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Search for a Light Particle
HyangKyu ParkCHEP, KyungPook National Univ.
HEP Seminar, KISTI
Sep. 29, 2009
Motivations for a Light Particle Search
Recent astroparticle observations:ATIC, PAMELA and etc.
Light Higgs particle in Next-to-Minimal SUSYB-factory is complementary to LHC.
HyperCP exotic eventBelle, BaBar, CLEO, D0 and E391a experiments
These topics are highly connected each other.
Search for a Light Particle from Particle Decays
Many experiments have searched for a light boson:
Astroparticle Observation:The ATIC Instrument & Program
ATIC 2 Flight from McMurdo 2002
Total of 4 flights – 3 successfulTotal of 4 flights – 3 successful
Goal: measure CR fluxes of electrons, protons, and nuclei to ~ 1 TeV
Instrument not optimized for electron detection.
Astroparticle Observation: ATIC Results
ATIC 1+2
Significance of bump for ATIC1+2 is about 3.8
This caused considerable excitement and speculation.
Recently analyized Flight 4 data shows same “bump” and significance of ATIC1+2+4 is 5.1
Dashed line indicates expected electron spectrum extrapolated from lower energy
ATIC 1+2+4
Preliminary
ATIC 1ATIC 2ATIC 4
Preliminary
Astroparticle Observation: PAMELA Satellite Experiment
Launched in Spring 2007Launched in Spring 2007A High Energy Electron EventA High Energy Electron Event
Magnetic Spectrometer measure sign of charge and momentumMagnetic Spectrometer measure sign of charge and momentum
Goal: measure e+/e-, p/ , Goal: measure e+/e-, p/ , HeHe/anti-/anti-HeHe, etc. as well as spectra, etc. as well as spectrap
Astroparticle Observation: Anti-Proton Fraction (PAMELA)
Nothing surprising seen in anti-proton / proton ratioNothing surprising seen in anti-proton / proton ratio
Anti-proton abundance consistent with expectations for secondary CR Anti-proton abundance consistent with expectations for secondary CR production off the Interstellar Mediumproduction off the Interstellar Medium
Astroparticle Observation: PAMELA Positron Fraction
Unexpected!Unexpected!Positron fraction increases above 10 GeV!
Note that Geomagnetic cut-off of primary cosmic rays is O(10 GeV)
Data below 10 GeV is dominated by trapped radiation and fluxes are sensitive to Solar Cycle
ATIC Electron Spectra & PAMELA eATIC Electron Spectra & PAMELA e++ Fraction caused excitement in 2008! Fraction caused excitement in 2008!
Plausible Explanation for ATIC & PAMELA
ATIC: excess in e+ + e- spectrum between 300 GeV and 800 GeV. PAMELA: excess in e+ spectrum from 10 GeV to 100 GeV.
No excess in proton and anti-proton spectrum Dark matter annihilation mediated by a extra gauge boson (U-
boson), mass < ~1 GeV.U-boson -> e+ e- , μ+ μ-
U
U
DM
DM
NMSSM (Next-to-Minimal SUSY SM) problem in MSSM (Minimal Supersymmetric Standard Model)
The simplest possible extension of the MSSM:
– Introduce just one extra gauge-singlet Higgs field N.– This is common in string models.– All the good properties of MSSM
are preserved. Higgs bosons in NMSSM
h0, H0, A0, H+,H-, s0, a0
LEP access at M2b~100 GeV is welldescribed:
(Note: The mass of the lightest Higgs in MSSM < 130 GeV)
[R. Dermisek & J. Gunion, PRD 73, 111701(2006)]
Light Higgs Search at D0
gg → h→aa, a→μ+μ-, τ+τ-
Search Range: 0.214 GeV≤ mA ≤ 20 GeV
2μ 2τ channel
Light Higgs Search at BaBar
Υ(2S,3S)→γa, a→μ+μ-
Search Range: 0.212 GeV≤ mA ≤ 9.3 GeV
Light Higgs Search at CLEO
Υ(1S)→γa, a→ μ+μ-, τ+τ- Search Range: 0.212 GeV≤ mA ≤ ~9.0 GeV
Light Particle Search at Belle
• HyperCP exotic event, X(214) B decays e+e- collisions
Eventually both analysese move to general light particle search.
Introduction : HyperCP Exotic Event, X(214)
Observation of 3 events for + p +- decaysH.K.Park et al. (HyperCP Collaboration), PRL 94, 021801 (2005)
Mass of X(214) : 214.3 MeV/c2 Possible interpretations
– Sgoldstino (pseudo-scalar): D.S.Gorbunov and V.A.Rubakov, PRD 73, 035002 (2006)
– Low mass Higgs: X.-G.He, J.Tandean and G.Valencia, PRL 98, 081802 (2007)
– U-boson (vector particle): M. Reece and L.-T. Wang JHEP 0907, 51 (2009),C.-H. Chen, C.-Q. Geng and C.-W. Kao, Phys. Lett. B 663, 100 (2008).
sgoldstino (I)
In SUSY, spontaneous SUSY breaking generates Goldstone fermion (Goldstino), which gives the longitudinal component of gravitino.There should exist superpartners of Goldstino: sgoldstinos, pseudoscalar P0 and scalar S0
The masses of P0 and S0 are generally arbitrary. Perhaps < a few GeV or a few MeV
P0 and S0 can couple with SM particles, quarks, leptons and gauge bosons.
Interactions of sgoldstinos P0 and S0 with quarks are given by
FCNC at tree level
Neutral current
sgoldstino (II)
If the masses of P0 and S0 are less than two pion masses, they can decay into photon or lepton pairs (D.S. Gorbunov, Nucl. Phys. B602 (2001) 213).
F : SUSY breaking scale, M : order of photino mass (~100 GeV) Al : soft mass term (~100 GeV)
Properties of HyperCP event, X(214)
Use B( + → pX0, X0 → ) and the uncertainty of muon g-2
Then, check the X0 contribution for the following processes:
Extract the couplings of s→dX0 and X0 →
X0
X0
X0
X0
Either pseudo-scalar or axial vector particleis allowed in present data. ~10-15 s (~10-7 MeV)
X(214) Search in Other Experiments
Hadron collider:– D0 Experiment (PRL 103, 061801 (2009))
e+ e- collider– BaBar (PRL 103, 081803 (2009))– CLEO (PRL 101, 151802 (2008))
Fixed Target– E391a@KEK (PRL 102, 051802(2009))– E949@BNL (PRD 79, 092004(2009))– KTeV@FNAL (ongoing analysis)
X(214) Search in E391a@KEK
Use the mode, KL→π0π0X, X →γγ:Assume that the X is a sgoldstiono particle (psedo-scalar)
Two photon invariant mass Upper Limit
Possible Decay Modes for X(214) in Heavy Quark Decays
Possible decay modes for sgoldstino in SUSY– Pseudo-scalar B and D meson decays to vector meson and X0
S.V.Demidov and D.S.Gorbunov, JETP 84, 479 (2006) • B(D X0, X0 +-) = 10-9 ~ 10-6
• B(B K* X0, X0 +-) = 10-9 ~ 10-6
• B(B X0, X0 +-) = 10-9 ~ 10-7
The listed channels above are possible for low mass Higgs search in NMSSM (Next-to-Minimal SUSY SM)
The listed channels can be used for a light particle search in model independent.
Large sample of (4S) BB-bar : 657M BB-bar pairs
B K*0X0, K*0 K+-, X0 +-
B 0X0, 0 +-, X0 +-
Assume that X0 is a scalar (or psedo-scalar) particle (spin 0) or vector (or axial-vector) particle (spin 1)
Decay modes
Event Selection (I)
Charged track Selection requirement
Good charged track
dr < 1.0 cm|dz| < 5.0 cm
electroneid > 0.9Plab > 0.395 GeV/c
muonid > 0.95Plab > 0.690 GeV/c
Kaon kid > 0.6
pionremaining tracks after selecting the lepton and K tracks
K*0 0.815 GeV/c2 < MK*0 < 0.975 GeV/c2
0 0.633 GeV/c2 < M0 < 0.908 GeV/c2
best B minimum 2 value of four charged tracks
Kinematic variables, E and Mbc, cut applied E = EB* - Ebeam*– (Mbc)2 = (MES)2 = (Ebeam*)2 - |pB*|2
Ebeam* : beam energy,pB* and EB* : momentum and energy of B candidate
Event selection (II)
signal box
sideband region
Signal efficiency
X0 window defined with dimuon mass resolution
214.3 3 (0.5 (HyperCP) + resol. (Belle)) [MeV/c2]
211.5 MeV/c2 < M+- < 217.1 MeV/c2
Decay modes
X0 as a Scalar particle X0 as a Vector particle
Dimuon mass
resolution [keV/c2]
Signal efficiency ()
Dimuon mass
resolution [keV/c2]
Signal efficiency ()
B K*0X0 427 14 26.3 %
B 0X0 428 15 23.5 %
Background Study
B K*0X0 B 0X0
B K*0X0 B 0X0
Counting method– Use MC samples of continuum and BB-bar which are
larger than data sample
Fitting methodFit MC data in sideband region (sideband is defined as 5 ~ 10 in E-Mbc)
Decay modeFitting the sideband
Counting
B K*0X0 0.13+0.04-0.03 0
B 0X0 0.11+0.03-0.02 0
- Shaded region is X0 window
Systematic and Upper limit No event is
observed in the signal region.
27
B K*0X0 B 0X0
Decay modes
Systematic
X0 as a Scalar particle X0 as a Vector particle
B K*0X0 5.2 %B 0X0 5.7 %Decay modes
Upper limit @ 90% C.L.
X0 as a Scalar particle X0 as a Vector particle
B K*0X0 2.01 10-8
B 0X0 1.51 10-8
Expected B.F as sgoldstino
September 10-13 2009 JPS Search for a light particle at Belle 28
S.V.Demidov and D.S.Gorbunov, JETP Letters, 2006, vol. 84, No. 9, pp479-484
Upper limits vs. Lifetime Constraints on Lifetime for X(214)
– 1.7 10-15 s x 2.5 10-11 s D.S.Gorbunov and V.A.Rubakov, PRD 73, 035002 (2006)
– 1.7 10-15 s x 4 10-14 s C.Q. Geng, Y.K. Hsiao, PLB 632, 215-218 (2006)
We choose lifetimes for this search as follows :0 s, 10-15 s, and 10-12 s
Now we are focusing on general light particle search: 212 MeV ≤ mx≤ 300 MeV
September 10-13 2009 JPS Search for a light particle at Belle 29
Upper limit doesn’t change in these life times.
X(214) Search with e+e- collisions (I)
Use the process e+ e- →γ X, X →μ+μ-
Signal and background processes
(e+ e- X0) ~ 1 pb to 5 ab @ s = 10 GeV [D. S. Gorbunov and V. A. Rubakov, PRD 73, 035002 (2006)]
X(214) Search with e+e- collisions (II) Background and systematics are studying Initial goal is for X(214) search, and move to
search for general mass and life times
Summary
Recent astroparticle observation would suggest a light gauge boson with masses in MeV to GeV range.
There is no evidence for a light Higgs boson in NMSSM so far.
There have been searches including the Belle for HyperCP exotic event with mass 214.3 MeV.No evidence is found.
A super-B factory would be a good place to search for a light particle in even LHC era
Once the X(214) is confirmed,I will provide
wine and cheese to people here !
Backup Slides
Systematic : 214.3 MeV/c2 and vectorDecay mode K*0X0 0X0
Source \ lifetime 0 s10-15
s10-12
s0 s
10-15 s
10-12 s
Integrated Luminosity (NBB-bar)
1.4 % 1.4 % 1.4 % 1.4 % 1.4 % 1.4 %
Signal efficiency
Muon ID 3.0 % 2.9 % 3.0 % 2.9 % 2.9 % 2.9 %
charged kaon ID
0.8 % 0.8 % 0.8 % - - -
charged pion ID
0.5 % 0.5 % 0.5 % 0.7 % 0.7 % 0.7 %
Tracking 4.2 % 4.2 % 4.2 % 4.3 % 4.3 % 4.3 %
MC statistics 0.1 % 0.1 % 0.1 % 0.1 % 0.1 % 0.1 %
Cut variables
Mbc 0.7 % 0.3 % 0.7% 0.6 % 0.6 % 0.5 %
E 0.7 % 0.3 % 0.7 % 0.6 % 0.6 % 0.5 %
K*0 mass 0.7 % 0.3 % 0.7 % - - -
0 mass - - - 0.6 % 0.6 % 0.5 %
Total 5.6 % 5.4 % 5.6 % 5.5 % 5.5 % 5.5%September 10-13 2009 JPS 35Search for a light particle at Belle
Systematic : 214.3 MeV/c2 and scalarDecay mode K*0X0 0X0
Source \ lifetime 0 s10-15
s10-12
s0 s
10-15 s
10-12 s
Integrated Luminosity (NBB-bar)
1.4 % 1.4 % 1.4 % 1.4 % 1.4 % 1.4 %
Signal efficiency
Muon ID 3.0 % 2.9 % 2.9 % 2.9 % 2.9 % 2.9 %
charged kaon ID
0.8 % 0.8 % 0.8 % - - -
charged pion ID
0.5 % 0.5 % 0.5 % 0.7 % 0.7 % 0.7 %
Tracking 3.8 % 4.2 % 4.2 % 4.4 % 4.3 % 4.3 %
MC statistics 0.1 % 0.1 % 0.1 % 0.1 % 0.1 % 0.1 %
Cut variables
Mbc 0.6 % 0.5 % 0.3 % 0.9 % 0.3 % 0.4 %
E 0.6 % 0.5 % 0.4 % 0.9 % 0.3 % 0.4%
K*0 mass 0.6 % 0.5 % 0.4 % - - -
0 mass - - - 0.9 % 0.3 % 0.5%
Total 5.2 % 5.4 % 5.4 % 5.7 % 5.4 % 5.5 %September 10-13 2009 JPS 36Search for a light particle at Belle
Lifetime scan : 214.3 MeV/c2
September 10-13 2009 JPS Search for a light particle at Belle 37
K*0X0
Lifetime 0 s 10-15 s 10-12 s
Mass resol. [keV/c2] 427.3 14.3 424.4 14.4 534.1 24.8
Mass region [MeV/c2]
(211.5, 217.1)
(211.6, 217.2)
(211.3, 217.5)
efficiency(26.3 0.1)%
(26.4 0.1)%
(26.1 0.1)%
0X0
Mass resol. [keV/c2] 427.7 15.1 424.5 14.7 536.9 25.9
Mass region [MeV/c2]
(211.5, 217.1)
(211.6, 217.2)
(211.3, 217.5)
efficiency(23.5 0.1)%
(23.8 0.1)%
(23.6 0.1)%
K*0X0
Lifetime 0 s 10-15 s 10-12 s
Mass resol. [keV/c2] 425.1 14.4 426.5 14.5 535.8 74.9
Mass region [MeV/c2]
(211.6, 217.2)
(211.6, 217.2)
(211.3, 217.5)
efficiency(26.3 0.1)%
(26.3 0.1)%
(26.4 0.1)%
0X0
Mass resol. [keV/c2] 424.9 14.7 428.7 15.0 538.0 25.0
Mass region [MeV/c2]
(211.6, 217.2)
(211.6, 217.2)
(211.3, 217.5)
efficiency(23.6 0.1)%
(23.8 0.1)%
(23.4 0.1)%
As a ScalarAs a Scalar
As a VectorAs a Vector
Possible decay modes for Further Search in NMSSM model
e+ e- (4S) +- (1S), e+ e- (3S) +- (1S)
One may still look for this mode,BK X0, X0+-
B((1S) X0, X0+-) ~10-8
X0 X0
No QED background, e+e- +-
[Michelangelo Mangano & Paolo Nason, hep-ph/0704.1719,CERN-PH-TH/2007-062]