Dan Holmes

1
Preliminary investigations into the physics
channels gg/qq?bbH(???) Dan Holmes, student at
Bristol. ( )
2
Overview

• I looked at 1 and 2 b-jet requirement for each
  of
• SM qq/gg?bbH(??), MH125 GeV
• MSSM bbh(??).
• MSSM bbH(??), tanß30, MA116 GeV (MH128)

b
?
H
gg
?
b
b
H
qq
b

• Motivation measurement of Yukawa b-H coupling,
  ratio of H-b/H-t etc.., Higgs verification, MSSM
  verification
• I used Pythia vers 6.215
• Also Spiras HQQ (Hbb production x-sect) and
  HDECAY (BR of H???) (HDECAY vers 3.0) and HQQ
  (verslt1.1!!)

3
Background

• The principle background for this channel is
  qq/gg??? with a jet (or 2) from ISR faking my
  b(s).
• I made pre-selection cuts in the production of my
  background so that the mass of the hard
  scattering subsystem (in effect the invariant
  mass of the ??) was 15 GeV from my Higgs mass.

4
Standard Model, H

• Scan over MH to find where BRx-sect (seff) is
  biggest
• Spira? x-sect, BR.
• ..then work out efficiency from addition of
  acceptance cuts (require 1 bgt30 GeV and 2 ? gt20,
  gt30 GeV, all 3 in etalt2.5) using Pythia.

5
Standard Model, H
seff (fb) as a function of MH after acceptance
cuts.
biggest signal around MH125 GeV
6
Closer look at SM, MH125
Next, I ran some bigger Pythia samples for
signal(1 mill) and background (5 mill). Tables
below show the results for requiring 1 and 2 jets.
effectively zero background in case for
educated cuts, figure given comes from modeling
the exponential decay of the background.
7
Closer look at SM, MH125
Background (left) and signal for region of no
background (right) plotted below in 2-d cut
space cutting on Pt of max jet and delta gamma
Pt. ..both are decaying exponentials, background
is bigger but decays faster. (plots from 1-jet
case)
8
SM, MH125 max pt jet
Plots below of Pt of max jet, only acceptance
cuts applied. (200k signal, 2.4 mill back.)
signal
background
..so hopefully b-tagging efficiency will also be
a very useful cut at the next stage.. (you can
also see why Pt_jet_max was such a good cut..)
9
SM H thoughts..

• 2 jet case
• Signal too small 1.1 event past acceptance for
  100 fb-1
• 1 jet case
• Signal exists (26 signal evts past acceptance for
  100 fb-1)
• ..also possible almost complete reduction of
  principal background, especially once I use
  realistic b-tagging.
• ..worth looking at further..

worth re-checking with latest version of HQQ,
maybe up to a factor 2 bigger x-sect..
10
MSSM light h
again the caveat of the new HQQ might give me
a bigger x-sect but it aint gonna be massive.

• Scan over MA, tanß.
• hi tanß means better b coupling but big
  reduction in H?? ?.

..so the signal for MSSM h is really tiny ..lt0.7
fb over MA, tanß range scanned. ..gets better
with reducing tanß but ltbewaregt even some of
range on this plot is excluded by LEP.
_at_ MA300 GeV tan ß(30), Mh127GeV tan ß(5),
Mh122 GeV
_at_ MA150 GeV tan ß(30), Mh127GeV tan ß(5),
Mh115 GeV
11
MSSM heavier H

• Scan over MA, tanß.

There is some signal here Best is high tanß,
low MA
this is worth looking at further..
_at_ MA116 GeV tan ß(30), MH128GeV tan ß(5),
MH139 GeV
_at_ MA300 GeV tan ß(30), MH300GeV tan ß(5),
MH303 GeV
12
MSSM H, tie down MA, tanß

• Closer look at seff in MA for tanß30 (4
  different models for BR.)

Spira told me to use models 1 or 4 ..so the
eclectic approach suggests I have a 3-4 fb signal
for MA about 116.
take MA116, tanß30 ..this makes MH128GeV
13
MSSM H, acceptances cleverer cuts

• I ran some Pythia samples (200k signal, 1.2mill
  back) again and imposed acceptance cuts followed
  by some more educated ones

effectively zero background in case for
educated cuts, figure given comes from modeling
the exponential decay of the background.
14
MSSM big H (2-d) cuts
Signal (left) and background (right)
..as before with SM H, both are decaying
exponentially in 2-d cut space background is
bigger but decays much faster. There appears to
be some periodicity in the signal.
15
MSSM big H Pt of jets
Plots below of Pt of the 2 jets, only acceptance
cuts applied. Signal 200k, back 1.2 mill.
Pt jet Max
signal
background
signal
Pt jet Min
background
..so I rekon b-tagging efficiency will be very
useful at the next stage, maybe the 2-jet case
will be a better prospect than the 1-jet because
of it.
16
MSSM big H thoughts..

• Signal seen in both 1 and 2 jet required samples.
  For both it seems to be possible to get rid of
  the background. The 2 jet case may well be the
  best choice once realistic b-tagging is
  implemented.
• ..worth taking further..

17
qq/gg?bbH(??) conclusions

• SM, MH125 GeV, 1-jet case 26 events past accept
  for 100-1 fb, background may be killable.
• MSSM, H, MA116, tanß30 (MH128 GeV)
• 1-jet case 53.5 evts past cleverer cuts for
  100 fb-1, principle background effectively zero
• 2-jet case 37.7 past cleverer cuts for 100
  fb-1, principle background effectively zero

These two look promising so i will have a look at
these with CMSJET to introduce some smearing and
b-tagging ..maybe use compHEP/MADGraph for the
background..
SM, 2-jet case and MSSM h, signals are too tiny.