Post on 26-Dec-2015
Yael Shadmi FNAL DEC 09
Feng, Lester, Nir, YS 0712.0674 Feng, French, Lester, Nir, YS 0906.4215 Feng, Galon, Sanford, YS, Yu 0904.1416
Feng, French, Galon, Lester, Nir, Sanford, YS, Yu 0910.1618
Lepton Flavor at the LHC
e
Yael Shadmi FNAL DEC 09
LHC
Large Hierarchy ColliderLittle Higgs Collider
…Light Higgs Collider emphasis on new physics behind EWSB
why flavor?0th order: why not?
perhaps there is new physics that couples differently to electrons,
muons, taus?
Yael Shadmi FNAL DEC 09
quark masses: small (vastly different) parametersquark mixings: small (vastly different) parameters
leptons: small parameters in charged lepton masses
5 3 2( , , ) ~ 100 GeV (10 ,10 ,10 )em m m
large mixings: much less mysterious on their own but why so different from quark mixings?
Yael Shadmi FNAL DEC 09
flavor not center-stage
LHC:
flavor – secondary role: constraints on new physics
focus on new physics behind EWSB
Yael Shadmi FNAL DEC 09
indeed: new physics (if there) is doing a great job of hiding itself:
11
7
8
MEGA
BABAR
BELLE
Br( e ) < 1.2 10
Br( e ) < 1.1 10
Br( ) < 4.5 10
...
Yael Shadmi FNAL DEC 09
spreading belief: new physics is “flavor blind”
the only flavor-dependence, or generation-dependence in Nature is: SM Yukawa couplings
Yael Shadmi FNAL DEC 09
of course, SM Yukawas are there:
running: gauge+Yukawa
spectrum of new particles sensitive to Yukawas
but Yukawas are only source of flavor violation:
such models are Minimally Flavor ViolatingDAmbrosio,Giudice,Isidori, Strumia
Yael Shadmi FNAL DEC 09
will see:• this is overkill: natural SUSY models that are non-MFV
(contain new sources of flavor-dependence in lepton sector) and still < current bounds on flavor-violation
• if new physics is there and is non-MFV:1. affects signatures of new physics2. can teach us about flavor
• example today: supersymmetry (with new sources of flavor dependence)
Yael Shadmi FNAL DEC 09
PLAN: • motivation• flavor basics flavor symmetries• lepton flavor in supersymmetry basics: low
energy constraints, implications for model building
• example models: gauge-gravity hybrid models (concrete framework for studying flavor dependence at colliders)
Yael Shadmi FNAL DEC 09
tomorrow:
flavor measurements at LHC:• mass measurements• mixings measurementstake one specific model as example to illustrate
these in detail
Yael Shadmi FNAL DEC 09
why (charged) leptons?
1. experiment: easy first step:• “self-tagging”: flavor tagging much harder with quarks• cleaner: energy determination, QCD bckgnd
2. experiment (theory motivated): sleptons usually lighter than squarks
, ,e
Yael Shadmi FNAL DEC 09
2 2 22 1
2 23
2 2 22 1
2 23
GMSB: ,
mSUGRA: running ,
running
AMSB: sleptons even tachyonic..
sleptons appear at the end of decay chains
measur
l
q
l
q
m
m
m
m
ing their masses should be easier
Yael Shadmi FNAL DEC 09
3. theory: neutrinos: mixing is large in the lepton sector can affect slepton sector Feng Nir YS
Masina Savoy Paradisi … .
Yael Shadmi FNAL DEC 09
slepton flavor @ LHC• if interested in flavor:1. detecting flavor dependence?2. measuring flavor dependence?
1. slepton mass splittings 2. slepton mixings
3. lessons about theory of SUSY breaking? theory of flavor?• if not interested in flavor: should we still worry about it?
Yael Shadmi FNAL DEC 09
start with last question: Galon YS
common tool for measuring superpartner masses (differences): kinematic edges
1N
2N e
e e
Yael Shadmi FNAL DEC 09
e+ e- invariant mass has sharp endpoint
background: uncorrelated leptons:
2 2 2 2 22 1( )( )e e N e e Nm m m m m
( )e e e e
Yael Shadmi FNAL DEC 09
what is flavor? (a bad word..)
• really flavor=generation• each fermion (matter field of SM) carries: gauge indices (e.g. color index) a generation index i=1,2,3 (=flavor index)the only property that distinguishes fields withdifferent i’s is MASS“flavor” refers to masses of different-generation
fields
Yael Shadmi FNAL DEC 09
rephrasing in terms of symmetry:• if Yukawas=0: global symmetry: U(3)Q x U(3)U x U(3)D x U(3)L x U(3)E
(flavor symmetry)
• so: masses mij = Yij <H>
• break U(3)5 flavor symmetry
Yael Shadmi FNAL DEC 09
• when talk about flavor structure/parameters refer to the structure/parameters
of mass matrices/Yukawas pattern of flavor symmetry breaking
Yael Shadmi FNAL DEC 09
flavor symmetries (Froggatt-Nielsen)
consider charged lepton mass matrix:5
3
2
10
100 GeV 10
10leptonm
underlying theory?mass matrix breaks U(3)LxU(3)E -- but breaking is smallexplained by approximate symmetry ( within U(3)LxU(3)E )?
Yael Shadmi FNAL DEC 09
take flavor symmetry to be U(1): Li : charges QLi
Ei : charges QEi
Higgs: charge zeronew fields (charged under SM, flavor symm) at high scale Mbelow M: SM + singlet S (U(1) charge -1)
Yael Shadmi FNAL DEC 09
1
Li Ej
Li Ej
ij iQ j
Q Q
QML c HS L E
order 1
U(1) broken
with
c hoose 0.2
Li Ej
Li Ej
Li Ejij i j ij i
QQ Q
Q j
Q
Q
S
M
S
c HL E Y
M
c
M
S
Yael Shadmi FNAL DEC 09
small parameters in mass matrix arise as powers of (small) symmetry-breaking parameter lambda
can explain all quark lepton mass matrices this way
Yael Shadmi FNAL DEC 09
gaugino
e
egaugino
gaugino
2consider in ( , , ) basis:
in principle not diagonalsleptonm e
lepton flavor in SUSY:
defines slectron, smuon, stau
Yael Shadmi FNAL DEC 09
diagonalize it to form slepton mass eigenstates:
mixings:
gauginoil
jl
ijK i j
1 2 3 1 2 3, , : , , generically differentl l l m m m
new sources of flavor-dependence (generation-dependence)on top of SM Yukawas
rare decays?
Yael Shadmi FNAL DEC 09
2
2
ijij
ijKm
m
1. degeneracy:slepton mass matrix proportional to the identity
2. alignment:slepton mass matrix “aligned”with lepton mass matrix(so both are diagonal togetherand mixings are small)
susy breaking models (which generate the slepton masses)must give either:
3. decoupling: all sleptons heavy—not too interesting for us
or combination:today: 1+2
Yael Shadmi FNAL DEC 09
degeneracy has become holy grail of SUSY models:
• GMSB: by construction: superpartner masses determined by gauge
interactions• AMSB: automatically: superpartner masses
largely determined by SU(3)xSU(2)xU(1) representations and couplings
• Gravity mediation: by “wishful thinking”: start with common scalar masses at high scale
(mSUGRA)
Yael Shadmi FNAL DEC 09
in all of these:• only source of flavor dependence is Yukawas Minimally Flavor Violating• sleptons degenerate up to the effect of
Yukawas in the RGEs• smuon, selectron degenerate• no inter-generation mixing (as far as collider experiments go)
Yael Shadmi FNAL DEC 09
today will discuss “gauge-gravity hybrid” models Feng Lester Nir YS 0712.0674
non-MFV
flavor effects can be substantial Other examples:
Nomura Papucci Stolarsky Kribs Poppitz Weiner
focus isn`t on models—nothing fancy: just want a framework in which to study flavor measurements at the LHC
Yael Shadmi FNAL DEC 09
models: start with GMSB:
2
sleptonm GMSBgravity
mediation+
always there22 1 0 0
# 0 1 0 4
0 0 1mess
F
M
2
~ arbitrary texturePl
F
M
Yael Shadmi FNAL DEC 09
because
GMSBgravity
mediation
can get large mixings even with
identity matrix
rare decays?
arbitrary texture
>>
Yael Shadmi FNAL DEC 09
to suppress rare decays:
flavor symmetry [ U(1)xU(1) ]
• broken by small parameter• two roles:1. explains fermion masses: small numbers in fermion masses = powers of small parameter
Yael Shadmi FNAL DEC 09
2. suppresses FV in slepton sector (alignment): Nir Seiberg
off diagonal elements in both lepton and slepton mass-matrices are suppressed by powers of small parameter:
Yael Shadmi FNAL DEC 09
#
2
" " = ( )
1
, , (1)
-entry:
in fermion mass basis:
Li Lj
lepton
slepton
Q Q
m O
A
m B A B C O
C
ij
#
slepton matrix approximately diagonal
mixings can be small: ( )O
Yael Shadmi FNAL DEC 09
GMSB identity
gravitymediation small
close to diagonal(thanks to flavor symmetry)
so flavor constraints taken care of by a combination of:2degeneracy ( small )
and alignment ( small )ijK
m
Yael Shadmi FNAL DEC 09
different classes of models determined by:• messenger scale (x)• number of messengers NLSP: neutralino/charged slepton• flavor symmetry U(1)xU(1)• charges under flavor symmetry
charges chosen so that: 1. fermion mass parameters correct2. sufficient alignemt for specific x
Yael Shadmi FNAL DEC 09
4 specific classes of models ranging from pure alignment (high mess scale/no GMSB) to x=0.001 (mess scale at 10^14 GeV)
[below that FV comparable to Yukawa contributions]
[“class of models”=up to O(1) coeffs]
Yael Shadmi FNAL DEC 09
21 23
2 3
1
2
2
3
3
( ) ( )1 1
mixings:
~ (1,10 ,10 )
~ (10 ,1,0.1)
~ (10 ,0.1,1)
R R
R R
m m
m m
l
l
l
R-sector:
Yael Shadmi FNAL DEC 09
L-sector:
23121 2 3
3 6
A 1 1 no mixings
B 0.1 0.1 (1,10 ,10 )
mml l l
m m
3 6 6 3
2 2 2 2
3 3
(10 ,1,10 ) (10 ,10 ,1)
C 0.02 0.02 (1,10 ,10 ) (10 ,1,1) (10 ,1,1)
D 10 10 O(1) mixings
Yael Shadmi FNAL DEC 09
can we detect this sort of LFV?
[0th order: can LHC distinguish between MFV and non-MFV in leptons?]
can we measure such mass splittings?
if yes—can we measure such mixings?
Yael Shadmi FNAL DEC 09
meta-stab
le slepto
n
NL
SP
• everything visible:no missing energyreconstruct full event
•eliminate SM bgnd
tough: strategy (first stage): look for lost coin under lamp
Tarem et al (ATLAS)Chen et al (CMS)
Yael Shadmi FNAL DEC 09
meta-stable slepton LSP:
• being dominantly GMSB models: LSP can be gravitino with slepton NLSP (selectron, smuon OR stau: don`t know O(1)! )
• NLSP decays to gravitino outside detector so its track is observed in the muon detector
“slow muon”
but also possiblein SUGRA
Yael Shadmi FNAL DEC 09
EVENT FULLY RECONSTRUCTIBLEin principle: can measure all masses observe mixings on event-by event basis
Yael Shadmi FNAL DEC 09
so:
• new physics need not be flavor blind or MFV flavor could play interesting role at the LHC• in example today:hierarchy problem, EWSB: SUSYSM flavor (masses, mixings): flavor symmetry
(lepton, slepton)i: same charge qi under flavor symmetry
Yael Shadmi FNAL DEC 09
lepton masses, slepton masses determined by different combinations of qi’s
measuring slepton masses, mixings: more inputs(on top of lepton masses) to determine qi
not only lepton flavor constraining SUSY:SUSY could answer SM lepton flavor questions