super flat ir beam pipe super b factory ws in hawaii jan. 22, 2004 hidekazu kakuno (tit) hitoshi...

Super flat IR beam pipe

Super B Factory WS in Hawaii

Jan. 22, 2004

Hidekazu Kakuno (TIT)

Hitoshi Ozaki & Nobu Katayama (KEK)

Jan. 22, 2004 H.Kakuno, H. Ozaki & N. Katayama 2

Outline

• Motivation

• Super flat geometry

• Simulation method

• Simulation results– Vertexing and B/D separation

– Bs – Bs mixing parameter measurement

– B D branching fraction measurement

• Issues and conclusions


Single B samples

• It’s been discussed that many interesting measurements require “single B event” samples– B K– B ,Bs

– B D– b ul and other inclusive measurements– …


B reconstruction at (4S) • At B factories we can identify (reconstruct) only

much less than 1% of the actual B decays. This is because– B has many decay modes, and D has many decay

modes– Average multiplicity of the B decay is 5~6 charged, 3

neutralLots of combinatorial backgroundsCombinatorial background can be reduced using

topological information on tracks (combinations)– Continuum backgrounds as well (ccbar for BD and

uds for non-charm decays)


Standard Vertex Resolution• Thickness of the material before the first

measurement ~1mm (Au/Ag + Be + Si + …)• Distance between the vertices and the first

measurements minimum 2~3 cm• Resolution of the first measurement 7~30m

X, Z : 80~100 m

(Y:20m IP profile + B flight length) • Solid angle coverage of the first measurements

~92%


Super Vertexing• If the error in the vertex measurement, z

were less than 10 m, it helps in doing– B reconstruction

• We can separate B, Bbar, D and Dbar vertices, we can greatly reduce the combinatorial and continuum background and identify many B decays

– Continuum separation– Measurements of some decays such as B

D• Reconstruct momentum vector using two vertices

– Bs – Bs mixing measurements; even for X>15


B D reconstruction

• IP profile + D direction B vertex• B vertex + vertex (helix ext.) + mass

momentum (and the entire kinematics): 0c-fit• Make missing mass of the from B• Lots of combinatorial backgrounds but measure

Br. without full B reconstruction tag

D

BIP profile


• Much more difficult as we cannot measure the B decay vertex

• IP profile + 2 vertex (helix ext.) + 2 mass B vertex (and the entire kinematics): 0c-fit– Or + vertex of the other B to get Vx: 1c-fit

BIP profile

Bs reconstructions


Super flat geometry

• Make first measurements as close to IP as possible– Follow the flat beam profile (times >100 sigmas)– Flat because silicon wafer is flat (without thinning)

• Sort of ideal geometry for physics– Machine issues not seriously considered

• Keep hermeticity similar to what we have now (90% of 4)

• Geometry is not optimized (yet)


IP profile

• B factories have proven *y ~ 5 mm and bunch length of 5mm are possible

• For Super B factories, the parameters have been aggressively pushed to: 3mm and 3mm giving IP beam size of y< 2m– y is said to be limited by beam-beam effects– Due to X-Y coupling, y is also affected by *x

• IR beam pipe can be as small (and short) as the size of beams (times clearance, say, 100 sigmas)


Super KEKB beam parameters

• Assuming XY coupling of 5%

• z ~ 3 mm

@IP @±5cm

x 60 m 63 m

y 1.9 m 32 m

x 15 cm 17cm

y 3 mm 84 cm

Maybe parameters are somewhat old


Cross section of the S-F beam pipe

y

x

1 mm

10 mm

ＶａｃｕｕｍBeryllium ｂｅａｍｐｉｐｅ (500m)

Ｓｉｌｉｃｏｎ　ｖｅｒｔｅｘ　ｄｅｔｅｃｔｏｒ　（３００ m thick)

Cooling


Top view of the S-F beam pipeZ (boost)

1.4cm

±2.5 cm isEnough!

Detector length

1cm

Cone for 17°

Cone for 30°

PixelDetector

1.6

cm

Sensitive region is 1.4cm wide


Side view of S-F beam pipeＶａｃｕｕｍ or accelerator components (nano beta??)

Ｓｉｌｉｃｏｎ　ｖｅｒｔｅｘ　ｄｅｔｅｃｔｏｒ　（３００ m thick)

Beryllium beam pipe (500m)

1.6 cm


Study of the S-F beam pipe• Using Geant4 we defined the S-F

geometry; vacuum and beam pipe @IP and the silicon vertex detector

• In BelleG4, the event generator information written in Belle format is read in.

• After propagating the tracks in the above geometry, momentum and position of the tracks at r=2cm as well as hits on the silicon vertex detector are written out

• The silicon hits are smeared using DSSD intrinsic resolution

– sigma = 5 + 10.65*alpha (alpha in rad) for both Z and

• We then process the tracks (track by track trackerr) using the Belle SVD 1.x + old CDC geometry (100% effic)

• Explicit Kalman filter is applied to the inner silicon hits and multiple scattering in the silicln and beam pipe materials

• The tracks have been extrapolated at the vertex using IP constraint (y=0)

r inner/outer layer

Z (inner/outer layer)

Outer SVD resolution used in simulation


BD*l + BbarD


Inefficiency (no SVD hit) due to the aboveflat geometry is about 10% (1.4cm sensitiveRegion) for single track


1 mm


dr and dZ resolution at the vertex

(dr) (dZ) (deg)(deg)

(d

eg)

(d

eg)

<10m

<20m

<10m

<20m

<30m

p=1GeV/c muon


Background reduction

• By requiring a good vertex (prob.<1%), backgrounds become 1/3 with 1% signal reduction– first Si hit for both tracks– no. of CDC hits >20 for both

tracks– 17 < theta < 150 deg. for both

tracks– pt > 50 MeV/c for both tracks– IP info is not used in vertexing

• With primary, B and D/ vertices separated cleanly, combinatorial and continuum backgrounds can greatly be reduced

Dk w/wo vertex fit (no PID)


One BD, D K


BD,DK, resolution study (1)

• D vertexing efficiency and resolution– All three (K) tracks are to have

• CDC hits > 20• 17 < theta < 150deg; pt > 50 MeV/c

– If all three tracks hit the first SVD, use them for vertexing, if one misses, use the other two tracks

• vertexing efficiency = 96.9 0.2%• resolution ~10m


BD,DK, resolution study (2)

• B vertexing efficiency– Both () tracks are to have

• CDC hits > 20• 17 < theta < 150deg; pt > 50 MeV/c

– If both tracks hit the first SVD, use them for vertexing, if one misses, use the other track and IP profile

• vertexing efficiency: 98.60.2%• resolution ~10m


D flight distance from B decay

Generated (m) Measured (m)

Mean 310m

No degradation!!


S-F geometry vs current geom.

Error on flight distance (m) Error on flight distance (m)See difference in scale


Separating B and D with L/L

• Using a flight length cut (L/dL) we can separate B and D vertecies

• With S-F beam pipe, the separation is 4~5 times better

Significance (L/L)

S-F geometry

Current geometry

Better

Cut


Bs – Bs mixing

With S-F geometry, resolution is good enough to observe Bs – Bs mixing

We have generated events with X=15 for about 30 fb of (5S) running

Z distribution using generator information


Analysis using dileptons

• two same sign leptons (opposite sign events not used)

• p(lepton) > 1 GeV/c (for clean lepton ID)

• both lepton hit SVD 1st layer

• 30<theta<150 deg to reject bad z resolution region

• p*(lepton) > 1.2 GeV/c to reject 2nd lepton from charm


Z resolution andZ distributions with Z cuts

Gen Meas/no cut

50m 40m

30m 20m

FWHM/2.36 ~27m

Expected Z distribution

30m

Residual(Measured – generated)


Results and comments

((5S)) ~ 0.27 nb

Fraction of Bs: 0.263(Bs*Bs*), 0.022(Bs*Bs), 0.046(BsBs) (L=odd dominant, an estimation)We have not done fits but,It seems we can easily observe mixing if X=15 with a few tens of fb-1 @ 5S with the super flat beam pipe. Considering the vertex resolution, we can go up to X=20Note that we have not added other same sign dilepton backgrounds


Analysis using D*l+ B anything• D* D K/K3 vertexing with nominal D mass

and D* - D mass difference cuts• Signal side B vertex using D, l, and IP• Standard Belle tagging + vertrxing for the tag side• For now generator information is used to select

combinations• We generated 105 Bd - Bd events with X=15• We generated assuming y=15m. In super B

design it is 2m. Although smearing due to B flight length dominates (20m) results will be slightly worse than it could be in the following analyses


Vertex resolutions

=13m

=28m, Offset:14m


Results

• We can clearly see oscillation as well

• 105 events is ~6fb-1 at (5S)


B D analysis• Reconstruct D K and 3, extrapolate D

momentum vector from D vertex, make B vertex using IP, use the B vertex and vertex to calculate direction, calculate momentum using mass constraint

• Problem: 3 has lots of combinatorial background even in signal (with the other B decaying generically) Monte Carlo sample

• We use tight cuts for vertexing and flight length cuts requiring separation of vertices


B, Btag and vertex separation

True D Wrong D

The best candidate in a event is selected usingsum of 2 for the vertex fits


B D missing mass C = 2×p*D×p*B cos = MM2/C

Solid: this methodDotted: with generated direction


P and m reconstruction

after MM2 cutSolid: this methodDotted: generated momentum

Using the rest of event


Efficiencies (cumulative)

D mass, D vertex & vertex quality cut 20%

momentum reconstruction 19%

vertex position cuts ( |Vz(sig)-Vz(tag)| and |Vz()-Vz(tag)| )

6%

cos_theta_tau_nu > -0.5, M3 > 1GeV 4.5%

abs(MM2) < C 2.5%


ResultsS/N = 2427/264 ~ 10 where N is combinatorial

background in signal MCNeed to estimate background from generic B

decaysUsing D*l+generic (D*l+D*l) sample, treating l

as , we see 8(7) events in 100,000 samples

As we know all kinematical info for 3 we can compute polarization as well


Prospects• Br(B D ) 1%• Br(D final) ~10% (averaging D0 and D+) (D0

K, K3 D+ K2...)• Br( 3) 10%• Efficiency: 2%• Number of reconstructed signals = 0.01 × 0.1 ×

0.1 × 0.02 × 2 × 106 / fb= 4 events / fb

= 4k events / ab

(<200 / abfor full recon. tag method)

• We can observe B D and measure polarization “without full reconstruction”!


Difficulties/Further studies

• Beam clearance• Accidental damage• Image current: assume r = 0.5mm round bp

(Yamamoto)– r = 0.5mm, l = 2cm, Ibeam = 10amp.(LER)– bunch spacing = 0.6m, bunch-length(z) = 3mm.– total Wattage = 1.0 KW(LER) + 0.25KW(HER)

• HOM• Noise• Backgrounds• …


Conclusions• A simulation-reconstruction-analysis chain has

established using new (?) tools– The S-F beam pipe geometry has been implemented in a

simulation program using Geant4 and Belle data format– A track-by-track version of trackerr has been

implemented in Belle framework– A Kalman filter has been implemented for the S-F beam

pipe geometry• If we can separate (most of) B and D (and other)

vertices in an event, the B reconstruction and flavor tagging techniques will dramatically be improved– Need more studies

• Bs-Bsbar mixing possible @(5S)• New way of reconstruction technique is possible

– Use two vertices to obtain direction of momentum vector


Conclusions• We need to investigate feasibility of the S-F beam

pipe with the accelerator group– The round beam pipe design may have limitation in making

the first measurements as close as possible for the current flat beam profile. We can either go to round beams or flat beam pipe

– If the bunch length can be shorter, the flat beam pipe can be shorter

• L = 2~3*z+60*y+3 mm• The shorter the beam pipe the smaller heating will be

• SF beam pipe is very cheap, compared with the machine upgrade to get high luminosity to achieve the same “luminosity×efficiency” for many analyses


History of beam pipe radius

0

10

20

30

40

50

60

70

80

1975 1980 1985 1990 1995 2000 2005Year

Inne

r rad

ius

mm

（）

Belle

CLEO

1mm@2010!

super flat ir beam pipe super b factory ws in hawaii jan. 22, 2004 hidekazu kakuno (tit) hitoshi...

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