James Frost May Atlas UK SUSY/Exotics Meeting. Introduction Have been working in the Exotics group during the CSC analysis exercise, and will present.

James Frost May Atlas UK SUSY/Exotics Meeting

IntroductionHave been working in the Exotics group during the CSC analysis exercise, and will present a brief overview of it.

Many thanks to the rest of the subgroup:

Reminder:

Models with extra spatial dimensions (ED) can allow MPL ~ 1 TeV, and raise the intriguing possibility of producing short-lived t~10-26 s black holes.

Solves the hierarchy problem.

Much recent theoretical progress, and offers the possibility of studying quantum gravity.

James Frost – University of Cambridge Slide 2 May Atlas UK SUSY/Exotics Meeting

Event Properties (I)Black hole samples do not look the same – they can look very different, depending on the parameters.

Black hole events can be very crowded – some samples have average multiplicities of 12 or 16.

BUT this is not always the case, some have many events with only 4 or 5 particles, and look far more like backgrounds.

Background tails extend to high multiplicity

Selection needs to be robust over a wide range of theoretical uncertainties and different BH samples.


Event Properties (II)Left plot shows the sum of |Pt| - a variable that shows good independence across BH samples and good discrimination against backgrounds.

Event shapes variables depend strongly on BH parameters – not suited to hard cuts - though there is some background separation power, the greater cross-sections of the backgrounds preclude this.Sum |Pt| (MeV)

103


Signal SelectionCutting on |Pt| > 2.5 TeV reduces backgrounds drastically, leaving only high Pt QCD as the dominant cross-section.

A further cut requiring a lepton (Pt>50 GeV) reduces the backgrounds further, though there is a drop in signal efficiency.

Pt cut Both cuts

103


Selection & EfficienciesTwo efficient methods to select BH events were determined:

Method One: A cut on the sum of scalar Pt > 2.5 TeV and a requirement of one lepton (e,mu) with Pt > 50 GeV

Method Two: A cut of four objects with Pt > 200 TeV, one a lepton (e, mu)


One:

Two:(Numbers from M. Kaneda)

Mass Resolution

An indication of the accuracy with which the black hole mass can be reconstructed is given by the mass resolution

This can be further improved by applying a cut on Missing Et < 100 GeV, at a cost of some signal efficiency

This is important for the discovery reach, since our simulated data has an artificial BH mass threshold (below which the model's semi-classical approximations are not valid), which will not be present in data, where it would be sensible to make a cut on reconstructed mass.


How many extra dimensions?

Calculating the number of extra dimensions in a manner that is free from the theoretical uncertainties and independent of potential model parameters is difficult. Care must also be taken not to bias the selection such that the subsample passing the selection cuts is unrepresentative of the true BH distribution.

One method showing potential was first described in hep-ph/0411022, and has been made compatible with cuts for signal selection and background rejection. The probability of a hard emission (y-axis) for any number of extra dimensions should lie between upper and lower bounds that can be calculated theoretically as a function of BH mass (x-axis)

Method is also independent of some of the model uncertainties.

Greater luminosity than the 0.75 fb-1 shown here is needed, but the method shows promise.James Frost – University of Cambridge Slide 8 May Atlas UK SUSY/Exotics Meeting

Discovery at High MET?

This does not form part of our standard signal selection, but assuming it is well-calibrated, could provide an indication of new physics.

Plots show the distribution of events after a highly-efficient standard cut on |PT| < 2.5 TeV. The usual 2nd cut requiring a lepton, with lower signal efficiency (particularly at higher number of dimensions) is not needed.

A cut on MET > ~ 600 GeV would leave negligible background and plentiful signal. The high cross-section allows BH models to be distinguished easily from SUSY events, for which such high values of MET are rare.

Despite the early evidence of the presence of BH/new physics it could provide, such a selection allows a far less accurate mass reconstruction, limiting its use in cross-section measurement and discovery.

Black Hole events have a great range of Missing ET, with a long tail toward 2 TeV. This is currently under-estimated in our MC (graviton emission is not included), making these distributions conservative.


Toward Data : TAG Skimming on FDRFDR1 Jet stream – runs 3070 & 3071 – these are the most realistic event mixes

Six merged AOD files – 13 GB

Reproduced AOD file – using SumEt>2 TeV as TAG query – 23 MB

Black: All AODRed: Sum |PT| > 2.5 TeV applied at analysis step

Have investigated skimming events using a TAG query of: Sum ET > 2 TeV

Background reduced by O(103) with no loss of events passing tighter analysis cut.

Taking this one step further – the TAG database can also be queried – produces a TAG file of your events – can ask for “good detector status”, or a particular trigger – potentially luminosity information too.

Have determined a suitable variable for event selection to be incorporated into the Exotics TagWord


CSC BH Group Plan Group will continue to work beyond CSC notes, and its focus will change

from a very specific model search to a more signature based search Preparations for data taking:

detector performance, acceptance and miscalibrations, triggers systematic uncertainties SM backgrounds

Keep up with new theories warranting experimental investigation – needs suitable MC generators – study additional generators such as BlackMax and Catfish.

Expand the groups area from "BH signatures" to "TeV scale gravitational signatures“

Black holes Fireballs a la Lisa Randall String balls, time machines ….

New name of the group: “TeV scale gravitational signatures”


Backup Slides

James Frost – University of Cambridge Slide 12 November Exotics MeetingJames Frost – University of Cambridge Slide 12 May Atlas UK SUSY/Exotics Meeting

Theoretical Parameters

Theoretically uncertain parameter

Description Canonical Value

Alternate Value

Use a kinematic cut-off on the decay

If an unphysical, kinematically-disallowed decay energy is selected:True: End BH decay and do remnant decay into N-bodiesFalse: Continue to emit particles until MBH = MPL , then do remnant decay

True False

Allow TH to change with time

As the black hole decays, its radius and mass becomes smaller and its Hawking temperature rises.True: Hawking temperature is recalculated between emissionsFalse: Hawking temperature fixed at initial value

True False

Number of extra dimensions

2, 4, 7 3,5

Planck Scale Quantum gravity scale 1 TeV 2 TeV

Decay remnant to N-bodies

When the black hole reaches the remnant phase, it decays into N-bodies

2-body decays

4-body decays

There are a number of theoretical uncertainties associated with the model

These were investigated using ATLFAST samples.


Theoretical Uncertainties

N \ Efficiency Full Sim (%) Fast Sim (%) Kinematic Cutoff – turned off (%)

Temperature time variation turned off (%)

4-body remnant Decay (%)

2 45.8 42.9 47.2 48.7 47.9

3 - 33.2 - - -

4 27.4 26.6 - - -

5 - 21.7 - - -

7 16.1 15.9 29.2 16.6 27.4

The theoretical uncertainties are large – selection must be efficient across a wide range of potential signals. This was investigated using many Atlfast samples

Cuts: Sum |Pt| > 2.5 TeV

At least one lepton with Pt>50 GeV

Theoretical uncertainties are under control – the n=7 sample is the most challenging for signal selection.

The dominant theoretical uncertainty (particularly at high n) is the kinematic cut-off of emissions. With this turned off, the n=7 sample looks more spherical and less like QCD, and the selection efficiency improves.


Calculating n DetailsA particle emitted in the BH frame with an energy close to half the BH mass (within an energy Ed-here chosen to be 300 GeV), must have been the first particle emitted.

The particle energy spectrum for a given number of extra dimensions and Planck mass is known, but will be amended near the kinematic cut at half the (current) black hole mass.

Upper and lower bounds on the probability of a particle emission with close to half the energy of the black hole can be calculated.

The upper bound includes all the probability distribution of emission in the unphysical region, the lower bound excludes all of it.

A corrective factor is applied to account for the possibility of a soft first emission

See hep-ph/0411022 for more details


Triggers (I)Have a large number of high energy particles on which to trigger.

Particularly at high n, the probability of an event containing a high Pt electron or muon is not very high – better to use jet triggers

Considered: i) Single jet trigger eg. j400 – very efficient, but high background

ii) Multijet trigger such as 4j100 – less efficient at high n, but less QCD background. Danger of only selecting certain types of black holes – selection bias toward high multiplicity events.

iii) Sum ET trigger – not implemented in CSC-06

– scalar sum over all calo towers

Trigger efficiencies for 2 (5640), 4 (6640) and 7 (6641) extra dimensions

James Frost – University of Cambridge Slide 16 November Exotics Meeting

Triggers (II)Single Jet Trigger

The highest single jet threshold trigger gives an excellent efficiency for all signal samples, and should be robust against all types of black holes.

Important that it is unprescaled.

Simulated trigger efficiencies for different trigger thresholds as functions of the offline reconstructed jet Pt at LVL3

James Frost – University of Cambridge Slide 17 November Exotics Meeting

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James Frost May Atlas UK SUSY/Exotics Meeting. Introduction Have been working in the Exotics group during the CSC analysis exercise, and will present.

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