Charm at : status and prospects

DHEP Seminar February2, 2012

Gagan MohantyTata Institute, Mumbai

Outline of the talk1) Introduction and motivation

2) KEKB SuperKEKB

3) Enter Belle II detector

4) Status of the project

5) Conclusions and prospects

(1,0)

a,f2

(r,h)

(0,0)

2

With a Higgs boson beingdiscovered at the LHC, thestandard model (SM) is onthe verge of completion

What is the fuss about?

Three complementary ways to probe thenew physics (NP) beyond the SM

However, there are many compelling reasons to believe that the SM cannotbe the full story

1) About ten orders of magnitude difference between the matter-antimatterasymmetry in universe and CP violation content of the SM

2) What is the nature of dark matter?

3) and, the list goes onEnergy (ATLAS, CMS)

Luminosity (LHCb, Belle II) Cosmic (neutrino, ray)

(1,0)

a,f2

(r,h)

(0,0)

3

Why a flavor factory in the LHC era?

A flavor factory (FF) studies processes that occur at one-loop level in the SMbut may be of O(1) in NP: FCNC, neutral meson mixing, CP violation. Theseloops probe energy scales that cannot be directly accessed at the LHC.

For instance, if SUSY is found at the LHC, the next question will be: how is itbroken. By studying various flavor-violating couplings the FF can address that.

NP

reac

hin

term

so

fm

ass

NP flavor-violating coupling

Illustration purpose only

(1,0)

a,f2

(r,h)

(0,0)

4

What’s so special about Belle II?

Low background, high trigger efficiency, excellent photon & 0 reconstructioncapability, high flavor-tagging efficiency with low dilution factor

Good kinematic resolution Dalitz-plot analyses are straightforward

Absolute branching fraction can be measured

Ideal for measuring decay channels with large missing energy

Thanks to its pristine e+e environment:

A sample of measurements at Belle II

Belle II TDR, arXiv:1011.0352

(1,0)

a,f2

(r,h)

(0,0)

5

Now, all these sound good. But why charm? Charm provides an interesting test bed for NP as SM footprints in this sector

are tiny owing to a) large GIM/CKM suppression, and b) the lack of a largehierarchy in the down-type quark masses

CP violation is expected (in the SM) to be the order of 103 an excellentNP probe [most promising candidate: singly Cabibbo-suppressed decays]

While talking about percentage effect, one needs a good control on SMpredictions, something that is in general lacking in this sector because oflong-distance effects

PRD 75, 036008 (2007)

An example of “short vs. long”

(1,0)

a,f2

(r,h)

(0,0)

6

Direct CP violation: probe# 1 for Belle II

Luminosities (results) shown on the second (third) column are from Belle

Looking ahead, Belle II has a big advantage over LHCb for the final states withneutral mesons (0, and )

Mode Lint [fb¡1] ACP [%] Belle II with 50 ab¡1 [%]D0 ! K0

S¼0 791 ¡0:28§ 0:19§ 0:10 §0:05D0 ! ¼0¼0 976 ±ACP ¼ 0:6%D0 ! K0

S´ 791 +0:54§ 0:51§ 0:16 §0:10D0 ! K0

S´0 791 +0:98§ 0:67§ 0:14 §0:10D0 ! ¼+¼¡ 976 +0:55§ 0:36§ 0:09 0:07D0 ! K+K¡ 976 ¡0:32§ 0:21§ 0:09 0:05D0 ! ¼+¼¡¼0 532 +0:43§ 1:30D0 ! K+¼¡¼0 281 ¡0:6§ 5:3D0 ! K+¼¡¼+¼¡ 281 ¡1:8§ 4:4D+ ! Á¼+ 955 +0:51§ 0:28§ 0:05 §0:05D+ ! ´¼+ 791 +1:74§ 1:13§ 0:19 §0:20D+ ! ´0¼+ 791 ¡0:12§ 1:12§ 0:17 §0:20D+ ! K0

S¼+ 977 ¡0:363§ 0:094§ 0:067 §0:05D+ ! K0

SK+ 977 +0:08§ 0:28§ 0:14 §0:10

D+s ! K0

S¼+ 673 +5:45§ 2:50§ 0:33 §0:30D+s ! K0

SK+ 673 +0:12§ 0:36§ 0:22 §0:10

(1,0)

a,f2

(r,h)

(0,0)

7

Rare and forbidden decays: probe# 2 for Belle II

(top) FCNC decays and(bottom) lepton flavor(LF), lepton number (L)& baryon-lepton number(BL) violating decays

Shaded regions indicatethe decays with a or 0,where Belle II will havean edge

(1,0)

a,f2

(r,h)

(0,0)

8

Is it all about more data? Any innovation?

Already have some good working examples from Belle and BaBarSee the talk of A. Zupanc

Charm tagging at B factory

Great prospects for Belle II especially for channels with missing neutrinosviz. D(s) l l and D0 K/ l l

arXiv:1307.6240

(1,0)

a,f2

(r,h)

(0,0)

The list can go on, let’s move to the project

Need 50 more data Enter SuperKEKB

40 times higherluminosity

81035

SuperKEKB

10

(cm

2s

1)

(1) Smaller y*

(2) Increase beam currents

(3) Increase y

How to increase the luminosity?

Collision with very small spot-size beams

Invented by P. Raimondi at Frascati

“Nano-Beam” scheme

-

-

11

Machine design parameters of two machines

parametersKEKB SuperKEKB

unitsLER HER LER HER

Beam energy Eb 3.5 8 4 7 GeV

Half crossing angle φ 11 41.5 mrad

Horizontal emittance εx 18 24 3.2 4.6 nm

Emittance ratio κ 0.88 0.66 0.37 0.40 %

Beta functions at IP βx*/βy

* 1200/5.9 32/0.27 25/0.30 mm

Beam currents Ib 1.64 1.19 3.60 2.60 A

Beam-beam parameter ξy 0.129 0.090 0.0881 0.0807

Luminosity L 2.1 x 1034 8 x 1035 cm-2s-1

• Nano-beams and a factor of two more beam current to increase L• Large crossing angle• Change beam energies to solve the problem of short lifetime for the LER

12

e 2.6 A

e+ 3.6 A

To obtain 40 higher luminosity

Colliding bunches

Damping ring

Low emittance gun

Positron source

New beam pipe& bellows

Belle II

New IR

TiN-coated beam pipewith antechambers

Redesign the lattices of HER &LER to squeeze the emittance

Add / modify RF systemsfor higher beam current

New positron target /capture section

New superconducting/permanent final focusingquads near the IP

Low emittanceelectrons to inject

Low emittancepositrons to inject

Replace short dipoleswith longer ones (LER)

KEKB to SuperKEKB

13

Need to build a new detector

- low p m identification f smm efficiency- hermeticity f n “reconstruction”

- radiation damage and occupancy- fake hits and pile-up noise in the EM

- higher rate trigger, DAQ and computing

Critical issues at L= 8 1035 cm2s1

4 Higher background ( 10-20)

4 Higher event rate ( 10)

4 Require special features

Belle II

Have to employ and develop newtechnologies to make such anapparatus work!

Belle II TDR, arXiv:1011.0352 14

Enter Belle II

electrons (7 GeV)

positrons (4 GeV)

KL and muon detector:Resistive Plate Counter (barrel outer layers)Scintillator + WLS Fiber + SiPM (end-caps,inner 2 barrel layers)

Particle IdentificationTime-of-Propagation counter (barrel)Prox. focusing Aerogel RICH (forward)

Central Drift ChamberHe(50%):C2H6(50%), small cells, longlever arm, fast electronics

EM Calorimeter:CsI(Tl), waveform sampling (barrel)Pure CsI + waveform sampling (end-caps)

Vertex Detector2 layers DEPFET + 4 layers DSSD

Beryllium beam pipe2 cm diameter

15

Belle II compared with Belle

16

SVD: 4 DSSD layersg 2 DEPFET + 4 DSSD layersCDC: small cell, long lever armPID: ACC+TOFgTOP+A-RICHECL: waveform sampling (+pure CsI for endcaps)KLM: RPCg Scintillator+SiPM (endcaps, barrel inner 2 lyrs) 16

Vertex Detector (PXD+SVD)2 layers DEPFET + 4 layers DSSD

A close-up view of the vertex region

Beryllium beam pipe2cm diameter

17

SVD

PXD

Beam Pipe r = 10mmPXD (2 layers DEPFET)

Layer 1 r = 14mmLayer 2 r = 22mm

SVD (4 layers DSSD)Layer 3 r = 38mmLayer 4 r = 80mmLayer 5 r = 104mmLayer 6 r = 135mm

Few words on PXD

DEPFET sensor: very good S/N

Mechanical mockup of the pixel detector

DEPFET pixel sensor

DEPFET:http://aldebaran.hll.mpg.de/twiki/bin/view/DEPFET/WebHome

18

SVD: high-point and current status

Gearing up for ladder production!

Origami chip-on-sensor

19

Mechanical mockup

+KS

IP profile

B vertex

B decay point reconstructionusing the KS trajectory

Larger radial coverageof SVD

Performance comparison

sin

ba

p

20

Less Coulombscattering

Pixel detector closeto the beam pipe

CDC: Main tracking device

Much bigger than in Belle

21

Wire stringing in a clean room Exceeding the expectation

Aerogel radiatorHamamatsu HAPD + readout

Barrel PID: Time of Propagation Counter (TOP)

Aerogel radiator

Hamamatsu HAPD+ new ASIC

200mm

n~1.05

Endcap PID: Aerogel RICH (ARICH)

200

PID devices

Quartz radiatorFocusing mirror

Small expansion blockHamamatsu MCP-PMT (measure t, x and y)

22

Cherenkov ring imaging with precisetime measurement

Device uses the internal reflection ofCerenkov ring images from quartzsimilar to the BaBar DIRC

Reconstruct Cherenkov angle fromtwo hit coordinates and the time ofpropagation of the photon

Quartz radiator (2cm)

Photon detector (MCP-PMT)

Excellent time resolution ~40 ps

Single photon sensitivity in 1.5 T

Fast read-out electronics

Barrel PID: TOP counter

Hamamatsu SL10 MCP PMT 8 PMTs with read-out electronics

quartz bar

23

TOP performance

LikelihoodFunctions:

pK

tim

e

B0gK+p- fullsimulation results:

Ng (signal) = 22Ng (bkg) = 15

ep = 92 % (Belle: 89%)eK = 7.4 % (Belle: 12%)

24

Aerogel

Hamamatsu HAPD

Clear Cherenkov image observed

Endcap PID: Aerogel RICH

Test Beam setup

Cherenkov angle distribution

6.6 σ p/K at 4GeV/c !

RICH with a novel “focusing”radiator – a two-layer radiator

Employ multiple layers withdifferent refractive indicesCherenkov images from theindividual layers overlap onthe photon detector.

25

(1,0)

a,f2

(r,h)

(0,0)

26

Event size and rate: Belle II vs. LHC expts

(1,0)

a,f2

(r,h)

(0,0)

27

A snapshot of the Belle II computing model

28

Belle II: a truly global collaboration

Recently several new additions from Italy and USA

A very strong group of over 500 highly motivated scientists!

SuperKEKB and Belle II ScheduleCommissioning in three phases:

Phase 1: w/o final quads and Belle II

basic machine tuning

low emittance beam tuning

vacuum scrubbing (at least a month at beamcurrents of 0.5-1 A)

Damping ring commissioning

Phase 2: with final quads and Belle II,but no vertex detector

low * beam tuning

small x-y coupling tuning

collision tuning

study beam background (carefully check thebeam background before VXD installation)

Phase 3: with QCS and full Belle II

physics run

luminosity increase

29

SuperKEKB luminosity projection

Goal of Belle II/SuperKEKB

9 months/year20 days/month

Commissioning startsin early 2015

Shutdownfor upgrade

Inte

gra

ted

lum

ino

sit

y(a

b1)

Pe

ak

lum

ino

sit

y(c

m-2

s-1

)

Calendar Year

30

Same size data as Belle

Aim to reach 50 ab1 by the end of 2022

Conclusions and future prospect

31

e+e B factories have proven to be an excellent tool for flavor physics, producinga wealth of physics results, the most celebrated one being the confirmation of theKobayashi-Maskawa mechanism for CP violation in the SM

Thanks for your kind attention

Major upgrade of KEKB factory to SuperKEKB (50 data) will take this legacyforward by providing a suitable probe for NP complementary to LHC

Belle II at SuperKEKB should resolve current flavor puzzles from the presentgeneration B factory, e.g., difference in the UT angle 1 between b c tree andb s loop diagrams, possible enhanced loop contribution in B K decays

It will also have a prolific charm physics program: should greatly improve theprecision of mixing/CPV parameters (together with LHCb) and should probe NPby diligently searching for direct CP asymmetries and rare and forbidden decays

2008