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the hunt for the higgs boson is the main aim of the lhc to complete the validation of the basic principles of the standard model ( sm ) .
the main production mechanism of the higgs boson at hadron colliders is the gluon fusion via heavy quark loop .
therefore the number and nature of the quarks contributing to that loop play a crucial role . in the realm of the sm as we know it today , with 3 families , the main contribution is from the top quark .
however , the number of families in the sm is a free parameter and the lep-1 data fixes only the number of fermion families with a light ( @xmath3 ) neutrino . the ew precision data , on the other hand , favor the 3 and 4 family cases equally @xcite .
moreover a fifth and even a sixth family may be allowed depending on the precision measurements on @xmath4 boson properties . on the other hand ,
the upper limit on the number of families comes from the asymptotic freedom property of the qcd as 9 .
if there is a fourth sm family , as also implied by the flavour democracy hypothesis ( see @xcite and references therein ) , its quarks are expected to be heavier than 250 gev , contributing to the higgs boson production loop in addition to the top quark .
such a contribution enhances the production cross section for the higgs boson and makes the gluon fusion channel sensitive to new physics .
recently at the tevatron , the process @xmath5 is investigated after taking into account the possible enhancement due to a fourth sm family @xcite . this mode is the most promising for the higgs masses between 130 and 190 gev both at the tevatron and the lhc .
however , its observation at the tevatron requires the enhancement from the fourth family .    at the lhc , in three sm family case , for a heavy higgs of mass between 200 and 500 gev
the most prominent mode is the `` golden '' mode : @xmath6 . for an even heavier higgs , between 500 and 800 gev , the `` semi - golden '' mode ,
@xmath7 becomes the preferred mode of discovery . above 800 gev
, the discovery channel has to be the @xmath8 @xcite .
the fourth sm family quarks would increase the production cross section by a factor between 5 - 8 depending on the higgs boson mass @xcite decreasing the required luminosity for a 5@xmath9 discovery .
the other fourth family members , depending on their mass , could also allow new search channels for the higgs boson . in this note , we argue that the @xmath10 channel , called hereafter the `` silver '' mode , could be competitive with the golden mode for some region of the higgs and @xmath1 masses . fig .
[ fig : gold - silver ] contains the feynman diagrams of the golden and silver channels for the higgs boson discovery .
[ fig : gold - silver ]
the fourth family neutrino , @xmath1 , couples to the higgs boson with a vertex coefficient proportional to its mass providing a new decay channel .
the branching ratios as a function of the @xmath1 mass for two higgs mass values , 300 and 500 gev , are presented in fig .
[ fig : br ] . as seen br(@xmath11
is maximized between 90 and 100 gev as 8.8% for @xmath12300 gev and between 150 and 160 gev as 5.7% for @xmath12500 gev .
below we compare the `` golden '' and `` silver '' modes in these mass ranges .
values 300 gev ( dashed lines ) and 500 gev ( solid lines ) , title="fig:"][fig : br ]    the decays of the @xmath1 are governed by the leptonic 4x4 ckm matrix . for numerical calculations
, we consider the parameterization in @xcite which is compatible with the experimental data on the masses and the mixings in the sm leptonic sector . in this case , the br(@xmath13 and br(@xmath14 which imposes the main discovery signal as two muons and four jets considering the hadronic decays of the @xmath4 bosons in the final state .
note that the `` silver '' mode contains only muons compared to both electrons and muons of the `` golden '' mode .
this scenario with @xmath15 gev , leads to br(@xmath16=1.22@xmath17 which should be compared to the `` golden '' mode branching ratio of 1.12@xmath18 , giving an enhancement factor about 11 .
corresponding numbers for @xmath19 gev are 1.88@xmath17 and 1.25@xmath18 respectively , yielding an enhancement of about 15 times . we believe that an order of magnitude higher statistics would compensate the possible inefficiencies associated with jet detection and hadronic @xmath4 reconstruction .
an associated channel to the `` silver '' mode is the case where one of the @xmath4 boson decays leptonically : @xmath20 ( @xmath21 ) .
the final state in this case will be @xmath22 .
the number of such events is 63% of the `` silver '' mode discussed above , bringing the total enhancement factor up to 24 ( 18 ) compared to the `` golden '' mode for a higgs boson of @xmath23=500 ( 300 ) gev .
if the fourth family neutrino is of majorana nature , an experimentally clear signature would be available , namely same sign muons as decay products of @xmath1s .
although in this case , the number of expected signal events is halved , the sm background is practically negligible making this mode deserve the name `` platinum '' mode .
if nature allows , a double discovery in the first year of the lhc start up is in the realm of the possible : the fourth family neutrino and a heavy ( @xmath24 gev ) higgs boson . for @xmath15 ( 500 )
gev the fourth family quarks increase the higgs production cross section to 7@xmath2510@xmath26 ( 2.5@xmath27 ) fb compared to @xmath28 ( @xmath29 ) fb in the 3 family sm case @xcite .
consequently , the so called `` silver '' mode allows about 850 ( 470 ) higgs bosons ( and obviously twice as many @xmath1 ) to be reconstructed with 1fb@xmath2 luminosity for @xmath12300 ( 500 ) gev and @xmath30100 ( 150 ) gev . the monte carlo simulation to verify this statement is under progress .
s. s. would like to thank p. jenni for the provided support during his visit to cern .
g. u.s work is supported in part by u.s .
department of energy grant de fg0291er40679
. s. s. is also grateful to gazi university science and letters faculty deanship for relieving him from his teaching duties .
the authors would like to thank m. karagoz - unel for useful comments .
* note added : * after the submission of the first version of this note , an arxiv entry made one month ago , mentioning an enhancement to higgs discovery from @xmath31 channel was brought to our attention @xcite .
we investigate the possible enhancement to the discovery of the heavy higgs boson through the possible fourth sm family heavy neutrino . using the channel @xmath0 it is found that for certain ranges of the higgs boson and @xmath1 masses , lhc could discover both of them simultaneously with 1fb@xmath2 integrated luminosity .    
 s. sultansoy[multiblock footnote omitted][multiblock footnote omitted][multiblock footnote omitted ]