Yael Shadmi FNAL DEC 09 Feng, Lester, Nir, YS 0712.0674 Feng, French, Lester, Nir, YS 0906.4215...

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

http://bp3.blogger.com/_4D0Fa9rDwg8/R3xeqJkpIEI/AAAAAAAAAAM/aiGVFwrnhUg/S700/ice+cream.jpg

why flavor?


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?

beyond 0th order:

flavor is a fundamental puzzle in SM:why are fermion masses so

strange-looking?


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?


flavor not center-stage

LHC:

flavor – secondary role: constraints on new physics

focus on new physics behind EWSB


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

...


spreading belief: new physics is “flavor blind”

the only flavor-dependence, or generation-dependence in Nature is: SM Yukawa couplings


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


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)


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)


tomorrow:

flavor measurements at LHC:• mass measurements• mixings measurementstake one specific model as example to illustrate

these in detail


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


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


3. theory: neutrinos: mixing is large in the lepton sector can affect slepton sector Feng Nir YS

Masina Savoy Paradisi … .

end of motivation

now to our business:


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?


start with last question: Galon YS

common tool for measuring superpartner masses (differences): kinematic edges

1N

2N e

e e


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


but what if:

1N

2N

1,2l

,e ,e

1

2

cos sin

sin + cos

with small

l e

l e

m


edge smearedsignal degraded upon subtracting OF

should keep flavor in mind!

theory background: flavor and flavor symmetries


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


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


• when talk about flavor structure/parameters refer to the structure/parameters

of mass matrices/Yukawas pattern of flavor symmetry breaking


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 )?


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)


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


small parameters in mass matrix arise as powers of (small) symmetry-breaking parameter lambda

can explain all quark lepton mass matrices this way


theory background: lepton flavor in supersymmetry


gaugino

e

egaugino

gaugino

2consider in ( , , ) basis:

in principle not diagonalsleptonm e

lepton flavor in SUSY:

defines slectron, smuon, stau


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?


e

e

e

1l

2l

3l

2

2

ijij

ijKm

m

constrained quantities:


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


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)


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)


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


gauge-gravity hybrid models:


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


can vary by dialing messenger scalex

x GMSB

gravitymediation

1


because

GMSBgravity

mediation

can get large mixings even with

identity matrix

rare decays?

arbitrary texture

>>


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


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:


#

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


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


ijK

dial messenger scale (x) to scan:

2ijm


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


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]


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:


MFV models:

6 2 4 221 23( ) ( )10 tan 10 tan

mixings ~ 0

m m

m m


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


MFV models:

6 2 4 22312 ~ 10 tan ~10 tan

no mixings

mm

m m


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?


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)

http://images.google.com/imgres?imgurl=http://gfxdug.com/wp-content/gallery/illust/lamp%2520post%2520invitation.jpg&imgrefurl=http://gfxdug.com/&h=600&w=461&sz=31&hl=en&start=166&tbnid=GXTXHTYIT_K2kM:&tbnh=135&tbnw=104&prev=/images%3Fq%3Dlamp-post%26start%3D160%26gbv%3D2%26ndsp%3D20%26hl%3Den%26sa%3DN


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


EVENT FULLY RECONSTRUCTIBLEin principle: can measure all masses observe mixings on event-by event basis


1 ~ Rl e

bl

2N ,L il

al

1N

1 ~ Rl e

bl

2N ,L il

al e

1N

for example:


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


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


tomorrow:specific example in detail

[from theory POV: flavor-dependencenot by hand]

illustrate generic features: near-degeneracy, mixings

Yael Shadmi FNAL DEC 09 Feng, Lester, Nir, YS 0712.0674 Feng, French, Lester, Nir, YS 0906.4215...

Documents

Transcript of Yael Shadmi FNAL DEC 09 Feng, Lester, Nir, YS 0712.0674 Feng, French, Lester, Nir, YS 0906.4215...