# New two-particle correlations observed in the CMS detector at the LHC

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1. Sep 21, 2010

### arivero

Last edited by a moderator: May 4, 2017
2. Sep 21, 2010

### daschaich

3. Sep 21, 2010

### jal

Is it too early to rule out some models?
jal

4. Sep 21, 2010

### daschaich

The point of that remark, as I read it, was to keep everyone from assuming that this is just the same "near-side ridge" that was seen at RHIC a few years ago. Because that's what it looks like to me.

5. Sep 22, 2010

### arivero

While the structure appears for intermediate trasversal momemtum of about 3 GeV, it is also told that "At Level 1 (L1), the total transverse energy summed over the entire set of CMS calorimeters ... was required to be greater tan 60 GeV"

Does it mean that there are two relevant scales in the game?

6. Sep 22, 2010

### daschaich

I think it just means you have a lot of tracks, each with relatively little p_T.

7. Sep 22, 2010

### arivero

That was my first idea too, but then they should get the same result by just adding a lot of tracks from different colisions. So either they need a lot of *simultaneus* tracks to get some quantum interference in action, or they need really an object above 60 GeV.

8. Sep 22, 2010

### humanino

Why do you say that ? Adding particle tracks from different events will just reproduce random backgrounds (like accidentals), not signals.
Those correlations are seen in very high multiplicity events (~100 tracks) indeed.

9. Sep 22, 2010

### daschaich

Why do you say that? I see no reason that correlations within a single collision imply any correlation at all between separate collisions.

These tracks are all in single events... I don't know how much more simultaneous you can get.

Last edited: Sep 22, 2010
10. Sep 22, 2010

### arivero

Hmm, are you lads following the conversation from #5, or just answering the last post without correlatiing (pun intended) it with the previous ones? If the former, then it is my English... I was telling that it is not "just a lot of tracks", it is "a lot of tracks coming from a single event", which is a different beast in quantum mechanics. I think that the observation is so elementary that you both have thought that I was arguing something, when I was simply being pedantic about the use of "just a".

A poster at Dorigo's has given a pausible explanation: they need at least 3 jets to get correlations via mechanisms based in colour, and then the selection of having a lot of tracks enhances the selection of 3-jets.

11. Sep 22, 2010

### humanino

No, and please note that there was not much discussion before #5
Please note that a two jet event must be back to back, so can not be in the region $\Delta\phi\sim0$ with large $\Delta\eta$ whether the color argument is relevant or not.