-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 1

Hera-B Physics results

1. Data of the year 2000 limited statistics

2. Commissioning:trigger and detector not yet fully available(limited acceptance in xF)

3. Targets: C and Ti (partially simultaneously)

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 2

General view of Hera-B

vertex detector

outer trackerhi-Pt tracker

magnet (2 Tm)

inner trackermuon chambers (/h)

target

p

e

20 m

Rich

Trans. rad. det.

ECAL

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 3

Hera-B detector and trigger layout geared towards J/ :

1. Based on J/ e+ e- and J/ + - ;2. Good vertexing through Si- strips;3. e+ and e- in ECAL;4. + and - in Muondetector;5. Magnetic field for charge determination.

ECAL is also fine-grain photon detector.

Not used in this part of analysis:1. Rich2. Inner Tracker3. Trans. Rad. Detector

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 4

J/

J/ signal before cuts

+- inv. Mass:

J/ signal after cuts

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 5

e+ eInvariant mass spectrum

(| 1 - E/p| < 0.3)

No J/ signal …

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 6

beam e+

ECAL

e+

magnetic field

Bremsstrahlung recovery

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 7

eeInvariant mass spectrum

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 8

eeInvariant mass spectrum

(012) BR

(12) BR

(2) BR

before background subtraction after background subtraction

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 9

eeInvariant mass spectrum

with bremsstrahlung requirement

After background subtractionBefore background subtraction

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 10

J/ production

Hera-B has large xF (and good pT ) acceptance

xF xF

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 11

pT and xF distribution with e and sample:

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 12

Comparison with other experiments:

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 13

Fit ansatz: = a * (1 - |xF | )cd N(J/)

d xF

c = 6.2 + 0.6-

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 14

Energy dependence of exponent c

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 15

Energy dependence of width pT

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

Nuclear effects:

Hera-B uses up to 88 different target wires simultaneously (in 2000: CC and Ti). Ti).

Most uncertainties cancel out: can easily measure nuclear exponent as function of xF or other parameters.

Important: goodaccep-tance in negative xF. (use W and C targets…)

2000

2002

16a

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 17

Rc =

NJ/ *

Nc

Identification of c through : M = M(l +l - ) - M (l +l - ) uncertainty in J/ mass essentially cancels:Mc

= (MJ/2 + 2E EJ/ – 2ppJ/ )

Mc = MJ/ = 0.877 MJ/

(Mc - MJ/ ) = -0.123 MJ/

MJ/

Mc

Ratio of J/ from c :

c Production

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 18

M-spectrum:c-signal on top of

combinatorialbackground (J/ -- )

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 19

ADC shift

Dependency of c reconstruction onECAL miscalibration

Nc (relative)

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 20

Dependency of Rc

on

upper limit of tracks:Jvaries, butRc

constant.

Rc

Nvds

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 21

Rc

Nclus

Dependency of Rc

on

upper limit of Ecal clusters:

varies, butRc

constant.

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 22

Comparison of with previous experiments

Final result : Rc

= 0.321 + 0.064stat + 0.035syst

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 23

Rc as function

of energy

Hera-B

p-A

-A

CSMp

p

NRQCD CEM

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 24

bb-cross sectionPrevious data

Factor 7

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 25

Method:• B = 10-12 s• B only long lived decay

into J/• at 920 GeV: ~ 1 cm• look for detached J/• normalize using known

cross section and measured number of J/and BR B J/

• no efficiency/trigger/…knowledge required(well, “almost not required”…)

Monte Carlo

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 26

Invariant di-muon mass spectrum after detached event selection

(incl. likelihood-fit).

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 27

Data Monte Carlo

Invariant Mass:for downstreamand upstreamevents

clear signal of detached J/

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 28

Decay length fit

signal = 1.0 +/- 0.3 (MC = 0.83 +/- 0.03)

backgr. = 0.39 +/- 0.11

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 29

Single cut optimizationon downstream bkgr.

Simult. cut optimizationon downstream bkgr.

Simult. cut optimizationon upstream bkgr.

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 30

Final result: (bb) = 32 +15 + 8syst nb/nucleon-12 stat -

Uncertainties:Reference J/ cross sect. 11 %Trigger simulation: 5 %prompt J/ product. models 2.5 %b prod. and decay model 8 %A-dep. ignored 1.7 %prompt J/ counting 5 %b lifetime error 1 % J/ e+e- 1 % +- background shape 20 % +- background fluct. 23 % e+e- background shape 14 % e+e- background fluct 11 %

Total 24 % – 33 %

-- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 31

Conclusion

• Results of 2000 limited in statistics(though competitive: (bb), Rc

)

• Hera-B offers good possibilities:• Simultaneous different targets

small relative uncertainties• large acceptance in - negativenegative - xF;• full event capability: PID, , …

• Improved detector (trigger) in 2002:high statistics expected