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]