Lab Meeting -1/12/2004
Update on the
Photon + Dijet Analysis
Outline:
Old Photon + Dijet trigger
Photon Trigger Efficiency
Jets Trigger Efficiency
Monte Carlo events
News from the new trigger
Lab Meeting -1/12/2004
Introduction
Goal: Search for the W/Z Peak on Events with an
Associated Photon
Need 200-250 pb-1 with the new trigger (unprescaled)
Problem: NO TIME !!
Strategy 1: Sifting all the useful events we have now
(taken with Photon Triggers)
Strategy 2: Make an attempt to ask for a little more
Rate, just to get rid of the horrible DPS
Lab Meeting -1/12/2004
The Old +jets Trigger
PHOTON_DIJET:
L1 - EM8
L2 - EM18_ISO
L3 - 2 Jets with Et>18 GeV
1 Jet with Et>10 GeV
Like
25_ISO
First Run: 143938 (May 02)
Last Run : 167059 (Jul 03)
Total ~ 180 pb-1
Before GoodRun: ~3.5M
After GoodRun: ~1.7M
One is the photon
Found a bug on April 02
(Et>100) and Good data
only from May
Lab Meeting -1/12/2004
Event Selection
Step 1: Reproduce the Run I analysis
PHOTON_DIJET:
L1 - EM8
L2 - EM18_ISO
L3 - 2 Jets with Et>18 GeV
1 Jet with Et>10 GeV
 # Jets (0.7) > 2
 3rd Jet Et_corr < 10 GeV
 2nd Jet Et_corr > 10 GeV
 1st Jet Et_corr > 15 GeV
 #trk > 1 on 1st and 2nd jet
 Delta R(jet1,jet2) > 2
3 Sets of Cuts
A) Vertex and Met cuts
(only one good vtx, good z, and Met<0.8)
B) Photon Cuts
( Run I ~standard. Run II official cuts
Different. No Run II tight cut for serious
Photon analysis )
C) Jets Cuts
( Run I used harder data, 25_ISO trigger
With no jets requirement at trigger level)
( Offline cuts very close to trigger cuts,
Efficiency will suffer… )
Lab Meeting -1/12/2004
Event Selection
1615 K
Only
one vtx
900 K
Photon
Central
116 K
Photon
Isolation
A
25 K
B
C
Lab Meeting -1/12/2004
Trigger Efficiency
L1 : EM8 considered 100% efficient for Photon >18 GeV
L2 : 18_ISO feeds other triggers (25_ISO and DIPHOTON)
Other people already did this study (but for higher pt gamma)
Method I: Use an unbiased lower trigger
(in this case a L3_EM8) and check how
Often L2 is on for a good photon and make
The ratio. For L3 they use a similar method
(25_ISO / L3_18ISO )
Method II: Several discussions on photon
L2
Group about pi0 contamination in method I.
More sophisticated approach using electron
From Z and check when they fire the photon
Triggers.
Lab Meeting -1/12/2004
L3 Trigger Efficiency
L3 requires some additional quality to the photon
Same of the 25_ISO but I have lower pt photon…
… and also I have the jets to disentangle.
I need the efficiency for the photon part (ph ) and for
The jets (jets).
(not sure about that)
Trigger and analysis cuts too
Close. Not only Et threshold
But also eta is a problem.
Jet1 Eta
Jet2 Eta
Eta distribution after final selection
Lab Meeting -1/12/2004
Trigger Efficiency: Photon
To calculate ph with method I I need a sample
With only the L3 photon selection (jet unbiased) and
Then make the ratio, but I don’t have such a sample.
I need to reproduce offline the L3 cuts. Unfortunately
I can only apply the same cuts but it is different.
Events with L3_off
Tested on 25_ISO , a
Trigger with ONLY
Photon selection
18_ISO
18_ISO +
L3_25ISO
I assume the events with L3_off
Are good enough to be used in ratio.
Lab Meeting -1/12/2004
Trigger Efficiency: Jets
The L3_off events are also the unbiased sample
To study the jets efficiency (jets).
Et AND eta bias make the efficiency study very
Complicated ( 2d plot or several sets of 1d)
My approach is don’t care about them and go
Directly to what I want: the dijetmass distribution
The idea is have jets as a function of the dijet mass
Lab Meeting -1/12/2004
Trigger Efficiency: Jets
Dijet Mass Distribution
I compared the unbiased dijet mass
distribution with that one from
the PHOTON_DIJET trigger
Unbiased (L3_off)
Why so inefficient ??
Trigger
Jet1 Et Raw
(Jet1 Et>18 and Jet2 Et>10)
Jet2 Et Raw
Look at the unbiased events
that didn’t pass the trigger
(Blue – Red)
Lab Meeting -1/12/2004
Trigger Efficiency: Jets
Actually that distribution was real, the unbiased sample is
reasonable and really low Et jets make high Dijet distribution
Unbiased but not trigger
(Maybe useful for S/B separation)
Lab Meeting -1/12/2004
Use the 25_ISO ??
A possible approach is to use the unbiased (for jets) 25_ISO
Trigger for photon ET>26 and the DIJET trigger for 18< ET <26
DIJET All
DIJET And NO 25_ISO
Dijet All : 25.193
No 25_ISO: 14.075
(25 * 50% = 12.5)
(15 * 50%+10=17.5)
Lab Meeting -1/12/2004
Monte Carlo
MC under control now and started to produce Wg events
MC essential for acceptance study, almost done…
There is some room from improvement on the event
Selection and S/B separation, but the idea was to
Reproduce the run I results first. I’m not so sure anymore…
Example: FSR effect can be reduced
With some merging or bigger cone.
We have some experience on that…
Some tools already developed and
Ready to be exploited
FSR
MC
Lab Meeting -1/12/2004
EVD
Lab Meeting -1/12/2004
EVD
Lab Meeting -1/12/2004
EVD Data
Lab Meeting -1/12/2004
EVD Data
Lab Meeting -1/12/2004
News from the new trigger
New trigger replacing the PHO_DIJET in since Aug 03
Trigger rate higher than proposed (80 nb) because they
Didn’t implement all our cuts and for cosmic contamination
We didn’t take into account properly
Final number was around 230 nb and they put a DPS of
5:1:1, the first number for HiLum (L2>300Hz)
Several other problems with L2 ISO hardware, very
High rate (but not clear at the beginning…)
Lab Meeting -1/12/2004
New Trigger Rate
L2 rate
L3 rate
Problem not really fixed till last week (see table) …
… but now the HiLum (with L2 busy and L3 farm
Problems) made things even worse.
Lab Meeting -1/12/2004
Trigger Efficiency: Photon
Lab Meeting -1/12/2004
Conclusion/Plan/Future
In a real analysis attention to details are more
Important than I expected
On several of them I’m not an expert
(L2, L3, photon Isolation algo,etc..)
Several open issues and work in progress, probably too
Much. Maybe useful some middle term tasks/ deadlines
To focus on exclusively.
Or a “road map” to graduation to follow point by point…