Neutrino Mass Physics at LHC
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Transcript Neutrino Mass Physics at LHC
Neutrino Mass Origin of
Matter: Probing at LHC
R. N. Mohapatra
MPI-Heidelberg Seminar,2009
Universe is full of matter
and “no” anti-matter
How do we know ?
(i) Solar probes have not exploded(ii) Sun sends us billions of particles and no
antiparticles since there are no natural fireworks
in the sky(iii) Anti-matter fraction in cosmic rays: 1 in 10,000
(completely understandable in terms of known
particle physics.)
Big Bang Nucleosynthesis
In the beginning, when the Universe was only a
second old, there were only protons and
neutrons- so how did all the elements we are
made of formed ?
Nuclear Reactions
responsible:
Things would have
been different if there
was anti-matter…
Matter Amount
Detailed analysis
CMB
B
nB nB
(6.2 0.15) 1010
n
Was it put in by hand at
the beginning ?
Not tenable since inflation empties the
universe—
It must be created by microphysics during
evolution
Baryon asymmetry from
Microphysics
Sakharov Proposed 3 conditions for generating
baryon asymmetry using microphysics (1967)
Baryon number violation;
CP violation;
Out of Thermal Equilibrium.
Standard model cannot doalthough it has both CP and Bviolation (too small CPV and not light enough
Higgs).
Premise of the Talk:
Discovery of neutrino mass requires new
physics beyond SM which has provided a
promising possibility for explaining the matterantimatter asym.
Can we test this physics at LHC ?
TeV scale Z’ related to
(Blanchet, Chacko, Granor, RNM: arXiv:0904.2974)
-mass:
Seesaw Paradigm for
neutrino mass
Why m m
?
q ,l
N R to SM with
Add right handed neutrinos
Majorana mass:
LY h L HNR M R NN
Breaks B-L
2
2
sym. of SM:
h vwk
After electroweak m M
R
symmetry breaking
11
Note: if MR=0, h 10
(too small)
SM
whereas even with TeV MR, h he (more reasonable)
MR
B-L breaking crucial
to seesaw:
Minkowski; Gell-Mann, Ramond Slansky,Yanagida, R.N.M.,Senjanovic,Glashow
Seesaw and Origin of
matter
Proposal:
(Fukugita and Yanagida ,1986)
R (1 )
R (1 )
Generates lepton asymmetry:
Gets converted to baryons via sphaleron interactions
of SM (‘t Hooft)
(Kuzmin,Rubakov,Shaposnikov)
No new interactions needed other than those already
used for generating neutrino masses !!
Seesaw provides a common understanding of both
neutrino masses and origin of matter in the Universe.
Scale
What is the seesaw scale ?
Is scale right for baryogenesis ?
Important because scale determines
whether the idea is testable !!
Seesaw scale
Neutrino masses do not determine the seesaw
scale- we do not know mD h vwk in seesaw formula
2
Type
I
seesaw
+
matm
mD mt
M R 10 GeV
GUT -10
GeVSmall neutrino mass could be indication for SUSYGUT;
Many interesting SO(10) GUT models.
No collider signals ! Possible tests in nu-osc.
With SUSY, in e (dependent on SUSY scale)
mD me Seesaw scale is around TeV
(corresponding Yukawa~106 ) ;
16
14
-
Natural -protected by chiral sym. N N
Many collider signals, possibly
e , 0
Leptogenesis Scale
Diagrams:
Two classes of models depending on RH mass pattern
High Scale leptogenesis: Expected in GUT theories:
Adequate asymmetry M 109 GeV for lightest RH
(for hierarchical masses)(Buchmuller, Plumacher,di Bari; Davidson, Ibarra)
Resonant leptogenesis: degenerate
N’s, self
1
energy diagram dominates:~ M i 2 M j 2 M ;
Resonance when M i M j ;works for all B-L scales.
(Liu and Segre’94; Covi et al’95 ; Flanz et al.’95 Pilaftsis’97)
An Issue with High scale
SUSY Leptogenesis
Recall the lower bound on the lightest RH neutrino
mass M N 109 GeV for enough baryons in GUTs
Problem for supersymmetric models:
they have gravitinos with TeV mass that are produced during
inflation reheat along with all SM particlesWill overclose the universe if stable for TR>10^9 GeV.
If unstable, Once produced they live too long -affect
6 7
T
10
GeV . (Kohri et al.)
BBN. R
Possible tension between LFV and leptogen.
Tension between gravitino
and high scale leptogenesis
Overclosure for stable and BBN constraint for
unstable ones: (Kawasaki, Kohri, Moroi,Yatsuyanagi,2008)
Leptogenesis and e
Both depend on RH neutrino mass hierarchy !!
(Chun,Evans,Morrissey,Wells’08; Petcov,Rodejohann,Shindou,Takanishi’05)
No such conflict for TeV scale leptogenesis !!
Goes well with collider friendly TeV seesaw !
Minimal TeV scale seesaw
No new interactions: N production at LHC can
happen only through N mixing ;
cross section observable
only if N mixing is > 102
(del Aguila,Aguilar-Savedra, Pittau)
However observed neutrino masses via seesaw for
M N ~100 GeV implies 106 Not observable at LHC.
N
Exceptions possible with specific extra global
symmetries-
TeV Seesaw with B-L
forces (Z’)
Seesaw effect observable at LHC even with tiny
N mixings as in generic neutrino models.
pp Z’+X; Z’NN followed by N-decay;
Like sign dileptons is the tell-tale seesaw signal.
How plausible is Local B-L ?
Neutrino masses seesaw scale much lower than
Planck scale New symmetry (B-L).
Is B-L global or local ?
SM only Tr (B-L)[SU(2)]^2=0 but Tr ( B L)3 0
But SM + R Tr ( B L) 0
B-L is a potential gauge symmetry3
Gauged B-L eliminates R-parity problem of MSSM and
ensures proton stability and dark matter: Another
advantage of B-L (RNM’86; Martin’92)
Extend SM gauge symmetry to include B-L- many ways-
Two Faces of B-L
Separate B-L vs SO(10) inspired B-L:
For
low B-L scale(TeV range), need B-L=2 Higgs
0
R (1,1,2) to break symmetry to implement seesaw, if
no new physics upto Planck scale.
TeV Z’ cross section at LHC
LHC Z’ reach - 4 TeV
Cross section for ppZ’NN (Z’NN branching ratio
~20%)
2.5 TeV Z’
to
5 TeV
Testing seesaw with Z’
decay
xsection for a 3 TeV Z’ ~fb
Seesaw signal: N=Majorana
N l W
, Z
Wjj , l
Di and Multi-lepton events: (X=jjjj)
PPZ’+X;
( )
pp l l X , l l l E\ , l l l l E\
Important for signal to bg: very high pT leptons
coming from N-decay; inv mass reconstruction:
(Del Aguila, Aguilar-Saavedra; Aguilar-Saavedra )
TeV scale Resonant
leptogenesis with Z’
Conditions:
(i) RH neutrinos must be degenerate in mass;
M1 M 2 M1,2 since h >10^-5 degeneracy ok anywhere
from 102 1010 ;technically natural and enough for baryogenesis!
(ii) Since there are fast processes at that
temperature, the net lepton asymmetry and
primordial lepton asym are related by
where <1 (efficiency factor); depends on rates for Z’
med. scatt. e e NN ;inverse decay lH N
Finding
Details
:
(Buchmuller,di Bari Plumacher)
Note: very small, when S >> D- i.e. lighter Z’;
As MZ’ increases, S ~ D, gets bigger and there
is a large range where adequate leptogen is
possible.
Adequate leptogenesis implies a lower limit on MZ’
Questions:
Is the lower limit in the LHC
accessible range ?
Yes; MZ’ > 2.5 TeV for MZ’ > 2MN
Can LHC directly probe the
primordial lepton asymmetry ?
Can LHC Directly probe the
primordial lepton asym. ?
Since 10 , small efficiency means l large
2
B
l
; Search for where is tiny so l is order 1.
Detectable at LHC by searching for like sign leptons
(Blanchet, Chacko, Granor, RNM: arXiv:0904.2974)
Basic idea:
l
At LHC, PPZ’+X
12.5% of time
N l W ,Z
NNl Xl X
Look for a CP violating observable !
( )
Direct probe of resonant
leptogenesis, contd.
Direct link between primordial lepton
asymmetry and CP violating LHC observable:
[(ll ) (ll )] 2 l
[ ]
3
For a ranges of Z’-N mass,
very small so that l~0.1-1;
visible at LHC:
Similarly for tri-lepton events.
Lower bound on MZ’ >2.5 TeV.
Numbers
300 fb^-1, expect 255 dilepton events (85% det eff.)
90% of events with jets or one missing E.
With no CP violation: 16 ++ and - - events;
Should rule out 0.25 at 2 sigma level.
An observation will directly probe leptogenesis, if RH
mass deg. is inferred from inv mass study.
How to tell how many N’s ?
For one N, there are 5 observables, Nl l but only two
inputs; we have three relations of type: N e N ee N
For 2 N’s, 4 inputs and 5 observables; only one relation.
none for three !
How natural is degenerate
RH spectrum ?
Degenerate RH neutrino specctrum might look odd
since quark and charged lepton masses are very
hierarchical:
RH vs Q,L masses:
(i) RH nu’s are Majorana masses whereas q, l masses
are Dirac;
(ii) RH masses arise at different scale and from a
different mechanism (B-L breaking) as against the
Q, L masses which arise from SM symmetry br.
(iii) Already large neutrino mixings are an indication
that in the seesaw formula RH neutrinos must
have some peculiarity.
A model
Gauge group
SU(2) L U (1) I3 R U (1) BLxO(3)
O(3)Hglobal
with RH nu’s triplet under O(3)H – all other fermion
fields singlet.
(1,1,2)1; (1,0,0) a1,2 + SM like Higgs.
Higgs:
Seesaw arises from following Yukawa
Lagrangian:
i ,a N a i ,a N b j ,b
L fN a N a hLHNa
M
M
2
h.c.
5
~
10
Choose
will give desired parameters.
M
Since Dirac Yukawas are ~10^-5, RH neutrino mass
splitting is radiatively stable.
Left-right embedding
Left-right Model: SU(2) L SU(2) R U (1) BL
Solves SUSY and Strong CP in addition to automatic RP
Unless MWR > 18 TeV,
L-violating scatterings e.g.
eR uR N d R
will erase lepton asymmetry.
(Frere, Hambye and Vertongen)
- Sym br. to U(1)I3RxU(1)B-L SM at TeVto do resonant leptogenesis.
Avoiding the WR bound:
If there are heavy vector like D-quarks mixing with d
in such a way that the doublet coupling to WR
becomes: u R for D-mass in the 10 TeV range,
D d
R
R
the dominant process does not occur. We need
4
10 to avoid the WR bound.
WR can be in the LHC range but the decay modes
purely leptonic.
Resonant leptogenesis in
generic LR model
Key question is whether degenerate RH neutrino
spectrum is radiatively stable to have leptogeneesis
possible generic LR models !!
Yes- since largest rad correction to RH masses
M N
h2
is
6
~
10
16 2
MN
Im[(h h) 2 ]
~
Whereas CP asymmetry is:
~
h h
MN
Which gives for h~10^-5.5, ~ 10
Not visible from Z’ decay but nonetheless a viable low
scale model for leptogenesis and dark matter !!
5
M N
A specific LR model:
LR+extra symmetries: SU (2) L SU (2) R U (1) B L xU(1)xxU(1)Z
Leads to RH mass matrix of form:
M1
0
0
0
0
M
0
M
0
Leads to two deg RH nu’s;
Dirac mass matrix:
0 * *
* 0 *
* * 0
Leads to realistic nu masses and mixings as well as
resonant leptogenesis with tiny sym br. Effects.
New collider signals for LR
case
Even if WR may be out of reach due to baryogenesis
constraints, other exotic Higgs bosons in LHC reach
1
(1,1,2) gets embedded into 2
0
1
2
Predicts doubly charged Higgs bosons in the sub-TeV
mass range coupling to like sign dileptons:
Resonant leptogenesis e e ,
dominant modes;
No 3e but ee allowed.
Unification Prospects: An
SO(10) possibility
Triplets with B-L=2 hard to unify to SUSY SO(10).
Both for TeV Z’ and WR, unification possible with B-L
=1 doublets breaking
Malinsky, Romao, Valle’05);
U(1)B-L; (Deshpande, Keith and Rizzo; 93;
Neutrino masses
Requires double seesaw for neutrino masses: Add an extra singlet field S in
addition to left and RH neutrinos which are part of {16};
Double seesaw: (
(RNM’86; RNM,Valle’86)
0
hvwk
0
N
S)
hvwk
0
M
0
M
m mDT M 1M 1mD
mD hvwk
Important: Unlike type I seesaw, Majorana character of RH
N depends on how large M is.
Suppresses like sign dileptons at LHC unless M ~1.
Leptogenesis possible but visible only for
M
~1.
Low scale SUSY LR-an
Alternative to MSSM
MSSM:
SO(10) Unified SUSYLR
1.
Rapid p-decay due to 1.No dim4 p-decay due to B-L
RP breaking
2. Neutrino mass not easy 2.Double seesaw for nu mass
3.
EW baryo in a corner
of parameter space.
4. Light Higgs and stop
3. Explains Origin of matter
5.
4. Z’ and like sign dileptons
at LHC
5. DM gravitino/Neutralino
DM gravitino/Neutra
lino
Conclusion:
LHC can directly probe the seesaw mechanism for neutrino
masses if the seesaw scale is in the TeV range and there is a
TeV scale Z’ regardless of neutrino mass pattern.
For certain ranges of the Z’-N mass, LHC can probe
resonant leptogenesis mechanism for the origin of
matter directly -find Z’-N in the allowed range
simultaneously with large like sign dilepton CP
asymmetry.
Use of inv mass peak and large PT leptons to reduce
background.
There are left-right and SO(10) SUSY GUT models
where such scenarios can be embedded, providing
theoretical motivation for low scale Z’ as well as TeV
scale leptogenesis .
Extra slides
Post-sphaleron baryogenesis and color
sextet scalars at LHC.
What if RH neutrinos are TeV
scale but non-degenerate ?
Can one have seesaw scale around a TeV so
LHC can see it and still understand the origin
of matter related to seesaw physics ?
Yes- baryogenesis can arise from seesaw
related physics below 100 GeV (but not from
RH N decay) (post-sphaleron baryogenesis)
(Babu, RNM, Nasri’06)
Predicts light color sextet Higgs (< TeV) that
can be observed at LHC via decay to two tops.
Q-L unify TeV seesaw
SU(2)LxU(1)RxU(1)B-L SU(2)LxU(1)RxSU(4)PS.
u uR R
, ,
d L e L d R eR
Recall Origin of RH nu mass for seesaw is from NN
Q-L unif. implies quark partners for R R i.e. u
- color sextet scalars coupling to up quarks ;
similar for dd- only right handed quarks couple. Come
from (1, 1, 10)
R R
c c
u
SU(4)PS breaks to U(1)B-L
above 100 TeV
Baryon violation graph
+ ucuc d cd c d cd c R R
+ h. c.
B=2 but no B=1; hence proton is stable but
neutron can convert to anti-neutron!
N-N-bar diagram
coupling crucial to get baryogenesis (see later)
Origin of matter
(Babu, Nasri, RNM, 2006)
Call Re R R= Sr ; TeV mass : S-vev generates seesaw
and
leading to B-violating decays
Baryogenesis: Due to high dimension of operator, Bviolating process goes out of eq. below 100 GeV.
Upper limits on Sr and
color sextet masses:
Two key constraints:
MS < 500-700 GeV
to get right amount of
baryons.
Decay before QCD phase transition temp:
Implies MS< MX < 2 MS.
Two experimental implications:
n n oscillation: successful baryogenesis implies
that color sextets are light (< TeV)
RNM’08);
(Babu, RNM, Nasri,06; Babu, Dev,
n n arises via the diagram:
nn 10 10 sec.
9
11
Present limit: ILL >10^8 sec. similar bounds from
Soudan,S-K etc.
10^11 sec. reachable with available facilities !!
A collaboration for NNbar search with about 40
members exists-Exploration of various reactor sites
under way for a second round search.
Color sextet scalars at LHC
Low seesaw scale + baryogenesis requires that sextet scalars
must be around or below a TeV:
Two production modes at LHC:
(I) Single production:
xsection calculated in (RNM, Okada, Yu’07;) resonance peaks above
SM background- decay to tt or tj depending on RH nu
Majorana coupling; directly measures seesaw parameters.
(II) Drell-Yan pair production: qq G ucuc *ucuc
( Chen, Klem, Rentala, Wang, 08)
Leads to tt t t final states:
LHC reach < TeV
Single Sextet production at
LHC:
Diquark has a baryon number & LHC is ``pp’’ machine
Depends on Yukawa coupling
Pair Production of Deltas
Due to color sextet nature, Drell-Yan production
reasonable- independent of Yukawa coupling
Leads to tt t t final states:
Can be probed upto a TeV
using like sign dilepton mode.
Phenomenological Aspects
f ij d c d c di d cj ...
c
Constraints by rare processes
mixing
K K
u cuc exchange
d
sc
c
d
c
s
c
Similarly B-B-bar etc. Can generate
neutrino masses - satisfying FCNC
d cdc
Details of FCNC
constraints:
Hadronic:
e
Examples of color sextet
couplings that work.
Down sector:
2
10
f uu
.3 * *
* 0 *
* * .3
Fits neutrino mass via type I seesaw.
Collider signal with WR
Depends on mass of WR; for WR in the few TeV
range, N-decay profile changes:
1
1
1
No WR case:
N l jj l jj l l E
3
With WR (TeV)
3
3
\
3
3
1
N l jj l jj llljj
8
8
4
No missing E in second case;
Trilepton signal very sub-dominant.