.8% BR( 0 e + e )=1.17% BR( )=71.9% BR( e + e )=0.69% BR( + )=0.03% Dalitz decay is suppressed by ~1%. Figures are taken from L.G. Landsberg, Physics Reports 128 (1985) 301.

7 7/15 Form factor of (548 MeV, J P =0 ) Measured form factor of is well described by the quark triangular model. m u =m d =0.25 GeV, m s =0.35 GeV Dashed curve is the quark triangular model. * Real photon Figures and equation are taken from L.G. Landsberg, Physics Reports 128 (1985) 301.

8 8/15 Form factor of H (~125 GeV, J P =0 + )? Higgs decays via loops of top quark and W boson. If I use the equation of the quark triangular model in the previous page with m P =m H, m q =m t =m H /2=62.5 GeV and neglect the difference between scalar and pseudo scalar, I get the following q 2 =m 2 dependence. Even if the Higgs boson is point like particle, we expect some deviation of form factor from unity. However, in the low mass region m<20 GeV, deviation is small <5%. *

9 9/15 decay (arxiv: ) This production involves several diagrams. I m interested in these diagrams with one virtual photon.

10 10/15 decay (arxiv: ) e + e + + Red: tree diagram Thin solid: * pole Dashed: Z* pole Dotted: four point box Thick solid: total e + e is difficult at ATLAS, + is dominated by tree diagram. + is promising.

11 11/15 Irreducible background Background is continuous in m. Signal is a sharp peak in m. We can fit background with a simple function as H analysis does.

12 12/15 CMS showed preliminary results of at Moriond 2014 CMS PAS HIG (2014/03/24) Search for a Higgs boson decaying into * with dilepton mass below 20 GeV in pp collisions at sqrt(s)=8 TeV view/cmspublic/hig14003twiki The rare Higgs boson decay into the final state is rich in information that will not only increase our understanding of its basic properties, but can also probe novel couplings caused by extensions of the standard model of particle physics. They don t claim this decay is sensitive to the form factor. However, this is the channel I m interested in.

13 13/15 CMS event selection Two opposite sign muons and a photon Mass 110 GeV<m( )<170 GeV Muon Pseudo rapidity ( ) <2.4 Transverse momentum p T ( )>23 GeV for the highest p T muon p T ( )>4 GeV for next to highest p T muon p T ( )/m( )>0.3 Mass m( )<20 GeV 2.9<m( )<3.3 GeV is rejected to reduce J/. 9.3<m( )<9.7 GeV is rejected to reduce. Photon pseudo rapidity <1.44 Transverse momentum: p T ( )/m( )>0.3 Primary vertex The highest scalar sum of the p T 2 z <24 cm, r <2 cm d 0 <2 mm, z 0 <5 mm for muons Isolation Isolation cut is applied to photon and the highest pt muons. The next to highest pt muons are automatically within the isolation cone due to the muon pair mass. Selection looks reasonable.

14 14/15 CMS results with 19.7 fb 1 (=full) dataset at 8 TeV Statistically limited It will be very difficult to measure the form factor even at the High Luminosity LHC.

15 15/15 Summary and outlook The form factor of the observed Higgs boson can be measured in the decay channel of +. If the form factor deviates from unity, it (would) means the compositeness of the Higgs boson. However, the decay channel is very difficult to measure due to limited statistics Some papers claim that association production is sensitive to the form factor. arxiv: , arxiv: I d like to introduce these papers at the real AJW meeting at Kobe in May.