analysis of cp violating higgs in mssm using the process

20th july 07 India-CMS meeting 1

Analysis of CP Violating Higgs in MSSM using the process t->bH+, H+->WH1, H1->bb (Generetor level analysis)

Arun Nayak, Tariq Aziz (TIFR)Alexander Nikitenko (IC)


Introduction :

Higgs potential in MSSM at tree level is invariant under CP transformation, thus yielding CP conserving Higgs states.

The non vanishing phases of SUSY parameters (e.g. , At,b etc. ) induce CP mixing in Higgs sector through loop effects, thus providing indefinite CP neutral Higgs states Hi, i = 1, 2, 3

The effect of CP violation in Higgs sector results in a reduction of H1ZZ & H1tt couplingsand hence will affect Higgs production and decay rates.

CP violating benchmark scenario (CPX) corresponds to a certain value of CP violating SUSY parameters designed to showcase the CP violation in MSSM.

M~Q = M~

t = M~b = Msusy

= 4 Msusy |At| = |Ab| = 2 Msusy

Arg(At) = Arg(Ab) = cp


(LEP Higgs working group, hep-ex/0602042)

LEP limits for CPX scenario :

Because of the suppressed H1ZZ coupling, LEP can not exclude the presence of a light Higgs boson at low tan (~ 3.5 to 10)


Higgs Production in CPX scenario :

Phenomenological analysis by Ghosh, Godbole, Roy hep-ph/0412193

Because of the suppressed H1VV coupling one of the pseudo-scalar Higgs state is very lightSince there is correlation between the mass of charged Higgs and that of the pseudo-scalarHiggs state in MSSM, that implies a light charged Higgs, with MH+< Mt .

A suppressed H1VV coupling implies increase in H1H+W coupling because of the sum rule g2

HiVV + | gHiH+W- |2 = 1And that implies an increase in branching ratio of H+->H1W ( > 47% over the entire range)

The traditional decay mode H+-> is suppressed over an order of magnitude.

Hence both light H1 & H+ can be probed using this processpp -> t + t~ + X bH+ b~W

W H1 qq~(l) l(qq~) bb~

(hep-ph/0412193)


Generator Level Analysis :Total no. of events generated : 260000 for signal, (~30 fb-1) (generated using Pythia) 100000 for ttbb background(~30 fb-1)

2000000 for ttjj background cross section : signal cross section : parameters : (CP) = 90o, tan() = 5

M(H1) = 51 GeV, M(H+) = 133 GeV, M(top) = 175 GeV

* BR = 2 * 840 pb (ttbar NLO cross section) * 0.01(BR(t->bH+), using CPsuperH) * 0.567(BR(H+->H1W), using CPsuperH) * 0.99(BR(t->bW)) * 0.92(BR(H1->bb), using CPsuperH)

= 8.675 pb ttbb bkg cross section : 3.285 pb Generated using CompHEP with preselections : Pt(b)>15 GeV, |(b)|<3., DeltaR(b1,b2)>0.3, ttjj cross section : 506.99 pb CompHEP generated events with preselections : Pt(j)>15 GeV, |(j)|<3., DeltaR(j1,j2)>0.3


Reconstructions and selections:1) The events were generated with all possible W decay.

So the first selection was, the events with one W decaying to electron or muon and neutrino and other W decaying to 2 light quarks

were selected.The final state now contains 4 b quarks, 2 light quarks,

one charged electron or muon, and missing energy due to neutrino.

2) jets reconstructed in pythia using parameters MSTU(51)=100 , no. of eta bin MSTU(52)=70 , no. of phi bin PARU(51) =5.0 , total eta range PARU(52)=0.1 , tower threshold PARU(53)=20 , jet Et threshold PARU(54)=0.5 , cone size

3) events with Pt(b-quarks)>20 GeV, |(b-quarks)|<2.5 selected. events with 6 or more jets has been selected, b-jets found by matching jets to b-quarks in 0.4 cone, events with 4 b-jets found are considered. Remaining jets are treated as light quark jets.


4) Missing Et reconstructed from jets and charged lepton. By adding transverse momenta of jets and leptons vectorially.

5) one W reconstructed from charged lepton and missing Et. W boson momentum and energy calculated applying constraint on W mass as 80 GeV. This gives two solutions. Incase the solutions are imaginary, the event is neglected.

6) other W reconstructed from two light jets. Two light jets pair chosen from all possible combination of pair of light jets(if more than 2 light jets present) where the di-jet invariant mass lies within 65 to 95 GeV. If more than one jet pair fall within this mass window, the pair with invariant mass close to 80 GeV has been considered.

7) One top quark reconstructed from one of the b-jets and one of the W. total 12 combinations for quadratic ambiguity on W reconstruction from lepton and missing ET. The pair with inv. mass close to 175 GeV and within 150 to 200 GeV has been considered.


8) If the W used in 1st top reconstruction is one of Ws from l, then the other one has been considered as the wrong one and was neglected. On the other hand if the W used in 1st top reconstruction is from light jets, then there is quadratic ambiguity in the 2nd top reconstruction. 9) other top has been reconstructed from remaining 3 b-jets and remaining one W. (If quadratic ambiguity in W reconstruction and the W used in first top reconstruction is from light jets, then there are two combinations for 2nd top. The one close to top mass has been considered) The inv. mass cut for bbbW is 150 to 200 GeV.

10) H1 reconstructed from two b-jets ( out of 3-bjets in 2nd top, total 3 possible combinations. )

11) As seen in figure, peak of H1(2-bjets) mass distribution (distribution includes all backgrounds and also combinatorial backgrounds) lies around 50 GeV. So H1( or 2-bjets) with inv. mass close to 50 and falls within 35 to 65 GeV was used for H+ reconstruction. H+ has been reconstructed from H1 and W (in 2nd top) .


Top & W mass reconstruction :

The plots shows the reconstructed W mass for W->jj, and top mass for t->bl & t->bjj

The combinations with inv. mass close to W or top mass has been considered.

For t->bjj case, a mass window for jj inv. mass has been applied. 65 GeV < mjj < 95 GeV

W->j+j

t->b+l+MET t->b+j+j


Full simulation Jets using Iterative cone algorthim with cone size 0.5 (, )

W->j+jt->bW

W->j+jH+->H1W

Matching jets to quarks within 0.4 cone


t->b+l+MET t->b+j+jMatching jets to quarks within 0.4 cone


Top mass contd….

Distribution of top mass for t->bbbl & t->bbbjj , the combination with inv. mass close to top mass was considered. For t->bbbjj case, a mass window on jj inv. mass was applied.65 GeV < mjj < 95 GeV

t->3b+l+MET t->3b+j+j


Plots for 30 fb-1 data

H1 & H+ mass reconstruction :Reconstructed mass of H1(2 b jets) & H+(2 b jets and W). Plot includes both signal and background events. All combinatorial backgrounds are also included in 2 b-jet (H1) inv. massTwo b-jets with inv. mass close to peak of H1 mass distribution and lies within 15 GeV aroundthe peak were considered for H+ reconstruction.


2 lowest pT b-jets

pT difference of b-jets

Trying to get more such kinematical variables to get a likelihood function


ttjj background analysis :selection : selection of events similar to the signal events, one W-> lnu and other W->2 jets. Here the final state consists two b-jets from two top quark, atleast 4 light quark jets, one charged lepton.

One W reconstructed from charged lepton and mising Et with W mass constraint. Other W from two light jets( making all possible combination), W mass window 65 to 95 GeV. One top reconstructed from one of two b jets and one of two (or three) W.

Out of remaining light jets, two jets are selected as b-jets (to do a fake mis tagging) Assuming a maximum possiblity, two light jets which in combination with remaining one b and remaining one W gives the best top mass (within 175 ± 25 GeV), has been used as two b-jets. |(two selected jets)<2.5 Since I put a mass window on bbbW, I select 2-fake b-jets in this way. other light jets, if taken (mis tagged) as b-jets, will not survive in the selection cuts. This way of choosing two fake b-jets maximise the possible background from ttjj events.


Now there are 4 b-jets (including two fake b-jets), so one can reconstruct two top and H1 and H+ using the same procedure as signal eventswith same mass window for top, W and H1.

Since two fake b-jets has been considered, we multiply a constant(corresponding to mistagging rate) to the final selected events. Assuming that mistagging rate per jet is 1%, for two jets to bemistagged, a constant 0.01*0.01 = 0.0001 is multiplied to final selected ttjj events.

We assume a 50% b-tagging efficiency per jet. So we multiply a factor of 0.0625 (efficiency for tagging 4 b-jets) to signal and ttbb events and 0.25(efficiency for tagging 2 b-jets) to ttjj events.

Cross section of events after final selections : (i.e. no. of events in H+ mass distribution plots) signal : ~ 1.063 fb ttbb bkg : ~ 0.051 fb ttjj bkg : ~ 0.0296 fb


Signal & background contribution :

The major background to 2 b-jet invariant mass comes from the combinatorial backgroundswhich may make the distribution very wide and have long tail. But a clear peak on top of ithelps to chose the correct b-jet pair for the H+ reconstruction.

Plots for 30 fb-1 data


Selection details

Cross section

pb

(no. of events)

WlWqq

|(b)|

< 2.5

PT(b)> 20GeV

Atleast 6 jets

4 b-jets matched to b-quarks

RecoW(l+MET)

&W(2 jets)

65<mjj<95

Top(b-jet +W)

150<mt<200

Top(3 b-jets + W)

150<mt<200

H1

(2 b-jets)

35<mh1<65

signal 8.675(260000)

76100 17803 14265 6579 2634 2529 515 5101.063 fb

ttbb 3.285(100000)

29037 15563 13124 6672 2242 2212 27 250.051 fb

ttjj 506.99(2000000)

564403 458889 389639 340402

(2 b-jets only)

166713 152193 5109 46750.0296 fb

** multiply b-tag efficiency factor to final selected events to get the final state cross section


Simultaneous Top Reconstruction

Minimize sqrt((mrec(t->bW) – mtop)2 + (mrec(t->bbbW) – mtop)2)

Cross section

pb

(no. of events)

WlWqq

|(b)|

< 2.5

PT(b)> 20GeV

Atleast 6 jets

4 b-jets matched to b-quarks

RecoW(l+MET)

&W(2 jets)

65<mjj<95

Top(b-jet +W)

150 < mt <200

Top(3 b-jets + W)

150<

mt <

200

H1

(2 b-jets)

35 <

mh1

< 65

signal 8.675(260000)

76100 17803 14265 6579 2634 1793 892 8791.832 fb

ttbb 3.285(100000)

29037 15563 13124 6672 2242 1074 58 510.104 fb


Status : Started working with full simulated events generated using PYTHIA

First trying to understand reconstruction, b-tagging, jet energy correction etc…..

Joanne Cole & Claire Shepherd-Themistocleous (RAL), working using Fast Simulation (HERWIG+FAMOS) data. Trying to come out with a prescription for b-jets assignment to Top and Higgs (combinatorics), (optimize selection with cuts, Likelihood)

This was one of the discussion topic at LesHouches workshop, june 07. Other problem: background estimate from data (as in ttH->bb)


Backups


Separation of two b-jets used to reconstruct H1

analysis of cp violating higgs in mssm using the process

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