BTeV – A Dedicated B Physics Experiment at the Tevatron Collider

Klaus Honscheid 1Ohio State University

BTeV – A Dedicated B Physics Experiment at the Tevatron Collider

Klaus HonscheidThe Ohio State UniversityDPF 2002, May 24, 2001


BTeV Collaboration

Belarussian State- D .Drobychev,

A. Lobko, A. Lopatrik, R. Zouversky

UC Davis - P. Yager

Univ. of Colorado-J. Cumalat

Fermi National Lab

J. Appel, E. Barsotti, C. N. Brown ,

J. Butler, H. Cheung, G. Chiodini,

D. Christian, S. Cihangir, R. Coluucia,

I. Gaines, P. Garbincius, L. Garren,

E. Gottschalk, A. Hahn, P. Kasper,

P. Kasper, R. Kutschke, S. Kwan,

P. Lebrun, P. McBride, M. Votava,

M. Wang, J. Yarba

Univ. of Florida at Gainesville

P. Avery

University of Houston

M. Bukhari, K. Lau, B. W. Mayes,

V. Rodriguez, S. Subramania

Illinois Institute of Technology

R. A. Burnstein, D. M. Kaplan,

L. M. Lederman, H. A. Rubin,

C. White

Univ. of Illinois- M. Haney,

D. Kim, M. Selen, J. Wiss Univ. of Insubria in Como-P. Ratcliffe, M. Rovere

INFN - Frascati- M. Bertani,L. Benussi, S. Bianco, M. Caponero,F. Fabbri, F. Felli, M. Giardoni, A. La Monaca, E. Pace, M. Pallotta,A. Paolozzi

INFN - Milano - G. Alimonti, P. D’Angelo, L. Edera, S. Magni, D. Menasce, L. Moroni, D. Pedrini, S.Sala, L. Uplegger

INFN - Pavia - G. Boca, G. Liguori, & P. Torre

INFN - Torino – R. Arcidiacono, S. Argiro,S. Bagnasco, N. Cartiglia, R. Cester,F. Marchetto, E. Menichetti,R. Mussa, N. Pastrone

IHEP Protvino, Russia A. Derevschikov, Y. Goncharenko,V. Khodyrev, V. Kravtsov, A. Meschanin, V. Mochalov,

D. Morozov, L. Nogach, K. Shestermanov, L. Soloviev, A. Uzunian, A. Vasiliev

University of Iowa C. Newsom, & R. Braunger

University of Minnesota V. V. Frolov, Y. Kubota, R. Poling, & A. Smith Nanjing Univ. (China)T. Y. Chen, D. Gao, S. Du, M. Qi, B. P. Zhang, Z. Xi Zhang, J. W. Zhao

Ohio State UniversityK. Honscheid, & H. Kagan Univ. of PennsylvaniaW. Selove

Univ. of Puerto Rico A. Lopez, & W. Xiong

Univ. of Science & Tech. of China - G. Datao, L. Hao, Ge Jin, T. Yang, & X. Q. Yu Shandong Univ. (China)- C. F. Feng, Yu Fu, Mao He, J. Y. Li, L. Xue, N. Zhang, & X. Y. Zhang

Southern Methodist University - T. Coan

SUNY Albany - M. Alam

Syracuse University

M. Artuso, S. Blusk, C. Boulahouache, O. Dorjkhaidav, K. Khroustalev, R.Mountain, N. Raja, T. Skwarnicki, S. Stone, J. C. Wang

Univ. of Tennessee T. Handler, R. Mitchell

Vanderbilt University W. Johns, P. Sheldon, K. Stenson, E. Vaandering, & M. Webster

Univ. of Virginia:

M. Arenton, S. Conetti, B. Cox,

A. Ledovskoy

Wayne State UniversityG. Bonvicini, & D. Cinabro,

A. Shreiner

University of Wisconsin M. Sheaff

York University

S. Menary


CKM, CP and all that

MagnitudesBd, Bs Mixing Phases

From Hocker et al:Current constraints on bd CKM triangle

From Peskin:Many independentchecks are needed


Some crucial measurements

PhysicsQuantity

Decay Mode VertexTrigger

K/sep

det Decaytime

Lep-ton Id

sin(2) Bo

cos(2) Bo

sign(sin(2)) Bo & Bo

sin() Bs Ds K

sin() B+ Do K

sin() B K

sin() BoBs K

K

sin(2) Bs J/ J/

sin(2) Bo J/Ks

sin(2) BoKs,Ks, o

cos(2) Bo J/K* & Bs J/

xs Bs Ds

for Bs Bs

J/ KK

Ds


B Physics at Hadron Colliders

• The Opportunity– Lot’s of b’s

(a few times 1011 b-pairs per year at the Tevatron)

– “Broadband, High Luminosity B Factory”(Bd, Bu, Bs, b-baryon, and Bc )

– Tevatron luminosity will increase to at least 5x1032

– Cross sections at the LHC will be 5 times larger

– Because you are colliding gluons, it is intrinsically asymmetric so time evolution studies are possible (and integrated asymmetries are nonzero)

• The Challenge– Lot’s of background

(S/N 1:500 to 1:1000) – Complicated underlying

event– No stringent kinematic

constraints that one has at an e+e- machine

– Multiple interactions

These lead to questions about thetriggering, tagging, and reconstruction efficiency and the background rejection that can be achieved at a hadron collider


The Tevatron as a b & c sourceThe Tevatron as a b & c source

Value

Luminosityb cross-section# of b’s per 107 secb fractionc cross-sectionBunch SpacingLuminous region lengthLuminous region widthInteractions/crossing

2 x 1032

100 b4 x 1011

10-3

>500b132 nsz = 10-20 cm

x ~ y ~ 50 m

<2.0>

property


b production angle

Characteristics of hadronic b production

The higher momentum b’s are at larger ’s

b production peaks at large angles with large bb correlation

b production angle

BTeV BTeV

CentralDetectorsMean ~0.75


A simulated BTeV Event


The BTeV Spectrometer (revised)

• Single Arm• Full Pixel Detector• Full Trigger and DAQReduce costsNew baseline cost ~M$100

• Use extra bandwidth to loosen trigger• Better lepton id

Re-gain some performanceNew baseline performanceabout 70% of original two-arm spectrometer


Key Design Features of BTeV

A dipole magnet (1.6 T) and 2 1 spectrometer arms A precision vertex detector based on planar pixel arrays A detached vertex trigger at Level I High resolution tracking system (straws and silicon strips) Excellent particle identification based on a Ring Imaging

Cerenkov counter. A lead tungstate electromagnetic calorimeter for photon and

0 reconstruction Excellent identification of muons A very high capacity data acquisition system which frees us

from making excessively specific choices at the trigger level


Pixel Vertex Detector

Reasons for Pixel Detector:• Superior signal to noise• Excellent spatial resolution -- 5-10 microns depending on angle, etc• Very low occupancy• Very fast • Radiation hardSpecial features:• It is used directly in the L1 trigger• Pulse height is measured on every channel with a 3 bit FADC• It is inside a dipole and gives a crude standalone momentum


Pixels – Close up of 3/31 stations

•50m x 400m pixels - 30 million total•Two pixel planes per station (supported on a single substrate)•Detectors in vacuum•Half planes move together when Tevatron beams are stable.

10 cm


Pixel Readout Chip

FPIX1

•Different problem than LHC pixels:132 ns crossing time (vs. 25ns) easierVery fast readout required harder

•R&D started in 1997

•Two generations of prototype chips(FPIX0 & FPIX1) have been designed& tested, with & without sensors,including a beam test (1999) inwhich resolution <9 was demonstrated.

•New “deep submicron” radiationhard design (FPIX2):Three test chipdesigns have been produced & tested.Expect to submit the final design~Dec. 2001

A pixel

7.2 mm Test outputs

8 mm

Readout


Pixel Test Beam Results

Track angle (mr)

No changeafter 33 Mrad(10 years, worst case, BTeV)

Analog output of pixel amplifier before and after 33 Mrad irradiation.0.25 CMOS design verified radiationhard with both and protons.


Pixel detectors are hybrid assemblies

•Sensors & readout “bump bonded” to one another.•Readout chip is wire bondedto a “high density interconnect”which carries bias voltages,control signals, and output data.

Micrograph of FPIX1: bump bonds are visible

Sensor

Readout chip

HDI

HDI

Sensor(5 readout chips underneath)

Wire bonds


Distribution in L/ of Reconstructed Bs

Primary-secondary vertex separationMinus generated. = 138

proper (reconstructed) - proper (generated)= 46 fs

Mean = 44

Physics Performance of Pixel Detector


The BTeV Level I Detached Vertex Trigger

Three Key Requirements:– Reconstruct every beam crossing, run at 7.6 MHz– Find primary vertex– Find evidence for a B decaying downstream of primary

vertex

Five Key Ingredients:– A vertex detector with excellent spatial resolution, fast

readout, and low occupancy– A heavily pipelined and parallel processing architecture well

suited to tracking and vertex fining– Inexpensive processing nodes, optimized for specific tasks

within the overall architecture ~3000 CPUs– Sufficient memory to buffer the vent data while calculations

are carried out ~1 Terabyte– A switching and control network to orchestrate the data

movement through the system


Information available to the L1 vertex trigger

pp pp


Track segments found by the L1 vertex trigger

“entering” track segment“exiting” track segment


FPGAAssociative

MemoryDSP

Track Farm(4 DSPs per crossing)Average

Latency:0.4 s

AverageLatency:55 s

DSPVertex Farm

(1 DSP per crossing)

AverageLatency:77 s

Level 1 Vertex Trigger:FPGAs: ~ 500Track Farm DSPs: ~ 2000Vertex Farm DSPs: ~ 500Level 2/3 Trigger2500 high performanceLINUX processors

PixelSystem

PatternRecognition

TrackReconstruction

VertexReconstruction

Block Diagram of the Level 1 Vertex Trigger


Pixel Trigger Performance

Select number (N) of detached trackstypically pt> 0.5 GeV, N = 2

Select impact parameter (b) w.r.t. primary vertex

typically (b) = 6Options include cuts on vertex, vertex mass etc.

74%

1%

N=1

N=2

N=3

N=4

N=1

N=2

N=3

N=4


Trigger Simulation Results

• L1 acceptance: 1% 2%• Profile of accepted events

• 4 % from b quarks including 50-70% of all “analyzable” b events• 10 % from c quarks• 40 % from s quarks• 45 % pure fakes

• L2/L3 acceptance: 4 %• 4000 Hz output rate• 200 Mbytes/s

Level 1 Efficiency on Interesting Physics States


Trigger/DAQ

BTeV Data Acquisition Overview


Importance of Particle Identification

Cherenkov angle vs Mom. P

Gas

Liquid


• Two identical RICH detectors• Components:

– Gaseous Radiator (C4F10 )– Liquid Radiator (C5F12 )– Spherical mirrors – Photo-detectors (PM + HPD)– Vessel to contain gas volume

Cherenkov photons from Bo+ and rest of the beam collision

Ring Imaging Cherenkov (RICH)


RICH Readout: Hybrid Photodiodes (HPD)

• Commercial supplier from Holland (DEP)

• A number of prototypes was successfully produced and tested for CMS

• New silicon diode customized for BTeV at DEP (163 pixels per HPD)

• Challenges:– high voltages (20 kV!) – Signal ~5000e- need

low noise electronics (Viking)

– In the hottest region up to 40 channels fire per tube

– About 2000 tubes total (cost)


Use of RICH to extend Lepton Identification

• While the full detector aperture is 300 mr, the acceptance of the electromagnetic calorimeter and muon detector is only 200mr

• The RICH, however, has both electron-pion and muon-pion discrimination at low momentum. The wide angle particles are mostly at low momentum!

This gains us afactor of 2.4 for single lepton id and 3.9 if we require bothleptons to be identified


Electromagnetic Calorimeter

The main challenges include• Can the detector survive the high radiation environment ?• Can the detector handle the rate and occupancy ?• Can the detector achieve adequate angle and energy resolution ?BTeV now plans to use a PbWO4 calorimeter• Developed by CMS for use at the LHC• Large granularity

Block size 2.7 x 2.7 x 22 cm3 (25 Xo)~11000 crystals

• Photomultiplier readout (no magnetic field)• Pre-amp based on QIE chip (KTeV)• Energy resolution

Stochastic term 1.8%Constant term 0.33%

• Position resolution E/32.3x mm mm28.0


PbWO4 Calorimeter Properties

Property ValueDensity(gm/cm2) 8.28Radiation Length(cm) 0.89Interaction Length(cm) 22.4Light Decay time(ns) 5(39%) (3components) 15(60%)

100(1%)Refractive index 2.30Max of light emission 440nmTemperature Coefficient (%/oC) -2Light output/Na(Tl)(%) 1.3Light output(pe/MeV) into 2” PMT 10

Property ValueTransverse block size 2.7cm X 2.7 cmBlock Length 22 cmRadiation Length 25Front end Electronics PMTInner dimension +/-9.8cm (X,Y)Energy Resolution: Stochastic term 1.8% Constant term 0.33%Spatial Resolution: Outer Radius 140 cm--215 cm

$ drivenTotal Blocks/arm 11,500

E/32.3x mm

mm28.0


Electromagnetic Calorimeter Tests

• Lead Tungstate Crystals from Shanghai, Bogoroditsk, other vendors• Verify resolution, test radiation hardness (test beam at Protvino)• Test uniformity

Block from China’s Shanghai Institute

5X5 stack of blocks from Russia readyfor testing at Protvino


Preliminary Testbeam Results

• Resolution (energy and position) close to expectations• Some non-uniformity in light output• more Radiation Hardness studies

Position Resolution

Energy Resolution


EM calorimetry

*

CLEObarrel=89%

radius


Muon System

track from IP

toroid(s) / iron

~3 m

2.4 m halfheight

• Provides Muon ID and Trigger– Trigger for interesting

physics states– Check/debug pixel trigger

• fine-grained tracking + toroid– Stand-alone mom./mass trig.– Momentum “confirmation”

• Basic building block: Proportional tube “Planks”


Physics Reach (CKM) in 107 s

J/+-

Reaction B (B)(x10-6) # of Events S/B Parameter Error or (Value)

Bo+- 4.5 14,600 3 Asymmetry 0.030

Bs Ds K- 300 7500 7 8o

BoJ/KS J/l+ l- 445 168,000 10 sin(2) 0.017

Bs Ds- 3000 59,000 3 xs (75)

B-Do (K+-) K- 0.17 170 1

B-Do (K+K-) K- 1.1 1,000 >10 13o

B-KS - 12.1 4,600 1 <4o +

Bo K+- 18.8 62,100 20 theory errors

Bo+- 28 5,400 4.1

Booo 5 780 0.3 ~4o

BsJ/ 330 2,800 15

BsJ/ 670 9,800 30 0.024


Concluding Remarks

PAC Recommendation“ … BTeV has designed and prototyped an ambitious trigger that will use B decay displaced vertices as its primary criterion. This capability, together with BTeV’s excellent electromagnetic calorimetry and particle ID and enormous yields, will allow this experiment to study a broad array of B and Bs decays. BTeV has a broader physics reach than LHCb and should provide definitive measurements of CKM parameters and the most sensitive tests for new physics in the flavor sector.”

C0 Hall at the Tevatron


Additional Transparencies


Changes wrt Proposal in Event Yields & Sensitivities

• We lost one arm, factor = 0.5• We gained on dileptons

– From RICH ID– in proposal we used only +-, now we include e+e-

– factor = 2.4 (or 3.9), depending on whether analysis used single (dilepton) id

• We gained on bandwidth, factor = 1.15

• Gained on D2 for Bs only, factor = 1.3


Examples

mode Yield prop

Yield factor

Yieldone-arm

quan/Errprop (D2)

quan/Errone arm(D2)

BoJ/ Ks 80,500 0.5*3.9*1.15=2.24

168,000 sin(2)/ 0.025 (0.10)

sin(2)/0.017 (0.10)

BsJ/() 9,940

0.5*2.4*1.15=1.38

12,600 sin(2)/0.033 (0.10)

sin(2)/0.024 (0.13)

Bs Ds K- 13,100 0.5*1.15

=0.58 7,500 /

6o (0.10)

/ 8o (0.13)


Reconstructed Events in New Physics Modes: Comparison of BTeV with B-factories

Mode BTeV (107s) B-fact (500 fb-1)

Yield Tagged S/B Yield Tagged S/B

BsJ/ 12650 1645

>15 - -

B-K- 11000 11000 >10 700 700 4

BoKs 2000 200 5.2 250 75 4

BoK*+- 2530 2530 11 ~50 ~50 3

Bs +- 6 0.7 >15 0

Bo+- 1 0.1 >10 0

D*++Do, DoK+ ~108 ~108 large 8x105 8x105 large


Comparisons with LHCb

• Advantages of LHCb b 5x larger at LHC, while t is only 1.6x larger

– The mean number of interactions per beam crossing is 3x lower at LHC, when the FNAL bunch spacing is 132 ns

• Advantages of BTeV (machine specific)– The 25 ns bunch spacing at LHC causes increased

electronic noise. It makes 1st level detached vertex triggering more difficult; in fact LHCb only does vertexing in level 2


Comparisons with LHCb II

– The 7x larger LHC beam energy causes problems: much larger range of track momenta that need to be analyzed and large increase in track multiplicity, which causes triggering and tracking problems

– The long interaction region at FNAL, =30 cm compared with 5 cm at LHC, somewhat compensates for the larger number of interactions per crossing, since the interactions are well separated

– There is an ion-trapping problem that stops them from moving their silicon closer than ~1 cm (compared to 6 mm for BTeV)


Comparisons with LHCb III

• Advantages of BTeV (detector specific)– BTeV has vertex detector in magnetic field which allows

rejection of high multiple scattering (low p) tracks in the trigger– BTeV is designed around a pixel vertex detector which has

much less occupancy, and allows for a detached vertex trigger in the first trigger level.

• Important for accumulation of large samples of rare hadronic decays and charm physics.

• Allows BTeV to run with multiple interactions per crossing, L in excess of 2x1032 cm-2 s-1

– BTeV will have a much better EM calorimeter– BTeV is planning to read out 5x as many b's/second


Specific Comparisons with LHC-b

Yields in important final states

Mode BRYield S/B

Yield S/B

Bs Ds K- 3.0x10-4 7530 7 7660 7

Bo+- 2.8x10-5 5400 4.1 2140 0.8

Booo 0.5x10-5 776 0.3 880 not known

BTeV LHC-b


Fundamentals: Decay Time Resolution

• Excellent decay time resolution– Reduces background– Allows detached vertex

trigger• The average decay distance

and the uncertainty in the average decay distance are functions of B momentum:

<L> = c

= 480 m x pB/mB

from b

L/ L/

direct

CDF/D0region LHC-b

region


Trigger

BTeV – A Dedicated B Physics Experiment at the Tevatron Collider

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