Transcript Search for Lepton Flavor Violation in the m + N -> t + N conversion (preliminary) S.N.

Search for Lepton Flavor Violation
in the m + N -> t + N conversion
(preliminary)
S.N. Gninenko
INR, Moscow
SPSC meeting, Villars,
September 22-28, 2004
SPSC, Villars, September 22-28, 2004
S.N.Gninenko
Outline
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Introduction
m+N->t+N conversion
Choice of signature
Experimental setup
Signal/Background simulations
Results
Summary
SPSC, Villars, September 22-28, 2004
S.N.Gninenko
Introduction
 SuperK'98 result: nu and/or nt are not massless, nu-nt mixing is large.
First observation of the LFV process with neutral leptons.
SM has no LFV: New physics.
 Suggests LFV for associated m, t –leptons
 LFV involving charged leptons has never been observed.
In many models LVF is natural
- SUSY
- Left-Right Symmetric Model
- Top seesaw,
- Extra dimensions
- Higgs mediated LFV
 In some models LFV processes for tau are enhanced over muon
processes
SPSC, Villars, September 22-28, 2004
S.N.Gninenko
Experimental Limits on LFV
Future Plans
Focus on m-e sector:
BNL: m -+Al->e-+Al < 10-16
PSI: m - ->e-+g < 10-14
J- Parc : m - ->e- < 10-18
For m-t sector
limits are quite
modest
SPSC, Villars, September 22-28, 2004
S.N.Gninenko
Why m + N -> t + N ?
e ~105 MeV
 What is the m+A->e+A conversion?
stop
capture
m
target
m
atom g.s.
conversion
 The similar experiment to search for
t+A->m+A would be very interesting, but too short
t-lifetime (< 0.3 ps) makes it unrealistic.
 Inverse process m+ N->t+N is possible
for muon energy Em > ~3 GeV at p or n.
 Is it interesting?
Gninenko at el.(2002), Sher & Turan. (2004)
 More theoretical attention is required compare to m+A->e+A
SPSC, Villars, September 22-28, 2004
S.N.Gninenko
Phenomenology
m
t
q
q’
Limits on L
S
PS
Black et al.
V
A
1/L2(m G t) (qa G qb)
t-> c : week limit on L for (mt)(u c)
enhances motivation to search
for m-t conversion
 emphasizes need to test LFV in
both rare t decays and in m-t
conversion at high energies
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Note: L~Br(t->. . .)-1/4
SPSC, Villars, September 22-28, 2004
S.N.Gninenko
Cross section for DIS m + N -> t + N
 cross section is model
dependent
 S cross section is ~ 1fb
at ~100 GeV
L=2.6 TeV
Scalar
 V cross section is suppressed
by the limit on L, s~1/L4
 primary muon energy should
be more than ~20 GeV
SPSC, Villars, September 22-28, 2004
L=12 TeV
Vector
S.N.Gninenko
Rate estimate for m + N -> t + N
N
m->t
= Nm s L r N A Br(t->..) e
muon energy Em=100 GeV
cross section s ~ 1 fb
muon integral flux Nm =10 15
target length L = 100 cm
target density r ~10 g/cm3,
e.g. PWO crystals
 branching ratio Br(t->..) ~ 17 %
t->m n n 17%
t->en n 17%
t->p n
11%
 efficiency e~100 %
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SPSC, Villars, September 22-28, 2004
t
m
Target
For (m t)(q q), q=u,d
N m->t = 120 events
For (m t)(u c) N m ->t
could be much higher
S.N.Gninenko
m + N -> t + N: Choice of the Signature
 DIS: m + N -> t +X (e, g, m, h, ..)
• for any t decay mode, the
m photoproduction is the main
source of background,
s(m-t)/sm(g) < 10-10
• complicated final state and analysis
• many possibilities for background
 quasi-elastic (QE) m + N ->t + N’,
and/or coherent m + A-> t + A (?)
• two-body reaction,
• low momentum transfer
• smaller cross sections
• enhancement for coherent m-t ?
• monoenergetic t
• small energy of N’ or N* , < ~ 1 GeV
SPSC, Villars, September 22-28, 2004
So far t->m n n, p n
Signature:
• single m, p
• large missing E
• missing Pt
• small ETARGET
S.N.Gninenko
Comment on background
Large missing energy is one of the keys,
m
good hermiticity is important
If detector is hermeticleakages are mostly due to X
neutrino decays: X -> n + Ln
(associated lepton,
LF conservation !).
100 GeV
If neutrino energy is ~a few 10s
GeV, small E L from X -> n + Ln
is very unlikely.
N
High suppression of
photoproduction.
m
<50 GeV
L
X
n
>50 GeV
of missing E
Week m->n reactions are
another source of background,
s(m->t)/s(m->n) ~10-4- 10-2
SPSC, Villars, September 22-28, 2004
S.N.Gninenko
Experimental Setup
 high rate capability: simple design
 active target with low energy threshold
 hermetic (good ~4p coverage) detector
 electromagnetic & hadronic calorimeter energy resolution, granularity
 high in/out going muon momentum resolution
 particles ID
Signature:
ECAL target
m/p
m
• single m, p
• large missing E
• missing Pt
HCAL
Hermiticity might confront m/p precision measurements
SPSC, Villars, September 22-28, 2004
• small ETARGET
• no EHCAL
S.N.Gninenko
Simulations
Analogy with n-induced reactions
used in simulations, e.g. :
nt + n -> t + p
Nomad configuration/software
(WA-96, Search for nm->nt)
m + n -> t + n
 nt + p -> t + n
m + p -> t + p
 nCC

mCC
......
SPSC, Villars, September 22-28, 2004
S.N.Gninenko
QE: m+ N->t+N signal simulation
mnn
 monochromatic t
 ~60% m below 50 GeV
 ECAL energy <1 GeV
 Pt < 1.5 GeV/c
SPSC, Villars, September 22-28, 2004
S.N.Gninenko
Background sources for QE (m->t) + t->m n n
The goal is to search for a few, at most ~100 m-t induced events among ~1012
m interactions. Background sources have to be explored down to 10-12
m n n final state
 Beam related:
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- low energy tail E < 50 GeV
QE or Coherent trilepton
- p /K decays in flight:
fp x PDec x Pm(E<E cut) x PECAL
K decays are more dangerous
mCC: m+N->n+X->m+ …
production m+A->m+n+n+A
 Coherent p production
m+A->n+p+A
m+n
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DIS like QEL
 Single charm production:
- m+N->m’+ neutrals + leakage
m+d,s->n+c -> s+m+n
- m+N->m’+ X->L+ n +……
(beam sign is important !)
SPSC, Villars, September 22-28, 2004
 ....
S.N.Gninenko
m+ N >n+X (mCC) sample
m+...
104 simulated events at 100 GeV
1 event found
SPSC, Villars, September 22-28, 2004
S.N.Gninenko
Coherent m+A->n+p+A
m+n
 Additional suppression
due to p decay in flight
~50% m < 10 GeV
 ECAL < 1 GeV
 Pt < 1.5 GeV/c
SPSC, Villars, September 22-28, 2004
S.N.Gninenko
Coherent trilepton production
m+A->n+m+n+A
CHARM II ’91: s~0.03 fb
at <E>~24 GeV
SPSC, Villars, September 22-28, 2004
S.N.Gninenko
Summary of background for
the QE reaction : m+ N->t + N-> m n n + N
Source of
background
Rate per m interaction
(very preliminary)
E< ~50 GeV muons in the beam
from p/K decays
tbd
m photoproduction
tbd
DIS m CC
~10-14
Coherent trilepton
m+A->m+n+n+A
~10-14
Coherent p production
m+A->n+p+A
~10-15
single charm in mCC
<10-14
SPSC, Villars, September 22-28, 2004
S.N.Gninenko
People/Institutes involved
Experimental groups
 LAPP, Annecy
 INR, Moscow
 IHEP, Protvino
 ETH, Zurich (help/experience with simulations, A.Rubbia’s group)
Theoretical groups
 College William and Merry, Williamsburg
 INR, Moscow
Also,
 Osaka Univ. , S. Kanemura et al., talk at Tau’04, 16 Sept. 2004.
 JINR, Dubna, S. Kovalenko
 H. Kosmas’s group (Ioannina and Tuebingen) , coherent m-t
cross section
SPSC, Villars, September 22-28, 2004
S.N.Gninenko
Summary
 search for LFV in muon to tau conversion would be interesting
and challenging
 further work is required to study
• muon beam : energy, intensity, purity, …
• target: composition, mass, …
• detector: rate capability, precision, ...
• production mechanism and cross sections
• best experimental signature
• signal/background: MC simulations, tools, …
and demonstrate feasibility of the experiment
SPSC, Villars, September 22-28, 2004
S.N.Gninenko