searches for dark forces and particles at belle and belle

1

Gianluca Inguglia- DESY11/12/2015

χ

χ

P.P.R.C. Physics SeminarQueen Mary University of London

Searches for dark forces and particles at Belle and Belle IISearches for dark forces and particles at Belle and Belle IIA personal overview A personal overview

Part two: Physics

Introduction to dark matter and dark sector(s) searchesSearch for a long lived dark photon at BelleB meson disappearance, current limits and plans for Belle 2Y(1S) disappearance, current limits and plans for Belle 2

Searches for dark forces and particles at Belle and Belle IISearches for dark forces and particles at Belle and Belle IIA personal overview A personal overview

1

Gianluca Inguglia- DESY11/12/2015

e-(e+

)

e+(e-)

γ

e+ ,μ+ ,π+ ..

e - ,μ- ,π- ...

A '

Part one: Belle 2 status and plans

Belle 2 @ SuperKEKB: toward the e+e- intensity frontierLuminosity design and status of SuperKEKBThe Belle 2 detector and the new VXDBelle 2 first steps: The BEAST

Background studies (back-up)

SuperKEKB is the e+e- intensity frontier

40 times higher luminosity

KEKB

PEP-II

3

Latest SuperKEKB Luminosity Profile

N.B. To realize this steep turn-on, requires close cooperation between Belle II and SuperKEKB [and international collaboration on the accelerator].

Belle/KEKB recorded ~1000 fb-1 . Now change units on y-axis to ab-1

Assumes full operation funding profile.

Assumes adequate staffing of SuperKEKB

year

cm-2s-1

ab-1

e- 2.6 A

e+ 3.6 A

To obtain x40 higher luminosity

Colliding bunches

Damping ring

Low emittance gun

Positron source

New beam pipe& bellows

Belle II

New IR

TiN-coated beam pipe with antechambers

Redesign the lattices of HER & LER to squeeze the emittance

Add / modify RF systems for higher beam current

New positron target / capture section

New superconducting /permanent final focusing quads near the IP

Low emittance electrons to inject

Low emittance positrons to inject

Replace short dipoles with longer ones (LER)

KEKB to SuperKEKB

5

6

40 times higher luminosity2.1x1034 8x1035 cm-2s-1

KEKB to SuperKEKBNano-Beam scheme

extremely small y*

low emittanceBeam current X 2

Redesign the lattice to reduce the emittance (replace short dipoles with longer ones, increase wiggler cycles) (all magnets installed 8/2014)

Replace beam pipes with TiN-coated beam pipes with antechambers (installed)

New superconducting final focusing magnets near the IP

New e+ Damping Ringconstructed

Upgrade positron capture section

e- 2.6A e+ 3.6A

Injector Linac upgrade

DR tunnel

Improve monitors and control system

Low emittanceRF electron gun

Reinforce RF systems forhigher beam currents

L 2ere

1 y

*

x*

Iy

y*

RL

Ry

2015: Basic hardware (except final focus) now in place

SuperKEKB: Getting Ready!!

DETECTOR ELEMENTS

VXD: Belle II Vertexing/Inner Tracking Detectors

Beampipe r= 10 mmDEPFET pixels (Germany, Czech Republic, Spain…) Layer 1 r=14 mm Layer 2 r= 22 mmDSSD (double sided silicon detectors) Layer 3 r=38 mm (Australia) Layer 4 r=80 mm (India) Layer 5 r=115 mm (Austria) Layer 6 r=140 mm (Japan)

+Poland, Korea

Vertexing for time-dependent measurements;

Vertexing of KS modes;

Tracking of low momentum particles that curl up at small radii (pT < 200 MeV) [notice the forward lampshades in the SVD]

Exercise: Why are they tilted ?

Pixel Detector

DEPFET sensor: very good S/N but only 75 μm thick. However, complex CO2 cooling plant needed for high power readout chips.

Mechanical mockup of pixel detector

DEPFET pixel sensor

At the end of Belle running, the inner most layer of the SVD had occupancy ~10% → Have to move to pixelated detectors rather than strips to handle occupancy

Internal gate modulates the current through the MOSFET.

Pixel Detector

DEPFET sensor: very good S/N but only 75 μm thick. However, complex CO2 cooling plant needed for high power readout chips.

Mechanical mockup of pixel detector

DEPFET pixel sensor

At the end of Belle running, the inner most layer of the SVD had occupancy ~10% Have to move to pixelated detectors rather than strips to handle occupancy

Internal gate modulates the current through the MOSFET.

M.P.G./H.L.L.

FIRST FINAL MODULE

Thermal mock-up

BEASTPHASES

WHEN DOES THE BELLE 2 EXPERIMENT START?

What is the BEAST (II)?What is the BEAST (II)?

What is the BEAST (II)?What is the BEAST (II)?

Plus many other components around that will be removed before physics run...

17

Y(1S) invisible decays: signal and background Y(1S) invisible decays: signal and background Y(1S) invisible decays: signal and background Y(1S) invisible decays: signal and background Conclusions PART ONEConclusions PART ONE

BEASTPHASES

WHEN DOES THE BELLE 2 EXPERIMENT START?We are getting there!!!

2

Dark sector searches @ BELLE and BELLE 2: Why?Dark sector searches @ BELLE and BELLE 2: Why?

χ

χ SM

SM

2


χ

χ SM

SM

Dir

ect

det

ecti

on

Search for interaction of DM particles with (usually) underground detectors: heat, scintillation light, etc..

2


χ

χ SM

SM

Indirect detection

Dir

ect

det

ecti

on


Space/earth based experiments: gamma ray energy excess, anti-particle excess, HE neutrinos etc.

2


χ

χ SM

SM

Indirect detection

Direct production @ colliders

Dir

ect

det

ecti

on

Search for events with missing energy, particle disappearance, dark forces, etc.



2

Dark sector/matter searches @ BELLE 2: Why?Dark sector/matter searches @ BELLE 2: Why?

χ

χ SM

SM

Indirect detection

Dir

ect

det

ecti

on




Direct production @ colliders

2

Dark sector/matter searches @ BELLE 2: Why?Dark sector/matter searches @ BELLE 2: Why?

χ

χ SM

SM

Indirect detection

Dir

ect

det

ecti

on




Direct production @ Belle 2

● Various reasons to agree that dark matter (DM) exists● But the nature of DM is unknown and understanding what dark matter is represents

one of the biggest challenge our community is facing this days

● One possibility is represented by the lightest SUSY particle (which is stable)● But why should we have only one DM particle when density of DM is 5 times larger

the density of visible matter (i.e. many SM particles)?

● Many new models have been and are currently being developed to propose a more complex sector for dark matter explaining also anomalies observed in astrophysical process → dark sector(s).

● Within dark sector models, ADM theories assign a certain importance to the fact that Ω

DM/Ω

BM~5. As for the BAU a tiny difference between particle-antiparticle in the early

Universe has evolved to the observed ΩBM

today after the other particles-antiparticles have annihilated each other, something similar happened to DM particles-antiparticles.

● I will not discuss details of the models but will rather discuss experimental signatures and smocking guns at Belle/Belle2

2



Most dark sector models require an additional U(1) symmetry responsible for the “interactions” between dark sector particles and SM particles through its gauge boson A' .

P. Fayet, Phys. Lett. B 95, 285 (1980),P. Fayet Nucl. Phys. B 187, 184 (1981).B. Holdom, Phys. Lett. B 166, 196 (1986)

Kinetic mixing strength

A massive force mediator of the extra U(1) symmetry requires the U(1) symmetry to be broken: extended Higgs sector

12ϵFμν

Y F 'μ ν

3






12ϵFμν

Y F 'μ ν

3

BaBar, ArXiv: 1406.2980 [Hep-Ex]A '→ e+ e- ,μ+

μ-

[ prompt ]



● M(A') ~ GeV scale → mixing with the photon, SM final states accessible

● M(A') ~ EW scale → mixing with Z0, effects in rare decays (Y, B, ..) through loops1

● M(A') ~ TeV scale → effects in rare decays (Y, B, ..) through loops1

● M(HD)~ GeV scale → dark higgs-strahlung, rare decays (not covered today)

● M(χ) ~ GeV scale: B→χχ,B→νχ; Y(1S)→χχ;Y(3S)→χχγ, AD

→ χχ

Invisible B/Y decays not accessible at hadron colliders→BELLE2!




12ϵFμν

Y F 'μ ν

1Remember the lesson from the past, new particles are first seen indirectly or in loops: Z0, charm, top

3

A'= dark photon, HD= dark Higgs boson, χ= dark matter

29

hDχ

1

χ2 (?)

( ... )

- mixingγ A '

A '

Dark sector : how does it look like?Dark sector : how does it look like?

A very simple example...

30

e-(e+

)

e+(e-

)

γ

e+ ,μ+ ,π+ ..

e- ,μ- ,π- ...

A '

A'= dark photon, L= long lived light gauge boson.A' decays to SM final states through kinetic mixing (if allowed by kinematics). Low multiplicity final states. 2 charged tracks and 1 photon, prompt or displaced vertex decay. Could require dedicated trigger to increase efficiencies, especially for the displaced vertex case.

“A' ” decays depend on MA' :

-Decays to leptons require MA'>1.02 MeV/c2

-Decays to hadrons require MA'>0.36 GeV/c2

New search just started for the reaction:

A ' /L

e+ ,μ+ ,π+ ..

e- ,μ- ,π- ..~mm−cm

M A' [GeV /c2]ArXiv:0903.0363 [hep-ph]

h+ h-

e+e-→Y (2S ); Y (2S)→π

+π

-Y (1S);Y (1S)→ A0

γ ; A0→χ

0χ

0

Dark photon and long lived gauge bosons @ BELLE Dark photon and long lived gauge bosons @ BELLE

31

BABAR: ArXiv: 1406.2980 [Hep-Ex]

'

A '→ e+ e- ,μ+μ

- , prompt

arXiv:1506.00424 [hep-ex]Long lived, decays to leptons

NA48 arXiv:1504.00607π0 decays

Many constraints for different region of the parameter space from different experiments.Shown here: -top left: BaBar , -bottom left NA48, -bottom right CMS (containing ATLAS)

dark photon explanation of (g-2)

μ

ruled out for A' →e+e-

Dark photon: current limits Dark photon: current limits

A '→ e+ e- ,μ+μ

-[ prompt ]

BaBar, ArXiv: 1406.2980 [Hep-Ex]

ATLAS + CMS:

highly model-dependent!

32

A ' /Le+ ,μ+ ,π+ ,..

e- ,μ- ,π- ,..~mm−cm

A ' /L→e+e - ,μ+μ

- ,π+π

-

L→e+μ

- , e -μ

+ ,K +K -

M A' /L=0.1−10GeV /c2

W A' /L=1KeV /c2

c τ=1, 5, 10 cm

A ' /L→μ+μ- , c τ (L)=10cm

Ongoing analysis, approaching final stage

BELLE SIMULATION

Dark photon and long lived gauge bosons @ BELLE Dark photon and long lived gauge bosons @ BELLE

33

A ' f + f -

~mm−cm

I. JaegleUniversity of Hawaii

This search is a part of more general search for long lived gauge bosons currently performed with Belle data. For this more general analysis we are studying the decays:

With Belle 2 data (Bellex40) and improved detector/trigger/software performance one would expect a much higher discovery potential (i.e. ε~10-6).

Long lived dark photon search @ BELLE: expected limits Long lived dark photon search @ BELLE: expected limits

A ' /L→e+e- ,μ+μ

- ,π+π

-

L→e+μ

- , e -μ

+ ,K +K -

M A' /L=0.1−10GeV /c2

34

Dark photon, decays to SM particles: expected limits Dark photon, decays to SM particles: expected limits at Belle II compared to other experimentsat Belle II compared to other experiments

From Christopher Hearty, University of British Columbia/IPPBelle II Theory Interface Platform meeting 2014Belle II limits scaled from BABAR

e+e-→γ A '→γe+ e- ,γμ+μ- , prompt

35

e-(e+

)

e+(e-

)

γ

χ

χA '

A'= dark photon, χ= dark matter particle (neutral under SU(3)xSU(2)xU(1))A' decays to dark matter. On-shell or off-shell with different gamma spectrum .

radiative production in e+e- collisions only one photon in the final state with No existing limits

Requires high rate single photon trigger, not available in Belle. Belle 2 will have a single photon trigger.

Eγ*=(s−M A'

2)/2√s

Dark photon decays to dark matter searches @ BELLE II Dark photon decays to dark matter searches @ BELLE II

See R. Essig et al. JHEP11 (2013) 167.Igal Jaegle, University of Hawaii

36

Dark photon, decays to DM particles: expected limits Dark photon, decays to DM particles: expected limits at Belle II compared to other experimentsat Belle II compared to other experiments

From Christopher Hearty, University of British Columbia/IPPBelle II Theory Interface Platform meeting 2014Belle II limits scaled from BABAR

e+e-→γ A '→γ χ χ

37

B→νν , ν ν γ

BABAR (471×106 B B pairs) : BR(B→ν ν̄)<2.4 10−5(ϵsig∼18×10−4

),

BR(B→ν ν̄ γ)<1.7 10−5(ϵsig∼16×10−4)

BELLE (657×106B B pairs) : BR(B→ν ν̄)<1.3 10−4 (ϵsig∼2.2×10−4)Phys. Rev. D 86, 032002 (2012)

Phys. Rev. D 86, 051105 (2012)

Ongoing sensitivity studies at Belle 2, probably up to BR~10-6

B meson disappearance B meson disappearance

38

B→νν , ν ν γ

BTAG

BSIG

ν

ν̄

Reconstructed final state particles

Y (4 S)

e+

e-

What does a signal look like?


39

B→νν , ν ν γ BTAG 1

BTAG 2

Y (4 S)

e+

e -


DOUBLE TAG

EXTRA ECL ENERGY Phys. Rev. D 86, 032002 (2012)


40

B→νν , ν ν γ

BTAG

BSIG

ν

ν̄


Y (4 S)

e+

e-

What does a signal look like? A signal is represented by an excess of events over the expected background in the extra ECL energy distribution around zero


41

B→νν , ν ν γ

Additional decay topologies arise from new physics modelsThese new topologies will affect the BR of B to invisible final states, if they exist, making B to invisible “observable” (BR as high as 10-6) [Phys. Rev. D 65, 015001 (2002)].Of course this is a high risk measurement..


42

B→νν , ν ν γ

BABAR (471×106 B B pairs) : BR(B→ν ν̄)<2.4 10−5(ϵsig∼18×10−4

),

BR(B→ν ν̄ γ)<1.7 10−5(ϵsig∼16×10−4)

BELLE (657×106B B pairs) : BR(B→ν ν̄)<1.3 10−4 (ϵsig∼2.2×10−4)Phys. Rev. D 86, 032002 (2012)

Phys. Rev. D 86, 051105 (2012)

Ongoing sensitivity studies at Belle 2, probably up to BR~10-6


43

BTAG

Y (4 S)

e+

e -


π+

D* -

π+

D0

B0→νν

B0→D* + π-

D * +→D 0 πS+

D0→K -

π+

(BR=0.2)

D0→K -

π+π

0(BR=0.2)

D 0→K -

π+π

+π

-(BR=0.2)

D0→K -K+ (BR=0.2)

D 0→π

-π

+(BR=0.2)

Simulation

M [GeV/c2]

Simulation

Simulation

44

BTAG

Y (4 S)

e -


π+

D* -

π+

D0

B0→νν

B0→D* + π-

D * +→D 0 πS+

D0→K -

π+

(BR=0.2)

D0→K -

π+π

0(BR=0.2)

D 0→K -

π+π

+π

-(BR=0.2)

D0→K -K+ (BR=0.2)

D 0→π

-π

+(BR=0.2)

EXTRA ECL ENERGY Phys. Rev. D 86, 032002 (2012)

e+

Simulation

45

e+e-→Y (3 S)↓

Y (3 S)→π+π

-Y (1S)↓

Y (1S)→ invisible

e+e-→Y (2S )↓

Y (2 S)→π+π

-Y (1 S)↓

Y (1 S)→ invisible

➔ Low mass dark matter particles however might might play a role in the decays of Y(1S), having Y(1S)→χχ if kinematic allowed. [Phys. Rev. D 80, 115019, 2009]

➔ Also, new mediators (Z', A0, h0) or SUSY particles might enhance Y(1S)→νν(γ). [Phys. Rev. D 81, 054025, 2010]

➔ In absence of new physics enhancement, Belle2 should be able to observe the SM Y(1S)→νν

M Y (3S )=10.355GeV /c2, M Y (2S )=10.023GeV / c2 , M Y (1S )=9.460GeV /c2

~ 900MeV available for Pπ π


BR (Y (1S )→ν ν̄)

BR(Y (1S )→e+e-)=

27G2M Y (1S)4

64 π2 α2 (−1+43

sin2θW )

2

=4.14×10−4

BR (Y (1S )→ν ν̄)∼9.9×10−6

Belle2 SimulationY(3S)→π+π-Y(1S), Y(1S)→ νν

Y(1S) invisible decays at Belle 2Y(1S) invisible decays at Belle 2

(4.4%)

(18.1%)

Y(nS): bound state of a b quark and a b antiquark

46

e+e-→Y (3 S)↓

Y (3 S)→π+π

-Y (1S)↓

Y (1S)→ invisible

e+e-→Y (2S )↓

Y (2 S)→π+π

-Y (1 S)↓





BR (Y (1S )→ν ν̄)

BR(Y (1S )→e+e-)=

27G2M Y (1S)4

64 π2 α2 (−1+43

sin2θW )

2

=4.14×10−4

BR (Y (1S )→ν ν̄)∼9.9×10−6



(4.4%)

(18.1%)

A signal of Y(1S)→invisible is an excess of events over the background in the M

r distribution at a mass

equivalent to that of the Y(1S) (9.460 GeV/c2)

M r2=s+M

π+π

-−2√s Eπ+π

-

CMS

47

[belle]: http://arxiv.org/abs/hep-ex/0611041(1 week running @ Y(3S))

[babar]: http://arxiv.org/abs/0908.2840(2 months running @ Y(3S))

2.9 fb-1 @ Y(3S) 28.5 fb-1 @ Y(3S)

Y(1S) invisible decays: signal and background Y(1S) invisible decays: signal and background

http://arxiv.org/abs/hep-ex/0611041

http://arxiv.org/abs/0908.2840

48



Irreducible peaking background when final states go undetected (i.e. detector supports, beampipe etc.) in the process Y (3 S)→π

+π

-Y (1S) ,Y (1S )→undetected f . s .

2.9 fb-1 @ Y(3S) 28.5 fb-1 @ Y(3S)

Y(1S) invisible decays: signal and background Y(1S) invisible decays: signal and background MUJ 2015 / Annual Meeting Matter and Universe Forschungszentrum Jülich, Germany Gianluca Inguglia (DESY)



49

[belle]: http://arxiv.org/abs/hep-ex/0611041[babar]: http://arxiv.org/abs/0908.2840

Irreducible peaking background when final states go undetected (i.e. detector supports, beampipe etc.) in the process Y (3 S)→π

+π

-Y (1S) ,Y (1S )→undetected f . s .

Belle2 Simulation

Y(3S)→π+π-Y(1S), Y(1S)→ μ+μ- (along the beampipe, invisible)

Y(1S) invisible decays: signal and background Y(1S) invisible decays: signal and background

50



No signal was observed over the expected background and upper limits have been obtained: BR(Y→νν) < 2.5x10-4 (BaBar) and BR(Y→νν) < 3.0x10-3(Belle).

At Belle 2 one would expect to collect >200fb-1 of data @ Y(3S) (ongoing discussion for Y(2S) data taking and trigger) allowing one to reconstruct between 30 and 300 events,assuming 10-5 (SM)<BR(Y→invisible)< 10-4 (NP) and Belle efficiencies.

2.9 fb-1 @ Y(3S) 28.5 fb-1 @ Y(3S)

Y(1S) invisible decays: what to expect Y(1S) invisible decays: what to expect



51M Y (3S )=10.355GeV /c2 , M Y (2S )=10.023GeV / c2 , M Y (1S )=9.460GeV /c2


Y(3S)Y(3S)→π→π++ππ--Y(1S), Y(1S)→μY(1S), Y(1S)→μ++μμ-- decays at Belle 2 decays at Belle 2

Belle2 SimulationY(3S)→π+π-Y(1S)


Belle: hep-ex 0611041

Belle: hep-ex 0611041

ππ-system mass Mππμμ

-Mμμ

52

M Y (3S )=10.355GeV /c2 , M Y (2S )=10.023GeV / c2, M Y (1S )=9.460GeV /c2


Y(3S)Y(3S)→π→π++ππ--Y(1S), Y(1S)→invisible/μY(1S), Y(1S)→invisible/μ++μμ-- decays at Belle 2 decays at Belle 2

π-+

π+-



53

Trigger considerationsTrigger considerations

dataMC

Control sample(3S) (1S)(1S)

Trigger eff. = 89.8% r > 30o

ptfull > 0.30 GeV/c ptshort > 0.17 GeV/c other cuts (following slides)

Too low efficiency with usual condition (>135o) Higher efficiency with looser condition Special trigger condition was implemented　　 (~850 Hz, twice as usual condition)

Single track trigger was implemented, toowith 1/500 pre-scale rate (pt>250 MeV/c) 2-track trigger & 1-track trigger 1-track trigger for efficiency monitoring

(3S) (1S)(1S)

π-+

π+-

54



Too low efficiency with usual condition (>135o) Higher efficiency with looser condition Special trigger condition was implemented　　 (~850 Hz, twice as usual condition)

Single track trigger was implemented, toowith 1/500 pre-scale rate (pt>250 MeV/c) 2-track trigger & 1-track trigger 1-track trigger for efficiency monitoring

(3S) (1S)(1S)

π-+

π+-

98% of π's seen in CDC79% of π's seen in outer sub-det

Simulation

55

e+e-→Y (3 S)↓

Y (3 S)→π+π

-Y (1S)↓

Y (1S)→ invisible

e+e-→Y (2S )↓

Y (2 S)→π+π

-Y (1 S)↓





BR (Y (1S )→ν ν̄)

BR(Y (1S )→e+e-)=

27G2M Y (1S)4

64 π2 α2 (−1+43

sin2θW )

2

=4.14×10−4

BR (Y (1S )→ν ν̄)∼9.9×10−6



(4.4%)

(18.1%)

No signal was observed over the expected background and upper limits have been obtained: BR(Y→νν) < 2.5x10-4 (BaBar) and BR(Y→νν) < 3.0x10-3(Belle).

If we collect >200fb-1 of data @ Y(3S) [Y(2S)] we should reconstruct between 30 and 300 [~200 and ~2000] events , assuming 10-5 (SM)<BR

Y→invisible< 10-4 (NP) and ε

tot=10%.

56

DARKSECTOR

B→ invisible Y (1S )→ invisible

LonglivedA '

B→invisible+γ Y (1S )→ invisible+γ

Y (3 S)→ invisible+γ

Y(1S) invisible decays: signal and background Y(1S) invisible decays: signal and background Y(1S) invisible decays: signal and background Y(1S) invisible decays: signal and background DARK SECTOR SEARCHES AT THE BELLE 2 EXPERIMENTDARK SECTOR SEARCHES AT THE BELLE 2 EXPERIMENT

Prompt A ' Dark Higgs

➔ Many decay topologies are available at (Super) flavour factories to constraint and eventually discover dark sector particles.

➔ A task force aimed at the study of dark sector, giving particular relevance to final states with missing energy will be created.

➔ It is a high risk project, but it would allow one to fully exploit the Belle 2 experiment in terms of the complementarity wrt other projects (i.e. LHCb) and potential discoveries will have a strong impact on future research.➔ In the hypothesis of null outcome in terms of new physics one could however be

able to observe and measure the rare decay Y(1S)→νν which would provide additional insights about the flavour structure of the standard model: win-win study.

57

Y(1S) invisible decays: signal and background Y(1S) invisible decays: signal and background Y(1S) invisible decays: signal and background Y(1S) invisible decays: signal and background ConclusionsConclusions

● Discovering dark matter is today one of the biggest challenges we are facing, but more important is the understanding of its nature● Synergy between different experiments and Collaborations is required.

● Many searches at the Belle experiment are ongoing and higher precision will be reached thanks to the great luminosity of Belle 2 at Super-KEK and to improved hardware/software.

● Searches for dark sector(s) at Belle 2 will be performed, and thanks to the possibility to study invisible final states one can fully exploit the complementarity with respect to hadron collider experiments.

Thank you for your attention!

1

58

Y(1S) invisible decays: signal and background Y(1S) invisible decays: signal and background Y(1S) invisible decays: signal and background Y(1S) invisible decays: signal and background Back-up slidesBack-up slides

1

59

Diamond sensorsDiamond sensors

Backgrounds (2-photon, Touschek, RBB) have been studied from simulation in terms of particle fluence and energy deposit for both diamond sensors and ASIC's

Diamond sensors considered at various position (in Φ) and different orientation ( ║/┴ to beampipe) to evaluate best position as radiation monitors (Φ= 0°, 45°, 135°, 180°,║/┴ shown here), results suggested that during phase 2 a sensible choice would be to put the VXD system along the x-direction (Φ= 0°).

0 45 135 180 ║ ┴ ║ ┴ ║ ┴ ║ ┴

0 45 135 180 ║ ┴ ║ ┴ ║ ┴ ║ ┴

0 45 135 180 ║ ┴ ║ ┴ ║ ┴ ║ ┴

0 45 135 180 ║ ┴ ║ ┴ ║ ┴ ║ ┴

Example of particle fluence (e-) as a function of diamond sensors position and orientation wrt to z-axis showing that most particles passes through the sensor positioned at Φ= 0°

Energy deposit as a function of diamond sensors position and orientation wrt to z-axis showing that the largest energy deposit is observed at Φ= 0° and in the orthogonal orientation, the same trend is observed with larger integration time windows.

En

erg

y d

ep

osi

t E

/(G

eV/2

ms )

e- h

i ts

pe

r 2

ms

Note: nominal luminosity assumed

DHPDCD

Switchers

Studies for all ladders of PXD show that a combination of 2-photon + RBB + Touschek backgrounds produces a fluence expressed as the number of neutrons per cm2 per s smaller than 20000 for all switchers/DCD/DHP, suggesting that neutrons effects will be under control.

We plan to study the correlation between particles hits in the beam abort systems (diamond sensors) and particles hits in the PXD+SVD regions where ASIC's are installed; in this way we can infer background levels on sensors and electronic components from the hits in the diamonds. The work is ongoing for both PXD and SVD and will be finished by next B2GM.

PXD ASIC's as seen from simulation

Note: nominal luminosity assumed

Backgrounds (2-photon, Touschek, RBB) have been studied from simulation in terms of particle fluence and energy deposit for both diamond sensors and ASIC's

For the ASIC's, neutron fluence and energy deposit has been studied in PXD to evaluate degradation.

62M Y (3S )=10.355GeV /c2, M Y (2S )=10.023GeV / c2 , M Y (1S )=9.460GeV /c2


Y(2S)Y(2S)→π→π++ππ--Y(1S), Y(1S)→μY(1S), Y(1S)→μ++μμ-- /invisible decays at Belle 2 /invisible decays at Belle 2

ππ-system mass Mππμμ

-Mμμ

63M Y (3S )=10.355GeV /c2, M Y (2S )=10.023GeV / c2 , M Y (1S )=9.460GeV /c2


Y(2S)Y(2S)→π→π++ππ--Y(1S), Y(1S)→Y(1S), Y(1S)→invisible decays at Belle 2invisible decays at Belle 2

π-+

π+-

64



● In the search for invisible decays, at least one pion will likely stay inside DC due to low momentum (some should go outside DC with 250 MeV/c momentum)

● Couldn't find Belle information for this transition (due probably to extremely low trigger eff.)● BR((2S) (1S)) = 4.5 x BR ((3S) (1S))The CLEO Collaboration (hep-ex/0612051) analysis was based on AXIAL trigger tracks (tracks observed in the inner 16 axial drift chamber layers) with a prescale factor of 20

π-+

π+-

(2S) (1S), (1S)

65



● In the search for invisible decays, at least one pion will likely stay inside DC due to low momentum (some should go outside DC with 250 MeV/c momentum)


π-+

π+-

(2S) (1S), (1S)

21% of events

30% of events

49% of events

66



(2S) (1S), (1S)

π-+

π+-

● In the search for invisible decays, at least one pion will likely stay inside DC due to low momentum (~40% will go outside DC with 250 MeV/c momentum)


97% of π's seen in CDC39% of π's seen in outer sub-det

21% of events

30% of events

49% of events

Need dedicated trigger

searches for dark forces and particles at belle and belle

Documents