# Presentation: 939586

## Fun with J/  e+ e-

- Jan Stark
- LPSC Grenoble

- All D0 meeting, February 20th, 2004

## Introduction

- This is a short talk – the main motivation is to flash some cool event displays.
- What is so cool about these displays of candidate J/  e+ e- events ?
-     They are a great illustration of the performance of the Run II D0 detector, both at the
-     trigger+DAQ level:
- 	CTT + CFT + Calorimeter + fancy algorithms at L3
- 	to be added in a matter of weeks (trigger list v13):
- 		CPS
- 		L2 (CTT – calorimeter matching)
-     and at the offline level:
- 	as above + SMT
- This performance is the result of year-long hard work by many collaborators.
- Nothing is perfect, and there are also some not yet so beautiful things to be reported – more on this later.
- With this channel, one cannot test the muon system, but I can confirm that they see the J/ as well.

- All D0 meeting, Feb. 20th, 2004

- Jan Stark

## Flashback

**Motivation:** 	Determine the offset in the electron energy response (calorimeter).
- 				This offset “is an important systematic uncertainty in the
- 				[measurement of] the MW/MZ mass ratio”.

- All D0 meeting, Feb. 20th, 2004

- Jan Stark

## Flashback

-  21 signal events (significance: 6)
- Mass:   		3.102  0.035 (stat) GeV
- Resolution: 	115  25 MeV

_**Dataset:**_
-   “A set of special runs at the end of
-     Run Ia and at the beginning of Run Ib.”
_**Trigger:**_
-   L1:  two EM towers above 2.5 GeV with
-          less than 1 GeV in the hadronic part
-          of the tower (in the CC, I guess).
-   L2:  two L2EM objects above 3 GeV,
-          isolation < 0.40 in a 0.4 x 0.4 cone (/).

- All D0 meeting, Feb. 20th, 2004

- Jan Stark

## Run II trigger

- A new low-pT di-EM trigger was introduced in trigger list v12.
- Summary of the selection criteria used by this trigger:
- 	L1:	CEM(2,3.) CEM(1,6.) TTK(2,3.) TTK(1,5.)
- 	L2:	|| restriction to central region
- 	L3:	two road electrons ( > 3 GeV and > 5 GeV, one tight one loose)
-    (for details, see J. Stark, “*Low-p**T** di-EM triggers: status and plans*”,
-     Trigger board meeting, October 17th, 2003; and references therein).
- This trigger typically runs unprescaled up to 35E30.
- Rates:   190/150/1.3 (0.3 unique) Hz at L1/L2/L3 at 30E30.
- Comments on improvements for trigger list v13: last slide.

- All D0 meeting, Feb. 20th, 2004

- Jan Stark

## J/ yields

- 38.4 pb-1

- 2151 J/

- 348 J/

- 727 J/

- Reconstruction using road method (track-based).

- Reconstruction using calorimeter clusters
- (two different H-matrix cuts).

- Resolution not quite
- as good as in Run I

- All D0 meeting, Feb. 20th, 2004

- Jan Stark

## An example event

- Two tracks, triggered
- on by CTT.
- CTT also knows that
- these tracks are isolated.

- All D0 meeting, Feb. 20th, 2004

- Jan Stark

## Another example

- All D0 meeting, Feb. 20th, 2004

- Jan Stark

## One more

- All D0 meeting, Feb. 20th, 2004

- Jan Stark

## Summary and Outlook

- J/  e+ e- is a tough test for our sophisticated detector/trigger/DAQ system.
- Obtained good results; have nice publicity material to illustrate that it is working.
- The J/  e+ e- sample is used for a variety of detector studies:
- central preshower response
-            - tracker/CPS/CAL matching
-            - efficiency
-            - CPS weight in energy determination
-  calorimeter resolution and energy calibration (room for improvement)
-  validate H-matrix and electron likelihood,
-   improve quality of simulation for discriminating variables
-  CTT/CAL matching at L2
-  efficiency of the road method which we will ultimately use for b-tagging
-   (single tags vs. double tags)
-  ...
- Improvements for trigger list v13 (being finalised right now):
-     - include CPS,
-     - use L1 isolation,
-     - use L2 to combine information from different subsystems.
-     The J/   e+ e- fun has been and continues to be a testing ground for new trigger features that we have to rely on
-     more and more as the Tevatron sets new records.
- Thanks to everybody who has contributed.

- All D0 meeting, Feb. 20th, 2004

- Jan Stark

## Backup slides

- 				Road method
- 				 Trigger bias
- 	     (for details, see J. Stark, “*Low-p**T** di-EM triggers: status and plans*”,
-     	      Trigger board meeting, October 17th, 2003; and references therein).

- All D0 meeting, Feb. 20th, 2004

- Jan Stark

## Different methods to reconstruct J/  e+ e-

- Before we consider the selection at trigger level, let’s discuss how we can
- reconstruct J/  e+ e- offline.
- One way to reconstruct J/  e+ e- is to proceed just like for Z  e+ e- :
-  Look for EM clusters in calorimeter to reconstruct electrons.
-  Possibly require EM clusters to be matched to tracks.
-  Combine two clusters to make J/. Calculate J/ mass from cluster energies
-    or track momenta.
- This procedure works well for Z  e+ e-. As we will see, it also works well for J/  e+ e- from
- direct J/ production. J/ from direct production tend to be isolated.
- But electrons from b  J/  e+ e- tend to be non-isolated (hidden in jets)
-         do not find separate clusters.
- An alternative method to reconstruct non-isolated electrons is available: the road method
- (F. Beaudette, J.-F. Grivaz, D0 notes 3976 & 4032).
- 	Start from reconstructed tracks.
- 	Look at energy deposited in narrow *road* around the track extrapolated through the
- 	calorimeter. Require energy-deposit to be EM-like.
- When the road method is used, the J/ mass is reconstructed from the track momenta.

- All D0 meeting, Feb. 20th, 2004

- Jan Stark

## Results on Monte Carlo

- Use road method and scone clusters to reconstruct J/  e+ e- in two different p14.3 Monte Carlo samples:
- J/ from b decays and direct J/ production.
- Require one electron track with pT > 3 GeV, one with pT > 5 GeV (inspired by L3 criteria of new trigger).

**J/******** from b decays**

**direct J/******** production**

**Road method**
- (tight cuts)

**Scone clusters**
- EM fraction > 0.9
- isolation < 0.15
- HMx8 < 50
- “track matched”
- to road electrons
- (one loose,
- one tight)

- radiative tail

- low efficiency,
- non-gaussian shape
- because non-isolated

- GeV

- J/ mass

- All D0 meeting, Feb. 20th, 2004

- Jan Stark

## Effect of trigger selection

- Take the two Monte Carlo J/ samples (road method) from the previous slide, and turn on
- the trigger requirements (TrigSim). Start with L3, then add TTK, then CEM.
- The plots below show the trigger efficiency w.r.t. offline reconstruction as a function of pT (J/).

- pT (J/)  [GeV]

- pT (J/)  [GeV]

**J/******** from b decays**

**direct J/******** production**

- L3 requirement

- L3 & TTK

- L3 & TTK
-   & CEM(2,3.)

- L3 & TTK
-   & CEM(2,3.)
-   & CEM(1,6.)

- Efficiency of CEM terms tower than for
- J/ from b decays. The latter events get
- help from the rest of the b jet.

- All D0 meeting, Feb. 20th, 2004

- Jan Stark

## Effect of trigger selection

- Take the MC sample of J/ from direct production reconstructed using scones, and turn on
- trigger requirements.

- offline cuts
- only

- offline & L3
-  & TTK

- offline & L3
-  & TTK
-  & CEM(2,3.)

- offline & L3
-  & TTK
-  & CEM(2,3.)
-  & CEM(1,6.)

- mean: 3.295
- width: 0.262

- mean: 3.297
- width: 0.248

- mean: 3.337
- width: 0.232

- mean: 3.366
- width: 0.229

- The CEM requirements increase the mean and reduce the width of the mass distribution.
- They “eat into the distribution” from the left.

- All D0 meeting, Feb. 20th, 2004

- Jan Stark

## Track-mass plot with numbers

- Signal model used in the fit (Crystal Ball function):

- 38.4 pb-1

- All D0 meeting, Feb. 20th, 2004

- Jan Stark