Higgs excluded from 130 GeV to 480 GeV (Illustrative)

August 29, 2011

There are a few interesting workshops and conferences on today that are presenting results from LHC and Tevatron. In particular the “Implications of LHC results for TeV-scale physics” meeting at CERN all this week is the most likely place to look for new results, and indeed the following plot has just been shown by Eilam Gross.

This is an “illustrative” combination of the ATLAS and CMS Higgs searches which appears to be based on the data presented at lepton-Photon-2011. If you look carefully at where the black line crosses the 95% confidence level limit you will see that it excludes the standard model Higgs between 130 GeV and 480 GeV.

A Higgs below 130 GeV disfavours the standard model on its own because of vacuum instability. It might be OK if the vacuum remains metastable with a sufficiently long lifetime but if the mass is a bit smaller then such a universe becomes a very dangerous place to live. The safer explanation would be that the light Higgs is stabilised by extra particles which would have to look very much like a Higgsino or a stop. I.e. SUSY.

The excesses above 130 GeV are still there. It is difficult to read their size from this plot but they are obviously not due to a standard model Higgs. They could be from another boson with a smaller cross-section, or they may just be the effects of uncertainty in measuring the missing energy of the neutrinos in the WW channel.

No doubt more data will added soon and some possibilties are:

  • Excesses at 120 GeV could grow to a robust signal of a light Higgs, suggesting supersymmetry
  • The curve may continue to descend until the whole mass range is excluded according to the standard model
  • The 140 GeV excess could bounce back up from the grave to provide a standalone Higgs boson solution
  • The Higgs could appear at higher mass than 480 GeV, posing other problems for the standard model.
  • Some completely unexpected signal of electro-weak symmetry breaking could emerge.

Of course the plot is marked as “Illustrative” and I have no idea what other caveats the speaker has added (but see remarks in comment section from the speaker).

Update: For the record it turns out that the above plot used a combination formula which is not too good for observed CLs. See comments from its constructor below. It would be wrong to use it to draw any conclusions. You should think of it as an illustration of how missleading a combination can be if not done correctly. :) It was removed from the uploaded slides.

My own combinations use a different formula which I believe is much better. They do not yet show an exclusion at 140 GeV.


Higgs Hunting 2011

July 31, 2011

After the hectic EPS conference last week there are a number of followup workshops organised for people to discuss the new results concerning the Higgs boson and possible new physics. The first is the three day meeting “Higgs Hunting 2011″ in Orsay which ended yesterday. For such a workshop the words of the presenters and discussions after are what count, but these are not webcast so all we have to go on as outsiders are the slides (Update 5-Aug-2011: video recordings of the talks have now also been made available at the same link). Nevertheless there are some interesting points in the slides and it is worth picking out some highlights. The workshop started with a talk by Massimiliano Grazzini with this slide showing the main new Higgs results and how it makes the theorists feel These exclusion plots only tell part of the story and it is easy to be misled by excesses that look convincing because they have lots of substructure that makes them appear to show complex signals. In truth the excess comes from a small number of events often seen in just one channel, with the detailed noise coming from the background. A slide from James Olsen for CMS shows the event data from the diphoton channel. On the lefthand plot you can see some excesses at 120 GeV and 140 GeV that make bumps in the exclusion plots but on their own they don’t count for very much. If you look at enough plots you are bound to see excesses of this size somewhere. A slide shown by Elisabetta Pianori shows some signals at around 120 GeV in the same diphoton channels. These are still weak and they are not seen elsewhere. It’s easy to get carried away if you are selective about what you show Here is an more extreme example from Aurelio Juste (see also Paul Thompson). This slide shows events recorded by ATLAS in the H-> ZZ->4l channels. As you can see there are not a lot of events there. This leads to the exclusion limits on the right. As you can see there are bumps giving nearly two sigma excesses, but they correspond to single events. These are not signals on their own. When we combine all the channels and all the experiments we do get some slightly better signals, but still the signal is quite weak. Ben Kilminster has conveniently lined up the plots to show us where they agree, Draw your own conclusions. Here is the update from Matthias Schott on behalf of the gfitter group As you can see they wont include the ATLAS and CMS data anymore claiming that it is “not trivial anymore”. This did not stop John Ellis using the “bloggers combination” to draw some tentative conclusions about the standard model Higgs

The discussion was not just about Higgs but I just have the energy to show one slide summarising the mass limits on various possible new particles according to Paris Sphicas on behalf of ATLAS


Big Day for Higgs Boson

July 22, 2011

Today at the EPS conference in Grenoble the worlds largest hadron colliders will be revealing the results of their latest searches for the Higgs boson, using data collected up until the last few weeks. We will be posting the plots here as they appear.

The individual experiments Dzero, CDF, ATLAS and CMS will each show their all channel combined plots. There will also be separated plots for individual channels and some separate searches for a charged Higgs as predicted in some models such as MSSM.

Our expectation is that the Tevatron plots (Dzero and CDF) will show some good exclusion limits but we will have to wait for the plenary talks next week to see the full Tevatron combined plot. From a press release last night we already know that they will claim to limit the Higgs to a region of 114 geV to 137 GeV, but that is not the end of the story. Above 185 GeV they only use indirect measurements to exclude the Higgs and these assume that no new particles beyond the standard model exist. That could be a weak assumption.

Later today the CMS and ATLAS plots will tell us about those heavier mass regions with direct searches. They should be able to exclude a heavy Higgs or provide a plausible signal above 190 GeV, so what will it be?

We wont get a full combined LHC plot at this confernece but the individual  plots for ATLAS and CMS will already have strong results.

Click on big titles below to bring up the full slide presentation.

Dzero

First up is Dzero with this combined plot that we first saw a couple of days ago

It shows a good exclusion from 162GeV to 170 GeV, not a new result but good to see that the limits imposed by the individual experiments at Fermilab are already strong.

CDF

The CDF combined plot is not very different.

CMS ττ

In the Higgs to tau lepton pair decay channel CMS produce this plot. Remember that the observed limit has to drop below the horizontal line at 1.0 to provide a 95% confidence level exclusion. There is not enough data to do that here, but this data will go into the combined plot later too. It is good to see that 1.1/fb is being used. The same presentation also provides good SUSY exclusion results.

CMS γγ

The Higgs decay into two photons is a crucial channel for finding the Higgs. The LHC do not yet have enough data in this region but with this new plot we see just how close they are getting. A full combination of Tevatron and LHC data at this time might almost have something to say about low mass Higgs if this is anything to go by.

ATLAS γγ

Much the same from ATLAS

ATLAS bb

ATLAS have looked at the decays of a Higgs to decay into a bottom quark pair in conjunction with a W or Z boson. They see no excess at twenty times the standard model Higgs signal.

CMS ZZ

Tow Z bosons from a Higgs can decay into pairs of leptons, quarks or neutrinos giving different channels to search in. First the 2 leptons plus two quarks plot. This is an exciting result that comes close to exclusion at some points, but why has it been cut-off below 220 GeV?

The decay into two leptons and two neutrinos gets even closer

Finally the golden channel of four leptons crosses the line with a tiny exclusion around 185 GeV

ATLAS ZZ

The story from ATLAS is pretty much the same

The 2lepton+2 neutrino channel even has a good exclusion on its own

The golden channel is close to expectation levels for no Higgs

ATLAS WW

This splits into two main channels, first each W decays to a lepton and a neutrino. Here we get an impressive exclusion.

The lepton neutrino 2 quark channel is not so strong

CMS WW

For CMS just one combined plot for the WW channel is all we need

ATLAS

Combined result. WOW!


CMS

Finally the CMS combined plot. The exclusions are from CMS are 149-206 and 300-340 GeV with some large exclusions in the space between.


Conclusion

We still have to see the combined CMS plot and the combined Tevatron plot but already we have some strong results. Much of the Higgs mass range has now been excluded leaving just a window from about 114 GeV to 137 GeV and 205 GeV to 295 GeV. the higher range is excluded by precision tests for a standard Higgs, but a combination of massive particles is not ruled out.

There are excess in the 140 GeV to 150 GeV and a curious deficit at 350 GeV, seen consistently across the data. These results are compatible with a number of options including a light Higgs and a multiplet of Higges. More data will be required to finish and we should get enough this year but already we see that a standard model Higgs on its own only just fits the data if around 130 GeV. This is an outstanding result.

See also TRF for more discussion especially about the deficit.


Highlights of EPS first morning

July 21, 2011

Undoubtedly the most talked about presentation so far will be the CDF search for ZZ resonances (Robson) with this striking peek at 327 GeV. This is the only talk so far that has not seen everything consistent with standard model. The talks themselves have not been broadcast so we only have the slides to go by. It would be nice to know what questions were asked at this one.

Another controversial topic that is not so new is the Wjj bump observed by CDF. This morning we had new discussions about this from CDF (Cavalier) themselves  and D0 (Sekaric) who have refuted the bump with their data. CDF points to some differences between the analysis, especially some morphing that D0 use to remove systematics. Did this remove the bump too? A task force will compare the two calculations step by step to see where the discrepancy comes from. (see also below for the ATLAS contribution on Wjj)

The first talk with all new LHC data came from Kai Yi who presented searches for new physics in all hadronic final states at CMS. This included dijet resonances in 1.01/fb with nothing showing up to very high masses. A number of exotics including black holes are excluded up to one or two TeV

This was followed by Gibson who provided the matching dijet resonance data from ATLAS with 0.81/fb. The negative conclusion was the same.

CMS returned with another null search from leptons plus gamma presented by Leonidopoulos.

ATLAS also covered the same channel and found nothing in their talk about exotics by Berger-Hryn’ova. This presentataion covered a number of interesting areas but one worthy of particular note is a repeat of the Wjj search with 1.02/fb. They found nothing so they are tending to side with D0 in refuting the bump seen by CDF

One last search by CMS was for two electrons or muons presented by Tucker. As usual they produced some colourful plots but no resonances.

Although these negative search results are disappointing there is still plenty of space to find exotics with more data this year, or with more energy in a few years time. Meanwhile it is the Higgs and SUSY searches that are the most promising and those are still to come


CDF report 327 GeV anomaly in 4l channel

July 21, 2011

In a presentation at EPS-HEP today CFD will show a surprising cluster of 4 events in the 4 lepton “golden channel” consistent with a particle at 327GeV. There are four other events also consistent with decays via two Z bosons but at lower masses. The background expectation was 0.01 events for events over 300 GeV so the four 327GeV events are an exceptional find in 6/fb of data. The others are consistent with the background.

Other excesses at these matters have been seen elsewhere, but has D0, ATLAS or CMS seen anything simialr in the 4 lepton channel? Hopefully we will find out in the next two days.

See The Reference Frame for further details


Higgs Update from D0 and CDF

July 21, 2011

At Moriond earlier in March D0 showed us this confidence level plot with their first exclusions.


This week they will give us this update (Thanks to Walter for the pointer)

The small amount of additional data helps to extend the exclusion range, but we will need to see a combination with CDF to get the best limits. In March it looked like this

Update: Tevatron Higgs results for individual channels were presented in four talks this afternoon (21st july 2011)

Tomorrow we will see the channels combined for each experiment and in the plenary session we hope to see a new fully combined result for the Tevatron.

Second Update: Fermilab has now made a press release to say that they have shown that the Higgs must lie between 114 Gev and 137 GeV. This just means that they have extended their exclusion zone by about 20 GeV either side and that is not surprising. Their claim depends on the indirect exclusion above 185 GeV due to precision measurements, however this is only true on the condition of some fairly weak assumptions about physics at higher energies. In fact anything outside the standard model could invalidate this analysis.

The funniest thing that could happen now would be for CMS and ATLAS to find a signal for the Higgs at 200 GeV. See also TRF


Europhys HEP opening address (poll)

July 20, 2011

Last year at the ICHEP conference President Sorkozy surprised everyone by turning up to deliver the opening address.

ICHEP runs every two years but the Europhys HEP Conference in Grenoble follows the same format and has an unallocated slot for the opening. Perhaps Sarcozy will appear again, or perhaps he has set a precedent that another world leader will want to follow. On the other hand they may be all too shy, leaving the place to some scientist or celebrity.

So who do we think it could or should be. Cast your vote in our poll!

Update 21-July-2011: The voting is running neck and neck for the DG and Miss World, please keep voting.

Update 23-Jul-2011: Since I added the pictures Miss World has run ahead. I hope the conference organizers can make the necessary arrangements.


EPS Early Posters showing up to 1.21/fb from ATLAS

July 20, 2011

The Europhysics HEP conference (EPS) starts in earnest tomorrow with a good chance that some very strong results on Higgs searches will be revealed. There is likely to be either a plausible signal or an extensive exclusion, and maybe both.

The conference will include hundreds of talks during parallel sessions followed by the plenary talks. In addition there will be some posters which traditionally display some less important results on one poster-size page so that anyone interested can go and talk to the authors about them.

The LHC collaborations are being careful not to reveal their best results in advance of the big show, but some posters have already been made available and some are not so unimportant. Already five of them are showing plots using up to 1.21/fb of recorded data from ATLAS. Here are some brief summaries.

ttbar resonance searches in ATLAS by Reina Camacho: reports a search for heavy particles decaying into t-tbar pairs with 200/pb worth of data. At least some of these results were shown at PLHC last month but nice colourful plots are always worth looking at again.

Measurement of the top quark pair production cross section in dilepton final states with ATLAS by Hovhannes Khandanyan: measures the top quark cross-section using 0.7/fb.

The answer is 176 ± 6 (stat) ± 10 (syst) ± 6 (lum) pb

This poster refers to an ATLAS conference note number 117 whereas the latest note available is number 94. This gives an indication of just how many new results are being held back to release in the next few days.

First measurements of jet substructure in ATLAS by David Miller: is a technical note about how to squeeze more information out of QCD jets. The poster includes this plot using 0.6/fb

Search for high mass dimuon resonances in ATLAS by Simon Viel: ATLAS must be congratulated for showing plots using almost all the data recorded before the conference, 1.21/fb no less.

Search for high mass dielectron resonances at ATLAS by Sarah Heim: is doing the same thing using electrons instead of muons. 1.08/fb is searched for dielectron resonances.

Both these last two posters report that no new resonances are found and new limits are set on Z’ and Randall-Sundrum gravitons

If any more posters with new LHC data turn up today I will update this post.


Strings 2011

June 27, 2011

The strings 2011 conference has opend today in Sweden. You can watch videos of the talks live or recorded straight after, starting with the introduction by David Gross.

Gross asked the usual questions starting with the number one “What is String Theory?” and ending with number 11 “What will we learn from the LHC?”

He is a bit disappointed that the LHC has not found anything surprising yet, but he still holds high hopes for SUSY.

There have been promising new results in trying to solve large-N SUSY gauge theory which has beautiful mathematics: twistors, polytopes in the grasmanian for example. Since this theory is dual to string theory Gross thinks these discoveries could tell us about the fundamentals of string theory.

He goes on to mention entropic gravity which he said was also promising but he had a little smirk on his face when he said it and also implied that it is ambitious. There will be a talk from Verlinde later in the conference.

Apparently it is unfortunate that we seem to live in De Sitter space. The theories work much better in anti- De Sitter space. There are lots of questions but the most important product of knowledge is ignorance, then again it would be nice to have some answers he said at the end.

 

 

 

 


Another LHC Update

June 9, 2011

For the past 11 days the Large Hadron Collider has been running with a 1092 bunch filling scheme adding 325/pb to the total data delivered. Based on an average peak luminosity of 1.13/nb/s this gives a Hübner Factor of 0.3 which is very respectable for this early stage of the run.

During this time the beams have been dumped frequently by problems such as software errors that are being rapidly fixed. UFOs have been another major headache. These are thought to be dust particles that fall into the beam. There is so far no sign of their numbers dropping as the beam zaps them up, but the dump thresholds can be changed in the worst hit areas to reduce the number of UFOs that cause a run to be aborted. This means that overall the run efficiency should improve and the expectation should be for a somewhat better Hübner Factor once they settle into the longer run.

The first successful fill with 144 bunch injection ran last night. The longer train length means a few more bunches can be fitted into the ring. They just need two long fills with this filling scheme before they can step up to 1226 bunches in each beam, so higher luminosities should be with us soon.

The schedule for the rest of the year has been modified to replace the four planned maintenance breaks with just three breaks, but slightly longer in duration. The immediate effect is that the next stop moves back from 16th June to 29th June, allowing more data to be collected in time for the big HEP-EPS conference at the end of July.

This week it has been the Physics at LHC conference in Perugia that has been grabbing most attention. There have already been some new limits shown, such as seen on these plots from a talk today on ATLAS top physics by Marina Cobal.

The talks on the final day tomorrow are the ones most likely to declare any new observations rather than just exclusions using the 240/pb on offer. Indications from conference notes already released suggest that we should not expect too much. A lot of the talks have not explored beyond the 40/pb dataset from 2010.

A pessimist would say that they have concentrated on the best-hope channels for presentations at this conference so the absence of new observations beyond the standard model here means that nothing new is showing up yet. An optimist, however, might say that they have only been able to approve the less interesting searches in the time available. All the best results may be in the places where no new data was shown this week because they will want to wait a little longer for more data to get conclusive results. We wont have long to wait until the EPS-HEP conference where 1000/pb of data should be on the table.

Meanwhile the main buzz is about the CDF bump at 150 GeV. Tomorrow there should be a seminar at Fermilab from the D0 group to tell us whether or not they also see the bump. It will be webcast here. Another version of the talk will be seen at PLHC on Saturday. Woit has already passed on a rumour that says the answer will be negative. Even if he is right, this will leave open the question of how the bump seen by CDF can be explained. The results should be consistent so the two groups will need to compare their analysis methods to find out what went wrong.

Update 9-Jun-2011: I have checked all of the talks at PLHC 2011. There are 10 talks from ATLAS and one from CMS where new searches using 2011 data up to 236/pb are presented. They all correspond to notes already published last week so we know that only new exclusions limits are found. No new physics is forthcoming this week from the LHC, unless they slip in an extra last minute talk.


Follow

Get every new post delivered to your Inbox.

Join 275 other followers